全文获取类型
收费全文 | 3561篇 |
免费 | 100篇 |
国内免费 | 14篇 |
专业分类
化学 | 2458篇 |
晶体学 | 22篇 |
力学 | 42篇 |
数学 | 507篇 |
物理学 | 646篇 |
出版年
2022年 | 23篇 |
2021年 | 25篇 |
2020年 | 44篇 |
2019年 | 52篇 |
2018年 | 23篇 |
2016年 | 70篇 |
2015年 | 73篇 |
2014年 | 89篇 |
2013年 | 107篇 |
2012年 | 148篇 |
2011年 | 180篇 |
2010年 | 110篇 |
2009年 | 83篇 |
2008年 | 121篇 |
2007年 | 154篇 |
2006年 | 174篇 |
2005年 | 162篇 |
2004年 | 105篇 |
2003年 | 101篇 |
2002年 | 103篇 |
2001年 | 91篇 |
2000年 | 68篇 |
1999年 | 55篇 |
1998年 | 53篇 |
1997年 | 48篇 |
1996年 | 58篇 |
1995年 | 71篇 |
1994年 | 58篇 |
1993年 | 54篇 |
1992年 | 66篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 50篇 |
1987年 | 56篇 |
1986年 | 36篇 |
1985年 | 49篇 |
1984年 | 40篇 |
1983年 | 31篇 |
1982年 | 36篇 |
1981年 | 43篇 |
1980年 | 48篇 |
1979年 | 34篇 |
1978年 | 40篇 |
1977年 | 41篇 |
1976年 | 43篇 |
1975年 | 42篇 |
1974年 | 50篇 |
1973年 | 43篇 |
1971年 | 27篇 |
排序方式: 共有3675条查询结果,搜索用时 15 毫秒
81.
Richard Steiner 《Applied Categorical Structures》1993,1(3):247-284
The theory of directed complexes is a higher-dimensional generalisation of the theory of directed graphs. In a directed graph, the simple directed paths form a subset of the free category which they generate; if the graph has no directed cycles, then the simple directed paths constitute the entire category. Generalising this, in a directed complex there is a class of split subsets which is contained in and generates a free -category; when a simple loop-freeness condition is satisfied, the split sets constitute the entire -category. The class of directed complexes is closed under the natural product and join constructions. The free -categories generated by directed complexes include the important examples associated to cubes and simplexes. 相似文献
82.
Vaporization of Silver in a Stream of Oxygen Using a transport equipment the vaporization of silver at 611–721°C in a stream of oxygen has been measured. Experiments with detachable cuffs of silver or with wools of silver in a bulb made from quartzglass or silver lead to the same results. By variation of the O2-pressure and the activity of silver is observed that the vaporization happens as Ag2O,g, see “Inhaltsübersicht”. The solid was at first pure silver. During long lasting experiments, however, it is covered with a thin layer of oxygen or silver oxide, which lowers the concentration of Ag2O,g in the equilibrium gas to a smaller, yet constant value. The following measurements using N2 as carrier gas lead to the decomposition of this layer and ends with the very small vapor pressure of silver. The layer of oxygen or silver oxide on the metal could be shown after Davies [2] using mercury. 相似文献
83.
The potential of micellar electrokinetic capillary chromatography (MEKC) with UV-detection for the simultaneous determination of various selected pesticides in water samples was investigated. The developed method using solid-phase extraction showed high efficiency and good resolution with detection limits in the 0.2 to 0.5 ppm range. Comparison of several SPE cartridges demonstrates their suitability for the extraction of pesticides with different hydrophobicity achieving 5000-fold enrichment. The described method involving SPE procedure and MEKC separation enables the successful determination of a wide spectrum of pesticides in water in the range of maximum residue limits (MRLs). 相似文献
84.
The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process. 相似文献
85.
Harald Rotzsche und Harald Rösler 《Fresenius' Journal of Analytical Chemistry》1961,181(1):407-417
Zusammenfassung Bei der Herstellung von Siliconkautschuk verursachte eine uns nicht bekannte Komponente im Ausgangsmaterial Octamethylcyclotetrasiloxan Schwierigkeiten. Es traten bei der Polymerisation mitunter unerwünschte Vernetzungen auf. Gaschromatographisch wurde festgestellt, daß das Vorprodukt Dimethyldichlorsilan noch Methylhydrodichlorsilan enthielt. In dem aus einem solchen Dimethyldichlorsilan hergestellten Octamethylcyclotetrasiloxan fanden wir ebenfalls gaschromatographisch zwischen 0,02 und 0,2% einer uns nicht bekannten Substanz, die an Silicium gebundenen Wasserstoff aufwies. Die gleiche Substanz konnte durch Cohydrolyse der beiden Chlorsilane neben anderen cyclischen Verbindungen dargestellt und isoliert werden. Ihr Retentionsvolumen wurde unter anderem an der Verteilungsflüssigkeit Siliconöl DC 703 bestimmt. Trug man die Logarithmen der Retentionsvolumina dieser cyclischen Verbindungen als Funktion des Molgewichtes auf, so zeigte sich, daß es sich bei dem störenden Bestandteil um Heptamethylcyclotetrasiloxan handelte. An Modellgemischen wurde festgestellt, daß diese Verbindung die D4-Polymerisation tatsächlich stört.Auf die gleiche Weise konnte eine Reihe anderer, bisher noch nicht beschriebener Cyclosiloxane mit Si-H-Bindungen in dem Cohydrolysat aus (CH3)2SiCl2 und CH3HSiCl2 festgestellt werden. In einer Tabelle sind die effektiven und relativen Retentionsvolumina von 18 Cyclosiloxanen angegeben.Bei mehreren dieser Verbindungen sind diese gaschromatographischen Kennzahlen die ersten gemessenen physikalisch-chemischen Daten, da die Mehrzahl der Methylhydrocyclosiloxane noch nicht in reiner Form isoliert worden ist.50. Mitteilung: Rich. Müller, R. Köhne u. S. Sliwinski, J. prakt. Chem., [4] 11, 336 (1960). 相似文献
86.
Siegfried Steiner 《manuscripta mathematica》1985,52(1-3):21-35
It is well known (and rather trivial to prove) that the square F2 of a Finsler norm F:TM on a differentiable manifold M is differentiable at the zero section if and only if F is the norm function of a Riemannian metric. However, the corresponding question for a general p-areal on M is far less trivial to settle and leads to interesting algebraic and combinatorial problems concerning multiquadratic forms. For p=2, the results are closely related to known properties of the curvature tensor of a Riemannian metric. 相似文献
87.
88.
George Hohlneicher Harald Pulm Hans-Joachim Freund 《Journal of Electron Spectroscopy and Related Phenomena》1985,37(2):209-224
First, we show that the quantity Δβ(i) = ΔEA(kii) + 2ΔEB(i) — ΔEB(k) is directly related to the final state relaxation contribution ΔER(i) of the binding energy shift ΔEB(i). ΔEA(kii) is the kinetic energy shift of the Auger transition which corresponds to the decay of a hole state with a hole in level k into a final state with two holes in level i. The shift parameter Δβ(i), which is based on information on two binding energies, is conceptually similar to Wagner's Auger parameter. To establish the relation between Δβ(i) and ΔR(i) one needs, however, less drastic approximations than in the case of Auger parameter shifts. The only approximation necessary is the assumption that ΔR(i) is determined by coulomb contributions.Secondly, we use Δβ (i) to analyse the experimental data of eighteen gaseous phosphorus-containing compounds obtained by Sodhi and Cavell1. It is shown that ΔR(P2p) is strongly related to changes in the polarizability of the ligands. The initial state effects derived from our study deviate from those expected on the basis of simple electronegativity considerations. 相似文献
89.
90.
Eric Steiner Carl Djerassi Ernesto Fattorusso Silvana Magno Luciano Mayol Circo Santacroce Donato Sica 《Helvetica chimica acta》1977,60(2):475-481
Two acetylenic steroids, cholest-5-en-23-yn-3β-ol ( 5 ) and 26,27-dinorcholest-5-en-23-yn-3β-ol ( 3 ), and another unsaturated steroidalcohol, stigmasta-5,23-dien-3β-ol ( 7 ), were isolated from the sponge Calyx nicaaensis. The structures of these two acetylenic steroids were established by synthesis. Several attempts to synthesize the marine steroids alcohol calysterol ( 1 ), with a cyclopropene-containing side chain, starting from cholest-5-en-23-yn-3β-ol are also recorded. Addition of ethyl-diazo-acetate to the triple bond was performed, but the reduction to the methyl derivative yielded decomposition products. 相似文献