全文获取类型
收费全文 | 58854篇 |
免费 | 4960篇 |
国内免费 | 2400篇 |
出版年
2023年 | 477篇 |
2022年 | 495篇 |
2021年 | 2089篇 |
2020年 | 1364篇 |
2019年 | 1696篇 |
2018年 | 1642篇 |
2017年 | 1316篇 |
2016年 | 1950篇 |
2015年 | 3103篇 |
2014年 | 3597篇 |
2013年 | 4034篇 |
2012年 | 4730篇 |
2011年 | 4596篇 |
2010年 | 2725篇 |
2009年 | 2533篇 |
2008年 | 3099篇 |
2007年 | 2965篇 |
2006年 | 2626篇 |
2005年 | 2453篇 |
2004年 | 2212篇 |
2003年 | 1894篇 |
2002年 | 1745篇 |
2001年 | 1114篇 |
2000年 | 955篇 |
1999年 | 956篇 |
1998年 | 709篇 |
1997年 | 623篇 |
1996年 | 543篇 |
1995年 | 512篇 |
1994年 | 517篇 |
1993年 | 434篇 |
1992年 | 597篇 |
1991年 | 525篇 |
1990年 | 454篇 |
1989年 | 396篇 |
1988年 | 348篇 |
1987年 | 333篇 |
1986年 | 250篇 |
1985年 | 321篇 |
1984年 | 245篇 |
1983年 | 222篇 |
1982年 | 216篇 |
1981年 | 181篇 |
1980年 | 152篇 |
1979年 | 165篇 |
1978年 | 149篇 |
1977年 | 141篇 |
1976年 | 121篇 |
1974年 | 124篇 |
1973年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
The influence of fruit ingestion by the bat, Sturnira lilium, on germination of the seeds of the tree Solanum riparium was studied in a secondary rain forest in northwestern Argentina. Bat frequencies in disturbed areas were analyzed by mist net captures. Germination rates were determined for seeds collected from trees and bat feces. S. lilium was the most abundant fruit bat in the study area. Fruit digestion and the passage of seeds through the intestine did not significantly affect germination in S. riparium. In this case the fruit bats, therefore, probably provide only seed dispersal. 相似文献
2.
Yi-Hua Wu Chia-Pei Chang Chin-I Chien Yi-Kuan Tseng Chien-Chia Wang 《Molecular and cellular biology》2013,33(17):3515-3523
The yeast Saccharomyces cerevisiae possesses two distinct glycyl-tRNA synthetase (GlyRS) genes: GRS1 and GRS2. GRS1 is dually functional, encoding both cytoplasmic and mitochondrial activities, while GRS2 is dysfunctional and not required for growth. The protein products of these two genes, GlyRS1 and GlyRS2, are much alike but are distinguished by an insertion peptide of GlyRS1, which is absent from GlyRS2 and other eukaryotic homologues. We show that deletion or mutation of the insertion peptide modestly impaired the enzyme''s catalytic efficiency in vitro (with a 2- to 3-fold increase in Km and a 5- to 8-fold decrease in kcat). Consistently, GRS2 can be conveniently converted to a functional gene via codon optimization, and the insertion peptide is dispensable for protein stability and the rescue activity of GRS1 at 30°C in vivo. A phylogenetic analysis further showed that GRS1 and GRS2 are paralogues that arose from a gene duplication event relatively recently, with GRS1 being the predecessor. These results indicate that GlyRS2 is an active enzyme essentially resembling the insertion peptide-deleted form of GlyRS1. Our study suggests that the insertion peptide represents a novel auxiliary domain, which facilitates both productive docking and catalysis of cognate tRNAs. 相似文献
3.
4.
5.
Vernon Shattuck Frank R. Katterman 《Biochemical and biophysical research communications》1982,109(3):1017-1025
When cotyledonary tissue of cotton are treated with the mutagen ethyl methanesulfonate and then germinated, an enhanced, unscheduled DNA synthesis response is observed, along with a concomitant increase in the thymidine triphosphate precursor pool size. The implications of these results are discussed in this paper. 相似文献
6.
7.
Frank J. Turano Kenneth Glade Wilson 《In vitro cellular & developmental biology. Plant》1985,21(3):135-139
Summary The feasibility of using plant cell culture to measure toxicity was determined by investigating the toxicological effects
of three chemical compounds, allyl alcohol, propargylglycine, and cadmium chloride, on cell cultures ofCatharanthus roseus G. Don (Madagascar periwinkle). Suspension cultures ofC. roseus were maintained in modified B5 medium and transferred every 5 d. Five-day-old cell cultures were exposed to various concentrations
(10,3,1,0.3,0.1,0.03,0.01,0.003,0.001,0.0003,0.0001, 0.00003, and 0.0 mM) of the toxicants in both acute and chronic toxicity tests.
In the acute test, cells were exposed to the toxicant for 24 h, washed three times with sterile medium, and plated in petri
plates with an equal volume of 1.4% agar medium. Cells in the chronic test were plated with an equal volume of 1.4% agar medium
containing various concentrations of the toxicant. Cells were incubated 28 d at 30°C in the dark. The colonies were counted
and the results plotted as percent survival versus toxicant concentration. The results indicate, at the concentrations tested,
thatC. roseus assay may be feasible in that it fulfills the criteria for a practical assay (e.g., rapid, simple, quantifiable, and reproducible).
This work was submitted to the faculty of Miami University in partial fulfillment of the requirements for the degree of Master
of Environmental Science, Institute of Environmental Sciences. 相似文献
8.
9.
10.
Sylvester J. T.; Harabin A. L.; Peake M. D.; Frank R. S. 《Journal of applied physiology》1980,49(5):820-825