全文获取类型
收费全文 | 78143篇 |
免费 | 18552篇 |
国内免费 | 78篇 |
专业分类
化学 | 73344篇 |
晶体学 | 216篇 |
力学 | 2743篇 |
数学 | 8787篇 |
物理学 | 11683篇 |
出版年
2023年 | 4151篇 |
2022年 | 1512篇 |
2021年 | 2620篇 |
2020年 | 4828篇 |
2019年 | 2488篇 |
2018年 | 2618篇 |
2017年 | 972篇 |
2016年 | 6272篇 |
2015年 | 6081篇 |
2014年 | 5618篇 |
2013年 | 6892篇 |
2012年 | 4549篇 |
2011年 | 2877篇 |
2010年 | 4169篇 |
2009年 | 3914篇 |
2008年 | 2759篇 |
2007年 | 2437篇 |
2006年 | 1705篇 |
2005年 | 1483篇 |
2004年 | 1190篇 |
2003年 | 1001篇 |
2002年 | 930篇 |
2001年 | 792篇 |
2000年 | 695篇 |
1999年 | 491篇 |
1997年 | 490篇 |
1996年 | 589篇 |
1995年 | 602篇 |
1994年 | 565篇 |
1993年 | 752篇 |
1992年 | 559篇 |
1990年 | 442篇 |
1985年 | 570篇 |
1984年 | 566篇 |
1983年 | 531篇 |
1982年 | 566篇 |
1981年 | 594篇 |
1980年 | 597篇 |
1979年 | 538篇 |
1978年 | 590篇 |
1977年 | 682篇 |
1976年 | 681篇 |
1975年 | 766篇 |
1974年 | 757篇 |
1973年 | 595篇 |
1972年 | 485篇 |
1971年 | 482篇 |
1970年 | 692篇 |
1969年 | 549篇 |
1968年 | 605篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
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
132.
133.
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
134.
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
135.
Rainer Löwen 《Journal of Geometry》1989,36(1-2):110-116
We prove that a spread S over a locally compact nondlscrete field F defines a topological translation plane if and only if the spread is compact. For F=R, this is implicit in Breuning's thesis [Bre], cf. [B 2]. For the proof, we describe the point set of the projective translation plane as a quotient space of some projective space, with identifications taking place in one hyperplane. This is new even for F=R. 相似文献
136.
Stefan Nörtemann 《Applied Categorical Structures》2002,10(4):417-429
The Hahn–Banach Theorem for partially ordered totally convex modules [3] and a necessary and sufficient condition for the existence of an extension of a morphism from a submodule C
0 of a partially ordered totally convex module C (with the ordered unit ball of the reals as codomain) to C, are proved. Moreover, the categories of partially ordered positively convex and superconvex modules are introduced and for both categories the Hahn–Banach Theorem is proved. 相似文献
137.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
138.
Erik Fooladi Bjrn Dalhus Christian Rmming Mats Tilset 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):m567-m569
In the title compound, [Rh(CH3)2(C2H3N)(C9H21N3)](C24H20B), the geometry around the RhIII centre is distorted octahedral, with elongated Rh—N bonds trans to the metal‐bonded methyl groups. The metal‐containing cations are located in channels formed by an anionic supramolecular mesh, in which aromatic π–π interactions between anionic [B(Ph)4]? units play a major role. 相似文献
139.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
140.
de Souza P. A. Garg V. K. Klingelhöfer G. Gellert R. Gütlich P. 《Hyperfine Interactions》2002,139(1-4):705-714
A portable Mössbauer spectrometer, developed for extraterrestrial applications, opens up new industrial applications of MBS. But for industrial applications, an available tool for fast data analysis is also required, and it should be easy to handle. The analysis of Mössbauer spectra and their parameters is a barrier for the popularity of this wide-applicable spectroscopic technique in industry. Based on experience, the analysis of a Mössbauer spectrum is time-consuming and requires the dedication of a specialist. However, the analysis of Mössbauer spectra, from the fitting to the identification of the sample phases, can be faster using by genetic algorithms, fuzzy logic and artificial neural networks. Industrial applications are very specific ones and the data analysis can be performed using these algorithms. In combination with an automatic analysis, the Mössbauer spectrometer can be used as a probe instrument which covers the main industrial needs for an on-line monitoring of its products, processes and case studies. Some of these real industrial applications will be discussed. 相似文献