全文获取类型
收费全文 | 8127篇 |
免费 | 365篇 |
国内免费 | 37篇 |
专业分类
化学 | 5687篇 |
晶体学 | 20篇 |
力学 | 203篇 |
数学 | 1398篇 |
物理学 | 1221篇 |
出版年
2023年 | 77篇 |
2022年 | 112篇 |
2021年 | 135篇 |
2020年 | 189篇 |
2019年 | 190篇 |
2018年 | 115篇 |
2017年 | 115篇 |
2016年 | 357篇 |
2015年 | 314篇 |
2014年 | 296篇 |
2013年 | 472篇 |
2012年 | 554篇 |
2011年 | 652篇 |
2010年 | 378篇 |
2009年 | 321篇 |
2008年 | 515篇 |
2007年 | 462篇 |
2006年 | 438篇 |
2005年 | 410篇 |
2004年 | 347篇 |
2003年 | 315篇 |
2002年 | 288篇 |
2001年 | 169篇 |
2000年 | 121篇 |
1999年 | 120篇 |
1998年 | 93篇 |
1997年 | 102篇 |
1996年 | 103篇 |
1995年 | 85篇 |
1994年 | 59篇 |
1993年 | 62篇 |
1992年 | 53篇 |
1991年 | 35篇 |
1990年 | 36篇 |
1989年 | 29篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 31篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 21篇 |
1977年 | 13篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1970年 | 8篇 |
排序方式: 共有8529条查询结果,搜索用时 15 毫秒
151.
Serdar Serdas Alexander Schwarz Jörg Schröder Stefan Turek Abderrahim Ouazzi Masoud Nickaeen 《PAMM》2014,14(1):623-624
In this contribution we present the least-squares finite element method (LSFEM) for the incompressible Navier-Stokes equations. In detail, we consider a non-Newtonian fluid flow, which is described by a power-law model, see [1]. The second-order problem is reformulated by introducing a first-order div-grad system consisting of the equilibrium condition, the incompressibility condition and the constitutive equation, which are written in residual forms, see [2]. Here, higher-order finite elements which are an important aspect regarding accuracy for the present formulation are investigated. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
152.
H Stahnke S Kittlaus G Kempe C Hemmerling L Alder 《Journal of mass spectrometry : JMS》2012,47(7):875-884
This study investigates to which extent the design of electrospray ion sources influences the susceptibility to matrix effects (MEs) in liquid chromatography-tandem mass spectrometry (LC-MS/MS). For this purpose, MEs were measured under comparable conditions (identical sample extracts, identical LC column, same chromatographic method and always positive ion mode) on four LC-MS/MS instrument platforms. The instruments were combined with five electrospray ion sources, viz. Turbo Ion Spray, Turbo V(TM) Source, Standard ESI, Jet Stream ESI and Standard Z-Spray Source. The comparison of MEs could be made at all retention times because the method of permanent postcolumn infusion was applied. The MEs ascertained for 45 pesticides showed for each electrospray ion source the same pattern, i.e. the same number of characteristic signal suppressions at equivalent retention times in the chromatogram. The Turbo Ion Spray (off-axis geometry), Turbo V(TM) Source (orthogonal geometry) and the Standard Z-Spray Source (double orthogonal geometry) did not differ much in their susceptibility to MEs. The Jet Stream ESI (orthogonal geometry) reaches a higher sensitivity by an additional heated sheath gas, but suffers at the same time from significantly stronger signal suppressions than the comparable Standard ESI (orthogonal geometry) without sheath gas. No relation between source geometry and extent of signal suppression was found in this study. 相似文献
153.
154.
The purpose of this paper is to present optimal preconditioned iterative methods to solve indefinite linear systems of equations arising from symmetric coupling of finite elements and boundary elements. This is a block‐diagonal preconditioner together with a conjugate residual method and a preconditioned inner–outer iteration. We prove the efficiency of these methods by showing that the number of iterations to preserve a given accuracy is bounded independent of the number of unknowns. Numerical examples underline the efficiency of these methods. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
155.
In this study, we start from a multi-source variant of the two-stage capacitated facility location problem (TSCFLP) and propose a robust optimization model of the problem that involves the uncertainty of transportation costs. Since large dimensions of the robust TSCFLP could not be solved to optimality, we design a memetic algorithm (MA), which represents a combination of an evolutionary algorithm (EA) and a modified simulated annealing heuristic (SA) that uses a short-term memory of undesirable moves from previous iterations. A set of computational experiments is conducted to examine the impact of different protection levels on the deviation of the objective function value. We also investigate the impact of variations of transportation costs that may occur on both transhipment stages on the total cost for a fixed protection level. The obtained results may help in identifying a sustainable and efficient strategy for designing a two stage capacitated transportation network with uncertain transportation costs, and may be applicable in the design and management of similar transportation networks. 相似文献
156.
Stefan Pitsch Patrick A. Weiss Xiaolin Wu Damian Ackermann Thomas Honegger 《Helvetica chimica acta》1999,82(10):1753-1761
Two sets of RNA phosphoramidites, carrying the (fluoride-labile) 2′-O-[(triisopropylsilyl)oxy]methyl (=tom) group and the (photolabile) [(R)-1-(2-nitrophenyl)ethoxy]methyl (=(R)-npeom) group, were prepared (see 1 – 4 and 5 – 8 , resp.). The two protecting groups were completely orthogonal to each other. Three ribozyme-substrate constructs, protected each by a (R)-npeom group, were synthesized; on photolysis, efficient cleavage of this remaining protecting group occurred (Scheme 3). It could be demonstrated that the presence of one (R)-npeom group within a RNA strand has only a minor influence on the pairing properties of corresponding duplexes. 相似文献
157.
Cover Picture: Absolute Configuration from Different Multifragmentation Pathways in Light‐Induced Coulomb Explosion Imaging (ChemPhysChem 16/2016) 下载免费PDF全文
Dr. Martin Pitzer Gregor Kastirke Dr. Maksim Kunitski Dr. Till Jahnke Dr. Tobias Bauer Christoph Goihl Florian Trinter Carl Schober Kevin Henrichs Jasper Becht Stefan Zeller Helena Gassert Markus Waitz Andreas Kuhlins Hendrik Sann Felix Sturm Florian Wiegandt Dr. Robert Wallauer Dr. Lothar Ph. H. Schmidt Allan S. Johnson Manuel Mazenauer Benjamin Spenger Sabrina Marquardt Sebastian Marquardt Prof. Dr. Horst Schmidt‐Böcking Prof. Dr. Jürgen Stohner Prof. Dr. Reinhard Dörner Dr. Markus Schöffler Prof. Dr. Robert Berger 《Chemphyschem》2016,17(16):2448-2448
158.
Dietmar Fratzky Matthias Schneider Stefan Rabe Manfred Meisel 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):740-741
Tetraammonium disodium decavanadate decahydrate crystallizes in the triclinic system in space group P. The structure contains typical centrosymmetric OV6 double octahedra and centrosymmetric pairs of edge‐shared NaO6 double octahedra forming a layered structure. In contrast to other monovalent cationic decavanadates, the NaO6 double octahedra are integrated in the layer. 相似文献
159.
A straightforward chiral pool synthesis for the glycosidase inhibitor calystegine A7 (isolated from Lycium chinense) from methyl α-d-glucopyranoside is described. Keysteps of this synthesis include a ultrasound assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst mediated ring closure metathesis. 相似文献
160.
Tavana H Yang G Yip CM Appelhans D Zschoche S Grundke K Hair ML Neumann AW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(2):628-636
Contact angles of a series of n-alkanes (i.e., n-heptane to n-hexadecane) are studied on two functionalized maleimide copolymers (i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF)). On the homogeneous ETMF films, all liquids show a smooth motion of the three-phase line. In contrast, on ODMF surfaces that are found to consist of mainly fluorocarbons and small patches of hydrocarbons, short-chain n-alkanes show a stick-slip pattern. By increasing the chain length of the probe liquids, stick-slip is reduced significantly. The phenomenon is discussed in the framework of the Cassie equation. It is found that the upper limit of contact angles in the stick-slip pattern is given by the advancing angle that would be obtained on the pure fluorocarbon surface, whereas the lower limit of the stick-slip pattern is given by the Cassie angle. 相似文献