全文获取类型
收费全文 | 330753篇 |
免费 | 2673篇 |
国内免费 | 1093篇 |
专业分类
化学 | 143715篇 |
晶体学 | 4439篇 |
力学 | 19508篇 |
综合类 | 7篇 |
数学 | 67881篇 |
物理学 | 98969篇 |
出版年
2021年 | 1012篇 |
2020年 | 1148篇 |
2019年 | 1172篇 |
2018年 | 18361篇 |
2017年 | 19046篇 |
2016年 | 11144篇 |
2015年 | 3526篇 |
2014年 | 2907篇 |
2013年 | 8183篇 |
2012年 | 13448篇 |
2011年 | 28260篇 |
2010年 | 16525篇 |
2009年 | 17019篇 |
2008年 | 22945篇 |
2007年 | 27993篇 |
2006年 | 7444篇 |
2005年 | 14836篇 |
2004年 | 10726篇 |
2003年 | 10100篇 |
2002年 | 7215篇 |
2001年 | 6388篇 |
2000年 | 5096篇 |
1999年 | 3648篇 |
1998年 | 2835篇 |
1997年 | 2754篇 |
1996年 | 2877篇 |
1995年 | 2469篇 |
1994年 | 2307篇 |
1993年 | 2181篇 |
1992年 | 2453篇 |
1991年 | 2428篇 |
1990年 | 2127篇 |
1989年 | 2120篇 |
1988年 | 2154篇 |
1987年 | 2090篇 |
1986年 | 1994篇 |
1985年 | 2900篇 |
1984年 | 2884篇 |
1983年 | 2338篇 |
1982年 | 2515篇 |
1981年 | 2388篇 |
1980年 | 2354篇 |
1979年 | 2315篇 |
1978年 | 2389篇 |
1977年 | 2253篇 |
1976年 | 2207篇 |
1975年 | 2183篇 |
1974年 | 2080篇 |
1973年 | 2205篇 |
1972年 | 1248篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions,
which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered
are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right
scalar multiplication (including the case where λ=0+) and pointwise addition.
相似文献
962.
J. C. Spehner 《Semigroup Forum》1989,39(1):323-334
The main results about automatas and the languages they accept are easily extended to automatas which recognize a family of
languages (Li)iεI of a free monoid, that is to automatas which recognize simultaneously all the languages Li. This generalization enhances the notion of automata of type (p,r) introduced by S. Eilenberg [4].
In a similar way the notion of syntactic monoid of a family of languages extends the notion of syntactic monoid of a language.
This extension is far from being trivial since we show that every finite monoid is the syntactic monoid of a recognizable
partition of a free monoid, though this is false for the syntactic monoids of languages.
相似文献
963.
G. Gargaro F. Gasparrini D. Misiti G. Palmieri M. Pierini C. Villani 《Chromatographia》1987,24(1):505-509
Summary Enantiomers of several sulfoxides and some selenoxides can be easily separated by using a new chiral stationary phase (CSP-DACH-DNB)
containing the 3,5-dinitrobenzoyl derivative of R,R-(-)1,2-diamino-cyclohexane as selector, covalently bonded to the siliceous
matrix. The easy operative conditions and the high enantioselectivity values (α) allow a direct transfer of the analytical
separations to a semi-preparative and preparative scale. 相似文献
964.
This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate
(KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity
and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity
increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant
load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density
associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied
by X-ray diffraction and Fourier transform infrared spectroscopy.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
965.
Oliver Lorscheid 《Archiv der Mathematik》2007,88(4):344-348
This paper shows that for a local field K, a subfield k ⊂ K and a variety X over k, X is complete if and only if for every finite field extension Kʹ | K, the set X(Kʹ) is compact in its strong topology.
The author likes to thank Florian Pop, Jakob Stix, Stefan Wewers, Gunther Cornelissen and his own parents for their support.
Received: 13 April 2006 相似文献
966.
Area,coarea, and approximation in <Emphasis Type="Italic">W</Emphasis><Superscript>1,1</Superscript>
David Swanson 《Arkiv f?r Matematik》2007,45(2):381-399
Let Ω⊂ℝ
n
be an arbitrary open set. We characterize the space W
1,1
loc(Ω) using variants of the classical area and coarea formulas. We use these characterizations to obtain a norm approximation
and trace theorems for functions in the space W
1,1(ℝ
n
). 相似文献
967.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure,
over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative
measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique
of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained
quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely
different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms
of cyclic coarse-grained quantum logics. 相似文献
968.
K Cooper S C Brailsford R Davies 《The Journal of the Operational Research Society》2007,58(2):168-176
Economic evaluation, such as cost effectiveness analysis, provides a method for comparing healthcare interventions. These evaluations often use modelling techniques such as decision trees, Markov processes and discrete event simulations (DES). With the aid of examples from coronary heart disease, the use of these techniques in different health care situations is discussed. Guidelines for the choice of modelling technique are developed according to the characteristics of the health care intervention.The choice of modelling technique is shown to depend on the acceptance of the modelling technique, model ‘error’, model appropriateness, dimensionality and ease and speed of model development. Generally decision trees are suitable for acute interventions but they cannot model recursion and Markov models are suitable for simple chronic interventions. It is further recommended that population based models be used in order to provide health care outcomes for the likely cost, health benefits and cost effectiveness of the intervention. The population approach will complicate the construction of the model. DES will allow the modeller to construct more complex, dynamic and accurate systems but these may involve a corresponding increase in development time and expense. The modeller will need to make a judgement on the necessary complexity of the model in terms of interaction of individuals and model size and whether queuing for resources, resource constraints or the interactions between individuals are significant issues in the health care system. 相似文献
969.
Zuo-liang Xu 《应用数学学报(英文版)》2007,23(4):629-636
In this paper,we study mixed elastico-plasticity problems in which part of the boundary is known,while the other part of the boundary is unknown and is a free boundary.Under certain conditions,this problemcan be transformed into a Riemann-Hilbert boundary value problem for analytic functions and a mixed boundaryvalue problem for complex equations.Using the theory of generalized analytic functions,the solvability of theproblem is discussed. 相似文献
970.
The Efficient Determination Criterion (EDC) generalizes the AIC and BIC criteria and provides a class of consistent estimators
for the order of a Markov chain with finite state space. In this note, we derive rates of convergence for the EDC estimates.
*Partially supported by CNPq, CAPES/PROCAD, FAPDF/PRONEX, FINATEC and FUNPE/UnB.
**Partially supported by CAPES. 相似文献