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   428246篇
  免费   47975篇
  国内免费   192篇
  476413篇
  2018年   3837篇
  2017年   3760篇
  2016年   5162篇
  2015年   7063篇
  2014年   8233篇
  2013年   12030篇
  2012年   13694篇
  2011年   13830篇
  2010年   9244篇
  2009年   8552篇
  2008年   12553篇
  2007年   12737篇
  2006年   12210篇
  2005年   11570篇
  2004年   11491篇
  2003年   11117篇
  2002年   10791篇
  2001年   19105篇
  2000年   19224篇
  1999年   15751篇
  1998年   5735篇
  1997年   5921篇
  1996年   5692篇
  1995年   5194篇
  1994年   5320篇
  1993年   5171篇
  1992年   13062篇
  1991年   12488篇
  1990年   12396篇
  1989年   12345篇
  1988年   11283篇
  1987年   10706篇
  1986年   9938篇
  1985年   10008篇
  1984年   8145篇
  1983年   7116篇
  1982年   5462篇
  1981年   4836篇
  1980年   4694篇
  1979年   7761篇
  1978年   6030篇
  1977年   5374篇
  1976年   5192篇
  1975年   5594篇
  1974年   5846篇
  1973年   5748篇
  1972年   5203篇
  1971年   4586篇
  1970年   4049篇
  1969年   3759篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Energy expenditure was measured during pregnancy in seven primigravid women at 12-15, 25-28, and 34-36 weeks and after the cessation of lactation. On each occasion the resting metabolic rate and the increase in metabolic rate after ingestion of a liquid test meal were measured by indirect calorimetry. In absolute terms the resting metabolic rate increased steadily during pregnancy but when expressed per unit of body weight no change was found. The energetic response to a mixed constituent meal was significantly reduced by 28% in the middle trimester of pregnancy. These findings suggest a possible maternal adaptation to increase energetic efficiency at a time when the energy demands of the fetus are high.  相似文献   
992.
P J McLeod 《CMAJ》1987,136(7):709-712
Twelve Canadian medical schools that had an organized faculty development program were surveyed to evaluate the extent to which such programs were used and to estimate their effectiveness. Common practices included sabbaticals and programs designed to improve instructional skills. The main problems included underfunding, poor participation and inadequate instructor evaluation.  相似文献   
993.
The myeloarchitectonics of the specific human fields 40, 39, 37c, 37b of neocortex and also fields 17 and 19 which are the cortex end of visual analyzer has been studied with the help of neurohistological and quantitative methods. According to the character of the fibrous bundles, their diameter, the quantity of the fibrous in them and the diameter of the fibrous gradual changes from field 17 to field 19 and further to field 39 have been shown. It is an evidence of the succession between phylogenetically older and younger fields of the cortex. The peculiarities of the field quantitative myeloarchitectonics differing in the function and genesis are marked by heterochronous growth of these fields square in the process of evolution.  相似文献   
994.
A simplified method of manual calculation for inbreeding coefficient (and/or relationship) from complicated pedigree tables presented in a nongraphic mode is offered. The method is based on the use of positional dual codes of ancestors in which all genealogical links of the proband are reflected.  相似文献   
995.
Previously, it was found that the ancient Chinese remedy of Suanzaorentang could be a promising anxiolytic drug (Chen and Hsieh, 1985a, Chen and Hsieh, 1985b). To understand the mechanism of the action of Suanzaorentang, the effects of Suanzaorentang on behavior changes and central monoamines and their metabolites were studied in rats. It was found that Suanzaorentang significantly (1) prolonged the period from the onset of clonic to tonic convulsions induced by pentylenetetrazol or picrotoxin, (2) prolonged the sleep duration induced by hexobarbital, (3) reduced locomotor activity, (4) enhanced the hypomotility induced by alpha-MT, (5) reduced the locomotor stimulation produced by levodopa plus benserazide, and (6) reduced central HVA, VMA, and 5-HIAA, but had no significant effects on central DA, NA, and 5-HT. These facts implied that Suanzaorentang decreased the turnover rate of central monoamines and central catecholaminergic activity.  相似文献   
996.
G A Rappold  J Trowsdale  P Lichter 《Genomics》1992,13(4):1337-1339
The gene TCTE3 from the mouse t-complex region is expressed specifically in testicular germ cells. It maps in the central subregion of the t-complex on mouse chromosome 17 containing loci involved in transmission ratio distortion and male sterility. In this study, somatic cell hybrid lines have been used to map the human homologue, TCTE3, to the long arm of chromosome 6. CISS hybridization with the human lambda clone h117 refined this chromosome assignment to the very distal position of chromosome 6q27, thus providing further evidence that loci from the t-complex of mouse chromosome 17 can map to opposite arms of human chromosome 6.  相似文献   
997.
998.
The kainate (KA) and the quisqualate (QUIS) receptors that activate cation channels in the central nervous system have previously been defined as two of the major glutamate receptor types. In amphibian brain, an exceptionally rich source of these sites, they can be coextracted by octylglucoside and shown to behave as one entity in all analyses made in solution. When partly purified by lectin affinity, ion-exchange chromatography or by sucrose gradient centrifugation, the two activities comigrate in a 1:1 ratio. When the QUIS component is bound to an immobilized specific QUIS agonist, the KA component is extracted in parallel with it. There are equivalent numbers of the QUIS and KA sites and the two sites show a single affinity series for the binding of glutamatergic agonists. We deduce that KA or QUIS select different conformations of a single KA/QUIS receptor binding site, leading thus to the different channel-opening events that have been reported for these two agonists.  相似文献   
999.
In a double-bind controlled study, oral Acyclovir has been compared to a placebo in a series of 39 consecutive patients undergoing bone marrow transplantation. A dose of 200 mg was given every 6 h from day 8 to day 35 after transplantation. Pharmacokinetic studies have shown the good absorption of the drug despite intestinal damage related to chemoradiotherapy or gut graft-versus-host disease (GVHD), there was no sign of toxicity. The protection against herpes simplex virus (HSV) infection was complete in the treated group when compared to the control group even in patients with high anti-HSV antibody titres. The same protection was observed against cytomegalovirus (CMV) infection. The incidence of HSV and CMV was the same in both groups after treatment ended. This study confirms the efficacy of Acyclovir against HSV infection and possibly against CMV infection when it is given prophylactically after bone marrow transplantation.  相似文献   
1000.
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