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11.
Banerjee D Mitra S Mukherjee S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(6):1271-1278
Proton transfer processes of 4-hydroxy-3-formyl benzoic acid (HFBA) have been studied in a number of different protic solvents by means of absorption, emission and nanosecond transient spectroscopy at room temperature and 77K. Intermolecular interaction occurs in polar protic solvents only in presence of a base in the ground state whereas in the excited state, intermolecular complex formation and proton transfer occurs even in pure protic solvents. The dianion is detected in water, methanol, ethanol and TFE in presence of base. HFBA shows phosphorescence in pure ethanol at 77K. The occurrence of phosphorescence is due to rupture of the intramolecular bond and rotation of the formyl group. We have calculated quantum yields of fluorescence and also estimated decay rates from nanosecond measurements. The energetics of the ground and excited state proton transfer in HFBA have been investigated at the AM1 level of approximation. The ground singlet is predicted to have a large activation barrier on the proton transfer path, while the barrier height is much lower on the corresponding excited singlet surface. 相似文献
12.
The catalytic activity of Chromobacterium viscosum lipase (CV-lipase) was estimated across varying surfactant tail lengths (C-10-C-18) in water-in-oil (w/o) microemulsions of cationic surfactants containing four different hydroxyethyl-substituted head groups. An attempt to find a correlation, if any, between the activity of interfacially solubilized lipase and the varying surfactant tails was made for the first time in micellar enzymology. The second-order rate constant, k2, in lipase-catalyzed hydrolysis of p-nitrophenyl-n-hexanoate at pH 6.0 and 25 degrees C shows an improvement in enzyme activity (approximately 30-140%) across different head groups of amphiphiles with increasing tail lengths in varying solution compositions. Improvement of enzyme activity is prominent in ascending from C-10 to C-14/C-16, depending on the nature of polar head group. The hydrolytic activity of lipase in different surfactant (50 mM)/water/isooctane/n-hexanol with varying z= [alcohol]/[surfactant] (6.4 or 4.8) was amplified by 25-250% with increment in surfactant tail length in comparison with widely used cationic w/o microemulsions having solution compositions (z=16). As a notable outcome of this research, we found w/o microemulsions of 25 mM tetradecyltrimethylammonium bromide/water/isooctane/n-hexanol (z=8) producing the highest ever activity of lipase in any w/o microemulsions. 相似文献
13.
Talukder P Datta A Mitra S Rosair G El Fallah MS Ribas J 《Dalton transactions (Cambridge, England : 2003)》2004,(24):4161-4167
A new tridentate Schiff base ligand HL (L = C14H19N2O), derived from the condensation of benzoylacetone and 2-dimethylaminoethylamine in a 1:1 ratio, reacts with copper(ii) acetate and cyanate, thiocyanate or azide, to give rise to several end-to-end polymeric complexes of formulae [CuL(mu(1,3)-NCO)]n 1, [CuL(mu(1,3)-NCS)]n 2 and the complex 3 has two crystallographically independent units of formula [CuL(N3)] in the asymmetric unit cell. Complex 3 exists in dimeric form rather than as a polymeric chain. Compound 1 is the first report of a singly end-to-end cyanate bridged polymeric chain of Cu(II) with a Schiff base as a co-ligand. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones such as compound 2. We have characterized these complexes by analytical, spectroscopic, structural and variable temperature magnetic susceptibility measurements. The coordination geometry around the Cu(II) centers is distorted square pyramidal for 1 and 2 and square planar for complex 3. The magnetic susceptibility data show slight antiferromagnetic coupling for the polymers having J values -0.19 and -0.57 cm(-1) for complexes 1 and 2 respectively. The low values of J are consistent with the equatorial-axial disposition of the bridges in the polymers. 相似文献
14.
Amino Acid based cationic surfactants in aqueous solution: physicochemical study and application of supramolecular chirality in ketone reduction 总被引:2,自引:0,他引:2
Roy S Das D Dasgupta A Mitra RN Das PK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10398-10404
The present study provides a molecular understanding of the origin of the chirality in aqueous micelles and its correlation with the proficiency of stereoselective ketone reduction. The effects of varied headgroup architecture on the surface-active properties as well as on other microstructural parameters were studied and correlated to the structural differences of these naturally occurring amino acid containing surfactants (1-4). Micropolarity sensed by pyrene showed that the micelles prepared using 1-4 are mostly hydrated; particularly large headgroup size surfactant produces more polar environment. A theoretical study was done to quantify the varied spatial dissymmetry for all four surfactants. Asymmetric reduction of prochiral ketones was carried out at the aqueous micellar interface of these chiral amphiphiles by exploiting the supramolecular chirality as evidenced from a circular dichroism study. The enantioselectivity of the reduction process is rationally improved through increase in spatial dissymmetry and steric constraint imposed at the micellar interface by the polar head of surfactants. 相似文献
15.
Premamoy Ghosh Partha Sarathi Mitra Amar Nath Banerjee 《Journal of polymer science. Part A, Polymer chemistry》1973,11(8):2021-2030
Low concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free-radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems. 相似文献
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18.
Some new complexes of rhenium containing monocoordinating acetylacetone viz. [Re(NO)(acac)2(Cl)H2O], Re(NO)(acac)3(acacH)(H2O)2 have been synthesized by reacting acetylacetone with either Re(NO)Cl3 · H2O or Re(NO)(OH)3 · H2O. The preparation of [Re(NO)(py)(acac)2(Cl) · H2O], [Re(NO)(acac)(OH)(Cl) · H2O], [Re2(NO)2(acacH)3(acac)2 · Cl4], [Re(NO)(acac)2(OH) · H2O] · 2 H2O have also been described. These complexes were characterized through their elemental analyses, u.v., vis, i.r., 1Hn.m.r., magnetic, and conductance data. 相似文献
19.
Detailed average magnetic susceptibility (295-4.2 K) and average magnetisation (20-2 K, 50-10 kOe) are reported for two novel spin-mixed iron(III) porphyrins, namely Fe(TPP)ClO4 and Fe(OEP)ClO4. The results confirm an S = 3/2 ground state substantially spin-mixed with a low-lying S = 5/2 state, but do not agree in detail with the crystal-field model of Maltempo. 相似文献
20.
D.?Mitra S.?Francis L.?VarshneyEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):821-829
DSC and TG studies were carried out on -radiation processed Indian natural products of medicinal importance, namely Ashwagandha (Withania Somnifera), Amla (Emblica Officinalis) and Hartiki (Terminalia chebula). DSC thermoanalytical curves were recorded from 35 to 400°C in air and nitrogen atmosphere. Similarly, TG thermoanalytical curves were taken from 35 to 700°C in air and nitrogen atmosphere. Irradiated products gave significantly different thermoanalytical profiles in comparison to non-irradiated samples. The differences were observed above decomposition temperature of 200°C and were non-linear with respect to radiation dose. Partial oxidation of the products during irradiation in air could be responsible for the observed differences. 相似文献