全文获取类型
收费全文 | 1849篇 |
免费 | 27篇 |
国内免费 | 13篇 |
专业分类
化学 | 1071篇 |
晶体学 | 24篇 |
力学 | 45篇 |
数学 | 316篇 |
物理学 | 433篇 |
出版年
2021年 | 19篇 |
2020年 | 18篇 |
2019年 | 22篇 |
2018年 | 17篇 |
2016年 | 31篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 53篇 |
2012年 | 89篇 |
2011年 | 94篇 |
2010年 | 53篇 |
2009年 | 39篇 |
2008年 | 75篇 |
2007年 | 79篇 |
2006年 | 81篇 |
2005年 | 69篇 |
2004年 | 70篇 |
2003年 | 69篇 |
2002年 | 60篇 |
2001年 | 48篇 |
2000年 | 46篇 |
1999年 | 34篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 24篇 |
1995年 | 28篇 |
1994年 | 37篇 |
1993年 | 42篇 |
1992年 | 34篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 17篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 27篇 |
1983年 | 27篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 28篇 |
1973年 | 22篇 |
1972年 | 11篇 |
1967年 | 15篇 |
排序方式: 共有1889条查询结果,搜索用时 281 毫秒
1.
Condeixa Lucas Dias Silva Pierry Moah Diego Farias Brenda Leiras Adriana 《Central European Journal of Operations Research》2022,30(3):921-940
Central European Journal of Operations Research - Societal awareness and legislation changes concerning sustainability have affected how organizations generate value for stakeholders, as well as... 相似文献
2.
Susan Baker Lisa Kelchner Barbara Weinrich Linda Lee Paul Willging Robin Cotton Karen Zur 《Journal of voice》2006,20(4):631-641
Laryngotracheal stenosis is defined as a congenital or acquired narrowing of the airway. Congenital causes may include subglottic membranous or cartilaginous narrowing. Acquired causes may include trauma due to prolonged endotracheal or tracheal intubation or laryngotracheal injury. Although advances have been made over the past 30 years in reconstructive surgeries to improve airway patency in these patients, long-term laryngeal function for voice production is not well defined in this population. This review examines causes, symptoms and signs, and methods for diagnosing laryngotracheal stenosis. Surgical management procedures are briefly summarized. The current literature on voice outcomes is summarized. The predominant voice characteristics in the population are presented, although results are challenged by the heterogeneity of voice presentation and paucity of data from instrumental measures. Considerations for subjective and instrumental assessment, measures of quality of life, instrumental methods, and treatment options specific to the needs of this population are discussed. Research strategies to identify long-term outcomes of surgical and behavioral treatments in this population are posed. 相似文献
3.
Robert W. Baker Geoffrey R. Pocock Melvyn V. Sargent Edi Twiss 《Tetrahedron: Asymmetry》1993,4(12):2423-2426
Introduction of a 2-isopropoxycarbonyl or 2-NN-dimethylcarbamoyl group into homochiral 1-p-tolyl- or 1-t-butyl-sulfinylnaphthalenes, via directed metalation reaction, followed by ligand coupling reaction with 1-naphthylmagnesium bromide, furnished atropisomeric 1,1′-binaphthyls in 82–95% enantiomeric excess (e.e.). 相似文献
4.
Arthur G. Maki John C. Grecu Brenda Winnewisser Manfred Winnewisser 《Journal of Molecular Spectroscopy》2003,222(2):198-212
High-resolution spectra of 15N12C12C15N and 14N13C13C14N have been measured and analyzed from 200 to 3600 cm−1. All the vibrational levels below 900 cm−1 have been observed and characterized. The Fermi resonance between ν2 and 2ν4 has been studied and the resonance constant has been determined for several cases. Several Σ− states have been directly observed for the first time for each isotopomer, the (0001111)0f, (0011111)0f, and (0002222)0f states. The pattern of the energy levels for clusters of l-type resonance coupled levels, such as 0001131,3, has been determined for cyanogen for the first time. Among other things this involved the determination of the vibrational l-type resonance constant, r45. Many of the power series constants, αi and xij, and higher order constants have been determined. 相似文献
5.
The intention of the research reported here was to seek explanations for low achievement in school mathematics, as conventionally assessed, that derive from broad understandings of mathematics as social. Such a broad social perspective can provide explanations for low achievement, which could lead to different understandings and hence to different teaching approaches. This study centered on 5- to 8-year-old children from a White working-class area in England. Data were collected during visits to the children in school, in their homes, and in the broader community over a 3-year period. Parents, teachers, and other professionals in the broad school context were interviewed, and data were also collected from school documents and policy statements. Interpretations of these data in terms of ways of understanding children's achievements in school mathematics are put forward. The potential effects of these factors on low schooled numeracy attainment are discussed, together with some possible strategic implications for practice and policy. 相似文献
6.
Differential algebraic equations with after-effect 总被引:4,自引:0,他引:4
C. T. H. Baker C. A. H. Paul H. Tian 《Journal of Computational and Applied Mathematics》2002,140(1-2):63-80
In this paper, we are concerned with the solution of delay differential algebraic equations. These are differential algebraic equations with after-effect, or constrained delay differential equations. The general semi-explicit form of the problem consists of a set of delay differential equations combined with a set of constraints that may involve retarded arguments. Even simply stated problems of this type can give rise to difficult analytical and numerical problems. The more tractable examples can be shown to be equivalent to systems of delay or neutral delay differential equations. Our purpose is to highlight some of the complexities and obstacles that can arise when solving these problems, and to indicate problems that require further research. 相似文献
7.
8.
A new method for one-electron propagator calculations of molecular inization potentials is proposed, using a large matrix technique The results of some trial calculations on molecular nitrogen are given. 相似文献
9.
Jon Baker 《Journal of computational chemistry》1992,13(2):240-253
An efficient algorithm for constrained geometry optimization in Cartesian coordinates is presented. It incorporates mode-following techniques within both the classical method of Lagrange multipliers and the penalty function method. Both constrained minima and transition states can be located and, unlike the standard Z-matrix using internal coordinates, the desired constraints do not have to be satisfied in the initial structure. The algorithm is as efficient as a Z-matrix optimization while presenting several additional advantages. 相似文献
10.
Brenda J. Latka 《Journal of Graph Theory》2003,42(3):165-192
A finite tournament T is tight if the class of finite tournaments omitting T is well‐quasi‐ordered. We show here that a certain tournament N5 on five vertices is tight. This is one of the main steps in an exact classification of the tight tournaments, as explained in [10]; the third and final step is carried out in [11]. The proof involves an encoding of the indecomposable tournaments omitting N5 by a finite alphabet, followed by an application of Kruskal's Tree Theorem. This problem arises in model theory and in computational complexity in a more general form, which remains open: the problem is to give an effective criterion for a finite set {T1,…,Tk} of finite tournaments to be tight in the sense that the class of all finite tournaments omitting each of T1,…,Tk is well‐quasi‐ordered. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 165–192, 2003 相似文献