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211.
Ground state single determinant LCAO-MO-SCF wave functions, using a large contracted Gaussian basis set (6s, 2p, 1d/3s, 1p), have been computed for the 9 electron molecular systems of CH3 and NH. The minimum energies obtained using Roothaan's open shell SCF procedure for the planar equilibrium geometries were ?39.5703 Hartree for CH3 and ?55.8945 Hartree for NH. Additional properties such as electron populations and multiple moments were calculated from the planar wave functions. 相似文献
212.
Thieno[3,4-b]pyrazines: synthesis,structure, and reactivity 总被引:1,自引:0,他引:1
Kenning DD Mitchell KA Calhoun TR Funfar MR Sattler DJ Rasmussen SC 《The Journal of organic chemistry》2002,67(25):9073-9076
A general synthetic route has been developed for the efficient preparation of 2,3-disubstituted thieno[3,4-b]pyrazines. These methods eliminate problems in the preparation of the precursor 3,4-diaminothiophene and utilize alpha-diones prepared through the reaction of the appropriate organocuprates with oxalyl chloride. This combination allows the convenient preparation of thieno[3,4-b]pyrazine and its 2,3-disubstituted analogues (where substituent = methyl, hexyl, octyl, decyl, dodecyl, and phenyl) in high yield. Characterization of the structure and reactivity of this class of compounds is also described, including the results of structural, electrochemical, and pK(a) studies. 相似文献
213.
Jos W. H. M. Uiterwijk Gerrit J. van Hummel Sybolt Harkema Veronika M. L. J. Aarts Kari Daasvatn Jan Geevers Herman J. den Hertog Jr. David N. Reinhoudt 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(1):79-100
The preparation and X-ray structure determinations of six complexes of urea and (O-n-butyliso)uronium salts with crown ethers are presented. Urea forms isostructural 5:1 adducts with 18-crown-6 (1) and aza-18-crown-6 (2), in which two urea molecules are each hydrogen bonded to two neighbouring hetero atoms of the macroring. The remaining urea molecules form two-dimensional layers alternating with crown ether layers. In both complexes the macroring has theg
+
g
+
a ag
–
a ag
–
a g
–
g
–
a ag
+
a ag
+
a conformation withC
i symmetry. In the solid 1:1 complex of O-n-butylisouronium picrate with 18-crown-6 (3) two types of conformations of the macroring were observed: theg
+
g
+
a ag
–
a ag
+
a ag
–
g
–
ag
–
a ag
+
a conformation with approximateC
m symmetry and to a lesser extent theg
+
g
+
a ag
–
a ag
+
a g
+
g
+
a ag
–
a ag
+
a conformation with approximateC
2 symmetry. Both conformations allow the guest to form three hydrogen bonds to the macrocyclic host. Three complexes of 18-crown-6 and uronium salts have been prepared and characterized by X-ray crystallography. The 1:1 complexes with uronium nitrate (4) and uronium picrate (5) both exhibit the sameC
2 conformation and the same hydrogen bonding scheme as in the least occupied form of the previous complex. A 1:2 complex with uroniump-toluenesulphonate (6) has a different hydrogen bonding scheme (two hydrogen bonds per cation to neighbouring oxygen atoms of the macroring) and a different conformation of the host molecule (theag
+
a ag
–
a ag
+
a ag
–
a ag
+
a ag
–
a conformation with almostD
3d symmetry). An attempt to prepare a solid uronium nitrate complex with diaza-18-crown-6 in the same way as the 18-crown-6·uronium nitrate (1:1) complex did not yield the expected result. Instead X-ray analysis revealed that the uronium ion is dissociated, resulting in the nitrate salt of the diprotonated diaza crown ether (7).
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82058 (26 pages). 相似文献
214.
Frey J Tock C Collin JP Heitz V Sauvage JP Rissanen K 《Journal of the American Chemical Society》2008,130(33):11013-11022
Variously substituted coordinating rigid rods have been synthesized which incorporate a central 4,7-phenanthroline nucleus attached to two 2-pyridyl groups via its 3 and 8 positions, so as to yield bis-bidentate chelates, the two-coordinating axes of the chelates being parallel to one another. Regardless of the nature of the substituents borne by the rods, the copper(I)-induced threading reaction of two such rods through the rings of two bis-macrocycles affords in a quantitative yield the 4-copper(I) threaded assembly. The [2]pseudorotaxane tetramers thus obtained have been fully characterized in solution and, for one of them, an X-ray structure could be obtained, confirming the threaded nature of the complex and providing important structural information. 相似文献
215.
Ruuska H Arola E Kannus K Rantala TT Valkealahti S 《The Journal of chemical physics》2008,128(6):064109
Feasibility of density functional theory (DFT) to predict dielectric properties such as polarizability of saturated polymers is investigated. Small saturated molecules, methane and propane, which is a monomer of polypropylene chain, are used in testing the methods. Results for polarizabilities based on several density functionals together with different basis sets are compared and contrasted with each other, with results by Hartree-Fock and second-order Moller-Plesset perturbation theory, as well as experimental data. The generalized gradient approximation PW91 method together with the 6-311++G(**) basis set is found to be the most suitable method, in terms of sufficient accuracy and computational efficiency, to calculate polarizabilities for large oligomers of polypropylene. The dielectric constant is then determined using the calculated polarizabilities and the Clausius-Mossotti equation. The molecular DFT methods at the PW916-311++G(**) level together with the Clausius-Mossotti equation give dielectric constants for saturated polymers such as polypropylene in good accordance with the experimental values. 相似文献
216.
217.
Samal Tayrabekova Päivi Mäki-Arvela Markus Peurla Petriina Paturi Kari Eränen Gaukhar E. Ergazieva Atte Aho Dmitry Yu. Murzin Kusman Dossumov 《Comptes Rendus Chimie》2018,21(3-4):194-209
The purpose of this work was to investigate biomass-derived ethanol dehydrogenation into acetaldehyde using several mono- and multicomponent (CuO, ZnO and Cr2O3)-containing catalysts supported on industrial size Al2O3 beads. The catalysts, prepared with either solution combustion or incipient wetness method, were characterized by using various physico-chemical methods, such as EDXA, SEM-EDXA, TEM, XRD, XPS, pyridine adsorption desorption FTIR, and ζ-potential measurements. The results revealed that the multicomponent catalysts exhibited superior activity compared to the metal oxide catalysts containing only one metal oxide. In addition, the most selective catalyst towards acetaldehyde formation, with 50% selectivity at 55% conversion of ethanol at 300 °C and WHSV 1 h?1 was CuOCr2O3/Al2O3 prepared by using the solution combustion method, indicating that this inexpensive and rapid catalyst preparation method is promising for other applications. 相似文献
218.
Mukhopadhyay P Sarkar B Bharadwaj PK Nättinen K Rissanen K 《Inorganic chemistry》2003,42(16):4955-4960
The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[[2-(3-(oxomethyl)phenyl)oxy]ethyl]amine readily forms mononuclear inclusion complexes with both transition and main-group metal ions. In these complexes, the metal ion occupies the tren-end of the cavity making bonds with the three secondary amino and the bridgehead N atoms. When a strong pi-acceptor group such as 2,4-dinitrobenzene is attached to one of the secondary amines, the binding property of the cryptand changes drastically. When perchlorate or tetrafluoroborate salts of Ni(II), Cu(II), Zn(II), or Cd(II) are used, the metal ion enters the cavity which can be monitored by the hypsochromic shift of the intramolecular charge-transfer transition from the donor amino N atom to the acceptor dinitrobenzene. However, in the presence of coordinating ions such as Cl(-), N(3)(-), and SCN(-), the metal ion comes out of the cavity and binds the cryptand outside the cavity at a site away from the dinitrobenzene moiety. Four such complexes are characterized by X-ray crystallography. Thus, a metal ion can translocate between inside and outside of the cryptand cavity depending upon the nature of the counter anion. 相似文献
219.
Photocontrolled On‐Surface Pseudorotaxane Formation with Well‐Ordered Macrocycle Multilayers 下载免费PDF全文
Felix B. Schwarz Thomas Heinrich J. Ole Kaufmann Andreas Lippitz Dr. Rakesh Puttreddy Acad. Prof. Kari Rissanen Dr. Wolfgang E. S. Unger Prof. Christoph A. Schalley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14383-14389
The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine‐terminated SAMs and subsequently with multilayers of macrocycles through layer‐by‐layer self assembly. A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled deposition of the axle into the surface‐bound macrocycle‐multilayers was monitored by UV/Vis spectroscopy and led to an increase of the molecular order, as indicated by more substantial linear dichroism effects in angle‐resolved NEXAFS spectra. 相似文献
220.
Desorption atmospheric pressure photoionization high‐resolution mass spectrometry: a complementary approach for the chemical analysis of atmospheric aerosols 下载免费PDF全文