全文获取类型
收费全文 | 457134篇 |
免费 | 2927篇 |
国内免费 | 882篇 |
专业分类
化学 | 218100篇 |
晶体学 | 7140篇 |
力学 | 24410篇 |
综合类 | 7篇 |
数学 | 61461篇 |
物理学 | 149825篇 |
出版年
2021年 | 4078篇 |
2020年 | 4527篇 |
2019年 | 5374篇 |
2018年 | 7677篇 |
2017年 | 7811篇 |
2016年 | 10253篇 |
2015年 | 5202篇 |
2014年 | 9335篇 |
2013年 | 19210篇 |
2012年 | 15543篇 |
2011年 | 18440篇 |
2010年 | 14324篇 |
2009年 | 14405篇 |
2008年 | 17403篇 |
2007年 | 17398篇 |
2006年 | 15991篇 |
2005年 | 14085篇 |
2004年 | 13416篇 |
2003年 | 12184篇 |
2002年 | 12321篇 |
2001年 | 12813篇 |
2000年 | 10053篇 |
1999年 | 7565篇 |
1998年 | 6717篇 |
1997年 | 6566篇 |
1996年 | 5999篇 |
1995年 | 5495篇 |
1994年 | 5410篇 |
1993年 | 5299篇 |
1992年 | 5658篇 |
1991年 | 6012篇 |
1990年 | 5921篇 |
1989年 | 5708篇 |
1988年 | 5556篇 |
1987年 | 5624篇 |
1986年 | 5187篇 |
1985年 | 6338篇 |
1984年 | 6783篇 |
1983年 | 5692篇 |
1982年 | 6082篇 |
1981年 | 5750篇 |
1980年 | 5408篇 |
1979年 | 5935篇 |
1978年 | 6103篇 |
1977年 | 6195篇 |
1976年 | 6351篇 |
1975年 | 5875篇 |
1974年 | 5716篇 |
1973年 | 6002篇 |
1972年 | 4578篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
993.
The possible types of ordering diagrams of ternary substutional alloys with an fcc lattice are analyzed, taking account of interactions in two coordination spheres.Ural Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 38–41, December, 1992. 相似文献
994.
Dr.-Ing. M. Millies Dipl.-Ing. St. v. Bose Dipl.-Ing. A. Tokarz Univ.-Prof.Dr.-Ing. D. Mewes 《Heat and Mass Transfer》1994,30(1):17-25
The common methods for calculating the mass transfer across liquid-liquid interfaces in technical applications take into account the mass transfer resistances within the bulk phases. The transfer resistance of the interface and a possible coupling between the momentum and the mass transport is not taken into account. In the present paper a survey is given of theoretical approaches which can describe this coupling and the additional mass transfer resistance. A theory is proposed by Hampe which can be used to explain the coupling between momentum and mass transport employing thermodynamics of irreversible processes. On the basis of this work, the influence of the dilatation of a flat interface on the mass transfer is deduced. It is also concluded from this theory that the diffusion coefficients within the bulk phases are coupled near the thermodynamic equilibrium. 相似文献
995.
Novel 3-phenyloxy substituted propane-1,2-diol derivatives, 4-(4-n-hexyloxyphenyl)-butane-1,2-diol and 4-(trans-4-n-pyropylcyclohexyl)-butane-1,2-diol have been synthesized and their thermal behaviour has been studied. These compounds exhibit thermotropic and, after addition of water, also lyotropic liquid-crystalline behaviour. The clearing temperatures of the smectic mesophases were found to be strongly dependent on the alkyl chain length and on the structural units that link the aromatic ring to the alkyl chain and to the diol unit. The behaviour of the aromatic compounds is compared with that of the cyclohexane derivative. Thereby it has been realized that the mesophase stability of the amphiphilic diols incorporating a rigid unit is largely determined by both, the molecular geometry (molecular shape and intramolecular flexibility) and the amphiphilic structural pattern. 相似文献
996.
997.
Keka Chakraborty S K Paranjpe V Siruguri O D Jayakumar S K Kulshreshtha 《Pramana》1997,48(6):1115-1122
Neutron diffraction and M?ssbauer measurements have been carried out on the cubic Laves phase intermetallic TbMnFe. The magnetic
moment on the transition metal atom is found to be low, 0.2μ
B, at room temperature. This moment is temperature independent down to 10 K. Magnetic moment on the rare earth atom varies
from 2.5μ
B at 296 K to 7.27μ
B at 10 K. M?ssbauer spectra recorded at 298 K and 78 K have magnetic character but there is a large distribution of hyperfine
field values. Both these features arise due to magnetic frustration created in the sample due to the competing ferro and antiferromagnetic
interactions between the transition metal atoms. 相似文献
998.
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
999.
D. Trunec 《等离子体物理论文集》1992,32(5):523-534
In the paper new methods of the computation of second-order derivative of probe characteristic are proposed. All methods are tested on testing data as well as on experimental measured probe characteristic. 相似文献
1000.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation. 相似文献