全文获取类型
收费全文 | 149979篇 |
免费 | 1580篇 |
国内免费 | 378篇 |
专业分类
化学 | 80079篇 |
晶体学 | 1651篇 |
力学 | 6589篇 |
综合类 | 7篇 |
数学 | 15202篇 |
物理学 | 48409篇 |
出版年
2020年 | 1111篇 |
2019年 | 1171篇 |
2018年 | 1475篇 |
2017年 | 1451篇 |
2016年 | 2466篇 |
2015年 | 1545篇 |
2014年 | 2422篇 |
2013年 | 6312篇 |
2012年 | 4925篇 |
2011年 | 6257篇 |
2010年 | 4277篇 |
2009年 | 4289篇 |
2008年 | 5690篇 |
2007年 | 5763篇 |
2006年 | 5403篇 |
2005年 | 4993篇 |
2004年 | 4409篇 |
2003年 | 3852篇 |
2002年 | 3660篇 |
2001年 | 4162篇 |
2000年 | 3108篇 |
1999年 | 2345篇 |
1998年 | 2041篇 |
1997年 | 2032篇 |
1996年 | 1837篇 |
1995年 | 1844篇 |
1994年 | 1842篇 |
1993年 | 1672篇 |
1992年 | 1943篇 |
1991年 | 2078篇 |
1990年 | 1867篇 |
1989年 | 1876篇 |
1988年 | 1822篇 |
1987年 | 1719篇 |
1986年 | 1659篇 |
1985年 | 2156篇 |
1984年 | 2299篇 |
1983年 | 1866篇 |
1982年 | 2051篇 |
1981年 | 1937篇 |
1980年 | 1857篇 |
1979年 | 2009篇 |
1978年 | 2177篇 |
1977年 | 2050篇 |
1976年 | 2090篇 |
1975年 | 2004篇 |
1974年 | 2059篇 |
1973年 | 2044篇 |
1972年 | 1341篇 |
1971年 | 1197篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Substituted Tetraaza‐ and Hexaazahexacenes and their N,N′‐Dihydro Derivatives: Syntheses,Properties, and Structures 下载免费PDF全文
Jens U. Engelhart Dr. Benjamin D. Lindner Manuel Schaffroth David Schrempp Olena Tverskoy Prof. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8121-8129
The palladium‐catalyzed coupling of a substituted o‐diaminoanthracene and a substituted o‐diaminophenazine to substituted 2,3‐dichloroquinoxalines furnishes 10 differently substituted N,N′‐dihydrotetraaza‐ or ‐hexaazahexacenes with the quinoxaline group of the azaacenes carrying fluorine, chlorine, or nitro groups. The N,N′‐dihydrotetraazahexacenes with hydrogen, chlorine, and fluorine subtituents are oxidized to azaacenes, whereas only the parent N,N′‐dihydrohexaazahexacenes, with hydrogen substituents, are oxidized by MnO2. The resultant azaacenes are characterized by their optical and spectroscopic data. In addition, single‐crystal X‐ray structures have been obtained for the parent tetraazahexacenes and their difluoro‐substituted derivatives. The di‐ and tetrachloro derivatives of the N,N′‐dihydrohexaazahexacene have also been structurally characterized. 相似文献
93.
94.
95.
96.
Redox‐Active Tetraruthenium Macrocycles Built from 1,4‐Divinylphenylene‐Bridged Diruthenium Complexes 下载免费PDF全文
Stefan Scheerer Dr. Michael Linseis Dr. Evelyn Wuttke Sabrina Weickert Prof. Dr. Malte Drescher Dr. Oliver Tröppner Prof. Dr. Ivana Ivanović‐Burmazović Andreas Irmler Prof. Dr. Fabian Pauly Prof. Dr. Rainer F. Winter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9574-9590
Metallamacrocylic tetraruthenium complexes were generated by treatment of 1,4‐divinylphenylene‐bridged diruthenium complexes with functionalized 1,3‐benzene dicarboxylic acids and characterized by HR ESI‐MS and multinuclear NMR spectroscopy. Every divinylphenylene diruthenium subunit is oxidized in two consecutive one‐electron steps with half‐wave potential splittings in the range of 250 to 330 mV. Additional, smaller redox‐splittings between the +/2+ and 0/+ and the 3+/4+ and 2+/3+ redox processes, corresponding to the first and the second oxidations of every divinylphenylene diruthenium entity, are due to electrostatic effects. The lack of electronic coupling through bond or through space is explained by the nodal properties of the relevant molecular orbitals and the lateral side‐by‐side arrangement of the divinylphenylene linkers. The polyelectrochromic behavior of the divinylphenylene diruthenium precursors is retained and even amplified in these metallamacrocyclic structures. EPR studies down to T=4 K indicate that the dications 1‐H2+ and 1‐OBu2+ are paramagnetic. The dications and the tetracation of macrocycle 3‐H display intense (dications) or weak ( 3‐H4+ ) EPR signals. Quantum chemical calculations indicate that the four most stable conformers of the macrocycles are largely devoid of strain. Bond parameters, energies as well as charge and spin density distributions of model macrocycle 5‐HMe were calculated for the different charge and spin states. 相似文献
97.
Development and validation of a bioanalytical method by LC‐MS/MS for the quantification of the LAFIS 10 – an antimalarial candidate – and its pharmacokinetics first evaluation 下载免费PDF全文
J. V. Laureano F. Barreto S. Gnoatto L. Tasso T. Dalla Costa B. V. de Araujo 《Biomedical chromatography : BMC》2015,29(5):664-670
A rapid and highly sensitive method by LC‐MS/MS was developed and validated for the quantification of an antimalarial candidate (LAFIS10) in rat plasma using dexamethasone as internal standard (IS). The chromatographic separation was performed with a Poroshell 120 EC‐C18 column. The mobile phase consisted of water (A) and acetonitrile (B), both containing 10 m m of ammonium formate and 0.1% formic acid, delivered in the form of elution gradient. The LAFIS10 was monitored using an electrospray ionization interface operating in the positive mode in multiple reaction monitoring mode, monitoring the transitions 681.47 → 538.2 for LAFIS10 and 393.20 → 355.30 for the IS. The flow rate was 500 μL/min. The column temperature was kept at 40 °C and the injection volume was 2 μL. The lower limit of quantification was of 10 ng/mL and linearity between 10 and 1000 ng/mL was observed, with an R2 > 0.99. The accuracy of the method was >90%. The relative standard deviations intra‐ and interday were <8.80 and <6.37%, respectively. The method showed sensitivity, linearity, precision, accuracy and selectivity required to quantify LAFIS 10 in preclinical pharmacokinetic studies according to criteria established by the US Food and Drug Administration and European Medicines Agency. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
98.
99.
100.
From superhydrophobic‐ to superhydrophilic‐patterned poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) architectures as a novel platform for biotechnological applications 下载免费PDF全文
Vanessa F. Cardoso Ana R. Machado Vânia C. Pinto Paulo J. Sousa Gabriela Botelho Graça Minas Senentxu Lanceros‐Méndez 《Journal of Polymer Science.Polymer Physics》2016,54(18):1802-1810
The manufacture of three‐dimensional patterned electroactive poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) microstructures with tailored architecture, morphology, and wettability is presented. The patterned microstructures are fabricated using a simple, effective, low cost, and reproducible technique based on microfluidic technology. These novel structures can represent innovative platforms for advanced strategies in a wide range of biotechnological applications, including tissue engineering, drug delivery, microfluidic, and sensors and actuators devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1802–1810 相似文献