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81.
Jean-Luc Decout Alain Lablache-Combier Claude Loucheux 《Journal of polymer science. Part A, Polymer chemistry》1980,18(7):2371-2390
Vinylpyridine-N-oxide units were introduced in polymeric chains in order to study their photocrosslinking. Copolymers of styrene and 4-vinylpyridine-N-oxide were especially synthesized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubility and of the swelling ratio. The Cleavage of the N-oxide bond was responsible for the photocrosslinking. The competitive formation of carbonyl compounds took place and decreased the rate of photocrosslinking. This last reaction is favored by triplet-state quenchers. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used. When the photocrosslinking proceeded, a film of the copolymeric material became transparent in the 280–320-nm range. Thick films could therefore be completely photocrosslinked when irradiated in this range of wavelength. 相似文献
82.
Baseline separation of ten new substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives, with one chiral center, was achieved by CD-EKC using highly sulfated CDs (alpha, beta, gamma highly S-CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The highly S-CDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times inferior to 2.5 min and resolution factors R(s) of 3.73, 3.90, 1.40, and 4.35 for compounds 1, 2, 3, and 5, respectively, using 25 mM phosphate buffer at pH 2.5 containing either highly S-alpha-CD, highly S-beta-CD, and highly S-gamma-CD (3 or 4% w/v) at 298 K, with an applied field of 0.30 kV/cm. The determination of the enantiomer migration order for the various analytes and the study of the analyte structure-enantioseparation relationships display the high contribution of the interactions between the analytes phenyl ring and the CDs to the enantiorecognition process. The thermodynamic study of the analyte-CD affinities permits us to improve our knowledge about the enantioseparation mechanism. 相似文献
83.
Using cyclodextrin capillary zone electrophoresis (CD-CZE), baseline separation of synthetic tetrahydronaphthalenic derivatives, potential melatoninergic compounds, was achieved. A method for the enantioresolution of these tetralins and determination of their enantiomeric purity was developed using anionic CDs (highly sulfated-CD or highly S-CD) as chiral selectors and capillaries dynamically coated with polyethylene oxide (PEO). Operational parameters such as the nature and concentration of the chiral selectors, buffer pH, organic modifiers, temperature and applied voltage were investigated. The use of charged CDs provides a driving force for our neutral compounds in the running buffer and enantiomeric resolution by inclusion of compounds in the CD cavity. The highly S-beta-CD was found to be the most effective complexing agent, allowing good enantiomeric resolution. The complete resolution of three tetralin compounds was obtained using 25 mM phosphate buffer at pH 2.5 containing 2.5% w/v of highly S-beta-CD at 25 degrees C with an applied field of 0.25 kV/cm. The apparent association constants of the inclusion complexes were calculated. This optimized method was validated in terms of linearity, sensitivity, accuracy and recovery. The enantiomeric purity for the three molecules was determined and the detection limit of enantiomer impurities is about 0.3-0.6%. 相似文献
84.
Baseline separation of ten new, substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives with one chiral center was achieved using cyclodextrin-capillary zone electrophoresis (CD-CZE). A method for the enantiomeric resolution of these compounds was developed using neutral CDs (native alpha-, beta-, gamma-CDs or alpha-, beta-, gamma-hydroxypropyl (HP)-CDs) as chiral selectors. Operational parameters including the nature and concentration of the chiral selectors, pH, ionic strength, organic modifiers, temperature, and applied voltage were investigated. The use of neutral CDs provides enantiomeric resolution by inclusion of compounds in the CD cavity. The HP-alpha-CD and HP-beta-CD were found to be the most effective complexing agents and allowed efficient enantiomeric resolutions. Optimal separation of N-imidazole derivatives was obtained using 50 mM phosphate buffer at pH 2.5 containing either HP-alpha-CD or HP-beta-CD (7.5-12.5 mM) at 25 degrees C, with an applied field of 0.50 kV.cm(-1) giving resolution factors Rs superior to 1.70 with migration times of the second enantiomer less than 13 min. The same enantiomer migration order observed for all molecules can be related to a close interaction mechanism with CDs. The influence of structural features of the solutes on Rs and tm was studied. The lipophilic character (log kw) of the solutes and the apparent and averaged association constants of inclusion complexes for four compounds with the six different CDs led us to rationalize the enantioseparation mechanisms. The conclusions were corroborated with reversed-phase high-performance liquid chromatography (HPLC) on chiral stationary phases (CSPs) based on CDs. 相似文献
85.
The effect (on the energy of the different states) of including doubly excited configurations in a - plus -configuration interaction treatment, is studied within the CNDO/2 framework. For moderately large molecules the problem of the choice of the type ( or ) of configurations taken into account is examined. When possible, comparison is made with similar non empirical calculations.
Zusammenfassung Im Rahmen der CNDO/2 Methode wird der Einfluß (auf die Energien verschiedener Zustände) des Einschlusses doppelt angeregter Konfigurationen in einer - und -Konfigurationswechsel-wirkungs-Behandlung studiert. Für nicht allzu große Moleküle wird das Problem der Wahl der Art ( oder ) der berücksichtigten Konfigurationen untersucht. Soweit möglich, werden die Resultate mit denen ähnlicher nichtempirischer Rechnungen verglichen.
Résumé L'effet (sur l'énergie des différents états) de l'introduction de configurations diexcitées dans une interaction de configuration plus , est étudié dans le cadre de la méthode CNDO/2. Pour des molécules de taille moyenne le problème du choix du type ou des configurations est examiné. Les résultats obtenus sont comparés aux calculs non-empirique similaires disponibles.相似文献
86.
Claude Leroy 《Czechoslovak Journal of Physics》1991,41(1):36-41
Experimental results from the HELIOS set-up (High Energy Lepton and Ion Spectrometer, in operation at the CERN Super Proton Synchrotron to study high-energy nucleus-nucleus collisions) are presented and discussed. The transverse energy differential cross section can be parametrized by a geometrical model. The energy density reached in these collisions is much larger than that inside the nucleon and is in the region of the critical value 2·5 GeV/fm3 obtained from lattice QCD calculations for the deconfinement transition. The transverse momentum spectra of photons agree in shape and absolute cross section with the photon spectra expected from hadronic sources.Presented at the IIIrd International Symposium High Energy Experiments And Methods (HEXAM '89), Bechyn, Czechoslovakia, June 25–30, 1989.I would like to thank the organizers of the HEXAM'89 Symposium in Bechyn for giving me the opportunity to participate in this very pleasant and stimulating conference and the hospitality they have extended. This work was supported in part by the National Sciences and Engineering Research Council of Canada (NSERC). 相似文献
87.
88.
89.
Using cyclodextrin-capillary zone electrophoresis (CD-CZE), baseline separation of baclofen phaclofen, saclofen, and hydroxy-saclofen, potent gamma-aminobutyric acid(B) (GABA(B)) agonist or antagonists was achieved. A method for the enantioresolution of those analogs of GABA was developed using anionic cyclodextrins (highly sulfated CD or highly S-CD) as chiral selectors and capillaries dynamically coated with polyethylene oxide (PEO). With charged CDs we observed good resolutions due to the large electrophoretic mobility of these chiral selectors opposite to the mobility of the solutes. The highly S-alpha-CD and S-beta-CD were found to be complementary and the most effective complexing agent, allowing good enantiomeric resolution in short runtimes. The complete resolution was obtained using 25 mM phosphate buffer at pH 2.5 containing 3% w/v of highly S-alpha-CD or S-beta-CD at 25 degrees C with an applied field of 0.30 kV/cm. The apparent binding constants of the inclusion complexes were evaluated and the migration order was determined. A comparison was possible to investigate the importance of the anionic group of the molecules in the separations. The pK(a) values were determined for all four compounds in order to explain relative electrophoretic migration of the solutes. 相似文献
90.
James Courmarcel Gildas Le Gland Loic Toupet Fr d ric Paul Claude Lapinte 《Journal of organometallic chemistry》2003,670(1-2):108-122
The synthesis of the new (η2-dppe)(η5-C5Me5)Fe---CC---1,3-(C6H4X) (m-2a/2b; X=F/Br) and (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4I) (2c) complexes, as well as the solid-state structure of the known (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4F) (2a) complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated. Starting from the known (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4Br) complex (2b), the synthesis of the (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4)---CC---H complex (6d) and of the corresponding silyl-protected precursors (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4)CC---SiR3 (6b/6c; R=iPr/Me) are reported. By use of lithium---bromine exchange reactions on 2b, the silyl- (7a; E=Si; R=Me) and tin- (7b–7d; E=Sn; R=Me, Bu, Ph) substituted analogues (η2-dppe)(η5-C5Me5)Fe---CC---1,4-(C6H4)ER3 are also isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are presented and the electronic substituent parameters for the “(η2-dppe)(η5-C5Me5)Fe---CC” group are determined by means of 19F-NMR. 相似文献