全文获取类型
收费全文 | 6596篇 |
免费 | 153篇 |
国内免费 | 2篇 |
专业分类
化学 | 3710篇 |
晶体学 | 31篇 |
力学 | 152篇 |
数学 | 1472篇 |
物理学 | 1386篇 |
出版年
2023年 | 36篇 |
2021年 | 69篇 |
2020年 | 61篇 |
2019年 | 70篇 |
2018年 | 153篇 |
2017年 | 140篇 |
2016年 | 226篇 |
2015年 | 168篇 |
2014年 | 223篇 |
2013年 | 522篇 |
2012年 | 343篇 |
2011年 | 456篇 |
2010年 | 241篇 |
2009年 | 210篇 |
2008年 | 367篇 |
2007年 | 372篇 |
2006年 | 340篇 |
2005年 | 269篇 |
2004年 | 234篇 |
2003年 | 165篇 |
2002年 | 154篇 |
2001年 | 105篇 |
2000年 | 86篇 |
1999年 | 68篇 |
1998年 | 54篇 |
1997年 | 58篇 |
1996年 | 60篇 |
1995年 | 50篇 |
1993年 | 47篇 |
1992年 | 56篇 |
1991年 | 47篇 |
1990年 | 48篇 |
1989年 | 51篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 62篇 |
1984年 | 70篇 |
1983年 | 68篇 |
1982年 | 64篇 |
1981年 | 42篇 |
1980年 | 58篇 |
1979年 | 47篇 |
1978年 | 71篇 |
1977年 | 40篇 |
1976年 | 52篇 |
1975年 | 41篇 |
1974年 | 52篇 |
1973年 | 40篇 |
1972年 | 33篇 |
排序方式: 共有6751条查询结果,搜索用时 15 毫秒
951.
Pawlukojć A Natkaniec I Bator G Sobczyk L Grech E Nowicka-Scheibe J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(3):766-773
The results of inelastic neutron scattering (INS), Raman and infrared (IR) studies on 1,2,4,5-tetramethylbenzene (durene), tetramethylpyrazine (TMP) and tetramethyl-1,4-benzoquinone (TMBQ) in the solid state are reported. The observed frequencies are analyzed on the basis of DFT calculations. The low frequency region, below 400 cm(-1), related to the torsional and bending out-of-plane vibrations of the CH(3) groups, is of particular interest. The detailed analysis is possible due to the simulation of the INS spectra by using the auntie-CLIMAX program. It is shown that the observed low frequency INS bands are dramatically shifted, compared to the calculated ones, towards higher frequencies. Although one cannot exclude deficiencies of theoretical methods as applied to low frequency modes, it seems more probable the interpretation based on an existence of non-conventional CH(...)pi, CH(...)N, CH(...)O hydrogen bonds formed by the methyl groups in crystalline phases. 相似文献
952.
Hydride affinities (HAs) of the ethynes substituted by a wide range of different substituents are considered by using the B3LYP methodology. The computed values are in fair agreement with available experimental data, which are unfortunately scarce. The trend of changes of the HAs is rationalized by trichotomy formula. One of the important results of this analysis is a finding that similar HA values might result from completely different effects. Alternative sites of the H- attack are examined and the difference in energies relative to the most susceptible positions is interpreted. Structural features of substituted ethyne hydrides are briefly discussed. 相似文献
953.
A review of results of bioactivity and reactivity examinations of marine sesquiterpene (hydro)quinones is presented. The article is focused mostly on friedo- rearranged drimane structural types, isolated from sponges of the order Dictyoceratida. Examples of structural correlations are outlined. Available results on the mechanism of redox processes and examinations of chemo- and regioselectivity in addition reactions are presented and, where possible, analyzed in relation to established bioactivities. Most of the bioactivity examinations are concerned with antitumor activities and the mechanism thereof, such as DNA damage, arylation of nucleophiles, tubulin assembly inhibition, protein kinase inhibition, inhibition of the arachidonic cascade, etc. Perspectives on marine drug development are discussed with respect to biotechnological methods and synthesis. Examples of the recognition of validated core structures and synthesis of structurally simplified compounds retaining modes of activity are analyzed. 相似文献
954.
Josipa-Pina Milišić 《Journal of Differential Equations》2018,264(9):5629-5658
In this paper we consider a degenerate pseudoparabolic equation for the wetting saturation of an unsaturated two-phase flow in porous media with dynamic capillary pressure-saturation relationship where the relaxation parameter depends on the saturation. Following the approach given in [13] the existence of a weak solution is proved using Galerkin approximation and regularization techniques. A priori estimates needed for passing to the limit when the regularization parameter goes to zero are obtained by using appropriate test-functions, motivated by the fact that considered PDE allows a natural generalization of the classical Kullback entropy. Finally, a special care was given in obtaining an estimate of the mixed-derivative term by combining the information from the capillary pressure with the obtained a priori estimates on the saturation. 相似文献
955.
Thomas Chen Younghun Hong Nataša Pavlović 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2018,35(2):393-416
In this paper, we study the dynamics of a system of infinitely many fermions in dimensions near thermal equilibrium and prove scattering in the case of small perturbation around equilibrium in a certain generalized Sobolev space of density operators. This work is a continuation of our previous paper [11], and extends the important recent result of M. Lewin and J. Sabin in [19] of a similar type for dimension . In the work at hand, we establish new, improved Strichartz estimates that allow us to control the case . 相似文献
956.
Bojan Vučković 《Discrete Mathematics》2018,341(3):820-824
Let be a graph without isolated edges, and let be a coloring of the edges, where adjacent edges may be colored the same. The color code of a vertex is the ordered -tuple , where is the number of edges incident with that are colored . If every two adjacent vertices of have different color codes, such a coloring is called multi-set neighbor distinguishing. In this paper, we prove that three colors are sufficient to produce a multi-set neighbor distinguishing edge coloring for every graph without isolated edges. 相似文献
957.
Suzana Aleksić Zoran D. Mitrović Stojan Radenović 《Periodica Mathematica Hungarica》2018,77(2):224-231
In this paper, we prove the common fixed point theorem of Jungck in \(b_v(s)\)-metric spaces. As a corollary, a common fixed point theorem in the rectangular b-metric space and the well known common fixed point theorem in b-metric spaces are obtained. 相似文献
958.
In this paper we introduce and study the notion of a graded (strongly) nil clean ring which is group graded. We also deal with extensions of graded (strongly) nil clean rings to graded matrix rings and to graded group rings. The question of when nil cleanness of the component, which corresponds to the neutral element of a group, implies graded nil cleanness of the whole graded ring is examined. Similar question is discussed in the case of groupoid graded rings as well. 相似文献
959.
Yuanyuan Ke Dragana S. Cvetković-Ilić Jelena Višnjić 《Linear and Multilinear Algebra》2018,66(3):447-458
In this paper, we present some necessary and sufficient conditions for the existence of the (b, c)-inverse and several representations for the (b, c)-inverse related to the group inverse. Since Mary inverse, core inverse, dual core inverse and Bott–Duffin (e, f)-inverse are all the special cases of the (b, c)-inverse, related results for these inverses are obtained. 相似文献
960.
Dušan Lj. Djukić Aleksandar V. Pejčev Miodrag M. Spalević 《Numerical Algorithms》2018,77(4):1003-1028
We consider the Gauss-Kronrod quadrature formulae for the Bernstein-Szeg? weight functions consisting of any one of the four Chebyshev weights divided by the polynomial \(\rho (t)=1-\frac {4\gamma }{(1+\gamma )^{2}}\,t^{2},\quad t\in (-1,1),\ -1<\gamma \le 0\). For analytic functions, the remainder term of this quadrature formula can be represented as a contour integral with a complex kernel. We study the kernel, on elliptic contours with foci at the points ? 1 and sum of semi-axes ρ > 1, for the given quadrature formula. Starting from the explicit expression of the kernel, we determine the locations on the ellipses where maximum modulus of the kernel is attained. So we derive effective error bounds for this quadrature formula. An alternative approach, which has initiated this research, has been proposed by S. Notaris (Numer. Math. 103, 99–127, 2006). 相似文献