全文获取类型
收费全文 | 364043篇 |
免费 | 1579篇 |
国内免费 | 349篇 |
专业分类
化学 | 156477篇 |
晶体学 | 5380篇 |
力学 | 22483篇 |
综合类 | 3篇 |
数学 | 61518篇 |
物理学 | 120110篇 |
出版年
2021年 | 3092篇 |
2020年 | 3413篇 |
2019年 | 4191篇 |
2018年 | 11866篇 |
2017年 | 12350篇 |
2016年 | 10667篇 |
2015年 | 3968篇 |
2014年 | 6932篇 |
2013年 | 12167篇 |
2012年 | 13165篇 |
2011年 | 20445篇 |
2010年 | 14696篇 |
2009年 | 15026篇 |
2008年 | 18746篇 |
2007年 | 21160篇 |
2006年 | 10087篇 |
2005年 | 12394篇 |
2004年 | 10253篇 |
2003年 | 10152篇 |
2002年 | 9155篇 |
2001年 | 7770篇 |
2000年 | 6339篇 |
1999年 | 4525篇 |
1998年 | 4290篇 |
1997年 | 4135篇 |
1996年 | 3904篇 |
1995年 | 3405篇 |
1994年 | 3452篇 |
1993年 | 3455篇 |
1992年 | 3449篇 |
1991年 | 3863篇 |
1990年 | 3865篇 |
1989年 | 3881篇 |
1988年 | 3641篇 |
1987年 | 3719篇 |
1986年 | 3404篇 |
1985年 | 3944篇 |
1984年 | 4196篇 |
1983年 | 3588篇 |
1982年 | 3783篇 |
1981年 | 3468篇 |
1980年 | 3225篇 |
1979年 | 3734篇 |
1978年 | 3809篇 |
1977年 | 3889篇 |
1976年 | 3999篇 |
1975年 | 3725篇 |
1974年 | 3578篇 |
1973年 | 3780篇 |
1972年 | 3217篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Identification of nonlinear elliptic equations 总被引:1,自引:0,他引:1
An optimization theoretic approach and algorithm for the estimation of state-dependent coefficients in nonlinear elliptic equation is presented. It is based on a splitting method combined with convex analysis techniques. Convergence of the algorithm is established and numerical examples are included.The research of K. Kunisch was supported in part by a grant from the Bundesministerium für Wissenschaft und Forschung, Austria. 相似文献
992.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 194, pp. 124–133, 1992. 相似文献
993.
P. C. Morais A. C. Oliveira V. K. Garg M. L. Silva E. F. C. Alcântara F. Q. Soares D. Rabelo 《Hyperfine Interactions》2007,177(1-3):51-56
We have used time-differential perturbed angular correlation (PAC) spectroscopy with 181Ta-probes to study the electric field gradient at Zr-sites in synthetic zircon and hafnon between room temperature and 1,200°C. PAC spectra are similar to those obtained from naturally occurring zircons. In particular, a change in slope of the quadrupole coupling vs. temperature is observed in the synthetic zircon at the same temperature as seen in natural zircons from the Mud Tank carbonatite (Australia). The synthetic hafnon data also shows this feature but at somewhat higher temperature. Low-temperature PAC spectra of both synthetic zircon and hafnon have a clearly reduced anisotropy. We believe that the cause for this is a electronic defect, possibly created during the β-decay of the probe parent nucleus. 相似文献
994.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献
995.
James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2007,45(18):4331-4340
The irradiation of hybrid photopolymer systems consisting of a free radically polymerizable multifunctional acrylate monomer and a cationically polymerizable epoxide or oxetane monomer was conducted under conditions where only the free radical polymerization takes place. This results in the formation of a free‐standing polyacrylate network film containing quiescent oxonium ions along with the unreacted cyclic ether monomer. The subsequent application of a point source of heat to the film ignites a cationic ring‐opening frontal polymerization that emanates from that site and propagates to all portions of the irradiated sample. This article examines the impact of various molecular structural and experimental parameters on these novel hybrid frontal polymerizations that produce interpenetrating network polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4331–4340, 2007 相似文献
996.
With the use of an analytical approach developed, the influence of distribution of a tangential load on the stress concentration
in uniaxially tensioned flat specimens of high-strength unidirectional composites near the grips of a testing machine is evaluated.
In view of singularity of the analytical solution derived at the points of discontinuity of boundary conditions, for estimating
the stress concentration, it is suggested to employ the averaged value of longitudinal stresses, which is calculated by means
of an improper integral across the thickness of a near-surface layer.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 787–796, November–December, 2006. 相似文献
997.
I. V. Gaishun 《Proceedings of the Steklov Institute of Mathematics》2006,255(2):S47-S53
For a linear nonautonomous system with one output, the existence conditions for an identifier that estimates the current state with exponential rate are established. An algorithm for constructing such an identifier is described and its dependence on small perturbations of coefficients is studied. 相似文献
998.
999.
M. N. Vidyakin Yu. N. Lazareva Yu. P. Yampolskii A. Yu. Alentiev D. Yu. Likhachev A. L. Rusanov O. V. Kozlova 《Polymer Science Series A》2006,48(6):596-600
The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H2, He, O2, N2, CO, CO2, and CH4; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases. 相似文献
1000.
The energy band structure, equation of state, density of states, and elastic moduli of a new allotropic carbon modification, namely, fullerite C24 with a simple cubic lattice (known previously as cubic graphite), are calculated by the full-potential linearized augmented-plane-wave (FLAPW) method with geometry optimization for the first time. The dependence of the total energy on the lattice constant exhibits a minimum for a 0 = 0.60546 nm. In this case, the lengths of the C-C bonds between fullerene molecules, the lengths of the 6,6-bonds shared by hexagons, and the lengths of the 4,6-bonds shared by a square and a hexagon are equal to 0.1614, 0.1503, and 0.1637 nm, respectively. An analysis of the energy band structure and the density of states demonstrates that the simple cubic fullerite C24 is a direct-band-gap insulator or a semiconductor with a band gap of 1.6 eV. The calculated bulk modulus B 0 = 196 GPa and the elastic moduli C 11 = 338 GPa, C 12 = 139 GPa, and C 44 = 30 GPa indicate that the fullerite under investigation is a mechanically stable material. The inference is made that the simple cubic fullerite C24 is a new diamond-like molecular zeolite with a unique combination of properties, such as the porosity and nonpolarizability, on the one hand, and the mechanical strength, chemical inertness, and high thermal conductivity, on the other hand. The simple cubic fullerite C24 can be considered a promising low-dielectric-constant (low-k) material (?0 < 5.7) for use in fabricating interconnections and substrates intended for integrated circuits and nanoelectronics. 相似文献