全文获取类型
收费全文 | 8236篇 |
免费 | 424篇 |
国内免费 | 6篇 |
专业分类
8666篇 |
出版年
2022年 | 42篇 |
2021年 | 72篇 |
2020年 | 42篇 |
2019年 | 46篇 |
2018年 | 90篇 |
2017年 | 79篇 |
2016年 | 141篇 |
2015年 | 192篇 |
2014年 | 235篇 |
2013年 | 816篇 |
2012年 | 416篇 |
2011年 | 495篇 |
2010年 | 288篇 |
2009年 | 273篇 |
2008年 | 478篇 |
2007年 | 490篇 |
2006年 | 504篇 |
2005年 | 512篇 |
2004年 | 484篇 |
2003年 | 465篇 |
2002年 | 533篇 |
2001年 | 89篇 |
2000年 | 75篇 |
1999年 | 92篇 |
1998年 | 140篇 |
1997年 | 104篇 |
1996年 | 99篇 |
1995年 | 96篇 |
1994年 | 85篇 |
1993年 | 123篇 |
1992年 | 96篇 |
1991年 | 61篇 |
1990年 | 46篇 |
1989年 | 66篇 |
1988年 | 53篇 |
1987年 | 51篇 |
1986年 | 45篇 |
1985年 | 48篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 73篇 |
1981年 | 56篇 |
1980年 | 58篇 |
1979年 | 30篇 |
1978年 | 39篇 |
1977年 | 26篇 |
1976年 | 34篇 |
1974年 | 24篇 |
1973年 | 26篇 |
1972年 | 23篇 |
排序方式: 共有8666条查询结果,搜索用时 8 毫秒
21.
The nucleotide sequence data reported in this paper have been submitted to the GSDB, DDBJ, EMBL, and NCBI nucleotide sequence databases and have been assigned the accession numbers D49841 (RCD28), D49844 (RCTLA-4), D49842 (RCD80), and D49843 (RCD86) 相似文献
22.
Application of bacterial magnetic particles as novel DNA carriers for ballistic transformation of a marine cyanobacterium 总被引:4,自引:0,他引:4
Haruko Takeyama Akira Yamazawa Chikashi Nakamura Tadashi Matsunaga 《Biotechnology Techniques》1995,9(5):355-360
Summary Bacterial magnetite particles (BMPs) of 50 to 100nm diam were used as DNA carriers for the ballistic transformation of the marine cyanobacteriumSynechococcus. BMPs were bombarded into the cyanobacterial cells at several bombardment velocities using a particle gun. Successful transformation and gene expression were confirmed by Southern hybridization and CAT assay, respectively. The BMPs were also observed in the cyanobacterial cells by transmission electron microscopy. These results suggested that BMPs can be used as carriers for introducing DNA into bacterial cells. 相似文献
23.
Summary Effects of divalent cations on oscillations of membrane potentials (i.e., spontaneous repetitive hyperpolarizing responses) and on hyperpolarizing responses induced by electrical stimuli as well as on resting potentials were studied in large nondividing L cells. Deprivation of Ca2+ from the external medium inhibited these hyperpolarizing responses accompanying slight depolarization of the resting potential. Sr2+ or Mn2+ applied to the external medium in place of Ca2+ was able to substitute for Ca2+ in the generation of hyperpolarizing responses, while Mg2+, Ba2+ or La3+ suppressed hyperpolarizing responses. The addition of A23187 to the bathing medium or intracellular injection of Ca2+, Sr2+, Mn2+ or La3+ induced membrane hyperpolarization. When the external Ca2+, Sr2+ or Mn2+ concentration was increased, the resting potential also hyperpolarized, in a saturating manner. The amplitude of maximum hyperpolarization produced by high external Ca2+ was of the same order of magnitude as those of hyperpolarizing responses and was dependent on the external K+ concentration. In the light of these experimental observations, it was deduced that the K+ conductance increase associated with the hyperpolarizing excitation is the result of an increase in the intracellular concentration of free Ca2+ mainly derived from the external solution. 相似文献
24.
K Nagahama T Ogawa T Fujii M Tazaki S Tanase Y Morino H Fukuda 《Journal of general microbiology》1991,137(10):2281-2286
A novel ethylene-forming enzyme that catalyses the formation of ethylene from 2-oxoglutarate was purified from a cell-free extract of Pseudomonas syringae pv. phaseolicola PK2. It was purified about 2800-fold with an overall yield of 53% to a single band of protein after SDS-PAGE. The purified enzyme had a specific activity of 660 nmol ethylene min-1 (mg protein)-1. The molecular mass of the enzyme was approximately 36 kDa by gel filtration and 42 kDa by SDS-PAGE. The isoelectric point and optimum pH were 5.9 and ca. 7.0-7.5, respectively. There was no homology between the N-terminal amino acid sequence of the ethylene-forming enzyme of Ps. syringae pv. phaseolicola PK2 and the sequence of the ethylene-forming enzyme of the fungus Penicillium digitatum IFO 9372. However, the two enzymes have the following properties in common. The presence of 2-oxoglutarate, L-arginine, Fe2+ and oxygen is essential for the enzymic reaction. The enzymes are highly specific for 2-oxoglutarate as substrate and L-arginine as cofactor. EDTA, Tiron, DTNB [5,5'-dithio-bis(2-nitrobenzoate)] and hydrogen peroxide are all effective inhibitors. 相似文献
25.
Kuriyama Akira; Takeuchi Masayuki; Kawai Fumio; Kanamori Masao 《Plant & cell physiology》1992,33(5):647-650
The formation of sporophytic shoots, which is induced by treatmentwith benzylaminopurine of gametophyte tissue of Equisetum arvense,can be divided into initiation and developmental phases. Thenitrogen in MS medium was suitable for two phases as well as gametophytic growth, buta reduction in the concentration of available nitrogen was neededfor the development of shoots. ions alone were effective for gametophytic growth and the initiationof sporophytic shoots, but both and ions was required for the developmental phase. (Received February 18, 1992; Accepted April 14, 1992) 相似文献
26.
Yoshiharu Inoue Hiromi Tsuchiyama Nobuhiko Kosugi Akira Kimura 《Applied microbiology and biotechnology》1992,36(4):469-472
Summary Glyoxalase I was extracted from Hansenula mrakii IFO 0895 by incubating the cells with buffer solution containing 50% acetone (enzyme activity 35 units/g cells) or 50% ethyl acetate (enzyme activity 28 units/g cells) at 30°C for 10 h. Glyoxalase II was also extracted from the cells, although the activity of the enzyme was lost during incubation with organic solvents, especially at higher temperature (30°C). By using the organic-solvent-extracted fraction of H. mrakii, enzymatic production of S-lactoylglutathione was studied, and approximately 82 mmol/l (30 g/l) of S-lactoylglutathione was produced from 120 mmol/l glutathione.
Offprint requests to: A. Kimura 相似文献
27.
Hope C. Taylor David C. Richardson Jane S. Richardson Alexander Wlodawer Akira Komoriya Irwin M. Chaiken 《Journal of molecular biology》1981,149(2):313-317
We have studied the integrity of folded structure of a fully active semi-synthetic ribonuclease-S which lacks amino acid residues 16 through 20, and an inactive one with the same residues deleted and 4-fluoro-l-histidine substituted for active site histidine 12. Using “Y” form crystals, we obtained X-ray structural data to a resolution of 2·6 Å and, incorporating phase information calculated from refined ribonuclease-S coordinates, prepared several types of electron density maps. These showed that the overall backbone structure and active site configuration of both analogues do not differ noticeably from those of the native protein. Structural homology extends to the catalytically relevant side-chain at position 12; 4-F-His2 assumes the same position as does His in active ribonuclease-S. This supports the view that the 4-F-Hisl2 analogue is inactive due to a change in histidine 12 imidazole basicity, rather than to any significant conformational distortion within the active site. 相似文献
28.
Shinkichi Kamata Akira Okada Takehiko Watanabe Yasunaru Kawashima Hiroshi Wada 《Journal of neurochemistry》1980,35(5):1190-1199
The etiologic relationship between disturbances in metabolism of amino acids and amines and hepatic coma was investigated by examining the effects of diets containing various mixtures of amino acids on brain amine metabolism in rats with a portacaval shunt, using a method for simultaneous analysis of amino acids and amines. Rats with a portacaval shunt were fed on four different amino acid compositions with increased amounts of various amino acids suspected to be etiologically related to hepatic coma, such as methionine, phenylalanine, tyrosine, and tryptophan. The animals were killed 4 weeks after operation. During the experimental period, these animals did not become comatose, but exhibited various behavioral abnormalities. Marked increase in the plasma and brain levels of the augmented amino acids, especially methionine and tyrosine, were observed in rats with a portacaval shunt. Brain noradrenaline, dopamine, and serotonin levels were significantly decreased when the brain tyrosine level was increased. These results indicate that in rats with a portacaval shunt the dietary levels of amino acids greatly influence the brain levels of both amino acids and transmitter amines. 相似文献
29.
30.
Effect of ethylene on DNA synthesis in potato tuber discs 总被引:2,自引:0,他引:2
The effect of ethylene on DNA synthesis in potato tuber discsinduced by cutting was examined. Continuous presence of ethylenein the ambient atmosphere of the slices lowered the rate ofinduced DNA synthesis by about 50%, but did not alter the timecourse pattern of development of DNA synthesis. RNA and proteinsyntheses were not affected. The inhibitory effect on DNA synthesiswas observed at as low as 0.01 µl/liter and was due tothe specific action of ethylene, not to a non-specific actionof gaseous hydrocarbons. Ethylene also decreased the numberof cells which could synthesize DNA. The results of ethylenetreatment of various durations at various times after cuttingindicate that a process prerequisite for DNA synthesis and susceptibleto ethylene action starts at about 6 hr after cutting and continuesfor only a limited period. (Received July 5, 1976; ) 相似文献