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101.
Michael E. Böttcher Nadja Neubert Katja von Allmen Elias Samankassou Thomas F. Nägler 《Isotopes in environmental and health studies》2018,54(3):324-335
In this study, we present the experimental results for stable barium (Ba) isotope fractionation (137Ba/134Ba) during the transformation of aragonite (CaCO3) and gypsum (CaSO4·2H2O) in Ba-bearing aqueous solution to witherite (BaCO3) and barite (BaSO4), respectively. The process was studied at three temperatures between 4 and 60?°C. In all cases, the transformation leads to a relative enrichment of the lighter 134Ba isotope in the solid compared to the aqueous solution, with 137/134Ba enrichment factors between –0.11 and ?0.17?‰ for BaCO3, and –0.21 and –0.26?‰ for BaSO4. The corresponding mass-dependent 138/134Ba enrichment factors are ?0.15 to –0.23?‰ for BaCO3, and –0.28 to –0.35?‰ for BaSO4. The magnitude of isotope fractionation is within the range of recent reports for witherite and barite formation, as well as trace Ba incorporation into orthorhombic aragonite, and no substantial impact of temperature can be found between 4 and 80?°C. In previous studies, ion (de)solvation has been suggested to impact both the crystallization process of Ba-bearing solids and associated Ba isotope fractionation. Precipitation experiments of BaSO4 and BaCO3 using an methanol-containing aqueous solution indicate only a minor effect of ion and crystal surface (de)solvation on the overall Ba isotope fractionation process. 相似文献
102.
Riollet V Quadrelli EA Copéret C Basset JM Andersen RA Köhler K Böttcher RM Herdtweck E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7358-7365
The reaction of [Mn(CH2tBu)2(tmeda)] (1) and a silica partially dehydroxylated at 700 degrees C (SiO(2/700)) yields a single surface species [([triple bond]SiO)Mn(CH2tBu)(tmeda)] (2a; tmeda = tetramethylethylendiamine), while a mixture of 2a and [([triple bond]SiO)2Mn(tmeda)] (2b) is obtained by using SiO(2/200), SiO(2/300), or SiO(2/500) as evidenced by mass balance analysis, and IR and EPR spectroscopy. The reaction of 1 and (c-C5H9)7Si7O12SiOH (3), a soluble silanol that is a molecular model for a silica support, generates the bis-siloxy complex 4, [[(c-C5H9)7Si7O12SiO]2Mn(tmeda)2], in a quantitative yield; compound 4 was characterized by single-crystal X-ray diffraction. These reactions exemplify the limitation of considering molecular silanol derivatives as straightforward and reliable homogeneous models for silica, and address the need for thorough characterization of surface species by the use of surface-science techniques. These studies show the possibility of preparing coordinatively and geometrically unique surface species that would be difficult to prepare by solution chemistry methods; insights into the chemical and physical properties of these surface species are also gained. 相似文献
103.
Steady-state simulations of fluid flow and temperature field are presented for an equipment that is used to grow Zinc Selenide single crystals from the gaseous phases via physical (PVT) or chemical vapour transport (CVT). Due to the horizontal arrangement of the air-filled furnace pipe calculating the natural convection in the air requires a 3D (three-dimensional) treatment of the problem. The simulations have been done by applying the commercial finite-element package FIDAP. The Navier-Stokes equation is solved with the Boussinesq approximation. The heat transfer analysis comprises also internal radiation wall-to-wall exchange. Due to the presence of the ampoule in the pipe, the development of vortices with higher velocities is restrained, so that the maximum velocity is roughly 1/4 of that in the case without an ampoule. 相似文献
104.
105.
Albrecht Bö ttcher Yuri I. Karlovich 《Transactions of the American Mathematical Society》1999,351(8):3143-3196
We describe the spectra and essential spectra of Toeplitz operators with piecewise continuous symbols on the Hardy space in case , is a Carleson Jordan curve and is a Muckenhoupt weight in . Classical results tell us that the essential spectrum of the operator is obtained from the essential range of the symbol by filling in line segments or circular arcs between the endpoints of the jumps if both the curve and the weight are sufficiently nice. Only recently it was discovered by Spitkovsky that these line segments or circular arcs metamorphose into horns if the curve is nice and is an arbitrary Muckenhoupt weight, while the authors observed that certain special so-called logarithmic leaves emerge in the case of arbitrary Carleson curves with nice weights. In this paper we show that for general Carleson curves and general Muckenhoupt weights the sets in question are logarithmic leaves with a halo, and we present final results concerning the shape of the halo.
106.
107.
Na2Mn2S3 was prepared by reacting manganese powder with an excess of anhydrous sodium carbonate and elemental sulfur at 870 K. Extraction of the solidified melt with water and alcohol yielded well developed, bright red crystals. Na2Mn2S3 crystallizes with a new monoclinic structure type, space group , with a = 14.942(2)Å, b = 13.276(2)Å, c = 6.851(2)Å, and β = 116.50(1)°. The crystal structure was determined from single crystal diffractometer data and refined to a conventional R value of 0.026 for 1613 observed reflections. The atomic arrangement shows sulfur-manganese-sulfur slabs which are separated from each other by corrugated layers of sodium atoms. A prominent feature of the crystal structure is the formation of short, four-membered zigzag chains built up by MnS4 tetradedra sharing edges. These chains are further connected by the remaining apices to form an infinite sheet. Short MnMn distances (3.02 and 3.05 Å, respectively) are found within the four membered chains. Susceptibility measurements show antiferromagnetic interactions between the Mn atoms. 相似文献
108.
Synthesis and Crystal Structure of the Adducts [DB-18C6] · CH3CN · CH3CSOH and [DC-18C6](CH3CSOH)2 as well as of the Salt-like Compounds [Cs(B-15C5)2]CH3CSS and [Cs(DB-18C6)]2S5(DMF)21) The reaction products of crown ethers, cesium, and sulfur in aprotic solvents like acetonitrile and dimethylformamide strongly depend on the reaction conditions. Using CH3CN as a solvent, sometimes neutral host-guest adducts crystallize only, e.g., [dibenzo-18C6] · CH3CN · CH3CSOH (monoclinic, S. G. P21/c, Z = 4, a = 9.73(1) Å, b = 22.03(1) Å, c = 11.86(1) Å, β = 91.8(1)°) or [dicyclohexyl-18C6](CH3CSOH)2 (monoclinic, S. G. P21/n, Z = 2, a = 7.75(1) Å, b = 10.32(1) Å, c = 17.73(1) Å, β = 95.7(1)°). The monothioacetic acid, CH3CSOH, must be regarded as the first product of the hydrolysis of CH3CN. Furthermore, another product of this kind of hydrolysis, CH3CSSH, is obtained too. Therefore, we also obtain the salt-like compound [Cs(benzo-15C5)2]CH3CSS (monoclinic, S. G. C2/c, Z = 4, a = 16.05(1) Å, b = 16.73(1) Å, c = 13.11(1) Å, β = 106.3(1)°). If the solvent DMF is used, the pentasulfide [Cs(dibenzo-18C6)]2S5(DMF)2 crystallizes (monoclinic, S. G. P21/n, Z = 4, a = 14.79(1) Å, b = 14.24(1) Å, c = 25.74(1) Å, β = 92.7(1°. The S52? anions show the cis-conformation. 相似文献
109.
110.
Crystals of the title compound were obtained by annealing a powder of Tl2Te3 in a vertical temperature gradient (230 °C–240 °C, 4 weeks). Tl2Te3 crystallizes in space group C2/c with lattice parameters of a = 13.275(1) Å, b = 6.562(1) Å, c = 7.918(1) Å, and β = 107.14°(2). The tellurium atoms form chains [Te32–], consisting of interconnected linear triatomic · Te–^Te–Te · groups which are isosteric with XeF2. The Te–Te distances of the XeF2-like units are 3.02 Å, the connecting ones 2.83 Å. 相似文献