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91.
François Piriou Karl Lintner Hung Lam-Thanh Flavio Toma Serge Fermandjian 《Tetrahedron》1978,34(5):553-556
In order to analyze completely the ring conformation of [S]-Proline (l-thiazolidine-4-carboxylic acid) this compound has been synthesized with its Cδ atom enriched at 90% in 13C. The 1H-1H, 13C-1H, 13C-13C vicinal coupling constants measured at several pH values describe well the geometry of the thiazolidine ring. The results suggest that the ring has an average planar conformation only in a narrow range of pH close to the pK of the amine group. Above and below this pH the ring tends to adopt preferentially the Sγendo and Sγexo puckered conformations respectively. It is concluded that a good correlation exists between the value of the dihedral angle ø and the character Sγendo or Sγexo of the ring. 相似文献
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Toma L Lescouëzec R Vaissermann J Delgado FS Ruiz-Pérez C Carrasco R Cano J Lloret F Julve M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):6130-6145
The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties. 相似文献
95.
Diego Colombo Fiamma Ronchetti Antonio Scala Lucio Toma 《Journal of carbohydrate chemistry》2013,32(1):89-94
Abstract Methyl 6-O-butyryl-α-D- and L-glucopyranosides and methyl 6-deoxy-α-D- and L-glucopyranosides have been submitted to lipase catalyzed butyrylation, using porcine pancreatic, Candida cylindracea, and Pseudomonas cepacia lipases in organic solvents. The influence of the orientation of the secondary hydroxyl groups on the regioselectivity of the butyrylation is discussed. 相似文献
96.
The use of a newly synthesized fluorescent probe, ABM (conditional name), to determine changes of membrane composition (fluidity), biomass yield, ethanol productivity, and yield of Zymomonas mobilis under anaerobic conditions was investigated. A strong correlation between ABM spectral characteristics in cell suspension and all obtained parameters was observed. It was concluded that application of ABM is a useful tool to detect temperature-induced changes in the membrane composition of Zymomonas mobilis. 相似文献
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Toma Albu 《Journal of Pure and Applied Algebra》2007,208(1):101-106
Abstract Cogalois Theory for arbitrary profinite groups was initiated by T. Albu and ?.A. Basarab [An Abstract Cogalois Theory for profinite groups, J. Pure. Appl. Algebra 200 (2005) 227-250]. The aim of this paper is twofold: firstly, to present the abstract group theoretic versions of various types of Kummer field extensions, and secondly, to show how some basic results of the (Field Theoretic) Cogalois Theory can be very easily deduced from their abstract versions. 相似文献
100.
Perić Mato Nižetić Sandro Garašić Ivica Gubeljak Nenad Vuherer Tomaž Tonković Zdenko 《Journal of Thermal Analysis and Calorimetry》2020,141(1):313-322
Journal of Thermal Analysis and Calorimetry - In this investigation, a T-joint numerical welding simulation of thick steel plates is performed to estimate transient temperature distributions,... 相似文献