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   531713篇
  免费   59273篇
  国内免费   328篇
  2018年   5232篇
  2017年   5104篇
  2016年   6978篇
  2015年   8815篇
  2014年   10516篇
  2013年   15308篇
  2012年   17031篇
  2011年   17422篇
  2010年   11746篇
  2009年   10793篇
  2008年   15209篇
  2007年   15764篇
  2006年   14717篇
  2005年   14107篇
  2004年   13973篇
  2003年   13319篇
  2002年   12840篇
  2001年   28336篇
  2000年   28205篇
  1999年   21869篇
  1998年   6549篇
  1997年   7133篇
  1996年   6531篇
  1995年   6204篇
  1994年   5983篇
  1993年   5952篇
  1992年   17034篇
  1991年   16289篇
  1990年   15693篇
  1989年   15210篇
  1988年   13917篇
  1987年   12936篇
  1986年   12039篇
  1985年   11809篇
  1984年   9657篇
  1983年   8081篇
  1982年   5994篇
  1981年   5374篇
  1980年   5093篇
  1979年   8940篇
  1978年   6809篇
  1977年   6272篇
  1976年   5646篇
  1975年   6234篇
  1974年   6758篇
  1973年   6534篇
  1972年   5975篇
  1971年   5427篇
  1970年   4678篇
  1969年   4399篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We compared two different methods of observing trainees at work in general practice: the traditional one of a senior or training general practitioner sitting in during selected surgeries and the more modern video recording, with the patients'' written consent. Patients who had experienced the presence of a second doctor during the consultation were less likely to show an increase in arousal after their consultations than those who had been recorded on video. Patients who refused consent to be recorded were more highly stressed than those who agreed and showed smaller decreases in stress after consultations. The presence of two doctors generated fewer reductions in stress after the consultation than video recording did, but this was a non-significant trend. The group that was recorded on video did not differ appreciably from a control group in changes in stress or arousal.  相似文献   
992.
993.
Aspiration pneumonia is defined as pulmonary infiltration caused by inhaled material, either solid or liquid, that is inherently toxic or that initiates a toxic response. We present the case of a solitary lung mass of unknown etiology in which cytology of a fine needle aspiration provided a definitive diagnosis of this disorder.  相似文献   
994.
One particular kind of structure offers possible explanations, for long-term memory, efficient consolidation of stored information from the environment, clustering of data strings and multimodal functioning. It is a possible model for pieces of neural structure and its use offers a uniform method for both studying and constructing an extensive class of mechanisms.  相似文献   
995.
996.
The aim of this study was to ascertain the effects of training and ACTH administration on the steroidogenic in vitro response in the adrenal cortex of the rat when the tissue was incubated with ACTH. ACTH in vivo treatment resulted in a highly significant increase in the steroidogenic response (P less than 0.001) whereas training as such caused only a slight but insignificant increase in the steroidogenic responsiveness (P greater than 0.05). Training furthermore strongly suppressed the ACTH in vivo induced response (P less than 0.001). ACTH as such revealed the smallest effect on adrenal mass but the biggest effect on the steroidogenic response. It would seem that long term exercise resulted in an overall increase in the mass and size of the adrenal glands by either increasing the size of existing cells or by increasing the number of cells or both. The latter exercise-induced proliferation of adrenal tissue may involve an adaptive mechanism whereby larger total quantities of adrenal tissue of lowered steroidogenic efficiencies (on a mass basis) are produced in order to meet the stress resulting from the training program.  相似文献   
997.
Summary By use of a specific antiserum against synthetic ovine corticotropin-releasing factor (CRF) in the peroxidase-antiperoxidase (PAP) immunocytochemical procedure (Vandesande and Dierickx 1976), CRF-like antigenic determinants were demonstrated in the central nervous system of a human fetus, the Wistar rat, the frog Rana ridibunda, and the American cockroach Periplaneta americana. The immunoreactive CRF-producing cells occur mainly in the nucleus paraventricularis of the rat, while in Rana ridibunda these cells occur in the nucleus praeopticus. Immunoreactive CRF-containing fibres were also visualized. Very clear CRF-immunoreactive products were observed in the brain as well as the corpora cardiaca (CC) and corpora allata (CA) of the cockroach Periplaneta americana. ACTH-immunoreactivity was also demonstrated in the brain-CC-CA complex of this insect. Double immunohistochemical staining (Vandesande 1983) also revealed that both the CRFand ACTH-like substances occur in different neurosecretory neurons and nerve fibres. These results suggest that the antigenic determinants of CRF are very similar in vertebrates and insects bespeaking their very long evolutionary history.  相似文献   
998.
Immunohistochemistry was used to study the changes in the number of G cells in the antral part of the stomach of rats (40 animals) with cystamine-induced duodenal ulcer treated with beta-endorphine. In the stomach of rats with cystamine-induced ulcer the number of G cells was discovered to be significantly increased, which was removed by an opioid peptide. Naloxone did not block the action of beta-endorphine. Thus, beta-endorphine changes the number of G cells, the drug action being not associated with opiate receptors.  相似文献   
999.
Indirect radioimmunoassay and immunoperoxidase studies provided further evidence of human serum reactivity with murine mammary tumor virus (MMTV) structural proteins. Examination of over 400 human sera from breast cancer (BC) patients and controls has shown that the incidence of antibodies which react with MMTV structural proteins was significantly higher in BC patients (50%) than in patients with carcinomas of other organs (3%) or normal women (3%). However, the percentage of subjects immune to MMTV was higher in pregnant women (10%) as compared with normal subjects. All the women with BC of the first clinical stage had antibodies to MMTV. The percentage of immune donors was lower among patients with BC of the later stages (IIa, 90%, IIb, 76%, III, 27%, IV, 0%). Thus, a good agreement has been demonstrated between the first stages of BC and expression of antibodies to MMTV.  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