全文获取类型
收费全文 | 5226篇 |
免费 | 660篇 |
国内免费 | 4篇 |
出版年
2021年 | 70篇 |
2018年 | 71篇 |
2017年 | 50篇 |
2016年 | 110篇 |
2015年 | 148篇 |
2014年 | 171篇 |
2013年 | 176篇 |
2012年 | 267篇 |
2011年 | 246篇 |
2010年 | 145篇 |
2009年 | 149篇 |
2008年 | 175篇 |
2007年 | 204篇 |
2006年 | 184篇 |
2005年 | 191篇 |
2004年 | 148篇 |
2003年 | 175篇 |
2002年 | 170篇 |
2001年 | 180篇 |
2000年 | 170篇 |
1999年 | 130篇 |
1998年 | 75篇 |
1997年 | 54篇 |
1996年 | 62篇 |
1995年 | 51篇 |
1994年 | 66篇 |
1993年 | 47篇 |
1992年 | 108篇 |
1991年 | 114篇 |
1990年 | 96篇 |
1989年 | 121篇 |
1988年 | 85篇 |
1987年 | 107篇 |
1986年 | 80篇 |
1985年 | 92篇 |
1984年 | 76篇 |
1983年 | 60篇 |
1982年 | 59篇 |
1981年 | 51篇 |
1980年 | 51篇 |
1979年 | 72篇 |
1978年 | 49篇 |
1977年 | 52篇 |
1976年 | 46篇 |
1974年 | 58篇 |
1973年 | 58篇 |
1972年 | 68篇 |
1970年 | 51篇 |
1969年 | 54篇 |
1968年 | 46篇 |
排序方式: 共有5890条查询结果,搜索用时 46 毫秒
151.
152.
Cody Raul Cardenas Andrew J. Mularo Andreas S. Chavez Rachelle M. M. Adams 《Biotropica》2023,55(1):145-159
The coevolutionary relationship between fungus-growing ants (Formicidae: Attini: Attina) and their symbionts has been well studied in the Panamanian rain forests. To further understand the ecological context of these evolutionary relationships, we have examined the population-genetic structure of the fungus-growing ant species Mycetomoellerius mikromelanos Cardenas, Schultz, Adams 2021 in the Panama Canal Zone. We specifically investigated the presence of population structure, the significance of geographic features (i.e., creeks) limiting gene flow, and relatedness between ant colonies. To accomplish this, we genotyped 85 ant colonies from nine creeks across an approximately 30 km transect in Parque National Soberanía, Panama, using double-digest restriction-site-associated DNA sequencing. We did not find distinct population structure using two genetic clustering methods; however, we did detect an effect of isolation by distance. Furthermore, related colonies were frequently detected on the same creek or neighboring creeks, and some at further geographic distances. Collectively, these findings demonstrate that new colonies tend to establish on natal creeks and occasionally on distant creeks following long-distance dispersal events. We discuss how population-genetic patterns reveal the natural history of M. mikromelanos in Parque National Soberanía and how these results fit into the context of fungus-growing ant mutualisms. Abstract in Spanish is available with online material. 相似文献
153.
154.
Mapping of electrical muscle stimulation using MRI 总被引:7,自引:0,他引:7
Adams G. R.; Harris R. T.; Woodard D.; Dudley G. A. 《Journal of applied physiology》1993,74(2):532-537
155.
D R Spitz D T Adams C M Sherman R J Roberts 《Archives of biochemistry and biophysics》1992,292(1):221-227
An H2O2-resistant variant (OC14) of the HA1 Chinese hamster fibroblast cell line which demonstrates a 20-fold increase in catalase activity was utilized in the study of mechanisms responsible for cellular resistance to hydrogen peroxide, oxygen, and 4-hydroxy-2-nonenal toxicity. HA1 and OC14 cells were treated with 9 mM aminotriazole which resulted in a 60 to 80% reduction in catalase activity. Pretreatment with aminotriazole resulted in significant sensitization to the toxicity of 1-h exposures to exogenously applied H2O2, which was proportional to the reduction in catalase activity. Treatment with aminotriazole produced significant sensitization to the toxicity of 95% O2 after 45 h of O2 exposure but no sensitization to the toxicity of a 1-h exposure to 50 microM 4-hydroxy-2-nonenal. Inhibition of catalase activity by aminotriazole had no effect on the metabolism of 4-hydroxy-2-nonenal by either cell line tested. These results support the conclusion that in H2O2-resistant cells, catalase activity is a major determinant of cellular resistance to H2O2 toxicity, whereas catalase activity has a limited role in cellular resistance to an acute exposure to 95% O2 and is unrelated to cellular resistance to 4-hydroxy-2-nonenal. 相似文献
156.
157.
Lisa Beltz Opendra Narayan Robert J. Adams Stephen J. Noga Albert D. Donnenberg 《Journal of medical primatology》1991,20(4):144-151
Rhesus progenitor-enriched BM was exposed overnight to SIV and cultured in a limiting dilution assay where the potential for progenitor interaction with lymphocytes or macrophages was low. Virus was consistently isolated late in culture, detection being aided by coculture with CEM174 lymphoblasts. Although infected cells had reduced clonogenic activity, colonies were indistinguishable from those derived from uninfected BM with respect to proliferative potential, morphology, and longevity in culture. Primate immunodeficiency viruses, therefore, may infect immature BM populations, directly affecting hematopoietic activity. 相似文献
158.
C. Moritz S. Donnellan M. Adams P. R. Baverstock 《Evolution; international journal of organic evolution》1989,43(5):994-1003
Variation at 18 allozyme loci was assayed among representatives of the geographically widespread, triploid parthenogenetic form of Heteronotia binoei. A minimum of 52 different genotypes were observed among 143 individuals. Virtually all localities sampled had multiple genotypes among the unisexuals. This represents unusually high genotypic diversity for a unisexual vertebrate. Heterozygosity in the triploids was higher than in diploid bisexual populations of H. binoei. Comparison with the alleles present in the diploid bisexuals confirms that the parthenogens are hybrids and indicates that most of the genotypic diversity stems from repetitive hybrid origins. However, the presence of some alleles unique to the parthenogens suggests that mutation adds to their genetic diversity. The genetic structure of this geographically widespread parthenogen suggests the hypothesis that the persistence and spread of the unisexual lineages is facilitated by genotypic diversity. 相似文献
159.
160.