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101.
Leonard R. Fisher Jacob N. Israelachvili 《Journal of colloid and interface science》1981,80(2):528-541
The thermodynamic properties of liquids trapped in microscopic pores are described in theory by the Kelvin equation, which relates the equilibrium meniscus curvature to the relative vapor pressure. We report here two series of experiments designed to test the validity of the Kelvin equation by direct measurement of the mean radius of curvature of the surface of cyclohexane condensed between crossed mica cylinders. In one series of experiments, the relative vapor pressure of the volatile cyclohexane was controlled by mixing it with a relatively involatile solute (n-dodecane or n-hexadecane). We found that the mean radius of curvature rapidly reached that predicted by the Kelvin equation at each relative vapor pressure of the volatile liquid, but that there was also a slow, but continuous, accumulation of the “involatile” solute at the point of condensation as the system approached true equilibrium. Such accumulation of very low vapor pressure materials may be one factor responsible for the discordant results reported by earlier workers. We find that the process of impurity buildup is complex, and suggest that studies of real porous systems may be affected by accumulation of “involatile” impurities through the vapor phase and by surface diffusion. The other series of experiments was designed to eliminate the impurity problem by maintaining the vapor pressure by temperature control of the pure liquid. The results from this series of experiments were not time dependent, and no evidence of contamination was found. The measured radii were within ±6% of those predicted by the Kelvin equation, for radii in the range 4–20 nm. We conclude that the thermodynamic basis of the Kelvin equation is valid in principle for menisci with radii as low as 4 nm. 相似文献
102.
Zhu BX Zhang QL Zhang YQ Zhu T Clegg JK Lindoy LF Wei G 《Inorganic chemistry》2008,47(21):10053-10061
The interaction of the diastereopure N,N'-bis(acetylacetone)cyclohexanediimine ligands, L(1)(1R,2R), L(2)(1S,2S), and their 1:1 mixture, with Zn(II) chloride has been investigated. Four new coordination polymers, [ZnL(1)Cl2 x H2O]n (1), [ZnL(2)Cl2 x H2O]n (2), [ZnL(2)Cl2]n (3), and [Zn6(L(2))6Cl12 x 2 H2O]n (4), each consisting of an infinite single helical chain displaying different pitches and/or handedness have been isolated. The complexed Schiff base ligands are present in their deprotonated enol forms, and the nitrogen atoms, which do not coordinate, are protonated because of proton transfer from the adjacent enol oxygen (coupled with concomitant N-H...O bond formation); each bound ligand is thus pseudo-zwitterionic. The respective zinc centers are bound to two chloro ligands and two oxygen donors from acacH-imine units belonging to different N,N'-bis(acetylacetone)cyclohexanediimine ligands such that the coordination at each zinc is distorted tetrahedral. Compounds 1 and 2, prepared from enantiopure L(1) and L(2), respectively, are enantiomers with similar structures, with the helical pitch in each being 17.0 A. Overall, the structure of 3 may be described as a one-dimensional helical chain with a pitch of 17.3 A, with each period corresponding to two L(2) ligands and two metal centers. The structure of [(Zn6L(2)6Cl12) x 2 H2O]n (4) contains six Zn(II) centers connected via six L(2) ligands to form a "bowed" helical repeat unit, with the pitch of the helix corresponding to 43.5 A. Supramolecular (intra- and intermolecular) aspects of all these unusual polymeric structures are discussed. Finally, the synthesis and characterization of an unprecedented six zinc-node discrete supramolecular assembly, [Zn6(L(1))3(L(2))3Cl12] (5), incorporating a 78-membered metallacycle, is also reported. 相似文献
103.
[reaction: see text] The Ti(IV) complex 2c bearing a C3-symmetric triphenolate amine ligand is an air and moisture tolerant complex that efficiently catalyzes sulfoxidation reactions at room temperature without previous activation (catalyst loading down to 0.01%, TONs up to 8000, TOFs up to 1700 h-1, quantitative yields). Reactions were performed with aqueous hydrogen peroxide as oxidant, which adds value to the methodology from the environmental viewpoint. 相似文献
104.
Current methods of analysis for ethylene oxide (EO) in medical devices include headspace and simulated-use extractions followed by gas chromatography with either a packed or a capillary column. The quantitation limits are about 0.5-1.0 microg/g for a packed column and about 0.1-0.2 microg/g for a capillary column. The current allowable levels of EO on medical devices sterilized with EO gas as outlined in International Organization for Standardization (ISO) 10993-7 may be significantly reduced from current levels by applying the ISO Draft International Standard 10993-17 method for establishing allowable limits. This may require EO test methods with detection and quantitation limits that are much lower than those of the currently available methods. This paper describes a new method that was developed for the determination of low-level EO by solid-phase microextraction using the direct-immersion method. Factors such as temperature and stirring were found to affect absorption efficiency and absorption time. A low extraction temperature (about 6 degrees C) was found to be more efficient than room-temperature extraction. Stirring was found to reduce absorption time by about 50%. Under these conditions, detection and quantitation limits of 0.002 and 0.009 microg/g, respectively, were obtained by using a capillary column. As a result, this method makes compliance with lower EO limits feasible. 相似文献
105.
H. E. Zaugg J. E. Leonard R. W. Denet D. L. Arendsen 《Journal of heterocyclic chemistry》1974,11(5):797-802
The previously discovered neighboring group reaction has been extended to the synthesis of chroman derivatives (i.e., 4, 5, 6) containing geminal methyls in the 2-position, a feature common to certain physiologically active natural chromans. In two instances, cyclic ortho ester by-products (8), not observed in previous work, were formed as a result of the intramolecular trapping of tetrahedral intermediates. Reasons for the incursion of this unexpected side reaction are discussed. 相似文献
106.
Two series (S and F) of poly p-isopropyl α-methylstyrene were characterized by viscometry, light scattering (LS), osmometry and gel permeation chromatography (GPC). S-samples were prepared by bulk anionic polymerization whereas F-samples were obtained on fractionation by preparative GPC of a polymer also prepared in bulk but with a different initiator. The K parameter in the Mark-Houwink relation was 5.55 × 10?4 for series-S and 4.50 × 10?4 for series-F, whereas the exponent a was 0.55 for both series. The Mark-Houwink equations for series-S and -F hold good at 25 and 30° for both toluene and tetrahydrofuran as solvents and have been corrected for polydispersity. The chain dimensions obtained with LS were much higher than those computed from the viscosity data indicating that the hydrodynamic theories in their present state should not be used for the calculation of chain dimensions. The deviations from the GPC universal calibration curve of polystyrene observed with some samples were attributed to structural differences among the polymers and to their high polydispersity. 相似文献
107.
Vasilescu IM Bray DJ Clegg JK Lindoy LF Meehan GV Wei G 《Dalton transactions (Cambridge, England : 2003)》2006,(43):5115-5117
Four previously documented ligand design strategies for achieving Ag(I) discrimination have been applied to the design of a new N-benzylated N2S3-donor macrocycle; the latter shows high selectivity for Ag(I) over Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) in log K and bulk membrane transport studies. 相似文献
108.
Cosa S Mabinya LV Olaniran AO Okoh OO Bernard K Deyzel S Okoh AI 《Molecules (Basel, Switzerland)》2011,16(3):2431-2442
A bioflocculant-producing marine bacterium previously isolated from marine sediment of Algoa Bay was screened for flocculant production. Comparative analysis of 16S rDNA sequence identified the isolate to have 99% similarity to Virgibacillus sp. XQ-1 and it was deposited in the GenBank as Virgibacillus sp. Rob with accession number HQ537127. The bacterium produced biflocculants optimally in glucose (70.4%) and peptone (70.4%) as sole sources of carbon and nitrogen, alkaline pH (12) (74%); and the presence of Fe2+ (74%). Chemical analysis of the bioflocculant revealed it to be a polysaccharide. 相似文献
109.
Tan L Yasuda N Yoshikawa N Hartner FW Eng KK Leonard WR Tsay FR Volante RP Tillyer RD 《The Journal of organic chemistry》2005,70(20):8027-8034
[Chemical reaction: See text] A Et3Al mediated intramolecular epoxide opening, cyclopropanation reaction is described. The transformation provided highly functionalized bicyclo[3.1.0]hexane systems in high efficiency and with perfect H or F endo selectivity. Application of this reaction to the synthesis of mGluR2/3 agonist 1 (43% overall yield) and a few intermediates suitable for the synthesis of other bicyclo[3.1.0]hexane mGluR2/3 agonists is discussed. 相似文献
110.
The complete analysis of the complex (1)H NMR spectra of some monosubstituted cyclobutanes was achieved to give all the (1)H chemical shifts and (n)J(HH) (n = 2, 3 and 4) coupling constants in these molecules. The substituent chemical shifts of the substituents in the cyclobutane ring differ significantly from those in acyclic systems. For example, the OH and the NH(2) groups in cyclobutanol and cyclobutylamine produce a large shielding of the hydrogens of the opposite CH(2) group of the ring compared with little effect on the comparable methylene protons of butane. These effects and the other (1)H shifts in the cyclobutanes were modelled successfully in the CHARGE program. The RMS error (calculated vs observed shifts) for the 34 (1)H shifts recorded was 0.053 ppm. The conformational equilibrium in these compounds between the axial and the equatorial conformers was obtained by comparing the observed and the calculated (4)J(HH) couplings. These couplings in cyclobutanes, in contrast to the corresponding (3)J(HH) couplings, show a pronounced orientation dependence; (4)J(eq-eq) is ca 5 Hz and (4)J(ax-ax) ca 0 Hz. The couplings in the individual conformers were calculated at the B3LYP/EPR-III level. The conformer energy differences ΔG(ax-eq) vary from 1.1 kcal mol(-1) for OH to 0.2 kcal mol(-1) for the CH(2)OH substituent. The values of the conformer energy differences are compared with the previous IR data and the corresponding theoretical values from molecular mechanics (MM) and DFT theory. Generally, good agreement is observed although both the MM and the DFT calculations deviate significantly from the observed values for some substituents. 相似文献