全文获取类型
收费全文 | 636496篇 |
免费 | 66880篇 |
国内免费 | 1058篇 |
专业分类
704434篇 |
出版年
2018年 | 17350篇 |
2017年 | 16082篇 |
2016年 | 13891篇 |
2015年 | 8433篇 |
2014年 | 9600篇 |
2013年 | 13489篇 |
2012年 | 19741篇 |
2011年 | 29697篇 |
2010年 | 23665篇 |
2009年 | 19461篇 |
2008年 | 24760篇 |
2007年 | 27510篇 |
2006年 | 13267篇 |
2005年 | 14093篇 |
2004年 | 13783篇 |
2003年 | 13578篇 |
2002年 | 12812篇 |
2001年 | 22980篇 |
2000年 | 23452篇 |
1999年 | 18614篇 |
1998年 | 6654篇 |
1997年 | 7067篇 |
1996年 | 6850篇 |
1995年 | 6575篇 |
1994年 | 6557篇 |
1993年 | 6504篇 |
1992年 | 16260篇 |
1991年 | 16188篇 |
1990年 | 15817篇 |
1989年 | 15382篇 |
1988年 | 14386篇 |
1987年 | 13830篇 |
1986年 | 12924篇 |
1985年 | 13069篇 |
1984年 | 10984篇 |
1983年 | 9713篇 |
1982年 | 7488篇 |
1981年 | 7012篇 |
1980年 | 6595篇 |
1979年 | 10961篇 |
1978年 | 8525篇 |
1977年 | 7848篇 |
1976年 | 7457篇 |
1975年 | 8271篇 |
1974年 | 8562篇 |
1973年 | 8405篇 |
1972年 | 8534篇 |
1971年 | 7476篇 |
1970年 | 6062篇 |
1969年 | 5716篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
952.
The flap endonuclease, FEN1, plays a critical role in DNA replication and repair. Human FEN1 exhibits both a 5' to 3' exonucleolytic and a structure-specific endonucleolytic activity. On primer-template substrates containing an unannealed 5'-tail, or flap structure, FEN1 employs a unique mechanism to cleave at the point of annealing, releasing the 5'-tail intact. FEN1 appears to track along the full length of the flap from the 5'-end to the point of cleavage. Substrates containing structural modifications to the flap have been used to explore the mechanism of tracking. To determine whether the nuclease must recognize a succession of nucleotides on the flap, chemical linkers were used to replace an interior nucleotide. The nuclease could readily traverse this site. The footprint of the nuclease at the time of cleavage does not extend beyond 25 nucleotides on the flap. Eleven-nucleotide branches attached to the flap beyond the footprinted region do not prevent cleavage. Single- or double-thymine dimers also allow cleavage. cis-Platinum adducts outside the protected region are moderately inhibitory. Platinum-modified branch structures are completely inert to cleavage. These results show that some flap modifications can prevent or inhibit tracking, but the tracking mechanism tolerates a variety of flap modifications. FEN1 has a flexible loop structure through which the flap has been proposed to thread. However, efficient cleavage of branched structures is inconsistent with threading the flap through a hole in the protein. 相似文献
953.
954.
955.
Are all plant populations metapopulations? 总被引:2,自引:1,他引:1
956.
957.
P Sinibaldi R Muraro M Centanni M G Giganti 《Bollettino della Società italiana di biologia sperimentale》1983,59(1):112-116
The behaviour of Na+/K+ ATPase during cell growth has been studied. Human cultured fibroblasts were used in the presence or absence of EGF. Sample and control cultures were stopped by gathering and washing the cells with tris buffer. Homogenates were tested for Na+/K+ ATPase activity by the method of incubating and for the -SH groups content (Ellman). Na+/K+ ATPase activity that slightly increases in the controls is strongly reduced by the addition of EGF. The behaviour shows evidence for a double mechanism of action: I) involvement of the cAMP system 2) decrease of the -SH group availability. 相似文献
958.
959.
W J Koopman M H Gillis J R David 《Journal of immunology (Baltimore, Md. : 1950)》1973,110(6):1609-1614
960.
Isolation of mucin from human submaxillary secretions 总被引:2,自引:0,他引:2
M M Baig R J Winzler W M Rennert 《Journal of immunology (Baltimore, Md. : 1950)》1973,111(6):1826-1833