全文获取类型
收费全文 | 456009篇 |
免费 | 52466篇 |
国内免费 | 747篇 |
专业分类
509222篇 |
出版年
2018年 | 4334篇 |
2017年 | 4144篇 |
2016年 | 5942篇 |
2015年 | 8665篇 |
2014年 | 10068篇 |
2013年 | 13508篇 |
2012年 | 16098篇 |
2011年 | 16472篇 |
2010年 | 10917篇 |
2009年 | 9918篇 |
2008年 | 14468篇 |
2007年 | 14885篇 |
2006年 | 13963篇 |
2005年 | 13350篇 |
2004年 | 13402篇 |
2003年 | 12531篇 |
2002年 | 12116篇 |
2001年 | 19049篇 |
2000年 | 18978篇 |
1999年 | 15209篇 |
1998年 | 5789篇 |
1997年 | 5748篇 |
1996年 | 5483篇 |
1995年 | 5265篇 |
1994年 | 4938篇 |
1993年 | 4934篇 |
1992年 | 12588篇 |
1991年 | 12539篇 |
1990年 | 12285篇 |
1989年 | 11739篇 |
1988年 | 10918篇 |
1987年 | 10277篇 |
1986年 | 9805篇 |
1985年 | 9574篇 |
1984年 | 7969篇 |
1983年 | 6891篇 |
1982年 | 5199篇 |
1981年 | 4700篇 |
1980年 | 4365篇 |
1979年 | 7414篇 |
1978年 | 6039篇 |
1977年 | 5342篇 |
1976年 | 5007篇 |
1975年 | 5813篇 |
1974年 | 6347篇 |
1973年 | 6184篇 |
1972年 | 5497篇 |
1971年 | 5109篇 |
1970年 | 4314篇 |
1969年 | 4235篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
801.
Summary Two previously identified forms of macrophage were investigated in primary cultures of cerebral cortical cells. Dynamic features were revealed through time-lapse video recording and aspects of macrophage function were assessed. The two cell forms were shown to be different pre-mitotic stages of a single cell type. The cell cycle for these cells involved an initial large, flat, quiescent cell which retracted to yield a slightly rounded form with numerous processes. This latter form lost processes and developed profuse filopodia as it became very rounded just prior to division; both resulting daughter cells then regained the initial large flat appearance. These cells possessed several properties of macrophages, including phagocytosis, nucleoside diphosphatase enzyme, and CR3 receptors. These properties were transient, expressed just before and after mitosis, but subsequently down-regulated in the flat daughter cells. Because of this feature, it was difficult to determine the exact size of this cell population; however, the observed rate of proliferation suggests it may be substantial. It is suggested that these cells correspond to non-microglial macrophages of brain tissue and, because of their significant down-regulation, they may be difficult to detect. This may be important in studies of brain accessory immune cells in tissue culture. 相似文献
802.
803.
804.
805.
A method for the preparation of highly specific conjugates on the basis of antibodies obtained as a result of dissociation of the immune complex HBsAg--anti-HBsAg, formed in vitro, is proposed. ELISA was performed according to Walters with some modifications in the concentration of the assay ingredients and in the time of incubation. The technique of the assay of blood sera for the presence of HBsAg with the use of reagents manufactured in the USSR has been worked out. 相似文献
806.
807.
808.
N. A. Volkova N. A. Zinovieva L. A. Volkova L. K. Ernst 《Russian Journal of Genetics》2006,42(1):72-75
The data on the in vitro and in vivo (into embryonic disk) retroviral-mediated transfer of genetic information into chicken embryonic cells are presented. The estimated transformation frequency of the cultured target cells constituted 8 × 10?4 to 5 × 10?3. A transgenic rooster, carrying recombinant DNA in blood, heart, liver, and intestine cells, was obtained. 相似文献
809.
810.
Acquisition of Resistance to Extended-Spectrum Cephalosporins by Salmonella enterica subsp. enterica Serovar Newport and Escherichia coli in the Turkey Poult Intestinal Tract 下载免费PDF全文