全文获取类型
收费全文 | 798479篇 |
免费 | 82634篇 |
国内免费 | 245篇 |
专业分类
881358篇 |
出版年
2018年 | 7954篇 |
2017年 | 7611篇 |
2016年 | 10679篇 |
2015年 | 13505篇 |
2014年 | 16107篇 |
2013年 | 23241篇 |
2012年 | 26062篇 |
2011年 | 26838篇 |
2010年 | 18341篇 |
2009年 | 16954篇 |
2008年 | 24008篇 |
2007年 | 24989篇 |
2006年 | 23356篇 |
2005年 | 22447篇 |
2004年 | 22221篇 |
2003年 | 21358篇 |
2002年 | 20884篇 |
2001年 | 34797篇 |
2000年 | 34257篇 |
1999年 | 27635篇 |
1998年 | 10206篇 |
1997年 | 10294篇 |
1996年 | 9853篇 |
1995年 | 9081篇 |
1994年 | 8753篇 |
1993年 | 8766篇 |
1992年 | 22381篇 |
1991年 | 21958篇 |
1990年 | 21421篇 |
1989年 | 20860篇 |
1988年 | 19123篇 |
1987年 | 18362篇 |
1986年 | 17126篇 |
1985年 | 16981篇 |
1984年 | 13950篇 |
1983年 | 12198篇 |
1982年 | 9254篇 |
1981年 | 8367篇 |
1980年 | 7765篇 |
1979年 | 12963篇 |
1978年 | 10223篇 |
1977年 | 9204篇 |
1976年 | 8815篇 |
1975年 | 9830篇 |
1974年 | 10502篇 |
1973年 | 10358篇 |
1972年 | 9485篇 |
1971年 | 8459篇 |
1970年 | 7390篇 |
1969年 | 7261篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The ECF™ lateral flow assay test is marketed to detect non-pregnancy in mares. The objectives of the present study were to determine the accuracy of the ECF test, the accuracy of the electronic reader accompanying the ECF test, and agreement between two human readers and the electronic reader. Serum samples were collected from anestrus, cycling but not inseminated, and inseminated mares, and were evaluated with the ECF™ test (EDP Biotech Company, Knoxville, TN, USA) at The Ohio State University and at the EDP Biotech Laboratory. Specificity ranged from 0.07 to 0.16, the negative predictive value ranged from 0.15 to 0.33, and accuracy ranged from 0.43 to 0.52. The electronic reader did not add improve the accuracy or predictive values of the test. Based on the electronic reader, 80.0% of the serum samples collected from the anestrus mares were false positives; Readers 1 and 2 had 60.0 and 33.3% false positives, respectively. For samples collected during the estrous cycle, 83.9% were false positives by the electronic reader, whereas Readers 1 and 2 had 43.7 and 26.4% false positives. We concluded that, regardless of whether the test strips were evaluated by a human or electronic reader, this assay was not accurate for determination of the non-pregnant mare. 相似文献
992.
993.
994.
995.
In the experiments on redox potential measurement for a series of identical samples of purified and presettled water it was found that the response to ultraviolet irradiation varies appreciably within a few days after treatment, including stepwise changes. In a few hours after exposure, leading to a higher content of reactive oxygen species as compared with the equilibrium values, long-term changes including variations in redox potential and optical system parameters are recorded in water and diluted aqueous media. We propose a heuristic organization model of the water-gas system with an increased content of reactive oxygen species. 相似文献
996.
997.
Abstract The parasitoid wasp Trichogramma dendrolimi Matsumura sets the number of progeny allocated to its insect egg hosts according to the duration of its initial transit walk across the host surface. Although cooling the wasp reduces its walking speed, reduced temperature does not affect progeny allocation. By locally heating and cooling the wasps, the initial transit can be thermally uncoupled from the subsequent oviposition. Using this technique we show that the timing of initial transit duration is temperature-dependent. These findings suggest that short interval timing by Trichogramma differs physiologically from the temperature compensated clocks that have been described for other insects. 相似文献
998.
A A Shandra L S Godlevski? A M Mazarati R S Vast'ianov 《Biulleten' eksperimental'no? biologii i meditsiny》1992,113(3):236-239
It is shown that both intracerebral and intraperitoneal neurotropin administration resulted in a decrease of seizure susceptibility of preliminary picrotoxin--kindled rats. On the other hand, neurotropin did not change the course of kindling development. Under conditions of acute picrotoxin--induced seizures it was observed that preliminary cycloheximide (protein-synthesis blocker) administration abolished anticonvulsant properties of neurotropin. It is concluded that anticonvulsant effects of neurotropin are realized via modulation of endogenous peptides synthesis and, in particular, cerulein. 相似文献
999.
G. N. Mishina G. V. Serezhkina T. V. Avetisyan A. S. Ryabchenko L. N. Andreev 《Biology Bulletin》2001,28(4):354-360
A cytophysiological study was carried out of the functional status of a halo as a response of the host plant to contact with a powdery mildew pathogen. Interactions of the powdery mildew causative agents with barley, wheat, wheat–wheat-grass hybrids, wheat-aegilops lines, and aegilops with different genotypic resistance lead to the expression of haloes during pathogens, which are induced by infection pegs of the primary growth tubes, appressoria, and hyphal lobes. Haloes are visualized using cytochemical reactions to proteins and scanning electron microscopy. The observed differences in the size of haloes and intensity of their staining (uniform or zonal) are related, to a great extent, to individual reactions of the plant cell at the penetration site and, to a lesser extent, to the level of genotypic resistance. An analysis of electron microscopy and cytochemistry studies suggests that the halo as a physiologically active zone is localized at the level of the plant cell plasmalemma. Active taxis of the cell organelles to the site of infection during the formation of a halo suggests that some kind of informational signals to changes in the cell metabolism are spread from the halo zone, which lead to compatible or incompatible interactions. 相似文献
1000.