全文获取类型
收费全文 | 4462篇 |
免费 | 174篇 |
国内免费 | 2篇 |
专业分类
化学 | 2658篇 |
晶体学 | 8篇 |
力学 | 125篇 |
数学 | 660篇 |
物理学 | 1187篇 |
出版年
2023年 | 32篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 66篇 |
2019年 | 52篇 |
2018年 | 52篇 |
2017年 | 41篇 |
2016年 | 112篇 |
2015年 | 89篇 |
2014年 | 121篇 |
2013年 | 211篇 |
2012年 | 276篇 |
2011年 | 293篇 |
2010年 | 135篇 |
2009年 | 124篇 |
2008年 | 263篇 |
2007年 | 264篇 |
2006年 | 274篇 |
2005年 | 262篇 |
2004年 | 194篇 |
2003年 | 170篇 |
2002年 | 160篇 |
2001年 | 115篇 |
2000年 | 78篇 |
1999年 | 53篇 |
1998年 | 29篇 |
1997年 | 52篇 |
1996年 | 35篇 |
1995年 | 46篇 |
1994年 | 29篇 |
1993年 | 33篇 |
1992年 | 34篇 |
1991年 | 25篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 35篇 |
1985年 | 44篇 |
1984年 | 53篇 |
1983年 | 44篇 |
1982年 | 66篇 |
1981年 | 55篇 |
1980年 | 48篇 |
1979年 | 50篇 |
1978年 | 50篇 |
1977年 | 49篇 |
1976年 | 38篇 |
1975年 | 35篇 |
1974年 | 43篇 |
1973年 | 42篇 |
排序方式: 共有4638条查询结果,搜索用时 31 毫秒
1.
2.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
3.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
4.
5.
It is proved that biorthogonal polynomials obey two different kinds of Christoffel-Darboux-type formulae, one linking polynomials with a different parameter and one combining polynomials with different degrees. This is used to produce a mixed recurrence relation, which is valid for all biorthogonal polynomials. This recurrence relation establishes several results on interlacing property of zeros of successive biorthogonal polynomials and leads to a new result on the interlace of zeros of orthogonal polynomials (of equal degrees) with respect to two distributionsdψ(x) andx p dψ(x), 0<p≤1, with support in either [0, 1] or [1, ∞). 相似文献
6.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
7.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献
8.
The graph-theoretic operation of rooted subtree prune and regraft is increasingly being used as a tool for understanding and modelling reticulation events in evolutionary biology. In this paper, we show that computing the rooted subtree prune and regraft distance between two rooted binary phylogenetic trees on the same label set is NP-hard. This resolves a longstanding open problem. Furthermore, we show that this distance is fixed parameter tractable when parameterised by the distance between the two trees.Received March 16, 2004 相似文献
9.
Emiliana Damian Lars Eriksson Magnus Sandstrm 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):m419-m420
Sodium trichloromethanesulfonate monohydrate, Na+·CCl3SO3−·H2O, crystallizes in P21/a with all the atoms located in general positions. The trichloromethanesulfonate (trichlate) anion consists of pyramidal SO3 and CCl3 groups connected via an S—C bond in a staggered conformation with approximate C3v symmetry. The water molecule is hydrogen bonded to the sulfonate O atoms, with one water H atom forming weak bifurcated O—H⋯O hydrogen bonds to two different trichlate ions. Two water O atoms and three O atoms from different SO3 groups form a square‐pyramidal arrangement around the sodium ion. 相似文献
10.
In this work, the melting-point depression and molecular dynamics of hexamethyldisilane confined within five controlled pore
glasses, with mean diameters ranging from 7.9 to 23.9 nm, are studied by high-field (9.4 T) nuclear magnetic resonance (NMR),
and the results are discussed with reference to the bulk substance. The melting-point depression in pores with radiusR follows the simplified Gibbs-Thompson equation ΔT=k
p/(R−s) with ak
p value of 74 K · nm and ans value of 1 nm. To our knowledge, this is the first time thek
p value of hexamethyldisilane is reported. Proton spin-lattice relaxation times (T
1), spin-spin relaxation times (T
2), and diffusivities (D) are reported as a function of temperature. The confinement in the pores gives rise to substantial changes in the molecular
dynamics and the phase behavior. The line-shape measurements reveal a two-phase system assigned to a relatively mobile component
at the pore walls and a crystalline solid at the center of the pores. However, theT
2 measurements show that the mobile phase also embraces a minor component attributed to nonfrozen liquid in pockets or micropores.
The diffusivity of the major narrow-line component is approximately three orders of magnitude larger than that in the plastic
bulk phase, reflecting fast diffusion of mobile molecules. Below the melting region,T
1 of the narrow line is significantly shorter thanT
1 of the broad line, suggesting that the molecular reorientation is more hindered close to the surface than at the center of
the pore. 相似文献