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71.
Contrary to the precedents, 1,3-anti stereoselection was found in the intramolecular Michael addition of ethyl ,5-carbamoyloxy-4-trialkylsilyloxy-2-hexenoate to culminate in a synthesis of N-benzoyl-,-daunosomine. The antiperiplanar effect due to the group at 4-position was revealed to play a major role in the stereoselection in this type of reactions. N-benzoyl-,-3-epidaunosamine was also synthesized by 1,2-syn asymmetric induction. 相似文献
72.
A simple one-step conversion of carboxylic acids to urethanes was achieved by diphenyl phosphorazidate (DPPA). The reaction procedure is quite simple, occurring by refluxing an equimolecular mixture of a carboxylic acid, DPPA, and triethylamine in the presence of a hydroxyl component. Aromatic, aliphatic, and heterocyclic carboxylic acids underwent rearrangements in satisfactory yields. As this modified Curtins reaction is much simpler and less laborious than the classical Curtius reaction and proceeds under mild conditions, it may have a broad synthetic utility. 相似文献
73.
74.
Takeo Fujino Hiroaki Tagawa Takeo Adachi Hiroshi Hashitani 《Analytica chimica acta》1978,98(2):373-383
A simple gravimetric determination of oxygen in uranium oxides and ternary uranium oxides is described. In alkaline earth uranates which are formed by heating in air at 800–1100°C, uranium is in the hexavalent state over certain continuous ranges of alkaline earth-to-uranium ratios. Thus, if an alkaline earth uranate or a compound containing an alkaline earth element, e.g. MgO, is mixed with the oxide sample and heated in air under suitable conditions, oxygen can be determined from the weight change before and after the reaction. The standard deviation of the O:U ratio for a UO2+x test sample is ±0.0008–0.001, if a correction is applied for atmospheric moisture absorbed during mixing. 相似文献
75.
76.
Takeo Katami Tomokuni Hayakawa Masamichi Furukawa Shozo Shibata Tadashi Hara 《Analytica chimica acta》1986
An extraction-spectrophotometric method is described for the determination of traces of zinc with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid. The reagent forms a stable, blue 1:2 zinc/reagent complex that can be extracted into chloroform. The apparent molar absorptivity of the zinc(II) complex is 1.26 × 105 l mol?1 cm?1 at 610 nm in chloroform. The reagent is relatively selective; interferences from cobalt, copper and nickel can be masked with dimethylglyoxime and aluminium and iron with a mixture of sodium fluoride and triethanolamine. The method is applied to the determination of zinc in coal fly ash and pond sediments with good precision and accuracy. 相似文献
77.
Ichikawa K Shimomura N Yamada M Ohkubo N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3235-3241
In vitro biomimetic mineralization by means of nanotechnology allows the formation of calcium carbonate polymorphs at low temperatures (<25 degrees C) under a CO(2) atmosphere of 500-1500 ppm. A two-dimensional zinc-ion ordered array (zinc array), which acts as an active-site mimic of carbonic anhydrase, has been prepared by immersing the self-organized monolayer of 3-(2-imidazolin-1-y)propyltriethosilane on mica (ImSi substrate) into aqueous zinc solution. The zinc array mounted on the ImSi substrate catalyzed the conversion from CO(2) to HCO(3) (-), and accelerated the formation of calcium carbonate. In situ X-ray diffraction data of the formed calcium carbonate on the poly(L-aspartate)-coated chitin substrate (pAsp substrate), with calcium ion-recognition sites, demonstrated that the interaction between the zinc array and pAsp substrates formed both vaterite and calcite at low temperature (15 degrees C) and mainly vaterite at 25 degrees C; this interaction also controlled the morphology of calcium carbonate formed on pAsp substrate. 相似文献
78.
Jun-ichi Yamada Yasushi Nishimoto Satoru Tanaka Rie Nakanishi Kenji Hagiya Hiroyuki Anzai 《Tetrahedron letters》1995,36(52):9509-9512
The synthesis of BEDT-TTF derivatives fused with heterocycles (3–7) has been accomplished via the BF3-promoted reaction of organotin thiolates (8 and 9) with electrophiles (10 and 11). Electrical conductivities of radical cation salts derived from some of them were also investigated. 相似文献
79.
Takeo Saegusa Hirosuke Imai Shu-Ichi Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》1968,6(3):459-465
Kinetic studies were carried out on the polymerization of tetrahydrofuran with catalyst systems of aluminum alkyl–epichlorohydrin. As aluminium alkyl species AlEt3, AlEt3–H2O (1:0.1 to 1:1.0), and “oxyaluminum ethyl” were employed. The polymerizations with these catalysts are characterized by a mechanism of stepwise addition without chain transfer or termination, which is expressed by the kinetic relation Rp = Kp[P*] ([M]–[M]e), where [M] and [M]e are the instantaneous and equilibrium concentrations of monomer and [P*] is the concentration of propagating species calculated from the amount and molecular weight of the product polymer. The determination of the rate constant kp for these catalysts has shown that the polymerization rate varied considerably with the change of aluminum alkyl species, i.e., with the water-to-aluminum ratio, but the propagation rate constant itself varied very little. The variation of polymerization rate was, therefore, attributed primarily to the differences in concentration of the propagating species, i.e. the efficiency of the catalyst in forming propagating species. The catalyst efficiency was closely related to the acid strength of the aluminum alkyl species, which was estimated from the magnitude of shift of the xanthone carbonyl band in the infrared spectrum of its coordination complex with aluminum alkyl. The maximal catalyst efficiency was attained at about [H2O]/[AlEt3] = 0.75. 相似文献
80.
Tomihiro Nishiyama Shigeki Matsui Fukiko Yamada 《Journal of heterocyclic chemistry》1986,23(5):1427-1429
Heterocyclic compounds of four 5-methyl-3-phenyl-1,3-oxazolidin-2-ones have been synthesized by the reaction of N-2-hydroxyethyl- or N-2-hydroxypropylanilines with phosgene in the presence of pyridine. From the spectral behavior, the title compounds are found to exist in the trans and cis forms. 相似文献