全文获取类型
收费全文 | 230541篇 |
免费 | 1510篇 |
国内免费 | 483篇 |
专业分类
化学 | 104980篇 |
晶体学 | 3610篇 |
力学 | 12134篇 |
综合类 | 5篇 |
数学 | 37177篇 |
物理学 | 74628篇 |
出版年
2018年 | 10138篇 |
2017年 | 11054篇 |
2016年 | 5624篇 |
2015年 | 1944篇 |
2014年 | 1459篇 |
2013年 | 4909篇 |
2012年 | 8021篇 |
2011年 | 17730篇 |
2010年 | 10456篇 |
2009年 | 10334篇 |
2008年 | 15291篇 |
2007年 | 19177篇 |
2006年 | 4254篇 |
2005年 | 11413篇 |
2004年 | 7198篇 |
2003年 | 6776篇 |
2002年 | 4560篇 |
2001年 | 3744篇 |
2000年 | 2999篇 |
1999年 | 2237篇 |
1998年 | 1934篇 |
1997年 | 1892篇 |
1996年 | 1982篇 |
1995年 | 1878篇 |
1994年 | 1639篇 |
1993年 | 1615篇 |
1992年 | 1821篇 |
1991年 | 1823篇 |
1990年 | 1752篇 |
1989年 | 1766篇 |
1988年 | 1778篇 |
1987年 | 1765篇 |
1986年 | 1667篇 |
1985年 | 2229篇 |
1984年 | 2364篇 |
1983年 | 1979篇 |
1982年 | 2297篇 |
1981年 | 2112篇 |
1980年 | 2159篇 |
1979年 | 2165篇 |
1978年 | 2296篇 |
1977年 | 2123篇 |
1976年 | 2183篇 |
1975年 | 2103篇 |
1974年 | 1944篇 |
1973年 | 2196篇 |
1972年 | 1322篇 |
1971年 | 1001篇 |
1968年 | 1152篇 |
1967年 | 1133篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. Deptuła T. Olczak W. Łada B. Sartowska A.G. Chmielewski C. Alvani P.L. Carconi A. Di Bartolomeo F. Pierdominici S. Casadio 《Journal of Sol-Gel Science and Technology》2003,26(1-3):207-212
Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier. 相似文献
992.
Nonlinear processes caused by the propagation of low-frequency and high-frequency acoustic pulses in an unbounded medium and the propagation of continuous waves in a ring resonator are theoretically studied on the basis of two hysteretic equations of state for media with imperfect elasticity. The profiles and parameters of pulses, the resonance curve and the Q factor of the resonator, and the ratio of the nonlinear resonance frequency shift to the nonlinear damping decrement are determined. For nonlinear wave processes in such media, the distinctive features that allow one to choose an appropriate hysteretic equation of state for analytically describing the experimental data are revealed. 相似文献
993.
Richard P. Stanley 《Israel Journal of Mathematics》2004,143(1):317-339
We survey three recent developments in algebraic combinatorics. The first is the theory of cluster algebras and the Laurent
phenomenon of Sergey Fomin and Andrei Zelevinsky. The second is the construction of toric Schur functions and their application
to computing three-point Gromov-Witten invariants, by Alexander Postnikov. The third development is the construction of intersection
cohomology for nonrational fans by Paul Bressler and Valery Lunts and its application by Kalle Karu to the torich-vector of a nonrational polytope. We also briefly discuss the “half hard Lefschetz theorem” of Ed Swartz and its application
to matroid complexes.
Partially supported by NSF grant #DMS-9988459. 相似文献
994.
995.
We study the minimal and maximal closed extension of a differential operator A on a manifold B with conical singularities, when A acts as an unbounded operator on weighted L
p
-spaces over B, 1<p<∞. Under suitable ellipticity assumptions we can define a family of complex powers A
z
, zℂ. We also obtain sufficient information on the resolvent of A to show the boundedness of the purely imaginary powers. Examples concern unique solvability and maximal regularity for the
solution of the Cauchy problem for the Laplacian on conical manifolds as well as certain quasilinear diffusion equations.
Received: 12 June 2001; in final form: 3 June 2002 /
Published online: 1 April 2003
Mathematics Subject Classification (2000): 35J70, 47A10, 35K57 相似文献
996.
V. V. Pakal’nis I. V. Zerova S. I. Yakimovich 《Russian Journal of General Chemistry》2007,77(10):1732-1741
Acylhydrazines react with 1,3-diketones of the general formula CF3COCH2COR (where R is an aryl or hetaryl group) at both carbonyl groups. The reaction at the trifluoroacetyl group is favored by donor substituents in the aromatic ring of the 1,3-diketone or by the 2-furyl and, especially, 2-thienyl group as a hetaryl substituent, as well as by elevated temperature. The condensation products at the carbonyl group contiguous to the aryl or hetaryl ring have the structure of 5-hydroxy-4,5-dihydropyrazoles and do not undergo tautomeric transformations in solution. The condensation products at the trifluoroacetyl group have either 5-hydroxy-4,5-dihydropyrazole or hydrazone structure and give rise to ring-chain tautomeric equilibrium in solution. Electron-withdrawing substituents in the aromatic ring of the 1,3-dicarbonyl fragment and CDCl3 as solvent favor formation of the cyclic tautomer. The state of the tautomeric equilibrium is weakly sensitive to structural variations in the hydrazine component. 相似文献
997.
The reaction of 2-(2-acetoxyethyl)amino-4-chloro-6-methylpyrimidine with aromatic amines leads to a series of 4-arylamino-2-(2-acetoxyethyl)amino-6-methylpyrimidines. Deacetylation of these compounds proceeds in both acidic and basic media. Most of the arylaminopyrimides obtained exhibit a pronounced antituberculous effect. 相似文献
998.
Elżbieta Godlewska M. Mitoraj F. Devred B. E. Nieuwenhuys 《Journal of Thermal Analysis and Calorimetry》2007,88(1):225-230
A Ti–45.9Al–8Nb
(at%) alloy with a lamellar structure (γ+α2)
was oxidised in air at 700, 800, 850 and 900°C in isothermal and thermal
cycling conditions. The reaction progress was followed by thermogravimetric
measurements. In isothermal conditions the oxidation kinetics followed approximately
a parabolic rate law and the rate constants ranged from about 10–12
kg2 m–4 s–1
at 700°C to 10–10 kg2
m–4 s–1
at 900°C. The oxide scales were built of Al2O3
and TiO2, the former being the main component of the
outermost layer. The oxidation behaviour of Ti–45.9Al–8Nb was
referred to a commercial titanium alloy, WT4 (Ti–6Al–1Mn), and
selected oxidation-resistant alloys. 相似文献
999.
All homothetic self-similar solutions of the Brans-Dicke scalar field in three-dimensional spacetime with circular symmetry
are found in closed form. 相似文献
1000.
U. Goginava 《分析论及其应用》2007,23(3):255-265
In this paper we prove that iff ∈ C([-π,π]2) and the function f is bounded partial p-variation for some p ∈ [1, ∞), then the double trigonometric Fourier series of a function f is uniformly (C;-α,-β) summable (α β< 1/p,α,β> 0) in the sense of Pringsheim. If α β≥ 1/p, then there exists a continuous function f0 of bounded partial double trigonometric Fourier series of fo diverge over cubes. 相似文献