全文获取类型
收费全文 | 28320篇 |
免费 | 787篇 |
国内免费 | 230篇 |
专业分类
化学 | 19282篇 |
晶体学 | 128篇 |
力学 | 648篇 |
综合类 | 1篇 |
数学 | 5385篇 |
物理学 | 3893篇 |
出版年
2022年 | 183篇 |
2021年 | 276篇 |
2020年 | 347篇 |
2019年 | 313篇 |
2018年 | 276篇 |
2017年 | 292篇 |
2016年 | 600篇 |
2015年 | 621篇 |
2014年 | 659篇 |
2013年 | 1406篇 |
2012年 | 1407篇 |
2011年 | 1706篇 |
2010年 | 952篇 |
2009年 | 814篇 |
2008年 | 1464篇 |
2007年 | 1466篇 |
2006年 | 1553篇 |
2005年 | 1394篇 |
2004年 | 1327篇 |
2003年 | 1098篇 |
2002年 | 1046篇 |
2001年 | 453篇 |
2000年 | 407篇 |
1999年 | 395篇 |
1998年 | 385篇 |
1997年 | 432篇 |
1996年 | 398篇 |
1995年 | 360篇 |
1994年 | 391篇 |
1993年 | 344篇 |
1992年 | 320篇 |
1991年 | 320篇 |
1990年 | 278篇 |
1989年 | 280篇 |
1988年 | 260篇 |
1987年 | 218篇 |
1986年 | 245篇 |
1985年 | 361篇 |
1984年 | 370篇 |
1983年 | 315篇 |
1982年 | 348篇 |
1981年 | 316篇 |
1980年 | 338篇 |
1979年 | 270篇 |
1978年 | 300篇 |
1977年 | 279篇 |
1976年 | 223篇 |
1975年 | 190篇 |
1974年 | 195篇 |
1973年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Peter Otte 《Journal of Mathematical Analysis and Applications》2004,289(1):167-179
Given a semi-group U(t) of bounded linear operators with bounded self-adjoint generator A we estimate the logarithm of the section determinants of U(t) in terms of A. When A is subject to an additional condition, which is related to so-called Følner sequences of orthogonal projections, this estimate implies a Szeg? type theorem for bounded, self-adjoint, and strictly positive operators. We show that the condition mentioned is satisfied when A is a Toeplitz operator or a compact operator. 相似文献
122.
We consider ruin probabilities for an insurance company, which can
also invest in the stock market. The risk process is modeled by a compound Poisson
process and the stock price by geometric Brownian motion. We show that if the tails
of the claims are light tailed, then the optimal strategy is asymptotically given by
holding a constant $-value in the stock position. Furthermore, we show that a kind of
Cramér–Lundberg approximation holds for the minimal ruin probability. Everything
is shown under assumptions, which are analogous to the assumptions in the case of the
classical Cramér–Lundberg approximation without investment. 相似文献
123.
Peter J. Cameron 《组合设计杂志》2005,13(6):466-470
It is shown that there is a function g on the natural numbers such that a partial Steiner triple system U on u points can be embedded in a Steiner triple system V on ν points, in such a way that all automorphisms of U can be extended to V, for every admissible ν satisfying ν > g(u). We find exponential upper and lower bounds for g. © 2005 Wiley Periodicals, Inc. J Combin Designs. 相似文献
124.
Agnieszka Grzelka Marek Cypryk Peter C. Hupfield 《Journal of organometallic chemistry》2004,689(4):705-713
Kinetics studies of the condensation of model hydroxyl-terminated oligosiloxanes, pentamethyldisiloxane-1-ol (MDH) and heptamethyltrisiloxane-1-ol (MD2H), catalysed by protic complex of tetrakis(pentafluorophenyl)borate in the toluene solution were performed. The dominating reaction was condensation, which was accompanied by disproportionation of oligosiloxanols. Water released in the condensation forms separate dispersed phase, but the phase separation and the presence of water does not affect the rate of the polycondensation. Both processes, condensation and disproportionation, show analogous kinetic laws being first order in silanol and half order in catalyst. They exhibit also similar values of activation parameters. The kinetics are explained by the formation of a reactive protic complex of silanol with borate being in fast preequilibrium with an unreactive complex including two borate molecules and the silanol molecules. The equilibrium lies to the side of the unreactive borate complex. 相似文献
125.
Norma L. Ortiz Peter R. Wolenski 《Journal of Mathematical Analysis and Applications》2004,289(1):260-265
This note proves an existence theorem for a generalized Bolza-type problem that has time delays in both the state and velocity variables. The assumptions are stated in terms of a modification of the classical Hamiltonian, and extend ideas of Rockafellar to the delay case. 相似文献
126.
127.
The field of medicinal inorganic chemistry is rapidly advancing. In particular organometallic complexes have much potential as therapeutic and diagnostic agents. The carbon‐bound and other ligands allow the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. The establishment of structure–activity relationships and elucidation of the speciation of complexes under conditions relevant to drug testing and formulation are crucial for the further development of promising medicinal applications of organometallic complexes. Specific examples involving the design of ruthenium and osmium arene complexes as anticancer agents are discussed. 相似文献
128.
129.
Andrew C. Brooks Peter Day John D. Wallis 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(5):o245-o247
The crystal structure of the title compound [systematic name: 2‐(1,3‐dithiolo[4,5‐b][1,4]dithiin‐2‐ylidene)‐6,6‐bis(methoxyethoxymethoxymethyl)‐1,3‐dithiolo[4,5‐b][1,4]dithiepine], C21H30O6S8, a spiro‐substituted BEDT–TTF analogue [BEDT–TTF is bis(ethylenedithio)tetrathiafulvalene], has a strongly bent heterocyclic framework. The seven‐membered ring adopts a pseudo‐chair conformation with notably widened ring bond angles, especially at the methylene C atoms [119.49 (11) and 117.60 (11)°]. The axial side chain adopts an extended conformation, but the equatorial side chain curls back on itself and the O atom nearest the ring system is involved in three short contacts to H atoms (2.45–2.53 Å). The molecules pack in centrosymmetrically related pairs, which are isolated from each other by columns of the polyether side chains. This study emphasizes the ease of distortion of the neutral bis(propylenedithio)tetrathiafulvalene ring structure, and how the need to accommodate side chains can easily override the tendency of these donor systems to form stacks in the crystalline state. 相似文献
130.
An explicit derivation of dispersion relations and spectra for periodic Schrödinger operators on carbon nano-structures (including graphene and all types of single-wall nano-tubes) is provided. 相似文献