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21.
Becerra R Bowes SJ Ogden JS Cannady JP Almond MJ Walsh R 《The journal of physical chemistry. A》2005,109(6):1071-1080
Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by laser flash photolysis of phenylsilane, have been carried out to obtain rate constants for its bimolecular reaction with NO. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF6 bath gas at five temperatures in the range 299-592 K. The second-order rate constants at 10 Torr fitted the Arrhenius equation log(k/cm3 molecule(-1) s(-1)) = (-11.66 +/- 0.01) + (6.20 +/- 0.10 kJ mol(-1))/RT ln 10 The rate constants showed a variation with pressure of a factor of ca. 2 over the available range, almost independent of temperature. The data could not be fitted by RRKM calculations to a simple third body assisted association reaction alone. However, a mechanistic model with an additional (pressure independent) side channel gave a reasonable fit to the data. Ab initio calculations at the G3 level supported a mechanism in which the initial adduct, bent H2SiNO, can ring close to form cyclo-H2SiNO, which is partially collisionally stabilized. In addition, bent H2SiNO can undergo a low barrier isomerization reaction leading, via a sequence of steps, ultimately to dissociation products of which the lowest energy pair are NH2 + SiO. The rate controlling barrier for this latter pathway is only 16 kJ mol(-1) below the energy of SiH2 + NO. This is consistent with the kinetic findings. A particular outcome of this work is that, despite the pressure dependence and the effects of the secondary barrier (in the side reaction), the initial encounter of SiH2 with NO occurs at the collision rate. Thus, silylene can be as reactive with odd electron molecules as with many even electron species. Some comparisons are drawn with the reactions of CH2 + NO and SiCl2 + NO. 相似文献
22.
Previous theoretical work in multiple-objective optimization has focused entirely on vector orders representable by positive cones. Here, we treat multiple-objective problems in which solutions are sought which are maximal (efficient, nondominated) under an order which may be nonconical. Compactness conditions under which maximal solutions exist and bound the remaining alternatives are given. First-order necessary conditions and first-order sufficient conditions for maximality in general normed linear spaces are derived, and a scalarization result is given. A small computational example is also presented. Several previous results are special cases of those given here. 相似文献
23.
E. Rühl C. Heinzel H. Baumgärtel M. Lavollée P. Morin 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(4):245-251
Fragmentation of doubly charged argon clusters is reported. Neutral argon clusters are excited with monochromatized synchrotron radiation in the energy regime of the argonL 3/L 2 absorption edges (240–260 eV) leading predominantly to cluster dication formation. All charged particles are detected in a photoelectron-photoion-photoion-concidence (PEPIPICO) experiment. Symmetric and asymmetric charge separation reactions (Coulomb explosion) are identified for clusters below the critical size of stable dication formation. The peak shapes of the coincidence signals are investigated as a function of neutral cluster size. Characteristic changes in peak shape are observed which are used to derive fragmentation mechanisms involving sequential evaporation of neutrals before and after charge separation. The spectra indicate in accordance with low kinetic energy releases occurring in charge separation of large dissociative cluster dications (Ar n 2+ , withn>50) that due to large charge separation distances the momenta of both singly charged fragments are not any more directed into opposite direction, as it is typical for Coulomb explosion. The results are compared to collision induced fragmentation of mass selected argon cluster dications as well as photon stimulated desorption spectra of condensed argon. 相似文献
24.
Jerald S. Bradshaw Patricia K. Thompson Reed M. Izatt Frederick G. Morin David M. Grant 《Journal of heterocyclic chemistry》1984,21(3):897-901
A series of chiral diphenyl-substituted macrocyclic polyether-diester ligands have been prepared from the chiral diphenyl-substituted tetraethylene glycol. Enantiomeric recogntion by the chiral diphenyl-substituted pyridino-diester-18-crown-6 compound ( 7 ) was studied by temperature dependent 1H NMR spectroscopy in deuteriodichloromethane. This ligand exhibited chiral recognition when complexed with the hydrogen per-chlorate salts of (R)- and (S)-α-(1-naphthyl)ethylamine and (R)- and (S)-methyl phenylalaninate. 相似文献
25.
Sandra K Stals I Sandra P Claeyssens M Van Beeumen J Devreese B 《Journal of chromatography. A》2004,1058(1-2):263-272
N-Glycosylation of cellobiohydrolase I from the fungus Trichoderma reesei (strain Rut-C30) is studied using a combination of electrophoretic, chromatographic and mass spectrometric techniques. As four potential N-glycosylation sites and several uncharged and phosphorylated high-mannose glycans are present, a large number of glycoforms and phospho-isoforms can be expected. Isoelectric focusing both in gel and in capillary format was successfully applied for the separation of the phospho-isoforms. They were extracted in their intact form from the gel and subsequently analysed by nanospray-Q-TOF-MS, thereby making use of a powerful two-dimensional technique. Nano-LC/MS/MS on a Q-Trap MS further allowed the determination of the glycosylation sites. As a novel approach, an oxonium ion was used in precursor ion scanning for selective detection of glycopeptides containing phosphorylated high-mannose glycans. 相似文献
26.
P. Morin M. B. Amran S. Favier R. Heimburger M. Leroy 《Fresenius' Journal of Analytical Chemistry》1992,342(4-5):357-362
Summary Capillary zone electrophoresis (CZE) in capillary silica columns has been used for the separation of arsenite (AsO
2
–
), arsenate (AsO
4
3–
), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The separation of these ionic species has been achieved using a capillary silica column (72 cm×50 m i.d.) with an acidic phosphate buffer and with an on-column UV detection (190 nm). Optimization of experimental parameters (pH, temperature, voltage) were studied. The selectivity of the separation can be improved by working in the pH-range of 4.5–6.5. For analytical inorganic separations of UV-absorbing anions, capillary zone electrophoresis has advantages because of the relatively simple equipment, the short analysis time (15 min), the high efficiency and the low mass detection limit (40 pg for arsenate). 相似文献
27.
Morin N. Chilouet A. Millet J. Rouland J.-C. 《Journal of Thermal Analysis and Calorimetry》2000,62(1):187-201
The complexation of bifonazole, an antimycotic hydrophobic imidazole derivative, with β-cyclodextrin (β-CD) was investigated
in solid phase, using the following complementary techniques: differential scanning calorimetry (DSC), thermogravimetric analysis
(TG) and X-ray powder diffractometry. The β-CD-bifonazole samples were prepared in both aqueous medium by coprecipitation
and in solid state by kneading method and the β-CD-bifonazole binary diagrams were drawn. The experimental results demonstrate
the formation of two binary compounds, β-CD-bifonazole and (β-CD)x bifonazole (x =2 or 4). The first compound may be an inclusion compound and the second a crystallized compound, in which the bifonazole
is not necessarily included in the cyclodextrin internal cavity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
28.
Anusuya Choudhury Michael E. Pierce Dieu Nguyen Louis Storace Pat N. Confalone 《Tetrahedron letters》2005,46(47):8099-8102
D-D4FC (1) is an anti-HIV agent currently under phase II clinical trial (Pharmaset Inc). Its molecular architecture is suitable for a Ferrier rearrangement kind of operation on a furanoid glycal to fix the position of the double bond and the relative stereochemistry. Despite the fact that classical Ferrier rearrangement does not work on furanoid glycals, a palladium mediated modified protocol has been developed for the glycosidation of an aromatization prone xylo-furanoid glycal (5) for the synthesis of D-D4FC. 相似文献
29.
Polfer NC Haselmann KF Zubarev RA Langridge-Smith PR 《Rapid communications in mass spectrometry : RCM》2002,16(10):936-943
Electron capture dissociation (ECD) of polypeptides has been demonstrated using a commercially available 3 Tesla Fourier transform ion cyclotron resonance (FTICR) instrument. A conventional rhenium filament, designed for high-energy electron impact ionisation, was used to effect ECD of substance P, bee venom melittin and bovine insulin, oxidised B chain. A retarding field analysis of the effective electron kinetic energy distribution entering the ICR cell suggests that one of the most important parameters governing ECD for this particular instrument is the need to employ low trapping plate voltages. This is shown to maximise the abundance of low-energy electrons. The demonstration of ECD at this relatively low magnetic field strength could offer the prospect of more routine ECD analysis for the wider research community, given the reduced cost of such magnets and (at least theoretically) the greater ease of electron/ion cloud overlap at lower field. 相似文献
30.