首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2446篇
  免费   169篇
  国内免费   10篇
耳鼻咽喉   26篇
儿科学   93篇
妇产科学   176篇
基础医学   362篇
口腔科学   68篇
临床医学   206篇
内科学   474篇
皮肤病学   83篇
神经病学   154篇
特种医学   26篇
外科学   284篇
综合类   22篇
一般理论   3篇
预防医学   170篇
眼科学   65篇
药学   154篇
中国医学   5篇
肿瘤学   254篇
  2023年   14篇
  2022年   61篇
  2021年   77篇
  2020年   47篇
  2019年   71篇
  2018年   100篇
  2017年   53篇
  2016年   58篇
  2015年   63篇
  2014年   66篇
  2013年   109篇
  2012年   159篇
  2011年   137篇
  2010年   117篇
  2009年   79篇
  2008年   140篇
  2007年   145篇
  2006年   165篇
  2005年   115篇
  2004年   108篇
  2003年   103篇
  2002年   101篇
  2001年   42篇
  2000年   38篇
  1999年   40篇
  1998年   22篇
  1997年   16篇
  1996年   16篇
  1995年   13篇
  1994年   11篇
  1993年   11篇
  1992年   22篇
  1991年   18篇
  1990年   28篇
  1989年   20篇
  1988年   15篇
  1987年   18篇
  1986年   17篇
  1985年   15篇
  1984年   15篇
  1983年   9篇
  1982年   10篇
  1980年   10篇
  1943年   7篇
  1942年   7篇
  1940年   8篇
  1938年   7篇
  1937年   6篇
  1936年   5篇
  1933年   5篇
排序方式: 共有2625条查询结果,搜索用时 31 毫秒
51.
52.
Objective: To define modified Prenatal Growth Assessment Scores (mPGAS) for single and composite biometric parameters and determine their reference ranges in normal fetuses.

Methods: Nine anatomical parameters (ap) were measured and the weight estimated (EWTa, EWTb) in a longitudinal study of 119 fetuses with normal neonatal growth outcomes. Expected third trimester size trajectories, obtained from second trimester Rossavik size models, were used in calculating Percent Deviations (% Dev's) and their age-specific reference ranges in each fetus. The components of individual % Dev's values outside their reference ranges, designated +iapPGAS, -iapPGAS, were averaged to give +apPGAS and ?apPGAS values for the 3rd trimester. The +iapPGAS and ?iapPGAS values for different combinations of ap (c1a (HC, AC, FDL, ThC, EWTa), c1b (HC, AC, FDL, ThC, EWTb), c2 (ThC, ArmC, AVol, TVol), c3 (HC, AC, FDL, EWTa)) were then averaged to give +icPGAS and ?icPGAS values at different time points or at the end of the third trimester (+cPGAS, ?cPGAS). Values for iapPGAS, ic1bPGAS, and ic2PGAS were compared to their respective apPGAS or cPGAS reference ranges.

Results: All mPGAS values had one 95% range boundary at 0.0%. Upper boundaries of 1D +apPGAS values ranged from 0.0% (HC) to +0.49% (ThC) and were +0.06%, +2.3% and +1.8% for EWT, AVol and TVol, respectively. Comparable values for ?apPGAS were 0.0% (BPD, FDL, HDL), to ?0.58% (ArmC), ?0.13% (EWT), ?0.8% (AVol), and 0.0% (TVol). The +cPGAS, 95% reference range upper boundaries varied from +0.36% (c1b) to +0.89% (c2). Comparable values for ?cPGAS lower boundaries were ?0.17% (c1b) to ?0.43% (c2).

Conclusions: The original PGAS concept has now been extended to individual biometric parameters and their combinations. With the standards provided, mPGAS values can now be tested to see if detection of different types of third trimester growth problems is improved.  相似文献   

53.
Objective: To evaluate the impact of late 3rd trimester fetal growth cessation on anatomical birth characteristic predictions used in classifying SGA neonates.

Methods: A prospective longitudinal study was performed in 119 pregnancies with normal neonatal growth outcomes. Seven biometric parameters were measured at 3–4 weeks intervals using 3D ultrasonography. Rossavik size models were determined to predict birth characteristics at different ages. Percent Differences (% Diff) were calculated from predicted and measured birth characteristics. Growth Cessation Ages (GCA) were identified when no systematic change in % Diff values occurred after specified prediction ages. Systematic and random prediction errors were compared using different assumptions about the GCA. Predicted and measured size parameters were used to determine six new Growth Potential Realization Index (GPRI) reference ranges. Five were used to sub-classify 34 SGA neonates (weight?<?10th percentile) based on the number of abnormal GPRI values.

Results: Growth cessation ages were 38 weeks for HC, AC, mid-thigh circumference, estimated weight and mid-arm circumference. Crown-heel length GCA was 38.5 weeks. At GCA, birth characteristics had prediction errors that varied from 0.08?±?3.4% to 15.7?±?9.1% and zero % Diff slopes after 38 weeks. Assuming growth to delivery gave increased systematic and random prediction errors as well as positive % Diff slopes after 38 weeks, MA. Seventeen of the SGA neonates had 0 or 1 abnormal GPRI values [Subgroup 1] and 17 others had 2 or more abnormal values [Subgroup 2]. In Subgroup 1, 4/85 (4.7%) of GPRI's were abnormal while in Subgroup 2, 43/85 (50.6%) were abnormal. Use of only one type of GPRI for SGA subclassification resulted in substantial false negative and some false positive rates when compared to subclassification based on all five GPRI values.

Conclusions: Growth cessation occurred at approximately 38 weeks for all six birth characteristics studied. SGA neonates can be separated into normal and growth restricted subgroups based on the frequency of abnormal GPRI values (GPRI Profile Classification).  相似文献   

54.
55.
The availability of genetically tractable organisms with simple genomes is critical for the rapid, systems-level understanding of basic biological processes. Mycoplasma bacteria, with the smallest known genomes among free-living cellular organisms, are ideal models for this purpose, but the natural versions of these cells have genome complexities still too great to offer a comprehensive view of a fundamental life form. Here we describe an efficient method for reducing genomes from these organisms by identifying individually deletable regions using transposon mutagenesis and progressively clustering deleted genomic segments using meiotic recombination between the bacterial genomes harbored in yeast. Mycoplasmal genomes subjected to this process and transplanted into recipient cells yielded two mycoplasma strains. The first simultaneously lacked eight singly deletable regions of the genome, representing a total of 91 genes and ∼10% of the original genome. The second strain lacked seven of the eight regions, representing 84 genes. Growth assay data revealed an absence of genetic interactions among the 91 genes under tested conditions. Despite predicted effects of the deletions on sugar metabolism and the proteome, growth rates were unaffected by the gene deletions in the seven-deletion strain. These results support the feasibility of using single-gene disruption data to design and construct viable genomes lacking multiple genes, paving the way toward genome minimization. The progressive clustering method is expected to be effective for the reorganization of any mega-sized DNA molecules cloned in yeast, facilitating the construction of designer genomes in microbes as well as genomic fragments for genetic engineering of higher eukaryotes.Complexities of natural biological systems make it difficult to understand and define precisely the roles of individual genes and their integrated functions. The use of model organisms with a relatively small number of genes enables the isolation of core biological processes from their complex regulatory networks for extensive characterization. However, even the simplest natural microbes contain many genes of unknown function, as well as genes that can be singly or simultaneously deleted without any noticeable effect on growth rate in a laboratory setting (Hutchison et al. 1999; Glass et al. 2006; Posfai et al. 2006). Ill-defined genes and those mediating functional redundancies both compound the challenge of understanding even the simplest life forms.Toward generating a minimal cell where every gene is essential for the axenic viability of the organism, we are pursuing strategies to reduce the 1-Mb genome of Mycoplasma mycoides JCVI-syn1.0 (Gibson et al. 2010). Because we can (1) introduce this genome into yeast and maintain it as a plasmid (Benders et al. 2010; Karas et al. 2013a); and (2) “transplant” the genome from yeast into mycoplasma recipient cells (Lartigue et al. 2009), genetic tools in yeast are available for reducing this bacterial genome. Several systems offer advanced tools for bacterial genome engineering. Here we further exploit distinctive features of yeast for this purpose.Methods for serially replacing genomic regions with selectable markers are limited by the number of available markers. One effective approach is to reuse the same marker after precise and scarless marker excision (Storici et al. 2001). We have previously used a self-excising marker (Noskov et al. 2010) six times in yeast to generate a JCVI-syn1.0 genome lacking all six restriction systems (JCVI-syn1.0 ∆1-6) (Karas et al. 2013a). Despite the advantages of scarless engineering, sequential procedures are time-consuming. When applied to poorly characterized genes with the potential to interact with other genes, some paths for multigene knockout may lead to dead ends that result from synergistic mutant phenotypes. When a dead end is reached, sequentially returning to a previous genome in an effort to find a detour to a viable higher-order multimutant may be prohibitively time-consuming.An alternative approach to multigene engineering, available in yeast, is to prepare a set of single mutants and combine the deletions into a single strain via cycles of mating and meiotic recombination (Fig. 1A; Pinel et al. 2011; Suzuki et al. 2011, 2012). With a green fluorescent protein (GFP) reporter gene inserted in each deletion locus, the enrichment of higher-order yeast deletion strains in the meiotic population can be accomplished using flow cytometry. Here we apply this method to the JCVI-syn1.0 ∆1-6 exogenous, bacterial genome harbored in yeast to nonsequentially assemble deletions for genes predicted to be individually deletable based on biological knowledge or transposon-mediated disruption data. The functional identification of simultaneously deletable regions is expected to accelerate the effort to construct a minimal genome.Open in a separate windowFigure 1.Progressive clustering of deleted genomic segments. (A) Scheme of the method. Light blue oval represents a bacterial cell. Black ring or horizontal line denotes a bacterial genome, with the orange box indicating the yeast vector used as a site for linearization and recircularization. Gray shape denotes a yeast cell. Green dot in the genome indicates a deletion replaced with a GFP marker. (B) Map of deleted regions. Orange box indicates the yeast vector sequence used for genome linearization and recircularization. Green boxes indicate regions deleted in multimutant mycoplasma strains. Blue boxes denote restriction modification (RM) systems that are also deleted in the strains. (C) Pulsed-gel electrophoresis result for deleted genomes. The starting strain was the JCVI-syn1.0 ∆1–6 strain (1062 kb). Two strains were analyzed for each design of simultaneous deletion (962 kb for eight-deletion or 974 kb for seven-deletion genome). Ladder is a set of yeast chromosomes (New England BioLabs). (D) GFP-RFP ratio sorting result. Standard sorting was compared with sorting based on a GFP-RFP ratio (Methods).  相似文献   
56.
Background: Patients in cardiac arrest must receive algorithm-based management such as basic life support and advanced (cardiac) life support. International guidelines dictate diagnosing and treating any factor that may have caused the arrest or may be complicating the resuscitation. Ultrasound may be of potential value in this process and can be used in a prehospital setting. The objective is to evaluate the use of prehospital ultrasound during traumatic and non-traumatic CPR and determine its impact on prehospital treatment decisions in a Dutch helicopter emergency medical service (HEMS). Methods: We conducted an observational study in cardiac arrest patients, of any cause, in whom the Nijmegen HEMS performed CPR with concurrent echocardiography. The participating physicians had to adhere to Advanced Life Support protocols as per standard operating procedure. Simultaneous with the interruptions of chest compressions to allow for heart rhythm analysis, ultrasound-trained HEMS physicians performed echocardiography according to study protocol. The HEMS nurse and physician recorded patient data and data on impacted (supported or altered) patient treatment decisions. Results: From February 2014 through November 2016, we included 56 patients who underwent 102 ultrasound examinations. Sixty-two (61%) ultrasound examinations impacted 78 treatment decisions in 49 patients (88%). The impacted treatment was related to termination of CPR in 32 (57%), fluid management (14%), drugs selection and doses (14%), and choice of destination hospital (5%). Causes of cardiac arrest included trauma (48%), cardiac (21%), medical (14%), asphyxia (9%), and other (7%). Conclusion: Prehospital echocardiography has an impact on patient treatment and may be a useful tool to support decision-making during CPR in a Dutch HEMS.  相似文献   
57.
ABSTRACT

The current study examined whether emotional concern over one’s security situation is connected with death anxiety during an ongoing terror wave, and whether type of exposure (media exposure vs. contact with witnesses) moderates this connection. A total of 345 individuals, aged 18–70, were sampled during an ongoing wave of terror in Israel and filled out scales measuring death anxiety, concern over security situation, and type of exposure. Results indicated that increased concern was connected with enhanced death anxiety. Moreover, this connection was more pronounced among individuals exposed to the events through the media, in comparison with individuals who had first-hand contact with witnesses.  相似文献   
58.
Purpose: To investigate the relationship between disease factors, body functions and structures, activities, personal and environmental factors with independence in self-care activities in children with myelomeningocele (MMC), utilizing the International Classification of Function model.

Method: 113 children with MMC, aged 3–18 years were assessed during an annual MMC-clinic visit. Data on the personal and environmental factors, disease factors, hand function, mobility, visual perception, cognition, and communication were assessed in relation to the Pediatric Evaluation of Disability Inventory (PEDI) self-care domain.

Results: The mean PEDI caregiver assistance score was 22.1 (ranged between <10 and 62) well below the norms. The most significant determinant of dependence in self-care activities was the presence of hydrocephalus, a child with hydrocephalus scored a mean of 9.2 points less on the PEDI caregiver scale (p?=?0.02). By using a linear regression, the most significant factors associated with the PEDI scores among children with hydrocephalus were the age of the child, function of the non-dominant hand, ambulation, and cognitive function.

Conclusion: In children with MMC the presence of hydrocephalus appears to be more significantly associated with functional independence than the neurological level. The International Classification of Function model provides an in-depth multidisciplinary model that facilitates in investigating independence in self-care activities in children with MMC. It is important to take personal factors and various functional impairments into account when working with these children to promote independence.
  • Implications for Rehabilitation
  • When working with children with myelomeningocele on independence in daily living activities, it is necessary that health professionals demonstrate a holistic view of the child and his/her disability.

  • Health professionals should take into account information on all factors of the International Classification of Function, in order to help the children, achieve maximal independence.

  • It is important for health professionals to consider presence or lack of hydrocephalus when working with children with myelomeningocele to achieve functional gains.

  • Improving upper extremity function and cognitive ability in children with myelomeningocele may help promote independence in activities of daily living.

  • It is necessary for health professionals to continue to work with children with myelomeningocele on maximizing independence as they get older, for it is possible for them to achieve independence at a later age.

  • While this study did not explore participation, this is an essential part of the International Classification of Function and is generally related to function. Participation allows a child to be involved in life situations, contributes to life satisfaction and prepares children for critical adult roles. It is therefore important to assess and monitor this measure. Further studies should examine associations between independence in self-care activities and participation.

  相似文献   
59.
Detached ciliary tufts of columnar epithelial cells from the female genital tract may be mistakenly identified as protozoa when examined in wet mounts of fluid specimens in the laboratory because of their appearance and motility, although they are generally identified correctly in fixed specimens prepared for cytologic examination. A case of such mistaken identity in specimens from a gynecologic patient was documented, and the literature on ciliary tufts was reviewed. Infectious disease and gynecology consultants should be alert to the potential confusion arising from the presence of ciliary tufts in body fluids.  相似文献   
60.
The growth and differentiation of the central nervous system are closely related to the presence of iodine and thyroid hormones. It has been hypothesized that neurobehavioral disabilities of childhood, such as attention deficit hyperactivity disorder (ADHD), learning disorders, and autism can be attributed to fetal thyroidal endocrine disruption in utero. To determine whether there is an association between neonatal thyroid status and a subsequent diagnosis of a neurobehavioral disability, neonatal thyroxine (T(4)) levels have been used as the indicator of the presence of intrauterine thyroidal dysfunction. Neonatal T(4) levels were obtained from the neonatal hypothyroidism screening program. All cases were diagnosed at medical school diagnostic clinics, the diagnostic categories being ADHD, autism spectrum disorder, behavioral disorder, cognitive disorder, developmental delay, emotional disorder, learning disability, and speech/language disorder. Conditional logistic regression analysis was performed for each clinical condition. Odds ratios for the conditions ranged from 0.92 to 1.13 with p values ranging between 0.19 and 0.84. No significant differences were detected between neonatal T(4) values of the cases and the controls for any of the neurobehavioral conditions. All neonatal T(4) values were within normal ranges. The data provide no evidence to suggest that intrauterine thyroid status as reflected by the neonatal T(4) values had an impact on the neurologic disorders diagnosed in childhood.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号