全文获取类型
收费全文 | 1541篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
化学 | 1040篇 |
晶体学 | 21篇 |
力学 | 36篇 |
数学 | 311篇 |
物理学 | 176篇 |
出版年
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 41篇 |
2020年 | 34篇 |
2019年 | 31篇 |
2018年 | 20篇 |
2017年 | 11篇 |
2016年 | 58篇 |
2015年 | 39篇 |
2014年 | 38篇 |
2013年 | 71篇 |
2012年 | 89篇 |
2011年 | 86篇 |
2010年 | 63篇 |
2009年 | 53篇 |
2008年 | 96篇 |
2007年 | 88篇 |
2006年 | 83篇 |
2005年 | 82篇 |
2004年 | 70篇 |
2003年 | 44篇 |
2002年 | 58篇 |
2001年 | 16篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1891年 | 2篇 |
排序方式: 共有1584条查询结果,搜索用时 15 毫秒
1.
Methylcyanide, CH3CN, is an important interstellar species, and therefore the accurate knowledge of precise rest frequencies for rotational transitions as well as ground-state rotational and hyperfine constants is needed. In this work the hyperfine structure of the millimeter- and submillimeter-wave spectra of CH3CN has been further investigated. In addition, accurate THz measurements have been carried out for the first time. Consequently, the present investigation allowed us to provide the most accurate ground state rotational and hyperfine parameters known at the moment for CH3C14N. To resolve the hyperfine structure of the rotational transitions observed, the Lamb-dip technique has been exploited. Both frequency-modulated and video-type detections have been employed. 相似文献
2.
The essential self-adjointness on a natural domain of the sharp-time Wick powers of the relativistic free field in two space-time dimension is proven. Other results on Wick powers are reviewed and discussed. 相似文献
3.
Gabriele Bonanno 《Journal of Global Optimization》1998,12(1):101-104
In this note we introduce a suitable class of functionals, including the class of integral functionals, and prove that any (strict) local minimum of a functional of this class, defined on a decomposable space, is a (strict) global minimum. So, the recent result obtained by Giner in [1] is specified and extended. 相似文献
4.
5.
Stephan Dahlke Gabriele Steidl Gerd Teschke 《Journal of Fourier Analysis and Applications》2004,10(5):507-539
This article is concerned with frame constructions on domains and manifolds. The
starting point is a unitary group representation which is square integrable modulo a suitable
subgroup and therefore gives rise to a generalized continuous wavelet transform. Then generalized
coorbit spaces can be defined by collecting all functions for which this wavelet transform
is contained in a weighted Lp-space. Moreover, we show that a judicious discretization of the
representation leads to an atomic decomposition and to Banach frames for these coorbit spaces. 相似文献
6.
7.
8.
Let L be an odd unimodular lattice of dimension n with shadow n−16. If min(L)?3 then dim(L)?46 and there is a unique such lattice in dimension 46 and no lattices in dimensions 44 and 45. To prove this, a shadow theory for theta series with spherical coefficients is developed. 相似文献
9.
The 29th PME research forum on theories included only one European perspective on mathematics education. In order to convey trends in theory usage in Europe we compile, survey and analyze a large subset of the research papers from the 4th European Congress on Mathematics Education (CERME4). That is, this paper includes a discussion of trends seen within CERME4 reports1 on theory usage by European researchers inseven of the fourteen working groups and (a) Outlines similarities and differences in theory usage and (b) takes a futuristic stance on ways in which researchers from different traditions could understand each other. Such an enterprise would further Hans-Georg Steiner's vision of bridging theoretical traditions which are independently formulated in different regions of the world. 相似文献
10.
Würthwein EU Lang G Schappele LH Mayr H 《Journal of the American Chemical Society》2002,124(15):4084-4092
A literature survey on the kinetics of hydride abstractions from CH-groups by carbocations reveals a general phenomenon: Variation of the hydride acceptor affects the rates of hydride transfer to a considerably greater extent than an equal change of the thermodynamic driving force caused by variation of the hydride donor. The origin of this relationship was investigated by quantum chemical calculations on various levels of ab initio and DFT theory for the transfer of an allylic hydrogen from 1-mono- and 1,1-disubstituted propenes (XYC=CH-CH(3)) to the 3-position of 1-mono- and 1,1-disubstituted allyl cations (XYC=CH-CH(2)(+)). The discussion is based on the results of the MP2/6-31+G(d,p)//RHF/6-31+G(d,p) calculations. Electron-releasing substituents X and Y in the hydride donors increase the exothermicity of the reaction, while electron-releasing substituents in the hydride acceptors decrease exothermicity. In line with Hammond's postulate, increasing exothermicity shifts the transition states on the reaction coordinate toward reactants, as revealed by the geometry parameters and the charge distribution in the activated complexes. Independent of the location of the transition state on the reaction coordinate, a value of 0.72 is found for Hammond-Leffler's alpha = deltaDeltaG/deltaDelta(r)G degrees when the hydride acceptor is varied, while alpha = 0.28 when the hydride donor is varied. The value of alpha thus cannot be related with the position of the transition state. Investigation of the degenerate reactions XYC=CH-CH(3) + XYC=CH-CH(2)(+) indicates that the migrating hydrogen carries a partial positive charge in the transition state and that the intrinsic barriers increase with increasing electron-releasing abilities of X and Y. Substituent variation in the donor thus influences reaction enthalpy and intrinsic barriers in the opposite sense, while substituent variation in the acceptor affects both terms in the same sense, in accord with the experimental findings. Marcus theory is employed to treat these effects quantitatively. 相似文献