全文获取类型
收费全文 | 850576篇 |
免费 | 97589篇 |
国内免费 | 338篇 |
出版年
2016年 | 9215篇 |
2015年 | 12699篇 |
2014年 | 15112篇 |
2013年 | 21937篇 |
2012年 | 24049篇 |
2011年 | 24557篇 |
2010年 | 16494篇 |
2009年 | 15412篇 |
2008年 | 21911篇 |
2007年 | 23169篇 |
2006年 | 21662篇 |
2005年 | 20885篇 |
2004年 | 20889篇 |
2003年 | 20288篇 |
2002年 | 19776篇 |
2001年 | 34944篇 |
2000年 | 35480篇 |
1999年 | 28293篇 |
1998年 | 10099篇 |
1997年 | 10642篇 |
1996年 | 10194篇 |
1995年 | 10055篇 |
1994年 | 9959篇 |
1993年 | 9892篇 |
1992年 | 25009篇 |
1991年 | 24774篇 |
1990年 | 24550篇 |
1989年 | 24021篇 |
1988年 | 22437篇 |
1987年 | 21500篇 |
1986年 | 20145篇 |
1985年 | 20662篇 |
1984年 | 17228篇 |
1983年 | 15064篇 |
1982年 | 11696篇 |
1981年 | 10795篇 |
1980年 | 10081篇 |
1979年 | 16942篇 |
1978年 | 13289篇 |
1977年 | 12397篇 |
1976年 | 11789篇 |
1975年 | 12966篇 |
1974年 | 13800篇 |
1973年 | 13550篇 |
1972年 | 12770篇 |
1971年 | 11288篇 |
1970年 | 9867篇 |
1969年 | 9521篇 |
1968年 | 8818篇 |
1967年 | 7676篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
H.U. Schweikert U.W. Tunn U.-F. Habenicht J. Arnold Th. Senge H. Schulze F.H. Schrder J.H.M. Blom O. Ennemoser W. Horniger G. Bartsch 《The Journal of steroid biochemistry and molecular biology》1993,44(4-6):573-576
Sex steroids are thought to play an essential role in the pathogenesis of human benign prostatic hyperplasia (BPH). Since recent studies in animal models and in men have shown that estrogens might be causally linked to the onset and maintenance of BPH, we examined the effect of 1-methyl-androsta-1,4-diene-3,17-dione (Atamestane), a newly developed aromatase inhibitor, in men with BPH. In an open multicenter study 49 men (mean age 70.1 years, range 55 to 84) with obstructive BPH were treated with atamestane (3 × 200 mg/day) for 3 months. Of the 49 patients 44 completed the treatment period; the other patients discontinued the study for reasons unrelated to treatment. With treatment BPH-related symptoms such as daytime voiding frequency, nycturia, peak flow and residual urine improved considerably; however, these parameters did not reach statistical significance. The mean prostatic volume decreased significantly from 74.2 ± 31.7 to 64.0 ± 31 ml (mean ± SD). Serum estrogen levels decreased markedly during treatment. In addition intraprostatic estrogen concentration decreased with treatment as compared to estrogen levels in hyperplastic prostates from untreated patients. The following conclusions can be drawn from this study: first, estrogens appear to have an important supportive role in established BPH, and second, estrogen deprivation improved BPH-related symptoms and reduced significantly prostatic volume. 相似文献
32.
33.
John R. Williams 《CMAJ》1993,149(11):1707-1708
34.
E. Smyk-Randall O. R. Brown A. Wilke A. Eisenstark D. H. Flint 《Free radical biology & medicine》1993,14(6):609-613
The effects of near ultraviolet (NUV) light on a NUV chromophore-containing oxidant-sensitive enzyme, dihydroxyacid dehydratase (DHAD), were measured in seven strains of Escherichia coli. The strains differed in production of the oxidant-defense enzymes, superoxide dismutases (Fe-SOD and Mn-SOD), and catalases HPI and HPII. With the stress of aerobic growth but without NUV exposure, the strains lacking either Fe or Mn SOD or both SODs had 57%, 25%, and 12%, respectively, of the DHAD-specific activity of the parent (K12) strain. Under the same conditions, the catalase strains that were wild type, overproducing, and deficient had comparable DHAD-specific activities. When aerobic cultures were exposed for 30 min to NUV with a fluence of 216 J/m2/s at 310–400 nm, the percentage decreases in DHAD-specific activities were similar (ranging from 75% to 89%) in strains with none, either, or both SODs missing, and in the catalase-overproducing strain. However, the decreases were only 58% and 52% in the strain with catalase missing and in its parent, respectively. The NUV-induced loss of DHAD enzyme activity was not accompanied by any detectable loss of the DHAD protein as measured by polyclonal antibody to DHAD. 相似文献
35.
36.
37.
38.
Shallow water rissoiform gastropods collected by the Norwegian Scientific Expedition (1937-1938) to Tristan da Cunha are described. The fauna consists of Powellisefia cf. philomelae (Watson) (Rissoidae), three new species of Eatoniella, E. trochiformisa, E. lineuta , and E. tristanensis (Eatoniellidae). two new species of Onoba, O. crassicordara and O. tristanensis (Rissoidae) and Rissoella cf. irma (Bartsch) (Rissoellidae). A small collection from Cough Island is also described, containing three species referred to Onoha , one of which is described as new. O. merelinoides , and a species of Eutoniella. The biogeographie relationships of the fauna are briefly discussed. 相似文献
39.
40.
Brutlag Douglas L.; Galper Adam R.; Millis David H. 《Bioinformatics (Oxford, England)》1991,7(1):9-19
We have developed a knowledge-based simulation of DNA metabolismthat accurately predicts the actions of enzymes on DNA undera large number of environmental conditions. Previous simulationsof enzyme systems rely predominantly on mathematical models.We use a frame-based representation to model enzymes, substratesand conditions. Interactions between these objects are expressedusing production rules and an underlying truth maintenance system.The system performs rapid inference and can explain its reasoning.A graphical interface provides access to all elements of thesimulation, including object representations and explanationgraphs. Predicting enzyme action is the first step in the developmentof a large knowledge base to envision the metabolic pathwaysof DNA replication and repair.
Received on February 1, 1990; accepted on October 2, 1990 相似文献