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31.
T.M. Tsai 《Journal of solid state chemistry》2004,177(10):3301-3309
MgO and Co1−xO powders in 9:1 and 1:9 molar ratio (denoted as M9C1 and M1C9, respectively) were sintered and homogenized at 1600°C followed by annealing at 850°C and 800°C, respectively to form defect clusters and precipitates. Analytical electron microscopic observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M9C1 sample, however with spinel paracrystal precipitated from the M1C9 sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e., four octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The spacing of such defect clusters is 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co3−δO4, indicating a higher defect cluster concentration than undoped Co3−δO4. The {111} faulting of Mg-doped Co3−δO4/Co1−xO in the annealed M1C9 sample implies the possible presence of zinc blend-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane. 相似文献
32.
A solid-phase microextraction (SPME) device was used as a time-weighted average sampler for n-valeraldehyde. The SPME device was first modified to improve the wearer's acceptance as a passive sampler. Then a poly(dimethylsiloxane)-divinylbenzene fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was loaded onto the fiber. Vapors of known concentrations around the threshold limit values time-weighted average of n-valeraldehyde and specific relative humidities (RHs) were generated by syringe pumps in a dynamic generation system. n-Valeraldehyde vapors in gas bags were also generated. An exposure chamber was designed to allow measurement of face velocities, temperatures, exposing vapor concentrations, and RHs. Gas chromatography with flame ionization detection was used for sample analysis. The appropriate adsorption time for SPME coating PFBHA was determined to be 2 min and the desorption time for oxime formed after sampling was optimized to be 2 min. The experimental sampling constant was found to be (3.86+/-0.13) x 10(-2) cm3/min and face velocity was not expect to have effect on the sampler. 相似文献
33.
LoSecco JM Bionta RM Biewitt G Bratton CB Casper D Chrysicopoulou P Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG Lehmann E Park HS Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1985,54(21):2299-2301
34.
D. M. Lowe T. J. Kennett W. V. Prestwich J. -S. Tsai 《Journal of Radioanalytical and Nuclear Chemistry》1983,78(2):359-366
The application of an α-γ coincidence method for measuring226Ra concentrations in water is investigated. the experimental system, sample preparation, and results of several measurements
are discussed. In addition, the lower limit of detection for the coincidence system is calculated. 相似文献
35.
We report completely optimized ONIOM DFT/AM1 molecular orbital calculations on several collagen-like triple helices based upon the repeating triad, ProProGly. The requirement of Gly as every third amino acid in collagen can be attributed to its enantiomorphic nature, as it behaves as a Damino acid in collagen. We, therefore, explored related collagen-like triple helices with one of the central Gly's mutated to either L or DAla; l-Ala appreciably destabilizes, while d-Ala slightly stabilizes the triple helical structure. Mutation of the same Gly to DSer, which is simply DAla with an OH in place of one of the methyl H's, induces a much greater stabilization due to an additional H-bond formed between this OH and a C=O on an adjacent peptide strand. Energies are presented for the triple helices and their component strands (both optimized and distorted to their triple helical geometries) relative to the component amino acids. The variation of relative energies with the chosen reference is delineated. 相似文献
36.
Giovanna Marini-Bettòlo Soumya P. Sahoo Gerald A. Poulton Thomas Y.R. Tsai Karel Wiesner 《Tetrahedron》1980,36(6):719-721
Some years ago an empirical rule, which allows the prediction of product stereochemistry in cis-photocycloaddition reactions of α,β-unsaturated ketones and olefins was tentatively proposed. Several additional examples, both selected from the literature and synthesized in our laboratory, seem to strengthen the validity of the rule. 相似文献
37.
We developed a sensitive microbore HPLC method coupled with an on-line microdialysis system to simultaneously measure endogenous 5-hydroxytryptamine (serotonin; 5-HT) and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the rat blood in vivo. A dialysis tube was placed in the right jugular vein. The validity of the procedure is demonstrated because analysis of the aggregating agents, collagen (I mg/kg) plus epinephrine (0.3 mg/kg) after intravenous injection, showed that they induced an increase in 5-HT and 5-HIAA levels in the jugular vein of the rat. 相似文献
38.
3,5,7-Trioxapentacyclo[7.2.1.02,8.04,11.06,10]dodecane, the parent compound of novel diacetal trioxa-cages, was synthesized from maleic anhydride cyclopentadiene adduct 1 by a four-step sequence. Attempts for the synthesis of monoaza dioxa-cage 12 failed. Ozonolysis of compound 9 in CH2Cl2-EtOH(1:1) at ?78°C followed by reduction with Me2S gave 13 in 65% yield. 相似文献
39.
Under the agency of the potent lithiating agent, n-butyllithium in TMEDA, an array of organosilanes was found to undergo 1, n-silyl rearrangements via carbanionic intermediates. Unambiguous 1, 2-, 1, 3- and 1, 4-silyl shifts were uncovered in 1-trimethylsilyl-1, 1, 2-triphenylethane, 1, 1-bis(trimethylsilyl)-1-phenylalkanes and 1, 2-bis(trimethylsilyl)-1, 2-diphenylethane, respectively. Cross-over and competition experiments established that these rearrangements generally are intramolecular and occur with decreasing ease in the order, 1, 2 > 1, 3 > 1, 4. In other compounds, such as 1, 1-bis(trimethylsilyl)-1, 2-diphenylethane, 1, n-bis(trimethylsilyl)benzenes and triphenyl(trimethylsilyl)methane, competing 1, n-silyl shifts occurred. Attack of the organolithium intermediates on solvent and silicon—lithium exchange were significant side reactions in some instances. 1-Trimethylgermyl-1, 1, 2-triphenylgermane underwent no discernible rearrangement but rather gave the product expected from germanium—lithium exchange. By conducting time and competition studies, it was shown that lithiation is the product-determining step in these rearrangements and that dual pathways, namely 1, 3-versus consecutive 1, 2- 1, 4-pathways, are operative in certain rearrangements. 相似文献
40.
Hong-Bing Tsai Yu-Der Lee 《Journal of polymer science. Part A, Polymer chemistry》1987,25(8):2195-2206
The kinetics of interfacial polycondensation of bisphenol A with isophthaloyl chloride and terephthaloyl chloride in dichloromethane with triethylbenzylammonium chloride (TEBAC) as the catalyst was investigated via measurements of bisphenolate concentration by UV. The reaction was found to be second order with respect to bisphenolate. The dependence of the rate constant on stirring speed, amount of TEBAC, and reaction temperature was studied. The rate constant was increased with an increase of stirring speed, quantity of TEBAC added, as well as the reaction temperature. The activation energy was found to be 7.7 kcal/mol at a stirring speed of 700 rpm in the presence of 0.160 of TEBAC. The role of TEBAC was found to be interesting. It did not alter the equilibrium (the partition coefficient remained the same in the presence of TEBAC), but it did enhance the transfer rate of bisphenolate. 相似文献