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141.
Summary The calculation of vibrational states using a gradient extremal path is discussed. Gradient extremal paths are defined by local criteria, which lead to stable solutions. This has certain advantages in comparison with a steepest-descent path, which is often difficult to determine accurately. For cases where a reaction path formalism is applicable, a path based on the gradient extremal concept gives results in close agreement with those obtained using traditional steepest-descent methods. We present algorithms for carrying out such calculations and also give some numerical results. 相似文献
142.
In this paper we propose a method for carrying out variational transition state theory calculations without first obtaining
a converged minimum-energy path (MEP). We illustrate the method in two ways, first of all by employing an unconverged MEP
and secondly by using a dynamically optimized distinguished reaction path. Preliminary tests of the algorithm for the reactions
OH+H2→H2O+H and C2H5→C2H4+H are very encouraging.
Received: 22 January 1997 / Accepted: 11 March 1997 相似文献
143.
The lattice model of associated solutions was used to calculate the concentration dependences of the chemical shifts of13C magnetic nuclei in the acrylamide molecule in water—DMSO solvent. Each pair of bonds between the acrylamide group containing
a magnetic nucleus and the neighboring solvent molecule was assumed to additively contribute to the change in the chemical
shift of the nucleus in question. The new approach affords the same accuracy in describing the experimental data at any ratios
of the solution components. It was shown that the chemical shifts and the excess heat of mixing of the water—DMSO binary solution
can be simultaneously described using the same set of energy parameters of the model. The model makes it possible to employ
experimental data on chemical shifts for studying intermolecular interactions in solutions.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1983–1987, October, 1998. 相似文献
144.
A delayed coincidence method, time-interval analysis (TIA), has been applied to successive – decay events on the millisecond time-scale. Such decay events are part of the 220Rn216Po (T1/2 145 ms) (Th-series) and 219Rn215Po (T1/2 1.78 ms) (Ac-series). By using TIA in addition to measurement of 226Ra (U-series) from -spectrometry by liquid scintillation counting (LSC), two natural decay series could be identified and separated. The TIA detection efficiency was improved by using the pulse-shape discrimination technique (PSD) to reject -pulses, by solvent extraction of Ra combined with simple chemical separation, and by purging the scintillation solution with dry N2 gas. The U- and Th-series together with the Ac-series were determined, respectively, from alpha spectra and TIA carried out immediately after Ra-extraction. Using the 221Fr217At (T1/2 32.3 ms) decay process as a tracer, overall yields were estimated from application of TIA to the 225Ra (Np-decay series) at the time of maximum growth. The present method has proven useful for simultaneous determination of three radioactive decay series in environmental samples. 相似文献
145.
We present a method for computing classical Newtonian trajectories that minimize the path length or transit time from reactant
to product. Our approach is based on a generalization of the fast-marching method, which allows us to construct the solution
of the Hamilton-Jacobi equation for the action that optimizes the desired quantity. The resulting “reactive paths” can be
interpreted as reaction coordinates but, unlike more conventional choices, they contain dynamical information about the chemical
system of interest. 相似文献
146.
147.
Summary A new, highly sensitive and selective gas chromatography method, using radiochemical detection (GC-DR) was developed for the
selective determination of3H-labelled deramciclane and its N-desmethyl metabolite in dog plasma. Inter-day accuracy and precision, as well as system
suitability of the GC-RD method was investigated during the method validation. The calibration curve was proved to be linear
(r=0.9986) in a wide concentration range (13–1000 ngeqv mL−1)
The lower limit of quantitation (LLOQ) was 13.7 ngeqv mL−1, and the limit of the detection (LOD) was 1 ngeqv mL−1.
Using this new GC-RD method, plasma levels of3H-labelled deramciclane and its metabolite were determined in dogs, after the administration of a single 10 mg kg−1 oral dose. Pharmacokinetic curves and the calculated pharmacokinetic parameters were compared to those obtained using a previously
elaborated gas chromatography-nitrogen selective detection method (GC-NPD) and to those obtained by measuring the plasma level
of total radioactivity (liquid scintillation counting, LSC). Pharmacokinetic curves and the calculated pharmacokinetic parameters
obtained with the two different gas chromatography detection methods (NPD and RD) showed good correlation. Comparison of these
results to those acquired by total radioactivity measurement demonstrated that deramciclane was intensively metabolised. Moreover,
the biological half-life (t
1
2/β
) of the unknown metabolites proved to be more than a magnitude longer than the half-life of the parent compound or that of
N-desmethyl metabolite.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
148.
This paper is considering the problem of traveling wave solutions (TWS) for a susceptible-exposed-infectious-recovered (SEIR) epidemic model with discrete diffusion. The threshold condition for the existence and nonexistence of TWS is obtained. More specifically, such kind of solutions are governed by the threshold number ?0. We can find a critical wave speed c? if ?0 > 1, by employing the Schauder's fixed point theorem, limiting argument and two-sided Laplace transform, we confirm that there exists TWS for c > c?, while there exists no TWS for c < c?. We also obtain the nonexistence of TWS for ?0 ≤ 1. At last, we give some biological explanations from the epidemiological perspective. 相似文献
149.
150.