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   260533篇
  免费   2956篇
  国内免费   800篇
化学   141719篇
晶体学   3878篇
力学   11099篇
综合类   12篇
数学   26701篇
物理学   80880篇
  2018年   2033篇
  2017年   1945篇
  2016年   3594篇
  2015年   2418篇
  2014年   3583篇
  2013年   10609篇
  2012年   7846篇
  2011年   10039篇
  2010年   6669篇
  2009年   6483篇
  2008年   9092篇
  2007年   9199篇
  2006年   8894篇
  2005年   8398篇
  2004年   7402篇
  2003年   6618篇
  2002年   6553篇
  2001年   7326篇
  2000年   5614篇
  1999年   4509篇
  1998年   3926篇
  1997年   3822篇
  1996年   3585篇
  1995年   3461篇
  1994年   3257篇
  1993年   3086篇
  1992年   3552篇
  1991年   3607篇
  1990年   3363篇
  1989年   3368篇
  1988年   3318篇
  1987年   3226篇
  1986年   3075篇
  1985年   4095篇
  1984年   4304篇
  1983年   3557篇
  1982年   4005篇
  1981年   3728篇
  1980年   3730篇
  1979年   3840篇
  1978年   4095篇
  1977年   3914篇
  1976年   3979篇
  1975年   3812篇
  1974年   3737篇
  1973年   3944篇
  1972年   2489篇
  1971年   2065篇
  1968年   2030篇
  1967年   2087篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
52.
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field.  相似文献   
53.
Echabaane  M.  Hfaiedh  S.  Smiri  B.  Saidi  F.  Dridi  C. 《Journal of Solid State Electrochemistry》2021,25(6):1797-1806
Journal of Solid State Electrochemistry - The fast and sensitive detection of copper ions would be essential for water monitoring. Herein, we report a novel development of an impedimetric sensor...  相似文献   
54.
Journal of Thermal Analysis and Calorimetry - Novel porous carbon sheets were developed as green, renewable, cost-effective, and efficient flame retardant material for thermoplastic polymers....  相似文献   
55.
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided.  相似文献   
56.
Journal of Thermal Analysis and Calorimetry - The paper focuses on the analytical analysis of the propagation of a normal shock wave in an adiabatic gas flow with nanoparticles. A modified...  相似文献   
57.
Journal of Dynamics and Differential Equations - We deal with a weakly coupled system of ODEs of the type $$\begin{aligned} x_j'' + n_j^2 \,x_j + h_j(x_1,\ldots ,x_d) = p_j(t), \qquad...  相似文献   
58.
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded.  相似文献   
59.
Russian Journal of Organic Chemistry - Selenopheno[2,3-d]pyrimidine- and selenopheno[2,3-d][1,2,3]triazine-containing compounds were synthesized starting from...  相似文献   
60.
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