全文获取类型
收费全文 | 502113篇 |
免费 | 5615篇 |
国内免费 | 1851篇 |
专业分类
化学 | 269514篇 |
晶体学 | 7302篇 |
力学 | 21279篇 |
综合类 | 9篇 |
数学 | 61611篇 |
物理学 | 149864篇 |
出版年
2020年 | 3446篇 |
2019年 | 3664篇 |
2018年 | 4978篇 |
2017年 | 4901篇 |
2016年 | 7440篇 |
2015年 | 5546篇 |
2014年 | 7719篇 |
2013年 | 22834篇 |
2012年 | 17329篇 |
2011年 | 21197篇 |
2010年 | 13474篇 |
2009年 | 13464篇 |
2008年 | 18900篇 |
2007年 | 19181篇 |
2006年 | 18218篇 |
2005年 | 18842篇 |
2004年 | 16959篇 |
2003年 | 14362篇 |
2002年 | 13058篇 |
2001年 | 14632篇 |
2000年 | 11241篇 |
1999年 | 8990篇 |
1998年 | 7381篇 |
1997年 | 7217篇 |
1996年 | 7059篇 |
1995年 | 6511篇 |
1994年 | 6183篇 |
1993年 | 6059篇 |
1992年 | 6704篇 |
1991年 | 6645篇 |
1990年 | 6236篇 |
1989年 | 6071篇 |
1988年 | 6298篇 |
1987年 | 5970篇 |
1986年 | 5763篇 |
1985年 | 8171篇 |
1984年 | 8369篇 |
1983年 | 6848篇 |
1982年 | 7468篇 |
1981年 | 7364篇 |
1980年 | 7115篇 |
1979年 | 7198篇 |
1978年 | 7439篇 |
1977年 | 7285篇 |
1976年 | 7354篇 |
1975年 | 6944篇 |
1974年 | 6908篇 |
1973年 | 7253篇 |
1972年 | 4375篇 |
1971年 | 3296篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献
22.
23.
24.
The effect of iodine sorption on the free volume of polycarbonate is investigated by Positron Annihilation Lifetime method.
The observed results are interpreted in terms of the Charge Transfer Complex formation and precipitation of iodine at the
initial and final stages of sorption, respectively. At higher levels of sorption, changes in the second lifetime and its intensity
seem to suggest a conformational transformation, probably due to the net change in the amorphous-crystalline boundary regions
of the polymer matrix. The free volume cavities have been predominantly occupied by I-
3 species and the diffusion process obeys Fick’s law. An exponential type correlation has been observed between fractional
free volume and the diffusion coefficient.
Received: 13 June 1996/Accepted: 20 September 1996 相似文献
25.
We provide a characterization of the limit periodic sets for analytic families of vector fields under the hypothesis that the first jet is non-vanishing at any singular point. Also, applying the family desingularization method, we reduce the complexity of some of these sets. 相似文献
26.
Daniel L. Feldheim Del R. Lawson Charles R. Martin 《Journal of Polymer Science.Polymer Physics》1993,31(8):953-957
We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc. 相似文献
27.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
28.
A simple method is proposed for increasing the accuracy of computation of the eigenvalues of elliptic operators, which does not require high-order accurate schemes.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 63, pp. 63–68, 1987. 相似文献
29.
The reaction of 2-(2 pyridytcarbonyl)benzoic acid with thionyl chloride affords an unexpected product of the intramolecular acylation of the pyridine nitrogen atom, namely, 6,11-dioxo-6,11-dihydrobenzo[blquinotizinium chloride. At the same time, 2-(2-quinotylcarbonyl)benzoic acid forms the expected cyclic acid chloride, namely, 3-(2-gitinotyl)-3-chlorophthalide in this reaction. Both compounds acylate ammonia and primary amines, including those with bulky alkyl groups (tert-butyl, 1-adamantyl, and 1,1,3,3-tetramethylbutyl) with the formation of 2-R-3-hydroxy-3-(2pyridyl- or 2-quinolyl)isoindolines. The protonation of the pyridine nitrogen atom of N-(1,1,3,3-tetramethylbutyl)-2-(2pyridylcarbonyl)benzamide, obtained in the open amide form, is accompanied by the closing of the isoindotinone ring; the deprotonation is accompanied by ring opening.Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 499–504, April, 1994. Original article submitted March 17, 1994. 相似文献
30.
Chromatographia - A theoretical model is used to predict retention times of divalent metal cations in single-column ion chromatography using one or more ligands in the eluent. Stability constants... 相似文献