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991.
Zunin P Boggia R Lanteri S Leardi R De Andreis R Evangelisti F 《Journal of chromatography. A》2004,1023(2):271-276
The instrumental performances of a Thermo Desorption-Cooled Injection System coupled with a gas chromatography-mass spectrometer (GC-MS) were improved by a Plackett-Burman experimental design for the direct thermal extraction of volatile compounds from extra-virgin olive oils. The obtained experimental conditions were applied to the analysis of samples from West Liguria (cv. Taggiasca > or = 90%) and Spain (cv. Arbequina), which shared such similar sensorial features that Taste Panel did not distinguish them. Principal component analysis (PCA) was then applied to the experimental data. Three linear combinations of the amounts of the lipoxygenase oxidation products proved to be decisive and sufficient in the differentiation of the two groups of samples. 相似文献
992.
993.
Paola Bassani E. Gariboldi G. Vimercati 《Journal of Thermal Analysis and Calorimetry》2007,87(1):247-253
An Al–4.4Cu–0.5Mg–0.9Si–0.8Mn alloy (IADS 2014
grade) in the solution annealed and peak aged condition was exposed at 170°C
for relatively long times (up to about 1800 h) in order to check the stability
of the alloy. The investigated aging temperature was in the frame of a research
on the long-term mechanical behaviour of such alloy. Microstructure evolution
was monitored via calorimetric analyses, metallographic inspections and hardness
measurements. Further, X-ray analyses were carried out on selected samples.
The attention was focused on differential scanning calorimetry performed at
different scanning rates, with the aim of evaluating the kinetics of the precipitation
phenomena. Notwithstanding the wide industrial diffusion of this alloy, literature
survey showed that there is not a consensus view on the precipitation sequences
and on calorimetric peak identification.
The present results show
the progressive evolution of calorimetric peaks, corresponding to that of
strengthening particles towards more stable phases, proved by the disappearance
of exothermic peaks. Activation energy from Kissinger kinetic analysis in
the case of aged samples provided scattered values that could be reasonably
attributed to an overlapping of transformation peaks. Moreover, in these samples
transformations partially occurred before DSC scans, providing non-constant
transformation fraction at signal peak temperatures and resulting in different
activation energies. 相似文献
994.
Donatella Capitani Paola Laurienzo Mario Malinconico Noemi Proietti Antonio Roviello 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3916-3928
A new series of alkoxy‐substituted poly(p‐phenylene 1,3,4‐oxadiazole)s modified by the insertion of small percentages of various comonomers were synthesized through the precursor polyhydrazides. The comonomers used contained trans double bonds or meta‐alkoxy‐substituted aromatic rings to improve the solubility of the final polymers. The synthesized copolymers were chemically characterized by 1H NMR and Fourier transform infrared spectroscopy. In some cases, the copolymers really showed improved solubility in organic solvents. The 15N solid‐state NMR technique was applied to examine the degree of conversion from the precursor polyhydrazides to the final polymers, which determined the effective conjugated length in the target polyoxadiazoles. Thermal stability and structural characteristics of all the polymers as well as a preliminary investigation on the optical properties of polyoxadiazoles are also reported. The copolymers retained high absorbance in the UV region and high transmission in the whole telecommunication range. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3916–3928, 2003 相似文献
995.
996.
997.
Antoniotti P Bottizzo E Operti L Rabezzana R Borocci S Grandinetti F 《Journal of mass spectrometry : JMS》2011,46(5):465-477
The gas-phase ion chemistry of GeF(4) and of its mixtures with water, ammonia and hydrocarbons was investigated by ion trap mass spectrometry (ITMS) and ab initio calculations. Under ITMS conditions, the only fragment detected from ionized GeF(4) is GeF(3)(+). This cation is a strong Lewis acid, able to react with H(2)O, NH(3) and the unsaturated C(2)H(2), C(2)H(4) and C(6)H(6) by addition-HF elimination reactions to form F(2)Ge(XH)(+), FGe(XH)(2)(+), Ge(XH)(3)(+) (X = OH or NH(2)), F(2)GeC(2)H(+), F(2)GeC(2)H(3)(+) and F(2)GeC(6)H(5)(+). The structure, stability and thermochemistry of these products and the mechanistic aspects of the exemplary reactions of GeF(3)(+) with H(2)O, NH(3) and C(6)H(6) were investigated by MP2 and coupled cluster calculations. The experimental proton affinity (PA) and gas basicity (GB) of GeF(4) were estimated as 121.5 ± 6.0 and 117.1 ± 6.0 kcal mol(-1), respectively, and GeF(4)H(+) was theoretically characterized as an ion-dipole complex between GeF(3)(+) and HF. Consistently, it reacts with simple inorganic and organic molecules to form GeF(3)(+)-L complexes (L = H(2)O, NH(3), C(2)H(2), C(2)H(4), C(6)H(6), CO(2), SO(2) and GeF(4)). The theoretical investigation of the stability of these ions with respect to GeF(3)(+) and L disclosed nearly linear correlations between their dissociation enthalpies and free energies and the PA and GB of L. Comparing the behavior of GeF(3)(+) with the previously investigated CF(3)(+) and SiF(3)(+) revealed a periodically reversed order of reactivity CF(3)(+) < GeF(3)(+) < SiF(3)(+). This parallels the order of the Lewis acidities of the three cations. 相似文献
998.
Manca P Pilo MI Sanna G Zucca A Bergamini G Ceroni P 《Chemical communications (Cambridge, England)》2011,47(12):3413-3415
Two Ru(2+) complexes containing terpyridine ligands appended with terthiophene units connected by a methyleneoxy or an alkynyl bridge show very different luminescent behaviours: the former is non-luminescent at 298 K owing to a photoinduced energy transfer process to the terthiophene moiety, while the latter exhibits an extraordinary long excited state lifetime because of an energy reservoir effect. 相似文献
999.
Fang Y Nguyen P Ivasenko O Aviles MP Kebede E Askari MS Ottenwaelder X Ziener U Siri O Cuccia LA 《Chemical communications (Cambridge, England)》2011,47(40):11255-11257
Charge-assisted hydrogen bond-directed self-assembly of a zwitterionic quinonemonoimine was investigated at the liquid/solid interface using scanning tunnelling microscopy. Factors governing morphology, chirality and multilayer formation are discussed, presenting an important foundation for understanding the properties of a large family of related molecules with interesting potential in supramolecular design. 相似文献