全文获取类型
收费全文 | 3257篇 |
免费 | 215篇 |
国内免费 | 6篇 |
出版年
2022年 | 21篇 |
2021年 | 25篇 |
2019年 | 16篇 |
2018年 | 27篇 |
2017年 | 28篇 |
2016年 | 35篇 |
2015年 | 60篇 |
2014年 | 62篇 |
2013年 | 264篇 |
2012年 | 133篇 |
2011年 | 184篇 |
2010年 | 103篇 |
2009年 | 118篇 |
2008年 | 196篇 |
2007年 | 183篇 |
2006年 | 180篇 |
2005年 | 186篇 |
2004年 | 185篇 |
2003年 | 203篇 |
2002年 | 196篇 |
2001年 | 52篇 |
2000年 | 42篇 |
1999年 | 72篇 |
1998年 | 69篇 |
1997年 | 41篇 |
1996年 | 47篇 |
1995年 | 43篇 |
1994年 | 36篇 |
1993年 | 50篇 |
1992年 | 51篇 |
1991年 | 40篇 |
1990年 | 43篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 37篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1975年 | 31篇 |
1974年 | 21篇 |
1973年 | 20篇 |
1970年 | 12篇 |
排序方式: 共有3478条查询结果,搜索用时 359 毫秒
81.
Carboxyphosphonoenolpyruvate phosphonomutase, a novel enzyme catalyzing C-P bond formation. 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
T Hidaka S Imai O Hara H Anzai T Murakami K Nagaoka H Seto 《Journal of bacteriology》1990,172(6):3066-3072
An enzyme catalyzing the formation of an unusual C-P bond that is involved in the biosynthesis of the antibiotic bialaphos (BA) was isolated from the cell extract of a mutant (NP71) of Streptomyces hygroscopicus SF1293. This enzyme, carboxyphosphonoenolpyruvate (CPEP) phosphonomutase, was first identified as a protein lacking in a mutant (NP213) defective in one of the steps in the pathway to BA. The first 30 residues of the amino terminus of this protein were identical to those predicted by the nucleotide sequence of the gene that restored BA production to NP213. The substrate of the enzyme, a P-carboxylated derivative of phosphoenolpyruvate named CPEP, was also isolated from the broth filtrate of NP213 as a new biosynthetic intermediate of BA. CPEP phosphonomutase catalyzes the rearrangement of the carboxyphosphono group of CPEP to form the C-P bond of phosphinopyruvate. 相似文献
82.
83.
Hydrogen exchange kinetics of nucleic acids: Double and triple helices with Hoogsteen-type basepairs
Yuzuru Hayashi Mamoru Nakanishi Masamichi Tsuboi Toshikazu Fukui Morio Ikehara Ichiro Tazawa Yasuo Inoue 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,698(1):93-99
The kinetics of hydrogen-tritium exchange reaction have been followed by a Sephadex technique of a double-helical poly(ribo-2-methylthio-adenylic acid)·poly(ribouridylic acid) complex with the Hoogsteen-type basepair. Only one hydrogen in every 2-methylthio-adenine·uracil basepair has been found to exchange at a measurably slow rate, 0.023 s?1 (at 0°C), which is, however, much greater than that for a double-helix with the Watson-Crick type A·U pair. The kinetics of hydrogen-tritium exchange were also examined by triple-helical poly(rU)·poly(rA)·poly(rU) which involves both the Watson-Crick and Hoogsteen basepairings. Here, three hydrogens in every U·A·U base triplet have been found to exchange at a relatively slow rate, 0.0116 s?1 (at 0°C). The kinetics of hydrogen-deuterium exchange reactions of these polynucleotide helices have also been followed by a stopped-flow ultraviolet absorption spectrophotometry at various temperatures. On the basis of these experimental results, the mechanism of the hydrogen exchange reactions in these helical polynucleotides was discussed. In the triple helix, the rate-determining process of the slow exchange of the three (one uracil-imide and two adenine-amino) hydrogens is considered to be the opening of the Watson-Crick part of the U·A·U triplet. This opening is considered to take place only after the opening of the Hoogsteen part of the triplet. 相似文献
84.
Toshio Nakatani Kazue Ozawa Motokazu Asano Minoru Ukikusa Yasuo Kamiyama Takayoshi Tobe 《Life sciences》1981,28(3):257-264
The changes in the energy substrate utilized by the remnant liver were studied in relation to the changes in the cellular energy status of 25 and 70% hepatectomized rabbits. In 25% hepatectomized rabbits, the energy charge level of the remnant liver remained unchanged, the energy substrate of which was predominantly glucose, rather than fatty acid. In contrast, in 70% hepatectomized rabbits, the energy production by the mitochondria was mainly dependent upon fatty acid oxidation at the early period after hepatectomy when the energy charge level decreased remarkably, and then upon glucose oxidation, concomitant with the restoration of the energy charge. It is suggested that the changes in the energy substrate utilized are closely related to those in the energy charge level and the mitochondrial phosphorylative activity of the remnant liver following hepatectomy. 相似文献
85.
Photosynthetic activities of the thylakoid membranes modifiedwith pyridoxal phosphate (PLP) and sodium borohydride in lightwere studied and compared with those modified in the dark. PLPmodified the membrane-bound chloroplast coupling factor 1 (CF1)and inhibited photophosphorylation. Only PLP modification inlight stimulated basal electron transport. This stimulationof electron transport was prevented by the presence of ATP orcarbonylcyanide m-chlorophenylhydrazone in the modificationmixture. Magnesium ion was required for PLP modification. Theextent of lightinduced proton uptake was decreased by PLP modificationin light. N,N'-Dicyclohexylcarbodiimide lowered the stimulatedelectron transport to the basal level of unmodified chloroplastsand restored proton uptake. When chloroplasts were modified with 4 mM PLP in light and dark,11.6 and 11.0 mol of PLP were incorporated into mol of CF1,respectively. ATP could bind with high affinity to CF1 isolatedafter PLP modification in light. The results indicate that PLP modifies membrane-bound CF1 whichhas a conformation altered by energization of the thylakoidsin light, and causes an apparent uncoupling of phosphorylation(stimulation of basal electron transport). The results suggestthat this uncoupling is induced by the loss of the regulatoryfunction of CF1 for proton translocation after PLP modificationin light.
1 Presented at the ISRACON on Control Mechanisms in Photosynthesis.Aug. 31-Sept. 4, 1980, Acre, Israel (Received June 22, 1981; Accepted August 28, 1981) 相似文献
86.
87.
88.
Summary Ceramide is the fundamental structure and key intermediate of all sphingolipids. Biosynthesis and catabolism of brain ceramide, especially their relationship to the metabolism of more complex sphingolipids in brain, are reviewed. Human genetic diseases which involve altered ceramide metabolism are also discussed. 相似文献
89.
Yasuo Kishimoto Hiroshi Akanuma Inderjit Singh 《Molecular and cellular biochemistry》1979,28(1-3):93-105
Summary -Hydroxylation is an enzymatic reaction by which long-chain fatty acids are converted to their -hydroxy derivatives. This reaction, in animals, can be detected only in developing brain and is the rate-determining step in the synthesis of hydroxycerebroside, which is an indispensable and abundant myelin lipid. In addition to a particulate fraction from brain, two cytoplasmic factors, one heat-stable and the other heat-labile, are required for -hydroxylation. During the past eight years we have been investigating -hydroxylation. Our progress is summarized and discussed here. 相似文献
90.
Hiroshi Sagami Kyozo Ogura Shuichi Seto Tadashi Kurokawa 《Biochemical and biophysical research communications》1978,85(2):572-578
A new prenyltransferase which catalyzes the synthesis of geranyl pyrophosphate as the only product from dimethylallyl pyrophosphate and isopentenyl pyrophosphate has been separated from other known prenyltransferases from . This enzyme fraction is also capable of synthesizing all- geranylgeranyl pyrophosphate from farnesyl pyrophosphate and isopentenyl pyrophosphate though it lacks ability to synthesize farnesyl pyrophosphate. 相似文献