全文获取类型
收费全文 | 381699篇 |
免费 | 4122篇 |
国内免费 | 1037篇 |
专业分类
化学 | 189091篇 |
晶体学 | 5118篇 |
力学 | 19084篇 |
综合类 | 10篇 |
数学 | 67866篇 |
物理学 | 105689篇 |
出版年
2020年 | 2726篇 |
2019年 | 2921篇 |
2018年 | 13764篇 |
2017年 | 13553篇 |
2016年 | 11735篇 |
2015年 | 4713篇 |
2014年 | 5822篇 |
2013年 | 13840篇 |
2012年 | 14097篇 |
2011年 | 22016篇 |
2010年 | 13940篇 |
2009年 | 13928篇 |
2008年 | 17532篇 |
2007年 | 19526篇 |
2006年 | 10792篇 |
2005年 | 10928篇 |
2004年 | 10309篇 |
2003年 | 9791篇 |
2002年 | 8678篇 |
2001年 | 8334篇 |
2000年 | 6752篇 |
1999年 | 5090篇 |
1998年 | 4504篇 |
1997年 | 4348篇 |
1996年 | 4318篇 |
1995年 | 3813篇 |
1994年 | 4018篇 |
1993年 | 3693篇 |
1992年 | 4142篇 |
1991年 | 4100篇 |
1990年 | 4047篇 |
1989年 | 3841篇 |
1988年 | 3959篇 |
1987年 | 3819篇 |
1986年 | 3634篇 |
1985年 | 4801篇 |
1984年 | 5019篇 |
1983年 | 4198篇 |
1982年 | 4338篇 |
1981年 | 4274篇 |
1980年 | 4209篇 |
1979年 | 4166篇 |
1978年 | 4456篇 |
1977年 | 4353篇 |
1976年 | 4423篇 |
1975年 | 4069篇 |
1974年 | 4124篇 |
1973年 | 4307篇 |
1972年 | 2999篇 |
1971年 | 2491篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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
992.
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
993.
In this paper, the authors deal with bifunctions defined on complete metric spaces and with values in locally convex spaces ordered by closed convex cones. The aim is to provide a vector version of Ekeland’s theorem related to equilibrium problems. To prove this principle, a weak notion of continuity of a vector-valued function is considered, and some of its properties are presented. Via the vector Ekeland’s principle, existence results for vector equilibria are proved in both compact and noncompact domains. 相似文献
994.
995.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献
996.
A. G. Zhdanov A. K. Zvezdin A. P. Pyatakov T. B. Kosykh D. Viehland 《Physics of the Solid State》2006,48(1):88-95
The specific features of the “incommensurate-commensurate” phase transitions induced by a magnetic field in multiferroics
(materials with coexisting magnetic and electric ordering) are considered. These materials are ferroelectromagnets, for example,
bismuth ferrite BiFeO3 and BiFeO3-based compounds, which have spatially modulated spin structures. It is shown that the interaction between the electric and
magnetic subsystems of the multiferroic material can lead to an electric-field-induced shift of the critical magnetic field
corresponding to the transition from a spatially modulated state to a homogeneous antiferromagnetic state. According to the
theoretical estimates obtained for material parameters characteristic of the bismuth ferrite, this shift is of the order of
0.5 T in an electric field of 50 kV/cm. The phase diagrams are constructed in the “electric field-magnetic field” coordinates.
The results of calculations performed in the harmonic incommensurate structure approximation are compared with the exact soliton
solution. 相似文献
997.
I. V. Zavarzin N. G. Smirnova V. N. Yarovenko M. M. Krayushkin 《Russian Journal of Organic Chemistry》2006,42(2):273-274
A convenient procedure was developed for preparation of thiazolo[5,4-b]pyridine-2-carboxamides by oxidation of monothiooxamides synthesized from 3-aminopyridine. 相似文献
998.
I. G. Silinskaya A. V. Novoselova Yu. N. Sazanov A. V. Gribanov I. N. Serov V. I. Margolin 《Russian Journal of Applied Chemistry》2006,79(8):1378-1380
Mechanisms of orientation for the solutions of polyacrylonitrile synthesized under conditions of radical and anionic polymerization were studied. The effect of the fractal-matrix structuring agent developed by the AIRES foundation on the correlation parameters of the solution density and average squared fluctuation polarizability, which can be used to determine how the supramolecular structure changes by “self-orientation” and “induced orientation” mechanisms, was analyzed. 相似文献
999.
A. P. Suponina L. G. Kolzunova M. A. Karpenko 《Russian Journal of Applied Chemistry》2006,79(6):924-929
The effect of coatings based on a copolymer of acrylamide, N,N′-methylenebisaxcrylamide and formaldehyde deposited by electrochemical polymerization on the corrosion resistance of 08Kh18N10T stainless steel (field studies at sea) and low-carbon steel (laboratory experiments) was examined. 相似文献
1000.
C V Fabritius N L Madsen J Clausen J Larsen 《The Journal of the Operational Research Society》2006,57(12):1482-1490
An ontology is a classification model for a given domain. In information retrieval, ontologies are used to perform broad searches. An ontology can be visualized as nodes and edges. Each node represents an element and each edge a relation between a parent and a child element. Working with an ontology becomes easier with a visual representation. An idea is to use the expressive power of 3D representation to provide visualization for the user. In this paper, we propose a new method for positioning the elements of the visualized concept lattice in the 3D world based on operations research (OR) methods. One method uses a discrete location model to create an initial solution and we propose heuristic methods to further improve the visual result. We evaluate the visual results according to our success criteria and the feedback from users. Running times of the heuristic indicate that an improved version should be feasible for on-line processing and what-if analysis of ontologies. 相似文献