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   29888篇
  免费   711篇
  国内免费   118篇
化学   17537篇
晶体学   177篇
力学   894篇
综合类   9篇
数学   4071篇
物理学   8029篇
  2023年   145篇
  2022年   308篇
  2021年   587篇
  2020年   491篇
  2019年   452篇
  2018年   494篇
  2017年   440篇
  2016年   820篇
  2015年   667篇
  2014年   799篇
  2013年   1307篇
  2012年   1615篇
  2011年   1842篇
  2010年   1051篇
  2009年   1030篇
  2008年   1594篇
  2007年   1508篇
  2006年   1351篇
  2005年   1763篇
  2004年   1723篇
  2003年   1233篇
  2002年   859篇
  2001年   665篇
  2000年   602篇
  1999年   390篇
  1998年   323篇
  1997年   330篇
  1996年   400篇
  1995年   330篇
  1994年   337篇
  1993年   355篇
  1992年   340篇
  1991年   286篇
  1990年   228篇
  1989年   221篇
  1988年   195篇
  1987年   187篇
  1986年   182篇
  1985年   238篇
  1984年   227篇
  1983年   191篇
  1982年   201篇
  1981年   193篇
  1980年   181篇
  1979年   158篇
  1978年   178篇
  1977年   144篇
  1976年   144篇
  1974年   136篇
  1973年   125篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Annals of Global Analysis and Geometry - In this paper, we characterize round spheres in the Euclidean space under some suitable conditions on the r-mean curvature.  相似文献   
2.
CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45–55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo.  相似文献   
3.
4.
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.  相似文献   
5.
6.
7.
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...  相似文献   
8.
9.
10.
Raman chemical imaging provides chemical and spatial information about pharmaceutical drug product. By using resolution methods on acquired spectra, the objective is to calculate pure spectra and distribution maps of image compounds. With multivariate curve resolution-alternating least squares, constraints are used to improve the performance of the resolution and to decrease the ambiguity linked to the final solution. Non negativity and spatial local rank constraints have been identified as the most powerful constraints to be used.  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