首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   533篇
  免费   25篇
  国内免费   2篇
化学   430篇
晶体学   4篇
力学   21篇
数学   29篇
物理学   76篇
  2023年   4篇
  2022年   9篇
  2021年   8篇
  2020年   3篇
  2019年   6篇
  2018年   3篇
  2017年   3篇
  2016年   19篇
  2015年   18篇
  2014年   16篇
  2013年   36篇
  2012年   38篇
  2011年   41篇
  2010年   29篇
  2009年   36篇
  2008年   48篇
  2007年   27篇
  2006年   31篇
  2005年   34篇
  2004年   20篇
  2003年   24篇
  2002年   32篇
  2001年   8篇
  2000年   8篇
  1999年   7篇
  1998年   3篇
  1997年   1篇
  1996年   9篇
  1994年   2篇
  1993年   3篇
  1992年   1篇
  1991年   7篇
  1990年   5篇
  1989年   1篇
  1988年   3篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   3篇
  1979年   1篇
  1977年   1篇
  1974年   1篇
  1973年   1篇
  1900年   1篇
排序方式: 共有560条查询结果,搜索用时 31 毫秒
31.
Porous poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) membranes were prepared by solvent–nonsolvent evaporation technique. Morphology and porosity of the membranes were varied with different nonsolvents and had an effect on electrochemical properties. The porous membranes were functionalized with different liquid electrolyte solutions such as p-toluene sulfonic acid/phosphoric acid/sulfuric acid. Maximum electrolyte uptake and minimal electrolyte leakage were tailored by the optimized porosity of the membranes. Thermal behavior obtained in this study ensures the complete evaporation of nonsolvents and ensures its thermal stability. The pTSA-activated PVdF-HFP/THF membrane exhibited high ionic conductivity of about 27.27 mS/cm and a lower methanol permeability in the range of 9.7 × 10−8 cm2/s. High compatibility between pTSA solution and porous PVdF-HFP polymer electrolyte membrane enhances its electro chemical behavior than that of conventional liquid electrolytes.  相似文献   
32.
33.
34.
Chlamydia pneumoniae infection implicated as an important etiologic factor of atherosclerosis, especially in coronary artery disease (CAD), was found in vitro to be associated with the induction of matrix metalloproteinases (MMPs). An extracellular matrix metalloproteinase inducer (EMMPRIN)/ membrane-type 1 matrix metalloproteinase (MT1-MMP) system which induces and activates MMPs, is suggested to be functional and were upregulated in the failing myocardium. However, the upstream regulation of MMPs by C. pneumoniae within atheroma itself remains unclear. We evaluated the seroepidemiologic study of C. pneumoniae infection in CAD patients (n= 391) and controls (n=97) and performed histopathological and in vitro analysis in atherosclerotic vascular tissues obtained from patients with seropositive to C. pneumoniae (n=20), by using immunochemistry for C. pneumoniae, EMMPRIN/MT1-MMP, MMP-2, and MMP-9. The seropositive rates of both anti-C. pneumoniae IgG and IgA were 56.7% in CAD group and 43.3% in control group (P=0.033). Seropositive rate was increased in subgroups of CAD patients without conventional coronary risk factors compared to those with conventional risk factors. Immunoreactivities of EMMPRIN, MT1-MMP, MMP-2, and MMP-9 were increased in the atheromatous plaque itself, predominantly in immunoreactive macrophages/mononuclear cells to C. pneumoniae. Furthermore, Western blot analysis showed that EMMPRIN and MMP-2 were detected more prominently in atherosclerotic tissues infected with C. pneumoniae compared to control tissues. Zymographic analysis revealed that activities of MMP-2 and MMP-9 were more increased in atherosclerotic tissues infected with C. pneumoniae compared to control tissues. The present study demonstrated upstream regulation of MMPs can be induced by C. pneumoniae within atheromatous plaque itself. These findings help to understand the potential role of C. pneumoniae in the progression of atherosclerosis.  相似文献   
35.
36.
37.
Kee TW  Cicerone MT 《Optics letters》2004,29(23):2701-2703
Coherent anti-Stokes Raman scattering (CARS) microscopy is emerging as a powerful method for imaging materials and biological systems, partly because of its noninvasiveness and selective chemical sensitivity. However, its full potential for species-selective imaging is limited by a restricted spectral bandwidth. Recent increases in bandwidth are promising but still are not sufficient for the level of robust component discrimination that would be needed in a chemically complex milieu found, for example, in intracellular and extracellular environments. We demonstrate a truly broadband CARS imaging instrument that we use to acquire hyperspectral images with vibrational spectra over a bandwidth of 2500 cm(-1) with a resolution of 13 cm(-1).  相似文献   
38.
In our previous report, we showed that a rheometer equipped with a double concentric cylinder geometry with slotted rotor could effectively reduce wall slip effects and thus it could be used as an alternative to a rheometer with a vane geometry in yield stress measurements. Here, we use three-dimensional CFD simulation to compare these two geometries for rheological measurements of power law and yield stress fluids. Our results indicate that the double concentric cylinder rheometer with slotted rotor (DCCR/SR) is able to accurately measure rheological properties of a wider spectrum of test fluids than a vane rheometer because of significant reduction of the end and secondary flow effects.  相似文献   
39.
Single‐source organometallic precursors based on a number of homometallic clusters as well as heterometallic cluster RuOs3(CO)13(µ‐H)2 have been used for the chemical vapor deposition of osmium films and osmium–ruthenium alloy films, respectively. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
40.
In the title compound, [Pt(C3H2O4)(C7H16N2O2)], the Pt atom is coordinated to two O and two N atoms in a square‐planar arrangement. The two independent mol­ecules, which have very similar structures, are approximately related by pseudo‐twofold screw‐axis symmetry. The six‐membered chelate ring in the leaving ligand assumes a conformation intermediate between the half‐chair and boat forms. The seven‐membered ring in the carrier ligand assumes a twist‐chair conformation and the oxolane ring assumes an envelope conformation. The crystal packing consists of extensive hydrogen‐bonding networks which form two‐dimensional molecular layers, and there are weak van der Waals interactions between these layers.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号