全文获取类型
收费全文 | 1341篇 |
免费 | 42篇 |
国内免费 | 73篇 |
专业分类
化学 | 416篇 |
晶体学 | 4篇 |
力学 | 15篇 |
综合类 | 3篇 |
数学 | 456篇 |
物理学 | 227篇 |
综合类 | 335篇 |
出版年
2023年 | 8篇 |
2022年 | 20篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 26篇 |
2015年 | 32篇 |
2014年 | 52篇 |
2013年 | 76篇 |
2012年 | 48篇 |
2011年 | 61篇 |
2010年 | 58篇 |
2009年 | 69篇 |
2008年 | 74篇 |
2007年 | 61篇 |
2006年 | 50篇 |
2005年 | 56篇 |
2004年 | 45篇 |
2003年 | 43篇 |
2002年 | 56篇 |
2001年 | 34篇 |
2000年 | 48篇 |
1999年 | 27篇 |
1998年 | 19篇 |
1997年 | 23篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 37篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 21篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 16篇 |
1974年 | 18篇 |
1973年 | 19篇 |
排序方式: 共有1456条查询结果,搜索用时 8 毫秒
121.
Single crystals of U3+:LaBr3 were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm−1 range. Sixty-four experimental crystal-field energy levels of the U3+ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm−1. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f3→5f3 transitions. The effects of selected CCF operators on the splitting of some specific U3+ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses. 相似文献
122.
Dhanpat Rai Yuanxian Xia Linfeng Rao Nancy J. Hess Andrew R. Felmy Dean A. Moore David E. McCready 《Journal of solution chemistry》2005,34(4):469-498
The objectives of this study were to address uncertainties in the solubility product of (UO2)3(PO4)2⋅4H2O(c) and in the phosphate complexes of U(VI), and more importantly to develop needed thermodynamic data for the Pu(VI)-phosphate system in order to ascertain the extent to which U(VI) and Pu(VI) behave in an analogous fashion. Thus studies were conducted on (UO2)3(PO4)2⋅4H2O(c) and (PuO2)3(PO4)2⋅4H2O(am) solubilities for long-equilibration periods (up to 870 days) in a wide range of pH values (2.5 to 10.5) at fixed phosphate concentrations of 0.001 and 0.01 M, and in a range of phosphate concentrations (0.0001–1.0 M) at fixed pH values of about 3.5. A combination of techniques (XRD, DTA/TG, XAS, and thermodynamic analyses) was used to characterize the reaction products. The U(VI)-phosphate data for the most part agree closely with thermodynamic data presented in Guillaumont et al.,(1) although we cannot verify the existence of several U(VI) hydrolyses and phosphate species and we find the reported value for formation constant of UO2PO−4 is in error by more than two orders of magnitude. A comprehensive thermodynamic model for (PuO2)3(PO4)2⋅4H2O(am) solubility in the H+-Na+-OH−-Cl−-H2PO−4-HPO2−4-PO3−4-H2O system, previously unavailable, is presented and the data shows that the U(VI)-phosphate system is an excellent analog for the Pu(VI)-phosphate system. 相似文献
123.
陈漱渝 《武陵学刊:社会科学版》2009,(3):64-74
1937年9月-1942年8月,胡适在美国度过了5年外交生涯。任大使期间,在经费困难和国际环境险恶的情况下,他一方面与美国上层频繁接触,获得了美国的两笔贷款,为抗战筹措资金;另一方面豁出性命讲演,宣传蒋介石和国民政府的对日政策,为抗日作舆论宣传。但由于客观环境的限制和他人的误解,以及与宋子文之间的龃龉,最终被蒋介石免职。 相似文献
124.
钢筋砼抗渗结构的开裂是渗漏的主要原因,这个带有普遍性的问题长期困扰着广大施工技术人员。在普通砼中掺入适量的U型膨胀剂,减小了砼结构开裂的可能性,提高了砼的抗渗能力,为防水砼的施工提供一种借鉴的方法。 相似文献
125.
Matias L. del Hoyo 《Topology and its Applications》2008,155(11):1189-1200
We present an intrinsic and concrete development of the subdivision of small categories, give some simple examples and derive its fundamental properties. As an application, we deduce an alternative way to compare the homotopy categories of spaces and small categories, by using partially ordered sets. This yields a new conceptual proof to the well-known fact that these two homotopy categories are equivalent. 相似文献
126.
We show that extensions of algebraically closed fields induce full and faithful functors between the respective motivic stable
homotopy categories with finite coefficients. 相似文献
127.
利用语音压缩技术和ISDNU接口实现的数字用户环路倍增设备,可在一对用户线上传输多路高质量的话音或数据。介绍了该系统的技术基础、传输结构和软硬实现及其监控管理功能。 相似文献
128.
D.S. Franzblau 《Discrete Applied Mathematics》2008,156(10):1623-1632
A set cover for a set S is a collection C of special subsets whose union is S. Given covers A and B for two sets, the set-cover difference problem is to construct a new cover for the elements covered by A but not B. Applications include testing equivalence of set covers and maintaining a set cover dynamically. In this paper, we solve the set-cover difference problem by defining a difference operation A-B, which turns out to be a pseudocomplement on a distributive lattice. We give an algorithm for constructing this difference, and show how to implement the algorithm for two examples with applications in computer science: face covers on a hypercube, and rectangle covers on a grid. We derive an upper bound on the time complexity of the algorithm, and give upper and lower bounds on complexity for face covers and rectangle covers. 相似文献
129.
Schlosser 《Constructive Approximation》2008,19(2):163-178
Abstract. We give an r -dimensional generalization of H. S. Shukla's very-well-poised
8
ψ
8
summation formula. We work in the setting of multiple basic hypergeometric series very-well-poised over the root system
A
r-1
or, equivalently, the unitary group U(r) . Our proof, which is already new in the one-dimensional case, utilizes an A
r-1
nonterminating very-well-poised
6
φ
5
summation by S. C. Milne, a partial fraction decomposition, and analytic continuation. 相似文献
130.
Mahmoud Benkhalifa 《Topology and its Applications》2008,155(12):1350-1370
The purpose of this paper is to classify the quasi-isomorphism classes of 1-connected minimal free cochain algebras over a commutative ring. Our tool to address this problem is a “certain” long sequence, called the Whitehead exact sequence, which we construct for every such algebra. We introduce the notion of coherent isomorphisms between these exact sequences and we show that two 1-connected minimal free cochain algebras are quasi-isomorphic if and only if their respective Whitehead exact sequences are coherently isomorphic. 相似文献