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81.
An electrothermal atomic absorption (ETAAS) method for the determination of traces of iron (0.1-1.0 microgram g-1) in Fe-doped indium phosphide (InP) has been developed. In order to overcome the indium matrix-effect and to achieve a useful detection limit, a preliminary solvent-extraction of Fe(III) with acetylacetone (HAA) is necessary. After sample dissolution with hydrochloric acid (1 + 1) the digest is evaporated to dryness, Fe(II) is oxidized to Fe(III) with nitric acid, the residue is dissolved in 0.01 mol L-1 HCl and the iron is extracted at pH 2.0 with 0.5 mol L-1 HAA in toluene. The organic phase is injected into the graphite furnace and the iron is directly evaluated by external organic standard calibration. The limit of detection (3SB) resulting from further in-situ preconcentration is 0.03 microgram g-1. When the method was applied to the analysis of real samples containing 0.2-0.7 microgram g-1 Fe, the RSD was in the range 8-21%. Results were compared with those independently obtained on the decomposed sample solution with inductively coupled atomic emission spectrometry (ICP-AES). The detection limit of the ICP-AES method, that needs matrix-matched standards, is 0.20 microgram g-1. 相似文献
82.
Gabriella Cavallo Giancarlo Terraneo Alessandro Monfredini Marco Saccone Arri Priimagi Tullio Pilati Giuseppe Resnati Pierangelo Metrangolo Duncan W. Bruce 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(21):6408-6412
Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen‐bonded supramolecular anions [CnF2 n+1‐I⋅⋅⋅I⋅⋅⋅I‐CnF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen‐bonded liquid crystals, and 2) imidazolium‐based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. 相似文献
83.
Most known perylene diimides are lipophilic, with few exceptions of hydrophilic derivatives. Even in the latter case, the compounds have limited water solubility and show a strong tendency to self-aggregation. In this paper we present the synthesis of four new perylene derivatives with three and four basic side chains, obtained by functionalizing the bay-area of perylene. These molecules show great solubility in aqueous media as hydrochlorides and their tendency to self-aggregate is remarkably reduced with respect to the previously synthesized two-chained perylene diimides. Their different spectroscopic properties in various solvents and conditions are reported and discussed. 相似文献
84.
Ultrasound, an efficient and virtually innocuous means of activation in synthetic chemistry, has been employed for decades with varied success. Not only can this high-energy input enhance mechanical effects in heterogeneous processes, but it is also known to induce new reactivities leading to the formation of unexpected chemical species. What makes sonochemistry unique is the remarkable phenomenon of cavitation, currently the subject of intense research which has already yielded thought-provoking results. This critical review is aimed at discussing the present status of cavitational chemistry and some of the underlying phenomena, and to highlight some recent applications and trends in organic sonochemistry, especially in combination with other sustainable technologies. (151 references.). 相似文献
85.
Readily available chiral phosphoramidites are a promising class of ligands for nickel-catalyzed asymmetric hydrovinylation of vinyl arenes. Cooperative effects are operative when ligands with more than one element of chirality are used. Choosing the proper stereochemistry in each part of the modular ligand system leads to high chemoselectivities and excellent enantioselectivities up to 94%. Moreover, the catalysts derived from these ligands proved extremely efficient and remarkably robust performing up to 8300 catalytic turnovers at an initial turnover frequency beyond 1000 h-1. The large potential for structural variation and their straightforward synthesis make the phosphoramidites currently the best lead structure for catalyst development in this field. 相似文献
86.
Carina Schönherr Sounia Touchene Gaston Wilser Regine Peschka-Süss Giancarlo Francese 《Journal of chromatography. A》2009,1216(5):781-786
In recent decades the use of liposomal preparations as drug delivery systems has become very attractive in pharmaceutical development. Therefore, thorough characterization and quantification of the lipids which form liposomes is wished from both investigators and regulatory authorities when the application in humans is being considered. In this study a new HPLC method for the detection of lipids in liposomal formulations was established using corona charged aerosol detection (CAD) which has the advantage to be independent of the chemical properties of the analytes. The superiority of this method over UV detection was demonstrated. Compared to UV detection no absorption effects of the organic solvent in the mobile phase interfering with the lipid signals were observed with CAD. CAD showed good linearity (R2 > 0.990) for all liposomal compounds. The acceptance criteria for precision including repeatability were met. The average recovery for each of the excipients of the liposomal formulation was in the range of 90.0–110%. 相似文献
87.
Alessia Panusa Giancarlo Aldini Marica Orioli Giulio Vistoli Giuseppe Rossoni Marina Carini 《Rapid communications in mass spectrometry : RCM》2010,24(11):1583-1594
A new, simple, sensitive and specific liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI‐MS/MS) method in precursor ion scanning (PIS) mode has been developed for the rapid detection of methylprednisolone acetate (MPA) and its metabolites in rat urine. A suitable product ion specific for methylprednisolone (MP) and MPA was selected after a fragmentation study on 20 (cortico)steroids at different collision energies (5–40 eV). Urine samples were simply treated with acetonitrile then dried in a SpeedVac system. The method was validated and compared with other PIS methods for detecting corticosteroids in human urine. It was more sensitive, with limit of detection (LOD) and lower limit of quantitation (LLOQ), respectively, of 5 and 10 ng mL?1. The method was applied for the analysis of rat urine collected before and after (24, 48, 72 h) intra‐articular (IA) injection of a marketed formulation of MPA (Depo‐Medrol®). MS/MS acquisitions were taken at different collision energies for the precursor ions of interest, detected in PIS mode, to verify the MP‐related structure. Six different metabolites were detected in rat urine, and their chemical structures were assigned with a computational study. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
88.
Francesco Fassò Giancarlo Benettin 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1989,40(3):307-329
In this paper we exhibit a rigorous perturbation theory for nearly integrable Hamiltonian systems, based on the composition of Lie Transforms. Precisely, we first study the algorithm for the composition of Lie transforms, and provide rigorous estimates for the convergence radius and the truncation errors of the series; then we use our estimates for a particular model-example, namely a system of weakly coupled harmonic oscillators having Diophantine frequencies, and work out Nekhoroshev-like exponential estimates for the stability times. 相似文献
89.
Minardi Giovannina Mura Emanuela Pistuddi Angelo M. Solinas Costantino Bacchi Alessia Pelizzi Corrado Pelizzi Giancarlo Chelucci Giorgio 《Transition Metal Chemistry》1999,24(4):481-485
Chelating properties of C2-symmetric chiral bipyridine ligands are discussed. In particular we report the syntheses of the cobalt(II), nickel(II), zinc(II) and copper(II) complexes of (4S,5S)-2,2-dimethyl-4,5-bis(2-pyridyl)-1,3-dioxolane. All compounds have been characterized by IR spectroscopy, and an X-ray diffraction analysis has been carried out on one of them: Co(L)(NO3)2. The ligand coordinates the cobalt atom by the two nitrogen donors N(1) and N(2). A seven-membered chelation ring is formed, presenting a remarkable non-crystallographic twofold pseudosymmetry around the axis connecting Co and the midpoint of the C(6)–C(7) bond. The metal also binds two monodentate nitrates, thus completing a distorted coordination tetrahedron. 相似文献
90.
Let (ℋ
t
)
t≥0 be the Ornstein-Uhlenbeck semigroup on ℝ
d
with covariance matrix I and drift matrix −λ(I+R), where λ>0 and R is a skew-adjoint matrix and denote by γ
∞ the invariant measure for (ℋ
t
)
t≥0. Semigroups of this form are the basic building blocks of Ornstein-Uhlenbeck semigroups which are normal on L
2(γ
∞). We investigate the weak type 1 estimate of the Riesz transforms for (ℋ
t
)
t≥0. We prove that if the matrix R generates a one-parameter group of periodic rotations then the first order Riesz transforms are of weak type 1 with respect
to the invariant measure γ
∞. We also prove that the Riesz transforms of any order associated to a general Ornstein-Uhlenbeck semigroup are bounded on
L
p
(γ
∞) if 1<p<∞.
The authors have received support by the Italian MIUR-PRIN 2005 project “Harmonic Analysis” and by the EU IHP 2002-2006 project
“HARP”. 相似文献