全文获取类型
收费全文 | 12931篇 |
免费 | 437篇 |
国内免费 | 48篇 |
专业分类
化学 | 8909篇 |
晶体学 | 57篇 |
力学 | 423篇 |
数学 | 1718篇 |
物理学 | 2309篇 |
出版年
2023年 | 91篇 |
2022年 | 115篇 |
2021年 | 181篇 |
2020年 | 199篇 |
2019年 | 228篇 |
2018年 | 194篇 |
2017年 | 151篇 |
2016年 | 336篇 |
2015年 | 342篇 |
2014年 | 365篇 |
2013年 | 702篇 |
2012年 | 864篇 |
2011年 | 890篇 |
2010年 | 537篇 |
2009年 | 416篇 |
2008年 | 825篇 |
2007年 | 788篇 |
2006年 | 728篇 |
2005年 | 677篇 |
2004年 | 632篇 |
2003年 | 570篇 |
2002年 | 458篇 |
2001年 | 221篇 |
2000年 | 228篇 |
1999年 | 132篇 |
1998年 | 153篇 |
1997年 | 130篇 |
1996年 | 169篇 |
1995年 | 97篇 |
1994年 | 97篇 |
1993年 | 91篇 |
1992年 | 92篇 |
1991年 | 67篇 |
1990年 | 77篇 |
1989年 | 61篇 |
1988年 | 65篇 |
1986年 | 54篇 |
1985年 | 83篇 |
1984年 | 106篇 |
1983年 | 67篇 |
1982年 | 79篇 |
1981年 | 82篇 |
1980年 | 88篇 |
1979年 | 65篇 |
1978年 | 79篇 |
1977年 | 83篇 |
1976年 | 89篇 |
1975年 | 66篇 |
1974年 | 43篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Patrick Mather Nino Grizzuti Glenn Heffner Mathias Ricker Willie E. Rochefort Markus Seitz Hans-Werner Schmidt Dale S. Pearson 《Liquid crystals》1994,17(6):811-826
In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a 'model' polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range-from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations. 相似文献
72.
The electron impact ionization mass spectra of o-, m- and p-bis(1,4-dithiafulven-6-yl)benzenes were studied by means of accurate mass measurements, metastable analysis and collision-induced dissociation. Differences observed in the spectra of the ortho isomers are due to a cyclization reaction leading to molecular ions with the same structure as those generated from certain cyclic compounds, as confirmed by comparison of linked scans at constant B/E of metastable and collisionally activated molecular ions. Parallels of this cyclization of molecular ions with their electrochemical or acid-induced isomerization are also discussed. 相似文献
73.
74.
Marie‐France Llauro Julien Loiseau Fernande Boisson Frdric Delolme Catherine Ladavire J. Claverie 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5439-5462
Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004 相似文献
75.
Agnès Tourin 《Numerische Mathematik》1992,62(1):75-85
Summary The reconstruction from a shaded image of a Lambertian and not self-shadowing surface illuminated by a single distant pointwise light source may be written as a first-order Hamilton-Jacobi equation.In this paper, we continue the investigation begun in E. Rouy and A. Tourin into the uniqueness of the solution of this equation; the approach is based on the viscosity solutions theory and the dynamic programming principle.More precisely, we concentrate here on the uniqueness of the viscosity solution of this equation in case the measured luminous intensity reflected by the surface is discontinuous along a smooth curve. We prove a general comparison result for a piecewise Lipschitz continuous Hamiltonian and illustrate it by numerical experiments. 相似文献
76.
Hermann Grabert Gert-Ludwig Ingold Michel H. Devoret Daniel Estève Hugues Pothier Cristian Urbina 《Zeitschrift für Physik B Condensed Matter》1991,84(1):143-155
The rate of electron tunneling through normal metal tunnel junctions is calculated for the case of ultrasmall junction capacitances. The so-called Coulomb blockade of electron tunneling at low temperatures is shown to be strongly affected by the external electrical circuit. Under the common experimental condition of a low impedance environment the Coulomb blockade is suppressed for single tunnel junctions. However, a Coulomb gap structure emerges for junctions embedded in a high impedance environment. For a double junction setup a Coulomb blockade of tunneling arises even for low impedance environments due to the charge quantization on the metallic island between the junctions. An approach using circuit analysis is presented which allows to reduce the calculation of tunneling rates in multijunction circuits to those of a single junction in series with an effective capacitance. The range of validity of the socalled local rule and global rule rates is clarified. It is found that the tunneling rate tends towards the global rule rate as the number of junctions is increased. Some specific results are given for a one-dimensional array of tunnel junctions. 相似文献
77.
G. Meillère 《Analytical and bioanalytical chemistry》1899,38(9-10):674-675
78.
Christophe Rochais Vincent Lisowski Patrick Dallemagne Sylvain Rault 《Tetrahedron letters》2004,45(33):6353-6355
Novel arylpyrrolo- and pyrazolopyrrolizinones were prepared in three or four steps starting from aminoarylpyrrole and pyrazole carboxylates through the cyclisation of a Vilsmeier-Haack intermediate. This synthesis was enhanced by diverse N-protections of the aza-heterocycle and furnish new series with potential biological interest. 相似文献
79.
Paul A. Binding Patrick J. Browne Bruce A. Watson 《Journal of Mathematical Analysis and Applications》2004,291(1):246-261
Three inverse problems for a Sturm-Liouville boundary value problem −y″+qy=λy, y(0)cosα=y′(0)sinα and y′(1)=f(λ)y(1) are considered for rational f. It is shown that the Weyl m-function uniquely determines α, f, and q, and is in turn uniquely determined by either two spectra from different values of α or by the Prüfer angle. For this it is necessary to produce direct results, of independent interest, on asymptotics and oscillation. 相似文献
80.
Heinz H. Bauschke Patrick L. Combettes 《Proceedings of the American Mathematical Society》2003,131(12):3757-3766
An iterative method is proposed to construct the Bregman projection of a point onto a countable intersection of closed convex sets in a reflexive Banach space.