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91.
A new three-component domino reaction catalyzed by palladium was devised, producing polysubstituted bicyclic molecules in good yields from readily available substrates. The reaction conditions and the scope of the process were examined, and a possible mechanism is proposed. [reaction: see text] 相似文献
92.
The Crystal Structure of CsTcO4 CsTcO4 crystallizes orthorhombic with a = 5.727, b = 5.921 and c = 14.34 Å. Z = 4, space group Pnma (Nr. 62, I.T.). The metal positions were refined by single crystal data, the oxygen positions first determined: the CsTcO4 structure is a slight distortion of the scheelite arrangement (parameters: see text). The MADELUNG Part of Lattice Energy, MAPLE, ?Mean Effective Ionic Radii”?, MEIR, and Effective Coordination Numbers, ECoN, are calculated and discussed. 相似文献
93.
94.
With the aim of modeling reactive moieties and relevant intermediates on the surfaces of vanadium oxide based catalysts during oxygenation/dehydrogenation of organic substrates, mono- and dinuclear vanadium oxo complexes of doubly deprotonated p-tert-butylated tetrathiacalix[4]arene (H4TC) have been synthesized and characterized: PPh4[(H2TC)VOCl(2)] (1) and (PPh4)2[{(H2TC)V(O)(mu-O)}2] (2). According to the NMR spectra of the dissolved complexes they both retain the structures adopted in the crystalline state, as revealed by single-crystal X-ray crystallography. Compounds 1 and 2 were tested as catalysts for the oxidation of alcohols with O(2) at 80 degrees C. Both 1 and 2 efficiently catalyze the oxidation of benzyl alcohol, crotyl alcohol, 1-phenyl-1-propanol, and fluorenol, and in most cases dinuclear complex 2 is more active than mononuclear complex 1. Moreover, the two thiacalixarene complexes 1 and 2 are in many instances more active than oxovanadium(V) complexes containing "classical" calixarene ligands tested previously. Complexes 1 and 2 also show significant activity in the oxidation of dihydroanthracene. Further investigations led to the conclusion that 1 acts as precatalyst that is converted to the active species PPh4[(TC)V==O] (3) at 80 degrees C by double intramolecular HCl elimination. For complex 2, the results of mechanistic investigations indicated that the oxidation chemistry takes place at the bridging oxo ligands and that the two vanadium centers cooperate during the process. The intermediate (PPh4)2[{H2TCV(O)}2(mu-OH)(mu-OC13H9)] (4) was isolated and characterized, also with respect to its reactivity, and the results afforded a mechanistic proposal for a reasonable catalytic cycle. The implications which these findings gathered in solution may have for oxidation mechanisms on the surfaces of V-based heterogeneous catalysts are discussed. 相似文献
95.
Martin E. Keillor Craig E. Aalseth Anthony R. Day James E. Fast Eric W. Hoppe Brian J. Hyronimus Todd W. Hossbach Harry S. Miley Allen Seifert Glen A. Warren 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):703-708
Physics experiments, environmental surveillance, and treaty verification techniques continue to require increased sensitivity
for detecting and quantifying radionuclides of interest. This can be done by detecting a greater fraction of gamma emissions
from a sample (higher detection efficiency) and reducing instrument backgrounds. A current effort for increased sensitivity
in high resolution gamma spectroscopy will produce an intrinsic germanium (HPGe) array designed for high detection efficiency,
ultra-low-background performance, and useful coincidence efficiencies. The system design is optimized to accommodate filter
paper samples, e.g. samples collected by the Radionuclide Aerosol Sampler/Analyzer (RASA). The system will provide high sensitivity
for weak collections on atmospheric filter samples, as well as offering the potential to gather additional information from
more active filters using gamma cascade coincidence detection. The current effort is constructing an ultra-low-background
HPGe crystal array consisting of two vacuum cryostats, each housing a hexagonal array of 7 crystals on the order of 70% relative
efficiency per crystal. Traditional methods for constructing ultra-low-background detectors are used, including use of materials
known to be low in radioactive contaminants, use of ultra pure reagents, clean room assembly, etc. The cryostat will be constructed
mainly from copper electroformed into near-final geometry at PNNL. Details of the detector design, simulation of efficiency
and coincidence performance, HPGe crystal testing, and progress on cryostat construction are presented. 相似文献
96.
On Ca4Fe3F10 and Cs3TINi3F10 Single crystals of Cs4Fe3F10 (orthorhombic, a = 629.4, b = 1450,7, c = 1410.9 pm) and Cs3TlNi3F10 (orthorhombic, a = 610.1, b = 1442.0, c = 1366.8 pm) have been prepared. Results of X-ray investigation: Cs4Fe3F10 is isotypic to Cs4Mg3F10 and crystallizes in the space group Cmca (R = 3.97%, Rw = 2.75%, 1020 of 1020 I0(hkl), fourcircle diffractometer AED 2, Fa. Siemens). A monoclinic distortion could not be observed as supposed present. Cs4?xTlxNi3F10 (x≈?1), R = 7.75%, Rw = 4.96%, 1079 of 1294 I0(hkl), fourcircle diffraktometer PW 1100, Fa. Philips) confirm the possibility to substitute Cs against Tl in the Cs4Mg3F10-type. 相似文献
97.
98.
On ?Lithovanadates”?: Rb2[LiVO4] and Cs2[LiVO4] By heating of well ground mixtures of the binary oxides [A2O, Li2O, V2O5, A : Li: V = 2.2 : 1.1 : 1.0 (A = Rb, Cs); Ni-tube, 750° 25 d] we obtained Rb2[LiVO4] and Cs2[LiVO4] colourless, orthorhombic single crystals. We found a new type of ?Lithovanadate”?-structure: space group Cmc21; a = 587.9(1), b = 1170.1(1), c = 793.3(1) pm, Z = 4 (A = Rb) bzw. a = 610.5(1), b = 1222.6(3), c = 815.5(2) pm, Z = 4 (A = Cs). The structure was determined by four-circle diffractometer data [MoKα -radiation; 997 from 1157 I0(hkl), R = 7.75%, Rw = 5.54% (A = Rb); 686 from 686 I0(hkl), R = 6.97%, Rw = 4.20% (A = Cs)] parameters see text. The Madelung part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, have been calculated. 相似文献
99.
Sandrine Lamandé-Langle Jérôme Thibonnet Alain Duchêne 《Journal of organometallic chemistry》2009,694(15):2368-2374
Mono-, di-, tri- and tetra-functional organotin compounds were easily prepared in a sonicated Barbier reaction using ultrasound technology via coupling reaction of organo halides with tin halides (Bu3SnCl, Bu2SnCl2, BuSnCl3, SnCl4) mediated by magnesium metal. The di- and tri-functional organotin compounds were tested in a Stille cross-coupling reaction in order to ascertain how many groups were transferred. 相似文献
100.
Using a double Suzuki cross-coupling reaction ortho- or para-bromobenzyl bromides are easily transformed into unsymmetrical diaryl (or heteroaryl) methanes 相似文献