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   3644篇
  免费   504篇
  国内免费   246篇
化学   891篇
晶体学   57篇
力学   452篇
综合类   71篇
数学   1309篇
物理学   1614篇
  2024年   5篇
  2023年   22篇
  2022年   59篇
  2021年   68篇
  2020年   101篇
  2019年   89篇
  2018年   101篇
  2017年   90篇
  2016年   135篇
  2015年   87篇
  2014年   200篇
  2013年   233篇
  2012年   185篇
  2011年   237篇
  2010年   196篇
  2009年   218篇
  2008年   220篇
  2007年   242篇
  2006年   213篇
  2005年   206篇
  2004年   162篇
  2003年   160篇
  2002年   157篇
  2001年   121篇
  2000年   112篇
  1999年   87篇
  1998年   81篇
  1997年   65篇
  1996年   79篇
  1995年   37篇
  1994年   51篇
  1993年   42篇
  1992年   30篇
  1991年   33篇
  1990年   33篇
  1989年   24篇
  1988年   30篇
  1987年   21篇
  1986年   19篇
  1985年   19篇
  1984年   24篇
  1983年   7篇
  1982年   16篇
  1981年   19篇
  1980年   5篇
  1979年   8篇
  1978年   5篇
  1977年   12篇
  1976年   7篇
  1973年   7篇
排序方式: 共有4394条查询结果,搜索用时 15 毫秒
991.
应用群论及原子分子反应静力学方法推导了SiO2分子的电子态及其离解极限,采用B3P86方法,在6-311G**水平上,优化出SiO2基态分子稳定构型为单重态的C2V构型,其平衡核间距Re=RSi—O=0.1587 nm,∠OSiO=111.2°,能量为-440.4392 a.u..同时计算出基态的简正振动频率:对称伸缩振动频率ν(B2)=945.4cm-1,弯曲振动频率ν(A1)=273.5 cm-1和反对称伸缩振动频率ν(A1)=1362.9cm-1.在此基础上,使用多体项展式理论方法,导出了基态SiO2分子的全空间解析势能函数,该势能函数准确再现了SiO2(C2V)平衡结构.  相似文献   
992.
 本文列出了一维点阵非谐振动的非线性微分方程组,并求出了这组方程在相应边值条件下的解析解。据此算出了该点阵的热膨胀系数和热膨胀动态过程的特征时间,同时说明了它的物理意义。关于金属箔的实验结果,可以作为这一理论预言的一个验证。这些结果还告诉我们,在高速加热时,即使温度均匀而且膨胀自由,热应力仍然存在,不过将很快弛豫。  相似文献   
993.
In this article,the authors study the exact traveling wave solutions of modified Zakharov equations for plasmas with a quantum correction by hyperbolic tangent function expansion method,hyperbolic seca...  相似文献   
994.
本文中,我们引进了由$(s,t)$-微分算子和拟从属定义的一类广义双单叶函数类. 对该新函数类及其子类,利用Faber多项式展开式我们得到了前两项系数$|a_2|$, $|a_3|$和一般项系数$|a_n|~(n\geq 4)$的估计,然后也解决了Fekete-Szeg\"{o}问题.  相似文献   
995.
Efficient algorithms for Koblitz curves over fields of characteristic three   总被引:1,自引:0,他引:1  
The nonadjacent form method of Koblitz [Advances in Cryptology (CRYPTO'98), in: Lecture Notes in Comput. Sci., vol. 1462, 1998, pp. 327–337] is an efficient algorithm for point multiplication on a family of supersingular curves over a finite field of characteristic 3. In this paper, a further discussion of the method is given. A window nonadjacent form method is proposed and its validity is proved. Efficient reduction and pre-computations are given. Analysis shows that more than 30% of saving can be achieved.  相似文献   
996.
Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458  相似文献   
997.
Effective elastic moduli for 3D solid–solid phononic crystals of arbitrary anisotropy and oblique lattice structure are formulated analytically using the plane-wave expansion (PWE) method and the recently proposed monodromy-matrix (MM) method. The latter approach employs Fourier series in two dimensions with direct numerical integration along the third direction. As a result, the MM method converges much quicker to the exact moduli in comparison with the PWE as the number of Fourier coefficients increases. The MM method yields a more explicit formula than previous results, enabling a closed-form upper bound on the effective Christoffel tensor. The MM approach significantly improves the efficiency and accuracy of evaluating effective wave speeds for high-contrast composites and for configurations of closely spaced inclusions, as demonstrated by three-dimensional examples.  相似文献   
998.
《合成通讯》2013,43(24):4339-4345
Abstract

1,3-Thiazin-4-ones 9 and 10 have been prepared from the corresponding isothiazolones 7 and 8 by a clean and smooth reaction with tertiary amines at room temperature. This rearrangement is attributed to the abstraction of a methine proton from the 2-position isothiazolone substituent, followed by ring enlargement through cleavage of the S-N bond.  相似文献   
999.
In this study, experimental results are concerning “the optical bistability due to thermal lensing effect”, in colloidal solution of gold nanoparticles (Au Nps) which has been studied under CW laser illuminations. Two different CW laser beams (He–Ne and Nd-Yag) were used to interact with a vertical Fabry–Perot interferometer, containing colloid of the Au Nps. Hysteretic loops have been observed with regard to optical bistability and the results were fitted with theoretical curves. The radiated power to the resonator was elevated up to 50 mW for both the laser beams with the same spot size. Also, new method was defined to precise evaluation of the theoretical hysteretic loop which is describing the relation between nonlinear refractive index and the beam intensity inside the resonator. This dependency is due to thermal lensing effect and numerical simulations of this effect were also performed, in order to better understanding of it.  相似文献   
1000.
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