全文获取类型
收费全文 | 7435篇 |
免费 | 974篇 |
国内免费 | 1篇 |
专业分类
8410篇 |
出版年
2021年 | 94篇 |
2019年 | 65篇 |
2018年 | 80篇 |
2017年 | 75篇 |
2016年 | 110篇 |
2015年 | 184篇 |
2014年 | 200篇 |
2013年 | 270篇 |
2012年 | 321篇 |
2011年 | 323篇 |
2010年 | 234篇 |
2009年 | 181篇 |
2008年 | 314篇 |
2007年 | 265篇 |
2006年 | 274篇 |
2005年 | 224篇 |
2004年 | 251篇 |
2003年 | 250篇 |
2002年 | 220篇 |
2001年 | 219篇 |
2000年 | 207篇 |
1999年 | 177篇 |
1998年 | 121篇 |
1997年 | 103篇 |
1996年 | 102篇 |
1995年 | 98篇 |
1994年 | 91篇 |
1993年 | 88篇 |
1992年 | 142篇 |
1991年 | 182篇 |
1990年 | 196篇 |
1989年 | 139篇 |
1988年 | 148篇 |
1987年 | 152篇 |
1986年 | 144篇 |
1985年 | 133篇 |
1984年 | 117篇 |
1983年 | 104篇 |
1982年 | 95篇 |
1981年 | 100篇 |
1980年 | 100篇 |
1979年 | 111篇 |
1978年 | 101篇 |
1977年 | 84篇 |
1976年 | 72篇 |
1975年 | 69篇 |
1974年 | 95篇 |
1973年 | 95篇 |
1972年 | 83篇 |
1971年 | 79篇 |
排序方式: 共有8410条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
Jeffrey M. Boyd Daniel D. Clark Melissa A. Kofoed Scott A. Ensign 《The Journal of biological chemistry》2010,285(33):25232-25242
The bacterial metabolism of epoxypropane formed from propylene oxidation uses the atypical cofactor coenzyme M (CoM, 2-mercaptoethanesulfonate) as the nucleophile for epoxide ring opening and as a carrier of intermediates that undergo dehydrogenation, reductive cleavage, and carboxylation to form acetoacetate in a three-step metabolic pathway. 2-Ketopropyl-CoM carboxylase/oxidoreductase (2-KPCC), the terminal enzyme of this pathway, is the only known member of the disulfide oxidoreductase family of enzymes that is a carboxylase. In the present work, the CoM analog 2-bromoethanesulfonate (BES) is shown to be a reversible inhibitor of 2-KPCC and hydroxypropyl-CoM dehydrogenase but not of epoxyalkane:CoM transferase. Further investigations revealed that BES is a time-dependent inactivator of dithiothreitol-reduced 2-KPCC, where the redox active cysteines are in the free thiol forms. BES did not inactivate air-oxidized 2-KPCC, where the redox active cysteine pair is in the disulfide form. The inactivation of 2-KPCC exhibited saturation kinetics, and CoM slowed the rate of inactivation. Mass spectral analysis demonstrated that BES inactivation of reduced 2-KPCC occurs with covalent modification of the interchange thiol (Cys82) by a group with a molecular mass identical to that of ethylsulfonate. The flavin thiol Cys87 was not alkylated by BES under reducing conditions, and no amino acid residues were modified by BES in the oxidized enzyme. The UV-visible spectrum of BES-modifed 2-KPCC showed the characteristic charge transfer absorbance expected with alkylation at Cys82. These results identify BES as a reactive CoM analog that specifically alkylates the interchange thiol that facilitates thioether bond cleavage and enolacetone formation during catalysis. 相似文献
995.
Michael B. Albro Roland Li Rajan E. Banerjee Clark T. Hung Gerard A. Ateshian 《Journal of biomechanics》2010,43(12):2267-2273
Solute transport in biological tissues is a fundamental process necessary for cell metabolism. In connective soft tissues, such as articular cartilage, cells are embedded within a dense extracellular matrix that hinders the transport of solutes. However, according to a recent theoretical study (Mauck et al., 2003, J. Biomech. Eng. 125, 602–614), the convective motion of a dynamically loaded porous solid matrix can also impart momentum to solutes, pumping them into the tissue and giving rise to concentrations which exceed those achived under passive diffusion alone. In this study, the theoretical predictions of this model are verified against experimental measurements. The mechanical and transport properties of an agarose–dextran model system were characterized from independent measurements and substituted into the theory to predict solute uptake or desorption under dynamic mechanical loading for various agarose concentrations and dextran molecular weights, as well as different boundary and initial conditions. In every tested case, agreement was observed between experiments and theoretical predictions as assessed by coefficients of determination ranging from R2=0.61 to 0.95. These results provide strong support for the hypothesis that dynamic loading of a deformable porous tissue can produce active transport of solutes via a pumping mechanisms mediated by momentum exchange between the solute and solid matrix. 相似文献
996.
Tatjana Barisic‐Dujmovic Ivana Boban Stephen H. Clark 《Journal of cellular physiology》2010,222(3):703-712
Dermal fibroblasts/myofibroblasts involved in the wound healing are thought to originate from the resident fibroblast progenitors. To test the hypothesis of an extra dermal origin of the dermal fibroblasts/myofibroblasts, bone marrow (BM) transplantation and parabiosis experiments were initiated utilizing a collagen promoter green fluorescent protein (GFP) reporter transgene as a visible marker for dermal fibroblasts/myofibroblasts. BM transplantation experiments using BM from Col3.6GFPsapph transgenic mice showed no evidence that BM derived progenitors differentiated into dermal fibroblasts/myofibroblasts at the wound site. Rather the GFP positive cells (GFP+) observed at the wound site were not dermal fibroblasts/myofibroblasts but immune cells. These GFP+ cells were also detected in the lung and spleen. Furthermore, GFP+ fibroblasts were not detected in primary dermal fibroblast cultures initiated from BM chimeras. Using the same transgenic mice, parabiotic pairs were generated. One partner in the parabiosis carried a GFP expressing transgene while the other partner was a non‐transgenic C57BL/6 mouse. Similar to the BM transplantation experiments, GFP+ immune cells were detected in the wound of the non‐transgenic parabiont, however, GFP expressing dermal fibroblasts/myofibroblasts were not observed. Collectively, these data suggest that dermal fibroblast/myofibroblast progenitors do not readily circulate. The expression of the Col3.6GFPsapph in the hematopoietic cells confirmed that our methods were sensitive enough to detect Col3.6GFP expressing dermal fibroblasts derived from the peripheral circulation if they had originated in the BM. J. Cell. Physiol. 222: 703–712, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
997.
Tiago G. Fernandes Seok‐Joon Kwon Shyam Sundhar Bale Moo‐Yeal Lee Maria Margarida Diogo Douglas S. Clark Joaquim M.S. Cabral Jonathan S. Dordick 《Biotechnology and bioengineering》2010,106(1):106-118
We have developed a novel three‐dimensional (3D) cellular microarray platform to enable the rapid and efficient tracking of stem cell fate and quantification of specific stem cell markers. This platform consists of a miniaturized 3D cell culture array on a functionalized glass slide for spatially addressable high‐throughput screening. A microarray spotter was used to deposit cells onto a modified glass surface to yield an array consisting of cells encapsulated in alginate gel spots with volumes as low as 60 nL. A method based on an immunofluorescence technique scaled down to function on a cellular microarray was also used to quantify specific cell marker protein levels in situ. Our results revealed that this platform is suitable for studying the expansion of mouse embryonic stem (ES) cells as they retain their pluripotent and undifferentiated state. We also examined neural commitment of mouse ES cells on the microarray and observed the generation of neuroectodermal precursor cells characterized by expression of the neural marker Sox‐1, whose levels were also measured in situ using a GFP reporter system. In addition, the high‐throughput capacity of the platform was tested using a dual‐slide system that allowed rapid screening of the effects of tretinoin and fibroblast growth factor‐4 (FGF‐4) on the pluripotency of mouse ES cells. This high‐throughput platform is a powerful new tool for investigating cellular mechanisms involved in stem cell expansion and differentiation and provides the basis for rapid identification of signals and conditions that can be used to direct cellular responses. Biotechnol. Bioeng. 2010; 106: 106–118. © 2010 Wiley Periodicals, Inc. 相似文献
998.
999.
1000.
Kabir AM Clark JE Tanno M Cao X Hothersall JS Dashnyam S Gorog DA Bellahcene M Shattock MJ Marber MS 《American journal of physiology. Heart and circulatory physiology》2006,291(4):H1893-H1899
To examine whether cardioprotection initiated by reactive oxygen species (ROS) is dependent on protein kinase Cepsilon (PKCepsilon), isolated buffer-perfused mouse hearts were randomized to four groups: 1) antimycin A (AA) (0.1 microg/ml) for 3 min followed by 10 min washout and then 30 min global ischemia (I) and 2 h reperfusion (R); 2) controls of I/R alone; 3) AA bracketed with 13 min of N-2-mercaptopropionyl- glycine (MPG) followed by I/R; and 4) MPG (200 microM) alone, followed by I/R. Isolated adult rat ventricular myocytes (ARVM) were exposed to AA (0.1 microg/ml), and lucigenin was used to measure ROS production. Murine hearts and ARVM were exposed to AA (0.1 microg/ml) with or without MPG, and PKCepsilon translocation was measured by cell fractionation and subsequent Western blot analysis. Finally, the dependence of AA protection on PKCepsilon was determined by the use of knockout mice (-/-) lacking PKCepsilon. AA exposure caused ROS production, which was abolished by the mitochondrial uncoupler mesoxalonitrile 4-trifluoromethoxyphenylhydrazone. In addition, AA significantly reduced the percent infarction-left ventricular volume compared with control I/R (26 +/- 4 vs. 43 +/- 2%; P < 0.05). Bracketing AA with MPG caused a loss of protection (52 +/- 7 vs. 26 +/- 4%; P < 0.05). AA caused PKCepsilon translocation only in the absence of MPG, and protection was lost on the pkcepsilon(-/-) background (38 +/- 3 vs. 15 +/- 4%; P < 0.001). AA causes ROS production, on which protection and PKCepsilon translocation depend. In addition, protection is absent in PKCepsilon null hearts. Our results imply that, in common with ischemic preconditioning, PKCepsilon is crucial to ROS-mediated protection. 相似文献