全文获取类型
收费全文 | 5764篇 |
免费 | 568篇 |
国内免费 | 1篇 |
出版年
2023年 | 22篇 |
2022年 | 37篇 |
2021年 | 101篇 |
2020年 | 66篇 |
2019年 | 81篇 |
2018年 | 59篇 |
2017年 | 83篇 |
2016年 | 117篇 |
2015年 | 274篇 |
2014年 | 266篇 |
2013年 | 336篇 |
2012年 | 423篇 |
2011年 | 431篇 |
2010年 | 273篇 |
2009年 | 222篇 |
2008年 | 324篇 |
2007年 | 331篇 |
2006年 | 320篇 |
2005年 | 327篇 |
2004年 | 283篇 |
2003年 | 276篇 |
2002年 | 270篇 |
2001年 | 72篇 |
2000年 | 65篇 |
1999年 | 71篇 |
1998年 | 93篇 |
1997年 | 46篇 |
1996年 | 43篇 |
1995年 | 46篇 |
1994年 | 48篇 |
1993年 | 56篇 |
1992年 | 47篇 |
1991年 | 43篇 |
1990年 | 45篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 47篇 |
1986年 | 29篇 |
1985年 | 33篇 |
1984年 | 46篇 |
1983年 | 49篇 |
1982年 | 43篇 |
1981年 | 28篇 |
1980年 | 41篇 |
1979年 | 25篇 |
1978年 | 40篇 |
1977年 | 34篇 |
1976年 | 20篇 |
1974年 | 24篇 |
1973年 | 31篇 |
排序方式: 共有6333条查询结果,搜索用时 31 毫秒
1.
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
2.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
3.
4.
N. J. Belshaw S. Hakola H. Nevalainen M. Penttil? P. Suominen D. B. Archer 《Molecular & general genetics : MGG》1997,256(1):18-27
Three DNA fragments, trs1, 2 and 3, were isolated from the Trichoderma reesei genome on the basis of their ability to promote autonomous replication of plasmids in Saccharomyces cerevisiae. Each trs element bound specifically to the isolated T. reesei nuclear matrix in vitro, and two of them bound in vivo, indicating that they are matrix attachment regions (MARs). A similar
sequence previously isolated from Aspergillus nidulans (ans1) was also shown to bind specifically to the T. reesei nuclear matrix in vitro. The T. reesei MARs are AT-rich sequences containing 70%, 86% and 73% A+T over 2.9, 0.8 and 3.7 kb, respectively for trs1, 2 and 3. They exhibited no significant sequence homology, but were shown to contain a number of sequence motifs that occur frequently
in many MARs identified in other eukaryotes. However, these motifs occurred as frequently in the trs elements as in randomly generated sequences with the same A+T content. trs1 and 3 were shown to be present as single copies in the T. reesei genome. The presence of the trs elements in transforming plasmids enhanced the frequency of integrative transformation of T. reesei up to five fold over plasmids without a trs. No evidence was obtained to suggest that the trs elements promoted efficient replication of plasmids in T. reseei. A mechanism for the enhancement of transformation frequency by the trs elements is proposed.
Received: 1 March 1997 / Accepted: 13 May 1997 相似文献
5.
Benedict G. Archer 《Analytical biochemistry》1981,113(2):439-443
A gel filtration method has been developed for the complete removal of sodium dodecyl sulfate (SDS) from proteins and peptides. The protein or peptide (20 μg–10 mg) containing SDS (up to 30–60 mg) is dissolved in a mixture of propionic acid, formic acid, and water (2:1:2, ). Under these conditions, protein-SDS (or peptide-SDS) complexes, as well as SDS micelles, are dissociated. Subsequently, protein and SDS can be separated on a small Sephadex G-25 superfine column. The recovery of protein is typically 90% or more. 相似文献
6.
Summary An improved method for separating analogues of coenzyme F420 by isocratic reversed-phase high performance liquid chromatography is described. The method offers improved resolution, shorter chromatography runs and requires less complex apparatus. 相似文献
7.
8.
9.
10.
The seasonal growth and decline of a population of Elodea canadensis Mich. growing in an irrigation drain are described, together with some characteristics of the aquatic environment (turbidity, photosynthetically-available radiation, temperature and pH). Overwintering buds (up to 5000 m?2) in the form of swollen dormant stem apices are produced in autumn with the onset of cold weather, remain in the mud, and grow out in the spring. In late summer vegetative reproduction also occurs when large numbers of the leafless stem portions which are capable of growing into independent plants are swept downstream from established populations. Results suggest that control measures should be applied in early summer when populations are approaching nuisance size, and again in late summer before fragmentation occurs and overwintering propagules are initiated. In irrigation channels in Australia, where draining and drying are not feasible, biomass in successfully reduced by widespread use of herbicides. 相似文献