全文获取类型
收费全文 | 41966篇 |
免费 | 1150篇 |
国内免费 | 167篇 |
专业分类
化学 | 26982篇 |
晶体学 | 331篇 |
力学 | 721篇 |
综合类 | 4篇 |
数学 | 7345篇 |
物理学 | 7900篇 |
出版年
2023年 | 266篇 |
2022年 | 497篇 |
2021年 | 647篇 |
2020年 | 625篇 |
2019年 | 691篇 |
2018年 | 776篇 |
2017年 | 722篇 |
2016年 | 1421篇 |
2015年 | 1144篇 |
2014年 | 1232篇 |
2013年 | 2572篇 |
2012年 | 2530篇 |
2011年 | 2716篇 |
2010年 | 1722篇 |
2009年 | 1644篇 |
2008年 | 2391篇 |
2007年 | 2322篇 |
2006年 | 2111篇 |
2005年 | 1975篇 |
2004年 | 1669篇 |
2003年 | 1370篇 |
2002年 | 1172篇 |
2001年 | 880篇 |
2000年 | 788篇 |
1999年 | 619篇 |
1998年 | 472篇 |
1997年 | 460篇 |
1996年 | 561篇 |
1995年 | 415篇 |
1994年 | 444篇 |
1993年 | 406篇 |
1992年 | 383篇 |
1991年 | 350篇 |
1990年 | 326篇 |
1989年 | 278篇 |
1988年 | 268篇 |
1987年 | 257篇 |
1986年 | 260篇 |
1985年 | 333篇 |
1984年 | 350篇 |
1983年 | 231篇 |
1982年 | 254篇 |
1981年 | 250篇 |
1980年 | 249篇 |
1979年 | 178篇 |
1978年 | 179篇 |
1977年 | 187篇 |
1976年 | 154篇 |
1975年 | 144篇 |
1973年 | 139篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Under intrinsic and extrinsic curvature assumptions on a Riemannian spin manifold and its boundary, we show that there is
an isomorphism between the restriction to the boundary of parallel spinors and extrinsic Killing spinors of non-negative Killing constant. As a corollary, we prove that a complete Ricci-flat spin manifold with mean-convex boundary
isometric to a round sphere, is necessarily a flat disc.
Received: 2 February 2002; in final form: 1 August 2002 /
Published online: 1 April 2003
Mathematics Subject Classification (1991): 53C27, 53C40, 53C80, 58G25
The authors would like to thank Lars Andersson for helpful discussions and for bringing to our knowledge the information
regarding Remark 4. We are also grateful to the referee for pointing out that Corollary 5 and Corollary 6 are only valid when
the boundary is at least 2-dimensional.
Research of S. Montiel is partially supported by a Spanish MCyT grant No. BFM2001-2967 相似文献
122.
123.
Synthesis and Structure of K3N Two phases in the binary system K/N have been obtained via co‐deposition of potassium and nitrogen onto polished sapphire at 77 K and subsequent heating to room temperature. The powder diffraction pattern of one of these phases can be satisfactorily interpreted by assuming the composition K3N, and the anti‐TiI3 structure‐type, which is also adopted by Cs3O. The resulting hexagonal lattice constants are: a = 779.8(2), c = 759.2(9) pm, Z = 2, P63/mcm. Comparison with possible structures of K3N generated by computational methods and refined at Hartree‐Fock‐ and DFT level, reveals that the energetically most favoured structure has not formed (presumable Li3P‐type), but instead one of those with very low density. In this respect, the findings for K3N are analogous to the results on Na3N. The thermal evolution of the deposited starting mixture has been investigated. Hexagonal K3N transforms to another K/N phase at 233 K. Its XRD can be fully indexed resulting in an orthorhombic cell a = 1163, b = 596, c = 718 pm. Decomposition leaving elemental potassium as the only residue occurs at 263 K. 相似文献
124.
Leibniz agebras are a generalization of Lie algebras, where no symmetry properties of the bracket are required. In this Letter we introduce a notion of R-matrices for this structure and the related Yang–Baxter equations, and discuss some of their basic properties. 相似文献
125.
126.
In this paper, we use an algebraic type of closure, which is called vector closure, and through it we introduce some adaptations to the proper efficiency in the sense of Hurwicz, Benson, and Borwein in real linear spaces without any particular topology. Scalarization, multiplier rules, and saddle-point theorems are obtained in order to characterize the proper efficiency in vector optimization with and without constraints. The usual convexlikeness concepts used in such theorems are weakened through the vector closure. 相似文献
127.
The field of photonic crystals has, over the past few years, received dramatically increased attention. Photonic crystals are artificially engineered structures that exhibit a periodic variation in one, two, or three dimensions of the dielectric constant, with a period of the order of the pertinent light wavelength. Such structures in three dimensions should exhibit properties similar to solid-state electronic crystals, such as bandgaps, in other words wavelength regions where light cannot propagate in any direction. By introducing defects into the periodic arrangement, the photonic crystals exhibit properties analogous to those of solid-state crystals. The basic feature of a photonic bandgap was indeed experimentally demonstrated in the beginning of the 1990s, and sparked a large interest in, and in many ways revitalized, photonics research. There are several reasons for this attention. One is that photonic crystals, in their own right, offer a proliferation of challenging research tasks, involving a multitude of disciplines, such as electromagnetic theory, nanofabrication, semi-conductor technology, materials science, biotechnology, to name a few. Another reason is given by the somewhat more down-to-earth expectations that photonics crystals will create unique opportunities for novel devices and applications, and contribute to solving some of the issues that have plagued photonics such as large physical sizes, comparatively low functionality, and high costs. Herein, we will treat some basics of photonic crystal structures and discuss the state-of-the-art in fabrication as well give some examples of devices with unique properties, due to the use of photonic crystals. We will also point out some of the problems that still remain to be solved, and give a view on where photonic crystals currently stand. 相似文献
128.
K. Migléczi Gy. Somorjai M. Pátfalusi G. Tóth Gy. Horváth I. Hazai 《Chromatographia》2004,60(1):S67-S74
GYKI-16084 – (+)-(R)-2-{3-(benzo[1,4]dioxan-2-yl-methylamino)-1-propyl}-3(2H)-pyridazinone hydrochloride – is a new drug candidate for the treatment of benign prostatic hyperplasia. In our study the major metabolites formed in the rat and dog were isolated from dog and rat urine, then their structures were elucidated by means of MS and NMR. A two stage solid phase extraction (SPE) procedure and a semi-preparative HPLC method were developed utilizing various mechanisms of separation. The major metabolites proved to be isomeric glucuronides of the benzodioxane moiety hydroxylated at positions 6 or 7 and {2-(2-carboxyethyl)-3(2H)-pyridazinone}. 相似文献
129.
The quality of the surface of metallic wires is relevant for different applications. The reflection of a laser beam on the surface of a metallic cylindrical wire provides an efficient way to inspect the quality of its surface. Our interest is focused in the detection of axially oriented defects, which are the most relevant for the wire drawing process. We present a simple interference-geometrical model to describe the light pattern reflected from a wire with defects. This model adequately accounts for the observed results from an industrial prototype developed for the purpose. It incorporates three-laser beams incident on the wire at equidistant locations in its perimeter, which produce three reflection cones with a CCD. This configuration permits to explore the whole perimeter of the wire. Several results are presented, both in static operation and in production line, in agreement with qualitative and quantitative predictions. 相似文献
130.