全文获取类型
收费全文 | 3696篇 |
免费 | 288篇 |
专业分类
3984篇 |
出版年
2023年 | 42篇 |
2022年 | 78篇 |
2021年 | 141篇 |
2020年 | 99篇 |
2019年 | 126篇 |
2018年 | 113篇 |
2017年 | 117篇 |
2016年 | 152篇 |
2015年 | 228篇 |
2014年 | 215篇 |
2013年 | 271篇 |
2012年 | 276篇 |
2011年 | 245篇 |
2010年 | 149篇 |
2009年 | 115篇 |
2008年 | 168篇 |
2007年 | 180篇 |
2006年 | 159篇 |
2005年 | 147篇 |
2004年 | 139篇 |
2003年 | 108篇 |
2002年 | 102篇 |
2001年 | 72篇 |
2000年 | 42篇 |
1999年 | 43篇 |
1998年 | 28篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 34篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 7篇 |
1969年 | 7篇 |
排序方式: 共有3984条查询结果,搜索用时 15 毫秒
1.
Genome-wide analysis of the SET DOMAIN GROUP family in grapevine 总被引:1,自引:0,他引:1
The SET DOMAIN GROUP (SDG) proteins represent an evolutionarily-conserved family of epigenetic regulators present in eukaryotes
and are putative candidates for the catalysis of lysine methylation in histones. Plant genomes analyses of this family have
been performed in arabidopsis, maize, and rice and functional studies have shown that SDG genes are involved in the control
of plant development. In this work, we describe the identification and structural characterization of SDG genes in the Vitis vinifera genome. This analysis revealed the presence of 33 putative SDG genes that can be grouped into different classes, as it has
been previously described for plants. In addition to the SET domain, the proteins identified possessed other domains in the
different classes. As part of our study regarding the growth and development of grapevine, we selected eight genes and their
expression levels were analyzed in representative vegetative and reproductive organs of this species. The selected genes showed
different patterns of expression during inflorescence and fruit development, suggesting that they participate in these processes.
Furthermore, we showed that the expression of selected SDGs changes during viral infection, using as a model Grapevine Leafroll
Associated Virus 3-infected symptomatic grapevine leaves and fruits. Our results suggest that developmental changes caused
by this virus could be the result of alterations in SDG expression. 相似文献
2.
The potential for reducing the occurrence of shallow landslides through targeted reforestation of critical parts of a river basin is explored through mathematical modelling. Through the systematic investigation of land management options, modelling allows the optimum strategies to be selected ahead of any real intervention in the basin. Physically based models, for which the parameters can be evaluated using physical reasoning, offer particular advantages for predicting the effects of possible future changes in land use and climate. Typically a physically based landslide model consists of a coupled hydrological model (for soil moisture) and a geotechnical slope stability model, along with an impact model, such as basin sediment yield. An application of the SHETRAN model to the 65.8-km2 Guabalcón basin in central Ecuador demonstrates a technique for identifying the areas of a basin most susceptible to shallow landsliding and for quantifying the effects of different vegetation covers on landslide incidence. Thus, for the modelled scenario, increasing root cohesion from 300 to 1500 Pa causes a two-thirds reduction in the number of landslides. Useful information can be obtained even on the basis of imperfect data availability but model output should be interpreted carefully in the light of parameter uncertainty. 相似文献
3.
4.
5.
6.
F Villarroya A Felipe T Mampel 《Comparative biochemistry and physiology. A, Comparative physiology》1987,86(3):481-483
Brown adipose tissue properties as well as noradrenaline turnover in the tissue were determined in 15-day lactating rats and virgin controls. Brown adipose tissue thermogenic activity was reduced in lactating rats as shown by a decrease in weight, cytochrome oxidase activity and mitochondrial GDP-binding. The noradrenaline turnover rate was lower in brown adipose tissue from lactating rats. It is suggested that diminished sympathetic activity in brown adipose tissue may be a major cause of the reduced tissue thermogenic activity during lactation. 相似文献
7.
With the eventual goal of characterizingLegionella pneumophila serogroup 1 plasmids at the molecular level, we have analyzed the plasmid contents of 78 clinical and environmental Spanish isolates. After selection of a suitable alkaline lysis method, we detected plasmids with approximate molecular weights of 25, 36, 40, 61, 80, 85, 90, and 95 megadalton (MDal). Several factors (i.e., wide temporal and geographic distribution, high frequency in both clinical and environmental isolates, and apparent high copy number after subculturing) make the 36 MDal type IA plasmid an appropriate plasmid for further molecular studies. 相似文献
8.
9.
Synthesis and secretion of active lipoprotein lipase in Chinese-hamster ovary (CHO) cells. 总被引:1,自引:0,他引:1 下载免费PDF全文
Cultured Chinese-hamster ovary cells (CHO cells) were found to produce and secrete a lipase, which was identified as a lipoprotein lipase by the following criteria. Its activity was stimulated by serum and apolipoprotein CII, and was inhibited by high salt concentration. The lipase bound to heparin-agarose and co-eluted with 125I-labelled bovine lipoprotein lipase in a salt gradient. A chicken antiserum to bovine lipoprotein lipase inhibited the activity and precipitated a labelled protein of the same apparent size as bovine lipoprotein lipase from media of CHO cells labelled with [35S]methionine. The lipase activity and secretion were similar in growing cells and in cells that had reached confluency. Hence, lipoprotein lipase appears to be expressed constitutively in CHO cells and is not linked to certain growth conditions, as in pre-adipocyte and macrophage cell lines. At 37 degrees C, but not at 4 degrees C, heparin increased the release of lipase to the medium 2-4-fold. This increased release occurred without depletion of cell-associated lipase activity, suggesting that heparin enhanced release of newly synthesized lipase. 相似文献
10.
Generation and amplification of the cytosolic calcium signal during secretory responses to gonadotropin-releasing hormone 总被引:2,自引:0,他引:2
S S Stojilkovi? A Stutzin S Izumi S Dufour A Torsello M A Virmani E Rojas K J Catt 《The New biologist》1990,2(3):272-283
Gonadotropin-releasing hormone (GnRH) stimulates characteristic biphasic increases in cytosolic calcium concentration ([Ca2+]i) and in luteinizing hormone (LH) release in cultured gonadotrophs, with an early peak followed by a prolonged plateau in both responses. Analysis of [Ca2+]i by dual-wavelength fluorimetric assay and of LH release at 5-sec intervals in perifused pituitary cells revealed increases in both responses within a few seconds of exposure to GnRH. The maximum elevation of [Ca2+]i occurred within 20 sec, and the peak gonadotropin release in 35 sec; the total duration of the spike phase for both [Ca2+]i and LH release was 2.5 min. Under extracellular Ca2(+)-deficient conditions, the GnRH-induced peak in [Ca2+]i was reduced by about 20% and the plateau phase was abolished. Concomitantly, the magnitude of the acute phase of LH release was reduced by 40% and that of the second phase by about 90%. Recovery of the plateau phase of LH release occurred within 25 sec after addition of 1.25 mM Ca2+ to Ca2(+)-deficient medium. In a dose-dependent manner, the non-selective Ca2+ channel blockers Co2+ and Cd2+ reduced the Ca2+ current measured by whole-cell recording in pituitary gonadotrophs and abolished the extracellular Ca2(+)-dependent component of LH release. The selective calcium channel blocker, nifedipine, decreased the magnitude of the Ca2+ current and reduced the plateau phase of LH release by 50%; conversely, the dihydropyridine agonist methyl, 1,4,dihydro-2,6-dimethyl 3-nitro-4-(2-trifluorome) (Bay K 8644) consistently enhanced the amplitudes of both Ca2+ current and GnRH-induced LH release. These data reveal a close temporal correlation between changes in [Ca2+]i and LH release during GnRH action, with Ca2+ mobilization during the spike phase and Ca2+ influx through dihydropyridine-sensitive and insensitive sets of receptor-operated calcium channels during the spike and plateau phases. In addition, analysis of the magnitudes of the [Ca2+]i and LH responses to a wide range of GnRH concentrations in the presence and absence of extracellular Ca2+ is consistent with amplification of the [Ca2+]i signal in agonist-stimulated gonadotrops. 相似文献