全文获取类型
收费全文 | 459176篇 |
免费 | 3065篇 |
国内免费 | 1084篇 |
专业分类
化学 | 213919篇 |
晶体学 | 6730篇 |
力学 | 25053篇 |
综合类 | 18篇 |
数学 | 67279篇 |
物理学 | 150326篇 |
出版年
2020年 | 3499篇 |
2019年 | 4138篇 |
2018年 | 12049篇 |
2017年 | 12624篇 |
2016年 | 10922篇 |
2015年 | 4791篇 |
2014年 | 7518篇 |
2013年 | 16857篇 |
2012年 | 15933篇 |
2011年 | 24442篇 |
2010年 | 16960篇 |
2009年 | 17232篇 |
2008年 | 22133篇 |
2007年 | 24676篇 |
2006年 | 13522篇 |
2005年 | 16166篇 |
2004年 | 13147篇 |
2003年 | 12301篇 |
2002年 | 10938篇 |
2001年 | 11331篇 |
2000年 | 8973篇 |
1999年 | 6747篇 |
1998年 | 5934篇 |
1997年 | 5683篇 |
1996年 | 5368篇 |
1995年 | 4789篇 |
1994年 | 4734篇 |
1993年 | 4787篇 |
1992年 | 4932篇 |
1991年 | 5357篇 |
1990年 | 5043篇 |
1989年 | 5077篇 |
1988年 | 4979篇 |
1987年 | 4904篇 |
1986年 | 4612篇 |
1985年 | 6096篇 |
1984年 | 6292篇 |
1983年 | 5146篇 |
1982年 | 5470篇 |
1981年 | 5285篇 |
1980年 | 4940篇 |
1979年 | 5304篇 |
1978年 | 5585篇 |
1977年 | 5495篇 |
1976年 | 5679篇 |
1975年 | 5220篇 |
1974年 | 5177篇 |
1973年 | 5397篇 |
1972年 | 4017篇 |
1971年 | 3487篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
991.
Jerry P. Suits 《School science and mathematics》2004,104(6):248-257
A laboratory practical examination was used to compare the investigative skills developed in two different types of general‐chemistry laboratory courses. Science and engineering majors (SEM) in the control group used a traditional verification approach (SEM‐Ctrl), whereas those in the treatment group learned from an innovative, inquiry‐based approach (SEM‐Trt). A scoring rubric was developed from their examination sheets to assess six component investigative skills. Results indicated that SEM students in the SEM‐Trt group scored significantly higher than those in SEM‐Ctrl for all six skills. Furthermore, nursing and applied science majors (NonSEM) in the inquiry‐based group (NonSEM‐Trt) wrote significantly better discussions than did SEM students in SEM‐Ctrl group. Overall, competency at the mid‐range level of laboratory skills was attained by most SEM‐Trt students (72.5%) but by only 30.5% of SEM‐Ctrl and 28.6% of NonSEM‐Trt students. Apparently, during the semester students in the SEM‐Trt group were able to use the inquiry‐based method effectively to combine chemical tasks with writing tasks and postlaboratory discussions. One implication of this study for science instructors is that practical examinations can provide useful feedback regarding the quality of the laboratory experience. Another implication is that this study provides evidence for the use of the innovative inquiry‐based laboratory approach to support student learning of high‐level investigative skills. However, students' requisite background knowledge must match the level of these skills. 相似文献
992.
V E Krivonozhko O B Utkin A V Volodin I A Sablin M Patrin 《The Journal of the Operational Research Society》2004,55(10):1049-1058
The aim of the paper is to present and substantiate a technique to visualize DEA modelling results without any loss of mathematical rigour. The proposed family of parametric optimization methods allows one to construct an intersection of the multidimensional frontier with a two-dimensional plane determined by any pair of given directions. This approach reduces the efficiency analysis of production units to the investigation of well-known functions in economics. We also propose constructive methods to calculate marginal rates of substitution, marginal rates of transformation and so on. 相似文献
993.
994.
Malmquist indexes can be used to estimate technical change over time. The index generally represents the average effect of technical change on all outputs in a multi-output firm. However, changes in technology do not necessarily affect all outputs involved in the analysis equally. In this paper, a method for estimating the effect of technical change on each of the different outputs is proposed. This estimation is done by a modification of quasi-Malmquist indexes. An artificial data set has been used to validate the method proposed in this paper. 相似文献
995.
Tracing is a method of assigning flows in an electricity network to particular generators and loads, assuming perfect mixing at each node. It can be used to assign costs to transmission users. We show that the resulting allocation is equal to the Shapley value of an equivalent co-operative game. 相似文献
996.
997.
D. P. Zhelobenko 《Acta Appl Math》2004,81(1):347-354
A special class of associative algebras is introduced and studied. A criteria of semisimplicity for suitable category of modules is obtained. 相似文献
998.
D. P. Zhelobenko 《Acta Appl Math》2004,81(1):355-383
An algebraic approach to harmonic analysis on reductive Lie groups is proposed. The case of complex semisimple Lie groups is considered in details. Some problems for real reductive Lie groups are discussed. 相似文献
999.
Using the result by D. Gessler, we show that any invariant variational bivector (resp., variational 2-form) on an evolution equation with nondegenerate right-hand side is Hamiltonian (resp., symplectic). 相似文献
1000.
In this note we show how 1-factors in the middle two layers of the discrete cube can be used to construct 2-factors in the
Odd graph (the Kneser graph of (k − 1)-sets from a (2k − 1)-set). In particular, we use the lexical matchings of Kierstead and Trotter, and the modular matchings of Duffus, Kierstead
and Snevily, to give explicit constructions of two different 2-factorisations of the Odd graph.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献