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141.
Poly(crown ether)-catalysed derivatization of lower fatty acids with p-bromophenacyl bromide or pentafluorobenzyl bromide has been used for their determination in gaseous samples by gas chromatography (employing either flame-ionization or electron-capture detection). Stontium hydroxide was employed as a base for the derivatization, taking advantage of the fact that a column packed with strontium hydroxide-coated glass beads is very suitable for preconcentration of the fatty acids from ambient air. In situ derivatization of lower fatty acids, preconcentrated on the glass beads as their strontium salts, proceeded nearly quantitatively in acetonitrile. Traces of lower fatty acids in artificial sample gases could be determined successfully using this conventional derivatization followd by direct injection of the reaction mixture into a gas chromatograph. 相似文献
142.
[reaction: see text] We have established an enantioselective synthesis of both C2 symmetric and unsymmetric tetra-ortho-substituted axially chiral biaryls through rhodium-catalyzed double [2 + 2 + 2] cycloaddition (up to >99% ee). This method serves as an attractive new route to enantioenriched tetra-ortho-substituted axially chiral biaryls in view of the one-step access to substrate diynes and tetraynes starting from readily available alkynes. 相似文献
143.
Yoneda K Adachi K Hayami S Maeda Y Katada M Fuyuhiro A Kawata S Kaizaki S 《Chemical communications (Cambridge, England)》2006,(1):45-47
The variable temperature magnetic susceptibility, X-ray crystallography, and M?ssbauer and Raman spectra of a new dinuclear complex-based one-dimensional coordination polymer [[Fe(II)2(NCS)2(mu-bpypz)2](micro-4,4'-bpy)].MeOH demonstrated a steep one-step [HS-HS] to [LS-LS] spin transition. 相似文献
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145.
Tomonari Tanaka Masato Noguchi Masaki Ishihara Atsushi Kobayashi Shin-ichiro Shoda 《Macromolecular Symposia》2010,297(1):200-209
Summary: A cellotetraose-backboned hepta-saccharide (XXXG) (a capital X represents a glucopyranose residue that is substituted with a xylopyranose through an α-1,6 glycosidic bond, and a capital G represents a non-substituted glucopyranose residue) and a nona-saccharide (XLLG) (a capital L represents a glucopyranose residue that is substituted with a galactopyranoseβ(1-2)xylopyranose through an α-1,6 glycosidic bond) have directly been converted to the corresponding 4,6-dimethoxy-1,3,5-triazin-2-yl derivatives (DMT-β-XXXG 1 and DMT-β-XLLG 2 , respectively) by the action of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl morpholinium chloride (DMT-MM). The selective nucleophilic attack of the anomeric hydroxyl group to DMT-MM has been achieved in water without using any protection of the hydroxyl groups. The resulting activated oligosaccharide derivatives ( 1 and 2 ) were found to polymerize catalyzed by an endo-β-1,4-glucanase as catalyst. The polymerization took place in a complete regio- and stereo-selective manner, affording non-natural polysaccharides having a XXXG-repeating unit and a XLLG-repeating unit, respectively, in the main chain. It is extremely difficult to construct such definite repeating structures via the conventional synthetic routes including protection-deprotection procedures. 相似文献
146.
Keiichi Kinashi Shunsuke Takenaka Shigekazu Kusabayashi 《Molecular Crystals and Liquid Crystals》2013,570(1):49-58
Some mesogenic materials involving a piperazine skeleton were prepared and the thermal properties were examined by DSC and microscopic analyses. Although the piperazines have a thermal flexibility similar to cyclohexyl ring, a lateral interaction due to lone pair electrons of nitrogens largely enhances the thermal stability of the mesophase. The piperazine compounds tend to preserve a smectic arrangement. 相似文献
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149.
Keiichi Murai Lukas Lauterbach Kazuya Teramoto Zhiyang Quan Lena Barra Tsuyoshi Yamamoto Kenichi Nonaka Kazuro Shiomi Makoto Nishiyama Tomohisa Kuzuyama Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2019,58(42):15046-15050
The skeletons of some classes of terpenoids are unusual in that they contain a larger number of Me groups (or their biosynthetic equivalents such as olefinic methylene groups, hydroxymethyl groups, aldehydes, or carboxylic acids and their derivatives) than provided by their oligoprenyl diphosphate precursor. This is sometimes the result of an oxidative ring‐opening reaction at a terpene‐cyclase‐derived molecule containing the regular number of Me group equivalents, as observed for picrotoxan sesquiterpenes. In this study a sesquiterpene cyclase from Trichoderma spp. is described that can convert farnesyl diphosphate (FPP) directly via a remarkable skeletal rearrangement into trichobrasilenol, a new brasilane sesquiterpene with one additional Me group equivalent compared to FPP. A mechanistic hypothesis for the formation of the brasilane skeleton is supported by extensive isotopic labelling studies. 相似文献
150.
Keiichi Tomishige Masazumi Tamura Yoshinao Nakagawa 《Chemical record (New York, N.Y.)》2019,19(7):1354-1379
Recent progress on the CeO2 catalyzed synthesis of organic carbonates, ureas, and carbamates from CO2+alcohols, CO2+amines, and CO2+alcohols+amines, respectively, is reviewed. The reactions of CO2 with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H2O is essential in order to get the target product in high yield. One of the effective method of the H2O removal from the related reaction systems is the combination with the hydration of 2‐cyanopyridine to 2‐picolinamide, which is also catalyzed by CeO2. 相似文献