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991.
Thorium was precipitated from homogeneous solution by exposing solutions of thorium and periodate in dilute perchloric acid to 253.7 nm radiation from a low-pressure mercury lamp. Periodate is reduced photochemically to iodate which causes the formation of a dense precipitate of the basic iodate of thorium(IV). The precipitate was redissolved, the iodate reduced, the thorium precipitated first as the hydroxide, then as the oxalate and ignited to the dioxide for weighing. Thorium(IV) solutions containing 8-200 mg of ThO(2) gave quantitative results with a standard deviation (s) of 0.2 mg. Separations from 25 mg each of iron, calcium, magnesium, 50 mg of yttrium and up to 500 mg of uranium(VI) were quantitative (s = 0.25 mg). Separations from rare earths, except cerium, were accomplished by using hexamethylenetetramine rather than ammonia for the precipitation of the hydroxide. Cerium(III) was similarly precipitated and converted into CeO(2) for weighing. Quantitative results were obtained for 13-150 mg of CeO(2) with a standard deviation of 0.2 mg. Separations from 200 mg of uranium were quantitative. Other rare earths and yttrium interfered seriously. The precipitates of the basic cerium(IV) and thorium iodates obtained are more compact than those obtained by direct precipitation and can be handled easily. Attempts to duplicate Suzuki's method for separating cerium from neodymium and yttrium were not successful. 相似文献
992.
Agarwal PK 《Journal of the American Chemical Society》2005,127(43):15248-15256
An integrated view of protein structure, dynamics, and function is emerging, where proteins are considered as dynamically active assemblies and internal motions are closely linked to function such as enzyme catalysis. Further, the motion of solvent bound to external regions of protein impacts internal motions and, therefore, protein function. Recently, we discovered a network of protein vibrations in enzyme cyclophilin A, coupled to its catalytic activity of peptidyl-prolyl cis-trans isomerization. Detailed studies suggest that this network, extending from surface regions to active site, is a conserved part of enzyme structure and has a role in promoting catalysis. In this report, theoretical investigations of concerted conformational fluctuations occurring on microsecond and longer time scales within the discovered network are presented. Using a new technique, kinetic energy was added to protein vibrational modes corresponding to conformational fluctuations in the network. The results reveal that protein dynamics promotes catalysis by altering transition state barrier crossing behavior of reaction trajectories. An increase in transmission coefficient and number of productive trajectories with increasing amounts of kinetic energy in vibrational modes is observed. Variations in active site enzyme-substrate interactions near transition state are found to be correlated with barrier recrossings. Simulations also showed that energy transferred from first solvation shell to surface residues impacts catalysis through network fluctuations. The detailed characterization of network presented here indicates that protein dynamics plays a role in rate enhancement by enzymes. Therefore, coupled networks in enzymes have wide implications in understanding allostericity and cooperative effects, as well as protein engineering and drug design. 相似文献
993.
994.
D. D. Agarwal K. L. Madhok H. S. Goswami 《Reaction Kinetics and Catalysis Letters》1994,52(1):225-232
The vapor phase catalytic aerial oxidation of toluene to benzaldehyde (BzH) was carried out over La2MoO6 containing the same kind of layered structure as Bi2MoO6. The overall kinetic analysis indicated the oxidation of toluene to BzH to be first order with a frequency factor of log 0.63 and activation energy (Ea) of 26.3 kJ mol–1 and 34.0 kJ mol–1, respectively, for Bi2MoO6 and La2MoO6 catalysts. A relation between the activity and activation energy of conduction (E) is shown. 相似文献
995.
Vanadium phosphates function as catalysts for the selective oxidation of hydrocarbons with their activity being strongly dependent on their structure. Consequently, attempts have been made to synthesise novel phases in the VPO system through metal ion incorporation and evaluate the catalytic activity of these phases. It is shown that the incorporation of palladium or platinum leads to novel phases which vary according to the method of syntheses. The incorporated metal ions are catalytically active both for oxidation and reduction reactions with the activity varying according to the mode of incorporation. These phases constitute a novel class of compounds in which oxidation centres are substituted or dispersed within a VPO oxidation catalyst. 相似文献
996.
Shiv K. Agarwal Dr. Jagdish P. Tandon 《Monatshefte für Chemie / Chemical Monthly》1977,108(1):175-179
Specific magnetic susceptibilities (s) of several newly synthesized chelates of some of the lanthanons [La(III), Pr(III) and Nd(III)] are reported. These derivatives are of the general type,Ln(O-i-C3H7)3–n
(C6H5CHNRO)
n
[where,Ln=La(III), Pr(III) or Nd(III);n=1 or 2 and R=CH2CH2, CH2CHCH3 or C6H4] and have been prepared by the reaction of the alkoxides of the lanthanons withSchiff bases such as benzylidene-2-hydroxyethylamine (C6H5CHNCH2CH2OH), benzylidene-2-hydroxy-n-propylamine (C6H5CHNCH2CHOHCH3) and benzylidene-o-aminophenol (C6H5CHNC6H4OH) in different molar relations in dry benzene.The resulting crystalline derivatives are non-volatile, light to deep yellow or blackish in colour. These tend to polymerize on keeping as shown by their insoluble nature and higher melting points, the polymerisation possibly occurring by the intermolecular coordination through oxygen atoms as reported earlier1.UsingGouy method2, the bis-isopropoxy mono-Schiff base and mono-isopropoxy bis-Schiff base complexes of La(III) have been shown to be diamagnetic, with s values being in the range of –0.32 to –0.45×10–6 and –0.39 to –0.55×10–6 c.g.s. units at 305 K respectively.In the remaining derivatives, Pr(O-i-C3H7)3–n
(C6H5CH NRO)
n
and Nd(O-i-C3H7)3–n
(C6H5CHNRO)
n
(where,n=1 or 2 and R=CH2CH2, CH2CHCH3 or C6H4) the magnetic moment values range between 3.25 to 3.32 and 3.30 to 3.33 B respectively indicating their paramagnetic nature. 相似文献
997.
Summary The synthesis and physical properties of crystalline thorium(IV) complexes, Th(ClO4)4 · 6 LNO, ThX4 · 2 LNO (X = Br or SCN), ThX4 · 4 LNO (X = NO3 or I) andTh(ClO4)4 · 10 TMSO, Th(NO3)4 · 6 TMSO, ThX4 · 4 TMSO (X = Cl or Br), ThI4 · 6 TMSO and Th(NCS)4 · 2 TMSO (where LNO = 2,6-lutidine-N-oxide and TMSO = tetramethylene sulphoxide) are reported together with their i.r. spectra, molar conductivities, molecular weights, t. g. a. and d. t. a. data. In all the complexes, LNO and TMSO are bonded to thorium(IV) through oxygen. The coordination number of thorium(IV) in these complexes varies from six to ten depending upon the nature of the anions.Presented at the XVI Annual Convention of Chemists, Andhra University, Waltair, A. P. India, December 27–31, 1978. 相似文献
998.
We offer sufficient conditions for the oscillation of all solutions of the partial difference equations y(m - 1,n) + β(m,n)y(m, n - 1) -δ(m,n)+ P(m,n,y(m + k,n + l)) = Q(m,n,y(m + k,n + l)) and (y(m - 1,n)+ β(m,n)y(m,n - 1) - δ(m,n)y(m,n) + $$\mathop \Sigma \limits_{i = 1}^\tau $$ Pi(m,ny(m + ki,n + li)) = $$\mathop \Sigma \limits_{i = 1}^\tau $$ Qi(m,n,y9m + ki,n + li)). Several examples which dwell upon the importance of our results are also included. 相似文献
999.
A hybrid, potentially green solvent system composed of tetraethylene glycol (TEG) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) was investigated across all mole fractions with regard to the solvent properties of the mixture. For this purpose, a suite of absorbance- and fluorescence-based solvatochromic probes were utilized to explore solute-solvent and solvent-solvent interactions existing within the [bmim][PF(6)] + TEG system. These studies revealed an interesting and unusual synergistic solvent effect. In particular, a remarkable "hyperpolarity" was observed in which the E(T) value, comprising dipolarity/polarizability and hydrogen bond donor (HBD) acidity contributions, at intermediate mole fractions of the binary mixture well exceeded that of the most polar pure component (i.e., [bmim][PF(6)]). Independently determined dipolarity/polarizability (pi*) and HBD acidity (alpha) Kamlet-Taft values for the [bmim][PF(6)] + TEG mixtures were also observed to be anomalously high at intermediate mole fractions, whereas hydrogen bond acceptor (HBA) basicities (beta values) were much more in line with the ideal arithmetic values predicted on a mole fraction basis. Two well-established fluorescent polarity probes (pyrene and pyrene-1-carboxaldehyde) further illustrated notable hyperpolarity within [bmim][PF(6)] + TEG mixtures. Moreover, the steady-state fluorescence anisotropy of the molecular rotor rhodamine 6G and the excimer-to-monomer fluorescence ratio exhibited by the fluidity probe 1,3-bis-(1-pyrenyl)propane demonstrated that solute rotation and microfluidity within the [bmim][PF(6)] + TEG mixture were significantly reduced compared with expectations based on simple solvent mixing. A solvent ordering via formation of HBD/HBA complexes involving the C-2 proton of the [bmim(+)] cation and oxygen atoms of TEG, as well as interactions between [PF(6)(-)] and the terminal hydroxyl groups of TEG, is proposed to account for the observed behavior. Further spectroscopic evidence of strong intersolvent interactions occurring within the [bmim][PF(6)] + TEG mixture was provided, inter alia, by substantial frequency shifts in the [PF(6)(-)] asymmetric stretching mode observed in the infrared spectra as TEG was incrementally added to [bmim][PF(6)]. Overall, our observations contribute to a growing literature advocating the notion that ionic liquids and certain organic solvents form ordered, nanostructured, or microsegregated phases upon mixing. 相似文献
1000.
Podsiadlo P Kaushik AK Shim BS Agarwal A Tang Z Waas AM Arruda EM Kotov NA 《The journal of physical chemistry. B》2008,112(46):14359-14363
The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa. 相似文献