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81.
82.
Wege HA Aguilar JA Rodríguez-Valverde MA Toledano M Osorio R Cabrerizo-Vílchez MA 《Journal of colloid and interface science》2003,263(1):162-169
A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other. 相似文献
83.
Odn Arjona Roberto Fernndez de la Pradilla Angel Martin-Domenech Joaquin Plumet 《Tetrahedron》1990,46(24):8187-8198
The nucleophilic Sn2' bridge opening of 7-oxabicyclo[2.2.1] hept-5-en-2-ols with organolithium reagents occurs in a regio- and stereospecific fashion to produce 6-substituted-cyclohex-4-en-1,3-diols, regardless of the stereochemistry at C-2. A free alcohol functionality is necessary to attain complete regiocontrol of the process. The methodology is utilized to prepare an optically pure cyclohexene derivative, (+)-(1S,3S,6R)-6-n-butyl-3-methyl-cyclohex-4-en-1,3-diol (5b), as a model system. 相似文献
84.
Salt effects on the apparent stability of the cucurbit[7]uril-methyl viologen inclusion complex 总被引:1,自引:0,他引:1
The effects of the medium ionic composition on the apparent equilibrium association constant (K) for the formation of a 1:1 inclusion complex between the guest methyl viologen (MV(2+)) and the host cucurbit[7]uril (CB7) were studied in aqueous solutions. The K values were found to decrease with increasing ionic strength, with more pronounced effects for solutions containing divalent Ca(2+) ions than for solutions containing monovalent Na(+) ions. The competing ion-dipole interactions between Ca(2+) or Na(+) and MV(2+) ions appear to be responsible for the remarkable modulation of the K values observed in this work. 相似文献
85.
Izquierdo S Rúa F Sbai A Parella T Alvarez-Larena A Branchadell V Ortuño RM 《The Journal of organic chemistry》2005,70(20):7963-7971
[Chemical reaction: See text] Several derivatives of (+)- and (-)-2-aminocyclobutane-1-carboxylic acid, 1, have been prepared through enantiodivergent synthetic sequences. The stereoselective synthesis of free amino acid (+)-1 has been achieved, and this product has been fully characterized for the first time. Stereocontrolled alternative synthetic methodologies have been developed for the preparation of bis(cyclobutane) beta-dipeptides in high yields. Among them, enantio and diastereomers have been synthesized. beta,beta- and beta,delta-Dimers resulting from the coupling of a cyclobutane residue and a linear amino acid have also been prepared. The ability of the cyclobutane ring as a structure-promoting unit both in the monomers and in the dimers has been manifested. The NMR structural study and DFT theoretical calculations evidence the formation of strong intramolecular hydrogen bonds giving rise to cis-fused [4.2.0]octane structural units that confer high rigidity on these molecules both in solution and in the gas phase. The contribution of a cis-trans conformational equilibrium derived from the rotation around the carbamate N-C(O) bond has also been observed, the trans form being the major conformer. In the solid state, this equilibrium does not exist, and moreover, intermolecular hydrogen bonds are present. 相似文献
86.
87.
Jos L. Del Valle Cecilia Polo TomS Torroba Stefano Marcaccini 《Journal of heterocyclic chemistry》1995,32(3):899-901
The sodium salt of TOSMIC reacted with (E)-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-C-nitro-D-galacto- (1) and -D-manno-hept-1-enitol (2) to give 3-(D-galacto- (3) and 3-(D-manno-penta-O-acetylpentitol-1-yl)-4-nitropyrrole (4) , respectively. Compound 1 reacted with diaryl nitrile imines, affording 1,3-diaryl-4-(1,2,3,4,5-penta-O-acetyl-D-galacto-pentitol-1-yl)pyrazoles 5 and 6 . 相似文献
88.
Angel Alberola Celia Andrs Alfonso Gonzlez Ortega Rafael Pedrosa Martina Vicente 《Journal of heterocyclic chemistry》1987,24(3):709-713
Unsymmetrically substituted β-aminoenones react with malononitrile, cyanomethylphenylsulfone, benzoyl-acetonitrile and ethyl cyanoacetate, in very mild conditions, to yield regiospecifically 3-functionalized 2(1H)-pyridones in high yields. 相似文献
89.
90.
P. Gronchi A. Kaddouri P. Centola R. Del Rosso 《Journal of Sol-Gel Science and Technology》2003,26(1-3):843-846
SiO2 and Al2O3 supported Ni catalysts were synthesized in the form of xerogels: the SiO2 based materials were prepared starting from Ni propionate or glycolate salts and reacting them with tetraethoxysilane (TEOS) in propionic acid, Si(ethylene glycolate) or sodium silicate. The Al2O3 supported catalysts were prepared similarly from Ni propionate salts with Al iso-propoxide salts. Narrow metal particles and strong metal support interactions are observed in the sol-gel catalysts. The metal dispersion was higher for Al2O3 based materials than the SiO2 ones and it deeply depends on the Ni precursor for the silica supported Ni. Wet impregnated oxides with similar Ni loading have higher metal surface area than those from sol-gel processing. The influence of surface differences on the catalytic activity of the materials was studied following the CH4 and CO2 reaction in dry reforming conditions by pulse reaction tests. 相似文献