全文获取类型
收费全文 | 808263篇 |
免费 | 88960篇 |
国内免费 | 554篇 |
专业分类
897777篇 |
出版年
2018年 | 7647篇 |
2017年 | 7162篇 |
2016年 | 10377篇 |
2015年 | 14307篇 |
2014年 | 16696篇 |
2013年 | 23688篇 |
2012年 | 26538篇 |
2011年 | 26910篇 |
2010年 | 18271篇 |
2009年 | 16625篇 |
2008年 | 23773篇 |
2007年 | 24355篇 |
2006年 | 22968篇 |
2005年 | 22141篇 |
2004年 | 22037篇 |
2003年 | 21154篇 |
2002年 | 20373篇 |
2001年 | 38366篇 |
2000年 | 38574篇 |
1999年 | 30633篇 |
1998年 | 10707篇 |
1997年 | 11204篇 |
1996年 | 10512篇 |
1995年 | 9823篇 |
1994年 | 9552篇 |
1993年 | 9339篇 |
1992年 | 24780篇 |
1991年 | 24033篇 |
1990年 | 23425篇 |
1989年 | 22795篇 |
1988年 | 21154篇 |
1987年 | 19755篇 |
1986年 | 18311篇 |
1985年 | 18135篇 |
1984年 | 15044篇 |
1983年 | 12552篇 |
1982年 | 9523篇 |
1981年 | 8492篇 |
1980年 | 7947篇 |
1979年 | 13488篇 |
1978年 | 10496篇 |
1977年 | 9433篇 |
1976年 | 8539篇 |
1975年 | 9496篇 |
1974年 | 10132篇 |
1973年 | 10032篇 |
1972年 | 8956篇 |
1971年 | 8168篇 |
1970年 | 6971篇 |
1969年 | 6733篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
S Sayama R V Iozzo G S Lazarus N M Schechter 《The Journal of biological chemistry》1987,262(14):6808-6815
The subcellular localization of human skin chymase to mast cell granules was established by immunoelectron microscopy, and binding of chymase to the area of the dermo-epidermal junction, a basement membrane, was demonstrated immunocytochemically in cryosections incubated with purified proteinase prior to immunolabeling. Because heparin and heparan sulfate proteoglycans are major constituents of mast cell granules and basement membranes, respectively, the ability of chymase to bind to glycosaminoglycans (GAG) was investigated. Among a variety of GAGs, only binding of chymase to heparin and heparan sulfate appears physiologically significant. Binding was ionic strength-dependent, involved amino groups on the proteinase, and correlated with increasing GAG sulfate content, indicating a predominantly electrostatic association. Interaction with heparin was observed in solutions containing up to 0.5 M NaCl, and interaction with heparan sulfate was observed in solutions containing up to 0.3 M NaCl. Binding of heparin did not detectably affect catalysis of peptide substrates, but may reduce accessibility of proteinase to protein substrates. Measurements among a series of serine class proteinases indicated that heparin binding was a more common property of mast cell proteinases than proteinases stored in other secretory granules. Binding of chymase to heparin is likely to have a storage as well as a structural role within the mast cell granule, whereas binding of chymase to heparan sulfate may have physiological significance after degranulation. 相似文献
292.
Sylvester J. T.; Harabin A. L.; Peake M. D.; Frank R. S. 《Journal of applied physiology》1980,49(5):820-825
293.
294.
The experiment on (BALB/cXC57BL)F1 mice, showing a high level of delayed hypersensitivity (DH) when sensitized with BCG vaccine and Staphylococcus aureus strain B-243, has demonstrated the influence of such sensitization and DH reaction induced by the injection of a specific antigen (old tuberculin or staphylococcal phagolysate) into the sensitized animals on the cytotoxicity of macrophages, natural killers (NK) and antibody-dependent killers (ADK). Sensitization with BCG vaccine alone results in an insignificant rise in the activity of these effector cells, and sensitization with S. aureus produces no changes at all. The pronounced activation of the cytotoxicity of macrophages, NK and, to a lesser extent, ADK has been observed in DH reaction induced by the injection of a specific antigen into the sensitized mice. In the course of DH reaction a rise in the activity of NK and ADK not only against tumor target cells, but also against microbial ones (Candida albicans and S. aureus) has been found to occur. 相似文献
295.
296.
J M Clements S Craig A J Gearing M G Hunter C M Heyworth T M Dexter B I Lord 《Cytokine》1992,4(1):76-82
The murine macrophage inflammatory proteins-1 alpha (MIP-1 alpha) and MIP-1 beta are distinct but closely related cytokines. Partially purified mixtures of the two proteins affect neutrophil function and cause local inflammation and fever. The particular properties of MIP-1 alpha have not been well studied, although it has been identified as being identical to an inhibitor of haemopoietic stem cell growth. We have expressed MIP-1 alpha in yeast cells and purified it to sequence homogeneity. Structural analysis of this biologically active material by circular dichroism and fluorescence spectroscopy confirms that MIP-1 alpha has a very similar secondary and tertiary structure to platelet factor 4 and interleukin 8 with which it shares limited sequence homology. The in-vitro stem cell inhibitory properties have been confirmed using a range of murine progenitor cells including purified bone marrow progenitor cells (FACS-1), the FDCP-mix A4 cell line, and spleen colony forming unit (CFU-S) populations. Plateau levels of inhibition of stem cell growth were achieved using concentrations of 0.15 micrograms/ml MIP-1 alpha. We have also demonstrated that MIP-1 alpha is active in vivo: 5 micrograms of MIP-1 alpha per mouse given as a bolus injection, protects stem cells from subsequent in-vitro killing by tritiated thymidine. MIP-1 alpha was also shown to enhance the proliferation of more committed progenitor granulocyte macrophage-colony forming cells (GM-CFC) in response to granulocyte macrophage-colony stimulating factor (GM-CSF). 相似文献
297.
M. van den Boogaard 《Marine Micropaleontology》1985,9(5):468
298.
Secretory functions of the vascular endothelium. 总被引:3,自引:0,他引:3
The endothelial cells which line the blood vessels as a monolayer exert a remarkable control over the vascular system. Indeed, the endothelium can be regarded as a highly active metabolic and endocrine organ in its own right. On the hand, vasoactive substances such as serotonin and bradykinin are inactivated and on the other the cells can enzymatically produce the vasoconstrictor, angiotensin II and secrete endothelin-1 ((ET-1). Perhaps more importantly, the cells also produce two unstable vasodilator substances, which potently inhibit platelet clumping: prostacyclin and endothelium-derived relaxing factor (EDRF) which has been identified as nitric oxide (NO; 1). Both substances seem well designated as local hormones, released to influence adjacent cells. The endothelial cell, therefore, exerts control over the cardiovascular system by elaborating dilator substances as well as vasconstrictors. 相似文献
299.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献
300.
Human placental tissue stimulates bovine capillary endothelial cell growth,migration and protease production 总被引:2,自引:0,他引:2
A crude extract of human placenta has been demonstrated to stimulate growth, motility and the production of the proteases plasminogen activator and collagenase in cultured bovine capillary endothelial cells. These data are in keeping with the presence of an angiogenic factor(s) in human placenta. 相似文献