全文获取类型
收费全文 | 12389篇 |
免费 | 1253篇 |
国内免费 | 1545篇 |
出版年
2024年 | 38篇 |
2023年 | 188篇 |
2022年 | 459篇 |
2021年 | 729篇 |
2020年 | 541篇 |
2019年 | 640篇 |
2018年 | 554篇 |
2017年 | 433篇 |
2016年 | 577篇 |
2015年 | 886篇 |
2014年 | 1002篇 |
2013年 | 946篇 |
2012年 | 1169篇 |
2011年 | 1000篇 |
2010年 | 669篇 |
2009年 | 590篇 |
2008年 | 578篇 |
2007年 | 534篇 |
2006年 | 472篇 |
2005年 | 404篇 |
2004年 | 376篇 |
2003年 | 335篇 |
2002年 | 326篇 |
2001年 | 188篇 |
2000年 | 158篇 |
1999年 | 135篇 |
1998年 | 86篇 |
1997年 | 97篇 |
1996年 | 77篇 |
1995年 | 80篇 |
1994年 | 75篇 |
1993年 | 67篇 |
1992年 | 98篇 |
1991年 | 65篇 |
1990年 | 72篇 |
1989年 | 80篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 38篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 27篇 |
1979年 | 20篇 |
1977年 | 15篇 |
1972年 | 14篇 |
1971年 | 15篇 |
1970年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Fourier analysis was performed on the ground reaction force patterns during gait in 26 normals and 10 patients with knee joint disease prior to total knee replacement. A method was developed to determine the essential number of harmonics for each force component, based on data sampling rate and the level of accuracy required in reconstructing the original patterns. The criteria used to select the level of accuracy depend upon the type of analysis to be performed. Only the first two to four harmonics, plus the constant term, were found to be the dominating coefficients in describing each of the reaction force patterns, and they are subsequently used as the key parameters in differentiating normals and patients with knee joint disease. The advantages of this method and its implication to objective gait analysis in biomechanics are discussed. 相似文献
972.
Based on the results of phenotypic features, phylogenetic similarity of 16S rRNA gene sequences and BIOLOG test, a soil bacterium
was identified as Bacillus sp. DM-1. Using either growing cells or a cell-free extract, it transformed parathion and methyl parathion to amino derivatives
by reducing the nitro group. Pesticide transformation by a cell-free extract was specifically inhibited by three nitroreductase
inhibitors, indicating the presence of nitroreductase activity. The nitroreductase activity was NAD(P)H-dependent, O2-insensitive, and exhibited the substrate specificity for parathion and methyl parathion. Reductive transformation significantly
decreased the toxicity of pesticides. 相似文献
973.
Pseudomonas stutzeri SDM oxidized dl-lactic acid (25.5 g l-1) into pyruvic acid (22.6 g l-1) over 24 h. Both NAD+-independent d-lactate dehydrogenase and NAD+-independent l-lactate dehydrogenase were found for the first time in the bioconversion of lactate to pyruvate based on the enzyme activity
assay and proteomic analysis.
Jianrong Hao and Cuiqing Ma contributed equally to this work 相似文献
974.
High production of laccase by a new basidiomycete, <Emphasis Type="Italic">Trametes</Emphasis> sp 总被引:1,自引:0,他引:1
A new basidiomycete, Trametes sp. 420, produced laccase at 6,810 U l−1 (268 mg, 25.4 U mg−1 protein for guaiacol) in glucose medium and 7,870 U l−1 (310 mg) in cellobiose medium with induction by 0.5 mM Cu2+ and 6 mM o-toluidine. Laccase isozyme E (LacE) was the sole laccase in the fermentation products. It was stable at pH 5–9 and below
70°C over 30 min. The K
m values of LacE for four substrates (guaiacol ABTS, 2,6-dimethoxyphenol and syringaldazine) varied from 5 to 245 μM. The activity
of LacE was strongly inhibited by NaN3 but not by EDTA or dimethylsulfoxide. LacE at 0.5 U l−1 could decolorize industrial dyes. The open reading frame of the lacE gene was 2,130 bp and was interrupted by 10 introns. It displayed a high homology to laccases from other fungi.
Pingui Tong and Yuzhi Hong contributed equally to the study 相似文献
975.
Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+). 相似文献
976.
Tissue kallikrein infusion prevents cardiomyocyte apoptosis, inflammation and ventricular remodeling after myocardial infarction 总被引:4,自引:0,他引:4
We investigated the effect of tissue kallikrein infusion on cardiac protection at acute and sub-acute phases after myocardial infarction (MI). Immediately after MI, rats were infused with purified tissue kallikrein, with or without icatibant (a kinin B2 receptor antagonist). Intramyocardial injection of kallikrein reduced myocardial infarct size and inhibited cardiomyocyte apoptosis at 1 day after MI associated with increased nitric oxide levels, Akt and glycogen synthase kinase-3beta phosphorylation and decreased caspase-3 activation. Kallikrein infusion for 7 days improved cardiac function, normalized left ventricular wall thickness and decreased monocyte/macrophage infiltration in the infarct heart. Kallikrein treatment reduced NADH oxidase expression and activity, superoxide formation and malondialdehyde levels, and reduced MAPK and Ikappa-Balpha phosphorylation, NF-kappaB activation and MCP-1 and VCAM-1 expression. Kallikrein's effects were all blocked by icatibant. These results indicate that kallikrein through kinin B2 receptor activation prevents apoptosis, inflammation and ventricular remodeling by increased nitric oxide formation and suppression of oxidative stress-mediated signaling pathways. 相似文献
977.
Yang F Liu C Gao F Su M Wu X Zheng L Hong F Yang P 《Biological trace element research》2007,119(1):77-88
The improvement of spinach growth is proved to relate to N2 fixation by nano-anatase TiO2 in this study. The results show that all spinach leaves kept green by nano-anatase TiO2 treatment and all old leaves of control turned yellow white under culture with N-deficient solution. And the fresh weight,
dry weight, and contents of total nitrogen, , chlorophyll, and protein of spinach by nano-anatase TiO2 treatment presented obvious enhancement compared with control. Whereas the improvements of yield of spinach were not as good
as nano-anatase TiO2 treatment under N-deficient condition, confirming that nano-anatase TiO2 on exposure to sunlight could chemisorb N2 directly or reduce N2 to NH3 in the spinach leaves, transforming into organic nitrogen and improving the growth of spinach. Bulk TiO2 effect, however, was not as significant as nano-anatase TiO2. A possible metabolism of the function of nano-anatase TiO2 reducing N2 to NH3 was discussed. 相似文献
978.
Promoters play key roles in conferring temporal, spatial, chemical, developmental, or environmental regulation of gene expression.
Promoters that are subject to specific regulations are useful for manipulating foreign gene expression in plant cells, tissues,
or organs with desirable patterns and under controlled conditions, and have been important for both basic research and applications
in agriculture biotechnology. Recent advances in genomics technologies have greatly facilitated identification and study of
promoters in a genome scale with high efficiency. Previously we have generated a large T-DNA tagged rice mutant library (TRIM),
in which the T-DNA was designed with a gene/promoter trap system, by placing a promoter-less GUS gene next to the right border of T-DNA. GUS activity screens of this library offer in situ and in planta identifications
and analyses of promoter activities in their native configurations in the rice genome. In the present study, we systematically
performed GUS activity screens of the rice mutant library for genes/promoters constitutively, differentially, or specifically
active in vegetative and reproductive tissues. More than 8,200 lines have been screened, and 11% and 22% of them displayed
GUS staining in vegetative tissues and in flowers, respectively. Among the vegetative tissue active promoters, the ratio of
leaf active versus root active is about 1.6. Interestingly, all the flower active promoters are anther active, but with varied
activities in different flower tissues. To identify tissue specific ABA/stress up-regulated promoters, we compared microarray
data of ABA/stress induced genes with those of tissue-specific expression determined by promoter trap GUS staining. Following
this approach, we showed that the peroxidase 1 gene promoter was ABA up-regulated by 4 fold within 1 day of exposure to ABA and its expression is lateral root specific.
We suggest that this be an easy bioinformatics approach in identifying tissue/cell type specific promoters that are up-regulated
by hormones or other factors.
Su-May Yu and Swee-Suak Ko equally contributed to this work. 相似文献
979.
Detection of hepatitis B e antigen (HBeAg) in the sera of individuals infected with hepatitis B virus (HBV) can indicate both a high infectivity of the disease and a poor prognosis of disease treatment. Most of monoclonal antibodies raised against HBV e proteins interact with immuno-dominant epitopes, such as HBeAg-beta. In order to raise antibodies against non-dominant epitopes of HBV e protein, in this study, mice were immunized with both recombinant HBeAg (rHBeAg) and an anti-HBeAg antibody (EWB) recognizing a dominant antigenic epitope of HBeAg (HBeAg-beta epitope). With this strategy, we successfully selected two monoclonal antibodies, S-29-3 and S-72-3. Both S-29-3 and S-72-3 bind to recombinant HBeAg with a high affinity. The epitope mapping assay determined that the S-73-2 recognizes the N-terminal of HBeAg (1-118 aa) and the S-29-3 recognizes the C-terminal of HBeAg (91-149 aa). Further experiment showed that these two antibodies could be formed a pair-Abs that is used in detecting native HBeAg from the sera of HBV patients. The conclusion is that the developed method is useful to raise mAb against non-dominant epitopes in given Ag. 相似文献
980.
POL32 encodes a non-essential subunit of Polδ and plays a role in Polδ processivity and DNA repair. In order to understand how Pol32 is involved in these processes, we performed extensive genetic analysis and demonstrated that POL32 is required for Polζ-mediated translesion synthesis, but not for Polη-mediated activity. Unlike Polζ, inactivation of Pol32 does not result in decreased spontaneous mutagenesis, nor does it limit genome instability in the absence of the error-free postreplication repair pathway. In contrast, inactivation of Pol32 results in an increased rate of replication slippage and recombination. A genome-wide synthetic lethal screen revealed that in the absence of Pol32, homologous recombination repair and cell cycle checkpoints play crucial roles in maintaining cell survival and growth. These results are consistent with a model in which Pol32 functions as a coupling factor to facilitate a switch from replication to translesion synthesis when Polδ encounters replication-blocking lesions. When Pol32 is absent, the S-phase checkpoint complex Mrc1–Tof1 becomes crucial to stabilize the stalled replication fork and recruit Top3 and Sgs1. Lack of any of the above activities will cause double strand breaks at or near the replication fork that require recombination as well as Rad9 for cell survival. 相似文献