全文获取类型
收费全文 | 34734篇 |
免费 | 3411篇 |
国内免费 | 25篇 |
专业分类
38170篇 |
出版年
2021年 | 358篇 |
2019年 | 287篇 |
2018年 | 361篇 |
2017年 | 349篇 |
2016年 | 563篇 |
2015年 | 916篇 |
2014年 | 1000篇 |
2013年 | 1420篇 |
2012年 | 1618篇 |
2011年 | 1678篇 |
2010年 | 1249篇 |
2009年 | 1016篇 |
2008年 | 1362篇 |
2007年 | 1448篇 |
2006年 | 1385篇 |
2005年 | 1395篇 |
2004年 | 1507篇 |
2003年 | 1377篇 |
2002年 | 1360篇 |
2001年 | 811篇 |
2000年 | 778篇 |
1999年 | 799篇 |
1998年 | 495篇 |
1997年 | 467篇 |
1996年 | 476篇 |
1995年 | 418篇 |
1994年 | 409篇 |
1993年 | 407篇 |
1992年 | 701篇 |
1991年 | 597篇 |
1990年 | 636篇 |
1989年 | 632篇 |
1988年 | 526篇 |
1987年 | 528篇 |
1986年 | 470篇 |
1985年 | 504篇 |
1984年 | 540篇 |
1983年 | 430篇 |
1982年 | 454篇 |
1981年 | 465篇 |
1980年 | 424篇 |
1979年 | 436篇 |
1978年 | 410篇 |
1977年 | 414篇 |
1976年 | 324篇 |
1975年 | 327篇 |
1974年 | 364篇 |
1973年 | 330篇 |
1972年 | 240篇 |
1971年 | 240篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
61.
62.
Summary The influence of total nitrification to nitrate or partial nitrification to nitrite on the soil organic nitrogen status was examined. NH
4
+
–15N was added to the soil in the absence and the presence of NaClO3, respectively nitrapyrin. The first chemical inhibits only nitrate formation, the second inhibits total nitrification. The accumulation of nitrite nitrogen in the soil at levels up to 5 mg kg–1 increased the loss of nitrogen. Yet, it did not increase the binding of mineral nitrogen into soil organic matter, relative to the control soil. The data suggest that the biochemistry of the nitrite formation process, rather than the levels of nitrite ions formed, are of primary importance in the role of nitrification mediated nitrosation of soil organic matter. 相似文献
63.
64.
65.
We studied the course of early leaf area expansion and specificleaf area (SLA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (RL) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheRL (L < 1; mean: 17.9x 10-3°C-1 d-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheRL (L <1; mean: 7.1 x 10-3°C-1 d-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10-3°C-1 d-1), and bothvaried with year. SLAof potato increased nearly linearly withthermal time from 5 to 15 m2 kg-1at 50% emergence, to 20 to25 m2 kg-1at 155°Cd, and then decreased slightly. The SLAofboth winter and spring wheat began at 16 to 23 m2 kg-1and inmost cases increased slightly with thermal time. In potato,regression parameters of SLAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on RLof potato were not correlated with thoseon SLA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in SLA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofSLA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling 相似文献
66.
67.
The carbohydrate units of the rat erythrocyte membrane sialoglycoprotein rSGP-4 [Edge, A. S. B., & Weber, P. (1981) Arch. Biochem. Biophys. 209, 697-705] have been characterized. All of the carbohydrate of this Mr 19,000 glycoprotein occurs in O-glycosidic linkage to the peptide; following alkaline borohydride treatment and chromatography on Bio-Gel P-2, sialic acid containing oligosaccharides terminating in N-acetylgalactosaminitol were obtained. Their structures were determined by compositional analysis, exoglycosidase digestions, alkaline sulfite degradation, and periodate oxidation. The oligosaccharides were characterized for molecular weight and linkage by direct chemical ionization and gas-liquid chromatography/mass spectrometry, respectively. The structures are proposed to be NeuAc alpha 2----3Gal beta 1----3GalNAc-ol, Gal beta 1----3(NeuAc alpha 2----6)GalNAc-ol, NeuAc alpha 2----3Gal beta 1----3(NeuAc alpha 2----6)GalNAc-ol, and NeuAc alpha 2----3Gal beta 1----3(NeuAc alpha 2----3Gal beta 1----4GlcNAc beta 1----6)GalNAc-ol. Two of the N-acetylglucosamine-containing hexasaccharides were present per molecule of rSGP-4 along with two trisaccharides and seven tetrasaccharides. 相似文献
68.
Rabbit alveolar macrophages exhibit a chemiluminescent response which is associated with phagocytosis of zymosan and polystyrene-butadiene particles. The chemiluminescence reaches a peak in 15 to 25 minutes and then gradually diminishes over the next 1 to 3 hours. During the time of maximal light emission there appears to be no actual uptake of particles, but the response is dependent upon the particle concentration. The metabolic inhibitor, DNP (2,4-dinitrophenol), causes a rapid inhibition of the chemiluminescent response. The addition of ATP to the medium prior to exposure of the cells to particles causes the chemiluminescent response to be greatly diminished, i.e., 0.3mM ATP virtually abolishes the response. These experiments suggest that some metabolic response of the cell to phagocytosis is responsible for the chemiluminescence. 相似文献
69.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献
70.
G Mertens J J Cassiman H Van den Berghe J Vermylen G David 《The Journal of biological chemistry》1992,267(28):20435-20443
Human aortic endothelial cells (HAEC) and human umbilical vein endothelial cells (HUVEC) were labeled with 35SO(4)2- for 48 h. The membrane-associated proteoglycans were solubilized from these monolayers with detergent and purified by ion-exchange chromatography on Mono Q, incorporation in liposomes, and gel filtration. The liposome-intercalated proteoglycans were 125I-iodinated and treated with heparitinase before SDS-polyacrylamide gel electrophoresis. Radio-labeled proteins with apparent molecular masses of 130, 60, 46, 35, and 30 kDa (HAEC) and 180, 130, 62, 43, and 35 kDa (HUVEC) were detected by autoradiography. Further characterization by affinity chromatography on immobilized monoclonal antibodies and by Northern blot analysis provided evidence for the expression of syndecan, glypican, and fibroglycan in human endothelial cells. Most of the heparan sulfate which accumulated in the subendothelial matrix was implanted on a 400-kDa core protein. This protein was immunologically related to perlecan and bound to fibronectin. Binding studies on immobilized antithrombin III suggested that all membrane-associated heparan sulfate proteoglycan forms had the capacity to bind to antithrombin III but that high affinity binding was more typical for glypican. Most of the proteoglycans isolated from the extracellular matrix also bound only with low affinity to antithrombin III. These results imply that glypican may specifically contribute to the antithrombotic properties of the vascular wall. 相似文献