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991.
992.
Benjamin Eberle Dr. Olaf Hübner Alexandra Ziesak Dr. Elisabeth Kaifer Prof. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8578-8590
Organic electron donors are of importance for a number of applications. However, the factors that are essential for a directed design of compounds with desired reduction power are not clear. Here, we analyze these factors in detail. The intrinsic reduction power, which neglects the environment, has to be separated from extrinsic (e.g., solvent) effects. This power could be quantified by the gas‐phase ionization energy. The experimentally obtained redox potentials in solution and the calculated ionization energies in a solvent (modeled with the conductor‐like screening model (COSMO)) include both intrinsic and extrinsic factors. An increase in the conjugated π‐system of organic electron donors leads to an increase in the intrinsic reduction power, but also decreases the solvent stabilization. Hence, intrinsic and extrinsic effects compete against each other; generally the extrinsic effects dominate. We suggest a simple relationship between the redox potential in solution and the gas‐phase ionization energy and the volume of an organic electron donor. We finally arrive at formulas that allow for an estimate of the (gas‐phase) ionization energy of an electron donor or the (gas‐phase) electron affinity of an electron acceptor from the measured redox potentials in solution. The formulas could be used for neutral organic molecules with no or only small static dipole moment and relatively uniform charge distribution after oxidation/reduction. 相似文献
993.
From an Isolable Acyclic Phosphinosilylene Adduct to Donor‐Stabilized SiE Compounds (E=O,S, Se)
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Kerstin Hansen Dr. Tibor Szilvási Dr. Burgert Blom Dr. Elisabeth Irran Prof. Dr. Matthias Driess 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):18930-18933
Reaction of the arylchlorosilylene‐NHC adduct ArSi(NHC)Cl [Ar=2,6‐Trip2C6H3; NHC=(MeC)2(NMe)2C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC‐stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh2), which could be structurally characterized. Compound 2 , when reacted with one molar equiv selenium and sulfur, affords the silanechalcogenones 4 a and 4 b (ArSi(NHC)(?E)PPh2, 4 a : E=Se, 4 b : E=S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the Si?P bond, leads to 3 a and 3 b (ArSi(NHC)(?E)‐E‐P(?E)Ph2, 3 a : E=Se, 3 b : E=S), respectively. Additionally, the exposure of 2 to N2O or CO2 yielded the isolable NHC‐stabilized silanone 4 c , Ar(NHC)(Ph2P)Si?O. 相似文献
994.
We give a conceptual explanation of universal deformation formulas for unital associative algebras and prove some results on the structure of their moduli spaces. We then generalize universal deformation formulas to other types of algebras and their diagrams. 相似文献
995.
Hedok Lee Elisabeth Caparelli Haifang Li Amit Mandal S. David Smith Shaonan Zhang Thomas V. Bilfinger Helene Benveniste 《Magnetic resonance imaging》2013
Partial volume effects in proton magnetic resonance spectroscopy in the brain have been studied previously in terms of proper water concentration calculations, but there is a lack of disclosure in terms of voxel placement techniques that would affect the calculations. The purpose of this study is to facilitate a fully automated MRS voxel registration method which is time efficient, accurate, and can be extended to all imaging modalities. A total of thirteen healthy adults underwent single voxel 1H-MRS scans in 3.0 T MRI scanners. Transposition of a MRS voxel onto an anatomical scan is derived along with a full calculation of water concentration with a correction term to account for the partial volume effects. Five metabolites (tNAA, Glx, tCr, mI, and tCho) known to yield high reliability are studied. Pearson’s correlation analyses between tissue volume fractions and metabolite concentrations were statistically significant in parietal (tCr, Glx, and tNAA) lobe and occipital lobe (tNAA). MRS voxel overlaps quantified by dice metric over repeated visits yielded 60% ~ 70% and coefficients of variance in metabolites concentration were 4% ~ 10%. These findings reiterate an importance of considering the partial volume effects when tissue water is used as an internal concentration reference so as to avoid misinterpreting a morphometric difference as a metabolic difference. 相似文献
996.
Veronica Marin Elisabeth Holder Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(2):374-385
Methyl methacrylate‐containing bipyridine monomers were synthesized with a hydoxy‐functionalized bipyridine. The 4′‐methyl group of the 2,2′‐bipyridine was used to introduce hydoxy‐functionalized alkyl spacers of two different lengths. Two, different synthetic routes were applied for the preparation of the hydoxy‐functionalized bipyridine via a bromo‐(C7 spacer) or a silylated‐(C3 spacer) intermediate. A copolymer of poly(methyl methacrylate) with bipyridine units in the side chains was prepared by free‐radical copolymerization and characterized with 1H NMR, ultraviolet–visible, and IR spectroscopy as well as gel permeation chromatography. The bipyridine units of the copolymer were reacted with ruthenium bipyridine precursors. The resulting graft copolymers displayed promising photophysical and electrochemical properties, opening interesting perspectives for applications in the field of solar‐cell devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 374–385, 2004 相似文献
997.
Markus Gahleitner Bernd Kretzschmar Gerhard Van Vliet Jacques Devaux Doris Pospiech Klaus Bernreitner Elisabeth Ingolic 《Rheologica Acta》2006,45(4):322-330
Polypropylene/polyamide-6 (PP/PA-6) blends and their nanocomposites with unmodified and organically treated layered silicates (montmorillonite) were prepared in a melt compounding process to explore their mechanical performance. The rheology and morphology of these materials was studied. It could be shown that in all cases the inorganic filler enriched in the PA phase, resulting in a phase coarsening of the PP/PA nanocomposite as compared to the non-filled PP/PA blend. The mechanical properties of these nanoblends are consequently only slightly better than the pure polymers with respect to the modulus, while the impact level is below the pure polymers, reflecting the heterogeneity of the nanoblend. 相似文献
998.
Wagner J Barreto Maira R Ribeiro Maria C Solci leda S Scarminio Jorge Nozaki Elisabeth de Oliveira S?nia R G Barreto 《Analytical sciences》2005,21(3):209-214
The hydrological cycle of Lake Ipê and the principal parameters that could affect its abiotic parameters and its metal (Fe, Mn, and Cd) concentrations were investigated. A detailed study of seasonal variations using Principal Components Analysis (PCA) for the most relevant metals (Fe, Mn and Cd) was performed, assisted by the MINTEQA2 geochemical equilibrium program using 15 water abiotic parameters. The abiotic variables and metals in the lake were governed by the hydrological regimen of the Parana River and by the occurrence of occasional flood pulses and rainfall. The occurrence of cadmium is a concern; its presence could be due to industrial or agricultural activities or even to a natural geochemical process. 相似文献
999.
Viviane Nadège Nenkep~a Jovita Chi Shirri~a Hanh Trinh Van-Dufat~b Falindor Sipepnou~a Philippe Vérité~d Elisabeth Seguin~c Francois Tillequin~b Jean Wandji~ 《中国化学快报》2008,19(8):943-946
Two new compounds 7-hydroxy-5-O-(β-D-glucopyranoside) flavan (1) and (Z)-4',6'-dihydroxy-2'-O-(β-D-glucopyranoside) chalcone (2), along with eight known compounds, were isolated from the stem bark of Drypetes parvifolia (Euphorbiaceae). Their structures were established on the basis of spectroscopic analysis and chemical evidence. 相似文献
1000.
Cadmium dicyanamide Cd[N(CN)2]2 was synthesized through aqueous ion exchange at room temperature. A reversible phase transition was detected by in situ X‐ray powder diffractometry above 55 °C. The crystal structures of both phases were determined by X‐ray powder diffraction (β‐Cd[N(CN)2]2: T = 22 °C, a = 621.60(3), b = 748.76(4), c = 770.21(5) pm, β = 91.784(3)°, P21/n (no. 14), Z = 2, wRp = 0.063, Rp = 0.050, RF = 0.059; α‐Cd[N(CN)2]2: T = 150 °C, a = 624.62(5), b = 752.92(6), c = 768.30(7) pm, Pnnm (no. 58), Z = 2, wRp = 0.083, Rp = 0.064, RF = 0.087). Both polymorphs consist of Cd2+ and bent planar [N(CN)2]— ions. α‐Cd[N(CN)2]2 crystallizes analogously to rutile and is isotypic with MII[N(CN)2]2(M = Mg, Cr, Mn, Co, Ni, Cu). The monoclinic low‐temperature polymorph β‐Cd[N(CN)2]2 is closely related to that of the orthorhombic high‐temperature polymorph α‐Cd[N(CN)2]2 by a translationengleiche transition of index 2. 相似文献