全文获取类型
收费全文 | 818369篇 |
免费 | 86309篇 |
国内免费 | 571篇 |
专业分类
905249篇 |
出版年
2018年 | 11743篇 |
2017年 | 11423篇 |
2016年 | 12788篇 |
2015年 | 13043篇 |
2014年 | 15207篇 |
2013年 | 21885篇 |
2012年 | 26275篇 |
2011年 | 30285篇 |
2010年 | 21163篇 |
2009年 | 19663篇 |
2008年 | 26095篇 |
2007年 | 28155篇 |
2006年 | 21245篇 |
2005年 | 21149篇 |
2004年 | 20418篇 |
2003年 | 19819篇 |
2002年 | 19300篇 |
2001年 | 39483篇 |
2000年 | 39716篇 |
1999年 | 30732篇 |
1998年 | 9837篇 |
1997年 | 10433篇 |
1996年 | 9843篇 |
1995年 | 9076篇 |
1994年 | 8823篇 |
1993年 | 8706篇 |
1992年 | 24847篇 |
1991年 | 23910篇 |
1990年 | 23060篇 |
1989年 | 22348篇 |
1988年 | 20607篇 |
1987年 | 19286篇 |
1986年 | 17815篇 |
1985年 | 17575篇 |
1984年 | 14374篇 |
1983年 | 12320篇 |
1982年 | 9170篇 |
1981年 | 8165篇 |
1980年 | 7714篇 |
1979年 | 13625篇 |
1978年 | 10353篇 |
1977年 | 9509篇 |
1976年 | 8634篇 |
1975年 | 9692篇 |
1974年 | 10365篇 |
1973年 | 10103篇 |
1972年 | 9755篇 |
1971年 | 8722篇 |
1970年 | 7269篇 |
1969年 | 6877篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Summary The results of a recent quantitative analysis of the Teorell membrane oscillator are utilized to explore its role as an excitability analogue. Special attention is paid to its role as a mechano-electric transducer. A membrane of exceptionally well-defined pore structure has been used in this study. The analogue properties arise from nonlinear coupling between water and salt fluxes. When the membrane is simultaneously subjected to controlled gradients of hydrostatic pressure, electrical potential and concentration, bi-stable stationary states can be produced. These arise from the opposing effects of pressure and electro-osmosis on the volume flow. Transitions between these states show hysteresis. The factors governing such transitions are analogous to certain types of stimuli encountered in the natural excitation process. The membrane system also shows oscillatory behavior when the hydrostatic pressure gradient is allowed to vary under constant current conditions. This property is related to the bi-stable stationary state phenomena and is compared to the regenerative behavior found in biologically excitable tissues. Particular emphasis is placed upon analogies between the membrane oscillator and certain natural tissues. The importance of the nonlinear nature of the force-flux coupling in the analogue is stressed, and its possible relevance to biological excitability indicated. Some consideration is also given to the role of electro-osmotic flux coupling in biological tissues. 相似文献
52.
Formation of rings from Drosophila DNA fragments 总被引:1,自引:0,他引:1
53.
54.
Transcriptive expression during sea urchin embryogenesis 总被引:2,自引:0,他引:2
55.
56.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells. 相似文献
57.
58.
59.
T. B. Lapirova V. R. Mikryakova A. S. Mavrin G. A. Yinogradova 《Journal of Evolutionary Biochemistry and Physiology》2000,36(1):47-51
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon
exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic
character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and
structural-functional organization of the studied organs. 相似文献
60.
Markers for trans-Golgi Membranes and the Intermediate Compartment Localize to Induced Membranes with Distinct Replication Functions in Flavivirus-Infected Cells 下载免费PDF全文
Replication of the flavivirus Kunjin virus is associated with virus-induced membrane structures within the cytoplasm of infected cells; these membranes appear as packets of vesicles associated with the sites of viral RNA synthesis and as convoluted membranes (CM) and paracrystalline arrays (PC) containing the components of the virus-specified protease (E. G. Westaway, J. M. Mackenzie, M. T. Kenney, M. K. Jones, and A. A. Khromykh, J. Virol. 71:6650-6661, 1997). To determine the cellular origins of these membrane structures, we compared the immunolabelling patterns of several cell markers in relation to these sites by immunofluorescence and immunoelectron microscopy. A marker for the trans-Golgi membranes and the trans-Golgi network, 1,4-galactosyltransferase (GalT), was redistributed to large foci in the cytoplasm of Kunjin virus-infected cells, partially coincident with immunofluorescent foci associated with the putative sites of viral RNA synthesis. As determined by immunoelectron microscopy, the induced vesicle packets contained GalT, whereas the CM and PC contained a specific protein marker for the intermediate compartment (ERGIC53). A further indicator of the role of cellular organelles in their biogenesis was the observation that the Golgi apparatus-disrupting agent brefeldin A prevented further development of immunofluorescent foci of induced membranes if added before the end of the latent period but that once formed, these membrane foci were resistant to brefeldin A dispersion. Reticulum membranes emanating from the induced CM and PC were also labelled with the rough endoplasmic reticulum marker anti-protein disulfide isomerase and were obviously redistributed during infection. This is the first report identifying trans-Golgi membranes and the intermediate compartment as the apparent sources of the flavivirus-induced membranes involved in events of replication. 相似文献