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   19459篇
  免费   680篇
  国内免费   81篇
耳鼻咽喉   985篇
儿科学   564篇
妇产科学   1177篇
基础医学   2467篇
口腔科学   145篇
临床医学   1156篇
内科学   4093篇
皮肤病学   232篇
神经病学   1970篇
特种医学   408篇
外科学   1551篇
综合类   114篇
一般理论   4篇
预防医学   1315篇
眼科学   614篇
药学   2634篇
中国医学   55篇
肿瘤学   736篇
  2023年   94篇
  2022年   211篇
  2021年   382篇
  2020年   187篇
  2019年   330篇
  2018年   646篇
  2017年   429篇
  2016年   476篇
  2015年   417篇
  2014年   706篇
  2013年   1038篇
  2012年   1250篇
  2011年   1514篇
  2010年   802篇
  2009年   376篇
  2008年   970篇
  2007年   1339篇
  2006年   1422篇
  2005年   1320篇
  2004年   1393篇
  2003年   1388篇
  2002年   1119篇
  2001年   487篇
  2000年   521篇
  1999年   324篇
  1998年   117篇
  1997年   40篇
  1996年   28篇
  1995年   28篇
  1992年   29篇
  1991年   34篇
  1990年   54篇
  1989年   27篇
  1988年   34篇
  1987年   30篇
  1986年   40篇
  1985年   34篇
  1984年   24篇
  1983年   30篇
  1982年   24篇
  1981年   37篇
  1980年   27篇
  1979年   40篇
  1978年   40篇
  1977年   25篇
  1976年   22篇
  1975年   29篇
  1974年   22篇
  1972年   31篇
  1971年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
There is no published data about associations between the state of dentition and bone mass in adolescents. The objective of this study was to investigate whether the prevalence of caries and dental malocclusion is associated with bone mass during growth. In 123 healthy Caucasian subjects (72 males, 51 females) aged 14-18 yr, DMFT figures (decayed teeth, missing teeth, filled teeth) and presence of malocclusion, according to Angle classification, were determined. Participants completed a questionnaire regarding dental hygiene, physical activity level, and consumption of sweets. Anthropometry and pubertal stages were examined. Bone mineral density (BMD) was examined using dual energy X-ray absorptiometry (DXA) in the total body, head, and lumbar spine. No association was found between DMFT (mean+/-SD: 8.33+/-3.9) and BMD or Z-scores for BMD. Malocclusion was found in 49 subjects (39.8%) and was more prevalent in females than males. Malocclusion was associated with lower total BMD independently of body size (p=0.001; Z-scores: -0.21+/-0.27 vs +0.33+/-0.17; p=0.1) in males (but not females), producing odds ratio 1.6 (95% confidence interval: 1.09-2.34%; p=0.02). Head BMD was also lower in the males with malocclusion than in those without (p=0.004). Neither caries nor the tooth loss appear to be associated with BMD during growth. Boys with malocclusion are at higher risk of reduced BMD. This suggests that inadequate bone mass accrual in males coexists with impaired growth of the masticatory system in childhood and adolescence, however, the causal pathway is unknown. Factors that produce malocclusion may also affect bone mass or size but further prospective studies are needed to evaluate the relationship.  相似文献   
13.
Background: This study evaluated the ability of dexmedetomidine to provide analgesia and sedation for outpatient colonoscopy, examining outcomes including cardiorespiratory variables, side effects, and discharge readiness.

Methods: Sixty-four patients were randomly assigned to one of three treatment regimens. In group D, patients received 1 [mu]g/kg dexmedetomidine over 15 min followed by an infusion of 0.2 [mu]g [middle dot] kg-1 [middle dot] h-1. Group P received meperidine (1 mg/kg) with midazolam (0.05 mg/kg), and group F received fentanyl (0.1-0.2 mg intravenous) on demand. The assessment included measurements of heart rate, blood pressure, oxygen saturation, respiratory rate, quality of sedation/analgesia, and an evaluation of the recovery time.

Results: The study was terminated before the planned 90 patients had been recruited because of adverse events in group D. In all groups, negligible hemoglobin oxygen saturation and respiratory rate variations were observed. In group D, there was a significantly larger decrease in heart rate (to approximately 40 beats/min in 2 of 19 cases) and blood pressure (to less than 50% of the initial value in 4 of 19 patients). Supplemental fentanyl was required in 47% of patients receiving dexmedetomidine to achieve a satisfactory level of analgesia (vs. 42.8% of patients in group P and 79.2% of patients in group F). Vertigo (5 patients), nausea/vomiting (5 patients), and ventricular bigeminy (1 patient) were observed only in group D. Time to home readiness was longest in group D (85 +/- 74, 39 +/- 21, and 32 +/- 13 min in groups D, P and F, respectively; P = 0.007).  相似文献   

14.
In the presented paper the authors evaluate the long-term results of treatment for inflammatory and thromboembolic complications in knee joint alloplasty with cemented endoprostheses. The clinical material spanning the years 1998-2003 are 15 patients with analysed complications, it determine 9% of all operated. They have evaluated achieved results using the HSS knee rating scale in their own modification. As far as the authors are concerned, venographic examination is a prerequisite for appropriate care of the patients following knee joint alloplasty who might have deep venous thrombosis. It is necessary to provide similar treatment when developing infections are suspected in the perioperative period and in cases of late infections. Consequently, antibiotic therapy and a possible quick bacteriological checkup for healing a postoperative wound is a prerequisite for successful treatment. Achieved results induce statement, that thromboembolic and inflammatory complications caused at most operated chronic vein insufficiency, deficit of range of motion at operated joint and gait insufficiency. Thromboembolic complications was always related with inflammation of knee joint alloplasty in our own material.  相似文献   
15.
The accuracy of 2D phase contrast (PC) magnetic resonance angiography (MRA) depends on the alignment between the vessels and the imaging plane. PC MRA imaging of blood flow is challenging when the flow in several vessels is to be evaluated with one acquisition. For this purpose, semi-automatic determination of the plane most perpendicular to several vessels is proposed based on centerlines extracted from 3D MRA. Arterial centerlines are extracted from 3D MRA based on iterative estimation-prediction, multi-scale analysis of image moments, and a second-order shape model. The optimal plane is determined by minimizing misalignment between its normal vector and the centerlines’ tangent vectors. The method was evaluated on a phantom and on 35 patients, by seeking the optimal plane for cerebral blood flow quantification simultaneously in internal carotids and vertebral arteries. In the phantom, difference of orientation and of height between known and calculated planes was 1.2° and 2.5 mm, respectively. In the patients, all but one centerline were correctly extracted and the misalignment of the plane was within 12° per artery. Semi-automatic centerline extraction simplifies and automates determination of the plane orthogonal to one vessel, thereby permitting automatic simultaneous minimization of the misalignment with several vessels in PC MRA.  相似文献   
16.
Summary During studies on the helminth fauna of wolves inhabiting natural ecosystems of Poland, 86 scats were examined. All the samples were collected in the autumn of 2005. Spirocerca lupi was detected with decantation and flotation techniques. The prevalence was 2.32 %. This is the first record of the parasite from Poland and the third case of its occurrence in the wolf (Canis lupus L.) within its distribution range.  相似文献   
17.
After lindane administration in daily doses of 0.1 LD50 for one month (total dose 2.0 LD50) changes in the erythrocytes were found persisting for up to 4 months after withdrawal of the pesticide. A significant increase in the number of echinocytes, a greater per cent of reticulocytes, significantly raised level of denatured haemoglobin, and an increased number of erythrocytes of higher sensitivity to oxidating factors in relation to control group was observed.  相似文献   
18.
A quantified evaluation of planar cardiac perfusion scintigrams (the objective of the study), obtained using technetium-99m methoxyisobutylisonitrile (MIBI) was performed on the basis of an analysis of circumferential profile curves, representing the perfusion as seen in three typical projections. The analysis involved the curves obtained both at rest and after stress, and was based on a comparison of their shape (trend) with the normal trend (normative evaluation). The latter was obtained by means of an original method of iterative fitting of individual curves into the database. The base consisted of curves recorded in 53 patients (separately in males and females) with normal perfusion of the left ventricle (group I, the reference group). A group of 90 patients suspected of having coronary artery disease (group II) was subdivided into two subgroups on the basis of coronary arteriography: (a) those with and (b) those without critical stenosis of at least one artery. Profile curves characterising the LV perfusion were obtained at rest and after stress. Defects of perfusion were quantified by comparison of individual curves with the normal trends. By means of multivariate analysis it was demonstrated that vectors of mean values characterising the scintigraphically assessed defects of LV perfusion in the two subgroups of group II differed very significantly (P<10–5). Applying methods of discriminant analysis, a classification of patients from group II was performed into those with probable defects of perfusion and those free of such defects. The sensitivity, specificity and accuracy of diagnosis of coronary ischaemia, based on quantified planar99mTc-MIBI scintigraphy, reached 86%, 87% and 87%, respectively.  相似文献   
19.
AIM: To check on reproducibility of parameters of the cutaneous electrogastrogram registered at a close or a distant time span. METHODS: Twenty-two volunteers recruited by an advertisement (11 females and 11 males, median age 25 years, range: 18-35) underwent three surface electrogastrography examinations of which two were taken on consecutive days and the third one was accomplished at least 2 weeks before or after the two other sessions. The examination involved a 30-min fasted recording, followed by a 90-min postprandial registration after intake of a 394-kcal mixed solid-liquid test meal. RESULTS: Parameters of the electrogastrogram pertaining to the frequency of the gastric slow waves exhibited good to moderate reproducibility, whereas fair reproducibility characterized parameters expected to describe the power of gastric slow waves. With the exception of the difference fed minus fasted power (DeltaDP), in no instance was the medium term reproducibility any worse than the short term one. Categorical data analysis revealed that the relative time share of normogastria postprandially exhibited a better reproducibility than in the fasted period. The Cohen's kappa-value of 0.459 for the DeltaDP for the medium term reproducibility placed this parameter within the range of moderate agreement between repeat examinations. Of the two two-parameter combinations considered, the alliance of the fasted and fed normogastria performed worse than any of those parameters considered alone, whereas a combination of the DeltaDP with the fed-state normogastria revealed a kappa-value amounting to 0.510 for the medium term reproducibility. CONCLUSIONS: The feasibility of some electrogastrographic parameters to convey clinically useful information may be hampered by their fair reproducibility. Recoding of parameters of the cutaneous electrogastrogram from primary continuous to secondary categorical may help achieve a better agreement between repeat examinations.  相似文献   
20.
OBJECTIVES: Resin-modified glass ionomer cements (RMGI) are hybrid materials prepared by incorporation of polymerizable components (typically 2-hydroxyethyl methacrylate (HEMA) with possible addition of multifunctional methacrylates) into a conventional acid-base mixture (a polymeric acid with powdered calcium fluoro-aluminosilicate glasses). During setting, the photopolymerization process and the acid-base reaction affect each other. The aim of this work was to examine the effect of a 45% aqueous solution of poly(acrylic acid) (PAA) and the liquid component of a commercial glass ionomer cement on HEMA and triethyleneglycol dimethacrylate (TEGDMA) photopolymerization. METHODS: The polymerization was initiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA) and camphorquinone (CQ)/coinitiator system. The reaction course was monitored under Ar and air by isothermal differential scanning calorimetry. RESULTS: The main effect of addition of polyacid solution (PAA and commercial) up to 10wt% to HEMA on the polymerization initiated with DMPA was earlier onset of autoacceleration. For the process initiated by the CQ-based system, the addition of 5wt% of PAA solution strongly accelerated the polymerization and increased the conversion, both in Ar atmosphere as well as in air. TEGDMA photopolymerization was not influenced or slightly retarded by the presence of 3wt% of PAA solution (the upper limit of solubility), depending on the initiating system used. SIGNIFICANCE: Under initiation conditions used in curing of commercial dental products (CQ-based two component initiating system), the presence of polyacid-aqueous solution in HEMA-based photocurable component increases markedly the polymerization rate and the conversion both in Ar atmosphere as well as in air. This result contributes to a characterization of the setting process of RMGIs.  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