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   531327篇
  免费   8116篇
  国内免费   2617篇
化学   287124篇
晶体学   7745篇
力学   23170篇
综合类   74篇
数学   65830篇
物理学   158117篇
  2021年   3706篇
  2020年   4251篇
  2019年   4505篇
  2018年   5375篇
  2017年   5068篇
  2016年   8670篇
  2015年   6537篇
  2014年   9172篇
  2013年   24478篇
  2012年   19625篇
  2011年   23652篇
  2010年   15616篇
  2009年   15165篇
  2008年   21468篇
  2007年   21655篇
  2006年   20544篇
  2005年   18678篇
  2004年   16848篇
  2003年   14738篇
  2002年   14372篇
  2001年   15363篇
  2000年   11843篇
  1999年   9484篇
  1998年   7763篇
  1997年   7608篇
  1996年   7589篇
  1995年   6808篇
  1994年   6593篇
  1993年   6516篇
  1992年   7010篇
  1991年   6961篇
  1990年   6508篇
  1989年   6296篇
  1988年   6610篇
  1987年   6185篇
  1986年   5874篇
  1985年   8365篇
  1984年   8539篇
  1983年   7000篇
  1982年   7455篇
  1981年   7400篇
  1980年   7074篇
  1979年   7344篇
  1978年   7409篇
  1977年   7331篇
  1976年   7358篇
  1975年   6994篇
  1974年   6940篇
  1973年   7096篇
  1972年   4519篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
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   
82.
83.
Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups...  相似文献   
84.
85.
86.
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   
87.
88.
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   
89.
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   
90.
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