全文获取类型
收费全文 | 31418篇 |
免费 | 2971篇 |
国内免费 | 16篇 |
出版年
2022年 | 289篇 |
2021年 | 577篇 |
2020年 | 346篇 |
2019年 | 451篇 |
2018年 | 577篇 |
2017年 | 476篇 |
2016年 | 716篇 |
2015年 | 1298篇 |
2014年 | 1288篇 |
2013年 | 1804篇 |
2012年 | 2209篇 |
2011年 | 2109篇 |
2010年 | 1369篇 |
2009年 | 1252篇 |
2008年 | 1728篇 |
2007年 | 1807篇 |
2006年 | 1632篇 |
2005年 | 1686篇 |
2004年 | 1629篇 |
2003年 | 1551篇 |
2002年 | 1623篇 |
2001年 | 341篇 |
2000年 | 246篇 |
1999年 | 391篇 |
1998年 | 422篇 |
1997年 | 324篇 |
1996年 | 294篇 |
1995年 | 268篇 |
1994年 | 248篇 |
1993年 | 271篇 |
1992年 | 263篇 |
1991年 | 225篇 |
1990年 | 202篇 |
1989年 | 222篇 |
1988年 | 203篇 |
1987年 | 180篇 |
1986年 | 161篇 |
1985年 | 198篇 |
1984年 | 211篇 |
1983年 | 199篇 |
1982年 | 280篇 |
1981年 | 278篇 |
1980年 | 207篇 |
1979年 | 171篇 |
1978年 | 188篇 |
1977年 | 155篇 |
1976年 | 155篇 |
1975年 | 126篇 |
1974年 | 127篇 |
1973年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Joseph Bucukovski Neus Latorre-Margalef David E. Stallknecht Benjamin L. Miller 《PloS one》2015,10(8)
Influenza serology has traditionally relied on techniques such as hemagglutination inhibition, microneutralization, and ELISA. These assays are complex, challenging to implement in a format allowing detection of several types of antibody-analyte interactions at once (multiplex), and troublesome to implement in the field. As an alternative, we have developed a hemagglutinin microarray on the Arrayed Imaging Reflectometry (AIR) platform. AIR provides sensitive, rapid, and label-free multiplex detection of targets in complex analyte samples such as serum. In preliminary work, we demonstrated the application of this array to the testing of human samples from a vaccine trial. Here, we report the application of an expanded label-free hemagglutinin microarray to the analysis of avian serum samples. Samples from influenza virus challenge experiments in mallards yielded strong, selective detection of antibodies to the challenge antigen in most cases. Samples acquired in the field from mallards were also analyzed, and compared with viral hemagglutinin inhibition and microneutralization assays. We find that the AIR hemagglutinin microarray can provide a simple and robust alternative to standard methods, offering substantially greater information density from a simple workflow. 相似文献
32.
Pascal Griesmar Clément Sanchez Germain Puccetti Isabelle Ledoux Joseph Zyss 《Molecular Engineering》1991,1(3):205-220
Orientation of optically nonlinear organic molecules inside sol-gel matrices upon application of an external D.C. electrical field is demonstrated for the first time. The quadratic nonlinear response of silicon oxide or transition metal oxide based gels containing organic molecules has been determined from Electric Field Induced Second Harmonic (EFISH) measurements. Large concentrations of Optically Nonlinear Organic Molecules (ONOM) have been either incorporated inside the macromolecular network or chemically bonded to the oxide backbone of the gels. These results demonstrate the feasibility of permanently poled doped sol-gel matrices. Moreover, EFISH measurements performed on organic molecules appear to be a useful tool for monitoring the changes occurring during sol-gel transformations. 相似文献
33.
A frequent goal of flow cytometric analysis is to classify cells as positive or negative for a given marker, or to determine the precise ratio of positive to negative cells. This requires good and reproducible instrument setup, and careful use of controls for analyzing and interpreting the data. The type of controls to include in various kinds of flow cytometry experiments is a matter of some debate and discussion. In this tutorial, we classify controls in various categories, describe the options within each category, and discuss the merits of each option. 相似文献
34.
35.
Manuella Strukelj Suzanne Brais Marc J. Mazerolle David Paré Pierre Drapeau 《Ecosystems》2018,21(1):68-84
Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability. 相似文献
36.
Mechanics and modeling of plant cell growth 总被引:1,自引:0,他引:1
37.
38.
Elli Kohen Cahide Kohen Joseph G. Hirschberg Alain W. Wouters Bo Thorell 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,720(4):420-424
A microspectrofluorimetric study is made of the influence of dimethylnitrosamine on NADP reduction, following sequential microinjections into the same L cell, of two substrates: (1) isocitrate, with activity of isocitrate dehydrogenase both in the extramitochondrial and intramitochondrial compartments, (2) 6-phosphogluconate, with activity of the dehydrogenase in the extramitochondrial compartment. In control L cells a two-step reduction of NAD(P) is obtained followed by relatively slow reoxidation. In the minutes which follow addition of carcinogen, e.g., dimethylnitrosamine, to the cell medium the isocitrate and 6-phosphogluconate-induced transient NADP reoxidation is decreased in magnitude compared to control, while the rate constant of NADPH reoxidation is considerably accelerated, possibly due to requirements at the level of the microsomal metabolizing system. Observations within the first hour of carcinogen addition suggest an interesting system for evaluating the immediate actions of carcinogens at extranuclear sites: i.e., a comparative study of NADP reduction-reoxidation rate constants via injection of substrates for extra- vs. intramitochondrial pathways. 相似文献
39.
Using the imidate procedure, 2,3,4,6-tetra-O-benzyl-1-O-(N-methylacetimidoyl)-β-d-galactopyranose was condensed with various monosaccharides to provide, in good yield and with high stereoselectivity, α-linked disaccharides. 相似文献
40.
Stephen Gene Sullivan Joseph Dancis Rody P. Cox 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(2):135-141
Hypophysectomy caused a marked but transient increase in branched-chain α-keto acid decarboxylase activities in rat liver mitochondria, peaking at about nine days post-surgery. The magnitude of increase is different for each of the three branched-chain α-keto acids. The activities then fall to a new steady state in three weeks with α-ketoisovalerate decarboxylase activity within the normal range, α-keto-β-methylvalerate decarboxylase activity at twice normal, and α-ketoisocaproate decarboxylase activity decreased to a level too low for accurate measurements. 相似文献