全文获取类型
收费全文 | 475篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
化学 | 320篇 |
力学 | 15篇 |
数学 | 66篇 |
物理学 | 83篇 |
出版年
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 22篇 |
2011年 | 25篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 33篇 |
2007年 | 32篇 |
2006年 | 26篇 |
2005年 | 21篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1968年 | 2篇 |
1963年 | 2篇 |
排序方式: 共有484条查询结果,搜索用时 15 毫秒
1.
Pierluigi Contucci Sandro Graffi Stefano Isola 《Journal of statistical physics》2002,106(5-6):895-914
For the long-range deterministic spin models with glassy behaviour of Marinari, Parisi and Ritort we prove weighted factorization properties of the correlation functions which represent the natural generalization of the factorization rules valid for the Curie–Weiss case. 相似文献
2.
We use boundary value methods to compute consistent initial values for fully implicit nonlinear differential-algebraic equations.
The obtained algorithm uses variable order formulae and a deferred correction technique to evaluate the error. A rigorous
theory is stated for nonlinear index 1, 2 and 3 DAEs of Hessenberg form. Numerical tests on classical index 1, 2 and 3 DAE
problems are reported.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Bianco G Schmitt-Kopplin P Crescenzi A Comes S Kettrup A Cataldi TR 《Analytical and bioanalytical chemistry》2003,375(6):799-804
The glycoalkaloid content of transgenic potatoes was evaluated by an optimised method based on non-aqueous capillary electrophoresis coupled on-line with electrospray ionization-mass spectrometry (NACE-ESI-MS). The potato material consisted of tubers from a conventional cv. Désirée and from three lines of modified plants resistant, intermediate and susceptible to infection by potato virus Y (PVY). The main glycoalkaloids were confirmed to be alpha-solanine and alpha-chaconine with parent ion masses m/z 852 and 868, respectively. In addition, an unknown minor peak at m/z 850.6 was found both in conventional (control) and susceptible line potato tubers. Such a compound exhibited an MS(2) spectrum with fragments ions at 704 and 396 m/z derived by loss of two ions, i.e. m/z 146 and 307, most likely corresponding to a rhamnose unit and a [glucose-(rhamnose)(2)] moiety, respectively. Up to 30-80-fold higher concentrations of total glycoalkaloids were found in the peel compared to flesh samples of all tubers examined. TGA content was nearly doubled in peel samples of resistant compared to control lines, and these levels were lower than the limit recommended for food safety, i.e. 20-60 mg of TGA per 100 g fresh weight. Moreover, it was established that tubers produced by virus-resistant clones are substantially equivalent in glycoalkaloid contents to those produced by conventional potato varieties. 相似文献
4.
Pierluigi Contucci 《Journal of statistical physics》1996,82(5-6):1647-1657
We study the coexistence phase in the two-dimensional Ising model. Optimizing the cluster expansion technique, we are able to prove the phase separation phenomenon, with the Onsager value for the surface tension, in a range
, where
estimates from above the critical within 19% and essentially coincides with the entropic bound. 相似文献
5.
The solvent effect on 17O isotropic shielding was computed by different methods: the polarizable continuum model and a mixed approach, including a few real solvent molecules treated as the solute. The experimental data show that the behavior of protic and aprotic solvents is markedly different: we found that the continuum approach describes well the observed shielding at various dielectric constants for aprotic solvents, while the mixed procedure is needed when hydrogen bonds to the magnetic centre are present.Contribution to the Jacopo Tomasi Honorary Issue 相似文献
6.
Guido Barone Giuseppina Castronuovo Vittorio Crescenzi Vittorio Elia Eugenio Rizzo 《Journal of solution chemistry》1978,7(3):179-192
In order to clarify some aspects of the hydrophobic interactions, the enthalpies of dilution of monoethylurea, 1,3-dimethylurea,
and 1,3-diethylurea have been determined calorimetrically at 25°C. The calorimetric data, expressed in terms of excess enthalpy,
permit the evaluation of the pair and triplet interaction coefficients. The analyses of these and of the analogous coefficientsg
xx andg
xxx, derived from osmotic data, indicate a driving force favorable to the interactions among the hydrated solute molecules. Nevertheless,
the positive values of theh
xx andh
xxx coefficients seem to suggest that the source of the effect is a rearrangement of the water molecules rather than a direct
association of the solute molecules. There are evidences of a strict correlation between the enthalpic and the entropic effects.
Preliminary data were presented at the International Conferences on Chemical Thermodynamics at Baden (1973) and Montpellier
(1975). The experimental part was carried out at the Istituto Chimico of the University of Trieste.
To whom correspondence should be addressed. 相似文献
7.
Bruno Crociani Umberto Belluco Pierluigi Sandrini 《Journal of organometallic chemistry》1979,177(2):385-401
The reactions of the organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR″ [R = R″ = p-C6H4OMe, R′ = trans-PdCl(PPh3)2 (DAB); R = p-C6H4OMe, R″ = Me, R′ = trans-PdCl(PPh3)2 (DABI; R = R″ = p-C6H4OMe, R′ = Pd(dmtc)-(PPh3), dmtc = dimethyldithiocarbamate (DABII); R = R″ = p-C6H4OMe, R′ = PdCl(diphos), diphos = 1,2-bis(diphenylphosphino)ethane (DABIII)] with [RhCl(COD)]2 (COD = 1,5-cyclooctadiene, Pd/Rh ratio = ) depend on the nature of the ancillary ligands at the Pd atom in group R′. In the reactions with DAB and DABI transfer of one PPh3 ligand from Pd to Rh occurs yielding [RhCl(COD)(PPh3)] and the new binuclear complexes [Rh(COD) {RN=C(R?)-C(Me)=NR″}], in which the diazabutadiene moiety acts as a chelating bidentate ligand. Exchange of ligands between the two different metallic centers also occurs in the reaction with DABII. In this case, the migration of the bidentate dmtc anion yields [Rh(COD)Pdmtc] and [Rh(COD) {RN=C(R?)C(Me)=NR″}]. In contrast, the reaction with DABIII leads to the ionic product [Rh(COD)- (DABIII)][RhCl2(COD)], with no transfer of ligands. The cationic complex [Rh(COD)(DABIII)]+ can be isolated as the perchlorate salt from the same reaction (Pd/Rh ratio = 1/1) in the presence of an excess of NaClO4. In all the binuclear complexes the coordinated 1,5-cyclooctadiene can be readily displaced by carbon monoxide to give the corresponding dicarbonyl derivatives. The reaction of [RhCl(CO)2]2 with DAB and/or DABI yields trinuclear complexes of the type [RhCl(CO)2]2(DAB), in which the diazabutadiene group acts as a bridging bidentate ligand. Some reactions of the organic diazabutadiene RN=C(Me)C(Me)=NR (R = p-C6H4OMe) are also reported for comparison. 相似文献
8.
Density functional theory calculations at the B3LYP/6-31G* level on the dimerization reactions of acetonitrile oxide and para-chlorobenzonitrile oxide to form furoxans indicate that these processes are stepwise involving dinitrosoalkene intermediates that have considerable diradical character. The rate-determining steps for these two reactions correspond to C-C bond formation. The retardation of dimerization in aromatic nitrile oxides arises from the interruption of conjugation between the nitrile oxide and aryl groups in the C-C bond formation step. The present study also suggests that the isomerization of single-ring furoxans occurs via a diradical intermediate mechanism. 相似文献
9.
Quagliotto P Viscardi G Barolo C D'Angelo D Barni E Compari C Duce E Fisicaro E 《The Journal of organic chemistry》2005,70(24):9857-9866
[reaction: see text] In this work, we report the synthesis of a new series of glucocationic surfactants, a class of surfactants we introduced very recently. The preparation of the surfactants is based on the synthesis of the 2-bromoethyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside, whose preparation was studied in order to improve yields and stereoselectivity of this key intermediate. These glucocationic amphiphiles were prepared and studied as a model of cationic surfactants marked with a carbohydrate moiety. The use of carbohydrates as markers on cationic lipids was recently introduced to induce recognition by specific receptors, present on the surface of cell membranes. The chemicophysical characterization of these model structures can give more insight on the aggregation behavior. Conductivity and surface tension measurements were performed in order to characterize the compounds from the amphiphilic point of view. The results showed a different effect of the glucosidic moiety on the cmc value with respect to the glucopyridinium cationic surfactants. The surfactants also showed the tendency to form premicellar aggregates in solution when the hydrophobicity is raised. 相似文献
10.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献