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551.
A general method for one-pot reaction of hydroquinone derivatives and dienes has been developed. The system of Pb3O4 in tetrahydrofuran–trifluoroacetic acid was found to play dual roles as oxidant for the generation of quinones in situ and as catalyst for the Diels–Alder cycloaddition, which makes the one-pot reaction efficient and easy to carry out. Using this method, a variety of six-membered functionalized carbocyclic compounds can be easily prepared in medium to excellent yields at room temperature. 相似文献
552.
Kayahara E Yamada H Yamago S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(19):5272-5280
Generation of carbanions from organostibines and organobismuthines through heteroatom-metal exchange reactions was examined from synthetic and mechanistic viewpoints. The exchange reaction proceeded spontaneously upon treatment with various organometallic reagents, such as alkyl lithiums, tetraalkyl zincates, and alkyl magnesium halides to afford the corresponding carbanions quantitatively. Due to the high reactivity of these heteroatom compounds, the exchange reactions took place exclusively even in the presence of various polar functional groups, which potentially react with organometallic species. The advantage of this method was exemplified by the end-group transformation of living polymers that bear these heteroatom species at the ω-polymer end, prepared by using organostibine and bismuthine-mediated living radical polymerizations. Various polymers that bear polar functional groups and acidic hydrogen-for example, poly(methyl methacrylate), poly(butyl acrylate), poly(N-isopropyl acrylamide), and poly(2-hydroxyethyl methacrylate)-could be used in the exchange reactions, and subsequent trapping with electrophiles afforded the corresponding polymers with controlled molecular weights, molecular weight distributions, and end-group functionalities. Competition experiments showed that organostibines and organobismuthines were among the most reactive heteroatom compounds towards organometallic reagents and that their high reactivity was responsible for the high chemoselectivity in the exchange reaction. 相似文献
553.
554.
平台石墨炉原子吸收法直接测定镍基合金中铅和锑 总被引:2,自引:0,他引:2
平台石墨炉原子吸收法直接测定镍基合金中铅和锑谢文兵,姚金玉,胡庆兰(中国科学院长春应用化学研究所长春130022)关键词石墨炉原子吸收,镍合金,铅,锑,基体改进剂石墨炉原子吸收法是测定痕量元素最有效的方法之一。但是铅和锑都是易挥发元素,为了增强灰化过... 相似文献
555.
N. M. Laptash E. V. Kovaleva A. A. Mashkovskii A. Yu. Beloliptsev L. A. Zemnukhova 《Journal of Structural Chemistry》2007,48(5):848-854
Vibrational and 17O NMR spectroscopy in combination with quantum chemical calculations are used to investigate the hydrolysis of antimony(III) fluoride complexes. A hydrolytic decomposition of SbF3 and [SbF4]? is accompanied by oligomerization with the formation of edge-and corner-connected dimers ([Sb2O2F4]2?, [Sb2OF8]4?) and trimers ([Sb3O3F6]3?, [Sb3OF9]2?) with bridging oxygen atoms. The hydrolysis of [SbF4]? is also characterized by the presence in the solution of a discrete cation of [SbF5]2? which is least hydrolized. Only a partial isomorphic substitution of fluoride ion by hydroxide one is possible, which is reflected in the composition of K2Sb(OH)xF5?x (x = 0.3) crystals isolated from the fluoride aqueous solution. 相似文献
556.
557.
Masato Hirai Prof. Dr. François P. Gabbaï 《Angewandte Chemie (International ed. in English)》2015,54(4):1205-1209
Because of hydration, fluoride ions in water typically elude complexation by neutral Lewis acids. Here, we show how this limitation can be overcome with a bidentate Lewis acid containing two antimony(V) centers. This derivative ( 2 ) is obtained by the simple reaction of 4,5‐bis(diphenylstibino)‐9,9‐dimethylxanthene ( 1 ) with two equivalents of 3,4,5,6‐tetrachlorobenzoquinone (o‐chloranil). It features two square‐pyramidal stiborane units oriented in a face‐to‐face fashion. Titration experiments show that this new bidentate Lewis acid binds fluoride in aqueous solutions containing 95 % water with a binding constant (K) of 700±30 M ?1. The structure of the fluoride adduct confirms fluoride anion chelation between the two antimony centers. 相似文献
558.
Shigeru Yamago Prof. Dr. Takeshi Yamada Dr. Manabu Togai Yuu Ukai Eiichi Kayahara Na Pan Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):1018-1029
Several organostibine chain‐transfer agents possessing polar functional groups have been prepared by the reactions of azo initiators and tetramethyldistibine ( 1 ). Carbon‐centered radicals thermally generated from the azo initiators were trapped by 1 to yield the corresponding organostibine chain‐transfer agents. The high yields observed in the synthesis of the chain‐transfer agents strongly suggest that distibines have excellent radicophilic reactivity. As the reactions proceeded under neutral conditions, functional groups that are incompatible with ionic conditions were incorporated into the chain‐transfer agents. The chain‐transfer agents were used in living radical polymerization to synthesize the corresponding α‐functionalized polymers. As the functional groups in the chain‐transfer agents did not interfere with the polymerization reaction, well‐controlled polymers possessing number‐average molecular weights (Mns) predetermined by the monomer/transfer agent ratios were synthesized with low polydispersity indices (PDIs). The organostibanyl ω‐polymer ends were transformed into a number of different functional groups by radical‐coupling, radical‐addition, and oxidation reactions. Therefore, it was possible to synthesize well‐controlled telechelic polymers with the same and also with different functional groups at their α‐ and ω‐polymer ends. Distibine 1 was also found to increase PDI control in the living radical polymerization of styrene and methyl methacrylate (MMA) using a purified organostibine chain‐transfer agent. Well‐controlled poly(methyl methacrylate)s with Mn values ranging from 10 000 to 120 000 with low PDIs (1.05–1.15) were synthesized by the addition of a catalytic amount of 1 . The results have been attributed to the high reactivity of distibine 1 towards polymer‐end radicals, which are spontaneously deactivated to yield organostibine dormant species. 相似文献
559.
The compound CsAgSb4S7 has been synthesized by the reaction of the elements in a Cs2S3 flux at 773 K. The compound crystallizes in a new structure type with eight formula units in space group C2/c of the monoclinic system in a cell at 153 K of dimensions , , , β=97.650(1)°, and . The structure contains two-dimensional layers separated by Cs atoms. Each layer is built from edge-sharing one-dimensional and chains. Each Ag atom is tetrahedrally coordinated to four S atoms. Each Sb3+ center is pyramidally coordinated to three S atoms to form an SbS3 group. CsAgSb4S7 is insulating with an optical band gap of 2.04 eV. Extended Hückel calculations indicate that the band gap in CsAgSb4S7 is dominated by the Sb 5s and S 3p states above and below the Fermi level. 相似文献
560.
碱熔样电感耦合等离子体发射光谱法测定锑矿石中锑 总被引:2,自引:0,他引:2
建立了碱熔样电感耦合等离子体发射光谱法测定锑矿中总锑的方法。探讨了熔样时间、熔样温度、溶解液酸度及组成对测定结果的影响。以过氧化钠作为熔剂,于650℃熔样15 min,加入1.0 g/L酒石酸调节样品溶液的酸度以防止水解,用电感耦合等离子体发射光谱法测定锑的含量,方法线性范围为0.00~50.0 mg/L,检出限为50.0μg/g,8个样品独立测定结果的相对标准偏差均小于5%(n=11),标准样品测定结果与标准值基本吻合。该方法适用于锑矿中总锑的含量测定。 相似文献