全文获取类型
收费全文 | 16645篇 |
免费 | 1641篇 |
国内免费 | 97篇 |
出版年
2022年 | 194篇 |
2021年 | 248篇 |
2020年 | 137篇 |
2019年 | 193篇 |
2018年 | 229篇 |
2017年 | 196篇 |
2016年 | 382篇 |
2015年 | 662篇 |
2014年 | 684篇 |
2013年 | 870篇 |
2012年 | 1114篇 |
2011年 | 1029篇 |
2010年 | 680篇 |
2009年 | 622篇 |
2008年 | 915篇 |
2007年 | 878篇 |
2006年 | 829篇 |
2005年 | 789篇 |
2004年 | 757篇 |
2003年 | 747篇 |
2002年 | 624篇 |
2001年 | 373篇 |
2000年 | 336篇 |
1999年 | 303篇 |
1998年 | 202篇 |
1997年 | 137篇 |
1996年 | 159篇 |
1995年 | 133篇 |
1994年 | 141篇 |
1993年 | 149篇 |
1992年 | 222篇 |
1991年 | 177篇 |
1990年 | 181篇 |
1989年 | 187篇 |
1988年 | 147篇 |
1987年 | 160篇 |
1986年 | 178篇 |
1985年 | 188篇 |
1984年 | 157篇 |
1983年 | 148篇 |
1982年 | 139篇 |
1981年 | 127篇 |
1980年 | 121篇 |
1979年 | 158篇 |
1978年 | 126篇 |
1977年 | 110篇 |
1976年 | 101篇 |
1975年 | 88篇 |
1974年 | 110篇 |
1973年 | 93篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The genes encoding the six polypeptide components of the alkene monooxygenase from Xanthobacter Py2 have been sequenced. The predicted amino acid sequence of the first ORF shows homology with the iron binding subunits of binuclear non-haem iron containing monooxygenases including benzene monooxygenase, toluene 4-monooxygenase (>60% sequence similarity) and methane monooxygenase (>40% sequence similarity) and that the necessary sequence motifs associated with iron co-ordination are also present. Secondary structure prediction based on the amino acid sequence showed that the predominantly α-helical structure that surrounds the binuclear iron binding site was conserved allowing the sequence to be modelled on the co-ordinates of the methane monooxygenase α-subunit. Significant differences in the residues forming the hydrophobic cavity which forms the substrate binding site are discussed with reference to the differences in reaction specificity and stereospecificity of binuclear non-haem iron monooxygenases. 相似文献
12.
13.
14.
W J Allard C D Cheli D L Morris J Goldblatt Y Pierre L Kish Y Chen J Dai R L Vessella D W Chan M K Schwartz Z Zhou K K Yeung 《The International journal of biological markers》1999,14(2):73-83
We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1 complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1 PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10-day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02 microgram/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71-86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1-100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy. 相似文献
15.
R. M. Davydov Joanne Smieja S. A. Dikanov Y. Zang Lawrence Que Jr. M. K. Bowman 《Journal of biological inorganic chemistry》1999,4(3):292-301
Radiolytic reduction at 77 K of oxo-/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically
stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent
species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent
EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S=1/2 ground state with small g-anisotropy as characterized by the uniaxial component (g
z
–g
av /2<0.03) observable at temperatures as high as ∼100 K. In contrast, hydroxo-bridged mixed-valent species are characterized
by large g-anisotropy (g
z
–g
av /2>0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in
the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished
from each other and can help characterize the structure of mixed-valent centers in proteins.
Received: 27 June 1998 / Accepted: 25 February 1999 相似文献
16.
17.
Lawrence Que Jr. 《Journal of biological inorganic chemistry》2004,9(6):684-690
The oxygen activation mechanisms proposed for nonheme iron systems generally follow the heme paradigm in invoking the involvement of iron-peroxo and iron-oxo species in their catalytic cycles. However, the nonheme ligand environments allow for end-on and side-on dioxygen coordination and impart greater flexibility in the modes of dioxygen activation. The currently available evidence for nonheme iron-peroxo and iron-oxo intermediates is summarized and discussed in light of the ongoing discussion on the nature of the oxidant(s) in heme enzymes. 相似文献
18.
19.
20.
Maurice Chan 《Biochemical and biophysical research communications》2004,326(1):188-196
The important role of pyruvate kinase during malarial infection has prompted the cloning of a cDNA encoding Plasmodium falciparum pyruvate kinase (pfPyrK), using mRNA from intraerythrocytic-stage malaria parasites. The full-length cDNA encodes a protein with a computed molecular weight of 55.6 kDa and an isoelectric point of 7.5. The purified recombinant pfPyrK is enzymatically active and exists as a homotetramer in its active form. The enzyme exhibits hyperbolic kinetics with respect to phosphoenolpyruvate and ADP, with Km of 0.19 and 0.12 mM, respectively. pfPyrK is not affected by fructose-1,6-bisphosphate, a general activating factor of pyruvate kinase for most species. Glucose-6-phosphate, an activator of the Toxoplasma gondii enzyme, does not affect pfPyrK activity. Similar to rabbit pyruvate kinase, pfPyrK is susceptible to inactivation by 1 mM pyridoxal-5′-phosphate, but to a lesser extent. A screen for inhibitors to pfPyrK revealed that it is markedly inhibited by ATP and citrate. Detailed kinetic analysis revealed a transition from hyperbolic to sigmoidal kinetics for PEP in the presence of citrate, as well as competitive inhibitory behavior for ATP with respect to PEP. Citrate exhibits non-competitive inhibition with respect to ADP with a Ki of 0.8 mM. In conclusion, P. falciparum expresses an active pyruvate kinase during the intraerythrocytic-stage of its developmental cycle that may play important metabolic roles during infection. 相似文献