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   7232篇
  免费   588篇
  国内免费   16篇
耳鼻咽喉   15篇
儿科学   199篇
妇产科学   137篇
基础医学   839篇
口腔科学   116篇
临床医学   909篇
内科学   1489篇
皮肤病学   76篇
神经病学   586篇
特种医学   389篇
外科学   1281篇
综合类   238篇
一般理论   6篇
预防医学   719篇
眼科学   60篇
药学   392篇
中国医学   6篇
肿瘤学   379篇
  2022年   46篇
  2021年   103篇
  2020年   72篇
  2019年   111篇
  2018年   136篇
  2017年   91篇
  2016年   111篇
  2015年   109篇
  2014年   131篇
  2013年   272篇
  2012年   345篇
  2011年   382篇
  2010年   221篇
  2009年   156篇
  2008年   298篇
  2007年   325篇
  2006年   348篇
  2005年   279篇
  2004年   322篇
  2003年   283篇
  2002年   278篇
  2001年   258篇
  2000年   251篇
  1999年   232篇
  1998年   105篇
  1997年   91篇
  1996年   93篇
  1995年   58篇
  1994年   70篇
  1993年   71篇
  1992年   181篇
  1991年   186篇
  1990年   167篇
  1989年   161篇
  1988年   116篇
  1987年   130篇
  1986年   118篇
  1985年   127篇
  1984年   97篇
  1983年   85篇
  1982年   57篇
  1981年   49篇
  1980年   48篇
  1979年   71篇
  1978年   66篇
  1977年   51篇
  1976年   38篇
  1974年   44篇
  1973年   42篇
  1969年   35篇
排序方式: 共有7836条查询结果,搜索用时 9 毫秒
61.
Resistance exercise has been suggested to increase blood volume, increase the sensitivity of the carotid baroreceptor cardiac reflex response (BARO), and decrease leg compliance, all factors that are expected to improve orthostatic tolerance. To further test these hypotheses, cardiovascular responses to standing and to pre-syncopal limited lower body negative pressure (LBNP) were measured in two groups of sedentary men before and after a 12-week period of either exercise (n = 10) or no exercise (control, n = 9). Resistance exercise training consisted of nine isotonic exercises, four sets of each, 3 days per week, stressing all major muscle groups. After exercise training, leg muscle volumes increased (P?P = 0.00) by 2.0 (0.5)?kg, leg compliance and BARO were not significantly altered, and the maximal LBNP tolerated without pre-syncope was not significantly different. Supine resting heart rate was reduced (P = 0.03) without attenuating the heart rate or blood pressure responses during the stand test or LBNP. Also, blood volume (125I and 51Cr) and red cell mass were increased (P?相似文献   
62.
A number of studies using the repeat expansion detection (RED) technique have suggested an association between unknown large CAG/CTG repeats and schizophrenia. The polymorphic CAG/CTG repeat loci CTG18.1 and ERDA1 have been reported to account for a high proportion (approximately 90%) of the large repeats detected by RED and may therefore be responsible for the cited association. The recently described locus TGC13-7a contains a highly polymorphic CTA/TAG and CAG/CTG composite repeat, and is thus another authentic candidate. In the present investigation, each locus was analysed for association with schizophrenia in a sample of 206 patients and 219 group-matched controls. No evidence for association of CTG18.1, ERDA1 and/or TGC13-7a with schizophrenia was found. The combined data accounted for only 54% of the CAG/CTG arrays of > 40 repeats found in our previous RED analysis.  相似文献   
63.
64.
Summary A probable new member of the herpes virus group caused an outbreak of fatal infections in captive vervet monkeys. The pathological findings and some of the properties of the virus are described.Dedicated to ProfessorJohn V. Enders on the occasion of his 70th birthday.  相似文献   
65.
This study investigated whether the high expression of adhesion molecules on enriched preparations of circulating dendritic cells (DCs) was an intrinsic property of the cells or whether it was a consequence of the procedure used to isolate them from blood. Expression of the beta 1, beta 2 integrins (CD11/CD18 family) and other adhesion molecules on DCs in whole blood was compared with that on isolated DCs. Dendritic cells were identified by flow cytometry as leucocytes that were positive for human leucocyte antigen (HLA)-DR, but negative for CD3, CD14, CD16, CD19 and CD56. In contrast to a minority of DCs in whole blood, the majority of isolated DCs expressed the beta 2 integrins and there were a greater number of cells bearing CD44, CD54 and some of the beta 1 integrins (notably CD49b, CD49d, CD49e and CD29). An increase in the proportion of DCs bearing adhesion molecules was generally apparent at the isolation stage when mononuclear cells, which had been incubated overnight, were centrifuged on a metrizamide gradient to enrich for cells of low density. Inclusion of an inhibitor of protein glycosylation and exocytosis (brefeldin A) at all stages of separation partially prevented an increase in the percentage of DCs bearing CD18, C29 and C54 whereas the inclusion of cycloheximide (an inhibitor of polypeptide synthesis) interfered with increases in the percentage of cells bearing CD29 and CD54. Neither of these antagonists had an effect on the intensity of adhesion molecule expression. We suggest that some of the adhesion-dependent functions of isolated DCs are caused, in part, by an upregulation of surface adhesion molecules induced by the enrichment procedure.  相似文献   
66.
The article reports the 2-year follow-up of patients suffering persistent symptoms of schizophrenia who entered a single blind randomized controlled trial. Patients were randomly allocated to cognitive-behavioral therapy (CBT) plus routine care (RC), supportive counseling (SC) plus RC, or RC alone. Treatment took place over 3 months, and follow-up was made 12 and 24 months after treatment finished. Sixty-one patients were available to the 2-year follow-up and assessed for positive and negative symptoms and clinical improvement; all of the 87 patients who entered the trial were assessed for relapse over the follow-up period. On all measures, patients who received RC alone did significantly worse at 2 years. There were no significant differences at 2 years between the CBT and SC groups.  相似文献   
67.
Bosch–Boonstra–Schaaf Optic Atrophy Syndrome (BBSOAS) is an autosomal dominant neurodevelopmental disorder caused by loss‐of‐function variants in NR2F1 and characterized by visual impairment, developmental delay, and intellectual disability. Here we report 18 new cases, provide additional clinical information for 9 previously reported individuals, and review an additional 27 published cases to present a total of 54 patients. Among these are 22 individuals with point mutations or in‐frame deletions in the DNA‐binding domain (DBD), and 32 individuals with other types of variants including whole‐gene deletions, nonsense and frameshift variants, and point mutations outside the DBD. We corroborate previously described clinical characteristics including developmental delay, intellectual disability, autism spectrum disorder diagnoses/features thereof, cognitive/behavioral anomalies, hypotonia, feeding difficulties, abnormal brain MRI findings, and seizures. We also confirm a vision phenotype that includes optic nerve hypoplasia, optic atrophy, and cortical visual impairment. Additionally, we expand the vision phenotype to include alacrima and manifest latent nystagmus (fusional maldevelopment), and we broaden the behavioral phenotypic spectrum to include a love of music, an unusually good long‐term memory, sleep difficulties, a high pain tolerance, and touch sensitivity. Furthermore, we provide additional evidence for genotype–phenotype correlations, specifically supporting a more severe phenotype associated with DBD variants.  相似文献   
68.
The number of ampicillin-resistant enterococci (ARE) was noted to be increased at our teaching hospital. To determine the risk factors for acquiring this organism and to compare clinical outcomes, over a 5-month period 38 patients infected or colonized with ARE were compared with 76 patients, infected or colonized with ampicillin-susceptible enterococci (ASE). Risk factors included nosocomial acquisition, duration of hospitalization, admission to a medical service, prior antimicrobial therapy, and combination therapy for at least 7 days. The mortality rate of patients infected or colonized with ARE was higher than that of patients infected or colonized with ASE (34 versus 14%; P = 0.03), but most deaths did not appear to be related to enterococcal infection. Over a 2-year period, 16 patients with ARE bacteremia were also compared with 23 patients with ASE bacteremia. The risk factors associated with ARE bacteremia also included nosocomial acquisition, duration of hospitalization, and prior antimicrobial therapy. The mortality of patients with ARE bacteremia was also higher than that of patients with ASE bacteremia (81 versus 30%; P = 0.003), with most deaths being due to the underlying disease or a complication of it. Typing of ARE isolates by pulsed-field gel electrophoresis showed that two genotypes predominated in our institution. A prolonged hospital stay, exposure to multiple antimicrobial agents, and perhaps nosocomial transmission are important factors in acquiring ARE. The presence of ARE may also be a marker for poor outcome.  相似文献   
69.
Preparations of Amsacta moorei entomopox virions were obtained from virus-containing inclusions (VCI) by using a carbonate-thioglycolate solution (pH 10.7–11.5). The virions possessed a uniform coat (“halo”) surrounding the viral envelope and exhibited an RNA polymerase activity. The “halo” could be removed by prolonged exposure to the carbonate-thioglycolate solution. Virions obtained by this treatment, however, possessed low infectivity and no detectable RNA polymerase activity. Removal of the “halo” by trypsin resulted in virions which possessed RNA polymerase activity and relatively high infectivity.Preparations of particles with and without the “halo” were similar in percent DNA, protein per OD260, number of particles per OD260, and RNA polymerase activity. Particles without the “halo,” however, were less dense (1.262 g/cm3) in CsCl than those with the “halo” (1.282 g/cm3) and 15–45 times more infective.Parallel studies of “nonhaloed” Amsacta virions (trypsin-treated) and vaccinia virions showed that both viruses contained similar amounts of protein per OD260, but Amsacta virions contained only 36% of the DNA found in vaccinia.  相似文献   
70.
Adult male sexual behavior in mammals requires the neuronal organizing effects of gonadal steroids during a sensitive perinatal period. During development, estradiol differentiates the rat preoptic area (POA), an essential brain region in the male copulatory circuit. Here we report that increases in prostaglandin-E(2) (PGE(2)), resulting from changes in cyclooxygenase-2 (COX-2) regulation induced by perinatal exposure to estradiol, are necessary and sufficient to organize the crucial neural substrate that mediates male sexual behavior. Briefly preventing prostaglandin synthesis in newborn males with the COX inhibitor indomethacin permanently downregulates markers of dendritic spines in the POA and severely impairs male sexual behavior. Developmental exposure to the COX inhibitor aspirin results in mild impairment of sexual behavior. Conversely, administration of PGE(2) to newborn females masculinizes the POA and leads to male sex behavior in adults, thereby highlighting the pathway of steroid-independent brain masculinization. Our findings show that PGE(2) functions as a downstream effector of estradiol to permanently masculinize the brain.  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