全文获取类型
收费全文 | 59376篇 |
免费 | 4393篇 |
国内免费 | 3911篇 |
出版年
2024年 | 133篇 |
2023年 | 908篇 |
2022年 | 1225篇 |
2021年 | 1656篇 |
2020年 | 1731篇 |
2019年 | 2249篇 |
2018年 | 2001篇 |
2017年 | 1660篇 |
2016年 | 1671篇 |
2015年 | 1835篇 |
2014年 | 2804篇 |
2013年 | 3697篇 |
2012年 | 2304篇 |
2011年 | 2988篇 |
2010年 | 3145篇 |
2009年 | 3066篇 |
2008年 | 2946篇 |
2007年 | 3187篇 |
2006年 | 2928篇 |
2005年 | 2962篇 |
2004年 | 2831篇 |
2003年 | 2306篇 |
2002年 | 1899篇 |
2001年 | 1374篇 |
2000年 | 1171篇 |
1999年 | 1283篇 |
1998年 | 1147篇 |
1997年 | 998篇 |
1996年 | 944篇 |
1995年 | 988篇 |
1994年 | 888篇 |
1993年 | 788篇 |
1992年 | 716篇 |
1991年 | 617篇 |
1990年 | 525篇 |
1989年 | 501篇 |
1988年 | 447篇 |
1987年 | 372篇 |
1986年 | 340篇 |
1985年 | 358篇 |
1984年 | 391篇 |
1983年 | 231篇 |
1982年 | 316篇 |
1981年 | 222篇 |
1980年 | 227篇 |
1979年 | 151篇 |
1978年 | 119篇 |
1977年 | 101篇 |
1976年 | 97篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
《Process Biochemistry》2014,49(1):61-68
Cloning, over-expression, characterization and structural and functional analysis of two alkaline proteases from the newly isolated haloalkaliphilic bacteria: Oceanobacillus iheyensis O.M.A18 and Haloalkaliphilic bacterium O.M.E12 were carried out. The cloned protease genes were over-expressed in Escherichia coli within 6 h of the IPTG induction. The protease genes were sequenced and the sequence submitted to the GenBank with the accession numbers, HM219179 and HM219182. The recombinant proteases were active in the range of pH 8–11 and temperature 30–50 °C. The amino acid sequences of the alkaline proteases displayed hydrophobic character and stable configurations. The amino acids Asp 141, His 171 and Ser 324 formed the catalytic triad, while Ile, Leu and Ser were other amino acid moieties present in the active site. The characteristics of the recombinant proteases were compared and found to be similar to their native counterparts. On the basis of the in-silico analysis and inhibitor studies, the enzymes were confirmed as serine proteases. The study hold significance as only limited enzymes from the haloalkaliphilic bacteria have been cloned, sequenced and analyzed for the structure and function analysis. 相似文献
102.
103.
Jesus Torres-Bacete Prem Kumar Sinha Motoaki Sato Gaurav Patki Mou-Chieh Kao Akemi Matsuno-Yagi Takao Yagi 《The Journal of biological chemistry》2012,287(51):42763-42772
The bacterial H+-translocating NADH:quinone oxidoreductase (NDH-1) catalyzes electron transfer from NADH to quinone coupled with proton pumping across the cytoplasmic membrane. The NuoK subunit (counterpart of the mitochondrial ND4L subunit) is one of the seven hydrophobic subunits in the membrane domain and bears three transmembrane segments (TM1–3). Two glutamic residues located in the adjacent transmembrane helices of NuoK are important for the energy coupled activity of NDH-1. In particular, mutation of the highly conserved carboxyl residue (KGlu-36 in TM2) to Ala led to a complete loss of the NDH-1 activities. Mutation of the second conserved carboxyl residue (KGlu-72 in TM3) moderately reduced the activities. To clarify the contribution of NuoK to the mechanism of proton translocation, we relocated these two conserved residues. When we shifted KGlu-36 along TM2 to positions 32, 38, 39, and 40, the mutants largely retained energy transducing NDH-1 activities. According to the recent structural information, these positions are located in the vicinity of KGlu-36, present in the same helix phase, in an immediately before and after helix turn. In an earlier study, a double mutation of two arginine residues located in a short cytoplasmic loop between TM1 and TM2 (loop-1) showed a drastic effect on energy transducing activities. Therefore, the importance of this cytosolic loop of NuoK (KArg-25, KArg-26, and KAsn-27) for the energy transducing activities was extensively studied. The probable roles of subunit NuoK in the energy transducing mechanism of NDH-1 are discussed. 相似文献
104.
《Molecular cell》2021,81(17):3576-3588.e6
- Download : Download high-res image (149KB)
- Download : Download full-size image
105.
《Bioscience, biotechnology, and biochemistry》2013,77(5):1190-1198
The Rhynchosciara americana C3-22 gene is located in an amplified domain and is developmentally expressed. The aim of the present work was to identify intrinsically bent DNA sites in a segment containing the gene promoter and downstream sequence. The results indicated that this gene is flanked by intrinsically bent DNA sites. Three bent DNA sites (b?3, b?2, and b?1) were localized in the promoter, and one was localized downstream of the gene (b+1). These sites had helical parameters that confirmed the curved structure, as well as segments with left-handed superhelical writhe. In silico analysis of the promoters of four other insect genes, which encode secreted polypeptides, showed that they all had curved structures and similar helical parameters. Correlation with other results indicates that the detected intrinsically bent DNA sites that flank the C3-22 gene might be a consensus feature of the gene structure in the amplified domains. 相似文献
106.
We investigated the synthesis and translocation of amino compounds in Parasponia, a genus of the Ulmaceae that represents the only non-legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap of P. andersonii we identified asparagine. aspartate. glutamine, glutamated significant quantities of a non-protein amino acid. 4-methylglutamte(2-amino-4-methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples from P. andersonii and P. parviflora we also identified the related compounds 4-methyleneglutamate and 4-methyleneglulamine. Using 15N2 labelling and GC-Ms analysis of root nodule extracts we followed N2 fixation and ammonia assimilation in P. andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2-oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of 15N into 4-methylglutamate in nodules, demonstrating the de nova synthesis of this non protein amino acid and suggesting a role in the translation of N in symbioticParasponia. 相似文献
107.
Alysia M. Birkholz Amy R. Howell Mitchell Kronenberg 《The Journal of biological chemistry》2015,290(25):15365-15370
Glycosphingolipids are a subgroup of glycolipids that contain an amino alcohol sphingoid base linked to sugars. They are found in the membranes of cells ranging from bacteria to vertebrates. This group of lipids is known to stimulate the immune system through activation of a type of white blood cell known as natural killer T cell (NKT cell). Here we summarize the extensive research that has been done to identify the structures of natural glycolipids that stimulate NKT cells and to determine how these antigens are recognized. We also review studies designed to understand how glycolipid variants, both natural and synthetic, can alter the responses of NKT cells, leading to dramatic changes in the global immune response. 相似文献
108.
109.
Strategies for signal amplification in nucleic acid detection 总被引:3,自引:0,他引:3
S. Calin Andras J. Brian Power Edward C. Cocking Michael R. Davey 《Molecular biotechnology》2001,19(1):29-44
Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target
amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction,
Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification)
are summarized in the present review, together with their advantages and limitations. 相似文献
110.