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71.
Lenker HK Richard ME Reese KP Carter AF Zawisky JD Winter EF Bergeron TW Guydon KS Stockland RA 《The Journal of organic chemistry》2012,77(3):1378-1385
The addition of P(O)-H bonds to internal alkenes has been accomplished under solvent-free conditions without the addition of a catalyst or radical initiator. Using a prototypical secondary phosphine oxide, a range of substrates including cinnamates, crotonates, coumarins, sulfones, and chalcones were successfully functionalized. Highly activated acceptors such as isopropylidenemalononitrile and ethyl 2-cyano-3-methyl-2-butenoate underwent the phospha-Michael reaction upon simple trituration of the reagents at room temperature, whereas less activated substrates such as ethyl cinnamate and methyl crotonate required heating (>150 °C) in a microwave reactor to achieve significant consumption of the starting alkenes. For the latter alkenes, a competing reaction involving disproportionation of the ditolylphosphine oxide into ditolylphosphinic acid and ditolylphosphine was observed at the high temperatures needed to promote the addition reaction. 相似文献
72.
Levering LM Hayes CJ Callahan KM Hadad CM Allen HC 《The journal of physical chemistry. B》2006,110(12):6325-6331
Raman spectroscopy was used to examine the interactions of the free O-H bonds in n-octanol and ethanol with the organic solvents carbon tetrachloride (CCl(4)), cyclohexane, and benzene. These spectra reveal that the solvents CCl(4) and cyclohexane have a small effect on the free O-H peak of alcohols, whereas benzene as a solvent significantly red-shifts the free O-H band. Calculated spectra were generated via MP2/6-31G* calculations and the B3LYP/6-31+G**//MP2/6-31G*-derived Boltzmann populations of each ethanol complex and are consistent with the experimental results. Additional spectra were calculated using Boltzmann populations derived from single-point energies at the polarizable continuum model (PCM) level with the B3LYP/6-31+G** level of theory to take overall solvent effects into account, and these simulated spectra are also largely consistent with the experimental results. Analysis of the computational results reveals a lengthening of the O-H bond from the O-H interaction with the delocalized electronic structure of benzene as well as a bimodal distribution of the free O-H peak of the alcohol/benzene mixtures due to two distinctly different types of alcohol/benzene complexes. 相似文献
73.
74.
Richard Coupe Heather Welch Angela Pell E. Michael Thurman 《International journal of environmental analytical chemistry》2013,93(15):1127-1140
During 1996-1997, water samples were collected from five sites in the Yazoo River Basin and analysed for 14 herbicides and nine degradates. These included acetochlor, alachlor, atrazine, cyanazine, fluometuron, metolachlor, metribuzin, molinate, norflurazon, prometryn, propanil, propazine, simazine, trifluralin, three degradates of fluometuron, two degradates of atrazine, one degradate of cyanazine, norflurazon, prometryn, and propanil. Fluxes generally were higher in 1997 than in 1996 due to a greater rainfall in 1997 than 1996. Fluxes were much larger from streams in the alluvial plain (an area of very productive farmland) than from the Skuna River in the bluff hills (an area of small farms, pasture, and forest). Adding the flux of the atrazine degradates to the atrazine flux increased the total atrazine flux by an average of 14.5%. The fluometuron degradates added about 10% to the total fluometuron flux, and adding the norflurazon degradate flux to the norflurazon flux increased the flux by 82% in 1996 and by 171% in 1997. 相似文献
75.
Pure-silica-zeolite(PSZ) AST and LTA are synthesized successfully by using the same structure-directing agent(SDA) molecule,but at different concentrations.A dynamic organic SDA is proposed to discuss the mechanism of phase discrimination between AST and LTA.Data suggest that the SDA molecules can self-assemble into dimer or trimer complexes at different concentrations by π-π interactions,and these differences can be taken advantage of to selectively synthesize either PSZ AST or LTA.These deviations from the Liebau's rules indicate that small changes in SDA chemistry,structure,and order in solution can have a great impact on the structure selectivity of the zeolite synthesis. 相似文献
76.
Ming‐Han Liu Yao‐Hung Tseng Heather F. Greer Prof. Dr. Wuzong Zhou Prof. Dr. Chung‐Yuan Mou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(50):16104-16113
Mesocrystals of ZnO were synthesized hydrothermally by using gum arabic as a structure‐directing agent. Their hierarchical structure has a unique twin‐brush form consisting of vertically aligned nanorods in a single‐crystal‐like porous form. The formation mechanism of the twin‐brush ZnO was investigated by quenching a series of samples at different times and examining them by TEM, SEM, and XRD. The alignment of ZnO crystal units can be modulated by adding simple salts such as KCl to change the units from nanorods to nanoplates. This can be explained by screening the dipolar force of the polar crystal. Local cathodoluminescence of twin‐brush ZnO was used to follow the local structure changes. 相似文献
77.
Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P-P)H(2)](+) (P-P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H(2) in the presence of NaB(ArF)(4). Treatment with D(2) or T(2) gas leads to incorporation of deuterium or tritium in the dihydrogen ligand. Measurement of the resulting H-D and H-T couplings as a function of the temperature and magnetic field gives results consistent with computational studies which predict that the H-H bond distance will increase with temperature and will be significantly shortened by isotopic substitution. The degree of the observed temperature dependence is found to be a critical function of the ancillary ligand set. 相似文献
78.
Hai Ni Heather A. Nash James G. Worden Mark D. Soucek 《Journal of polymer science. Part A, Polymer chemistry》2002,40(11):1677-1688
The kinetics of the reaction of aliphatic isocyanate with water were investigated with hexyl isocyanate as a model compound. The kinetic study was carried out with a titration method to determine the concentration of the isocyanate group as a function of time. Gas chromatography was used to augment the kinetic data obtained from the titration method. The effects of an organic acid [p‐toluene sulfonic acid monohydrate (p‐TSA)], a tertiary amine {diazabicyclo[2.2.2]octane (DABCO)}, and an organotin compound [dibutyltin dilaurate (DBTDL)] on the reaction were investigated for the conversion of isocyanate to a urea. Under the reaction conditions in this study, urea was the only product observed. The rate constants indicated that p‐TSA had low catalytic activity, DABCO had intermediate catalytic activity, and DBTDL had high catalytic activity. A reaction mechanism was proposed for each of the catalysts. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1677–1688, 2002 相似文献
79.
Catchpoole HJ Andrew Shalliker R Dennis GR Guiochon G 《Journal of chromatography. A》2006,1117(2):137-145
Viscous fingering is an important fluid transport phenomenon that manifests itself when two fluids having different viscosities move in the same direction. Their interface is unstable and a complex fingering pattern may arise. This phenomenon is important in chromatography because it may lead to a decrease or even a failure in separations. The onset of viscous fingering was visually observed by packing a glass column with particles having the same refractive index as the mobile phase and injecting plugs of dye solutions having viscosities different from that of the mobile phase. Severe fingering effects are observed if the viscosity difference exceeds 0.17 cP. However, for smaller viscosity differences, band distortions are observed that may affect retention data, band efficiency, and band resolution. Careful attention should be paid to matching the mobile phase viscosity and that of the injection plug when accurate chromatographic information is required. 相似文献
80.
Heather L. Cuthbert Andrew I. Wallbank Nicholas J. Taylor John F. Corrigan 《无机化学与普通化学杂志》2002,628(11):2483-2488
Reaction of lithium phenylselenothiolate, generated in situ from the reductive cleavage of PhSe‐SiMe3 with alkyl lithium reagents and insertion of elemental sulfur, with triphenylphosphine solubilized CuCl affords the molecular cluster complex [Cu20Se4 (μ3‐SePh)12(PPh3)6] ( 1 ). The analogous reaction with AgCl yields the extended structure [Ag(SePh)]∞ ( 2 ) in which an infinite layer of AgI atoms is capped on either side by μ4‐SePh ligands. 1: space group P¯1, a = 17.9510(6), b = 18.1712(7), c = 31.4311(11) Å, a = 78.098(2), β = 82.905(2), γ = 70.012(2)°. 2: space group C2/c, a = 5.8762(6), b = 7.2989(7), c = 29.124(2) Å, β = 95.790(3)°. 相似文献