全文获取类型
收费全文 | 410460篇 |
免费 | 4222篇 |
国内免费 | 1254篇 |
专业分类
化学 | 223433篇 |
晶体学 | 6698篇 |
力学 | 17467篇 |
综合类 | 19篇 |
数学 | 42746篇 |
物理学 | 125573篇 |
出版年
2021年 | 3025篇 |
2020年 | 3492篇 |
2019年 | 3821篇 |
2018年 | 4567篇 |
2017年 | 4717篇 |
2016年 | 7325篇 |
2015年 | 4689篇 |
2014年 | 7115篇 |
2013年 | 18440篇 |
2012年 | 14228篇 |
2011年 | 17436篇 |
2010年 | 11932篇 |
2009年 | 12136篇 |
2008年 | 15754篇 |
2007年 | 15527篇 |
2006年 | 14792篇 |
2005年 | 13394篇 |
2004年 | 12251篇 |
2003年 | 10983篇 |
2002年 | 10746篇 |
2001年 | 12703篇 |
2000年 | 9660篇 |
1999年 | 7366篇 |
1998年 | 5865篇 |
1997年 | 5740篇 |
1996年 | 5491篇 |
1995年 | 5039篇 |
1994年 | 4851篇 |
1993年 | 4593篇 |
1992年 | 5508篇 |
1991年 | 5418篇 |
1990年 | 5106篇 |
1989年 | 5120篇 |
1988年 | 5081篇 |
1987年 | 5000篇 |
1986年 | 4739篇 |
1985年 | 6402篇 |
1984年 | 6476篇 |
1983年 | 5210篇 |
1982年 | 5434篇 |
1981年 | 5319篇 |
1980年 | 5065篇 |
1979年 | 5348篇 |
1978年 | 5506篇 |
1977年 | 5597篇 |
1976年 | 5307篇 |
1975年 | 5021篇 |
1974年 | 4941篇 |
1973年 | 4934篇 |
1972年 | 3249篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
181.
182.
Audrey A S G Lonni Ieda S Scarminio Lucas M C Silva Dalva T Ferreira 《Analytical sciences》2003,19(7):1013-1017
Phytochemical investigation of the aerial parts of three Baccharis species (Asteraceae family) was performed using HPLC and chemometric methods, with the objective of distinguishing between three morphologically very similar species: Baccharis genistelloides Persoon var. trimera (Less.) DC, B. milleflora (Less.) DC and B. articulata (Lam.) Persoon. With the help of Principal Component Analysis (PCA) and variance weights, it was possible to characterize the chromatographic profiles of the alcoholic extracts of the three species. Application of Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN) methods on a training set of 74 extracts resulted in models that correctly classified all eight samples in an independent test set. 相似文献
183.
V. T. Bublik S. Yu. Matsnev K. D. Shcherbachev M. V. Mezhennyi M. G. Mil’vidskii V. Ya. Reznik 《Physics of the Solid State》2003,45(10):1918-1925
Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined. 相似文献
184.
185.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
186.
187.
We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed. 相似文献
188.
189.
Summary A non-destructive method is described for the determination of major and minor constituents in archeological specimens by energy-dispersive X-ray fluorescence. Homogeneity tests are made by measuring at various sites of the specimen. In the same way, mean values are obtained for inhomogeneous specimen without taking samples. For calibration, powder standards are used. In case of the determination of elements with numbers up to 14 (Si) a vacuum chamber is used and the dimensions of the specimens are limited by the dimensions of that vacuum chamber, whereas for the determination of elements from K up to U specimens of any size, form or weight are suitable.
Zerstörungsfreie Analyse von archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse
Zusammenfassung Eine zerstörungsfreie Methode für die Bestimmung von Haupt- und Nebenbestandteilen in archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse wird beschrieben. Für Homogenitätstests wird an mehreren Stellen der Probe gemessen. In der gleichen Weise werden für inhomogene Proben Mittelwerte erhalten ohne Probenahme. Für die Eichung werden Pulverstandards verwendet. Im Falle der Bestimmung von Elementen mit Ordnungszahlen bis 14 (Si) wird eine Vakuumkammer eingesetzt, und die Dimensionen der Proben sind durch die Dimensionen dieser Vakuumkammer begrenzt, während für die Bestimmung der Elemente K bis U Proben jeder Größe, jeder Form oder jeden Gewichts verwendbar sind.相似文献
190.
J. Bartella K. Kastner K. Röll und K. -H. Schuller 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):289-291
Summary Besides functional behaviour of coatings their resistivity against corroding attack is a crucial criterion for quality. The application of special corroding and abrading tests yields after short times predictions about stability of the product in practical use. A number of tests have been applied to thin magnetic storage media. Besides tests of function and visual observations with light- and scanning electron microscopes, AES- and XPS-investigations were applied to discuss corrosion resistivity. 相似文献