全文获取类型
收费全文 | 1636篇 |
免费 | 104篇 |
国内免费 | 4篇 |
专业分类
1744篇 |
出版年
2022年 | 17篇 |
2021年 | 36篇 |
2020年 | 25篇 |
2019年 | 28篇 |
2018年 | 38篇 |
2017年 | 20篇 |
2016年 | 45篇 |
2015年 | 55篇 |
2014年 | 62篇 |
2013年 | 116篇 |
2012年 | 114篇 |
2011年 | 68篇 |
2010年 | 67篇 |
2009年 | 58篇 |
2008年 | 86篇 |
2007年 | 79篇 |
2006年 | 67篇 |
2005年 | 61篇 |
2004年 | 47篇 |
2003年 | 34篇 |
2002年 | 45篇 |
2001年 | 40篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 33篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 9篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1966年 | 11篇 |
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
1.
2.
Natural killer T (NKT) cells are a component of innate and adaptive immune systems implicated in immune, autoimmune responses and in the control of obesity and cancer. NKT cells develop from common CD4+ CD8+ double positive (DP) thymocyte precursors after the rearrangement and expression of T cell receptor (TCR) Vα14-Jα18 gene. Temporal regulation and late appearance of Vα14-Jα18 rearrangement in immature DP thymocytes has been demonstrated. However, the precise control of lifetime of DP thymocytes in vivo that enables distal rearrangements remains incompletely defined. Here we demonstrate that T cell factor (TCF)-1, encoded by the Tcf7 gene, is critical for the extended lifetime of DP thymocytes. TCF-1-deficient DP thymocytes fail to undergo TCR Vα14-Jα18 rearrangement and produce significantly fewer NKT cells. Ectopic expression of Bcl-xL permits Vα14-Jα18 rearrangement and rescues NKT cell development. We report that TCF-1 regulates expression of RORγt, which regulates DP thymocyte survival by controlling expression of Bcl-xL. We posit that TCF-1 along with its cofactors controls the lifetime of DP thymocytes in vivo. 相似文献
3.
Heteromazocraes mamaevi n. sp. is described from a cyprinid, Securicula gora (Ham.) from the Lucknow district, India. It is characterised by well-developed cephalic glands, the shape of the genital spines, the structure of the egg and the shape of the clamp sclerites. This is the first record of the genus Heteromazocraes Mamaev, 1981 from a cyprinid fish. 相似文献
4.
A novel ompC mutation of Escherichia coli K-12 that reduces OmpC and OmpF levels in the outer membrane 总被引:1,自引:0,他引:1
Rajeev Misra 《Molecular microbiology》1993,10(5):1029-1035
5.
6.
Heinz W. Kunz Andrea L. Cortese Hassett Tetsuo Inomata D. N. Misra Thomas J. Gill III 《Immunogenetics》1989,30(3):181-187
A new antigenic system in the rat homologous to theQa/TL antigen system in the mouse has been characterized. It was detected by antibodies raised in donor-recipient combinations
that were matched for theRT1. A, B, D, E loci in the major histocompatibility complex (MHC): (R11×BN)F1 anti-BN.1L(LEW), (R18×BN)F1 anti-BN.1L, and BN.1LV1(F344) anti-BN.1L. Absorption analyses using these antisera and a variety of inbred, congenic and
recombinant strains identified three alleles,RT1.G
a
,G
b
,G
c
, of whichG
c
is a null allele. The strain distribution of these alleles was determined, using 37 strains of rats representative of all
of the prototypic haplotypes and a number of congenic and recombinant strains. The use of the congenic and recombinant strains
showed that theRT1.G locus was linked to the MHC and that the most probable gene order wasA-E-G. Testcross analysis showed that the map distance betweenA andG was 1.4 cM(4/285 recombinants). The RT1.G antigen has a heavy chain ofM
r 46 000 and is present on both T and B cells. 相似文献
7.
Chemical and enzymatic incorporation of N2-(p-n-butylphenyl)-2''-deoxyguanosine into an oligodeoxyribonucleotide. 下载免费PDF全文
An 18mer oligodeoxyribonucleotide containing a N2-(p-n-butylphenyl)-2'-deoxyguanosine (BuPdG) residue at the 3' end has been synthesized by both chemical and enzymatic methods. Chemical synthesis involved attachment of 5'-DMT-BuPdG as the 3'-H-phosphonate to uridine-controlled pore glass (CPG), followed by extension via H-phosphonate chemistry. After oxidation of the backbone, deprotection of bases, and removal from CPG, the uridine residue was removed by periodate cleavage and beta-elimination. The resulting oligomer 3'-phosphate was digested with alkaline phosphatase to give the free BuPdG-18mer. E.coli DNA polymerase I (Klenow) incorporated BuPdGTP at the 3' end of the corresponding 17mer primer annealed to a complementary 29mer template, and the properties of this product were identical to those of chemically synthesized BuPdG-18mer. E.coli DNA polymerase I (Klenow) was unable to extend the BuPdG-18mer, and the 3' to 5' exonuclease activity of the enzyme was unable to remove the modified nucleotide. 相似文献
8.
9.
Sujata Misra Kshudiram Naskar Dwijen Sarkar Dilip Kumar Ghosh 《Molecular and cellular biochemistry》1991,102(1):13-18
Summary
Leishmania donovani, the etiological agent for the disease visceral leishmaniasis, attach themselves to the macrophages for initiation of the disease. The attachment process has been found to be regulated by Ca2+ ions. Verapamil, a Ca2+-channel blocker inhibits Leishmania-macrophage attachment. The inhibitory effect is increased with time. Nifedipine, another Ca2+-channel blocker exhibits the same effect. The attachment process is stimulated by Ca2+-ionophore alone. The inhibitory effects of the calcium channel blockers are reversed by the ionophore. 相似文献
10.
Nigel L. Brown Tapan K. Misra Joseph N. Winnie Annette Schmidt Michael Seiff Simon Silver 《Molecular & general genetics : MGG》1986,202(1):143-151
Summary The DNA sequences of the mercuric resistance determinants of plasmid R100 and transposon Tn501 distal to the gene (merA) coding for mercuric reductase have been determined. These 1.4 kilobase (kb) regions show 79% identity in their nucleotide sequence and in both sequences two common potential coding sequences have been identified. In R100, the end of the homologous sequence is disrupted by an 11.2 kb segment of DNA which encodes the sulfonamide and streptomycin resistance determinants of Tn21. This insert contains terminal inverted repeat sequences and is flanked by a 5 base pair (bp) direct repeat. The first of the common potential coding sequences is likely to be that of the merD gene. Induction experiments and mercury volatilization studies demonstrate an enhancing but non-essential role for these merA-distal coding sequences in mercury resistance and volatilization. The potential coding sequences have predicted codon usages similar to those found in other Tn501 and R100 mer genes. 相似文献