全文获取类型
收费全文 | 370843篇 |
免费 | 5050篇 |
国内免费 | 1388篇 |
专业分类
化学 | 187518篇 |
晶体学 | 4718篇 |
力学 | 17470篇 |
综合类 | 2篇 |
数学 | 66109篇 |
物理学 | 101464篇 |
出版年
2021年 | 2128篇 |
2020年 | 2609篇 |
2019年 | 2740篇 |
2018年 | 12989篇 |
2017年 | 12690篇 |
2016年 | 11094篇 |
2015年 | 4644篇 |
2014年 | 5610篇 |
2013年 | 14336篇 |
2012年 | 14353篇 |
2011年 | 22931篇 |
2010年 | 13602篇 |
2009年 | 13623篇 |
2008年 | 17950篇 |
2007年 | 19971篇 |
2006年 | 11145篇 |
2005年 | 11356篇 |
2004年 | 10426篇 |
2003年 | 9623篇 |
2002年 | 8652篇 |
2001年 | 8408篇 |
2000年 | 6520篇 |
1999年 | 5046篇 |
1998年 | 4386篇 |
1997年 | 4316篇 |
1996年 | 4245篇 |
1995年 | 3907篇 |
1994年 | 3767篇 |
1993年 | 3912篇 |
1992年 | 4034篇 |
1991年 | 3901篇 |
1990年 | 3737篇 |
1989年 | 3629篇 |
1988年 | 3715篇 |
1987年 | 3532篇 |
1986年 | 3411篇 |
1985年 | 4703篇 |
1984年 | 4820篇 |
1983年 | 3977篇 |
1982年 | 4325篇 |
1981年 | 4216篇 |
1980年 | 4085篇 |
1979年 | 4067篇 |
1978年 | 4329篇 |
1977年 | 4119篇 |
1976年 | 4249篇 |
1975年 | 3811篇 |
1974年 | 3945篇 |
1973年 | 4247篇 |
1972年 | 2566篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
181.
182.
TGA, DTA and DSC analyses indicate that benzotriazole is significantly more stable thermally than 1,2,3-triazole. 相似文献
183.
We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
184.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
185.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
186.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
187.
Hugh Thomas 《Order》2006,23(2-3):249-269
In this paper, we study lattices that posess both the properties of being extremal (in the sense of Markowsky) and of being left modular (in the sense of Blass and Sagan). We call such lattices trim and show that they posess some additional appealing properties, analogous to those of a distributive lattice. For example, trimness is preserved under taking intervals and suitable sublattices. Trim lattices satisfy a weakened form of modularity. The order complex of a trim lattice is contractible or homotopic to a sphere; the latter holds exactly if the maximum element of the lattice is a join of atoms. Any distributive lattice is trim, but trim lattices need not be graded. The main example of ungraded trim lattices are the Tamari lattices and generalizations of them. We show that the Cambrian lattices in types A and B defined by Reading are trim; we conjecture that all Cambrian lattices are trim. 相似文献
188.
189.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
190.
Abstract Under a suitable ellipticity condition, we show that classical SG-pseudodifferential operators of nonnegative order possess
complex powers. We show that the powers are again classical and derive an explicit formula for all homogeneous components.
Keywords: Complex power, Weighted symbols, Noncompact manifolds 相似文献