全文获取类型
收费全文 | 4557篇 |
免费 | 258篇 |
国内免费 | 2篇 |
出版年
2022年 | 27篇 |
2021年 | 50篇 |
2020年 | 26篇 |
2019年 | 36篇 |
2018年 | 52篇 |
2017年 | 46篇 |
2016年 | 82篇 |
2015年 | 145篇 |
2014年 | 172篇 |
2013年 | 280篇 |
2012年 | 255篇 |
2011年 | 241篇 |
2010年 | 147篇 |
2009年 | 194篇 |
2008年 | 276篇 |
2007年 | 256篇 |
2006年 | 259篇 |
2005年 | 269篇 |
2004年 | 248篇 |
2003年 | 243篇 |
2002年 | 284篇 |
2001年 | 121篇 |
2000年 | 99篇 |
1999年 | 82篇 |
1998年 | 56篇 |
1997年 | 46篇 |
1996年 | 44篇 |
1995年 | 31篇 |
1994年 | 42篇 |
1993年 | 44篇 |
1992年 | 72篇 |
1991年 | 59篇 |
1990年 | 48篇 |
1989年 | 52篇 |
1988年 | 40篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 27篇 |
1982年 | 46篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1976年 | 10篇 |
1974年 | 21篇 |
1971年 | 11篇 |
1969年 | 11篇 |
1968年 | 16篇 |
排序方式: 共有4817条查询结果,搜索用时 15 毫秒
91.
X-ray diffraction studies of enkephalins. Crystal structure of [(4''-bromo) Phe4,Leu5]enkephalin. 总被引:3,自引:1,他引:2 下载免费PDF全文
T Ishida M Kenmotsu Y Mino M Inoue T Fujiwara K Tomita T Kimura S Sakakibara 《The Biochemical journal》1984,218(3):677-689
In order to investigate the structure-activity relationship of [Leu5]- and [Met5]enkephalins, [(4'-bromo)Phe4, Leu5]-, [(4'-bromo)Phe4, Met5]- and [Met5] enkephalins were synthesized and crystallized. The crystal structure of [(4'-bromo) Phe4, Leu5]- enkephalin was determined by X-ray diffraction method using the heavy atom method and refined to R = 0.092 by the least-squares method. The molecule in this crystal took essentially the same type I' beta-turn conformation found in [Leu5]enkephalin [Smith & Griffin (1978) Science 199, 1214-1216). On the other hand, the preliminary three-dimensional Patterson analyses showed that the most probable conformations of [(4'-bromo)Phe4,Met5]- and [Met5]enkephalins are both the dimeric extended forms. Based on these insights, the biologically active conformation of enkephalin was discussed in relation to the mu- and delta-receptors. 相似文献
92.
Abstract A lignin substructure model, 1-(4-ethoxy-3,5-dimethoxyphenyl)-2-(4-ethoxy-3-methoxyphenyl)-propane-1,3-diol(I), was actively metabolized by a white-rot fungus Coriolus versicolor in low nitrogen stationary cultures favouring the ligninolytic activity in the fungus. Cleavage of the dimer I between Cα and Cβ of the propanoid side chain was the major degradative reaction by the fungus. 相似文献
93.
Toshimasa Ishida Ken-Ichi Tomita Masatoshi Inoue 《Archives of biochemistry and biophysics》1980,200(2):492-502
The crystal and molecular structures of the title complex has been determined by X-ray diffraction methods, as a model for tryptophan residues in protein-pyridine coenzyme interactions. The structure was solved by direct methods and was refined by standard methods (final R = 0.073). The light-green crystals consist of alternate layers of indole-3-acetic acid and 1-methyl-3-carbamoylpyridinium molecules piled up to the c-direction, and are stabilized by the crystal water participating in hydrogen bonds in the a- and b-directions. The parallel stackings and interplanar spacing distances between indole and pyridinium rings strongly suggest a II–II1 charge transfer from the indole ring to the lowest unoccupied orbital of the pyridinium ring in the ground state. Furthermore, this crystal structure provides evidence that quaternization of the N1 position enhances electron-acceptor properties of pyridine. On the other hand, the proton magnetic resonance spectra suggest that the stacking mode between both rings in solution is very similar to the one observed in the crystal structure. 相似文献
94.
To investigate the dynamics of membrane processes that may be integral components of specific transmembrane signaling events we have synthesized several novel paramagnetic probes and their photoreactive counterparts. The structure of these probes was designed to (1) restrict “flipping” across the membrane bilayer; (2) contain paramagnetic or photoreactive moieties that could be placed at specific depths within the bilayer; (3) provide information about membrane structure as well as dynamics of protein movement; and (4) in the case of the photoreactive probes, be of high specific radioactivity. The molecules described in this paper consist of amino acid, dipeptide, or carbohydrate groups attached to arylazide- or nitroxide-bearing fatty acids. The synthesis and initial characterization of these membrane probes is described. 相似文献
95.
96.
Hiroyuki Horitsu Yasushi Takahashi Junkō Tsuda Keiichi Kawai Yoshio Kawano 《Applied microbiology and biotechnology》1983,18(6):358-360
Summary Living Aspergillus terreus cells were entrapped in polyacrylamide gels and employed in both replacement batch and continuous column reactors to produce itaconic acid from glucose.With the replacement batch reactor, maximum itaconic acid productivity was observed under the following conditions: pH 2.50, temperature at 35°C, addition of NH4H2PO4 and MgSO4·7H2O. Using the continuous reactor, the maximum itaconic acid yield was 60 mg/h/40 g of gel. The biocatalyst activity or half-life was about 10 days. 相似文献
97.
H Ueda H Maruyama M Doi M Inoue T Ishida H Morioka T Tanaka S Nishikawa S Uesugi 《Journal of biochemistry》1991,109(6):882-889
An artificial gene coding for the human cap binding protein (hCBP: human IF-4E) was chemically synthesized and expressed in Escherichia coli under the control of a trp promoter. The DNA duplex of 662 bp was designed and constructed from 44 oligodeoxynucleotide fragments of typically 30 nucleotides in length. Although the hCBP gene was not directly expressed in E. coli HB101, we succeeded in its high-level expression as a fusion protein connected with a portion of human growth hormone through a tetradecapeptide (Asp-Asp-Pro-Pro-Thr-Val-Glu-Leu-Gln-Gly-Leu-Val-Pro-Arg) that contains the recognition sequence for a site-specific protease alpha-thrombin. Upon induction with 3-indoleacrylic acid, the fusion protein accumulated with a yield of about 20% of the total proteins of the host cell. Upon the treatment of the fusion protein with alpha-thrombin, which recognizes the sequence "Val-Pro-Arg," specific proteolysis at the fused junction occurred efficiently. In this system, nonspecific digestion by alpha-thrombin was not marked. About 15 mg of recombinant hCBP was obtained from a 1-liter culture. Association constants between the recombinant hCBP and mRNA cap structure analogues were determined by fluorescence spectroscopy. The values obtained for the m7GpppA, m7GTP, and m7GMP were almost the same as those reported for the IF-4E isolated from human erythrocyte cells.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
98.
A Yamamoto T Kaji K Tomoo T Ishida M Inoue M Murata K Kitamura 《Journal of molecular biology》1992,227(3):942-944
Cathepsin B from bovine spleen has been purified and crystallized as a complex with a specific inhibitor CA074 [N-(L-3-trans-propylcarbamoyloxirane-2-carbonyl)-L- isoleucyl-L-proline], using the hanging-drop method. The complex crystals obtained from 50 mM-citrate buffer (pH 3.5) belong to the tetragonal space group P4(1) (or P4(3)) with a = 73.06 A and c = 141.59 A, and diffract beyond 2.2 A resolution. There are two complex molecules per asymmetric unit giving a packing density of 3.37 A3/Da and indicating a high solvent content of 63.5%. 相似文献
99.
Stable transformants with preproendothelin-1 (preproET-1) cDNA were established for the study of the regulation of endothelin-1 (ET-1) biosynthesis in human cells. ET-1, a potent vasoconstrictor peptide, is produced by endothelial cells and is secreted into the blood at a low level. Human preproET-1 cDNA was introduced into two immortal human cell lines, t-HUE2, an endothelial cell line, and Raji, a B cell line, with Ecogpt selection. Several stable transformants of t-HUE2 expressed extraordinarily high levels of preproET-1 specific mRNA and secreted ET-1 into serum-free culture medium, while the transformants of Raji cells expressed high levels of ET-1 mRNA, but secreted a negligible amount of ET-1. Immunocytochemical studies of intracellular ET-1 content revealed that there were some defects in the translation or processing of preproET-1 in the B cell line transformants. In addition, the ratio of ET-1 to ET-1 precursor (big ET-1) was much higher in the t-HUE2 transformants than in normal endothelial cells, suggesting that t-HUE2 transformants (for example t-HUE2-1) possess high levels of endothelin converting enzyme (ECE). The establishment of stable transformants producing high levels of ET-1 in serum-free medium will be useful for the study of cell-type-specific translation and processing to mature ET-1, and of the regulatory factors of ECE. 相似文献
100.
Elevation of Cyclic AMP-Dependent Protein Kinase Activity during Migration of Primary Mesenchyme Cell in Sand Dollar Blastulae 总被引:1,自引:1,他引:0
Concetration of intracellular cyclic AMP (cAMP), and activities of adenylate cyclase and cAMP-dependent protein kinase were examined in swimming and mesenchyme blastulae and primary mesenchyme cells (PMCs) of the sand dollar, Clypeaster japonicus , respectively. In mesenchyme blastulae, the concentration of cAMP increased 45% from that in swimming blastulae. PMCs contained a concentration of cAMP 40% higher than that in whole embryos at the mesenchyme blastula stage. The activity of adenylate cyclase in mesenchyme blastulae was 100% higher than that in swimming blastulae. The activites of cAMP-dependent protein kinase in whole embryos at the above two developmental stages, on the other hand, were quite similar to each other. However, in PMCs the activity of the enzyme was conspicuously higher than that in these embryos, and it reached 190% higher than that in these embryos. Inhibition of cAMP-dependent protein kinase activity by a synthetic inhibitor, H8, caused severe inhibition of PMC migration but it did not exert any effect on PMC ingression. These results suggest that the cAMP-dependent protein kinase activity is involved in PMC migration, but not in PMC ingression. 相似文献