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   367343篇
  免费   6227篇
  国内免费   1186篇
化学   203650篇
晶体学   4703篇
力学   14792篇
综合类   16篇
数学   45613篇
物理学   105982篇
  2021年   2402篇
  2020年   2768篇
  2019年   2730篇
  2018年   3096篇
  2017年   2834篇
  2016年   5556篇
  2015年   4734篇
  2014年   5959篇
  2013年   16961篇
  2012年   14240篇
  2011年   17016篇
  2010年   10455篇
  2009年   10094篇
  2008年   15434篇
  2007年   15572篇
  2006年   14901篇
  2005年   14178篇
  2004年   12830篇
  2003年   10913篇
  2002年   10300篇
  2001年   10976篇
  2000年   8530篇
  1999年   6640篇
  1998年   5316篇
  1997年   5144篇
  1996年   5373篇
  1995年   4810篇
  1994年   4603篇
  1993年   4448篇
  1992年   4964篇
  1991年   4688篇
  1990年   4381篇
  1989年   4188篇
  1988年   4406篇
  1987年   4085篇
  1986年   3929篇
  1985年   5699篇
  1984年   5754篇
  1983年   4649篇
  1982年   5084篇
  1981年   5099篇
  1980年   4839篇
  1979年   4922篇
  1978年   4957篇
  1977年   4866篇
  1976年   4863篇
  1975年   4731篇
  1974年   4621篇
  1973年   4768篇
  1972年   2680篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
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   
53.
54.
55.
56.
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   
57.
58.
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   
59.
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   
60.
Journal of Thermal Analysis and Calorimetry - Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow...  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