全文获取类型
收费全文 | 3178篇 |
免费 | 228篇 |
国内免费 | 1篇 |
专业分类
3407篇 |
出版年
2023年 | 11篇 |
2022年 | 43篇 |
2021年 | 73篇 |
2020年 | 60篇 |
2019年 | 55篇 |
2018年 | 86篇 |
2017年 | 80篇 |
2016年 | 98篇 |
2015年 | 121篇 |
2014年 | 165篇 |
2013年 | 217篇 |
2012年 | 237篇 |
2011年 | 245篇 |
2010年 | 147篇 |
2009年 | 125篇 |
2008年 | 138篇 |
2007年 | 150篇 |
2006年 | 152篇 |
2005年 | 121篇 |
2004年 | 115篇 |
2003年 | 72篇 |
2002年 | 73篇 |
2001年 | 64篇 |
2000年 | 46篇 |
1999年 | 44篇 |
1998年 | 22篇 |
1997年 | 32篇 |
1996年 | 27篇 |
1995年 | 31篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 40篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 37篇 |
1981年 | 22篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 23篇 |
1974年 | 15篇 |
1973年 | 18篇 |
1972年 | 14篇 |
排序方式: 共有3407条查询结果,搜索用时 0 毫秒
1.
Background
Substituted catechols are important precursors for large-scale synthesis of pharmaceuticals and other industrial products. Most of the reported chemical synthesis methods are expensive and insufficient at industrial level. However, biological processes for production of substituted catechols could be highly selective and suitable for industrial purposes. 相似文献2.
Shailesh Kumar Atma P. Dwivedi Vivek Kr. Kashyap A.K. Saxena A.K. Dwivedi Ranjana Srivastava Devi P. Sahu 《Bioorganic & medicinal chemistry letters》2013,23(8):2404-2407
Synthesis of a library of novel trans 6-methoxy-1,1-dimethyl-2-phenyl-3-aryl-2,3-dihydro-1H-inden-4-yloxy alkyl amines and their antimycobacterial activity against drug sensitive and multidrug resistant strains of Mycobacterium tuberculosis have been reported. All the new compounds in the series exhibited MIC between 1.56 and 6.25 μg/ml. Two compounds 1i and 1j with low MIC and low cytotoxicity showed significant reduction in CFU in infected mouse macrophages at 1× MIC concentration. The compound 1i inhibited the growth of M. tuberculosis in mice at 100 mg/kg dose with 1.35 log10 reduction of CFU in lungs tissue and was active against non-replicating Mycobacterium tuberculosis under anaerobic condition. 相似文献
3.
The RAD6 gene of Saccharomyces cerevisiae, which encodes a ubiquitin-conjugating enzyme, is required for DNA repair, DNA damage-induced mutagenesis and sporulation. To evaluate the biological relevance of the thioester adduct between RAD6 protein and ubiquitin, formed as an obligatory, transient intermediate during ubiquitin conjugation to substrates, we altered cysteine 88 in RAD6 to serine. Esterification with ubiquitin occurs at serine 88 in the mutant protein, but conjugation of ubiquitin to the test substrate histone H2A is inactivated. Phenotypically, strains harboring the rad6 Ser88 allele are indistinguishable from rad6 deletion (rad6 delta) mutant cells. These findings argue against ligation of ubiquitin at cysteine 88 acting as a functional switch of a cryptic biochemical activity in RAD6. 相似文献
4.
Prakash M. Nadkarni 《Genomics》1995,30(3)
A consensus framework map of a chromosome is the single most useful map of the chromosome, because of the amount of information it holds as well as the quality of the supporting data backing the putative order of its objects. We describe data structures and algorithms to assist in framework map maintenance and to answer queries about order and distance on genomic objects. We show how these algorithms are efficiently implemented in a client-server relational database. We believe that our data structures are particularly suitable for databases to support collaborative mapping efforts that use heterogeneous methodologies. We summarize two applications that use these algorithms: CHROMINFO, a database specifically designed for framework map maintenance; and the shared client-server database for the chromosome 12 genome center. 相似文献
5.
Prakash Bhuta Stanislav Chládek 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,698(2):167-172
The effect of the antibiotics thiostrepton and micrococcin on EF-Tu-catalyzed (ribosome-dependent) GTP hydrolysis in the presence of A-Phe, C-A-Phe, or C-C-A-Phe (related to the sequence of the 3′-terminus of aminoacyl-tRNA)(System I) or by methanol (‘uncoupled GTPase’, System II) was investigated. In System I, thiostrepton increases the binding affinities of the effectors to the EF-Tu·GTP·70 S ribosome complex, as well as the extent of the GTP hydrolysis, while the KGTPm is virtually unchanged. Similarly, in the uncoupled system (System II) and in the absence of effectors, thiostrepton significantly increases VGTPmax, whereas KGTPm remains unaffected. Micrococcin is without any effect in both systems. The ‘uncoupled GTPase’ (in System II) is also strongly inhibited by C-A-Phe. The results indicate the crucial role of the EF-Tu site which binds the aminoacylated C-C-A terminus of aminoacyl-tRNA in promoting GTP hydrolysis. It follows that the binding of the model effectors (such as C-C-A-Phe) to that site is favorably influenced by the interaction of thiostrepton with the 50 S ribosomal subunit, whereas thiostrepton, per se, does not influence the affinity of EF-Tu for GTP. 相似文献
6.
A K Srivastava C Pandey K P Dwivedi V K Singh 《Indian journal of biochemistry & biophysics》1989,26(3):199-200
QSAR studies have been performed on the homologues of 3-triazines, using molecular connectivity index and van der Waal volume as structural parameters. The regression analysis has shown good correlation between antitumour activity and the two structural parameters. 相似文献
7.
8.
9.
10.
Katalin Rostas Prakash Rao Sista John Stanley Desh Pal S. Verma 《Molecular & general genetics : MGG》1984,197(2):230-235
Summary We report here successful mutagenesis with Transposon Tn5 of three slow-growing strains of Rhizobium japonicum USDA 122, 61A76, USDA 74 and one fast-growing strain, USDA 191. Strains were chosen as representatives of different DNA homology and serogroups of this divergent species, which effectively nodulate North American soybean cultivars. The source of Tn5 was the suicide plasmid pGS9, which possesses broad host range N-type transfer genes in a narrow host range p15A replicon. The selection of Tn5 mutants was facilitated by the expression of the Tn5 encoded streptomycin gene in R. japonicum. Kanamycin and streptomycin resistant colonies appeared from interspecific crosses with E. coli at optimal frequencies of 10-6 for R. japonicum USDA 61A76 and USDA 191 and 5x10-7 for R. japonicum USDA 122 and USDA 74. Altogether, 6550 Tn5 mutants were isolated in USDA 122 and 61A76, and a small number from USDA 74 and USDA 191. Colony hybridization showed that all tested mutants of 61A76 and USDA 122 contained Tn5. Physical analysis of total DNAs from representative numbers of USDA 122, 61A76 and USDA 191 mutants revealed that each of them carried one copy of the transposon integrated randomly in the genome. This was also true for most USDA 74 mutants. Screening of mutants for auxotrophy showed frequencies of 0.2% for USDA 122 and 0.08% for 61A76. Several symbiotically defective mutants were identified on plants, Glycine soja and G. max. 相似文献