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991.
992.
Ambient mass spectrometry: bringing MS into the “real world” 总被引:1,自引:0,他引:1
Rosana M. Alberici Rosineide C. Simas Gustavo B. Sanvido Wanderson Romão Priscila M. Lalli Mario Benassi Ildenize B. S. Cunha Marcos N. Eberlin 《Analytical and bioanalytical chemistry》2010,398(1):265-294
Mass spectrometry has recently undergone a second contemporary revolution with the introduction of a new group of desorption/ionization
(DI) techniques known collectively as ambient mass spectrometry. Performed in an open atmosphere directly on samples in their
natural environments or matrices, or by using auxiliary surfaces, ambient mass spectrometry (MS) has greatly simplified and
increased the speed of MS analysis. Since its debut in 2004 there has been explosive growth in the applications and variants
of ambient MS, and a very comprehensive set of techniques based on different desorption and ionization mechanisms is now available.
Most types of molecules with a large range of masses and polarities can be ionized with great ease and simplicity with the
outstanding combination of the speed, selectivity, and sensitivity of MS detection. This review describes and compares the
basis of ionization and the concepts of the most promising ambient MS techniques known to date and illustrates, via typical
analytical and bioanalytical applications, how ambient MS is helping to bring MS analysis deeper than ever into the “real
world” open atmosphere environment—to wherever MS is needed. 相似文献
993.
Svetlana V. Lamaka Maryna G. Taryba Mikhail L. Zheludkevich Mario G. S. Ferreira 《Electroanalysis》2009,21(22):2447-2453
The design and properties of novel type of solid‐contact ionophore‐based ion‐selective microelectrodes are reported. The microelectrode is based on an insulated needle‐shaped metallic wire with an exposed apex. The ion‐to‐electron transducer is made of poly(3‐octylthiophene‐2,5‐diyl) and placed between an ion‐selective membrane and the metallic tip. The ion‐selective polyvinyl chloride‐based membrane is deposited atop the layer of conductive polymer. The length of the ion‐sensitive part of the electrode is less than 10 μm. pH and Mg2+‐selective microelectrodes were constructed and tested showing stable potential and fast response that are essential properties for the practical application of microelectrodes for localized scanning measurements. 相似文献
994.
Using isoperimetry and symmetrization we provide a unified framework to study the classical and logarithmic Sobolev inequalities. In particular, we obtain new Gaussian symmetrization inequalities and connect them with logarithmic Sobolev inequalities. Our methods are very general and can be easily adapted to more general contexts. 相似文献
995.
de Carvalho MG do Rocha Gomes MS Fernandes Pereira AH de Souza Daniel JF Schripsema J 《Magnetic resonance in chemistry : MRC》2006,44(1):35-37
The (1)H and (13)C NMR spectra of 5-acetyl-7,4'-dimethoxyflavone-(6-8')-5'-acetyl-7',4'-dimethoxyflavone, a new agathisflavone derivative, were completely assigned on the basis of 1D and 2D NMR techniques. 相似文献
996.
Chrétien JM Zammattio F Gauthier D Le Grognec E Paris M Quintard JP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(26):6816-6828
The preparation of polymer-supported allyltin reagents was shown to be possible for both unfunctionalized and functionalized allyl units. These reagents were treated with aldehydes in the presence of cerium(III) or indium(III) salts to afford high yields of homoallylic alcohols, practically uncontaminated with organotin residues (less than 5 ppm). Some mechanism aspects are briefly discussed and the potential for regeneration and reuse of these supported reagents is pointed out. 相似文献
997.
Ciriminna R Hesemann P Moreau JJ Carraro M Campestrini S Pagliaro M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5220-5224
The replacement of toxic Cr(VI) for O2 and of chlorinated solvents for supercritical carbon dioxide (or ionic liquids) in the oxidation of alcohols remains hindered by the low selectivity and activity of the current heterogeneous catalysts. Using an integrated approach that combines sol-gel entrapped perruthenate as aerobic catalyst, an encapsulated ionic liquid as solubility promoter, and scCO2 as the reaction solvent, we have developed a system capable of rapidly converting different alcohols into carbonyl compounds with complete selectivity, including substrates which are otherwise difficult to oxidise. The methodology is generally applicable and may easily be extended to other waste-free, catalytic syntheses of fine chemicals. 相似文献
998.
Alicata R Barbuzzi T Giuffrida M Ballistreri A 《Rapid communications in mass spectrometry : RCM》2006,20(4):568-576
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of narrowly dispersed molecular weight gel permeation chromatography (GPC) fractions was used to characterize random and microblock poly[(R)-3-hydroxybutyrate-co-epsilon-caprolactone] [P(HB-co-CL)] copolymers obtained via the acid-catalyzed transesterification of the corresponding homopolymers, poly([(R)-3-hydroxybutyrate] (PHB) and poly(epsilon-caprolactone) (PCL). High-quality mass spectra were obtained, which made it possible to establish the nature of the polymer end groups. Besides the carboxylic termination, two other moieties were found: alcoholic and tosyl end groups. MALDI mass spectra of CL-rich samples possessed mostly tosyl end groups, while HB-rich samples possessed mostly alcoholic end groups, showing that the tosyl moiety is linked prevalently to CL terminal units. The higher resolution of electrospray ionization (ESI) mass spectra of lower molecular weight GPC fractions permitted the identification of the different oligomer species hypothesized in the assignment of the corresponding MALDI mass spectra. Partial methanolysis of these copolymers was explored as a method of producing mixed HB-CL oligomers to be utilized as new synthons, possessing a minor number of chiral centers from those obtained from hydrolysis of biotechnologically synthesized poly(hydroxyalkanoates) (PHAs). 相似文献
999.
Lopes Jesus AJ Rosado MT Reva I Fausto R Eusébio ME Redinha JS 《The journal of physical chemistry. A》2006,110(12):4169-4179
The FT-IR spectra of two diastereomers of 2,3-butanediol, (R,S) and (S,S), isolated in low-temperature argon and xenon matrixes were studied, allowing the identification of two different conformers for each compound. These conformers were characterized by a +/-gauche arrangement around the O-C-C-O dihedral angle, thus enabling the establishment of a very weak intramolecular hydrogen bond of the O...H-O type. No other forms of these compounds were identified in matrixes, despite the fact that these four conformers had calculated relative energies from 0 to 5.1 kJ mol(-1) and were expected to be thermally populated from 50 to 6% in the gaseous phase of each compound. The nonobservation of additional conformers was explained in terms of low barriers to intramolecular rotation, resulting in the conformational relaxation of the compounds during deposition of the matrixes. The barriers to internal rotation of the OH groups were computed to be less than 4 kJ mol(-1) and are easily overcome in matrixes within the family of conformers with the same heavy atom backbone. The barriers for intramolecular rearrangement of the O-C-C-O dihedral angle in both diastereomers were calculated to range from 20 to 30 kJ mol(-1). Interconversions between the latter conformers were not observed in matrixes, even after annealing up to 65 K. Energy calculations, barriers, and calculated infrared spectra were carried out at the DFT(B3LYP)/6-311++G theory. Additional MP2/6-311++G calculations of energies and vibrational frequencies were performed on the most relevant conformers. Finally, independent estimations of the hydrogen-bond enthalpy in the studied molecules were also obtained based on theoretical structural data and from vibrational frequencies (using well-established empirical correlations). The obtained values for -DeltaH for both diastereomers of 2,3-butanediol amount to ca. 6-8 kJ mol(-1). 相似文献
1000.