全文获取类型
收费全文 | 23829篇 |
免费 | 2647篇 |
国内免费 | 8篇 |
出版年
2021年 | 329篇 |
2020年 | 201篇 |
2019年 | 272篇 |
2018年 | 317篇 |
2017年 | 280篇 |
2016年 | 540篇 |
2015年 | 875篇 |
2014年 | 1022篇 |
2013年 | 1212篇 |
2012年 | 1496篇 |
2011年 | 1458篇 |
2010年 | 946篇 |
2009年 | 875篇 |
2008年 | 1231篇 |
2007年 | 1274篇 |
2006年 | 1190篇 |
2005年 | 1106篇 |
2004年 | 1042篇 |
2003年 | 1040篇 |
2002年 | 948篇 |
2001年 | 392篇 |
2000年 | 395篇 |
1999年 | 445篇 |
1998年 | 353篇 |
1997年 | 244篇 |
1996年 | 245篇 |
1995年 | 256篇 |
1994年 | 231篇 |
1993年 | 258篇 |
1992年 | 348篇 |
1991年 | 305篇 |
1990年 | 284篇 |
1989年 | 270篇 |
1988年 | 277篇 |
1987年 | 250篇 |
1986年 | 255篇 |
1985年 | 275篇 |
1984年 | 265篇 |
1983年 | 190篇 |
1982年 | 194篇 |
1981年 | 162篇 |
1980年 | 149篇 |
1979年 | 214篇 |
1978年 | 175篇 |
1977年 | 161篇 |
1976年 | 175篇 |
1975年 | 157篇 |
1974年 | 143篇 |
1973年 | 169篇 |
1972年 | 154篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
3.
4.
J E Pugh M R Horwitz D J Anderson E F Singleton 《American journal of physical anthropology》1973,38(2):351-356
A new technique for the continuous recording of peripheral bioelectrical activity in the auditory system of primates is described. Because of basic differences in the anatomy of the temporal bone, the approach to the round window of the cochlea is more difficult in most primates than in lower animals. A relatively simple surgical approach, which made possible the placement of an electrode into the perilymph of the inner ear via the well-demarcated horizontal semicircular canal was therefore developed and is described in detail. The bared tip of a Teflon-coated wire was cemented into the canal opening with carboxylate cement, and the wire attached to a permanent electrical connector on the skull. Cochlear microphonic and action potentials of 50 to 100 μV amplitude were thus recorded on a continuing basis at the same time that behavioral studies of primate auditory acuity were conducted. 相似文献
5.
David M. Anderson Richard H. Scheller James W. Posakony Linda B. McAllister Steven G. Trabert Clifford Beall Roy J. Britten Eric H. Davidson 《Journal of molecular biology》1981,145(1):5-28
Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA. 相似文献
6.
Kevin Karbstein Kathleen Prinz Frank Hellwig Christine Rmermann 《Ecology and evolution》2020,10(11):5015-5033
Intraspecific trait variation (ITV), based on available genetic diversity, is one of the major means plant populations can respond to environmental variability. The study of functional trait variation and diversity has become popular in ecological research, for example, as a proxy for plant performance influencing fitness. Up to now, it is unclear which aspects of intraspecific functional trait variation (iFDCV) can be attributed to the environment or genetics under natural conditions. Here, we examined 260 individuals from 13 locations of the rare (semi‐)dry calcareous grassland species Trifolium montanum L. in terms of iFDCV, within‐habitat heterogeneity, and genetic diversity. The iFDCV was assessed by measuring functional traits (releasing height, biomass, leaf area, specific leaf area, leaf dry matter content, Fv/Fm, performance index, stomatal pore surface, and stomatal pore area index). Abiotic within‐habitat heterogeneity was derived from altitude, slope exposure, slope, leaf area index, soil depth, and further soil factors. Based on microsatellites, we calculated expected heterozygosity (He) because it best‐explained, among other indices, iFDCV. We performed multiple linear regression models quantifying relationships among iFDCV, abiotic within‐habitat heterogeneity and genetic diversity, and also between separate functional traits and abiotic within‐habitat heterogeneity or genetic diversity. We found that abiotic within‐habitat heterogeneity influenced iFDCV twice as strong compared to genetic diversity. Both aspects together explained 77% of variation in iFDCV ( = .77, F2, 10 = 21.66, p < .001). The majority of functional traits (releasing height, biomass, specific leaf area, leaf dry matter content, Fv/Fm, and performance index) were related to abiotic habitat conditions indicating responses to environmental heterogeneity. In contrast, only morphology‐related functional traits (releasing height, biomass, and leaf area) were related to genetics. Our results suggest that both within‐habitat heterogeneity and genetic diversity affect iFDCV and are thus crucial to consider when aiming to understand or predict changes of plant species performance under changing environmental conditions. 相似文献
7.
8.
Sieve element pores in Nicotiana pith culture 总被引:3,自引:0,他引:3
9.
10.