全文获取类型
收费全文 | 37451篇 |
免费 | 3316篇 |
国内免费 | 19篇 |
专业分类
40786篇 |
出版年
2023年 | 116篇 |
2022年 | 332篇 |
2021年 | 616篇 |
2020年 | 372篇 |
2019年 | 488篇 |
2018年 | 611篇 |
2017年 | 546篇 |
2016年 | 958篇 |
2015年 | 1613篇 |
2014年 | 1745篇 |
2013年 | 2133篇 |
2012年 | 2895篇 |
2011年 | 2977篇 |
2010年 | 1831篇 |
2009年 | 1742篇 |
2008年 | 2463篇 |
2007年 | 2493篇 |
2006年 | 2335篇 |
2005年 | 2183篇 |
2004年 | 2149篇 |
2003年 | 1999篇 |
2002年 | 1938篇 |
2001年 | 473篇 |
2000年 | 340篇 |
1999年 | 455篇 |
1998年 | 504篇 |
1997年 | 358篇 |
1996年 | 321篇 |
1995年 | 295篇 |
1994年 | 263篇 |
1993年 | 286篇 |
1992年 | 265篇 |
1991年 | 219篇 |
1990年 | 189篇 |
1989年 | 208篇 |
1988年 | 166篇 |
1987年 | 159篇 |
1986年 | 128篇 |
1985年 | 158篇 |
1984年 | 182篇 |
1983年 | 138篇 |
1982年 | 149篇 |
1981年 | 126篇 |
1980年 | 110篇 |
1979年 | 73篇 |
1978年 | 81篇 |
1977年 | 75篇 |
1976年 | 54篇 |
1975年 | 47篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
M Carroll P McCrorie 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,88(1):7-12
1. Trypanosomes are unicellular parasites that cause human sleeping sickness in Africa and Chagas' disease in South America. Glycoproteins are important components of their plasma membrane. 2. The bloodstream form of the extracellular salivarian African trypanosome (e.g. Trypanosoma brucei) has the ability to express on its cell surface a repertoire of variant surface glycoproteins (VSGs) and in so doing, evades the immune response of the host (antigenic variation). 3. The VSG is probably synthesized initially in a manner like that of the membrane-bound glycoproteins of mammalian systems, but it also undergoes some novel post-translational modifications. 4. The stercorarian South American trypanosome (Trypanosoma cruzi) is an intracellular parasite which expresses different glycoproteins on its plasma membrane at various stages of its life-cycle, but does not exhibit antigenic variation. 5. The biosynthesis and functions of trypanosomal glycoproteins are compared with those of mammalian glycoproteins, and are discussed with particular reference to potential targets for chemotherapy and immunotherapy of trypanosomiasis. 相似文献
23.
Surface sediment diatoms from the east coast of Lake Tanganyika were analysed using ordination and classification techniques, and compared with assemblages previously described from the northern part of the lake. Grain-size analyses were performed on subsamples. Four groups of diatom assemblages were recognised. The first group clusters samples taken in the north, far from the Rusizi river mouth. The second group comprises samples taken on silty sediment along the Tanzanian coast, including one sample taken near the mouth of the Malagarazi river and those from the northernmost part of the lake. The third group comprises surface sediments along the Burundian coast (near Ramba and Magara), and the fourth is characterised by epipsammic taxa. A sample taken near the central arm of the Malagarazi river is included in the latter group. The impact of small rivers on the diatom assemblages in the surface sediments is restricted to the mouth area. 相似文献
24.
Joong Kyu Kim Mark Klinger Jonathan Benjamin Yuanyuan Xiao David J. Erle Dan R. Littman Nigel Killeen 《PloS one》2009,4(8)
Signaling through the T cell antigen receptor (TCR) is important for the homeostasis of naïve and memory CD4+ T cells. The significance of TCR signaling in regulatory T (Treg) cells has not been systematically addressed. Using an Ox40-cre allele that is prominently expressed in Treg cells, and a conditional null allele of the gene encoding p56Lck, we have examined the importance of TCR signaling in Treg cells. Inactivation of p56Lck resulted in abnormal Treg homeostasis characterized by impaired turnover, preferential redistribution to the lymph nodes, loss of suppressive function, and striking changes in gene expression. Abnormal Treg cell homeostasis and function did not reflect the involvement of p56Lck in CD4 function because these effects were not observed when CD4 expression was inactivated by Ox40-cre.The results make clear multiple aspects of Treg cell homeostasis and phenotype that are dependent on a sustained capacity to signal through the TCR. 相似文献
25.
26.
27.
Mark Wilkinson 《Acta biotheoretica》1998,46(2):109-116
The Le Quesne test of character compatibility uses pairwise comparisons of characters to detect homoplasy in phylogenetic character data. If a pair of characters fails this test we can conclude that a minimum of a single extra step is required by the pair of characters. The rationale of the Le Quesne test is extended to comparisons of triplets of characters. The triplet homoplasy test can reveal that that there is a minimum of four extra steps across a triplet of characters and thus that there are at least two extra steps associated with one of the characters. The triplet homoplasy test can thus detect higher orders of homoplasy than can be detected by the pairwise Le Quesne test. The possibility of quartet and other higher-order homoplasy tests is discussed. The utility of higher-order homoplasy tests is discussed. It is suggested higher-order homoplasy tests have potential uses analogous to the uses of the Le Quesne test, particularly with respect to data exploration. 相似文献
28.
29.
30.