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981.
讨论了沸点升高法测定混和溶剂化热和汽化熵的原理,并用拟静态法测定了乙醇-丙酮,并-四氯化碳和苯,甲苯三组混和溶剂在不同组成下的正常沸点,根据沸点数据求得了混和泶微分汽化热和汽化熵,实验结果表明,二元混和溶剂与理想溶液偏离不大时,其正常汽化熵符合Trouton规则。 相似文献
982.
Anuradha Mishra Malvika Bajpai Sunita Pal Monika Agrawal Sushant Pandey 《Colloid and polymer science》2006,285(2):161-168
The application of Tamarindus
indica seed mucilage (Tam), a food grade polysaccharide, and its acrylamide grafted copolymer as flocculants was assessed for the first time for removal of various types of dyes from model textile wastewater containing azo, basic, and reactive dyes. Acrylamide grafted T. indica mucilage (Tam-g-PAM) was obtained by ceric ion initiated polymerization technique. A series of contact time experiments were conducted to assess the system variables such as concentrations of mucilage and dyes and pH. These flocculants reduce the dye concentration by flocculation and settling. The grafted copolymer, Tam-g-PAM showed better results for dye removal. The optimal flocculant concentration, which was required to effect flocculation, was independent of dye concentration within the range examined. Both the flocculants performed better for removal of azo dyes than for reactive and basic dyes. 相似文献
983.
Snezana S.?MiticEmail author Gordana Z.?Miletic Aleksandra N.?Pavlovic Snezana B.?Tosic 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):927-936
Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H2O2. The optimum reaction conditions are PS (1.32·10–3mol·dm–3), H2O2 (0.32mol·dm–3), HClO4 (2.6·10–3mol·dm–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm–3 and a detection limit of 0.024ng·cm–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples. 相似文献
984.
Koen Vandyck 《Tetrahedron letters》2005,46(1):75-78
2,3,6,7-Tetrahydro-as-indacene-1,8-dione 4 was prepared in 4 steps starting from 2-methyl-furan by modification of a literature procedure. Appliance of Noyori’s asymmetric transfer hydrogenation, resulted in (1S,8S)-1,2,3,6,7,8-hexahydro-as-indacene-1,8-diol 5 in high yield (81%) and excellent enantioselectivity (>99% ee) or (8S)-8-hydroxy-3,6,7,8-tetrahydro-2H-as-indacen-1-one 6 in moderate yield (58%) and equally high enantioselectivity (98.5% ee), depending on the conditions. The asymmetric reduction was expected to yield the (S)-alcohols using the (S,S)-Ts-DPEN ligand, which was confirmed by the appliance of the exciton chirality method on the corresponding bis(p-dimethylamino)benzoate 7. 相似文献
985.
Sh. Sh. Nabiev I. I. Ostroukhova N. V. Revina L. P. Sukhanov 《Russian Chemical Bulletin》1998,47(3):417-422
The Raman spectra of ClOF2
+ cation in solutions of anhydrous HF were studied. In the ClOF2
+HF2
− and ClOF2
+BF4
−−HF systems, this cation exists as a pyramidal structure (C
s
symmetry), while in the ClOF2
+AuF6
−−HF system, it exists as a planar structure (C
2v
symmetry). Based on nonempirical calculations by the Hartree-Fock-Roothaan method, an explanation for the dependence of the
structure of the ClOF2
+ cation on the nature of the anion was proposed. For the Cl−O bond vibrations, the correlation functions of vibrational and
rotational relaxations were calculated, and the characteristic times of these processes were determined. The main contribution
to the formation of the band contours corresponding to the above-mentioned modes is made by the vibrational dephasing.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 432–437, March, 1998. 相似文献
986.
The selective solvation of silver(I) iodate was studied in methanoldimethyl sulohoxide mixtures at 30° C by solubility and
EMF measurements. The solubility of the salt increases continuously with the addition of dimethyl sulphoxide after a slight
decrease into XDMSO =0.1. The Gibbs energy of transfer of silver cation (determined on the basis of ferrocene reference method) decreases continuously
while that of the iodate ion increases with the addition of dimethyl sulphoxide. The solvent transport number passes through
a maximum (Δ = 2.0) around XDMSO
= 0.5. These results were interpreted as arising due to a heteroselective solvation of the salt, the silver ions being preferentially
solvated by dimethyl sulphoxide and the iodate ion by methanol in these mixtures. 相似文献
987.
A. L. Chistyakov I. V. Stankevich N. P. Gambaryan I. A. Tikhonova V. B. Shur 《Russian Chemical Bulletin》1995,44(6):997-1004
Geometries and electronic structures of the complexes of halide anions with cyclic trimerico-phenylenemercury, (o-C6H4Hg)3, perfluoro-o-phenylenemercury, (o-C6F4Hg)3, vinylenemercury, (C2H2Hg)3, and perfluorovinylenemercury, (C2F2Hg)3, were modelled by the MNDO method. Calculations were performed for [L-X]– semisandwich complexes, [X-L-X]2– bipyramidal complexes, and [L-X-L]– sandwich complexes (where X=Hal,L is a mercury-containing macrocycle). Based on the results of calculations, we concluded that it was advantageous to describe the chemical bonding between halide anions and mercury-containing macrocycles in terms of generalized chemical bonds, which were successfully used for -complexes of transition metals. In the [L-X]– semisandwich complexes, the halide anion and the metallacycle are involved in the formation of three generalized chemical bonds: one headlight-shaped -bond and two two-lobe -bonds. In the [X-L-X]2– bipyramidal complexes, each halide anion forms three generalized chemical bonds with the macrocycle. It is possible because the macrocycleL has unoccupied molecular orbitals suitable for the formation of such bonds; these MOs consist mainly of the orbitals of mercury atoms directed toward both the upper and lower halogen atoms. In the [L-X-L]– sandwich complexes, the halide anion cannot be bonded to each ringvia three bonds, and, hence, an unsymmetrical structure is formed, in which the rings are located at different distances from the central atom: the [L-X]– semisandwich complex solvated by macrocycleL.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1035–1042, June, 1995.The authors are grateful to V. I. Faustov for valuable remarks.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-18342). 相似文献
988.
Josef Scharf Karl Schlögl Michael Widhalm Johann Lex Werner Tückmantel Emanuel Vogel Franz Pertlik 《Monatshefte für Chemie / Chemical Monthly》1986,117(2):255-267
2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol–1.The CD spectra of mono and disubstituted anulenes (with C1 and C2 symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.
Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene
Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C1 bzw. C2-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.相似文献
989.
990.
用X_α方法对CH_4在Ni(Ⅲ)表面吸附解离反应的理论研究马晨生,马理,杨忠志(吉林大学理论化学研究所,长春,130023)关键词CH_4/Ni(Ⅲ)吸附体系,原子簇模型,CH_4/Mi_7,MS-X_α-SCF方法甲烷在Ni表面的催化重整反应在工业和国... 相似文献