全文获取类型
收费全文 | 6860篇 |
免费 | 204篇 |
国内免费 | 249篇 |
出版年
2024年 | 10篇 |
2023年 | 44篇 |
2022年 | 86篇 |
2021年 | 114篇 |
2020年 | 94篇 |
2019年 | 159篇 |
2018年 | 205篇 |
2017年 | 91篇 |
2016年 | 109篇 |
2015年 | 153篇 |
2014年 | 373篇 |
2013年 | 467篇 |
2012年 | 259篇 |
2011年 | 402篇 |
2010年 | 231篇 |
2009年 | 354篇 |
2008年 | 387篇 |
2007年 | 366篇 |
2006年 | 372篇 |
2005年 | 377篇 |
2004年 | 326篇 |
2003年 | 287篇 |
2002年 | 241篇 |
2001年 | 151篇 |
2000年 | 161篇 |
1999年 | 171篇 |
1998年 | 156篇 |
1997年 | 147篇 |
1996年 | 124篇 |
1995年 | 132篇 |
1994年 | 97篇 |
1993年 | 70篇 |
1992年 | 76篇 |
1991年 | 62篇 |
1990年 | 56篇 |
1989年 | 50篇 |
1988年 | 57篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 47篇 |
1984年 | 41篇 |
1983年 | 28篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1974年 | 3篇 |
排序方式: 共有7313条查询结果,搜索用时 15 毫秒
951.
《Bioscience, biotechnology, and biochemistry》2013,77(10):2356-2359
Jasmonic acid (JA) is a plant hormone that plays important roles in a large number of processes in stress adaptation and development in flowering plants. A search of genome database indicated the existence of allene oxide synthase (AOS), an enzyme of JA biosynthesis, in Physcomitrella patens, a model plant among mosses. In this study, the presence of JA was detected in P. patens. The recombinant AOS of P. patens, which was overexpressed in Escherichia coli, showed AOS activity. These data suggest that the octadecanoid pathway also exists in P. patens. 相似文献
952.
David M. Mueller 《Journal of bioenergetics and biomembranes》2000,32(4):391-400
The mitochondrial ATP synthase is a molecular motor that drives the phosphorylation ofADP to ATP. The yeast mitochondrial ATP synthase is composed of at least 19 differentpeptides, which comprise the F1 catalytic domain, the F0 proton pore, and two stalks, oneof which is thought to act as a stator to link and hold F1 to F0, and the other as a rotor.Genetic studies using yeast Saccharomyces cerevisiae have suggested the hypothesis thatthe yeast mitochondrial ATP synthase can be assembled in the absence of 1, and even 2, ofthe polypeptides that are thought to comprise the rotor. However, the enzyme complexassembled in the absence of the rotor is thought to be uncoupled, allowing protons to freelyflow through F0 into the mitochondrial matrix. Left uncontrolled, this is a lethal process andthe cell must eliminate this leak if it is to survive. In yeast, the cell is thought to lose ordelete its mitochondrial DNA (the petite mutation) thereby eliminating the genes encodingessential components of F0. Recent biochemical studies in yeast, and prior studies in E. coli,have provided support for the assembly of a partial ATP synthase in which the ATP synthaseis no longer coupled to proton translocation. 相似文献
953.
《Bioscience, biotechnology, and biochemistry》2013,77(5):1095-1103
Isocitrate lyase (ICL) and malate synthase (MS) of a psychrophilic marine bacterium, Colwellia maris, were purified to electrophoretically homogeneous state. The molecular mass of the ICL was found to be 240 kDa, composed of four identical subunits of 64.7 kDa. MS was a dimeric enzyme composed of 76.3 kDa subunits. N-Terminal amino acid sequences of the ICL and MS were analyzed. Purified ICL had its maximum activity at 20°C and was rapidly inactivated at the temperatures above 30°C, but the optimum temperature for the activity of MS was 45°C. NaCl was found to protect ICL from heat inactivation above 30°C, but the salt did not stabilize MS. Effects of temperatures on the kinetic parameters of both the enzymes were examined. The Km for the substrate (isocitrate) of ICL was decreased with decreasing temperature. On the other hand, the Km for the substrate (glyoxylate) of MS was increased with decreasing temperature. The calculated value of free energy of activation of ICL was on the same level as that of MS. 相似文献
954.
Abstract A genomic DNA sequence of Streptomyces strain ISP 5485 was cloned, sequenced and compared with corresponding information from nucleic acid data banks. The DNA sequence was unique, but showed homology to DNA coding for the condensing enzyme, 2-oxoacyl synthase, of the deoxyerythronolide B synthase complex (DEBS) from Saccharopolyspora erythraea NRRL 2338. A subfragment of the sequenced DNA was used to construct a gene-specific probe that formed part of the putative 2-oxoacyl synthase gene. The PCR-amplified and labelled probe was used in hybridization experiments involving 33 streptomycete strains that produced different classes of antibiotics. The probe showed widespread homology with DNA considered to be part of analogous genes within genomes of different polyketide producers. The implications of the probe homology to bacterial chromosomal DNA are discussed. 相似文献
955.
Abstract Amino acid sequence alignment of the Cephalosporium acremonium isopenicillin N synthase (cIPNS) to similar non-heme Fe2+ -containing enzymes from 28 different sources (bacterial, fungal, plant and animals) revealed a homologous region of high sequence conservation containing an invariant histidine residue at position 272 in cIPNS. The importance of this histidine residue in cIPNS was investigated through site-directed mutagenesis by replacing the histidine residue with leucine. The mutated gene was verified by DNA sequence analysis and expressed in Escherichia coli . When analyzed by denaturing gel electrophoresis and immunoblotting, the mutant cIPNS had identical mobility as that of the wild-type enzyme. Enzyme studies on the mutant enzyme showed loss of enzymatic activity indicating that His272 is essential for the catalytic function of cIPNS, possibly as a ligand for iron binding. 相似文献
956.
957.
958.
Xiaoping Tang Melodi Demiray Thomas Wirth Rudolf K. Allemann 《Bioorganic & medicinal chemistry》2018,26(7):1314-1319
Artemisinin is one of the most potent anti-malaria drugs and many often-lengthy routes have been developed for its synthesis. Amorphadiene synthase, a key enzyme in the biosynthetic pathway of artemisinin, is able to convert an oxygenated farnesyl diphosphate analogue directly to dihydroartemisinic aldehyde, which can be converted to artemisinin in only four chemical steps, resulting in an efficient synthetic route to the anti-malaria drug. 相似文献
959.
Daniel Maynard Sara Mareike Müller Monika Hahmeier Jana Löwe Ivo Feussner Harald Gröger Andrea Viehhauser Karl-Josef Dietz 《Bioorganic & medicinal chemistry》2018,26(7):1356-1364
Oxidation products of the poly-unsaturated fatty acids (PUFAs) arachidonic acid, α-linolenic acid and docosahexaenoic acid are bioactive in plants and animals as shown for the cyclopentenones prostaglandin 15d-PGJ2 and PGA2, cis-(+)-12-oxophytodienoic acid (12-OPDA), and 14-A-4 neuroprostane. In this study an inexpensive and simple enzymatic multi-step one-pot synthesis is presented for 12-OPDA, which is derived from α-linolenic acid, and the analogous docosahexaenoic acid (DHA)-derived cyclopentenone [(4Z,7Z,10Z)-12-[[-(1S,5S)-4-oxo-5-(2Z)-pent-2-en-1yl]-cyclopent-2-en-1yl] dodeca-4,7,10-trienoic acid, OCPD]. The three enzymes utilized in this multi-step cascade were crude soybean lipoxygenase or a recombinant lipoxygenase, allene oxide synthase and allene oxide cyclase from Arabidopsis thaliana. The DHA-derived 12-OPDA analog OCPD is predicted to have medicinal potential and signaling properties in planta. With OCPD in hand, it is shown that this compound interacts with chloroplast cyclophilin 20-3 and can be metabolized by 12-oxophytodienoic acid reductase (OPR3) which is an enzyme relevant for substrate bioactivity modulation in planta. 相似文献
960.