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   83331篇
  免费   659篇
  国内免费   136篇
化学   44475篇
晶体学   1274篇
力学   3386篇
综合类   2篇
数学   8610篇
物理学   26379篇
  2021年   898篇
  2020年   1018篇
  2019年   1153篇
  2018年   1639篇
  2017年   1709篇
  2016年   2223篇
  2015年   1093篇
  2014年   1794篇
  2013年   3400篇
  2012年   3057篇
  2011年   3473篇
  2010年   2775篇
  2009年   2725篇
  2008年   3160篇
  2007年   3083篇
  2006年   2967篇
  2005年   2608篇
  2004年   2393篇
  2003年   2218篇
  2002年   2265篇
  2001年   2370篇
  2000年   1740篇
  1999年   1351篇
  1998年   1199篇
  1997年   1111篇
  1996年   1001篇
  1995年   940篇
  1994年   928篇
  1993年   916篇
  1992年   994篇
  1991年   1019篇
  1990年   948篇
  1989年   966篇
  1988年   891篇
  1987年   854篇
  1986年   811篇
  1985年   948篇
  1984年   1026篇
  1983年   880篇
  1982年   924篇
  1981年   820篇
  1980年   769篇
  1979年   833篇
  1978年   964篇
  1977年   978篇
  1976年   861篇
  1975年   831篇
  1974年   856篇
  1973年   844篇
  1972年   599篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
A simple algebraic approach to calculate general Franck-Condon overlaps is extended to evaluate non-Condon factors for two one-dimensional harmonic oscillators. The method is based on the use of eigenstates of the harmonic oscillator annihilation operator which allows to obtain in terms of a multi-dimensional Hermite polynomial the overlap of harmonic oscillator functions associated with different Born-Oppenheimer potentials. The presented approach is self-contained, only basic concepts of quantum mechanics associated with the harmonic oscillator system are needed. The obtained expression for the Franck-Condon overlaps is similar to the Ansbacher’s formula and equivalent to the one calculated by Malkin and Man’ko. However our final expression has the advantages that only real numbers are involved and it is straightforward to get the limit case of equal frequencies. Concerning the non-Condon factors two approaches leading to different formulas are considered, both of which reduce to triple sums of products of three Hermite polynomials.  相似文献   
152.
153.
Ohne ZusammenfassungDiese Untersuchung ist vor mehr als Jahresfrist infolge Eintrittes in die chemische Praxis abgebrochen worden. Äussere Verhältnisse machen die Vollendung der begonnenen Versuche auch weiterhin unmöglich und sehe ich mich desshalb veranlasst, meine Beobachtungen zu veröffentlichen.  相似文献   
154.
Nuclear clustering in N = Z nuclei has been studied for many decades. Of particular relevance are states close to the decay thresholds, as described by the Ikeda diagram. Recent interest has focused on loosely bound systems as observed with exotic nuclei. Extreme deformations are simultaneously observed. In the deformed shell model these are referred to as super- and hyper-deformation. Another feature related to clustering is the development of octupole deformations. A possible approach to describe these states is to use explicitly molecular concepts, with neutrons in covalent binding orbits. Examples for molecular structure in beryllium isotopes and in other neutron-rich light nuclei (carbon and neon) are now well established. The predicted chain states in the carbon isotopes are the first example of structures with an axis ratio of 3:1. A threshold diagram for molecular configurations in nuclei with clusters and covalent neutrons can be established.  相似文献   
155.
156.
157.
Complexes of scandium, yttrium, and lanthanum nitrates with 3-chloro-9-hydroxy-2,4-dimethylpyrido[1,2-a]pyrimidinium perchlorate (HL1ClO4) and 9-hydroxy-2,4-dimethylpyrido[1,2-a]pyrimidinium perchlorate (HL2ClO4) were obtained. Their composition was formulated as Sc(LClO4)2(NO3) and M(LClO4)2(NO3)2 (L = L1 or L2; M = Y or La); structures for the complexes obtained were proposed. The crystal and molecular structure of HL1ClO4 was determined. Dissociation and complexation of HL1ClO4 and HL2ClO4 in aqueous ethanol were studied using the spectroscopic method. Ligand dissociation and complexation constants were calculated. It was shown that a chlorine-containing organic ligand only slightly changes the composition and stability of the metal complexes.  相似文献   
158.
An upper bound for the best approximation of summable functions of several variables by trigonometric polynomials in the metric of L is determined in terms of Fourier coefficients. We consider functions representable by trigonometric series with certain symmetry of coefficients satisfying a multiple analog of the Sidon–Telyakovskii conditions.  相似文献   
159.
A new method was developed for studying voids and channels in crystal structures based on the Voronoi-Dirichlet partition of crystal space, and 822 structurally characterized ternary compounds Li p X q O r were analyzed for the first time. For these compounds, the dimensionality was determined and the migration patterns of channel systems capable of providing lithium-ion transport were constructed. The calculated coordinates of lithium atoms in the centers of the voids are consistent (within 0.4 ?) with the known structural data. Among these compounds, 113 compounds have infinite channel systems, 60 compounds (18 structural types, STs) have been described earlier in the literature as solid electrolytes, and 53 compounds (23 STs) can be considered as potential one-, two-, or three-dimensional ionic conductors (13, 3, and 7 STs, respectively). Original Russian Text ? N.A. Anurova, V.A. Blatov, G.D. Ilyushin, O.A. Blatova, A.K. Ivanov-Shitz, L.N. Dem’yanets, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 987–993.  相似文献   
160.
We propose a dislocation model of a nanotwin, which is used to calculate the stress fields in the nanotwin. We consider the role of these stresses in the process of interdislocation interaction and nanotwin growth.  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