全文获取类型
收费全文 | 23290篇 |
免费 | 2199篇 |
国内免费 | 7篇 |
出版年
2021年 | 384篇 |
2020年 | 218篇 |
2019年 | 270篇 |
2018年 | 385篇 |
2017年 | 329篇 |
2016年 | 509篇 |
2015年 | 930篇 |
2014年 | 1010篇 |
2013年 | 1227篇 |
2012年 | 1737篇 |
2011年 | 1693篇 |
2010年 | 1016篇 |
2009年 | 1011篇 |
2008年 | 1363篇 |
2007年 | 1409篇 |
2006年 | 1279篇 |
2005年 | 1300篇 |
2004年 | 1127篇 |
2003年 | 1093篇 |
2002年 | 1063篇 |
2001年 | 365篇 |
2000年 | 306篇 |
1999年 | 313篇 |
1998年 | 345篇 |
1997年 | 213篇 |
1996年 | 206篇 |
1995年 | 192篇 |
1994年 | 190篇 |
1993年 | 162篇 |
1992年 | 203篇 |
1991年 | 196篇 |
1990年 | 186篇 |
1989年 | 207篇 |
1988年 | 162篇 |
1987年 | 162篇 |
1986年 | 153篇 |
1985年 | 168篇 |
1984年 | 173篇 |
1983年 | 135篇 |
1982年 | 145篇 |
1981年 | 155篇 |
1980年 | 137篇 |
1979年 | 127篇 |
1978年 | 112篇 |
1977年 | 104篇 |
1976年 | 83篇 |
1975年 | 77篇 |
1974年 | 114篇 |
1973年 | 93篇 |
1972年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
61.
Forrest H. Adams 《The Western journal of medicine》1956,85(2):67-69
Certain of the acute phase reactant tests were performed on the same specimen of blood from persons with the following states: Normal, acute respiratory disease, streptococcosis, acute rheumatic fever, acute glomerulonephritis, acute rheumatoid arthritis, inactive rheumatic fever, lupus erythematosus, malignant disease, obesity, asthma, and allergic rhinitis. Of the tests performed, the mucoprotein-tyrosine and the antistreptolysin-0 titer when done together appeared to be the most discriminating. It is suggested that the performance of such tests on the same sample of blood might aid in differentiating mild acute rheumatic fever and acute rheumatoid arthritis from each other and also from other disease states. 相似文献
62.
63.
64.
Recent studies suggest that nitric oxide (NO) may regulate hormone biosynthesis and secretion. This was tested by treating male rats with NG-nitro-L-arginine methyl ester (NAME), a NO synthase inhibitor, and measuring serum and testicular interstitial fluid testosterone and serum corticosterone, luteinizing hormone (LH), and prolactin (PRL). The effect of NG-nitro-L-arginine (NA), a less-soluble form of the same NO synthase inhibitor, on the reproductive suppressant actions of alcohol was also examined. NAME increased testosterone and corticosterone secretion dose-dependently without affecting LH and PRL secretion. The alcohol-induced suppression of testosterone or LH secretion was not altered by treatment with NA. Although effects of NAME and NA on other systems may be involved, these results indicate that testicular and adrenal steroidogenesis are negatively regulated by endogenous NO and that NO does not regulate LH and PRL secretion or inhibit the testicular steroidogenic pathway in the same way as alcohol. 相似文献
65.
Douglas S. Richmond† Brian A. Kunkel Nethi Somasekhar Parwinder S. Grewal 《Ecological Entomology》2004,29(3):353-360
Abstract. 1. The fungus Neotyphodium lolii forms a symbiotic relationship with its grass host Lolium perenne (perennial ryegrass). The fungus benefits from access to plant nutrients and photosynthate, whereas the plant benefits from acquired chemical defence against herbivory.
2. This study examined the potential for endophyte-mediated plant defences to influence interactions between fall armyworm Spodoptera frugiperda , and the entomopathogenic nematode Steinernema carpocapsae and clarified biological mechanisms underlying the observations made.
3. In laboratory and greenhouse experiments, S. frugiperda larvae were fed endophytic or non-endophytic L. perenne then exposed to S. carpocapsae or injected with the nematodes' symbiotic bacteria Xenorhabdus nematophila .
4. In all instances, S. frugiperda larvae fed endophyte-infected grass suffered significantly lower mortality than those fed non-endophytic plants. Although larvae fed endophyte-infected grass often had significantly lower biomass than those fed uninfected grass, these differences did not account for altered susceptibility to S. carpocapsae .
5. Endophyte-mediated reductions in herbivore susceptibility to the nematode pathogen represent a herbivore adaptation that effectively turns the tables on both plant and natural enemy by reducing the virulence of the nematodes' symbiotic bacteria while expanding the temporal window of herbivory. 相似文献
2. This study examined the potential for endophyte-mediated plant defences to influence interactions between fall armyworm Spodoptera frugiperda , and the entomopathogenic nematode Steinernema carpocapsae and clarified biological mechanisms underlying the observations made.
3. In laboratory and greenhouse experiments, S. frugiperda larvae were fed endophytic or non-endophytic L. perenne then exposed to S. carpocapsae or injected with the nematodes' symbiotic bacteria Xenorhabdus nematophila .
4. In all instances, S. frugiperda larvae fed endophyte-infected grass suffered significantly lower mortality than those fed non-endophytic plants. Although larvae fed endophyte-infected grass often had significantly lower biomass than those fed uninfected grass, these differences did not account for altered susceptibility to S. carpocapsae .
5. Endophyte-mediated reductions in herbivore susceptibility to the nematode pathogen represent a herbivore adaptation that effectively turns the tables on both plant and natural enemy by reducing the virulence of the nematodes' symbiotic bacteria while expanding the temporal window of herbivory. 相似文献
66.
67.
68.
Brian T. Shea 《International journal of primatology》1987,8(2):139-156
In order to understand fully the generally high level of encephalization observed in living primates, we must determine why
early primates exhibited moderately large relative brain sizes compared to their early Tertiary contemporaries. The relatively
high degree of encephalization in early primates may be related at least in part to the fact that they were highly unusualamong mammals in combining a small body size with a strongly precocial reporductive strategy. Other small, precocial mammals
also exhibit moderately high levels of encephalization; but primates appear to have been truly uniquein being the only such small-sized and highly precocial group to give rise to extensive radiations of larger descendants.
This is a key element in understanding primate brain evolution, because the initial “head start” of the early primates was
translated up to larger sizes in descendants. The possible relationships among encephalization, precociality, small size,
and arboreality are discussed, particularly in light of recent debates concerning the validity of the superorder Archonta.
This work emphasizes that we need to consider relative brain size as but one element in a complex synergistic network of morphological
and life-history features. 相似文献
69.
Small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been purified from 3 species of orchid in the genus Cymbidium by gel filtration followed by preparative sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution. The samples were subjected to amino acid composition analysis and partial N-terminal amino acid sequencing. The sequencing data clearly confirm that one of the species examined is the hybrid offspring of a cross between the other two. 相似文献
70.