全文获取类型
收费全文 | 449185篇 |
免费 | 51871篇 |
国内免费 | 746篇 |
专业分类
501802篇 |
出版年
2018年 | 4238篇 |
2017年 | 4087篇 |
2016年 | 5855篇 |
2015年 | 8432篇 |
2014年 | 9836篇 |
2013年 | 13192篇 |
2012年 | 15661篇 |
2011年 | 16084篇 |
2010年 | 10647篇 |
2009年 | 9647篇 |
2008年 | 14089篇 |
2007年 | 14513篇 |
2006年 | 13636篇 |
2005年 | 12987篇 |
2004年 | 13021篇 |
2003年 | 12141篇 |
2002年 | 11793篇 |
2001年 | 18955篇 |
2000年 | 18872篇 |
1999年 | 15093篇 |
1998年 | 5652篇 |
1997年 | 5649篇 |
1996年 | 5379篇 |
1995年 | 5157篇 |
1994年 | 4861篇 |
1993年 | 4871篇 |
1992年 | 12494篇 |
1991年 | 12455篇 |
1990年 | 12209篇 |
1989年 | 11681篇 |
1988年 | 10851篇 |
1987年 | 10218篇 |
1986年 | 9751篇 |
1985年 | 9524篇 |
1984年 | 7896篇 |
1983年 | 6845篇 |
1982年 | 5156篇 |
1981年 | 4638篇 |
1980年 | 4325篇 |
1979年 | 7361篇 |
1978年 | 5980篇 |
1977年 | 5300篇 |
1976年 | 4974篇 |
1975年 | 5781篇 |
1974年 | 6320篇 |
1973年 | 6137篇 |
1972年 | 5468篇 |
1971年 | 5086篇 |
1970年 | 4283篇 |
1969年 | 4209篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Synthesis of human walking: A planar model for single support 总被引:3,自引:0,他引:3
A mathematical model for the single support phase of normal, level, human walking is formulated. The motion of the lower extremity is synthesized using a preprogrammed set of inputs, recognized by the model as a simple collection of applied joint moments.
Two mechanisms are forwarded as candidates for producing the observed peaks in the vertical ground reaction. The first, stance knee flexion-extension, generates the necessary level of whole-body vertical acceleration during the initial region of single support (opposite toe-off to heel-off). A model accounting for the determinants of foot and knee interaction then predicts the second peak to be the result of an increasing ankle moment in the region from heel-off to opposite heel-strike. 相似文献
993.
994.
995.
A A Sumarokov L A Nefedova I Iu Iaroshevskaia L V Salmin N A Ozeretskovski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1977,(5):109-114
Prophylactic activity and side action of antiinfluenza lactoglobulin were studied under conditions of controlled epidemiological trial in 6361 persons during the epidemiological rise of influenza incidence. The data obtained pointed to the absence of any protective effect of antiinfluenza lactoglobulin. Marked allergenic properties of lactoglobulin and development of sensitization in the persons under observation were found during the study of the side-effect of the preparation. Thus, the absence of prophylactic efficacy and the sensitizing action of antiinfluenza lactoglobulin pointed to the inexpediency of its use for prophylactic and therapeutic purpose. 相似文献
996.
997.
D H L Bishop 《BMJ (Clinical research ed.)》1988,296(6638):1685-1686
998.
Nonlymphoid, stromal cells in the mouse thymus are believed to be important in T cell maturation and have been proposed to play a central role in the acquisition of major histocompatibility complex (MHC) restriction and self-tolerance by maturing thymocytes. Both cortical and medullary epithelial cells in the thymus express high levels of class II (A) major histocompatibility antigens (MHC Ags). We show here that a specific subset of these A– epithelial cells express a transformation-associated antigen (6C3Ag) found previously on the surfaces of Abelson murine leukemia virus-transformed pre-B cells and on those bone marrow-derived stromal cell clones which support normal and preneoplastic pre-B cell proliferation. Among solid lymphoid organs, only the thymus contains 6C3Ag1 cells and within the thymus, this antigen is found exclusively on A– epithelial cells in cortical regions. It is striking that the expression of the 6C3Ag on thymic epithelium is developmentally regulated, suggesting a role for this lymphostromal antigen in the maturation of the thymic microenvironment. 相似文献
999.
Nucleotide sequence of the mouse ornithine decarboxylase gene. 总被引:6,自引:3,他引:3
1000.