全文获取类型
收费全文 | 1393篇 |
免费 | 57篇 |
国内免费 | 25篇 |
专业分类
耳鼻咽喉 | 2篇 |
儿科学 | 53篇 |
妇产科学 | 32篇 |
基础医学 | 166篇 |
口腔科学 | 19篇 |
临床医学 | 138篇 |
内科学 | 311篇 |
皮肤病学 | 51篇 |
神经病学 | 102篇 |
特种医学 | 149篇 |
外科学 | 129篇 |
综合类 | 75篇 |
预防医学 | 111篇 |
眼科学 | 22篇 |
药学 | 58篇 |
中国医学 | 1篇 |
肿瘤学 | 56篇 |
出版年
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 33篇 |
2013年 | 70篇 |
2012年 | 36篇 |
2011年 | 44篇 |
2010年 | 38篇 |
2009年 | 41篇 |
2008年 | 39篇 |
2007年 | 59篇 |
2006年 | 44篇 |
2005年 | 55篇 |
2004年 | 34篇 |
2003年 | 45篇 |
2002年 | 33篇 |
2001年 | 26篇 |
2000年 | 42篇 |
1999年 | 34篇 |
1998年 | 57篇 |
1997年 | 56篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 38篇 |
1993年 | 39篇 |
1992年 | 27篇 |
1991年 | 17篇 |
1990年 | 19篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1969年 | 6篇 |
1963年 | 6篇 |
1941年 | 11篇 |
排序方式: 共有1475条查询结果,搜索用时 31 毫秒
11.
12.
13.
14.
Anderson RA; Evans LW; Irvine DS; McIntyre MA; Groome NP; Riley SC 《Human reproduction (Oxford, England)》1998,13(12):3319-3325
Follistatin is a binding protein for the activin and inhibin family of
hormones, regulating their biological activity. In the male reproductive
tract, the interaction of these factors is likely to be involved in the
regulation of the proliferation of several cell types. We have investigated
the presence of follistatin and activin A in seminal plasma using specific
immunoassays and have localized follistatin and activin/inhibin subunits in
the adult human testis, prostate and seminal vesicle to establish their
likely sources. High concentrations of immunoreactive follistatin were
present in seminal plasma in normal men (mean 97.9 ng/ml; 1.43 ng/ml in
peripheral plasma) and were similar in men with oligo/azoospermia and
following vasectomy. Follistatin immunoreactivity was localized to both
Leydig and Sertoli cells of the testis, and to epithelial cells of the
prostate gland and seminal vesicle, which are likely to be the predominant
sources of the hormone in seminal plasma. Activin A was also present in
seminal plasma in normal men but was undetectable following vasectomy, thus
deriving from the testis. Consistent with this finding, the betaA-subunit
was immunolocalized in Sertoli and Leydig cells but was not present in
seminal vesicle or prostate gland. The functional significance of the high
concentrations of follistatin secreted into seminal plasma by the prostate
gland and/or seminal vesicle is uncertain, but they may regulate the
biological activity of testis-derived activin A and inhibin B.
相似文献
15.
BACKGROUND: Worldwide, fire-related burns are a major cause of unintentional injury, morbidity and mortality, with the majority of deaths occurring in developing countries. In the US, as in other countries, most fatal fires occur in the home. Effective prevention strategies for residential fires are, however, currently underutilized. The news media is one available communication channel to promote such strategies, and analyzing current news coverage is a first step towards incorporating media advocacy into injury prevention efforts related to residential fires. METHODS: Four daily newspapers circulating widely in Maryland were monitored for 1 year. Articles describing residential fires were coded for measures of prominence, content and frame. Analysis focused on measures of issue newsworthiness, reporting of causation and consequences of fires, and inclusion of public health context and conveyance of prevention messages. RESULTS: The data indicate that fires are newsworthy, with 374 relevant news articles in a 1-year period, 32% of which appear on the first page of a section. Coverage generally concerned recent local fire events. Most articles discussed the consequences of fires (88%), and identified a causal factor (58%). Only 36%, however, included prevention information, and less than one-quarter set residential fires in a public health context. CONCLUSION: The newsworthiness of residential fires provides a clear opportunity for widespread communication around injury prevention. Improving media advocacy will entail framing discussion of recent fire events in such a way as to support inclusion of prevention strategies and a public health context in news coverage. 相似文献
16.
17.
The effect of isoluminant and isochromatic stimuli on latency and amplitude of saccades 总被引:2,自引:0,他引:2
When two stimuli are presented in different positions successively at short time intervals saccadic eye movements are usually directed at intermediate positions. This phenomenon of "averaging" of saccadic eye movements has been studied in responses to double-step target displacements in different stimulus conditions. In these conditions isoluminant and isochromatic stimuli were used with variable contrast and at different background luminances. Although the critical duration of temporal summation differed considerably in these stimulus conditions the duration of the phenomenon of "averaging" remained the same in all conditions. This indicates that temporal properties of the sensory system are not the prime cause of "averaging". Moreover, the onset time of "averaging" relative to the second target displacement turned out to be highly correlated with the mean latency of saccades in the different conditions. The implications of the results for models of oculomotor control are discussed. 相似文献
18.
19.
Non-linear increase in vertebral density induced by a synthetic steroid (Org OD 14) in women with established osteoporosis 总被引:4,自引:0,他引:4
The results of a 2-year placebo-controlled study in 38 female patients with osteoporosis are presented. This study was conducted to evaluate the efficacy of a daily oral dose of 2.5 mg Org OD 14 ((7 alpha, 17 alpha)-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one) in the treatment of established osteoporosis. Org OD 14 is a steroid which shows combined weak oestrogenic, androgenic and progestational activity. A total of 31 patients completed a 12-month study period (17 placebo, 14 Org OD 14) and 25 of these went on to complete the full 24-months (15 placebo, 10 Org OD 14). A significant increase in bone mineral density as measured by dual photon absorptiometry was recorded in the lumbar spine in the Org OD 14-treated patients at 8, 16 and 24 months. The gain in bone mass after 8 months averaged 4% (P less than 0.01) and after 24 months 8% (P less than 0.001). In the control group, a bone loss rate of 2% per year was recorded in the lumbar spine. No significant changes in bone density in the forearm as assessed by single photon absorptiometry were found in either group. The increase in spinal bone density in the Org OD 14 group was non-linear and followed an S-shaped upward pattern. Org OD 14, while inducing no appreciable endometrial stimulation, was found to be a bone-active compound with anti-resorbing as well as anabolic activity. Org OD 14 warrants consideration not only for the long-term prevention of bone loss but also for curative treatment of post-menopausal osteoporosis. 相似文献
20.
Effect of exercise on coronary endothelial function in patients with coronary artery disease 总被引:36,自引:0,他引:36
Hambrecht R Wolf A Gielen S Linke A Hofer J Erbs S Schoene N Schuler G 《The New England journal of medicine》2000,342(7):454-460
BACKGROUND: Studies of the cardioprotective effects of exercise training in patients with coronary artery disease have yielded contradictory results. Exercise training has been associated with improvement in myocardial perfusion even in patients who have progression of coronary atherosclerosis. We therefore conducted a prospective study of the effect of exercise training on endothelial function in patients with coronary artery disease. METHODS: We randomly assigned 19 patients with coronary endothelial dysfunction, indicated by abnormal acetylcholine-induced vasoconstriction, to an exercise-training group (10 patients) or a control group (9 patients). To reduce confounding, patients with coronary risk factors that could be influenced by exercise training (such as diabetes, hypertension, hypercholesterolemia, and smoking) were excluded. In an initial study and after four weeks, the changes in vascular diameter in response to the intracoronary infusion of increasing doses of acetylcholine (0.072, 0.72, and 7.2 microg per minute) were assessed. The mean peak flow velocity was measured by Doppler velocimetry, and the diameter of epicardial coronary vessels was measured by quantitative coronary angiography. RESULTS: In the initial study, the two groups had similar vasoconstrictive responses to acetylcholine. After four weeks of exercise training, coronary-artery constriction in response to acetylcholine at a dose of 7.2 microg per minute was reduced by 54 percent (from a mean [+/-SE] decrease in the luminal diameter of 0.41+/-0.05 mm in the initial study to a decrease of 0.19+/-0.07 mm at four weeks; P<0.05 for the comparison with the change in the control group). In the exercise-training group, the increases in mean peak flow velocity in response to 0.072, 0.72, and 7.2 microg of acetylcholine per minute were 12+/-7, 36+/-11, and 78+/-16 percent, respectively, in the initial study. After four weeks of exercise, the increases in response to acetylcholine were 27+/-7, 73+/-19, and 142+/-28 percent (P<0.01 for the comparison with the control group). Coronary blood-flow reserve (the ratio of the mean peak flow velocity after adenosine infusion to the resting velocity) increased by 29 percent after four weeks of exercise (from 2.8+/-0.2 in the initial study to 3.6+/-0.2 after four weeks; P<0.01 for the comparison with the control group). CONCLUSIONS: Exercise training improves endothelium-dependent vasodilatation both in epicardial coronary vessels and in resistance vessels in patients with coronary artery disease. 相似文献