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951.
Antiaromaticity to Aromaticity: From Boroles to 1,2‐Azaborinines by Ring Expansion with Azides 下载免费PDF全文
Prof. Dr. Holger Braunschweig Dr. Christian Hörl Lisa Mailänder Dr. Krzysztof Radacki Dr. Johannes Wahler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9858-9861
We have exploited the reactivity of antiaromatic boroles, gaining access to aryl‐substituted monocyclic 1,2‐azaborinines. The observed ring‐expansion reaction of inherently electron‐deficient boroles with organometallic and organic azides is demonstrated for representative examples. This substance class is expected to provide a new avenue into 1,2‐azaborinine chemistry, especially in the area of functional organoboron materials. Our results are based on NMR and UV/Vis spectroscopy as well as single‐crystal X‐ray crystallography and provide a virtually quantitative approach that also offers numerous points of variation. 相似文献
952.
Prot Pakoński Gregor Tanner Karol Życzkowski 《Journal of statistical physics》2003,111(5-6):1331-1352
Any directed graph G with N vertices and J edges has an associated line-graph L(G) where the J edges form the vertices of L(G). We show that the non-zero eigenvalues of the adjacency matrices are the same for all graphs of such a family L
n
(G). We give necessary and sufficient conditions for a line-graph to be quantisable and demonstrate that the spectra of associated quantum propagators follow the predictions of random matrices under very general conditions. Line-graphs may therefore serve as models to study the semiclassical limit (of large matrix size) of a quantum dynamics on graphs with fixed classical behaviour. 相似文献
953.
Mind the correct basis set: A case study for predicting gas phase acidities of small compounds using calculations from first principles 下载免费PDF全文
Nina Tymińska Marta Włoch A. Timothy Royappa 《International journal of quantum chemistry》2015,115(1):42-49
Some of the most popular computational methods have been utilized to determine a dependency of the acidity trend of the first‐row hydrides on a choice of basis set. For about three decades, methyl anion ( ) was known as the strongest base but after Tian et al. were able to produce the gas phase lithium monoxide anion (LiO–) they discovered it was a stronger base than (Tian et al., Proc Natl Acad Soc USA 2008, 105, 7647). Furthermore, the authors confirmed their experimental results using high‐level ab initio methods, namely W1 and W2C composite methods, as well as complete active space‐averaged quadratic coupled cluster and Brueckner Doubles with triple excitation contribution (BD(T)) within the aug‐cc‐pVQZ basis set. These methods are highly demanding in terms of the computational effort as well as a level of expertise needed from the user to correctly conduct such calculations. We have shown that the proper acidity trend, that is, , can be obtained with less expensive, ”black‐box” type methods if only the basis set is properly chosen. Our results prove that the diffuse augmented basis sets are absolutely necessary for appropriate predictions of acidities. Our calculations show that the correct order of is achieved by augmenting relatively small cc‐pVXZ (X = D,T) basis sets. A similar effect is observed for the family of Pople's basis sets. Our estimate for with CCSD(T)/aug‐cc‐pVTZ was 423.8 kcal/mol, which agrees very well with the experimental value 425.7 ± 6.1 kcal/mol. An important finding is that the proper acidity trend may be reversed if the basis sets are not correctly selected. © 2014 Wiley Periodicals, Inc. 相似文献
954.
This paper deals with a general combinatorial optimization problem in which closed intervals and fuzzy intervals model uncertain element weights. The notion of a deviation interval is introduced, which allows us to characterize the optimality and the robustness of solutions and elements. The problem of computing deviation intervals is addressed and some new complexity results in this field are provided. Possibility theory is then applied to generalize a deviation interval and a solution concept to fuzzy ones. 相似文献
955.
Dr. Carsten Lenczyk Dr. Dipak Kumar Roy Kai Oberdorf Dr. Jörn Nitsch Dr. Rian D. Dewhurst Dr. Krzysztof Radacki Prof. Dr. Jean-François Halet Prof. Dr. Todd B. Marder Prof. Dr. Matthias Bickelhaupt Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16544-16549
The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH2] (Dur=2,3,5,6-Me4C6H) and [(Me3Si)2NBH2] led to the formation of bridging borylene complexes of the form [(Cp*RuH)2BR] (Cp*=C5Me5; 1 a : R=Dur; 1 b : R=N(SiMe3)2) through oxidative addition of the B−H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF3)2-C6H3BH2] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)4[(Cp*Ru)2B4H5(3,5-(CF3)2C6H3)4] ( 4 ), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp*Ru)2(μ-H)B4H9] ( I ) indicates that there appear to be no classical σ-bonds between the boron atoms in complex I , whereas in the case of 4 the B4 chain better resembles a network of three B−B σ bonds, the central bond being significantly weaker than the other two. 相似文献
956.
Starosta R Puchalska M Cybińska J Barys M Mudring AV 《Dalton transactions (Cambridge, England : 2003)》2011,40(11):2459-2468
The luminescent complexes of triphenylphosphine and two interesting aminomethylphosphines: P(CH(2)N(CH(2)CH(2))(2)NCH(3))(3) and P(CH(2)N(CH(2)CH(2))(2)O)(3) with copper(I) iodide and 2,9-dimethyl-1,10-phenanthroline (dmp): [CuI(dmp)PPh(3)], [CuI(dmp)P(CH(2)N(CH(2)CH(2))(2)NCH(3))(3)] and [CuI(phen)P(CH(2)N(CH(2)CH(2))(2)O)(3)] are presented in this work. These complexes were characterized in solution by means of NMR spectroscopy and their structures were crystallographically determined in the solid state. All complexes crystallize as the discrete dimers bound by π-stacking interactions between dmp rings. The coordination geometry about the Cu(I) centre is pseudo-tetrahedral showing small flattening and large rocking distortions. The investigated compounds exhibit intense orange photoluminescence in the solid state (emission peaks at r.t.: λ(max) = 588-592 nm; τ = 1.7-2.2 and 6.4-10.0 μs; at 77 K: λ(max) = 605-612 nm; τ = 4.8-6.5 and 32-47 μs), which is several orders higher than the luminescence of the analogous complexes with 1,10-phenanthroline (phen). Electronic and structural properties of the [CuI(dmp/phen)PR(3)] complexes were characterized using DFT methods to interpret their photophysics. On the basis of TDDFT calculations the broad CT bands observed in UV-Vis spectra are interpreted as the two mixed transitions from σ(CuI) bond with a small admixture of σ(CuP) bond to π* phen or dmp ligand: (MX,MPR(3))LCT, while the emissions most probably occur from two triplet states which are in thermal equilibrium. 相似文献
957.
958.
Marek L. Główka Zbigniew J. Kamiński Gastone Gilli Valerio Bertolasi 《Journal of chemical crystallography》1986,16(4):569-576
C14H17NO4 crystallizes in the monoclinic space groupP21/n (Z=4) witha=10.208(2),b=10.888(2),c=11.909(2) Å, and=90.89(2)°. The structure was solved by direct methods and refined by full-matrix LSQ to anR factor of 0.036. The 4-oxo-1,3-dioxane ring is in a slightly distorted O(1)-sofa conformation flattened at the C(4) end with the 5-isopropyl substituent in a pseudoaxial position and planar lactone group. The molecules form dimers by means of intermolecular N-HO(4) hydrogen bonds of 3.091(2) Å. The1H NMR spectrum of the title compound shows unusual features. 相似文献
959.
Mária Hvastijová Jiri Kohout Marián Okruhlica Jerzy Mroziński Lothar Jäger 《Transition Metal Chemistry》1993,18(6):579-582
Summary Dicyanamide complexes of CuII, NiII and CoII of the type M[N(CN)2]2L2, where L = benzimidazole, 2-methyl- or 2-ethylbenzimidazole, have been prepared and studied by spectroscopy and magnetochemistry. The complexes, except for Co[N(CN)2]2 (benzimidazole)2, are six-coordinate, involving bidentate bridging dicyanamide groups. While the NiII complexes have practically octahedral structures, the CuII complexes are pseudooctahedral with similar tetragonal distortion. The ligand field strength in these complexes depends mainly on the steric effect of the benzimidazole ligands. The CoII complex of benzimidazole is monomeric tetrahedral, but that of 2-ethylbenzimidazole is tetragonal octahedral. The oridging function of dicyanamide in the six-coordinate complexes is realized either through both cyanide or through amide and cyanide nitrogens. The complex Cu[N(CN)2]2 (2-methylbenzimidazole)2 is a weak antiferromagnet (J = -0.1 cm–1), exhibiting under ca. 15 K a long-range antiferromagnetic ordering. 相似文献
960.
Mariusz Krupiński Beata Krupińska Krzysztof Labisz Zbigniew Rdzawski Wojciech Borek 《Journal of Thermal Analysis and Calorimetry》2014,118(2):1361-1367
In this study, the change of the cooling rate in the range of about 0.1–1 °C s?1 and the addition of Sr on the crystallization kinetics of the cast zinc alloys of the ZnAlCu type, as well as its relation to the microstructure were also investigated. Therefore, the aim of the rapid crystallisation is the achievement of materials with better properties, which can be obtained by refinement of the dendritic or eutectic microstructure, elimination of segregation, or creation of metastable phases and their morphology changes. In the investigated alloys, the change of cooling rate of 1 °C s?1 has caused microstructure’s refinement as well as increase in hardness. Increase in the cooling rate causes also morphology changes of the η + α eutectic, and makes generally a global overcooling of the alloy as well as change in the temperatures at the beginning of crystallization T DN and of the alloy crystallization T S. The presented investigations concerning the electron microscopy methods, including transmission electron microscopy, allow revealing the crystallographic structure, based on the d-spacing changes, as well as the diffraction method used for phase determination, which is a helpful tool for the explanation of the important points in the thermo-derivative analysis curve, where the relation between the amount of phase and the occurrence of new phases can be determined. 相似文献