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   297142篇
  免费   17223篇
  国内免费   417篇
耳鼻咽喉   4217篇
儿科学   10310篇
妇产科学   10281篇
基础医学   45079篇
口腔科学   7514篇
临床医学   24240篇
内科学   55946篇
皮肤病学   6327篇
神经病学   21145篇
特种医学   11651篇
外国民族医学   43篇
外科学   46762篇
综合类   7771篇
现状与发展   1篇
一般理论   164篇
预防医学   19982篇
眼科学   6976篇
药学   20936篇
中国医学   787篇
肿瘤学   14650篇
  2018年   3631篇
  2017年   2668篇
  2016年   3089篇
  2015年   3499篇
  2014年   4583篇
  2013年   7238篇
  2012年   9114篇
  2011年   9502篇
  2010年   6156篇
  2009年   5566篇
  2008年   8718篇
  2007年   9577篇
  2006年   9401篇
  2005年   9007篇
  2004年   8701篇
  2003年   8198篇
  2002年   7787篇
  2001年   13343篇
  2000年   13675篇
  1999年   11445篇
  1998年   3032篇
  1997年   2796篇
  1996年   2642篇
  1995年   2555篇
  1994年   2347篇
  1992年   8331篇
  1991年   8470篇
  1990年   8279篇
  1989年   8092篇
  1988年   7330篇
  1987年   7085篇
  1986年   6727篇
  1985年   6523篇
  1984年   4767篇
  1983年   4127篇
  1982年   2474篇
  1979年   4431篇
  1978年   3241篇
  1977年   2739篇
  1976年   2509篇
  1975年   2834篇
  1974年   3355篇
  1973年   3363篇
  1972年   3125篇
  1971年   2956篇
  1970年   2843篇
  1969年   2585篇
  1968年   2538篇
  1967年   2374篇
  1966年   2264篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
Abstract

This study was undertaken to compare the concentrations of pro- and anti-angiogenic growth factors, nitric oxide (NO) stable metabolites in maternal serum and embryonic left ventricular (LV) isovolumic relaxation time (IRT, ms) during the first trimester in two groups of women: with pregnancy conceived by assisted reproductive technologies (ART, n?=?39) and normally conceived (control group, n?=?68) pregnancy. The concentration of vasoconstrictor endothelin 1 was 45.5 times more in ART than in control group. On the contrary, the concentrations of NO stable metabolites in ART were 1.9 times less than in control women. The assessment of angiogenic suppressors in ART women demonstrates the decrease in s-endoglin concentration was 1.6 times and in soluble receptor to vascular endothelial growth factor concentration was 2.0 times in comparison with control group. There was a significant increase in LV IRT in ART embryos in comparison to control ones. These data suggest significant changes in pro- anti-angiogenic factors balance and increase in vascular impedance in ART-conceived embryos.  相似文献   
32.
33.
34.

This study sought to evaluate the antioxidant properties and effects of some edible wild seeds [Afzelia africana Sm. (AFZ), Cyperus esculentus L. (CYP), Eleusine coracana Gaertn. (ELE), Irvingia gabonensis (Aubry-Lecomte ex O’Rorke) Baill. (IRV), Monodora myristica Dunal. (MON) and Parinari curatellifolia Planch. ex Benth. (PAR)] on α-amylase and α-glucosidase activities. The phenolic content and antioxidant activities of aqueous extracts of the seeds as typified by 1,1-diphenyl-2 picrylhydrazyl (DPPH) and hydroxyl (OH) radicals scavenging abilities and inhibition of Fe2+-induced malondialdehyde (MDA) production in rat’s pancreas in vitro were also assessed. ELE had significantly (p < 0.05) higher total phenol content than the other seeds; however, AFZ had the highest flavonoid content. The extracts scavenged DPPH· and OH· in a dose-dependent manner with aqueous extracts of PAR having the highest DPPH· scavenging ability, while extracts from IRV had the highest OH· scavenging ability and inhibition of Fe2+-induced MDA production in rat’s pancreas. Furthermore, all the extracts inhibited α-amylase and α-glucosidase activities in a dose-dependent manner. The α-amylase inhibitory effect of MON (IC50 = 0.48 mg/mL) was comparable to that of acarbose (IC50 = 0.40 mg/mL), while the α-glucosidase inhibitory effect of AFZ (IC50 = 0.45 mg/mL) was comparable to that of acarbose (IC50 = 0.39 mg/mL). The results suggest the potential use of the seeds in the dietary management of blood glucose levels associated with type 2 diabetes.

  相似文献   
35.

Introduction

In the United States there has been a large increase in participation in lacrosse for both males and females. The purpose of this study was to analyze the number of head injuries, injury rates (calculated using the reported number of participants) and types of head injuries that are seen in emergency departments in the United States.

Methods

We compared injuries between male and female lacrosse participants. This was a retrospective study using a publicly available database produced by the US Consumer Product Safety Commission and information about lacrosse participation from US Lacrosse.

Results

A linear regression was performed and showed a positive correlation between number of head injuries to males and time from 2002 to 2010 (R2?=?0.823; p?=?0.001). While the number of injuries to the head in female lacrosse participants was not significant. There was a negative correlation between the number of head injuries to males from 2010 to 2016 (R2?=?0.800; p?=?0.007), but again, there was no significance for female injury count (R2?=?0.417; p?=?0.117). Other significant differences between head injuries in males and females included the mechanism of injury and the type of injury recorded.

Conclusion

The most recent data from 2010 to 2016, suggest that both males and females have had a decrease in injury rate. However the total number of female head injuries is not significantly decreasing and as the sport continues to grow there will likely be more total head injuries and visits to the emergency department.  相似文献   
36.
37.
38.
39.
Toby O. Smith   《Physiotherapy》2006,92(3):135-145
Pretibial lacerations and lower limb wounds are referred to plastic surgery teams for split skin graft surgery. Traditionally, these patients have been immobilised on bedrest following surgery. More recently, patients have commenced ambulation earlier to avoid medical complications and facilitate discharge. The objective of this literature review was to determine when such patients should begin walking. A literature search was undertaken using the electronic databases AMED, Cinahl, Embase, Medline (via Ovid), PEDro and Pubmed. Clinical trials using human subjects, written in English, were included. Seventeen (of 1137) papers met the inclusion criteria and were reviewed. The literature suggested that patients should begin walking immediately or at the earliest possible opportunity after lower limb skin graft surgery. Although the literature advocated early ambulation, the evidence base presented with a number of recurrent methodological limitations, including small sample sizes, lack of a control sample, and limited follow-up. Accordingly, further research employing large, well-designed, randomised controlled trials is recommended. It will then be possible to understand with greater certainty when patients should begin walking after lower extremity split skin graft surgery.  相似文献   
40.
OBJECTIVE: To establish reference intervals for the fetal right, left and total lung volumes and heart volume between 12 and 32 weeks of gestation. METHODS: Fetal lung and heart volumes were measured using three-dimensional (3D) ultrasound in 650 normal singleton pregnancies at 12-32 weeks. The VOCAL (Virtual Organ Computer-aided AnaLysis) technique was used to obtain a sequence of six sections of each lung and the heart around a fixed axis, each after a 30 degrees rotation from the previous one. The rotation axis for the lungs extended from the apex to the upper limit of the diaphragm dome, and the rotation axis for the heart extended from its apex to its connection to the great vessels. The contour of each of these organs was drawn manually in the six different rotation planes to obtain the 3D volume measurement. In 60 cases the fetal lungs and heart volumes were measured by the same sonographer twice and also by a second sonographer once in order to compare the measurements and calculate intra- and interobserver agreement. RESULTS: The total lung volume and heart volume increased with gestation, from respective mean values of 1.6 and 0.6 mL at 12 weeks to 10.9 and 4.3 mL at 20 weeks and 49.3 and 26.6 mL at 32 weeks. The right to left lung volume ratio did not change significantly with gestation (median, 0.7), whereas the heart to total lung volume ratio increased with gestation from about 0.3 at 12 weeks to 0.5 at 32 weeks. In the Bland-Altman plot, the difference between paired measurements by two sonographers was, in 95% of the cases, less than 0.05, 0.5 and 1.9 mL for each lung at 12-13, 19-22 and 29-32 weeks, respectively, and the corresponding values for the heart volumes were 0.04, 0.4 and 2.3 mL. CONCLUSIONS: In normal fetuses the lung and heart volumes increase between 12 and 32 weeks of gestation. The extent to which in pathological pregnancies possible deviations in these measurements from normal prove to be useful in the prediction of outcome remains to be determined.  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