全文获取类型
收费全文 | 8602篇 |
免费 | 179篇 |
国内免费 | 88篇 |
专业分类
化学 | 5357篇 |
晶体学 | 102篇 |
力学 | 180篇 |
数学 | 1856篇 |
物理学 | 1374篇 |
出版年
2022年 | 86篇 |
2021年 | 71篇 |
2020年 | 100篇 |
2019年 | 91篇 |
2018年 | 107篇 |
2017年 | 77篇 |
2016年 | 176篇 |
2015年 | 129篇 |
2014年 | 169篇 |
2013年 | 501篇 |
2012年 | 427篇 |
2011年 | 454篇 |
2010年 | 301篇 |
2009年 | 260篇 |
2008年 | 406篇 |
2007年 | 377篇 |
2006年 | 434篇 |
2005年 | 409篇 |
2004年 | 376篇 |
2003年 | 304篇 |
2002年 | 315篇 |
2001年 | 110篇 |
2000年 | 97篇 |
1999年 | 101篇 |
1998年 | 118篇 |
1997年 | 128篇 |
1996年 | 155篇 |
1995年 | 99篇 |
1994年 | 90篇 |
1993年 | 93篇 |
1992年 | 99篇 |
1991年 | 83篇 |
1990年 | 72篇 |
1989年 | 67篇 |
1988年 | 63篇 |
1987年 | 74篇 |
1986年 | 66篇 |
1985年 | 113篇 |
1984年 | 124篇 |
1983年 | 95篇 |
1982年 | 98篇 |
1981年 | 121篇 |
1980年 | 131篇 |
1979年 | 98篇 |
1978年 | 107篇 |
1977年 | 80篇 |
1976年 | 91篇 |
1975年 | 102篇 |
1974年 | 94篇 |
1973年 | 92篇 |
排序方式: 共有8869条查询结果,搜索用时 31 毫秒
71.
Charles Emenaker 《School science and mathematics》1996,96(2):75-84
This study examined the impact a problem-solving based mathematics content course for preservice elementary education teachers (PSTs) had on challenging the beliefs they held with respect to mathematics and themselves as doers of mathematics. Nine PSTs were interviewed to gain insight into changes that occurred to their belief systems and what aspect(s) of the course were instrumental in producing those changes. Surveys to measure how strongly PSTs subscribed to five mathematical beliefs were administered to 137 PSTs who were enrolled in the course. Significant positive changes (p < .01) were observed for four of the five beliefs. When changes were studied by achievement level, students with final grades of A or B showed statistically significant changes (p < .005) in three of the five beliefs. Students who were interviewed consistently reported increased confidence in their mathematical abilities as a result of the course. 相似文献
72.
73.
74.
75.
76.
Jorge Almeida 《Algebra Universalis》1989,26(1):16-32
For an ordinal and a class
of topological algebras of a given type (which may be infinite and may contain inflnitary operations), an-aryimplicit operation on
is any new-ary operation whose introduction does not eliminate any continuous homomorphisms between members of
. The set of all-ary implicit operations on
is denoted by
and forms an algebra of the given type which is endowed with the least topology making continuous all homomorphisms into members of
. With this topology,
is a topological algebra in which the subalgebra
of all-ary operations on
which are induced by terms is dense, provided that
is closed under the formation of closed subalgebras and finitary direct products. This is obtained by realizing
as an inverse limit of-generated members of
. These results are applied to pseudovarieties of topological and finite algebras.This work was supported, in part, by INIC grant 85/CEX/4. This paper was written while the author was a faculty member at the Universidade do Minho.Presented by Ralph McKenzie. 相似文献
77.
Martin Charles Golumbic 《Graphs and Combinatorics》1988,4(1):307-321
Let be a family of sets. The intersection graph of is obtained by representing each set in by a vertex and connecting two vertices by an edge if and only if their corresponding sets intersect. Of primary interest are those classes of intersection graphs of families of sets having some specific topological or other structure. The grandfather of all intersection graphs is the class of interval graphs, that is, the intersection graphs of intervals on a line.The scope of research that has been going on in this general area extends from the mathematical and algorithmic properties of intersection graphs, to their generalizations and graph parameters motivated by them. In addition, many real-world applications involve the solution of problems on such graphs.In this paper a number of topics in algorithmic combinatorics which involve intersection graphs and their representative families of sets are presented. Recent applications to computer science are also discussed. The intention of this presentation is to provide an understanding of the main research directions which have been investigated and to suggest possible new directions of research. 相似文献
78.
79.
Enthalpies of solution have been measured from 5 to 85°C for aqueous tetraethyl- and tetrapropylammonium bromides, and the integral heat method is employed to evaluate
for these electrolytes over a wide temperature range. Data taken from the literature have been used to evaluate
for aqueous Bu4NBr over a similar temperature range. These data, along with similar data for Me4NBr, previously reported, have been used to evaluate absolute ionic heat capacities. While the absolute values agree only qualitatively with two other methods of division, the temperature dependences of the three methods essentially agree up to 65°C. Heat capacities due to structural effects on the solvent, obtained by subtracting the inherent heat capacities of the ions, are extraordinarily positive for all four tetraalkylammonium ions and have negative temperature coefficients, indicating that all four ions, including the tetramethylammonium ion, are structure-making ions. 相似文献
80.
Charles Brown R. Harry Cragg Tim J. Miller David O''N. Smith 《Journal of organometallic chemistry》1981,220(3):C25-C26
The application of variable temperature 13C NMR to the study of a series of chlorodialkylaminophenylboranes has enabled G values for the rotational barrier, about the boron---nitrogen bond, to be determined. 相似文献