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51.
S. Szabó R. Khlafulla Sz. Szarvas M. Almás L. Ladányi Gy. Szókán 《Chromatographia》2000,51(1):S193-S201
Summary Indirect chiral separation methods based on enantiomeric derivatizations were developed in order to monitor optical purity
of uncoded amino acids and a new series of amino acid derivatives. Marfey's reagent was used for derivatization of amino groups:
whilst boxyl groups were derivatised with (1R, 2R)-or (1S, 2S)-2-amino-1(4-nitrophenyl)-1,3-propanediol reagents were used,
respectively. The separations of diastereomeric derivatives formed via derivatization were optimized in RP-HPLC and NP-HPLC
systems.
Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999 相似文献
52.
Four targeted octasubstituted zinc azaphthalocyanines (ZnAzaPc), substituted with thiophen-2-yl groups and ortho-substituted phenoxy groups, were obtained by cyclotetramerization of 5-aryloxy-6-(thiophen-2-yl)pyrazine-2,3-dicarbonitriles. Thiophen-2-yl substituents are known to extend the macrocyclic conjugation, and thereby cause red-shifted UV–Vis Q-bands. Peripheral phenoxy groups with bulky ortho substituents are expected to suppress aggregation and thereby improve solubility of these compounds. The reagent Zn(quinoline)2Cl2 was used for one-step syntheses of these ZnAzaPc. Four tetrasubstituted ZnAzaPc, with phenoxy, (2-isopropyloxy)phenoxy, (2-isopropyl)phenoxy or (2-tert-butyl)phenoxy substituents, were obtained as controls from 5-aryloxypyrazine-2,3-dicarbonitriles. The tetra- and octa-substituted ZnAzaPc, 5 and 6, were obtained in 30–50% yields after purification by chromatography on silica. UV–Vis Q-bands with high molar extinction coefficients (100 000–160 000), were observed at 635 nm for compounds 5, and at 660–665 nm for 6. Grass-green solutions were obtained of compounds 6 in most organic solvents, whereas the less soluble compounds 5 gave blue-green solutions. 2D NMR methods were applied in analyses of DMSO-d6 solutions of ZnAzaPc 5 and 6. Broad and partly overlapping 1H NMR signals for some of the compounds indicate some aggregation as well as presence of two or more structural isomers. Molecular ions of ZnAzaPc 5 and 6 were determined by mass spectrometry (MALDI-TOF). 相似文献
53.
Ján Derco Andreja Žgajnar Gotvajn Jana Zagorc-Končan Beáta Almásiová Angelika Kassai 《Chemical Papers》2010,64(2):237-245
Kinetics and efficiency of Fenton’s and ozonation processes for the pretreatment of two landfill leachates (fresh and mature)
resulting from municipal waste disposal were studied. Both samples presented high organic load, high toxicity and low biodegradability.
These were the reasons why oxidative treatment was proposed. Fresh and mature leachate showed different behaviors in the oxidation
experiments. The final extents of removal were attained in comparable time intervals in both oxidation systems. Maximal removal
of organics by the Fenton’s oxidation reached more than 50 % according to COD. Zero or first order kinetics were found the
best to describe the organic components (in terms of COD and DOC) removal by the Fenton’s oxidation for both landfill leachates.
Higher reaction rate values of the Fenton’s oxidation were achieved with fresh leachate samples. The efficiency of initial
organics removal with ozone was about 70 % for mature leachate, while in case of the fresh one only 41 % of COD were removed.
The best fits of COD and DOC experimental data from oxidation of fresh and mature leachates were obtained by a combined kinetic
model. No significant improvement of the biodegradability of landfill leachates was achieved using these treatment procedures.
Regarding toxicity, ozonation showed to be more effective than the Fenton’s oxidation. Advanced oxidation experiments confirmed
that the Fenton’s oxidation and ozonation are comparable oxidative treatment techniques for the reduction of organic pollution
in the investigated municipal landfill leachates. However, neither of them is effective enough to be used as a pretreatment
method followed by biological treatment. 相似文献
54.
Paterson MJ Christiansen O Pawłowski F Jorgensen P Hättig C Helgaker T Sałek P 《The Journal of chemical physics》2006,124(5):054322
We present a detailed study of the effects of electron correlation on two-photon absorption calculated by coupled cluster quadratic response theory. The hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3 has been used to investigate the effects of electron correlation on the two-photon absorption cross sections of formaldehyde (CH2O), diacetylene (C4H2), and water (H2O). In particular, the effects of triple excitations on two-photon transition cross sections are determined for the first time. In addition, we present a detailed comparison of the coupled cluster results with those obtained from Hartree-Fock and density-functional response theories. We have investigated the local-density approximation, the pure Becke-Lee-Yang-Parr (BLYP) functional, the hybrid Becke-3-parameter-Lee-Yang-Parr (B3LYP), and the Coulomb-attenuated B3LYP (CAM-B3LYP) functionals. Our results show that the CAM-B3LYP functional, when used in conjuction with a one-particle basis-set containing diffuse functions, has much promise; however, care must still be exercised for diffuse Rydberg-type states. 相似文献
55.
56.
Peach MJ Helgaker T Sałek P Keal TW Lutnaes OB Tozer DJ Handy NC 《Physical chemistry chemical physics : PCCP》2006,8(5):558-562
The recently proposed CAM-B3LYP exchange-correlation energy functional, based on a partitioning of the r operator in the exchange interaction into long- and short-range components, is assessed for the determination of molecular thermochemistry, structures, and second order response properties. Rydberg and charge transfer excitation energies and static electronic polarisabilities are notably improved over the standard B3LYP functional; classical reaction barriers also improve. Ionisation potentials, bond lengths, NMR shielding constants and indirect spin-spin coupling constants are comparable with the two functionals. CAM-B3LYP atomisation energies and diatomic harmonic vibrational wavenumbers are less accurate than those of B3LYP. Future research directions are outlined. 相似文献
57.
We describe a two-party wire-tap channel of type II in the framework of almost affine codes. Its cryptological performance is related to some relative profiles of a pair of almost affine codes. These profiles are analogues to relative generalized Hamming weights in the linear case. 相似文献
58.
Cybulski H Pecul M Helgaker T Jaszuński M 《The journal of physical chemistry. A》2005,109(18):4162-4171
The nuclear magnetic resonance (NMR) parameters in porphyrin and porphycene have been calculated to investigate their changes during the process of proton exchange, using density-functional theory (DFT) for both the spin-spin coupling constants and the shielding constants. In addition, in calculations on the smaller 1,3-bis(arylimino)isoindoline molecule, we have tested the performance of our computational approach against experimental data. The calculated nuclear spin-spin coupling constants and shielding constants have been analyzed as functions of the progress of the proton transfer between two nitrogen atoms. The one-bond couplings between proton and nitrogen, dominated by the Fermi-contact term, decay steeply as the internuclear distance increases. The small changes in the intramolecular J(HH) coupling between two inner protons are mainly determined by the sum of relatively large spin-orbit terms. The isotropic shielding constant shows a strong deshielding of the nitrogen nuclei as the proton migrates away. Both the isotropic shielding of the exchanged protons and the shielding anisotropy exhibit a minimum close to the transition states. 相似文献
59.
Jarle Holt Trygve Andreassen Jan M. Bakke Anne Fiksdahl 《Journal of heterocyclic chemistry》2005,42(2):259-264
We hereby report the first preparation of 3‐nitro‐4‐pyridyl isocyanate 9 and 5‐nitro‐2‐pyridyl isocyanate 18 . They were formed by Curtius rearrangement of the corresponding acyl azides 8 and 17 , prepared from methyl 3‐nitro‐4‐pyridinecarboxylate 6 via the hydrazide 7 and 5‐nitro‐picolinic acid 16 , respectively. The substrates 6 and 16 were generated by nitration of methyl 4‐pyridinecarboxylate 5 and nitration and oxidation of 2‐picoline 14 . 3‐Nitro‐4‐pyridyl isocyanate 9 can be stored in dry solution and is stable at room temperature for several weeks while 5‐nitro‐2‐pyridyl isocyanate 18 was less stable and should be used for synthetic purposes immediately. 相似文献
60.
In this paper we study 16 complete intersection K3-fibered Calabi--Yau variety types in biprojective space ℙ
n
1}×ℙ1. These are all the CICY-types that are K3 fibered by the projection on the second factor. We prove existence of isolated rational curves of bidegree (d,0) for every positive integer d on a general Calabi–Yau variety of these types. The proof depends heavily on existence theorems for curves on K3-surfaces proved by S. Mori and K. Oguiso. Some of these varieties are related to Calabi–Yau varieties in projective space
by a determinantal contraction, and we use this to prove existence of rational curves of every degree for a general Calabi–Yau
variety in projective space.
Received: 14 October 1997 / Revised version: 18 January 1998 相似文献