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The catalytic activity of untreated and pre-reduced copper chromite in the hydrogenation of cyclic polyenes has been investigated. A comparison is made with the hydrogenation of polyunsaturated fatty acids of soybean oil. The role of the different oxidation states of the copper and the influence of the geometry of the substrate on the hydrogenation rate are discussed. 相似文献
994.
Deborah Hemming Dan Yakir Per Ambus Mika Aurela Cathy Besson Kevin Black Nina Buchmann Regis Burlett Alessandro Cescatti Robert Clement Patrick Gross Andr Granier Thomas Grünwald Katarina Havrankova Dalibor Janous Ivan A. Janssens Alexander Knohl Barbara K
stner Andrew Kowalski Tuomas Laurila Catarina Mata Barbara Marcolla Giorgio Matteucci John Moncrieff Eddy J. Moors Bruce Osborne Joo Santos Pereira Mari Pihlatie Kim Pilegaard Francesca Ponti Zuzana Rosova Federica Rossi Andrea Scartazza Timo Vesala 《Global Change Biology》2005,11(7):1065-1093
We present carbon stable isotope, δ13C, results from air and organic matter samples collected during 98 individual field campaigns across a network of Carboeuroflux forest sites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis that δ13C values derived from large‐scale atmospheric measurements and models, which are routinely used to partition carbon fluxes between land and ocean, and potentially between respiration and photosynthesis on land, are consistent with directly measured ecosystem‐scale δ13C values. In this framework, we also tested the potential of δ13C in canopy air and plant organic matter to record regional‐scale ecophysiological patterns. Our network estimates for the mean δ13C of ecosystem respired CO2 and the related ‘discrimination’ of ecosystem respiration, δer and Δer, respectively, were ?25.6±1.9‰ and 17.8 ±2.0‰ in 2001 and ?26.6±1.5‰ and 19.0±1.6‰ in 2002. The results were in close agreement with δ13C values derived from regional‐scale atmospheric measurement programs for 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests that regional‐scale atmospheric sampling programs generally capture ecosystem δ13C signals over Europe, but may be limited in capturing some of the interannual variations. In 2001, but less so in 2002, there were discernable longitudinal and seasonal trends in δer. From west to east, across the network, there was a general enrichment in 13C (~3‰ and ~1‰ for the 2 years, respectively) consistent with increasing Gorczynski continentality index for warmer and drier conditions. In 2001 only, seasonal 13C enrichment between July and September, followed by depletion in November (from about ?26.0‰ to ?24.5‰ to ?30.0‰), was also observed. In 2001, July and August δer values across the network were significantly related to average daytime vapor pressure deficit (VPD), relative humidity (RH), and, to a lesser degree, air temperature (Ta), but not significantly with monthly average precipitation (Pm). In contrast, in 2002 (a much wetter peak season), δer was significantly related with Ta, but not significantly with VPD and RH. The important role of plant physiological processes on δer in 2001 was emphasized by a relatively rapid turnover (between 1 and 6 days) of assimilated carbon inferred from time‐lag analyses of δer vs. meteorological parameters. However, this was not evident in 2002. These analyses also noted corresponding diurnal cycles of δer and meteorological parameters in 2001, indicating a rapid transmission of daytime meteorology, via physiological responses, to the δer signal during this season. Organic matter δ13C results showed progressive 13C enrichment from leaves, through stems and roots to soil organic matter, which may be explained by 13C fractionation during respiration. This enrichment was species dependent and was prominent in angiosperms but not in gymnosperms. δ13C values of organic matter of any of the plant components did not well represent short‐term δer values during the seasonal cycle, and could not be used to partition ecosystem respiration into autotrophic and heterotrophic components. 相似文献
995.
Interaction between the N-terminal domain of human DNA topoisomerase I and the arginine-serine domain of its substrate determines phosphorylation of SF2/ASF splicing factor. 总被引:3,自引:0,他引:3 下载免费PDF全文
E Labourier F Rossi I E Gallouzi E Allemand G Divita J Tazi 《Nucleic acids research》1998,26(12):2955-2962
Human DNA topoisomerase I, known for its DNA-relaxing activity, is possibly one of the kinases phosphorylating members of the SR protein family of splicing factors, in vivo. Little is known about the mechanism of action of this novel kinase. Using the prototypical SR protein SF2/ASF (SRp30a) as model substrate, we demonstrate that serine residues phosphorylated by topo I/kinase exclusively located within the most extended arginine-serine repeats of the SF2/ASF RS domain. Unlike other kinases such as cdc2 and SRPK1, which also phosphorylated serines at the RS domain, topo I/kinase required several SR dipeptide repeats. These repeats possibly contribute to a versatile structure in the RS domain thereby facilitating phosphorylation. Furthermore, far-western, fluorescence spectroscopy and kinase assays using the SF2/ASF mutants, demonstrated that kinase activity and binding were tightly coupled. Since the deletion of N-terminal 174 amino acids of Topo I destroys SF2/ASF binding and kinase activity but not ATP binding, we conclude that at least two distinct domains of Topo I are necessary for kinase activity: one in the C-terminal region contributing to the ATP binding site and the other one in the N-terminal region that allows binding of SF2/ASF. 相似文献
996.
Carbachol-induced desensitization of PLC-beta pathway in rat myometrium: downregulation of Gqalpha /G11alpha 总被引:2,自引:0,他引:2
Lajat Sandrine; Harbon Simone; Tanfin Zahra 《American journal of physiology. Cell physiology》1998,275(3):C636
In the estrogen-treated rat myometrium, carbachol increased thegeneration of inositol phosphates by stimulating the muscarinic receptor-Gq/G11-phospholipaseC-3 (PLC-3) cascade. Exposure to carbachol resulted in a rapidand specific (homologous) attenuation of the subsequent muscarinicresponses in terms of inositol phosphate production, PLC-3translocation to membrane, and contraction. Refractoriness wasaccompanied by a reduction of membrane muscarinic binding sites and anuncoupled state of residual receptors. Protein kinase C (PKC) alteredthe functionality of muscarinic receptors and contributed to theinitial period of desensitization. A delayed phase of the muscarinicrefractoriness was PKC independent and was associated with adownregulation ofGq/G11.Atropine failed to induce desensitization as well asGq/G11downregulation, indicating that both events involve active occupancy ofthe receptor. Prolonged exposure toAlF4 reduced subsequent AlF4 as well as carbachol-mediatedinositol phosphate responses and similarly induced downregulation ofGq/G11. Data suggest that a decrease in the level ofGq/G11is subsequent to its activation and may account forheterologous desensitization. 相似文献
997.
Kinetic and enzymatic features of metabolic stimulation of alveolar and peritoneal macrophages challenged with bacteria 总被引:3,自引:0,他引:3
The rate of oxygen uptake and of 14C-1-glucose oxidation by peritoneal and alveolar macrophages has been simultaneously recorded before and after the exposure of the cells to B. mycoides. A stimulation of both processes was detected within seconds after the addition of bacteria. A comparison of 14C-1-glucose with 14C-6-glucose oxidation has indicated that the stimulation of the 14CO2 production from 14C-1-glucose is substantially to be ascribed to an increased activity of the HMP pathway. On approaching anaerobiosis, the rate of the HMP pathway fell to zero, showing a direct link between cell respiration and production of NADP+ for the pathway. The assay of an enzyme, catalysing the reaction: NADPH + H+ + O2 → NADP+ + H2O2, in 20 000 g pellets has shown that this oxidase has a higher activity in subcellular fractions derived from macrophages previously exposed to bacteria. The activation of this enzyme may be the most important event in the metabolic stimulation of macrophages challenged with bacteria. On the basis of experiments carried out with KCN, an inhibitor of both NADPH oxidase and catalase, it has been concluded that, under particular conditions, also the concerted action of GSH peroxidase and GSSG reductase might contribute to supporting the HMP pathway activity. 相似文献
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