全文获取类型
收费全文 | 5309篇 |
免费 | 524篇 |
国内免费 | 1篇 |
专业分类
5834篇 |
出版年
2023年 | 37篇 |
2022年 | 26篇 |
2021年 | 75篇 |
2020年 | 86篇 |
2019年 | 60篇 |
2018年 | 156篇 |
2017年 | 146篇 |
2016年 | 162篇 |
2015年 | 160篇 |
2014年 | 154篇 |
2013年 | 330篇 |
2012年 | 403篇 |
2011年 | 439篇 |
2010年 | 219篇 |
2009年 | 169篇 |
2008年 | 361篇 |
2007年 | 345篇 |
2006年 | 305篇 |
2005年 | 318篇 |
2004年 | 297篇 |
2003年 | 267篇 |
2002年 | 170篇 |
2001年 | 83篇 |
2000年 | 89篇 |
1999年 | 45篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 22篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 45篇 |
1991年 | 30篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 32篇 |
1987年 | 26篇 |
1985年 | 31篇 |
1984年 | 37篇 |
1983年 | 33篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1976年 | 21篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1972年 | 28篇 |
1971年 | 18篇 |
1968年 | 20篇 |
1964年 | 19篇 |
排序方式: 共有5834条查询结果,搜索用时 0 毫秒
1.
Inhibitory effect of the flavonoid silymarin on the erythrocyte hemolysis induced by phenylhydrazine
A Valenzuela T Barría R Guerra A Garrido 《Biochemical and biophysical research communications》1985,126(2):712-718
The flavonoid silymarin, which is used as a therapeutical agent in the treatment of liver diseases, can inhibit the hemolysis and lipid peroxidation induced by phenylhydrazine on erythrocytes obtained from rats treated with the flavonoid. This effect is ascribed to the antioxidant properties as a free radical scavenger exhibited by the flavonoid. Silymarin failed to inhibit the glutathione depletion induced by phenylhydrazine on erythrocytes. It is proposed that the flavonoid acts at the membrane level of the cell avoiding the lipid peroxidative and fluidizing effect of phenylhydrazine. 相似文献
2.
3.
4.
Corynebacterium equi IFO 3730 was found to oxidize a wide variety of sec-alcohols, including alkanols, substituted alkanols, alkenols and cyclic alcohols, in moderate to high yields. Among them, the sec-alcohols which have longer carbon chains were oxidized more smoothly than those with smaller numbers of carbon. Although both enantiomers of unsymmetrically disubstituted carbinols were oxidized, the S form of 2-dodecanol was converted to the corresponding ketone a little faster than the other enantiomer. 相似文献
5.
A radioimmunoassay for the regulatory allylic steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP)
J P Wiebe K J Barr K D Buckingham 《The Journal of steroid biochemistry and molecular biology》1991,38(4):505-512
The allylic steroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), found in gonadal and brain tissues by radiotracer and chemical methods, had been shown to play a role in gametogenesis, gonadotropin secretion and brain excitability. Since no simple assay was available, a radioimmunoassay for 3 alpha HP was developed using [3H]3 alpha HP and an antiserum raised against 3 alpha HP-20-CMO conjugated to bovine serum albumin. The specificity of the assay for the 3 alpha allylic configuration of 3 alpha HP was confirmed by examining 32 other steroids; cross-reaction with steroids containing different configurations (including metabolites of 3 alpha HP such as progesterone) was less than 0.9%. A Scatchard plot indicated a Ka of 1.56 X 10(9) M-1. Inter- and intra-assay coefficients of variation were 13.1 and 4.5%, respectively. The sensitivity of the assay was 6 pg and the 50% intercept of the standard curve was approx. 123 pg. The measurement by RIA of 3 alpha HP from standard solutions and HPLC purified tissue extracts was confirmed qualitatively and quantitatively by GC/MS methods. The RIA method was employed to determine 3 alpha HP levels in cultured Sertoli cells and in serum of intact and ovariectomized adult rats. Although for most uses, chromatography would not be necessary, two possible methods are presented to enable the separation of 3 alpha HP from other interfering steroids prior to RIA. 相似文献
6.
7.
8.
Aspirin and acetaminophen use by pregnant women and subsequent child IQ and attention decrements 总被引:1,自引:0,他引:1
A P Streissguth R P Treder H M Barr T H Shepard W A Bleyer P D Sampson D C Martin 《Teratology》1987,35(2):211-219
In a longitudinal prospective study of 1,529 women pregnant in 1974-1975, aspirin and acetaminophen were the two medications most frequently taken during the first half of pregnancy (46 and 41%, respectively). In a selected cohort of 421 offspring of these women, examined at 4 years of age, maternal aspirin use during the first half of pregnancy was significantly related to IQ and attention decrements in the exposed children. Multiple regression analyses were used to statistically adjust for a variety of potentially confounding factors including demographic characteristics, child characteristics, other exposures, and lifestyle/environmental variables. Continuous dose-response and step-function parameterizations of aspirin exposure were both statistically significant and not clearly distinguishable from each other. The estimated aspirin effect is significantly greater for girls than boys. Aspirin effects on offspring function were found in the absence of effects on physical size both at birth and at 4 years. Maternal acetaminophen use was not significantly related to child IQ or attention. As this exploratory research originated from observations of a data set gathered for other purposes, it would be desirable to have these findings replicated in other studies. Further follow-up of the children at a later age is planned. 相似文献
9.
10.
Yosiaki Itô 《Journal of Ethology》1987,5(2):115-124
Social behaviour ofRopalidia revolutionalis (de Saussure) was observed in Brisbane and Townsville. Nests were, as a rule, founded by association of females. Each nest
began as a single comb but, after the emergence of progeny adults, satellite combs were constructed near the original comb.
During the pre-emergence (single-comb) stage, each colony had a single egg-layer, despite the rare occurrence of intranidal
dominance acts among female wasps. When colonies had reached the multiple-comb stage, the frequency and intensity of intranidal
dominance-aggressive acts rose to a high level, comparable to those of typically aggressive colonies of e.g.Polistes canadensis in Panama. Colonies appeared to be still functionally haplometrotic during the early phase of multiple-comb stage, but several
potential egg-layers were present as colony size increased. Dominant females often performed wing vibration, rapid runs between
combs and tended to sit on the largest comb, whilst subordinate females tended to sit on smaller combs. 相似文献