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991.
In this paper, the solution of Cauchy reaction–diffusion problem is presented by means of variational iteration method. Reaction–diffusion equations have special importance in engineering and sciences and constitute a good model for many systems in various fields. Application of variational iteration technique to this problem shows the rapid convergence of the sequence constructed by this method to the exact solution. Moreover, this technique does not require any discretization, linearization or small perturbations and therefore it reduces significantly the numerical computations. 相似文献
992.
The viscosity coefficients for the gaseous states of N2 and O2 and their mixtures are determined at zero and moderately density regimes. The Lennard‐Jones 12–6 (LJ 12–6) potential energy function is used as the initial model potential required y the technique. The interaction potential energies from the inversion procedure reproduce the viscosity commensurate to the best measurements. The initial density dependence of gaseous viscosity coefficient according to the Rainwater‐Friend theory, which was given by Najafi et al., has been considered for pure N2 and pure O2. 相似文献
993.
This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and 1HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
994.
Mohammad Mehdi Fateh 《Nonlinear dynamics》2010,61(4):655-666
This paper focuses on the uncertainty bound parameter (UBP) to design the robust control of electrical manipulators. The UBP
is commonly obtained by considering the worst case of uncertainties in bounding functions. However, too high estimation of
UBP may cause saturation of input, higher frequency of chattering in the switching control laws, and thus a bad behavior of
the whole system, while too low estimation of UBP may cause a higher tracking error. A proper UBP is preferred to improve
the performance of robust control system. A simple, less dependent and proper UBP is proposed based on the nominal model of
electrical manipulator and feedbacks of joint accelerations. This work is motivated by recent experimental results in measuring
acceleration by optical encoder. Modeling of an electrical manipulator with presence of uncertainties is presented for control
purposes. The proposed robust control is justified by stability analysis. 相似文献
995.
A convenient and efficient procedure for the regioselective ring opening of epoxides in the presence of Dowex (strongly acidic cationic exchange resin), as reusable eco‐friendly catalyst under solvent free conditions is described. Thus, several β‐hydroxy thiocyanates, useful intermediates toward pharmaceutical and biologically active molecules, are easily obtained in high isolated yields. 相似文献
996.
The numerical solution of problems in calculus of variation using Chebyshev finite difference method
The Chebyshev finite difference method is used for finding the solution of the ordinary differential equations which arise from problems of calculus of variations. Our approach consists of reducing the problem to a set of algebraic equations. This method can be regarded as a non-uniform finite difference scheme. Some numerical results are also given to demonstrate the validity and applicability of the presented technique. The method is easy to implement and yields very accurate results. 相似文献
997.
998.
Faramarz Mehrnejad Mahmoud Khadem-Maaref Mohammad Mehdi Ghahremanpour Farahnoosh Doustdar 《Journal of computer-aided molecular design》2010,24(10):829-841
Urea and GdmCl are widely used to denature proteins at high concentrations. Here, we used MD simulations to study the denaturation
mechanisms of helical peptide in different concentrations of GdmCl and urea. It was found that the helical structure of the
peptide in water simulation is disappeared after 5 ns while the helicity of the peptide is disappeared after 70 ns in 2 M
urea and 25 ns in 1 M GdmCl. Surprisingly, this result shows that the helical structure in low concentration of denaturants
is remained more with respect to that solvated in water. The present work strongly suggests that urea interact more preferentially
to non-polar and aromatic side chains in 2 M urea; therefore, hydrophobic residues are in more favorable environment in 2 M
urea. Our results also reveal that the hydrogen bonds between urea and the backbone is the dominant mechanism by which the
peptide is destabilized in high concentration of urea. In 1 M and 2 M GdmCl, GdmCl molecules tend to engage in transient stacking
interactions with aromatics and hydrophobic planar side chains that lead to displacement of water from the hydration surface,
providing more favorable environment for them. This shows that accumulation of GdmCl around hydrophobic surfaces in 1 M and
2 M GdmCl solutions prevents proper solvation of the peptide at the beginning. In high GdmCl concentrations, water solvate
the peptide better than 1 M and 2 M GdmCl. Therefore, our results strongly suggest that hydrogen bonds between water and the
peptide are important factors in the destabilization of peptide in GdmCl solutions. 相似文献
999.
Mehdi Adib Ehsan Sheikhi Morteza Karimzadeh Hamid Reza Bijanzadeh Massoud Amanlou 《Helvetica chimica acta》2012,95(5):788-794
A simple synthesis of N2‐alkyl‐N3‐[2‐(1,3,4‐oxadiazol‐2‐yl)aryl]benzofuran‐2,3‐diamines 5 via a one‐pot four‐component reaction is described (Scheme 1). A mixture of N‐(isocyanoimino)triphenylphosphorane ( 1 ), a 2‐aminobenzoic acid 2 , a 2‐hydroxybenzaldehyde 3 , and an isocyanide 4 in absolute EtOH at room temperature undergoes a smooth reaction to afford 5 in excellent yields (Table). 相似文献
1000.
Sayed Mehdi Ghoreishi Mohsen Behpour Samaneh Mazaheri Hossein Naeimi 《Journal of Radioanalytical and Nuclear Chemistry》2012,293(1):201-210
The electrochemical determination of uranyl was investigated by using carbon paste electrode modified with a Schiff base namely N,N??-bis(salicylidene)-2-hydroxy-phenylmethanediamine (SHPMD/CPE) and also in the presence of carbon nanotube (SHPMD/CNT/CPE). The both modified electrodes displayed an irreversible peak at E pa?=?0.798?V versus Ag/AgCl. The electrocatalytic reduction of uranyl has been studied on SHPMD/CNT/CPE, using cyclic and differential pulse voltammetry, chronocoulometry and linear sweep techniques. Electrochemical parameters including the diffusion coefficient (D), the electron transfer coefficient (??), the ionic exchange current (i) and the redox reaction rate constant (K) were determined for the reduction of uranyl on the surface of the modified electrodes. Linear range concentration is 0.002?C0.6???mol?L?1 and the detection limit of uranyl is 0.206?nmol?L?1. The proposed method was used to detect uranyl in natural waters and good recovery was achieved. 相似文献