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   1431篇
  免费   117篇
  国内免费   60篇
耳鼻咽喉   53篇
儿科学   95篇
妇产科学   18篇
基础医学   244篇
口腔科学   27篇
临床医学   174篇
内科学   356篇
皮肤病学   18篇
神经病学   95篇
特种医学   130篇
外科学   92篇
综合类   31篇
预防医学   111篇
眼科学   6篇
药学   76篇
中国医学   2篇
肿瘤学   80篇
  2021年   14篇
  2019年   19篇
  2018年   30篇
  2017年   16篇
  2016年   24篇
  2015年   21篇
  2014年   37篇
  2013年   53篇
  2012年   43篇
  2011年   57篇
  2010年   49篇
  2009年   38篇
  2008年   66篇
  2007年   86篇
  2006年   49篇
  2005年   53篇
  2004年   52篇
  2003年   30篇
  2002年   35篇
  2001年   40篇
  2000年   41篇
  1999年   38篇
  1998年   48篇
  1997年   47篇
  1996年   33篇
  1995年   33篇
  1994年   38篇
  1993年   33篇
  1992年   21篇
  1991年   22篇
  1990年   19篇
  1989年   28篇
  1988年   31篇
  1987年   23篇
  1986年   11篇
  1985年   23篇
  1984年   13篇
  1983年   16篇
  1982年   19篇
  1981年   19篇
  1980年   17篇
  1979年   10篇
  1978年   21篇
  1977年   17篇
  1976年   15篇
  1975年   10篇
  1973年   13篇
  1971年   12篇
  1970年   9篇
  1967年   9篇
排序方式: 共有1608条查询结果,搜索用时 15 毫秒
1.
Abstract: Data from the National Education Longitudinal Study were combined with census data at the zip code level to examine the impact of neighborhood racial and ethnic diversity and consolidated inequality, in addition to individual, family, and school factors, on the likelihood of dropping out of high school. Results indicate that while the effects for diversity and consolidated inequality did not support the stated hypotheses, main effects for family risk and prior academic achievement were significant and in the stated direction. Also, when controlling for individual, family, school, and neighborhood characteristics, African Americans were less likely than White students to drop out of school. Implications for contextual effects research and educational outcomes are discussed.  相似文献   
2.
3.
Balloon dacryocystoplasty: indications and contraindications   总被引:3,自引:0,他引:3  
  相似文献   
4.
Although nausea and vomiting are diagnostic migraine symptoms, most patients can take tablets by mouth and a few say they can eat some food. This study was conducted to determine the proportion who could eat or drink, what was consumable and with what effect. One-hundred-and-nine migraineurs were asked what they could eat or drink at the beginning or height of their attacks; 59 could not take any food by mouth, but 50 could eat during the headache phase of their migraine attacks. Four ate normally, 5 took smaller amounts of their normal dietary intake, and 3 took lighter meals. Dry, carbohydrate foods were consumable by the remaining 38: a few had specific cravings, most stated the precise variety which, when eaten, reduced nausea, headache, other symptoms or length of attacks. Patients should therefore be encouraged to eat what they can tolerate, with their tablets taken as early as possible after the onset of attacks. Simultaneous nausea, tolerance or even craving for specific foods occur in other conditions, particularly high altitude headaches which share other features of migraine attacks. The observations in this paper support the notion that migraine is a central neuronal metabolic disturbance.  相似文献   
5.
Headaches in civil servants: effect on work and leisure   总被引:1,自引:0,他引:1  
Headaches in a group of civil servants and their effects on work and leisure activities, the medication taken, and numbers consulting their general practitioners during a year were assessed by a self administered questionnaire sent to 1000 civil servants in sections of a government department in London. The response rate was 74.7%. Altogether 77% of the respondents reported having had headaches in the previous 12 months. There was a higher prevalence in women (88%) than men (70%) and a significant decrease with increasing age. Women also had more frequent and severe headaches than men: 34% reported that headaches had interfered with work, either by impaired performance, making them leave work early, or by stopping them coming into work. About half of those who reported having severe headaches denied that they had affected their work, indicating difficulty in interpreting the term "severe." Nevertheless, 22% said that headaches interfered with their leisure activities as well as work which may be regarded as further evidence that the condition was truly disabling. Eighty per cent of those with headaches took medication, but within the past year only 11% had consulted their general practitioner and only 2.2% had been referred for further specialist opinion. Of the 22% who had not had a headache during the previous 12 months, 5.6% had never had a headache. In this group there was a larger proportion of men, a higher proportion with increasing age, and a higher proportion in non-desk working grades. Differentiation of the causes of headaches was not attempted in this survey but it is concluded that the extent to which they interfere with work and leisure is an important guide to their severity. It is suggested that the occupational health services may have an important role in assessing the causes of headaches and instituting preventive measures that benefit both the worker and industry.  相似文献   
6.
7.
The molecular mechanisms involved in luteolysis are still unclear in the primate. This study aimed to investigate the effect of induced luteolysis on the ovarian luteinizing hormone (LH) receptor and the steroidogenic enzyme, 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in the marmoset monkey. Luteolysis was induced in the mid-luteal phase either directly by systemic prostaglandin F2alpha (PGF2alpha), or indirectly by LH withdrawal using systemic gonadotrophin releasing hormone antagonist (GnRHant) treatment. The LH receptor was studied by isotopic mRNA in-situ hybridization and in-situ ligand binding and 3beta-HSD expression was studied using isotopic mRNA in-situ hybridization and immunohistochemistry. Induced luteolysis was associated with a reduction in the expression of LH receptor (P < 0.0001) and 3beta-HSD mRNA, closely followed by a reduction in the LH receptor (P < 0.05) and 3beta-HSD protein concentrations within 24 h. There were no differences in the findings whether luteolysis was induced with PGF2alpha or GnRHant. This study shows that disparate mechanisms to induce luteolysis in the primate result in an identical rapid loss of the LH receptor and 3beta-HSD. In conclusion, induced luteolysis leads to rapid loss of the steroidogenic pathway in luteal cells.   相似文献   
8.
For most experimental and therapeutic applications of gene transfer, regulation of the timing and level of gene expression is preferable to constitutive gene expression. Among the systems that have been developed for pharmacologically controlled gene expression in mammalian cells, the bacterial tetracycline (tet)-responsive system has the advantage that it is dependent on a drug (tet) that is both highly specific and non-toxic. The tet-responsive system has been previously used to modulate expression of cell cycle regulatory proteins in cultured cells, reporter genes in plants and transgenic mice and reporter genes directly injected into the heart. Here we show that orally or parenterally administered tet regulates expression of tet-responsive plasmids injected directly into mouse skeletal muscle. Reporter gene expression was suppressed by two orders of magnitude in the presence of tet, and that suppression was reversed when tet was withdrawn. These data show that skeletal muscle offers an accessible and well characterized target tissue for tet-controlled expression of genesin vivo, suggesting applications to developmental studies and gene therapy.  相似文献   
9.
10.
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