全文获取类型
收费全文 | 1618篇 |
免费 | 40篇 |
国内免费 | 25篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 25篇 |
2018年 | 31篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 13篇 |
2014年 | 59篇 |
2013年 | 78篇 |
2012年 | 32篇 |
2011年 | 77篇 |
2010年 | 39篇 |
2009年 | 61篇 |
2008年 | 41篇 |
2007年 | 54篇 |
2006年 | 59篇 |
2005年 | 53篇 |
2004年 | 46篇 |
2003年 | 46篇 |
2002年 | 51篇 |
2001年 | 31篇 |
2000年 | 21篇 |
1999年 | 26篇 |
1998年 | 43篇 |
1997年 | 50篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 39篇 |
1993年 | 34篇 |
1992年 | 34篇 |
1991年 | 37篇 |
1990年 | 45篇 |
1989年 | 32篇 |
1988年 | 44篇 |
1987年 | 25篇 |
1986年 | 43篇 |
1985年 | 39篇 |
1984年 | 54篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有1683条查询结果,搜索用时 15 毫秒
1.
Summary
Azotobacter chroococcum Fos 189 is a Tn1-induced mutant which, unlike the parent strain MCD1, does not fix nitrogen in air when provided with glucose or pyruvate as sole carbon sources. Fos 189 showed 5% of parental activity for phosphoenolpyruvate carboxylase though PEP synthetase activity was normal. The A. chroococcum phosphoenolpyruvate carboxylase (ppc) gene was isolated after complementation of an appropriate Escherichia coli mutant using a broad host range gene bank prepared from A. chroococcum genomic DNA. The gene was localised by transposon mutagenesis and subcloning on a minimum DNA fragment of 6.6 kb. Broad host range plasmids containing the A. chroococcum ppc gene complemented the mutation in Fos 189 thereby restoring aerotolerant nitrogen fixation. 相似文献
2.
Christian Paech John Pierce Stephen D. McCurry N.E. Tolbert 《Biochemical and biophysical research communications》1978,83(3):1084-1092
Xylulose-1,5-bisphosphate in preparations of ribulose-1,5-bisphosphate (ribulose-P2) arises from non-enzymic epimerization and inhibits the enzyme. Another inhibitor, a diketo degradation product from ribulose-P2, is also present. Both compounds simulate the substrate inhibition of ribulose-P2 carboxylase/oxygenase previously reported for ribulose-P2. Freshly prepared ribulose-P2 had little inhibitory activity. The instability of ribulose-P2 may be one reason for a high level of ribulose-P2 carboxylase in chloroplasts where the molarity of active sites exceeds that of ribulose-P2. Because the KD of the enzyme/substrate complex is ≤1 μM, all ribulose-P2 generated in situ may be stored as this complex to prevent decomposition. 相似文献
3.
Pyruvate carboxylase has been found in the mitochondrial fraction of two strains of Aspergillus niger along with the marker enzymes of citrate synthase and cytochrome c oxidase. The location of pyruvate carboxylase in A. nidulans was, however, confirmed to be in the cytosolic fraction. The enzyme from the former sources was dependent upon the presence of acetyl-CoA for full activity; the enzyme from A. nidulans was unaffected by the presence or absence of acetyl-CoA. 相似文献
4.
Michael E. Salvucci Archie R. Portis Jr. William L. Ogren 《Photosynthesis research》1985,7(2):193-201
Ribulosebisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rubisco) must be fully activated in order to catalyze the maximum rates of photosynthesis observed in plants. Activation of the isolated enzyme occurs spontaneously, but conditions required to observe full activation are inconsistent with those known to occur in illuminated chloroplasts. Genetic studies with a nutant of Arabidopsis
thaliana incapable of activating rubisco linked two chloroplast polypeptides to the activation process in vivo. Using a reconstituted light activation system, it was possible to demonstrate the participation of a chloroplast protein in rubisco activation. These results indicate that a specific chloroplast enzyme, rubisco activase, catalyzes the activation of rubisco in vivo. 相似文献
5.
Carbonic anhydrase (CA) activity in wheat leaves changed upon leaf dehydration: it decreased at mild stress (relative water
content, RWC, 81 %), but increased at severe water stress (RWC 74 %). Phosphoenopyruvate carboxylase activity was not significantly
affected by these stresses.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
John Pierce 《Physiologia plantarum》1988,72(3):690-698
Pierce, J. 1988. Prospects for manipulating the substrate specificity of ribulose bisphosphate carboxylase/oxygenase. - Physiol. Plant. 72: 690–698.
The idea of enhancing plant productivity by minimizing the apparently wasteful process of photorespiration has been an enduring one. Since the relative fluxes of carbon through the competing pathways of photosynthesis and photorespiration are determined by the kinetic properties of a single enzyme, ribulose bisphosphate carboxylase/oxygenase, it has been conjectured that genetic modification of this protein could provide more productive plants. Recent advances in techniques for studying ribulose bisphosphate carboxylase/oxygenase hold promise for determining whether such modifications will prove possible. 相似文献
The idea of enhancing plant productivity by minimizing the apparently wasteful process of photorespiration has been an enduring one. Since the relative fluxes of carbon through the competing pathways of photosynthesis and photorespiration are determined by the kinetic properties of a single enzyme, ribulose bisphosphate carboxylase/oxygenase, it has been conjectured that genetic modification of this protein could provide more productive plants. Recent advances in techniques for studying ribulose bisphosphate carboxylase/oxygenase hold promise for determining whether such modifications will prove possible. 相似文献
7.
The lateral lipid distribution within dipalmitoylphosphatidylethanolamine (DPPE)/dipalmitoylphosphatidylserine (DPPS) vesicle membranes was investigated under the influence of Ca2+ using a lipid cross-linking method. To characterize the phase transition in DPPE/DPPS vesicles and to correlate the different phase states of the membrane lipids with the obtained lipid distribution ESR measurements using a fatty acid spin label were carried out. It is shown that Ca2+ has a significant influence on the lateral lipid distribution within the fluid phase of the membrane lipids; instead of a slight alternating lipid arrangement in absence of Ca2+ due to the electrostatic interaction between the DPPS headgroups after addition of Ca2+ a lateral cluster structure is characteristic of the fluid phase. 相似文献
8.
9.
Daniel J. Burkett Brittney N. Wyatt Mallory Mews Anson Bautista Ryan Engel Chris Dockendorff William A. Donaldson Martin St. Maurice 《Bioorganic & medicinal chemistry》2019,27(18):4041-4047
Through a structure-based drug design project (SBDD), potent small molecule inhibitors of pyruvate carboxylase (PC) have been discovered. A series of α-keto acids (7) and α-hydroxycinnamic acids (8) were prepared and evaluated for inhibition of PC in two assays. The two most potent inhibitors were 3,3′-(1,4-phenylene)bis[2-hydroxy-2-propenoic acid] (8u) and 2-hydroxy-3-(quinoline-2-yl)propenoic acid (8v) with IC50 values of 3.0 ± 1.0 μM and 4.3 ± 1.5 μM respectively. Compound 8v is a competitive inhibitor with respect to pyruvate (Ki = 0.74 μM) and a mixed-type inhibitor with respect to ATP, indicating that it targets the unique carboxyltransferase (CT) domain of PC. Furthermore, compound 8v does not significantly inhibit human carbonic anhydrase II, matrix metalloproteinase-2, malate dehydrogenase or lactate dehydrogenase. 相似文献
10.
Prerana Gogoi Prerana Mordina Shankar Prasad Kanaujia 《Journal of structural biology》2019,205(1):67-77
5-Methylthioribose 1-phosphate isomerase (M1Pi) is a crucial enzyme involved in the universally conserved methionine salvage pathway (MSP) where it is known to catalyze the conversion of 5-methylthioribose 1-phosphate (MTR-1-P) to 5-methylthioribulose 1-phosphate (MTRu-1-P) via a mechanism which remains unspecified till date. Furthermore, although M1Pi has a discrete function, it surprisingly shares high structural similarity with two functionally non-related proteins such as ribose-1,5-bisphosphate isomerase (R15Pi) and the regulatory subunits of eukaryotic translation initiation factor 2B (eIF2B). To identify the distinct structural features that lead to divergent functional obligations of M1Pi as well as to understand the mechanism of enzyme catalysis, the crystal structure of M1Pi from a hyperthermophilic archaeon Pyrococcus horikoshii OT3 was determined. A meticulous structural investigation of the dimeric M1Pi revealed the presence of an N-terminal extension and a hydrophobic patch absent in R15Pi and the regulatory α-subunit of eIF2B. Furthermore, unlike R15Pi in which a kink formation is observed in one of the helices, the domain movement of M1Pi is distinguished by a forward shift in a loop covering the active-site pocket. All these structural attributes contribute towards a hydrophobic microenvironment in the vicinity of the active site of the enzyme making it favorable for the reaction mechanism to commence. Thus, a hydrophobic active-site microenvironment in addition to the availability of optimal amino-acid residues surrounding the catalytic residues in M1Pi led us to propose its probable reaction mechanism via a cis-phosphoenolate intermediate formation. 相似文献