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   19294篇
  免费   1261篇
  国内免费   899篇
化学   14046篇
晶体学   170篇
力学   481篇
综合类   66篇
数学   2998篇
物理学   3693篇
  2024年   12篇
  2023年   179篇
  2022年   345篇
  2021年   574篇
  2020年   534篇
  2019年   510篇
  2018年   455篇
  2017年   434篇
  2016年   838篇
  2015年   750篇
  2014年   825篇
  2013年   1300篇
  2012年   1528篇
  2011年   1724篇
  2010年   1162篇
  2009年   1017篇
  2008年   1420篇
  2007年   1337篇
  2006年   1210篇
  2005年   1020篇
  2004年   903篇
  2003年   616篇
  2002年   512篇
  2001年   244篇
  2000年   234篇
  1999年   194篇
  1998年   147篇
  1997年   145篇
  1996年   149篇
  1995年   110篇
  1994年   90篇
  1993年   90篇
  1992年   102篇
  1991年   72篇
  1990年   63篇
  1989年   46篇
  1988年   33篇
  1987年   44篇
  1986年   39篇
  1985年   57篇
  1984年   59篇
  1983年   31篇
  1982年   33篇
  1981年   35篇
  1980年   34篇
  1979年   23篇
  1978年   28篇
  1977年   27篇
  1974年   14篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
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   
3.
4.
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   
5.
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.  相似文献   
6.
7.
8.
Three key challenges are stimulating intensive research in the development of productive direct electron transfer mode enzyme electrodes: proper enzyme orientation, high enzyme loading, and full retention of enzyme activity. In this review, we summarize some significant advances that have been reported in the last years on the design of mesoporous and nanostructured electrodes as enzyme scaffolds and of innovative methodologies for wiring enzymes to electrodes. Particular attention is given to investigations on physical factors that determine a favorable enzyme immobilization, to provide rational guidelines for the design of productive enzymatic electrodes. Finally, some emerging trends focused on the spatial organization of either single enzymes or enzyme cascades are also briefly addressed.  相似文献   
9.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  相似文献   
10.
Meccanica - Fiber reinforced materials are used in assorted engineering application and for this reason, new additive manufacturing technologies have been developed for this type of materials. With...  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