全文获取类型
收费全文 | 224182篇 |
免费 | 14983篇 |
国内免费 | 45篇 |
专业分类
239210篇 |
出版年
2021年 | 1777篇 |
2018年 | 3130篇 |
2017年 | 3025篇 |
2016年 | 3667篇 |
2015年 | 3207篇 |
2014年 | 4450篇 |
2013年 | 6329篇 |
2012年 | 7553篇 |
2011年 | 8073篇 |
2010年 | 5726篇 |
2009年 | 4880篇 |
2008年 | 7203篇 |
2007年 | 7485篇 |
2006年 | 7184篇 |
2005年 | 6712篇 |
2004年 | 6855篇 |
2003年 | 6572篇 |
2002年 | 6525篇 |
2001年 | 9278篇 |
2000年 | 8958篇 |
1999年 | 6988篇 |
1998年 | 2122篇 |
1997年 | 1954篇 |
1996年 | 1819篇 |
1992年 | 5471篇 |
1991年 | 5682篇 |
1990年 | 5653篇 |
1989年 | 5624篇 |
1988年 | 5216篇 |
1987年 | 4866篇 |
1986年 | 4443篇 |
1985年 | 4681篇 |
1984年 | 3699篇 |
1983年 | 3026篇 |
1982年 | 2015篇 |
1981年 | 1722篇 |
1980年 | 1729篇 |
1979年 | 3345篇 |
1978年 | 2581篇 |
1977年 | 2388篇 |
1976年 | 2330篇 |
1975年 | 2830篇 |
1974年 | 3118篇 |
1973年 | 3087篇 |
1972年 | 2748篇 |
1971年 | 2606篇 |
1970年 | 2217篇 |
1969年 | 2160篇 |
1968年 | 2032篇 |
1967年 | 1801篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
S. T. Zakhidov T. L. Marshak E. A. Malolina A. Yu. Kulibin I.A. Zelenina S. M. Pavluchenkova V. M. Rudoi O. V. Dement’eva S. G. Skuridin Yu. M. Evdokimov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(3):293-296
The effect of gold nanoparticles on mouse epididymal sperm has been studied using the model system of nuclear chromatin decondensation
in vitro. It is shown that the treatment of gametes, preliminary membrane-freed by sodium dodecyl sulfate, in the mediums
containing gold nanoparticles (with diameter ∼2.5 nm) in concentrations 1.0 × 1015 or 0.5 × 1015 particles/ml and following incubation in dithiothreitol solution (DTT) resulted in failure of chromatin decondensation process
and nucleus structure. We conclude that gold nanoparticles possess spermatotoxicity. The mechanism of cytotoxic effect of
gold nanoparticles may be related with their interaction with molecules of double-helix DNA. The model system studied in this
research is applicable for further investigations of cytotoxic effects of nanoparticles of different origin and made of different
metals. 相似文献
144.
ESR spectra of gamma-irradiated and frozen at 77 K human oxyhemoglobin and partially denaturated methemoglobin solutions were analysed. The quartet signal ascribed to the anion-radical of proximal histidine was shown to dominate in the spectra of both solutions. The spectra of methemoglobin solution irradiated with relatively small doses have an intensive singlet ascribed to the stabilized electron. The formation mechanism of free radicals is discussed. 相似文献
145.
Abstract— The effect of excess leucine in the diet on serotonin metabolism in the brain was investigated in experimental animals. It was found that:
(1) Animals receiving diets containing 3 % and 8 % leucine and those receiving jowar diets had significantly lower levels of serotonin in the brain.
(2) Intraperitoneal administration of the precursor amino acid 5-HTP increased the serotonin concentration in brain in both control and leucine-fed animals. However, the serotonin concentration in leucine-fed animals was significantly lower than that of pairfed controls. Larger amounts of the synthesized serotonin were found to be catabolized in 3 hr in leucine-fed animals than in control animals.
(3) The in vitro uptake of [14 C]5-HTP by brain slices of animals fed leucine was found to be similar to that of control animals.
(4) The basal concentration of 5-HIAA in brain was higher in leucine-fed animals, suggesting a higher rate of catabolism of serotonin.
(5) Administration of nicotinic acid resulted in a further fall of serotonin concentration in the brains of leucine-fed animals but not in control animals. 相似文献
(1) Animals receiving diets containing 3 % and 8 % leucine and those receiving jowar diets had significantly lower levels of serotonin in the brain.
(2) Intraperitoneal administration of the precursor amino acid 5-HTP increased the serotonin concentration in brain in both control and leucine-fed animals. However, the serotonin concentration in leucine-fed animals was significantly lower than that of pairfed controls. Larger amounts of the synthesized serotonin were found to be catabolized in 3 hr in leucine-fed animals than in control animals.
(3) The in vitro uptake of [
(4) The basal concentration of 5-HIAA in brain was higher in leucine-fed animals, suggesting a higher rate of catabolism of serotonin.
(5) Administration of nicotinic acid resulted in a further fall of serotonin concentration in the brains of leucine-fed animals but not in control animals. 相似文献
146.
147.
148.
149.
150.
Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than
between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites
and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial
isolation of the population and gene drift. 相似文献