全文获取类型
收费全文 | 686篇 |
免费 | 36篇 |
国内免费 | 47篇 |
专业分类
769篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 26篇 |
2021年 | 45篇 |
2020年 | 26篇 |
2019年 | 37篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 36篇 |
2015年 | 27篇 |
2014年 | 53篇 |
2013年 | 62篇 |
2012年 | 71篇 |
2011年 | 52篇 |
2010年 | 36篇 |
2009年 | 30篇 |
2008年 | 31篇 |
2007年 | 21篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有769条查询结果,搜索用时 0 毫秒
51.
52.
53.
Qiulin Wu Lixia Gou Shuangjun Lin Jingdan Liang Jun Yin Xiufen Zhou Linquan Bai Derong An Zixin Deng Zhijun Wang 《Biochimie》2013
Calcimycin is a rare divalent cation specific ionophore antibiotic that has many biochemical and pharmaceutical applications. We have recently cloned and sequenced the Streptomyces chartreusis calcimycin biosynthesis gene cluster as well as identified the genes required for the synthesis of the polyketide backbone of calcimycin. Additional modifying or decorating enzymes are required to convert the polyketide backbone into the biologically active calcimycin. Using targeted mutagenesis of Streptomyces we were able to show that calM from the calcimycin biosynthesis gene cluster is required for calcimycin production. Inactivating calM by PCR targeting, caused high level accumulation of N-demethyl calcimycin. CalM in the presence of S-adenosyl-L-methionine converted N-demethyl calcimycin to calcimycin in vitro. The enzyme was determined to have a kinetic parameter of Km 276 μM, kcat 1.26 min−1 and kcat/Km 76.2 M−1 s−1. These results proved that CalM is a N-methyltransferase that is required for calcimycin biosynthesis, and they set the stage for generating much desired novel calcimycin derivatives by rational genetic and chemical engineering. 相似文献
54.
Protection of xenogeneic cells from human complement-mediated lysis by the expression of human DAF, CD59 and MCP 总被引:7,自引:0,他引:7
Jian Huang Deming Gou Congyi Zhen Dahe Jiang Xin Mao Wenxin Li Shi Chen Changchun Cai 《FEMS immunology and medical microbiology》2001,31(3):203-209
CD59 and membrane cofactor protein (MCP, CD46) are widely expressed cell surface glycoproteins that protect host cells from the effect of homologous complement attack. cDNAs encoding human CD59 and MCP cloned from Chinese human embryo were separately transfected into NIH/3T3 cells resulting in the expression of human CD59 and MCP protein on the cell surface. The functional properties of expressed proteins were studied. When the transfected cells were exposed to human serum as a source of complement and naturally occurring anti-mouse antibody, they were resistant to human complement-mediated cell killing. However, the cells remained sensitive to rabbit and guinea pig complement. Human CD59 and MCP can only protect NIH/3T3 cells from human complement-mediated lysis. These results demonstrated that complement inhibitory activity of these proteins is species-selective. The cDNAs of CD59 and MCP were also separately transfected into the endothelial cells (ECs) of the pigs transgenic for the human DAF gene to investigate a putative synergistic action. The ECs expressing both DAF and MCP proteins or both DAF and CD59 proteins exhibited more protection against cytolysis by human serum compared to the cells with only DAF expressed alone. 相似文献
55.
56.
Background
Accurate measurement of peripheral tissue perfusion is challenging but necessary to diagnose peripheral vascular insufficiency. Because near infrared (NIR) radiation can penetrate relatively deep into tissue, significant attention has been given to intravital NIR fluorescence imaging.Methodology/Principal Findings
We developed a new optical imaging-based strategy for quantitative measurement of peripheral tissue perfusion by time-series analysis of local pharmacokinetics of the NIR fluorophore, indocyanine green (ICG). Time-series NIR fluorescence images were obtained after injecting ICG intravenously in a murine hindlimb ischemia model. Mathematical modeling and computational simulations were used for translating time-series ICG images into quantitative pixel perfusion rates and a perfusion map. We could successfully predict the prognosis of ischemic hindlimbs based on the perfusion profiles obtained immediately after surgery, which were dependent on the preexisting collaterals. This method also reflected increases in perfusion and improvements in prognosis of ischemic hindlimbs induced by treatment with vascular endothelial growth factor and COMP-angiopoietin-1.Conclusions/Significance
We propose that this novel NIR-imaging-based strategy is a powerful tool for biomedical studies related to the evaluation of therapeutic interventions directed at stimulating angiogenesis. 相似文献57.
Investigation of bathymetry and water quality of Lake Nam Co, the largest lake on the central Tibetan Plateau, China 总被引:3,自引:0,他引:3
Junbo Wang Liping Zhu Gerhard Daut Jianting Ju Xiao Lin Yong Wang Xiaolin Zhen 《Limnology》2009,10(2):149-158
Comprehensive field investigations have been conducted four times on Nam Co, central Tibet, from September 2005 to September
2008. Here, we present the preliminary results focusing on the bathymetric survey and water quality measurements. The isobathic
map shows that Nam Co is a high-altitude, deep lake where a flat and large basin lies in the central part with a water depth
of more than 90 m. Water depth data from the northwestern bank areas of Nam Co provide unquestionable evidence of rising water
levels in the last 3 decades because of the formation of two small islands that were still peninsulas in the 1970s. Water
quality measurements taken at 19 stations during three summer field campaigns (2006, 2007 and 2008) covering almost all of
the lake areas showed that the temperature, pH, dissolved oxygen and electric conductivity of surface water are on average
11.43°C, 9.21, 8.90 mg l−1 and 1,851 μS cm−1, respectively. The surface water shows no obvious spatial variability among all the stations. Vertical fluctuations of profiles,
however, display some differences in thermocline and related parameters, such as pH and dissolved oxygen. According to the
vertical variations of water quality parameters, the water column in relatively deep lake areas of Nam Co could be divided
into three layers with distinctly various features: the epilimnion is from the surface to about 18–20 m depth in which the
parameters are homogeneous with higher temperature and abundant sunlight; the metalimnion ranged from 20–60 m where a thermocline
develops; the deepest layer forms a cold and dark hypolimnion. 相似文献
58.
Ai-Xia Cheng Jin-Ying Gou Xiao-Hong Yu Huijun Yang Xin Fang Xiao-Ya Chen Chang-Jun Liu 《植物生理学报》2013,(6):1889-1903
Cutinized and suberized cell walls in plants constitute physiologically important environment interfaces. They act as barriers limiting the loss of water and nutrients and protecting against radiation and invasion of pathogens. The roles of cutin- and suberin polyesters are often attributed to their dominant aliphatic components, but the contri- bution of aromatic composition to their physiological function remains unclear. By functionally screening a subset of Populus trichocarpa BAHD/HXXXD acyltransferases, we identified a hydroxycinnamoyltransferase that shows specific transacylation activity on ~0-hydroxyacids using both feruloyl- and p-coumaroyl- CoA as the acyl donors. We named this enzyme P. trichocarpa hydroxyacid/fatty alcohol hydroxycinnamoyltransferase 1 (PtFHT1). The ectopic expression of the PtFHT1 gene in Arabidopsis increased the incorporation of ferulate in root and seed suberins and in leaf cutin, but not that of p-coumarate, while the aliphatic load in both suberin and cutin polyesters essentially remained unaffected. The overaccumulation of ferulate in lipophilic polyester significantly increased the tolerance of transgenic plants to salt stress treatment; under sub-lethal conditions of salt stress, the ratios of their seed germination and seedling establishment were 50% higher than those of wild-type plants. Our study suggests that, although aromatics are the minor component of polyesters, they play important role in the sealing function of lipidic polymers in planta. 相似文献
59.
60.