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991.
992.
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
993.
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
994.
995.
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
996.
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
997.
A concise and efficient route for the synthesis of pyrimido[1,6-a]pyrimidines and imidazo[1,2-c]pyrimidines by simply refluxing a reaction mixture of different heterocyclic ketene aminals and N,N′-bis(arylmethylidene)arylmethane was developed. This protocol provides an alternative method for application in combinatorial and parallel synthesis in drug discovery. 相似文献
998.
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
999.
Eros G Nagy K Mehdi H Pápai I Nagy P Király P Tárkányi G Soós T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(2):574-585
Catalytic hydrogenation that utilizes frustrated Lewis pair (FLP) catalysts is a subject of growing interest because such catalysts offer a unique opportunity for the development of transition-metal-free hydrogenations. The aim of our recent efforts is to further increase the functional-group tolerance and chemoselectivity of FLP catalysts by means of size-exclusion catalyst design. Given that hydrogen molecule is the smallest molecule, our modified Lewis acids feature a highly shielded boron center that still allows the cleavage of the hydrogen but avoids undesirable FLP reactivity by simple physical constraint. As a result, greater latitude in substrate scope can be achieved, as exemplified by the chemoselective reduction of α,β-unsaturated imines, ketones, and quinolines. In addition to synthetic aspects, detailed NMR spectroscopic, DFT, and (2)H isotopic labeling studies were performed to gain further mechanistic insight into FLP hydrogenation. 相似文献
1000.
Mehdi Shakourian-Fard Mohammadreza Nasiri Alireza Fattahi Majid Vafaeezadeh 《Structural chemistry》2012,23(3):857-865
Influence of the addition of water molecules (n = 1–6) on the interaction energy between Li+, Na+, K+ cations and indole molecule as tryptophan amino acid residue is considered at MP2(FULL)/6-311++G(d,p)//B3LYP/6-311++G(d,p)
levels of theory. The calculations suggest that the size of cation and the number of water molecules are two important factors
that affect the interaction energy between the hydrated metal cation and indole molecule. The strength of cation–π interactions
get substantially reduced when the metal ion is solvated or the size of metal cation increases. Quantum theory of atoms in
molecules analysis of cation–π interaction indicates that there is a correlation between the electron density (ρ(r)) in the cage critical points generated upon complexation and the distance between metal cation and centroid of phenyl ring
in indole molecule. 相似文献