全文获取类型
收费全文 | 863篇 |
免费 | 112篇 |
出版年
2022年 | 6篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 32篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 72篇 |
2011年 | 63篇 |
2010年 | 31篇 |
2009年 | 42篇 |
2008年 | 52篇 |
2007年 | 48篇 |
2006年 | 41篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 30篇 |
2002年 | 34篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有975条查询结果,搜索用时 31 毫秒
1.
2.
Perturbation experiments, in which a certain gene is knocked out and the expression levels of other genes are observed, constitute a fundamental step in uncovering the intricate wiring diagrams in the living cell and elucidating the causal roles of genes in signaling and regulation. Here we present a novel framework for analyzing large cohorts of gene knockout experiments and their genome-wide effects on expression levels. We devise clustering-like algorithms that identify groups of genes that behave similarly with respect to the knockout data, and utilize them to predict knockout effects and to annotate physical interactions between proteins as inhibiting or activating. Differing from previous approaches, our prediction approach does not depend on physical network information; the latter is used only for the annotation task. Consequently, it is both more efficient and of wider applicability than previous methods. We evaluate our approach using a large scale collection of gene knockout experiments in yeast, comparing it to the state-of-the-art SPINE algorithm. In cross validation tests, our algorithm exhibits superior prediction accuracy, while at the same time increasing the coverage by over 25-fold. Significant coverage gains are obtained also in the annotation of the physical network. 相似文献
3.
Joshua Isaacson 《Evolution; international journal of organic evolution》2019,73(7):1492-1493
Species adapt to the selective pressures of novel environments. Here, Gleditsch and Sperry tested whether four nonnative frugivorous bird species on the Hawaiian island of O'ahu diverged morphologically from their ancestral populations. They found that all four species significantly diverged from populations in their native ranges, with a general trend of smaller body size and larger bills. These differences were likely due to a combination of adaptive and nonadaptive processes. 相似文献
4.
The effect of acute and chronic ethanol administration on serum corticosterone concentration in rats
The effect of intraperitoneally (i.p.) and intragastrically (i.g.) administered ethanol solution, and the influence of voluntary ethanol uptake (20% v/v) on adrenocortical activity of adult male rats was studied. Both i.p. and i.g. ethanol administration resulted in a significant activation of adrenocortical mechanisms, while voluntary ethanol uptake failed to induce elevation of serum corticosterone concentration. No difference was found in blood ethanol concentration among these groups. The responsiveness of adrenocortical mechanisms was also tested in rats which were given the free choice between ethanol solution (5% v/v) and tap-water for three weeks. Unavoidable electric foot-shocks, as stressor, resulted in an elevation of serum corticosterone concentration in control animals, but this response was found to be significantly reduced in chronically ethanol drinking rats. 相似文献
5.
Two phosphatidylcholines containing hydroxylated fatty acids, 1-palmitoyl-2-[5-hydroxy-6,8,11,14-eicosatetraenoyl]-sn-glycero-3- phosphocholine (1-palm-2-5HETE PC) and 1-palmitoyl-2-[15(S)-hydroxy-5,8,11,13- eicosatetraenoyl]-sn-glycero-3-phosphocholine (1-palm-2-15HETE PC), and one phosphatidylcholine containing nonhydroxylated fatty acids, 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (1-palm-2-arach PC) were synthesized. Permeation of small nonelectrolytes (glycerol, 1,2-propanediol, urea, methylurea, propionamide and dimethylformamide) was assessed in multilamellar liposomes containing these synthetic PCs plus egg yolk phosphatidycholine (EPC) in the presence and absence of cholesterol. In liposomes containing 23% cholesterol, 69.3% EPC and 7.7% of either 1-palm-2-5HETE PC or 1-palm-2-15HETE PC the permeability to small nonelectrolytes was 60 to 400% greater than in liposomes containing 23% cholesterol and 77% EPC. The HETE-containing PCs also increased permeability in liposomes without cholesterol but the effects were less striking. Addition of the synthetic PCs did not affect the energy of activation of permeation. 相似文献
6.
7.
Male rat thyroid glands were incubated for two hours in Krebs-Ringer bicarbonate buffer with different amounts of morphine and/or naloxone. Five micrograms/ml morphine produced a significant increase in the T4 concentration of incubation medium, and resulted in an accumulation of cAMP in the tissue. Naloxone did not change the T4 release but its incubation with morphine prevented the morphine-induced changes. Similarly, naloxone inhibited the morphine-induced accumulation of cAMP in the thyroid tissue. 相似文献
8.
3'-O-(4-benzoyl)benzoylcytidine 5'-triphosphate. A substrate and photoaffinity label for CMP-N-acetylneuraminic acid synthetase 总被引:1,自引:0,他引:1
C Abeijon J M Capasso D Tal W F Vann C B Hirschberg 《The Journal of biological chemistry》1986,261(24):11374-11377
A photoreactive, radiolabeled pyrimidine nucleotide, 3'-O-(4-benzoyl)benzoylcytidine 5'-triphosphate was synthesized from benzoylbenzoic acid and radiolabeled CTP. Benzoylbenzoyl-[5-3H]CTP could substitute for CTP, in an enzymatic reaction with N-acetylneuraminic acid catalyzed by Escherichia coli or rat liver CMP-NeuAc synthetase, to yield radiolabeled benzoyl-benzoyl-CMP-NeuAc. E. coli CMP-NeuAc synthetase could be specifically radiolabeled using benzoylbenzoyl-[alpha-32P]CTP as a photoaffinity label. This specific covalent binding occurred using enzyme preparations of different degrees of purity. These results suggest that benzoylbenzoic acid derivatives of pyrimidines should be of general use in the identification and active site mapping of pyrimidine-requiring proteins and enzymes. These include glycosyltransferases, sugar nucleotide synthetases, and transporters, and enzymes participating in the conjugation of bile acids and biosynthesis of nucleic acids and choline nucleotides. 相似文献
9.
Phytotoxins from Alternaria helianthi: radicinin,and the structures of deoxyradicinol and radianthin
A novel compound, radianthin, with phytotoxic activity was isolated from liquid cultures of Alternaria helianthi and identified as a pyrone related to radicinin. A second metabolite was identified as radicinin itself while deoxyradicinol is described for the first time as a natural product. 相似文献
10.
Moshe Tal 《Plant and Soil》1985,89(1-3):199-226
Summary An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments. 相似文献