全文获取类型
收费全文 | 3147篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 2246篇 |
晶体学 | 11篇 |
力学 | 42篇 |
数学 | 476篇 |
物理学 | 411篇 |
出版年
2018年 | 26篇 |
2017年 | 26篇 |
2016年 | 33篇 |
2015年 | 32篇 |
2014年 | 30篇 |
2013年 | 84篇 |
2012年 | 80篇 |
2011年 | 104篇 |
2010年 | 76篇 |
2009年 | 77篇 |
2008年 | 103篇 |
2007年 | 120篇 |
2006年 | 99篇 |
2005年 | 112篇 |
2004年 | 110篇 |
2003年 | 91篇 |
2002年 | 94篇 |
2001年 | 58篇 |
2000年 | 78篇 |
1999年 | 66篇 |
1998年 | 50篇 |
1997年 | 58篇 |
1996年 | 49篇 |
1995年 | 48篇 |
1994年 | 39篇 |
1993年 | 63篇 |
1992年 | 56篇 |
1991年 | 41篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 40篇 |
1987年 | 35篇 |
1986年 | 50篇 |
1985年 | 62篇 |
1984年 | 42篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 50篇 |
1980年 | 40篇 |
1979年 | 54篇 |
1978年 | 42篇 |
1977年 | 42篇 |
1976年 | 37篇 |
1975年 | 31篇 |
1974年 | 36篇 |
1973年 | 23篇 |
1972年 | 25篇 |
1971年 | 23篇 |
1970年 | 24篇 |
1934年 | 21篇 |
排序方式: 共有3186条查询结果,搜索用时 0 毫秒
101.
Volker Weinrich Kurt Polborn Christian Robl Karlheinz Sünkel Wolfgang Beck 《无机化学与普通化学杂志》2000,626(3):706-716
Hydrocarbon‐bridged Metal Complexes. L Dicarbonyl Cyclopentadienyl Pyridoyl Iron Complexes as Ligands Dicarbonyl‐cyclopentadienyl‐2‐ and 3‐pyridoyl‐iron (L1, L2) and 2,6‐dicarbonyl‐pyridine‐bis(dicarbonyl‐cyclopentadienyl‐iron) (L3) function as ligands in metal complexes and the N,O‐chelates [(OC)4M(L1)] (M = Mo, W, 8 a, b ) and [(Ph3P)2Cu(L1)]+BF4– ( 9 ) were prepared. Monodentate coordination of L1 and L2 through the pyridine N‐atom occurs in the palladium(II) complexes [Cl2Pd(PnBu3)(L1)] ( 10 ), [Cl2Pd(PnBu3)(L2)] ( 11 ) and [Cl2Pd(L2)2] ( 12 ). Ligand L3 forms the O,N,O‐bis(chelate) [Cl2Zn(L3)] ( 13 ). The crystal and molecular structures of L1, 8 b (M = W), 9–11 and 13 were determined by X‐ray diffraction. 相似文献
102.
Atom transfer radical polymerization conditions with copper(I) bromide/2,2′-bipyridine (Cu/2,2′-bpy) as the catalyst system were employed for the homopolymerization and random copolymerization of 1-phenoxycarbonyl ethyl methacrylate (PCMA) with methyl methacrylate (MMA). Temperature studies indicated that the polymerizations occurred smoothly in bulk at 110 °C. Poly(PCMA)(polydispersity index=1.27) homopolymer was characterized and then used as macroinitiator for increasing its molecular weight. The homopolymerization of PCMA was also carried out under free radical conditions using 2,2′-azobisisobutyronitrile as an initiator.The monomer and polymers were characterized by FT-IR and 1H and 13C-NMR techniques. The glass transition temperatures, the solubility parameters and average-molecular weights of the polymers were determined. Thermal stabilities of the polymers were given as compared with each other by using TGA curves. Thermal degradation products of poly(PCMA)s obtained by ATRP and free radical polymerization were compared with each other by using 1H-NMR technique. 相似文献
103.
V. Ondrus L' Fisera K. Polborn P. Ertl N. Prónayová 《Monatshefte für Chemie / Chemical Monthly》1995,126(8-9):961-969
Summary N-(3,5-Dichlorophenyl)-maleimide reacts smoothly with a variety of substituted fulvenes (1) to give onlyendo adducts (3) independent of the nature of fulvene substituent,Lewis acid catalyst, and reaction solvent and temperature. The structure of theDiels-Alder adduct3f was determined by X-ray crystallography. Semi-empirical quantum methods (AM1) were used to rationalize theendo stereoselectivity.Dedicated to Professor Fritz Sauter on the occasion of his 65th birthday 相似文献
104.
Svihla C. Kurt Dronawat Sundeep N. Hanley Thomas R. 《Applied biochemistry and biotechnology》1995,(1):355-366
It can be difficult to obtain reliable rheological data for filamentous fermentation broths using conventional instruments.
One common approach is to measure the torque drawn by an impeller rotating in the suspension (1–7). Many previous workers have assumed that the applicable shear rate in such a device is related to the impeller speed by
a fluid-independent constant determined by calibration with Newtonian and non-Newtonian fluids (1–9). The rheology ofAspergillus niger broths have been characterized using the impeller viscometer approach. The changes in the broth rheology were measured, and
used to interpret the growth of biomass and the evolution of the microorganism morphology. 相似文献
105.
106.
Michael Plate Sigrid Wocadlo Werner Massa Kurt Dehnicke Harald Krautscheid 《无机化学与普通化学杂志》1995,621(3):388-392
Functionalized Alkyne Complexes of Tungsten(VI). Syntheses and Crystal Structures of [WCl4(Et? Se? C?C? Se? Et)(THF)] and [WCl4(Et? Te? C?C? Te? Et)(THF)] The title compounds have been prepared by reactions of [WCl4(SEt2)2] with the alkynes Et? X? C?C? X? Et (X = Se, Te) in CCl4 solution and subsequent addition of tetrahydrofurane. Both complexes were characterized by crystal structure determinations. [WCl4(Et? Se? C?C? Se? Et)(THF)]: Space group P21/n, Z = 4, structure determination with 2942 unique reflections, R = 0.038. Lattice dimensions at 20°C: a = 934.2, b = 1639.5, c = 1189.5 pm, β = 96.497°. [WCl4(Et? Te? C?C? Te? Et)(THF)]: Space group P21/n, Z = 4, structure determination with 4097 unique reflections, R = 0.067, Lattice dimensions at ?70°C: a = 899.2, b = 1691.9, c = 1213.3 pm, β = 96.82°. The complexes have monomeric molecular structures with the oxygen atom of the THF molecules in trans-position to the side-on bound alkyne ligands. 相似文献
107.
Felora Heshmatpour Dirk Nußhr Ralf Garbe Sigrid Wocadlo Werner Massa Kurt Dehnicke Helmut Goesmann Dieter Fenske 《无机化学与普通化学杂志》1995,621(3):443-450
Syntheses and Crystal Structures of the Phosphorane Iminato Complexes [MCl2(NPPh3)]2 with M = Al and Ga, [SbCl2(NPMe3)(DMF)]2, and of the Phosphorane Imine Complex [Ph3PNH · BF3] · THF The phosphorane iminato complexes [MCl2(NPPh3)]2 with M = Al and Ga and [SbCl2(NPMe3)(DMF)]2 are formed as colourless crystals by reactions of the anhydrous trichlorides MCl3 (M = Al, Ga, Sb) with the corresponding silylated phosphorane imines Me3SiNPR3 in acetonitrile and in dimethyl formamide, respectively. The phosphorane imine derivative [Ph3PNH · BF3] · THF is formed from Me3SiNPPh3 and boron trifluoride etherate in boiling tetrahydrofuran. The compounds are characterized by their i. r. spectra and by crystal structure analyses. [AlCl2(NPPh3)]2 : Space group P1 , Z = 1, structure solution with 1 585 observed unique reflections, R = 0.061. Lattice dimensions at ?70°C: a = 917.6, b = 1 053.5, c = 1 145.2 pm, α = 111.72°, β = 100.80°, γ = 109.95°. [GaCl2(NPPh3)]2 : Space group P1 , Z = 1, structure solution with 2 586 observed unique reflections, R = 0.066. Lattice dimensions at ?70°C: a = 917.5, b = 1 058.3, c = 1 153.7 pm, α = 105.52°, β = 107.75°, γ = 109.88°. In both compounds the metal atoms are linked to planar M2N2 four-membered rings via the N-atoms of the phosphorane iminato groups. [SbCl2(NPMe3)(DMF)]2 : Space group P21/n, Z = 4, structure solution with 3 805 observed unique reflections, R = 0.038. Lattice dimensions at ?70°C: a = 1 913.0, b = 726.8, c = 2 040.7 pm, β = 113.62°. The unit cell contains two symmetry independent dimeric molecules, in which the antimony atoms are centrosymmetricly μ2 linked via the N-atoms of the phosphorane iminato groups. Along with the oxygen atom of the dimethyl formamide molecule the Sb atoms achieve a ψ-octahedral environment. [Ph3PNH · BF3] · THF : Space group C2/c, Z = 8, structure solution with 2 048 observed unique reflections, R = 0.058. Lattice dimensions at ?70°C: a = 2 460.4, b = 869.2, c = 1 978.0 pm, β = 116.35°. 相似文献
108.
Sylvain Rodriguez Jean-Luc Wolfender Kurt Hostettmann Gendaramyn Odontuya Ondognii Purev 《Helvetica chimica acta》1996,79(2):363-370
Chemical screening of the secondary metabolites from Halenia corniculata L. (CORNAZ ), by LC/UV,LC/TSP-MS (thermospray), and LC/ES-MS (electrospray) was used for the targeted isolation of corniculoside ( 1 ), a new biosidic ester secoiridoid. The structure was established as 7-β-[(E)-4′-O-(β-D -glucopyranosyl)caffeoyloxy]-sweroside by 1D- and 2D-NMR, LC/UV, LC/MS, and FAB-MS data, in combination with chemical reactions. 相似文献
109.
110.
The perturbed-chain statistical associating fluid theory (PC-SAFT) is studied for a wide range of temperature, T, pressure, p, and (effective) chain length, m, to establish the generic phase diagram of polymers according to this theory. In addition to the expected gas-liquid coexistence, two additional phase separations are found, termed "gas-gas" equilibrium (at very low densities) and "liquid-liquid" equilibrium (at densities where the system is expected to be solid already). These phase separations imply that in one-component polymer systems three critical points occur, as well as equilibria of three fluid phases at triple points. However, Monte Carlo simulations of the corresponding system yield no trace of the gas-gas and liquid-liquid equilibria, and we conclude that the latter are just artefacts of the PC-SAFT approach. Using PC-SAFT to correlate data for polybutadiene melts, we suggest that discrepancies in modelling the polymer density at ambient temperature and high pressure can be related to the presumably artificial liquid-liquid phase separation at lower temperatures. Thus, particular care is needed in engineering applications of the PC-SAFT theory that aims at predicting properties of macromolecular materials. 相似文献