全文获取类型
收费全文 | 413篇 |
免费 | 5篇 |
国内免费 | 13篇 |
专业分类
化学 | 233篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 95篇 |
物理学 | 95篇 |
出版年
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1938年 | 2篇 |
1931年 | 4篇 |
1930年 | 2篇 |
1927年 | 2篇 |
排序方式: 共有431条查询结果,搜索用时 15 毫秒
11.
The α,β:γ,δ-unsaturated tosylhydrazone lithium salts (4) undergo photolysis at ?60°C to give vinylcyclopropenes (10) and [l,2]diazeto[l,4-a] pyrroles (11) and/or (12). The formation of (11, X=H) establishes the intermediacy of (8, X=H) in the formation of the 3-1,2-diazepine (9). The diazoalkene (5, X=Me) showed opposite electrocyclisation periselectivity to its thermal cyclisation and gave (11, X=Me) (8, X=Me), rather than the pyrazoles (2) and (3). 相似文献
12.
Michael Sharp 《Analytica chimica acta》1975,76(1):165-176
Examinations of a number of possible electroactive substances for use in both liquid membrane and solid-state ion-selective electrodes were carried out. Liquid membrane electrodes incorporating organometallic salts of lead and thallium were considered as constituents of sulphate, chromate, carbonate and nitrate responsive sensors. No practically useful device was, however, found. Several electrically semiconducting metal-phthalocyanines, metal-tetracyanoethylene (TCNE) polymers and metal-coordination polymers were also synthesized and investigated with solid-state electrode constructional techniques. Metal-phthalocyanine electrodes were found to be responsive to anions rather than to cations and some anion selectivity was observed. Metal-TCNE polymer electrodes showed response to metal ions identical with those contained in the polymer, and some good selectivities, operational activity ranges and response times were found. Electrodes made from coordination polymers incorporating copper showed a limited response to copper ions whilst inclusion of cadmium and iron(III) in the polymer matrix produced an electrode with anion reponse and slight anion selectivity. 相似文献
13.
VOF3 is soluble in acetonitrile but is slowly reduced to give a vanadyl (IV) species as one product. It reacts rapidly with Me3SiNet2 in MeCN below ambient temperature; fluorine is replaced by -NEt2 ligands but the spectroscopic and magnetic properties of the products indicate that, in addition, reduction to VIV occurs not some extent. The products are formulated as VOF3-n(NEt2)n containing small quantities of VOF2-m(NEt2)m(NEt2H) (n = 1-3, m = 0-2). A similar reaction occurs between VOF3 and Me3SiOMe but with Me3SiOSiMe3 only VO2F is formed. 相似文献
14.
A. G. Pittman D. L. Sharp R. E. Lundin 《Journal of polymer science. Part A, Polymer chemistry》1966,4(10):2637-2647
The preparation and physical properties of some perhaloalkyl acrylate and methacrylate esters are discussed. In the synthetic route to the perhaloalkyl esters, acryloyl or methacryloyl chloride is made to react with a metal fluoride—perhaloketone adduct. A side reaction which accompanies esterification is the formation of acryloyl or methacryloyl fluoride. Possible mechanisms for the formation of acyl fluoride and ester are considered. Evidence is presented which suggests that acyl fluoride formation may occur by a breakdown of the fluoroalkyl esters through an intramolecular fluorine shift. 相似文献
15.
Treatment of L(2)MCl(2) (M = Pt, Pd; L(2) = Ph(2)PCMe(2)PPh(2) (dppip), Ph(2)PNMePPh(2) (dppma)) with AgX (X = OTf, BF(4), NO(3)) in wet CH(2)Cl(2) yields the dinuclear dihydroxo complexes [L(2)M(mu-OH)](2)(X)(2), the mononuclear aqua complexes [L(2)M(OH(2))(2)](X)(2), the mononuclear anion complexes L(2)MX(2), or mixtures of complexes. Addition of aromatic amines to these complexes or mixtures gives the dinuclear diamido complexes [L(2)Pt(mu-NHAr)](2)(BF(4))(2), the mononuclear amine complexes [L(2)M(NH(2)Ar)(2)](X)(2), or the dinuclear amido-hydroxo complex [Pt(2)(mu-OH)(mu-NHAr)(dppip)(2)](BF(4))(2). Deprotonation of the Pd and Pt amine or diamido complexes with M'N(SiMe(3))(2) (M' = Li, Na, K) gives the diimido complexes [L(2)M(mu-NAr)](2) associated with M' salts. Structural studies of the Li derivatives indicate association through coordination of the imido nitrogen atoms to Li(+). Deprotonation of the amido-hydroxo complex gives the imido-oxo complex [Pt(2)(mu-O)(mu-NAr)(dppip)(2)].LiBF(4).LiN(SiMe(3))(2), and deprotonation of the dppip Pt hydroxo complex gives the dioxo complex [Pt(mu-O)(dppip)](2).LiN(SiMe(3))(2).2LiBF(4). 相似文献
16.
Carl M. Bender Fred Cooper Gerald Guralnik Harvey A. Rose David H. Sharp 《Journal of statistical physics》1980,22(6):647-660
We discuss the simple, randomly driven systemdx/dt = –x –x3 +f(t), wheref(t) is a Gaussian random function or stirring force with f(t)f(t) = (t – t). We show how to obtain approximately the coefficients of the expansion of the equal-time Green's functions as power series in (1/R)n, whereR is the internal Reynolds number ()1/2/, by using a new expansion for the path integral representation of the generating functional for the correlation functions. Exploiting the fact that the action for the randomly driven system is related to that of a quantum mechanical anharmonic oscillator with Hamiltonianp
2/2 +m
2
x
2/2 +vx
4 +x
6/2, we evaluate the path integral on a lattice by assuming that thex
6 term dominates the action. This gives an expansion of the lattice theory Green's functions as power series in 1/(a)1/3, wherea is the lattice spacing. Using Padé approximants to extrapolate toa = 0, we obtain the desired large-Reynolds-number expansion of the two-point function.Supported financially by the National Science Foundation and the U.S. Department of Energy. 相似文献
17.
Kim Sharp 《Journal of computational chemistry》1991,12(4):454-468
The finite difference method for solving the Poisson–Boltzmann equation is used to calculate the reaction field acting on a macromolecular solute due to the surrounding water and ions. Comparisons with analytical test cases indicate that the solvation forces can be calculated rapidly and accurately with this method. These forces act to move charged solute atoms towards the solvent where they are better solvated, and to screen interactions between charges. A way of combining such calculations with conventional molecular dynamics force fields is proposed which requires little modification of existing molecular dynamics programs. Simulations on the alanine dipeptide show that solvent forces affect the conformational dynamics by reducing the preference for internal H-bonding forms, increasing the R-alpha helix preference and reducing transition barriers. These solvent effects are similar to previous explicit solvent simulations, but require little more computation than vacuum simulations. The method should scale up with little increase in computational cost to larger molecules such as proteins and nucleic acids. 相似文献
18.
Bis(methyl)disulphide and the organometallic compound {(Cp)Mo(CO)3}2 in low oxidation state under photolysis give especially with the hexa-fluorobut-2 yne a 18-electron olefin complexe {(Cp)Mo(CO)3(CF3C2CF3SCH3)}. The new compounds are reported and the reaction discussed. 相似文献
19.
The pK(a) values in DMSO of the monoprotic complexes [(L(2)Pt)(2)(mu-OH)(mu-NMePh)](2+) (4) (L(2) = Ph(2)PCH(2)CH(2)PPh(2) (dppe), Ph(2)PCMe(2)PPh(2) (dppip)) are 11.9 +/- 0.1 (L(2) = dppe) and 13.5 +/- 0.2 (L(2) = dppip) as determined by (31)P NMR equilibrium titration with bases of known pK(a). Complexes 4 were prepared by treatment of [L(2)Pt(mu-OH)](2)(2+) (1) with N-methylaniline. The oxo complexes [(L(2)Pt)(2)(mu-O)(mu-NMePh)](+), formed in the equilibrium titration reactions, were independently synthesized in THF by deprotonation of [(L(2)Pt)(2)(mu-OH)(mu-NMePh)](2+) with NaN(SiMe(3))(2) and characterized as NaBF(4) adducts. Similar experiments with diprotic [L(2)Pt(mu-OH)](2)(2+) (L(2) = dppe, Ph(2)PCH(2)CH(2)CH(2)PPh(2) (dppp)) were complicated by exchange processes and were less conclusive, giving pK(a1) < 18 and pK(a2) > 18 in DMSO. 相似文献
20.
There are increasing numbers of successful numerical simulations as well as laboratory tests of controlled quantum phenomena. However, little is understood about the control mechanisms, especially in strongly driven systems. In this paper, mechanism is defined in terms of the significant quantum pathways induced by the control field, connecting the initial state to the final target state. The present work focuses on understanding mechanism in the coordinate representation, which is natural for many dynamical systems. The quantum amplitudes defining the mechanistic pathways are determined by a special procedure called coding Hamiltonians to access mechanistic pathways (CHAMP). Numerical procedures are presented for performing CHAMP calculations in a stable fashion. Mechanism determination is illustrated for excitation of a model linear triatomic molecule. Mechanisms are revealed for optimal control fields as well as for suboptimally driven systems including snapshots in time of the evolving mechanism and the effect of field noise on the mechanism. The high order multiphoton processes involved in the example produce many interfering pathways to create the final state, yet the dynamics and the mechanism are robust to reasonable levels of noise. 相似文献