全文获取类型
收费全文 | 2239篇 |
免费 | 46篇 |
国内免费 | 79篇 |
专业分类
化学 | 323篇 |
晶体学 | 11篇 |
力学 | 15篇 |
综合类 | 1篇 |
数学 | 1788篇 |
物理学 | 226篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 56篇 |
2018年 | 51篇 |
2017年 | 37篇 |
2016年 | 28篇 |
2015年 | 28篇 |
2014年 | 67篇 |
2013年 | 137篇 |
2012年 | 55篇 |
2011年 | 136篇 |
2010年 | 104篇 |
2009年 | 143篇 |
2008年 | 197篇 |
2007年 | 160篇 |
2006年 | 144篇 |
2005年 | 126篇 |
2004年 | 95篇 |
2003年 | 75篇 |
2002年 | 56篇 |
2001年 | 68篇 |
2000年 | 46篇 |
1999年 | 55篇 |
1998年 | 41篇 |
1997年 | 41篇 |
1996年 | 75篇 |
1995年 | 52篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有2364条查询结果,搜索用时 31 毫秒
81.
The protonation constants of two nitro-Schiff bases SB1, SB2 and three asymmetric tetradentate diimines H2L1, H2L2 and H2L3 and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC6H4CHNR′ (2OH) type compounds [where R = R′ = phenyl for H2L1; R = naphthyl, R′ = phenyl for H2L2 and R = R′ = naphthyl for H2L3]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239). 相似文献
82.
Interpenetrating Polymer Networks (IPNs) based on Poly n-vinyl 2-pyrrolidone (PVP) and Acrylonitrile (AN) were prepared by irradiating PVP solutions prepared in AN. PVP/AN mixtures were irradiated by 60Co-γ rays at room temperature at a dose rate of 0.5 kGy/hour. IPNs were characterized by using FT-IR and Thermal Analysis techniques. The chelating adsorbents containing amidoxime groups were prepared by the reaction of these IPNs with hydroxylamine in aqueous NaOH solution at 50°C. These amidoxime containing adsorbents were used in adsorption studies for the recovery of uranium from aqueous systems. The adsorption capacity of an IPN with equivolume fraction of PVP and amidoximated PAN was found to be 750mg UO22+/g dry amidoximated IPN. 相似文献
83.
《Electroanalysis》2005,17(11):947-952
Iridium oxide films (IROFs) are known to have an enhanced or the so‐called super‐Nernstian (<59 mV/pH) pH‐sensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 μm thickness, deposited thermally on titanium or gold‐plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen‐containing solutions of 0.5 M H2SO4, 0.1 M KOH and 0.5 M H3PO4+KOH. Linear pH‐dependences of the stationary open‐circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V–0.8 V (RHE) in deaerated and at 0.8 V–1.2 V (RHE) in O2‐containing solutions. They were attributed to reversible Ir/Ir(OH)3 and Ir/ IrO2?nH2O metal‐oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super‐Nernstian pH‐sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH)3 electrode and the solubility product of Ir(OH)3 have been evaluated: =0.78±0.02 V and Ksp=3.3×10?64. 相似文献
84.
Humberto E. Prado 《Acta Appl Math》1991,25(1):87-98
Local transformation groups acting on a manifold X define a natural action of on a space D(X), of functions on X. The natural action induces a local representation of on a Hilbert subspace of the space of distributions on D(X). 相似文献
85.
William Kerby 《Aequationes Mathematicae》1991,41(1):187-191
Summary Nearfields of rank 2 over their kernel which are not Dickson nearfields have recently been constructed by H. Zassenhaus. Here it is shown that KT-nearfields of rank 2 over their kernels and of characteristic 2 are necessarily Dickson nearfields which are coupled to quadratic field extensions and their Dickson group is isomorphic to 2. Using results of Gröger one obtains all KT-nearfields of rank 2 over the field of rational numbers. 相似文献
86.
A new quantum group is derived from a nonstandard braid group representation by employing the Faddeev-Reshetikhin-Takhtajan constructive method. The classical limit is not a Lie superalgebra, despite relations like x
2–y
2=0. We classify all finite-dimensional irreducible representations of the new Hopf algebra and find only one- and two-dimensional ones. 相似文献
87.
Thierry Coulhon 《Potential Analysis》1992,1(4):343-353
One shows the equivalence between an abstract form of a Gagliardo-Nirenberg inequality and an estimate of the decay of the L
1–L
norm of a semigroup of operators. This equivalence, contrary to the one with the classical Sobolev inequalities, allows the treatment of situations where the decay is exponential. Related results and applications are given.
Cet article a pu être terminé pendant un séjour de l'auteur à l'université d'Edimbourg. 相似文献
88.
Rosa Caballol Josep M. Ribó Francesc R. Trull Asunción Vallés 《Monatshefte für Chemie / Chemical Monthly》1987,118(8-9):993-1010
The applicability of the MINDO/3 method is evaluated for calculations on dipyrrolic partial structures of bile pigments. It is shown that this method cannot be used for an accurate conformational analysis. However, when applying the frontier orbital model for reactivity parameters, a good picture of the HOMO and the LUMO distribution can be obtained in this type of molecules.
Reaktivität von Pyrrolpigmenten, 9. Mitt. MINDO/3-Rechnungen von dipyrrolischen Partialmodellen von Gallenpigmenten
Zusammenfassung Es werden die Einsatzmöglichkeiten von MINDO/3 für den Fall dipyrrolischer Partialstrukturen der Gallenpigmente aufgezeigt. Die Methode ist für eine genaue Konformationsanalyse nicht geeignet. Unter Verwendung der Reaktionsparameter des Frontier-Orbital-Modells läßt sich jedoch ein gutes Bild der HOMO- und LUMO-Verteilung für diesen Verbindungstyp gewinnen.相似文献
89.
Abdel-Wahab M. Nourein 《BIT Numerical Mathematics》1976,16(3):291-297
In this paper we describe a new technique for generating iteration formulas — of arbitrary order — for determining a zero (assumed simple) of a functionf, assumed analytic in a region containing the zero. The 1/p Padé Approximant (p0) to the functiong(t)f(z) is formed wherez=w+t, using the Taylor series forf at the pointw, an approxination to the zero off. The value oft for which the 1/p Padé Approximant vanishes provides the basis of iteration formulas of orderp+2.Some known iteration formulas, e.g., Newton-Raphson's, Halley's and Kiss's of order of convergence two, three and four, are directly obtained by settingp=0,1 and 2, respectively. 相似文献
90.
We classify moduli spaces of arrangements of 10 lines with quadruple points. We show that moduli spaces of arrangements of 10 lines with quadruple points may consist of more than 2 disconnected components, namely 3 or 4 distinct points. We also present defining equations to those arrangements whose moduli spaces are still reducible after taking quotients of complex conjugations. 相似文献