全文获取类型
收费全文 | 20446篇 |
免费 | 649篇 |
国内免费 | 717篇 |
专业分类
化学 | 4088篇 |
晶体学 | 858篇 |
力学 | 473篇 |
综合类 | 70篇 |
数学 | 13704篇 |
物理学 | 2619篇 |
出版年
2023年 | 76篇 |
2022年 | 166篇 |
2021年 | 163篇 |
2020年 | 165篇 |
2019年 | 463篇 |
2018年 | 516篇 |
2017年 | 359篇 |
2016年 | 353篇 |
2015年 | 351篇 |
2014年 | 658篇 |
2013年 | 1115篇 |
2012年 | 655篇 |
2011年 | 1312篇 |
2010年 | 1353篇 |
2009年 | 1550篇 |
2008年 | 1535篇 |
2007年 | 1572篇 |
2006年 | 1255篇 |
2005年 | 975篇 |
2004年 | 894篇 |
2003年 | 710篇 |
2002年 | 592篇 |
2001年 | 465篇 |
2000年 | 404篇 |
1999年 | 396篇 |
1998年 | 346篇 |
1997年 | 301篇 |
1996年 | 408篇 |
1995年 | 357篇 |
1994年 | 356篇 |
1993年 | 329篇 |
1992年 | 254篇 |
1991年 | 151篇 |
1990年 | 135篇 |
1989年 | 131篇 |
1988年 | 84篇 |
1987年 | 95篇 |
1986年 | 102篇 |
1985年 | 138篇 |
1984年 | 92篇 |
1983年 | 63篇 |
1982年 | 81篇 |
1981年 | 71篇 |
1980年 | 52篇 |
1979年 | 28篇 |
1978年 | 41篇 |
1977年 | 50篇 |
1976年 | 42篇 |
1974年 | 18篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《Mendeleev Communications》2022,32(4):537-539
The two novel conglomerates were obtained by crystallization of racemic (2'S,3aS,6aR)/(2'R,3aR,6aS) (glycoluril-1-yl)-3-methylbutanoic acid and (2'R,3aR,6aR)/(2'S,3aS,6aS) (4,6-dimethylglycoluril-1-yl)pentanoic acid synthesized by highly diastereoselective condensation of 4,5-dihydroxy- imidazolidin-2-ones with racemic ureido acids. The differences in the molecular geometry of synthesized racemates were studied by X-ray diffraction that showed them to crystallize as conglomerates in non-centrosymmetric space groups Pna21 and P212121, respectively 相似文献
2.
The growth-fragmentation equation describes a system of growing and dividing particles, and arises in models of cell division, protein polymerisation and even telecommunications protocols. Several important questions about the equation concern the asymptotic behaviour of solutions at large times: at what rate do they converge to zero or infinity, and what does the asymptotic profile of the solutions look like? Does the rescaled solution converge to its asymptotic profile at an exponential speed? These questions have traditionally been studied using analytic techniques such as entropy methods or splitting of operators. In this work, we present a probabilistic approach: we use a Feynman–Kac formula to relate the solution of the growth-fragmentation equation to the semigroup of a Markov process, and characterise the rate of decay or growth in terms of this process. We then identify the Malthus exponent and the asymptotic profile in terms of a related Markov process, and give a spectral interpretation in terms of the growth-fragmentation operator and its dual. 相似文献
3.
Tomasz Przebinda 《Journal of Functional Analysis》2018,274(5):1284-1305
We relate the distribution characters and the wave front sets of unitary representation for real reductive dual pairs of type I in the stable range. 相似文献
4.
5.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but ) nonlinearities. 相似文献
6.
It is believed that there are more fundamental gauge symmetries beyond those described by the Standard Model of particle physics. The scales of these new gauge symmetries are usually too high to be reachable by particle colliders. Considering that the phase transition (PT) relating to the spontaneous breaking of new gauge symmetries to the electroweak symmetry might be strongly first order, we propose considering the stochastic gravitational waves (GW) arising from this phase transition as an indirect way of detecting these new fundamental gauge symmetries. As an illustration, we explore the possibility of detecting the stochastic GW generated from the PT of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
in the space-based interferometer detectors. Our study demonstrates that the GW energy spectrum is reachable by the LISA, Tianqin, Taiji, BBO, and DECIGO experiments only for the case where the spontaneous breaking of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
is triggered by at least two electroweak singlet scalars. 相似文献
7.
We prove that to most of the known hypercyclic operators A on separable Banach spaces there exist compact (compact convex, compact connected) subsets K of E such that each compact (compact convex, compact connected) subset of E can be approximated with respect to Hausdorff's distance by for suitable .
Received July 8, 1997, in final form October 17, 1997 相似文献
8.
Andrea Blunck 《Monatshefte für Mathematik》1997,123(2):93-107
In this note we show that the chain space belonging to a quadric can be embedded into the chain geometry over a Clifford algebra via a generalized stereographic projection. 相似文献
9.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
10.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献