全文获取类型
收费全文 | 2621篇 |
免费 | 56篇 |
国内免费 | 13篇 |
专业分类
化学 | 1611篇 |
晶体学 | 21篇 |
力学 | 77篇 |
数学 | 322篇 |
物理学 | 659篇 |
出版年
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2016年 | 32篇 |
2015年 | 35篇 |
2014年 | 39篇 |
2013年 | 102篇 |
2012年 | 118篇 |
2011年 | 147篇 |
2010年 | 64篇 |
2009年 | 59篇 |
2008年 | 137篇 |
2007年 | 133篇 |
2006年 | 144篇 |
2005年 | 125篇 |
2004年 | 106篇 |
2003年 | 79篇 |
2002年 | 84篇 |
2001年 | 45篇 |
2000年 | 45篇 |
1999年 | 26篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 43篇 |
1995年 | 37篇 |
1994年 | 51篇 |
1993年 | 62篇 |
1992年 | 47篇 |
1991年 | 46篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 34篇 |
1982年 | 25篇 |
1981年 | 40篇 |
1980年 | 37篇 |
1979年 | 37篇 |
1978年 | 37篇 |
1977年 | 35篇 |
1976年 | 31篇 |
1975年 | 31篇 |
1974年 | 32篇 |
1973年 | 38篇 |
1972年 | 23篇 |
1971年 | 12篇 |
排序方式: 共有2690条查询结果,搜索用时 31 毫秒
1.
An optimal control model of exhaustible resources is used to clarify the long run relationship between mineral rent and depletion cost at the industry level. A standard first order condition of the time rate of change of rents is reformulated to reveal that rent data may be used to help forecast the rise in extraction costs resulting from resource depletion. This application of the theory of exhaustible resources is illustrated using historical mineral industry rent and extraction cost data. A forecast of U.S. coal extraction costs, following the method proposed in this paper, suggests that future rates of extraction cost increases will be similar to rates experienced in the past. 相似文献
2.
Michael K. Kinyon Kenneth Kunen J. D. Phillips 《Proceedings of the American Mathematical Society》2002,130(3):619-624
An A-loop is a loop in which every inner mapping is an automorphism. A problem which had been open since 1956 is settled by showing that every diassociative A-loop is Moufang.
3.
4.
5.
6.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
7.
T. Brian Cavitt Brian Phillips Charles E. Hoyle Bo Pan Sukhendu B. Hait Kalyanaraman Viswanathan Sonny Jnsson 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):4009-4015
Three‐component photoinitiators comprised of an N‐arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron‐deficient N‐arylphthalimide resulted in a greater acrylate polymerization rate than an electron‐rich N‐arylphthalimide. Triplet energies of each N‐arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N‐arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron–proton transfer from an intermediate radical species to the N‐arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009–4015, 2004 相似文献
8.
Aric Opdahl Roger A. Phillips Gabor A. Somorjai 《Journal of Polymer Science.Polymer Physics》2004,42(3):421-432
The surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004 相似文献
9.
H. M. Phillips D. L. Callahan R. Sauerbrey G. Szabo Z. Bor 《Applied Physics A: Materials Science & Processing》1992,54(2):158-165
Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. The characteristics of this interferometer as it applies to the ablation of these line structures, including linewidth and alignment sensitivity, are analyzed. The ability to control the linewidth by varying the average incident fluence is described theoretically and demonstrated experimentally. This externally generated period of 167 nm also prevents the spontaneous growth of laser induced periodic surface structures (LIPSS). 相似文献
10.