全文获取类型
收费全文 | 5295篇 |
免费 | 683篇 |
国内免费 | 538篇 |
专业分类
化学 | 3825篇 |
晶体学 | 49篇 |
力学 | 255篇 |
综合类 | 42篇 |
数学 | 771篇 |
物理学 | 1574篇 |
出版年
2024年 | 13篇 |
2023年 | 80篇 |
2022年 | 188篇 |
2021年 | 197篇 |
2020年 | 210篇 |
2019年 | 214篇 |
2018年 | 178篇 |
2017年 | 161篇 |
2016年 | 232篇 |
2015年 | 224篇 |
2014年 | 256篇 |
2013年 | 343篇 |
2012年 | 413篇 |
2011年 | 439篇 |
2010年 | 278篇 |
2009年 | 251篇 |
2008年 | 334篇 |
2007年 | 241篇 |
2006年 | 229篇 |
2005年 | 227篇 |
2004年 | 198篇 |
2003年 | 182篇 |
2002年 | 225篇 |
2001年 | 175篇 |
2000年 | 130篇 |
1999年 | 98篇 |
1998年 | 89篇 |
1997年 | 51篇 |
1996年 | 105篇 |
1995年 | 70篇 |
1994年 | 56篇 |
1993年 | 42篇 |
1992年 | 41篇 |
1991年 | 35篇 |
1990年 | 38篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 7篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 20篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 5篇 |
排序方式: 共有6516条查询结果,搜索用时 15 毫秒
181.
An approach was reported to synthesize silica hybridized ruthenium bipyridyl complex through amidation reaction by covalent attachment of bis(bipyridyl)-4,4'-dicarboxy-2,2'-bipyridyl-ruthenium to (3-aminopropyl)-triethoxysilane. The hybrid complex then was gelatinized through acid catalytic hydrolysis method and a sol-gel modified indium tin oxide electrode was prepared via spin coating technique. As prepared indium tin oxide electrode possesses good stability therein with excellent electrochemiluminescence behavior. 相似文献
182.
Summary An ,-appended eighteen carbon chains hypercin derivative (2) was synthesized starting from emodin. The overall yield of the seven step synthesis was 12%. The1H and13C NMR, absorption, and emission spectroscopic properties were measured;2 can be dissolved even in apolar solvents and polyethylene.
Synthese und Eigenschaften eines mit C18-Ketten ,-substituierten Hypericinderivats
Zusammenfassung Ein in den Positionen , mit zwei C18-Ketten substituiertes Derivat des Hypericins (2) wurde ausgehend von Emodin synthetisiert. Die Gesamtausbeute der siebenstufigen Synthese betrug 12%. Die1H- und13C-NMR, absorptions- und emissionsspektroskopischen Eigenschaften wurden gemessen;2 kann sogar in apolaren Lösungsmitteln und Polyethylen gelöst werden.相似文献
183.
I. M. Skvortsov I. V. Antipova Yu. A. Pentin Tran Suan Khoan' S. V. Vasil'kovskii 《Chemistry of Heterocyclic Compounds》1975,11(8):949-955
1-(2-Furyl)-3-amino-4,4-dimethylpentane was used to obtain 3-tert-butyl-1,2-dihydropyrrolizine, the catalytic hydrogenation of which over Rh/Al2O3 at room temperature gives a mixture of cis- and trans-3,8-H-3-ter-butylpyrrolizidines with predominance of the cis isomer, whereas hydrogenation at 90–100 °C gives a mixture containing the trans isomer as the principal component. The three-dimensional structures of the isomers follow from data on the catalytic hydrogenation and isomerization and the IR, Raman, and PME spectra. A considerable percentage of the trans-fused form is characteristic for cis-3,8-H-3-tert-butylpyrrolizidine. 相似文献
184.
The self-diffusion coefficient, D, of dibutyltin dilaurate and dibutyltin bismonobutylmaleate have been obtained at 35, 45 and 55° in samples of poly(vinyl chloride) plasticized with 34, 60 and 100 phr of di(2-ethylhexyl)phthalate. D at 2 phr of the laurate is 3–5 times larger than for the smaller maleate molecule. In all cases, D increases with increasing plasticizer concentration, an effect interpreted in terms of the free volume theory of diffusion. D for the laurate increases by a factor of about 2.7 when the laurate diffusant concentration is increased from 0 to 4 phr. The activation energies for diffusion, ED, lie between 50 and 90 kJ mol?1. They increase with increasing plasticizer concentration but become constant at higher plasticizer concentrations (60–100 phr). It is impossible to correlate all the known data on diffusion in plasticized PVC with an equation of the form log D0 = C1 + C2 ED/RT 相似文献
185.
Applications of poly(dimethylsiloxane) (PDMS)-based microfluidic systems are more popular nowadays. Previous fabrication methods of the masters for PDMS microchannels require complicated steps and/or special device. In this paper, we demonstrated that the toner printed on the transparency film with the office laser printer (1200 dpi) can be used as the positive relief of the masters. The transparency film was printed in two steps in order to obtain the same printing quality for the crossed lines. With the laser-printed master, the depth of the fabricated PDMS microchannels was ca. 10 microm and the smallest width was ca. 60 microm. Surface characteristics of the PDMS/PDMS microchannels were performed with SEM. Their electrokinetic properties were investigated by the aids of the measurement of electroosmotic flow (EOF) and the Ohm's curve. Using the PDMS/PDMS microchip CE systems, electroactive biological molecules and non-electroactive inorganic ions were well separated, respectively. This simple approach could make it easy to carry out the studies of PDMS microfluidic systems in more general labs without special devices. 相似文献
186.
A set S of permutations of k objects is -uniform, t-homogeneous if for every pair A, B of t-subsets of the ground set, there are exactly permutations in S mapping A onto B. Arithmetical conditions and symmetries are discussed. We describe the character-theoretic method which is useful if S is contained in a permutation group. A main result is the construction of a 2-uniform, 2-homogeneous set of permutations on 6 objects and of a 3-uniform, 3-homogeneous set of permutations on 9 objects. These are contained in the simple permutation groups PSL
2(5) and PSL
2(8), respectively. The result is useful in the framework of theoretical secrecy and authentication (see Stinson 1990, Bierbrauer and Tran 1991). 相似文献
187.
188.
C. -G. Bao 《Few-Body Systems》1992,13(1):41-56
A comparison has been made between the states of a 3-valence-electron system and a 3-valence-neutron system. The fermions are supposed to move in a sphere. The structures and internal motions of the head-states (the lowest of a given2S+1
L
) of these systems havingL=0,S=1/2 and 3/2, and even and odd parity have been investigated. We have found that the symmetry governing the particular quantum system plays an essential role. In particular, all the nodal surfaces in the head-states originate from symmetry but not from dynamics. Consequently, the head-states of different dynamic systems have similar structures and similar internal motions. 相似文献
189.
The general-relativistic effects of an extreme Reissner-Nordström black hole on the flux of radiation emitted by a hot spot orbiting the hole with a thin accretion disk are investigated. The light curves, the redshift factor, and the solid angle against the spot orbit position are given. The results are then compared with those of a spot orbiting a Schwarzschild black hole. 相似文献
190.