全文获取类型
收费全文 | 407篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
化学 | 164篇 |
晶体学 | 6篇 |
力学 | 15篇 |
数学 | 93篇 |
物理学 | 143篇 |
出版年
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 23篇 |
2012年 | 16篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 15篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有421条查询结果,搜索用时 421 毫秒
51.
52.
During the investigation of problems with the physical handling of sludge from a saline activated sludge wastewater system, pyrolysis/GC/MS was used in an attempt to determine whether changes in the bacterial population in the sludge were occurring. The pyrolysis GC/MS analysis revealed an unknown peak among other typical bacterial pyrolysis products. This unknown was identified as 2-methylpyrimidine. This pyrolysis product was only found in appreciable amounts in samples from other saline systems but not in freshwater systems analyzed as points of comparison for the system of concern. Further investigation confirmed the source of 2-methylpyrimidine to be ectoine, a compound produced by halophilic bacteria as a compatible solute for osmoadaptation. Pyrolysis GC/MS was shown to be a useful tool to indicate the presence of ectoine in halophilic bacteria. 相似文献
53.
Let H i be a sublattice subgroup of a lattice-ordered group G i (i = 1, 2). Suppose that H 1 and H 2 are isomorphic as lattice-ordered groups, say by φ. In general, there is no lattice-ordered group in which G 1 and G 2 can be embedded (as lattice-ordered groups) so that the embeddings agree on the images of H 1 and H 1 φ . In this article we prove that the group free product of G 1 and G 2 amalgamating H 1 and H 1 φ is right orderable and so embeddable (as a group) in a lattice-orderable group. To obtain this, we use our necessary and sufficient conditions for the free product of right-ordered groups with amalgamated subgroup to be right orderable [BLUDOV, V. V.—GLASS, A. M. W.: Word problems, embeddings, and free products of right-ordered groups with amalgamated subgroup, Proc. London Math. Soc. (3) 99 (2009), 585–608]. We also provide new limiting examples to show that amalgamation can fail in the category of lattice-ordered groups even when the amalgamating sublattice subgroups are convex and normal (?-ideals) and solve of Problem 1.42 from [KOPYTOV, V. M.—MEDVEDEV, N. YA.: Ordered groups. In: Selected Problems in Algebra. Collection of Works Dedicated to the Memory of N. Ya. Medvedev, Altaii State University, Barnaul, 2007, pp. 15–112 (Russian)]. 相似文献
54.
Abstract The assignment of a band near 1600 cm?1 in IR spectra of carbons has been controversial for four decades. However, many different carbons have been studied: effectively, a single band assignment was sought for an absorption appearing with three different classes of carbon. As these differ in over-all structure, not one but three explanations are needed. These are discussed. However, undue emphasis has been placed on a single absorption; attention should also be paid to other absorptions accompanying the 1600 cm?1 band. 相似文献
55.
The Cesàro operator is shown to be subdecomposable on the Bergman spaces Ap (\mathbbD) A^{p} (\mathbb{D}) for p \geqq 2 p \geqq 2 , extending a result of [12] to the case that p < 4. For A2 (\mathbbD) A^{2} (\mathbb{D}) , we show that Cesàro operator is in fact subscalar, but in contrast to the situation in the Hardy space, C |A2 C |_{A^2} fails to be hyponormal. 相似文献
56.
57.
58.
The reaction of OH with acetylene was studied in a discharge flow system at room temperature. OH was generated by the reaction of atomic hydrogen with NO2 and was monitored throughout the reaction using ESR spectroscopy. Mass-spectrometric analysis of the reaction products yielded the following results: (1) less than 3 molecules of OH were consumed, and less than 2 molecules of H2O were formed for every molecule of acetylene that reacted; (2) CO was identified as the major carbon-containing product; (3) NO, formed in the generation of OH, reacted with a reaction intermediate to give among other products N2O. These observations placed severe limitations on the choice of a reaction mechanism. A mechanism containing the reaction OH + C2H2 → HC2O + H2 better accounted for the experimental results than one involving the abstraction reaction OH + C2H2 → C2H + H2O. The rate constant for the initial reaction was measured as 1.9 ± 0.6 × 10?13 cm3 molecule?1 sec?1. 相似文献
59.
60.
The dispersion relation is obtained for a surface plasmon propagating parallel to the grooves of a large amplitude grating. Two variants of the Rayleigh method arc used: the first requires the evaluation of the zeros of a determinant; the second yields the dispersion relation in terms of the solution of a matrix eigenvalue problem. The dispersion relations are solved numerically for a sinusoidal and for a symmetric sawtooth grating profile, yielding in each case an infinity of discrete branches. 相似文献