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   339034篇
  免费   4869篇
  国内免费   1222篇
化学   184471篇
晶体学   4594篇
力学   13833篇
综合类   16篇
数学   40679篇
物理学   101532篇
  2021年   2094篇
  2020年   2382篇
  2019年   2296篇
  2018年   2384篇
  2017年   2246篇
  2016年   4492篇
  2015年   3766篇
  2014年   5072篇
  2013年   15015篇
  2012年   11965篇
  2011年   14805篇
  2010年   9099篇
  2009年   9019篇
  2008年   13527篇
  2007年   13769篇
  2006年   13338篇
  2005年   12624篇
  2004年   11525篇
  2003年   9865篇
  2002年   9397篇
  2001年   10629篇
  2000年   8269篇
  1999年   6411篇
  1998年   5150篇
  1997年   5002篇
  1996年   5168篇
  1995年   4729篇
  1994年   4479篇
  1993年   4352篇
  1992年   4794篇
  1991年   4574篇
  1990年   4247篇
  1989年   4052篇
  1988年   4318篇
  1987年   3994篇
  1986年   3865篇
  1985年   5547篇
  1984年   5580篇
  1983年   4541篇
  1982年   4949篇
  1981年   4959篇
  1980年   4707篇
  1979年   4797篇
  1978年   4839篇
  1977年   4770篇
  1976年   4725篇
  1975年   4611篇
  1974年   4486篇
  1973年   4635篇
  1972年   2621篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries.  相似文献   
35.
36.
37.
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   
38.
39.
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   
40.
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237  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