全文获取类型
收费全文 | 8044篇 |
免费 | 261篇 |
国内免费 | 62篇 |
专业分类
化学 | 5370篇 |
晶体学 | 41篇 |
力学 | 277篇 |
数学 | 1597篇 |
物理学 | 1082篇 |
出版年
2023年 | 51篇 |
2022年 | 170篇 |
2021年 | 189篇 |
2020年 | 155篇 |
2019年 | 162篇 |
2018年 | 139篇 |
2017年 | 114篇 |
2016年 | 277篇 |
2015年 | 236篇 |
2014年 | 241篇 |
2013年 | 444篇 |
2012年 | 533篇 |
2011年 | 596篇 |
2010年 | 363篇 |
2009年 | 353篇 |
2008年 | 521篇 |
2007年 | 486篇 |
2006年 | 487篇 |
2005年 | 414篇 |
2004年 | 352篇 |
2003年 | 280篇 |
2002年 | 293篇 |
2001年 | 100篇 |
2000年 | 73篇 |
1999年 | 67篇 |
1998年 | 81篇 |
1997年 | 88篇 |
1996年 | 98篇 |
1995年 | 59篇 |
1994年 | 79篇 |
1993年 | 55篇 |
1992年 | 56篇 |
1991年 | 43篇 |
1990年 | 53篇 |
1989年 | 48篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 44篇 |
1984年 | 63篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 31篇 |
1980年 | 40篇 |
1979年 | 29篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有8367条查询结果,搜索用时 0 毫秒
991.
Antonio R. Cano-Marín 《Tetrahedron》2005,61(2):395-400
The synthesis of first- and second-generation dendrimers bearing phenylenevinylene chromophores within the dendritic branches (stilbenoid dendrimers) and polyenes (3 and 5 double bonds) as cores is described. A preliminary study of the optical properties of the resulting compounds was conducted by UV/vis and fluorescence spectroscopy. 相似文献
992.
Antonio Jiménez-Martínez 《International Journal of Game Theory》2006,34(3):425-442
We propose a two-person game-theoretical model to study information sharing decisions at an interim stage when information is incomplete. The two agents have pieces of private information about the state of nature, and that information is improved by combining the pieces. Agents are both senders and receivers of information. There is an institutional arrangement that fixes a transfer of wealth from an agent who lies about her private information. In our model, we show that (1) there is a positive relation between information revelation and the amount of the transfers, and (2) information revelation has a collective action structure, in particular, the incentives of an agent to reveal decrease with respect to the amount of information disclosed by the other. 相似文献
993.
J. Vela R. Viguera M. Santiago A. García A. Jimnez I. Perian M.R. Snchez R. Pereíguez V.I. Martín E. Galbis R. Snchez R. Jimnez R. Prado-Gotor 《Chemical physics》2006,320(2-3):181-187
The substitution reaction of 4,4′-bpy (4,4′-bipyridine) for the aquo ligand in aquopentacyanoferrate (II) was studied in solutions containing -, β- and γ-cyclodextrins. We conclude that the well-known pseudophase model is equivalent to the Brönsted equation in regard to the interpretation of the cyclodextrins effects on reactivity. The equivalence follows from the fact that both pseudophase and Brönsted approaches can be used to rationalize kinetic data and permit to quantify the inclusion of the aromatic ligand in the cyclodextrins. 相似文献
994.
Let X be a separable superreflexive Banach space with a Schauder basis. We prove the existence of an equivalent uniformly smooth
(resp. uniformly rotund) renorming under which the given basis is monotone.
First author supported by the grants MTM2005-08379 of MECD (Spain), 00690/PI/04 of Fundación Séneca (CARM, Spain) and AP2003-4453
of MECD (Spain), Second author supported by AV0Z10190503 and A100190502. 相似文献
995.
This paper studies the existence of bounded solutions of a forced non-linear differential equation of arbitrary order. Necessary and sufficient conditions for the existence of such solutions are obtained. These results are inspired by classical results on the periodic problem, both in the resonant and non-resonant cases.
996.
In this paper we study existence and multiplicity results of geodesics joining two given events in Lorentzian manifolds with
lack of geodesic completeness. The considered Lorentzian manifolds are not necessarily static or stationary and satisfy a
condition of convexity on the boundary.
work supported by M.U.R.S.T. research founds 40%–60% 1992 相似文献
997.
Gleison Antonio Casagrande Ernesto Schulz Lang Prof. Dr. Bárbara Tirloni Robert Alan Burrow Gelson Manzoni de Oliveira Sebastião S. Lemos 《无机化学与普通化学杂志》2006,632(5):893-896
A three‐step one‐pot synthetic procedure to synthesize the neutral tellurium(IV) coordination compounds PhTeX3L (X = Br, I and L = ethylenethiourea) has been developed and is described in this article. Oxidative halogenation of PhTeTePh in methanol generates the tellurium(II) derivative, PhTeX, which is subsequently complexed with ethylenethiourea, and, finally, further oxidative addition of additional halogen affords the corresponding tellurium(IV) compound PhTeX3L in good yields. The final product was obtained by the slow evaporation of the reaction mixture as black crystals. The X‐ray structural analyses of the compounds show Te···X and X···X secondary interactions in the solid state and suggest a weak dependence of the formation of supramolecular assemblies on the nature of the halogen bonded to the tellurium atom. 相似文献
998.
Marquina's approximate Riemann solver for the compressible Euler equations for gas dynamics is generalized to an arbitrary equilibrium equation of state. Applications of this solver to some test problems in one and two space dimensions show the desired accuracy and robustness. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
999.
Matthew Herbert Francisco Montilla Raquel Moyano Antonio Pastor Eleuterio Álvarez Agustín Galindo 《Polyhedron》2009,28(18):3929-3934
Commercially available molybdenum(VI) compounds, including molybdenum trioxide, were successfully employed as catalyst precursors in the epoxidation of olefins with urea–hydrogen peroxide adduct (UHP) in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [C4mim][PF6]. After oxidation, the corresponding epoxides were isolated by extraction with diethyl ether. Additionally the ionic liquid–catalyst mixture was recycled and reused in further catalytic cycles. The catalytic species is assumed to be an oxodiperoxomolybdenum species which forms in situ. A representative complex of this type was thus isolated and characterised. Reaction of excess 4-methylpyridine-1-oxide (4-MepyO) with MoO3 dissolved in aqueous hydrogen peroxide afforded [Mo(O)(O2)2(4-MepyO)2]·H2O (1) as yellow crystals. Compound 1, an active epoxidation catalyst, was subsequently characterised and its structure determined by X-ray crystallography. 相似文献
1000.
Toughness enhancement of cellulose nanocomposites by alkali treatment of the reinforcing cellulose nanofibers 总被引:1,自引:0,他引:1
Nanocomposites were produced with NaOH aqueous solution-treated microfibrillated cellulose (MFC) and phenolic resin, and the
mechanical properties were compared with their microcomposite counterparts based on pulp fiber. Tensile tests showed that
strong alkali-treated MFC nanocomposites with resin content around 20 wt.% achieved strain at fracture values two times higher
than those of untreated MFC nanocomposites and five times higher than those of untreated pulp microcomposites. The improvement
in work of fracture of alkali-treated MFC nanocomposites was attributed to the ductility of the nanofibers caused by transformations
in the amorphous regions along the cellulose microfibrils. 相似文献