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   26772篇
  免费   2559篇
  国内免费   48篇
耳鼻咽喉   439篇
儿科学   781篇
妇产科学   481篇
基础医学   3711篇
口腔科学   659篇
临床医学   2784篇
内科学   4828篇
皮肤病学   314篇
神经病学   2115篇
特种医学   860篇
外科学   3874篇
综合类   577篇
一般理论   31篇
预防医学   3075篇
眼科学   731篇
药学   1748篇
中国医学   19篇
肿瘤学   2352篇
  2022年   193篇
  2021年   431篇
  2020年   273篇
  2019年   392篇
  2018年   510篇
  2017年   379篇
  2016年   428篇
  2015年   460篇
  2014年   637篇
  2013年   1010篇
  2012年   1387篇
  2011年   1321篇
  2010年   743篇
  2009年   649篇
  2008年   1155篇
  2007年   1240篇
  2006年   1182篇
  2005年   1152篇
  2004年   1058篇
  2003年   1063篇
  2002年   940篇
  2001年   829篇
  2000年   848篇
  1999年   724篇
  1998年   294篇
  1997年   270篇
  1996年   266篇
  1995年   232篇
  1994年   246篇
  1993年   225篇
  1992年   636篇
  1991年   562篇
  1990年   521篇
  1989年   544篇
  1988年   466篇
  1987年   464篇
  1986年   438篇
  1985年   424篇
  1984年   352篇
  1983年   284篇
  1982年   218篇
  1981年   225篇
  1979年   314篇
  1978年   282篇
  1977年   189篇
  1975年   192篇
  1974年   257篇
  1973年   199篇
  1972年   209篇
  1971年   176篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
Abstract This study illustrates how the Total Life Concept (TLC) program originated by AT&T was successfully transplanted to another work site, Sandia National Laboratories. Demographics of the participants at A T&T and Sandia differ and make comparisons difficult, but it is possible to assess program impact in terms of participation rates for each program. The original AT&T TLC pilot study had three major components: orientation, testing, and risk interpretation; lifestyle-improvement courses; and activities to promote health. Sandia kept the three major components of the AT&T TLC concept and made some modifications to meet Sandia's needs. Sandia's experience of adopting a model program and tailoring it to local needs worked well, demonstrating that an existing model can be successfully altered to meet the needs of different companies in varied settings.  相似文献   
154.
The purpose of the present study was to examine the interrelationships among phosphodiesterase (PDE) isozyme inhibition, cAMP formation, activation of cAMP-dependent protein kinase (cAPK), and positive inotropy in isolated guinea pig cardiac muscle mediated by the cardiotonic/vasodilator agent, milrinone. Milrinone was a potent and selective inhibitor of the "low Km" cAMP PDE isozyme (peak III) isolated by diethylaminoethyl ether cellulose chromatography, with IC50 values of 0.7 microM for peak III PDE and 100 microM for peak I PDE. In isolated papillary muscles frozen at peak inotropic responses, positive and significant correlations were evident between isometric force development as a function of cAMP content (r = 0.72, p less than 0.05) or cAPK activity ratio, an index of activation of cAPK (r = 0.79, p less than 0.001), for concentrations of milrinone from 0.1-1000 microM. Similar correlations were evident in muscles frozen at peak inotropic responses for the beta-adrenoreceptor agonist isoproterenol (r = 0.96, p less than 0.001; r = 0.98, p less than 0.001, respectively), but not for ouabain or Bay K-8644. The temporal sequence of these events was also quantitated for concentrations of milrinone (100 microM) and isoproterenol (3 nM) that produced approximately a 100% increase in isometric force. Whereas early time interval of force development (30 s, 1 min, isoproterenol; 30 s milrinone) were not accompanied by significant increases in either cAMP content or cAPK activity ratio, peak increases in force development for both isoproterenol (2 min) and milrinone (1 min) were related to peak increases in cAPK activity ratios. In summary, these results show that significant increases in cAMP content or cAPK activation are correlated with positive inotropy in isolated guinea pig papillary muscles with milrinone. These correlations occur at concentrations of milrinone that inhibit cardiac PDE isozymes and are similar to the known cAMP-dependent cardiostimulant isoproterenol. These data support the hypothesis that selective PDE isozyme inhibition is a mechanism by which milrinone effects positive inotropy.  相似文献   
155.
To exploit both the oxygen-mimetic and "pre-incubation" or continuous exposure effects of the 2-nitroimidazole radiosensitizers, we are conducting a Phase I trial of continuous infusion SR 2508 for patients receiving brachytherapy. Following the administration of a loading dose of 2 g/m2, SR 2508 is administered by continuous infusion for 48 hr. Twenty-one patients have completed treatment. The initial total dose was 8 g/m2 with patients currently receiving 15 g/m2. No toxicity has been observed. At the higher doses the steady-state plasma concentrations have been between 50 and 70 micrograms/ml. It is not yet known whether or not hypoxic sensitizers will be of benefit clinically, and if so, when during a course of treatment is the optimal time to use them. Given the lack of toxicity and plasma concentrations achievable with continuous infusion, future studies will be conducted using SR 2508 during both the external beam and brachytherapy aspects of treatment.  相似文献   
156.
Mosaic ring 12p and total anomalous pulmonary venous return   总被引:1,自引:0,他引:1  
An infant born with total anomalous pulmonary venous return (TAPVR) was found to have an extra chromosome present as a small ring. Spectral karyotyping and FISH analysis identified the material as a duplication involving the short arm of chromosome 12. Previous cases describing a variety of cytogenetic abnormalities that have been associated with TAPVR are reviewed along with prior cases of duplication 12p with their associated findings. We believe ours is the first case to report the occurrence of mosaic ring 12p and its association with TAPVR.  相似文献   
157.
A 4-month-old girl presented with myoclonic seizures and an electroencephalogram showing hypsarrhythmia. Hyperglycinuria and a cerebrospinal fluid to plasma glycine ratio of 0.2 suggested the diagnosis of non-ketotic hyperglycinaemia. Propionic acid and methyl citric acid were present in the urine, and propionyl coenzyme A carboxylase was deficient in leucocytes and fibroblasts. The ketotic and non-ketotic hyperglycinaemias cannot be differentiated by CSF: plasma glycine ratios.  相似文献   
158.
Variation has been observed in the structural polypeptides of swine vesicular disease viruses isolated from the United Kingdom and Hong Kong. Despite the limited number of isolates examined, several distinct polypeptide patterns were obtained when the virus structural proteins were examined by polyacrylamide gel electrophoresis. Isolates from outbreaks in the United Kingdom which were known to be connected gave the same polypeptide pattern, whereas viruses with different polypeptide patterns could not be traced to a common source. The different polypeptide patterns were obtained consistently and were not altered by passage of the virus in tissue culture. In general, isolates with identical polypeptide patterns could not be distinguished by neutralization or antibody blocking tests or by competition radioimmunoassays. However, isolates with different polypeptide patterns could be differentiated by antibody blocking tests or radioimmunoassay. The correlation between the serological tests and the polyacrylamide gel electrophoresis analyses illustrates the value of analyzing structural polypeptides in the epidemiological study of swine vesicular disease.  相似文献   
159.
160.
A model system for comparing carcinogen metabolism between human and rat colon has been developed. Tissue explants maintained under chemically defined conditions were treated with radioactively labeled carcinogens. After incubation for 24 hours, the binding of radioactive carcinogen to DNA was quantitated. Further, the carcinogen-DNA adducts and carcinogen metabolites released into the culture media were identified. Both human and rat colon activate benzo[a]pyrene (BP), aflatoxin B1 (AFB), and 1,2-dimethylhydrazine (DMH) into chemical species that reacted with cellular macromolecules. When human and rat colons were compared, the metabolism of AFB and DMH was qualitatively similar - the same major carcinogen-DNA adducts and metabolic profile. However, the mean binding levels of DMH and AFB to colonic DNA were higher in rats than in humans. BP-guanine adducts were the major adducts formed by both rat and human colonic DNA. However, BP-adenine adducts were observed in rat colonic DNA but not in human colonic DNA. A positive correlation for the binding of BP and DMH to human DNA of different individuals was observed, but no correlation was found between BP and AFB. The data suggest that similar enzyme systems may be involved in the metabolism of BP and DMH, whereas different enzymes might be involved in the metabolic activation of AFB.  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