全文获取类型
收费全文 | 9681篇 |
免费 | 871篇 |
国内免费 | 14篇 |
出版年
2023年 | 40篇 |
2022年 | 107篇 |
2021年 | 225篇 |
2020年 | 118篇 |
2019年 | 146篇 |
2018年 | 175篇 |
2017年 | 154篇 |
2016年 | 265篇 |
2015年 | 445篇 |
2014年 | 455篇 |
2013年 | 592篇 |
2012年 | 770篇 |
2011年 | 688篇 |
2010年 | 445篇 |
2009年 | 464篇 |
2008年 | 602篇 |
2007年 | 544篇 |
2006年 | 548篇 |
2005年 | 483篇 |
2004年 | 485篇 |
2003年 | 463篇 |
2002年 | 411篇 |
2001年 | 138篇 |
2000年 | 115篇 |
1999年 | 113篇 |
1998年 | 99篇 |
1997年 | 63篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 66篇 |
1993年 | 58篇 |
1992年 | 84篇 |
1991年 | 63篇 |
1990年 | 63篇 |
1989年 | 67篇 |
1988年 | 60篇 |
1987年 | 47篇 |
1986年 | 50篇 |
1985年 | 38篇 |
1984年 | 48篇 |
1983年 | 54篇 |
1982年 | 34篇 |
1981年 | 43篇 |
1980年 | 40篇 |
1979年 | 56篇 |
1977年 | 32篇 |
1976年 | 37篇 |
1975年 | 32篇 |
1974年 | 38篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Electron-paramagnetic-resonance studies on the molybdenum of nitrate reductase from Escherichia coli K12. 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Studies on the respiratory nitrate reductase (EC 1.7.99.4) from Escherichia coli K12 by electron-paramagnetic-resonance spectroscopy indicate that its molybdenum centre is comparable with that in other molybdenum-containing enzymes. Two Mo(V) signals may be observed; one shows interaction of Mo(V) with a proton exchangeable with the solvent and has: A (1H) 0.9-1.2mT; g1 = 1.999; g2=1.985; g3 = 1.964; gav. = 1.983. Molybdenum of both signal-giving species may be reduced with dithionite and reoxidized with nitrate. 相似文献
182.
A. Vincent Lombardi 《American journal of physical anthropology》1975,42(1):99-104
The traditional morphogenetic fields of the human dentition were evaluated by means of factor analysis of dental dimensions taken from a series of human crania. When crown length, crown width and crown index were considered separately, factors emerged which could be identified with the tooth group fields. But a combined crown length-crown width analysis generated factors which extended beyond the regional tooth groups. Crown width itself was revealed to be an important axis of morphologic intergration. It was concluded that univariate methods are not adequate for identifying morphogenetic fields; the teeth must be treated as multidimensional units where the correlation among dimensions is accounted for. 相似文献
183.
184.
Mlina Vaurs Julien Audry Kurt W Runge Vincent Gli Stphane Coulon 《Nucleic acids research》2022,50(20):11682
Telomere elongation is coupled with genome replication, raising the question of the repair of short telomeres in post-mitotic cells. We investigated the fate of a telomere-repeat capped end that mimics a single short telomere in quiescent fission yeast cells. We show that telomerase is able to elongate this single short telomere during quiescence despite the binding of Ku to the proto-telomere. While Taz1 and Rap1 repress telomerase in vegetative cells, both shelterin proteins are required for efficient telomere extension in quiescent cells, underscoring a distinct mode of telomerase control. We further show that Rad3ATR and Tel1ATM are redundantly required for telomere elongation in quiescence through the phosphorylation of Ccq1 and that Rif1 and its associated-PP1 phosphatases negatively regulate telomerase activity by opposing Ccq1 phosphorylation. The distinct mode of telomerase regulation in quiescent fission yeast cells may be relevant to that in human stem and progenitor cells. 相似文献
185.
186.
Vincent T. Netshituni Ross N. Cuthbert Farai Dondofema Tatenda Dalu 《Ecology and evolution》2022,12(10)
Plant invasions have been linked to displacement of native vegetation and altering of fire regimes and might influence vector mosquito populations by altering habitats or nutrient inputs. Whereas wildfire effects on terrestrial ecosystems are relatively well‐studied, ash depositions into aquatic ecosystems and effects on semi‐aquatic taxa such as mosquitoes have remained overlooked. Here, we investigated mosquito colonization in water treated with ash from native plants [quinine tree (Rauvolfia caffra), Transvaal milk plum (Englerophytum magalismontanum), apple leaf (Philenoptera violacea)] and invasive alien plants [i.e., lantana (Lantana camara), guava (Psidium guajava), red river gum (Eucalyptus camaldulensis)] in containers at two ash concentrations (i.e., 1, 2 g/L). Overall, there was no statistically clear difference in colonization between ash from native and alien species. We recorded colonization by two mosquito genera (Culex spp. and Anopheles spp.), with Culex generally much more abundant than Anopheles. Few differences were identified among the plants, with statistically clear effects of ash type and concentration on larval and pupal stages. High Culex egg and larval abundances were shown in lantana and apple leaf treatments compared to controls, and milkplum versus controls for pupae of both genera. Further research is required to elucidate the influence of nutrient inputs from different ash species on vector mosquito population dynamics. 相似文献
187.
Cortical activity in vertebrate eggs. I: The activation waves 总被引:4,自引:0,他引:4
We present a physical model for the propagation of chemical and mechanical waves on the surface of vertebrate eggs. As a first step we analyzed the propagation of the calcium wave observed to sweep over the surface of the Medaka egg (Gilkey et al., 1978). It has been assumed that this wave is driven by a mechanism of calcium-stimulated-calcium-release. By formulating this hypothesis mathematically we can use the observed wavefront data to obtain a map of cortical reactivity. This map indicates a gradient of reactivity along the egg: highest in the animal hemisphere and tapering off towards the vegetal hemisphere. The cortex of Xenopus eggs is also capable of propagating a calcium wave (Busa & Nuccitelli, 1985). At about the same time a wave of expansion followed by a wave of contraction sweeps across the egg surface (Takeichi et al., 1984). We have proposed a mechanism for this wave pair based on the physical chemistry of actomyosin gels. The calcium wave activates solation factors which sever some of the actin chains which leads to an osmotic swelling of the gel. Calcium also activates the contractile machinery of the actomyosin system which causes the gel to contract. The contraction lags the swelling because of the nature of the kinetics: solation and swelling is a more rapid process than contraction. By writing the equations for gel expansion and contraction we can mimic the mechanical and chemical wave propagation by a computer simulation. If the model is correct this provides a method for using the waves as a diagnostic of the mechanochemical properties of the egg cortex. 相似文献
188.
The neurotensin receptors from rat brain synaptosomal membranes differed in subunit structure from those in rat gastric fundus smooth muscle plasma membranes when studied following photoaffinity labelling or after exposure to cross-linking reagents. However, these two receptors were similar in their recognition properties. In this study we compared the target size of the two receptors by radiation inactivation and observed that the receptors in both tissues had similar target sizes (mean values 103,000 and 108,000 daltons). This suggests that the differences in size observed in biochemical studies may reflect changes occurring during the isolation procedures, or, on the other hand, there might be inherent difference in the subunit structure of these receptors. 相似文献
189.
J.E. Vincent F.J. Zijlstra A.M.W.C. v.c. Broek T.E. Gezel 《Prostaglandins & other lipid mediators》1986,32(1)
The effect of adrenalectomy on the formation of cyclo-oxygenase and lipoxygenase products by activated peritoneal rat macrophages was determined and compared with that of the spleen. After isolation, the cells and tissues were incubated with [1-14C] arachidonic acid and the Ca-ionophore A23187 and the metabolites isolated by HPLC chromatography. The main components formed in the macrophages of the controls are 6-keto-PGF1α, TxB2 and 12-HETE. One peak represents 5, 12 di HETE. Smaller amounts of PGF2α, PGE2, PGD2, LTB4 and 15-HETE are also present. After adrenalectomy, a considerable increase occurs in the amounts of LTB4, 15-HETE and 12-HETE. The increase in the PG is smaller. The compounds formed from endogenous arachidonic acid are also determined. In the cells of the controls, the formation of LTB4 is considerably increased after adrenalectomy. In the spleen, PGD2 and 12-HETE are decreased after adrenalectomy.The effect of the macrophages is most probably related to a diminished amount or inactivation of lipocortin, a glucocorticosteroid induced peptide with PlA2 inhibitory activity in adrenalectomized animals. In the decrease in formation in the spleen, the absence of the permissive effect of glucocorticosteroids on the hormone-induced lipolysis may play a role. 相似文献
190.