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   1355篇
  免费   81篇
  国内免费   1篇
化学   1003篇
晶体学   2篇
力学   24篇
数学   200篇
物理学   208篇
  2023年   33篇
  2022年   25篇
  2021年   31篇
  2020年   56篇
  2019年   66篇
  2018年   30篇
  2017年   30篇
  2016年   72篇
  2015年   65篇
  2014年   55篇
  2013年   55篇
  2012年   104篇
  2011年   93篇
  2010年   54篇
  2009年   35篇
  2008年   61篇
  2007年   76篇
  2006年   70篇
  2005年   76篇
  2004年   53篇
  2003年   29篇
  2002年   28篇
  2001年   10篇
  2000年   8篇
  1999年   17篇
  1998年   11篇
  1997年   12篇
  1996年   10篇
  1995年   4篇
  1994年   8篇
  1993年   5篇
  1992年   4篇
  1990年   6篇
  1989年   4篇
  1988年   8篇
  1987年   6篇
  1986年   10篇
  1985年   6篇
  1983年   6篇
  1980年   6篇
  1979年   9篇
  1976年   10篇
  1975年   5篇
  1973年   10篇
  1933年   3篇
  1932年   4篇
  1930年   4篇
  1924年   3篇
  1922年   3篇
  1921年   7篇
排序方式: 共有1437条查询结果,搜索用时 31 毫秒
41.
Lithuanian Mathematical Journal - We present upper bounds of the integral $$ {\int}_{-\infty}^{\infty }{\left|x\right|}^l\left|\mathrm{P}\left\{{Z}_N0\left({S}_N{X}_1+\dots +{X}_N\right) $$ of...  相似文献   
42.
Transport in Porous Media - The 4th order Darcy–Bénard eigenvalue problem for the onset of thermal convection in a 3D rectangular porous box is investigated. We start from a recent 2D...  相似文献   
43.
Small molecules are used in the G‐quadruplex (G4) research field in vivo and in vitro, and there are increasing demands for ligands that selectively stabilize different G4 structures. Thioflavin T (ThT) emits an enhanced fluorescence signal when binding to G4 structures. Herein, we show that ThT can be competitively displaced by the binding of small molecules to G4 structures and develop a ThT‐displacement high‐throughput screening assay to find novel and selective G4‐binding compounds. We screened approximately 28 000 compounds by using three different G4 structures and identified eight novel G4 binders. Analysis of the structural conformation and stability of the G4 structures in presence of these compounds demonstrated that the four compounds enhance the thermal stabilization of the structures without affecting their structural conformation. In addition, all four compounds also increased the G4‐structure block of DNA synthesis by Taq DNA polymerase. Also, two of these compounds showed selectivity between certain Schizosaccharomyces pombe G4 structures, thus suggesting that these compounds or their analogues can be used as selective tools for G4 DNA studies.  相似文献   
44.
45.
46.
Abstract

Some new norbornene thioester derivatives of endo configuration are sinthesized. Proofs are provided that thioester group has more preference for endo configuration than the ester group.  相似文献   
47.
We report second harmonic generation in a ferroelectric liquid crystalline trimer and ferroelectric liquid crystalline dendrimers of first, second and third generation. Thin cells were filled with the compounds by capillary forces at elevated temperature, and cooled from the surface stabilized ferroelectric state to below the glass transition temperature, while kept in an electric field. The cone motion viscosity and the threshold electric field for unwinding of the helix axis of the chiral tilted smectic mesophases were studied separately at elevated temperature, and these data were used to optimize the preparation of the films. The measured response time was between 0.3 and 3ms, which corresponds to a cone motion viscosity between 0.5 and 50 Pa s. Second harmonic generation was studied both at elevated temperature with an electric field and at room temperature with and without electric field. The first generation dendrimer exhibited a strong increase in the second order non-linear optical response with time at room temperature. The d 23-coefficient of this dendrimer was approximately four times larger than for the other macromolecules and was 0.045 pm V-1. The relatively large d-coefficient of the first generation dendrimer is ascribed to crystallization, which improved the orientation of the molecular dipoles.  相似文献   
48.
A palladium(II)-catalyzed decarboxylative protocol for the synthesis of aryl ketones has been developed. The addition of TFA was shown to improve the reaction yield and employing THF as solvent enabled the use of solid nitriles and in only a small excess. Using this method, five different benzoic acids reacted with a wide range of nitriles to produce 29 diverse (hetero)aryl ketone derivatives in up to 94% yield.  相似文献   
49.
This review summarizes various approaches for the analysis of low molecular weight (LMW) compounds by different laser desorption/ionization mass spectrometry techniques (LDI-MS). It is common to use an agent to assist the ionization, and small molecules are normally difficult to analyze by, e.g., matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) using the common matrices available today, because the latter are generally small organic compounds themselves. This often results in severe suppression of analyte peaks, or interference of the matrix and analyte signals in the low mass region. However, intrinsic properties of several LDI techniques such as high sensitivity, low sample consumption, high tolerance towards salts and solid particles, and rapid analysis have stimulated scientists to develop methods to circumvent matrix-related issues in the analysis of LMW molecules. Recent developments within this field as well as historical considerations and future prospects are presented in this review.  相似文献   
50.
Enzyme-catalyzed reactions play key roles in disease pathology, thus making them relevant subjects of therapeutic inhibitor screening experiments. Matrix-assisted laser desorption/ionization (MALDI) assays have been demonstrated to be able to replace established screening approaches. They offer increased sample throughput, but care must be taken to avoid instrumental bias from differences in ionization efficiencies. We compared a MALDI-triple-quadrupole (QqQ) method for the Dyrk1A peptide substrate woodtide to LC–MS, liquid chromatography with ultraviolet detection (LC–UV), luminescence, and radiometric assays. MALDI measurements were performed on a MALDI-QqQ instrument in the multiple-reaction monitoring mode. Different MALDI conditions were investigated to address whether matrix type, sample support, and MRM- or SIM-based detection conditions can be used to accommodate the molar responses of substrate peptide and its phosphorylated form. UV detection served as a reference method. The impact of MALDI matrix on IC50 values was small, even considering that matrix preparations were used that are known to alleviate response differences. IC50 values determined by MALDI were ca. 2-fold lower than those determined by LC–UV. Although MALDI generated lower ion yields for the phosphorylated peptide than for the peptide substrate, we found that a correction of compound potencies was readily possible using correction factors based on unbiased LC–UV results. A thorough method development delivered a robust assay with excellent performance (Z′ > 0.91) that was close to that seen for LC–UV.
Figure
?  相似文献   
[首页] « 上一页 [1] [2] [3] [4] 5 [6] [7] [8] [9] [10] [11] 下一页 » 末  页»
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