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61.
62.
Jean-Claude Yakoubsohn 《Numerical Algorithms》1994,6(1):63-88
We give a practical version of the exclusion algorithm for localizing the zeros of an analytic function and in particular of a polynomial in a compact of . We extend the real exclusion algorithm to a Jordan curve and give a method which excludes discs without any zero. The result of this algorithm is a set of discs arbitrarily small which contains the zeros of the analytic function. 相似文献
63.
Dulal C. Ghosh 《Journal of Chemical Sciences》1984,93(1):33-46
A cndo/2D study of the charge distribution obtained through Mulliken population analysis in the ground state of the title
compounds shows that the features of charge distribution found by severalab initio calculations are fairly well reproduced by this method. The one-particle density, the interference density at the mid-point
of the bond axis and the kinetic part of the interference energy calculated through the deorthogonalized density matrices
over a wide range of intermolecular separation between the donor and the acceptor show that the one-particle density and the
interference density steadily grow with decreasing internuclear separation, while the kinetic interference energy starts with
negative value at large distance, then decreases and passes through a minima near but above the equilibrium distance and then
increases rapidly below it conforming to the characteristic general behaviour of the kinetic component of Morse curve. The
orbital pairwise interference density and the corresponding kinetic energy components reveal that the orbitals involved in
the covalent binding are σ2p AO of B and 2S and σ2p AO of N and C atoms in H3B-NH3 and H3B-CO respectively. 相似文献
64.
Summary A strategy for the optimisation of direct chiral separation of omeprazole and a metabolite, hydroxi-omeprazole, in reversed
phase liquid chromatography is described.
A factorial design was used, where mobile phase pH, concentration of a mobile phase modifier, ionic strength and column temperature
were tested as the variables and enantioselective retention, column efficiency and asymmetry factor as the responses.
The experimental results were evaluated with multivariate analyses, which demonstrated that the column temperature and content
of mobile phase acetonitrile were by far the most important variables. The enantiomers of omeprazole and one of its metabolites
were baseline resolved within 15 minutes. The optimised chromatographic system was used for a separation of the enantiomers
of omeprazole and its main metabolite in a patient plasma sample. 相似文献
65.
G. Tamai H. Yoshida H. Imai T. Takashina K. Kotoo T. Fuwa Y. Tsuchioka H. Matsuura G. Kajiyama 《Chromatographia》1985,20(11):671-676
Summary New quinidine metabolites, including 10,11-dihydrodiol quinidine N-oxide, 10,11-dihydrodiol quinidine and their glucuronides, were found in human urine. A quinidine monitoring HPLC method including these metabolites, is proposed by the direct injection of body fluid samples onto the precolumn for deproteinization followed by reverse phase separation in the analytical column with a column switching technique. The recovery of spiked quinidine and its metabolites in plasma was quantitative (98–102%) with good reproducibility (C.V.: 1.6–4.0%). Several clinical samples such as whole blood and urine were analyzed by the present method. 相似文献
66.
Hayley A. Every Michael A. Hickner James E. McGrath Thomas A. Zawodzinski Jr. 《Journal of membrane science》2005,250(1-2):183-188
Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10−6 to 4.0 × 10−6 cm2 s−1. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10−6 to 2.5 × 10−6cm2 s−1. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10−6 and 6.4 × 10−7 cm2 s−1 for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations. 相似文献
67.
Summary A numerically stable and well-parallelizable curve variational algorithm is described for determining tangent curves of vector fields between two given stationary points. In particular, the method is suitable for finding reaction paths and saddle points on potential energy hypersurfaces (PHS). The stability of the procedure is illustrated by an artificial mathematical function, showing phases of following the reaction on the PHS.Dedicated to Professor Zoltán G. Szabó, the great teacher and scientist in reaction kinetics and in many other fields of physical chemistry, on his 84th birthday. 相似文献
68.
The effect of the chemical structure of styrene-based epoxides, namely, styrene epoxide (SE), α-methylstyrene epoxide (MSE), p-methylstyrene epoxide (pM-SE) and α-methyl-p-methylstyrene epoxide (pM-MSE), in conjunction with TiCl4, on the initiation efficiency (Ieff) in the carbocationic polymerization of isobutylene (IB) was investigated. SE yielded living polymerization, but the initiation efficiency was low when compared to MSE (Ieff=8% and 35%, respectively). pM-SE led to non-living IB polymerization, while pM-MSE revealed linear Mn-conversion plot and narrow MWD with a non-linear first order rate plot. Among the epoxides investigated, MSE was the best initiator to scale up the one-step synthesis of polyisobutylenes (PIBs) carrying one primary hydroxyl head group and one tertiary chloride end group. The hydroxyl functionality of these PIBs determined by 1H-NMR was Fn=1.09±0.16 from 24 experiments. 相似文献
69.
Lukasz Kraszkiewicz 《Tetrahedron》2004,60(41):9113-9119
Two ‘model’ deactivated arenes, benzoic acid and nitrobenzene, were effectively monoiodinated within 1 h at 25-30 °C, with strongly electrophilic I+ reagents, prior prepared from diiodine and various oxidants (CrO3, KMnO4, active MnO2, HIO3, NaIO3, or NaIO4) in 90% (v/v) concd sulfuric acid (ca. 75 mol% H2SO4). Next, an I2/NaIO3/90% (v/v) concd H2SO4 exemplary system was used to effectively mono- or diiodinate a number of deactivated arenes. All former papers dealing with the direct iodination of deactivated arenes are briefly reviewed. 相似文献
70.
Christophe Hoarau Alexis Du Fou de Kerdaniel Pierre Grandclaudon Francis Marsais 《Tetrahedron letters》2005,46(49):8573-8577
The efficient and regioselective palladium-catalyzed C-2 arylation of ethyl 4-oxazolecarboxylate 1 with phenyliodide is described. The different parameters (solvent, base, ligand and catalyst) for the optimal conditions of this arylation process have been screened. 相似文献