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941.
Alexander O. Mitrushchenkov Guido Fano Roberto Linguerri Paolo Palmieri 《International journal of quantum chemistry》2012,112(6):1606-1619
We investigate the importance of orbital localization in the application of the Density Matrix Renormalization Group (DMRG) technique to ab initio studies of molecular electronic structure. Our previous implementation of DMRG has been generalized to allow for the use of localized nonorthogonal orbitals. Simple cycles of equidistant hydrogen atoms, which are good examples of one dimensional metal‐like lattices with fully delocalized electronic structures, have been taken as test models. In this study, the efficiency of the DMRG method and the importance of orbital localization for the generation of the DMRG building blocks are confirmed. However, it is found that the convergence of the procedure based on nonorthogonal orbitals is slower and requires more DMRG components than the standard orthogonal formulation. Symmetrically orthonormalized atomic orbitals are shown to be a good compromise solution: they satisfy the requirement of orbital localization for the generation of the DMRG blocks and improve the convergence, reducing the number of components of the DMRG expansion. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
942.
Dr. Siree Tangbunsuk Dr. George R. Whittell Dr. Maxim G. Ryadnov Dr. Guido W. M. Vandermeulen Prof. Derek N. Woolfson Prof. Ian Manners 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(9):2524-2535
Conjugates of poly(ferrocenyldimethylsilane) (PFDMS) with Ac‐(GA)2‐OH, Ac‐A4‐OH, Ac‐G4‐OH and Ac‐V4‐OH have been prepared by reaction of the tetrapeptide units with the amino‐terminated metallopolymer. The number average degree of polymerisation (DPn) of the PFDMS was approximately 20 and comparable materials with shorter (DPn≈10) and/or amorphous chains have been prepared by the same procedure. Poly(ferrocenylethylmethylsilane) (PFEMS) was employed for the latter purpose. All conjugates were characterised by GPC, MALDI‐TOF MS, NMR and IR spectroscopy. With the exception of Ac‐V4‐PFDMS20, all materials exhibited some anti‐parallel β‐sheet structure in the solid state. The self‐assembly of the conjugates was studied in toluene by DLS. The vast majority of the materials, irrespective of peptide sequence or chain crystallinity, afforded fibres consisting of a peptidic core surrounded by a PFS corona. These fibres were found in the form of cross‐linked networks by TEM and AFM. The accessibility of the chemically reducing PFS corona has been demonstrated by the localised formation of silver nanoparticles on the surface of the fibres. 相似文献
943.
944.
Verbeck GF Ruotolo BT Gillig KJ Russell DH 《Journal of the American Society for Mass Spectrometry》2004,15(9):1320-1324
An extension of current mobility resolution equations as they apply to high-field ion mobility spectrometry is presented. The new resolution expression is applied to arrival time distributions for ions having a large range of ion mobilities and mass-to-charge ratios (m/z). The results indicate that the new equation can be utilized to predict the mobility resolution over a broader range of applied electric fields than previous ion mobility resolution expressions. 相似文献
945.
Oualid Talhi Guido R. Lopes Sérgio M. Santos Diana C. G. A. Pinto Artur M. S. Silva 《Journal of Physical Organic Chemistry》2014,27(9):756-763
The diastereoselective photodependent isomerization equilibrium of E/Z‐1,3‐ditolyl‐5‐[3‐oxobenzofuran‐2(3H)‐ylidene]imidazolidine‐2,4‐dione ( 5 ) is reported. Both diastereomers E-5 and Z-5 are stereochemically stable in solid state but show significant photosensibility in solutions of halogenated solvent. The photoisomerization equilibrium of E/Z‐ 5 is therefore deduced from the 1H NMR profile after visible‐light irradiation of both E-5 and Z-5 samples. The results of the kinetic study, monitored by UV‐HPLC, reveal that the E/Z equilibrium is diastereoselective and photodependent, being the transformation E ? Z proceeding faster than that of Z ? E, and the E/Z ratio at the equilibrium depends on the used solvent, light source, and temperature. Both diastereomers are visible‐light photosensitive tending to coexist together in equilibrium solutions at a determined ratio, which is always in favor of the Z‐product assuming a minimum thermodynamic energy and an increased entropy of the system. Time‐dependent density functional theory calculations suggest that the photoisomerization mechanism proceeds via a conical intersection involving the first‐excited state: Upon irradiation, the E-5 isomer is excited to the S1 potential energy surface, where it relaxes through rotation of the C=C bond and reaches a conical intersection with the ground‐state potential energy surface, thus yielding the Z-5 isomer. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
946.
The Multi-Handler Knapsack Problem under Uncertainty is a new stochastic knapsack problem where, given a set of items, characterized by volume and random profit, and a set of potential handlers, we want to find a subset of items which maximizes the expected total profit. The item profit is given by the sum of a deterministic profit plus a stochastic profit due to the random handling costs of the handlers. On the contrary of other stochastic problems in the literature, the probability distribution of the stochastic profit is unknown. By using the asymptotic theory of extreme values, a deterministic approximation for the stochastic problem is derived. The accuracy of such a deterministic approximation is tested against the two-stage with fixed recourse formulation of the problem. Very promising results are obtained on a large set of instances in negligible computing time. 相似文献
947.
Diazabicyclo[5.4.0]undecene (DBU) reacts with carbon dioxide and N-subsititued-2-chloroacetoamides in a very simple one-step procedure, to give the corresponding 3-substituted oxazolidin-2,4-diones in excellent yields. 相似文献
948.
The use of DNA as a molecular wire in nanoscale electronic architectures would greatly benefit from its capability of sequence-specific self-assembly. Although single electrons and positive charges have been shown to be transmitted by natural DNA over a distance of several base pairs, the high ohmic resistance of unmodified oligonucleotides imposes a serious obstacle. Exchanging some or all of the Watson–Crick base pairs in DNA by metal complexes may solve this problem and evolve DNA-like materials with superior conductivity for future nano-electronic applications. The so-called metal–base pairs are formed from suitable transition metal ions and ligand-like nucleosides which are introduced into both of the two pairing strands by automated DNA synthesis. This review illustrates the basic concepts of metal–base pairing and highlights recent developments in the field. 相似文献
949.
950.
Susanna Vogliardi Donata Favretto Giampietro Frison Sergio Maietti Guido Viel Roberta Seraglia Pietro Traldi Santo Davide Ferrara 《Analytical and bioanalytical chemistry》2010,396(7):2435-2440
The sensitivity and specificity of a novel method of screening for cocaine in hair, based on matrix-assisted laser desorption/ionisation
(MALDI) mass spectrometry (MS), have been evaluated. The method entails a rapid extraction procedure consisting of shaking
2.5 mg pulverised hair at high frequency in the presence of an acidic solution (160 μL of water, 20 μL of acetonitrile and
20 μL of 1 M trifluoroacetic acid) and a stainless-steel bullet. Following centrifugation, the supernatant is dried under
a nitrogen stream, and the residue is reconstituted in 10 μL of methanol/trifluoroacetic acid (7:3; v/v). One microlitre of the extract is deposed on a MALDI sample holder previously scrubbed with graphite; an α-cyano-4-hydroxycinnamic
acid (matrix) solution is electrosprayed over the dried sample surface to achieve a uniform distribution of matrix crystals.
The identification of cocaine is obtained by post-source decay experiments performed on its MH+ ion (m/z 304), with a limit of detection of 0.1 ng/mg of cocaine. A total of 304 hair samples were analysed in parallel by MALDI-MS
and a reference gas chromatography-MS method. The obtained results demonstrate specificity and sensitivity of 100% for MALDI-MS.
Evidence of cocaine presence was easily obtained even when hair samples exhibiting particularly low cocaine levels (<0.5 ng/mg)
were analysed. 相似文献