全文获取类型
收费全文 | 2567篇 |
免费 | 92篇 |
国内免费 | 16篇 |
专业分类
化学 | 1635篇 |
晶体学 | 48篇 |
力学 | 49篇 |
数学 | 271篇 |
物理学 | 672篇 |
出版年
2023年 | 13篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 43篇 |
2019年 | 41篇 |
2018年 | 54篇 |
2017年 | 41篇 |
2016年 | 86篇 |
2015年 | 64篇 |
2014年 | 74篇 |
2013年 | 168篇 |
2012年 | 165篇 |
2011年 | 204篇 |
2010年 | 102篇 |
2009年 | 116篇 |
2008年 | 148篇 |
2007年 | 155篇 |
2006年 | 125篇 |
2005年 | 97篇 |
2004年 | 102篇 |
2003年 | 83篇 |
2002年 | 84篇 |
2001年 | 52篇 |
2000年 | 52篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 20篇 |
1991年 | 13篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 11篇 |
排序方式: 共有2675条查询结果,搜索用时 15 毫秒
131.
132.
Anna A. Kończyk Joanna Szawkało Jan K. Maurin Zbigniew Czarnocki 《Helvetica chimica acta》2013,96(7):1348-1354
The highly functionalized tetrahydropyridine 4 was obtained in an indium(III) chloride catalyzed multi‐component reaction from benzaldehyde, 4‐methoxyaniline, and ethyl acetoacetate (=ethyl 3‐oxobutanoate) in the presence of [1,1′‐binaphthalene]‐2,2′‐diol (binol). It was found that binol played a beneficial role in this reaction, allowing a substantial decrease of the amount of indium salt. Also, simple organic Brønsted acids may serve as effective organocatalysts in this process. 相似文献
133.
The aim of the presented work is the comparison of aqueous and 1-octanol solubilities of different acyclovir derivatives and their hydroxypropyl-β-cyclodextrin inclusion complexes. The solubility measurements were carried out at different temperatures over the range 25–45 °C using water, 1-octanol, water saturated with 1-octanol, 1-octanol saturated with water, buffered aqueous solutions (pH = 5.5 and 7.0) and buffered aqueous solutions containing cyclodextrin as solvents. The aqueous solubilities of the compounds are very low but may be enhanced by complexation with hydroxypropyl-β-cyclodextrin, especially if the acyclovir derivatives have aromatic groups which may be included in the cyclodextrin cavity. The values of 1-octanol–water partition coefficients of acyclovir derivatives, obtained using extraction experiments, showed a similar sequence as the solubility results in 1-octanol. Additionally, some molecular mechanics and molecular dynamic calculations were performed to determine optimized structures of acyclovir derivative complexes with β-cyclodextrin treated as a model. 相似文献
134.
Ewa Gniazdowska Przemysław Koźmiński Leon Fuks 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):1171-1177
Two types of technetium-99m complexes: (i) with the Hynic ligand linked to Substance P(1–11) and (ii) of the type ‘4 + 1’ consisting of tetradentate tripodal chelator tris(2-mercaptoethyl)-amine and monodentate isocyanide ligand previously coupled with Substance P(1–11), have been prepared on the n.c.a. scale. The obtained conjugates exhibit different lipophilicity and high stability in neutral aqueous solutions, even in the presence of excess concentration of histidine/cysteine competitive standard ligands. The conjugate (99mTc(NS3)(CN))2–SP containing two technetium-99m species in the molecule may be expected to be an extremely good diagnostic radiopharmaceutical. 相似文献
135.
Kateřina Černovská Bedřich Košata Vladimíra Novotná Milada Glogarová 《Liquid crystals》2013,40(9):987-996
Several series of new benzofused thieno[3,2‐b]furan‐ and thieno[3,2‐b]thiophene‐based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications. 相似文献
136.
137.
Linlin Li Dr. Shengjie Peng Yanling Cheah Peifen Teh Jin Wang Grace Wee Yahwen Ko Dr. Chuiling Wong Prof. Madhavi Srinivasan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):5892-5898
Novel, porous NiCo2O4 nanotubes (NCO‐NTs) are prepared by a single‐spinneret electrospinning technique followed by calcination in air. The obtained NCO‐NTs display a one‐dimensional architecture with a porous structure and hollow interiors. The effect of precursor concentration on the morphologies of the products is investigated. Due to their unique structure, the prepared NCO‐NT electrode exhibits a high specific capacitance (1647 F g?1 at 1 A g?1), excellent rate capability (77.3 % capacity retention at 25 A g?1), and outstanding cycling stability (6.4 % loss after 3000 cycles), which indicates it has great potential for high‐performance electrochemical capacitors. The desirable enhanced capacitive performance of NCO‐NTs can be attributed to the relatively large specific surface area of these porous and hollow one‐dimensional nanostructures. 相似文献
138.
Prof. Dr. Andrei V. Malkov Dr. Sigitas Stončius Dr. Mark Bell Dr. Fabiomassimo Castelluzzo Dr. Pedro Ramírez‐López Dr. Lada Biedermannová Prof. Dr. Vratislav Langer Dr. Lubomír Rulíšek Prof. Dr. Pavel Kočovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(28):9167-9185
Detailed kinetic and computational investigation of the enantio‐ and diastereoselective allylation of aldehydes 1 with allyltrichlorosilanes 5 , employing the pyridine N‐oxides METHOX ( 9 ) and QUINOX ( 10 ) as chiral organocatalysts, indicate that the reaction can proceed through a dissociative (cationic) or associative (neutral) mechanism: METHOX apparently favors a pentacoordinate cationic transition state, while the less sterically demanding QUINOX is likely to operate via a hexacoordinate neutral complex. In both pathways, only one molecule of the catalyst is involved in the rate‐ and selectivity‐determining step, which is supported by both experimental and computational data. 相似文献
139.
Liang‐Yun Wang Jia‐Ling Ko Prof. Chien‐Chen Lai Yi‐Hung Liu Prof. Shie‐Ming Peng Prof. Sheng‐Hsien Chiu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8850-8860
Herein, we report a “threading followed by shrinking” approach for the synthesis of rotaxanes by using an “oxygen‐deficient” macrocycle that contained two arylmethyl sulfone units and the dumbbell‐shaped salt bis(3,5‐dimethylbenzyl)ammonium tetrakis(3,5‐trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO2 from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD3SOCD3 at 393 K for at least 5 h. 相似文献
140.
Preparation of Yolk‐Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties 下载免费PDF全文
In this study, we report the first preparation of phase‐pure Co9S8 yolk–shell microspheres in a facile two‐step process and their improved electrochemical properties. Yolk–shell Co3O4 precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co9S8 yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co9S8 microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co9S8 microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m2 g?1 with a mean pore size of 16 nm. The yolk–shell Co9S8 microspheres have initial discharge and charge capacities of 1008 and 767 mA h g?1 at a current density of 1000 mA g?1, respectively, while the filled Co9S8 microspheres have initial discharge and charge capacities of 838 and 638 mA h g?1, respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g?1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %. 相似文献