全文获取类型
收费全文 | 4589篇 |
免费 | 126篇 |
国内免费 | 30篇 |
专业分类
化学 | 2764篇 |
晶体学 | 35篇 |
力学 | 134篇 |
数学 | 714篇 |
物理学 | 1098篇 |
出版年
2022年 | 31篇 |
2021年 | 36篇 |
2020年 | 30篇 |
2019年 | 38篇 |
2018年 | 43篇 |
2017年 | 27篇 |
2016年 | 81篇 |
2015年 | 69篇 |
2014年 | 87篇 |
2013年 | 221篇 |
2012年 | 192篇 |
2011年 | 254篇 |
2010年 | 131篇 |
2009年 | 102篇 |
2008年 | 222篇 |
2007年 | 239篇 |
2006年 | 248篇 |
2005年 | 216篇 |
2004年 | 210篇 |
2003年 | 169篇 |
2002年 | 152篇 |
2001年 | 62篇 |
2000年 | 81篇 |
1999年 | 53篇 |
1998年 | 56篇 |
1997年 | 57篇 |
1996年 | 73篇 |
1995年 | 61篇 |
1994年 | 55篇 |
1993年 | 87篇 |
1992年 | 61篇 |
1991年 | 61篇 |
1990年 | 45篇 |
1989年 | 62篇 |
1988年 | 52篇 |
1987年 | 62篇 |
1986年 | 51篇 |
1985年 | 77篇 |
1984年 | 75篇 |
1983年 | 52篇 |
1982年 | 61篇 |
1981年 | 69篇 |
1980年 | 55篇 |
1979年 | 56篇 |
1978年 | 58篇 |
1977年 | 48篇 |
1976年 | 49篇 |
1975年 | 61篇 |
1974年 | 57篇 |
1973年 | 53篇 |
排序方式: 共有4745条查询结果,搜索用时 11 毫秒
21.
A simple and quite general approach is proposed to derive criteria for transience and ergodicity of a certain class of irreducibleN-dimensional Markov chains in
+
N
assuming a boundedness condition on the second moment of the jumps. The method consists in constructing convenient smooth supermartingales outside some compact set. The Lyapounov functions introduced belong to the set of quadratic forms in
+
N
and do not always have a definite sign. Existence and construction of these forms is shown to be basically equivalent to finding vectors satisfying a system of linear inequalities.Part I is restricted toN=2, in which case a complete characterization is obtained for the type of random walks analyzed by Malyshev and Mensikov, thus relaxing their condition of boundedness of the jumps. The motivation for this work is partly from a large class of queueing systems that give rise to random walks in
+
N
相似文献
22.
Stephen D. Cohen 《Monatshefte für Mathematik》1989,107(4):291-301
Chambers andSmeets [3] have designed a windmill arrangement of linear feedback shift registers (LFSRs) to generate pn-sequences overGF(2) with high speed. When the windmill hasv vanes, the associated minimal feedback polynomial (having degreen, relatively prime tov) can be taken to have the shapef
1(x
v
)+x
n
f
2(x
–v
), where the polynomialsf
1 andf
2 have degree [n/v]. Their numerical evidence, whenv is divisible by 4, suggests that, surprisingly, there areno such windmill polynomials which are irreducible ifn±3 (mod 8), while about twice as many irreducible and primitive windmill polynomials as they expected occur ifn±1 (mod 8). A discussion of this behaviour is presented here with proofs. The brief explanation is that the Galois group of the underlying generic windmill polynomial overGF (4) is equal to the alternating groupA
n
. 相似文献
23.
24.
E. Matsinos J. Guy E. Simopoulou W. Venus P. Allport M. Berggren M. Calicchio T. Coghen A. M. Cooper-Sarkar O. Erriquez N. Giannakopoulos G. T. Jones P. Marage M. M. Mobayyen D. R. O. Morrison S. O'Neale M. A. Parker J. Sacton R. A. Sansum N. Schmitz G. W. Van Apeldoorn K. Varvell A. Vayaki H. Wachsmuth W. Wittek BEBC WA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1989,44(1):79-87
Backward proton and pion production is studied in ν and \(\bar v\) charged current interactions in neon. The results are compared with other experiments and theory. The complete backward proton data is compatible with protons produced by reinteractions in the nucleus. However in events with only one proton, muon variables appear correlated to those for the backward proton, as expected by the two-nucleon correlation model. 相似文献
25.
[reaction: see text] The photochemistry of N-acyl-5,7-dinitroindoline (1) was studied in acetonitrile using nanosecond time-resolved infrared (TRIR) spectroscopy. Upon photolysis, two nearly but not completely overlapping sets of transient IR bands are observed that are assigned to two non-interconvertible conformers of mixed acetic nitronic anhydride 7. While syn-7 reverts rapidly to 1, anti-7 is long-lived and is able to acylate amines. Results of density functional theory calculations support conclusions based on experimental TRIR data. 相似文献
26.
Paolo Zatta Tamas KissMario Suwalsky Guy Berthon 《Coordination chemistry reviews》2002,228(2):271-284
Aluminium has been known as a neurotoxic agent to experimental animals since the last century (Arch. Exp. Pharmacol. 40 (1897) 98). However, great interest arose in it bioinorganic chemistry as well biology when it was demonstrated to be the causative agent in pathologies related to the long-term dialysis treatment of uremic subjects with renal failure (Life Chem. 11 (1994) 197), and as a potential etiopathogenic cofactor for several neurodegenerative diseases. The inorganic biochemistry of aluminium is still largely to be discovered. In this review the pro-oxidative property of aluminium toward biological membrane will be presented and its implications in involvement in human pathology will be discussed in an interdisciplinary frame from the bioinorganic point of view. 相似文献
27.
28.
M. Cohen L. Porte J-P Thomas J. Tousset 《Journal of Radioanalytical and Nuclear Chemistry》1973,17(1-2):65-77
Résumé Une méthode d'étude de la composition stoéchiométrique de couches minces (10 à 500 μg/cm2) de verres chalcogénures est développée. L'étude des réactions nucléaire; induites par bombardement de protons de basse énergie
(<4 MeV) sur les éléments constitutifs Ge, As, Te et S, conduit à choisir la diffusion élastique et la détection de gammas
prompts pour le dosage simulatené. La précision et la sensibilité de la méthode sont discutées à partir des résultats obtenus.
L'utilisation de la résonance fine sur le soufre (p, p'γ) est appliquée à l'étude de l'homogénéité des cibles. 相似文献
29.
In a previous paper, some 15 compounds were positively identified among the products of thermal degradation of bisphenol-A diglycidyl ether. The structures of an additional 22 compounds, all aromatic, were speculated upon on the basis of mass spectral analysis. In the present paper, mechanisms are proposed to account for all these products and the characteristics of their formation in the overall degradation process. 相似文献
30.