全文获取类型
收费全文 | 240766篇 |
免费 | 2452篇 |
国内免费 | 556篇 |
专业分类
化学 | 124759篇 |
晶体学 | 3577篇 |
力学 | 11306篇 |
综合类 | 14篇 |
数学 | 28325篇 |
物理学 | 75793篇 |
出版年
2021年 | 2289篇 |
2020年 | 2488篇 |
2019年 | 2927篇 |
2018年 | 4163篇 |
2017年 | 4164篇 |
2016年 | 5852篇 |
2015年 | 3131篇 |
2014年 | 5188篇 |
2013年 | 10446篇 |
2012年 | 8547篇 |
2011年 | 9876篇 |
2010年 | 7696篇 |
2009年 | 7691篇 |
2008年 | 9354篇 |
2007年 | 9192篇 |
2006年 | 8227篇 |
2005年 | 7267篇 |
2004年 | 6810篇 |
2003年 | 6109篇 |
2002年 | 5986篇 |
2001年 | 6378篇 |
2000年 | 4774篇 |
1999年 | 3586篇 |
1998年 | 3097篇 |
1997年 | 3139篇 |
1996年 | 3012篇 |
1995年 | 2651篇 |
1994年 | 2798篇 |
1993年 | 2715篇 |
1992年 | 3059篇 |
1991年 | 3004篇 |
1990年 | 2927篇 |
1989年 | 2962篇 |
1988年 | 2849篇 |
1987年 | 2885篇 |
1986年 | 2714篇 |
1985年 | 3520篇 |
1984年 | 3558篇 |
1983年 | 2986篇 |
1982年 | 2977篇 |
1981年 | 2925篇 |
1980年 | 2739篇 |
1979年 | 3100篇 |
1978年 | 3049篇 |
1977年 | 3254篇 |
1976年 | 3219篇 |
1975年 | 3006篇 |
1974年 | 2931篇 |
1973年 | 2988篇 |
1972年 | 2246篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
K. N. Ponomarev 《Algebra and Logic》2007,46(4):263-273
Various classes of non-associative algebras possessing the property of being rigid under abstract isomorphisms are studied.
Supported by RFBR grant No. 06-01-00159a.
__________
Translated from Algebra i Logika, Vol. 46, No. 4, pp. 483–502, July–August, 2007. 相似文献
992.
N J Curtis P J Dortmans J Ciuk 《The Journal of the Operational Research Society》2006,57(11):1300-1312
The essential first step of any OR investigation is to ensure that the ‘right problem’ is studied. Our approach is to propose a set of six ‘rights’ or questions whereby achievement against particular aspects of a problem space is made and these provide the basis for scoping the context, understanding the system, and proposing sound options to the decision-maker. This style of problem structuring is an essential element of the Defence problem domain, and especially so for the Land Force, where there exist multiple degrees of freedom for poorly defined problems in an environment of uncertainty and ambiguity. Central to this is performing conceptual rather than analytical modelling, as perturbations then provide a basis for exploring a space, rather than solving a problem. 相似文献
993.
We discuss the coarse-grained level density of the Hénon-Heiles system above the barrier energy, where the system is nearly
chaotic. We use periodic orbit theory to approximate its oscillating part semiclassically via Gutzwiller’s semiclassical trace
formula (extended by uniform approximations for the contributions of bifurcating orbits). Including only a few stable and
unstable orbits, we reproduce the quantum-mechanical density of states very accurately. We also present a perturbative calculation
of the stabilities of two infinite series of orbits (Rn and Lm), emanating from the shortest librating straight-line orbit (A) in a bifurcation cascade just below the barrier, which at the barrier have two common asymptotic Lyapunov exponents χR and χL. 相似文献
994.
Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic
QCD are reviewed with an emphasis on the BFKL color dipole and k
T
-factorization approaches.
The text was submitted by the authors in English. 相似文献
995.
E. E. Baranov A. M. Emel’yanov W. V. Lundin V. N. Petrov V. I. Sakharov I. T. Serenkov N. A. Sobolev A. N. Titkov E. I. Shek N. M. Shmidt 《Technical Physics》2006,51(12):1600-1603
The evolution of the structure organization of MOCVD-grown AlGaN/GaN superlattices subjected to erbium ion implantation with an energy of 1 MeV and dose of 3 × 1015 cm?2 and subsequent annealing is correlated with their photoluminescent properties. The structure organization is quantitatively estimated using parameter Δ (degree of violation of local symmetry), which is found via multifractal analysis of surface morphology patterns obtained with atomic force microscopy. It is shown that the implantation not only causes Ga segregation on the surface, but also changes the structure organization, which shows up in the finer grain structure compared with the starting one and disordering, as well as in an increase in Δ. As the annealing temperature rises from 700 to 800°C, Δ declines, indicating that the structure organization is improved, and the intensity of the dominating photoluminescence peak due to Er3+ ions (1.542 μm) grows. With a further increase in the annealing temperature to 1050°C, the structure organization degrades, domains get larger, voids 100–200 nm deep form, and the photoluminescence intensity drops. The formation of voids during high-temperature annealing is also substantiated by data for 230-keV proton scattering. It is thus established that the improvement of the superlattice structure organization activates erbium and causes the erbium-ion-related luminescence intensity to grow. 相似文献
996.
L. K. Altunina B. N. Manzhai M. S. Fufaeva 《Russian Journal of Applied Chemistry》2006,79(10):1669-1672
The effect of sodium chloride and technical-grade carbon (carbon black) on the mechanical and thermal properties of cryogels and foamed cryogels produced from homogeneous and heterogeneous (foamed) solutions of poly(vinyl alcohol) was studied. 相似文献
997.
Allison K. O'Brien Neil B. Cramer Christopher N. Bowman 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):2007-2014
The overall effects of oxygen on thiol–acrylate photopolymerizations were characterized. Specially, the choice of thiol monomer chemistry, functionality, and concentration on the extent of oxygen inhibition were considered. As thiol concentration was increased, the degree of oxygen inhibition was greatly reduced because of chain transfer from the peroxy radical to the thiol. When comparing the copolymerization of 1,6‐hexanediol diacrylate with the alkane‐based thiol (1,6‐hexane dithiol) to the copolymerization with the propionate thiol (glycol dimercaptopropionate), it was found that the propionate system was much more reactive and polymerized to a greater extent in the presence of oxygen. In addition, the functionality was considered where the glycol dimercaptopropionate was compared to a tetrafunctional propionate of similar chemistry (pentaerythritol tetrakis(mercaptopropionate)). Given the same thiol concentration, the higher functionality thiol imparted a faster polymerization rate, due to the increased polymer system viscosity, which limited oxygen diffusion and decreased the extent of overall oxygen inhibition. Thus, preliminary insight is provided into how thiol monomer choice affects the extent of oxygen inhibition in thiol–acrylate photopolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2007–2014, 2006 相似文献
998.
Irina N. Savina Bo Mattiasson Igor Yu. Galaev 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):1952-1963
Graft polymerization initiated by diperiodatocuprate(III) complex (Cu(III)) initiator was found to be an effective and convenient method for graft polymerization of vinyl monomers onto macroporous polyacrylamide gels, the so‐called cryogels (pAAm‐cryogels). The effect of time, temperature, monomer and initiator concentration during the graft polymerization in aqueous and aqueous‐organic media was studied. The graft polymerization of water‐soluble monomers as [2‐(methacryloyloxy)ethyl]‐trimethylammonium chloride, 2‐hydroxyethyl methacrylate, N‐isopropylacrylamide, and N,N‐dimethylacrylamide proceeds with higher grafting yield in aqueous medium, as compared with that in aqueous‐organic media. Graft polymerization in aqueous‐organic media such as water–DMSO solutions allows grafting of water‐insoluble monomers such as glycidyl methacrylate and N‐tert‐butylacrylamide with high grafting degrees of 100 and 410%, respectively. It was found that the deposition of initiator on the pore surface of cryogels promoted graft polymerization by facilitating the formation of the redox couple Cu(III)‐acrylamide group. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1952–1963, 2006 相似文献
999.
1000.
J. Ramier L. Chazeau C. Gauthier L. Guy M. N. Bouchereau 《Journal of Polymer Science.Polymer Physics》2006,44(1):143-152
The treatment of nanoscopic silica grafted in the blend during the processing of silica‐filled styrene butadiene rubber was performed with silane, introduced at different concentrations, or at a constant concentration with a given length of alkyl chain. From swelling measurements in water and in solvent, the maximum silane content that can be grafted has been calculated as a function of the length of the silane alkyl chains as well as their efficiency to cover the silica surface. The found values are close to the values found in the literature for grafting in solution. Moreover, a direct correspondence between the length of the silane alkyl chains and their concentration has been deduced. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 143–152, 2006 相似文献