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51.
Rameshwar Adhikari Matthias Buschnakowski Sven Henning Sylvia Goerlitz Trinh An Huy Werner Lebek Reinhold Godehardt Georg Hannes Michler Ralf Lach Kalman Geiger Konrad Knoll 《Macromolecular rapid communications》2004,25(5):653-658
Summary: The morphology and tensile deformation behaviour of a highly asymmetric styrene/butadiene star block copolymer (polystyrene (PS) content = 74%) containing random PS‐co‐PB (polybutadiene) copolymer as a rubbery phase were investigated. The existence of double yielding, similar to that observed in some semicrystalline polymers, was detected in this nanostructured amorphous polymer. The observed phenomenon may be correlated with two different micromechanical processes taking place at the initial stage of deformation.
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53.
Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities 总被引:11,自引:0,他引:11
Bollmann A Blann K Dixon JT Hess FM Killian E Maumela H McGuinness DS Morgan DH Neveling A Otto S Overett M Slawin AM Wasserscheid P Kuhlmann S 《Journal of the American Chemical Society》2004,126(45):14712-14713
Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system. 相似文献
54.
McCarthy MC Gottlieb CA Thaddeus P Thorwirth S Gauss J 《The Journal of chemical physics》2011,134(3):034306
The rotational spectra of two small silicon sulfides, silanethione H(2)SiS and the disilicon sulfide ring Si(2)S, have been detected in the centimeter band by Fourier transform microwave spectroscopy of a molecular beam; lines of H(2)SiS were also observed in the millimeter band up to 377 GHz in a glow discharge. Precise rotational and centrifugal distortionconstants have been determined for the normal and a number of the more abundant rare isotopic species of both closed-shell molecules. Theoretical equilibrium (r(e)) structures of H(2)SiS and Si(2)S were derived from coupled-cluster calculations that included triple and quadruple excitations, core correlation, and extrapolation to the basis-set limit. The r(e) structures agree to within 5×10(-4) A? and 0.1(°) with empirical equilibrium (r(e)(emp)) structures derived from the experimental rotational constants, combined with theoretical vibrational and electronic corrections. Both H(2)SiS and Si(2)S are good candidates for radioastronomical detection in the circumstellar shells of evolved carbon-rich stars such as IRC+10216, because they are fairly polar and are similar in composition to the abundant astronomical molecule SiS. 相似文献
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Dirk Pfefferkorn Sven Sonntag Samuel O. Kyeremateng Zofia Funke Hans‐Werner Kammer Jörg Kressler 《Journal of Polymer Science.Polymer Physics》2010,48(17):1893-1900
The pressure–volume–temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure–volume–temperature data, the reduction parameters for the Flory‐Orwoll‐Vrij equation‐of‐state were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable surface excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of ~0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation‐of‐state thermodynamics. The minimum of surface tension can be well explained by weak self‐association of PEO in the bulk. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1893–1900, 2010 相似文献
57.
Sven Fleischmann Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2010,48(21):4884-4888
Single‐electron transfer living radical polymerization (SET‐LRP) has developed as a reliable, robust and straight forward method for the construction well‐defined polymers. To span an even larger variety of functional monomers, we investigated the copolymerization of methyl methacrylate with methacrylic acid by SET‐LRP. Copolymerizations were catalyzed by Cu(0)/Me6‐TREN and performed in MeOH/H2O mixtures at 50 °C. The SET‐LRP copolymerizations of varying methacrylic acid content were evaluated by kinetic experiments. At low (2.5%) and moderate (10%) MAA loadings, the copolymerizations obeyed perfect first order kinetics (kpapp = 0.008 min?1 and kpapp = 0.006 min?1) and exhibited a linear increase in molecular weights with conversion providing narrow molecular weight distributions. The SET‐LRP of MMA/25%‐MAA was found to be significantly slower (kpapp = 0.0035 min?1). However, a reasonable first‐order kinetics in monomer consumption was maintained, and the control of the polymerization process was preserved since the molecular weight increased linearly with conversion and could therefore be adjusted. This work demonstrates that the copolymerization of methacrylic acid by SET‐LRP is feasible and the design of well‐defined macromolecules comprising acidic functionality can be achieved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
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59.
Jens Langer Sven Krieck Reinald Fischer Helmar Görls Matthias Westerhausen Prof. Dr. 《无机化学与普通化学杂志》2010,636(7):1190-1198
Iodide is a very soft and large anion and as such its extreme ability to be polarized leads to a flat energy surface with respect to the variation of the Ca–I distances in [(L)nCaI2] and [(L)nCa(R)I]. The influence of the donor strength and the bulkiness of the neutral coligands L on the Ca–I distances is studied. The base adducts of calcium diiodide can be isolated after the addition of L to CaI2 or from the Schlenk equilibrium after the direct synthesis of calcium powder with aryl iodides. As L the ethers diethyl ether (Et2O), tetrahydrofuran (thf), tetrahydropyran (thp), 1,2‐dimethoxyethane (dme), 18‐crown‐6 (18C6), bis(methoxyethyl)ether (diglyme), and amines tetramethylethylenediamine (tmeda), and hexamethyltriethylenetetramine (hmteta) are studied yielding the adducts [(thp)4Ca(Ph)I] ( 1a ), [(thf)4Ca(Ph)I] ( 1b ), [(dme)2(thf)Ca(Ph)I] ( 1c ), [(18C6)Ca(Ph)I] ( 1d ), and [(tmeda)2Ca(Ph)I] ( 1e ), as well as [(thp)4CaI2] ( 2a ), [(thf)4CaI2] ( 2b ), [(Et2O)4CaI2] ( 2c ), [(diglyme)(thf)2CaI2] ( 2d ), [(diglyme)(dme)CaI2] ( 2e ), [(dme)2(thf)CaI2] ( 2f ), [(18C6)CaI2] ( 2g ), [(tmeda)2CaI2] ( 2h ), and [(hmteta)CaI2] ( 2i ). For comparison reasons, [(thf)4Ca(Ph)Br] ( 3a ), [(thp)4CaBr2] ( 4a ), [(thf)4CaBr2] ( 4b ), and [(dme)2(AcOH)CaBr2] ( 4c ) with AcOH being acetic acid are included as well. The comparison shows that the coordination number of calcium itself only plays an insignificant role whereas bulkiness and donor strength of L represent the key influences. 相似文献
60.
Brauchli SY Constable EC Harris K Häussinger D Housecroft CE Rösel PJ Zampese JA 《Dalton transactions (Cambridge, England : 2003)》2010,39(44):10739-10748
The ligand 6,6"bis(4-methoxyphenyl)-4'-phenyl-2,2':6',2"terpyridine (2) has been prepared and characterized; deprotection using pyridinium chloride leads to the formation of 6,6"bis(4-hydroxyphenyl)-4'-phenyl-2,2':6',2"terpyridinium chloride ([H3]Cl). Treatment of the latter with 3-(2-(2-bromoethoxy)ethoxy)prop-1-ene under basic conditions yields ligand 4 containing pendant, alkene-terminated chains. Whereas direct complexation of 4 with ruthenium(II) proved problematical, the homoleptic complexes [Fe(2)(2)][PF(6)](2) and [Ru(2)(2)][PF(6)](2) were prepared in good to moderate yields. In the solid state, both complexes exhibit multiple face-to-face π-stacking of arene and pyridine rings which influences the coordination geometry about the metal ion. Consequential weakening of the ligand field results in [Fe(2)(2)][PF(6)](2) being high-spin. Variable temperature solution (1)H NMR spectroscopic studies confirm the iron(ii) centre remains high-spin between 200 and 295 K. The paramagnetically shifted (1)H NMR spectrum exhibits signals in the range δ 109.7 to -66.5 ppm and has been fully assigned. Paramagnetic relaxation enhancement (PRE) has been used to correlate the observed proton line-widths to the distances of the protons from the metal centre and these are in good agreement with the Fe···H separations observed in the solid state. The [Fe(2)(2)](2+) ion undergoes two dynamic processes (i) rotation of the pendant phenyl rings which is fast on the NMR timescale at 200 K, and (ii) twisting and sliding of the aromatic rings of the tpy and anisyl units which interconverts the two enantiomers of [Fe(2)(2)](2+) at 295 K. 相似文献