全文获取类型
收费全文 | 136749篇 |
免费 | 19885篇 |
国内免费 | 13723篇 |
专业分类
化学 | 71391篇 |
晶体学 | 1219篇 |
力学 | 6920篇 |
综合类 | 533篇 |
数学 | 11910篇 |
物理学 | 41754篇 |
无线电 | 36630篇 |
出版年
2024年 | 549篇 |
2023年 | 3277篇 |
2022年 | 4046篇 |
2021年 | 5418篇 |
2020年 | 5209篇 |
2019年 | 4886篇 |
2018年 | 4128篇 |
2017年 | 4072篇 |
2016年 | 5985篇 |
2015年 | 6140篇 |
2014年 | 7494篇 |
2013年 | 9606篇 |
2012年 | 11419篇 |
2011年 | 11648篇 |
2010年 | 8165篇 |
2009年 | 8108篇 |
2008年 | 8566篇 |
2007年 | 7760篇 |
2006年 | 7270篇 |
2005年 | 6326篇 |
2004年 | 4380篇 |
2003年 | 3672篇 |
2002年 | 3290篇 |
2001年 | 2744篇 |
2000年 | 2595篇 |
1999年 | 3017篇 |
1998年 | 2659篇 |
1997年 | 2317篇 |
1996年 | 2565篇 |
1995年 | 2032篇 |
1994年 | 1930篇 |
1993年 | 1551篇 |
1992年 | 1449篇 |
1991年 | 1276篇 |
1990年 | 989篇 |
1989年 | 692篇 |
1988年 | 559篇 |
1987年 | 442篇 |
1986年 | 428篇 |
1985年 | 372篇 |
1984年 | 276篇 |
1983年 | 198篇 |
1982年 | 165篇 |
1981年 | 115篇 |
1980年 | 88篇 |
1979年 | 53篇 |
1978年 | 40篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
92.
The kinetic behaviour of aluminum naphthenate/benzene system in the process of gelation and degradation was systematically studied. The results obtained from the kinetic experiments indicated that the gelation stage was in accordance with a kinetic model of an auto-catalytic first-order reaction, and the degradation stage was a simple first-order reaction. The rate constants in these two stages at various temperaturs were measured. And the determined apparent activation energies for the gelation stage and for the degradation stage are 27.5±2.0 and 37.7±2.3 kJ/mol, respectively. 相似文献
93.
The evaluation of the transverse electric (TE) surface field on an impedance boundary circular cylinder, excited by a magnetic current on the same surface is discussed. The source is of infinite axial extent. The integral which describes the field due to a single surface ray is evaluated numerically and asymptotically. The results compare well with each other as well as with the eigenfunction solution. The surface ray field has a uniform representation in the sense that it remains valid in the immediate vicinity of the infinitesimal source as well as in the deep shadow region. A comparison is made with a flat impedance plane to indicate the influence of curvature on the surface field. 相似文献
94.
In this paper we formulate a theorem on the persistence of elliptic lower-dimensional invariant tori for nearly integrable analytic Hamiltonian systems under the first Melnikov condition and Rüssmann’s non-degeneracy condition, and give the measure estimates of parameters for the non-resonance conditions under Rüssmann’s non-degeneracy condition, which is essential for the proof of our result. 相似文献
95.
The stagnation slip flow on an axially moving cylinder is studied.The NavierStokes and energy equations reduce to nonlinearordinary differential equations under a similarity transform.For large slip, the flow field decays exponentially into potentialflow. The heat transfer can be expressed as an incomplete gammafunction. In general, the heat transfer increases with slip,Prandtl number and Reynolds number. 相似文献
96.
A route to the total synthesis of koumine has been suggested. Five 4-substituted 1, 2-d hydropyridine derivatives, which are supposed to be a conjugated diene of Diels-Alder reaction to produce the isoquinuclidine ring of koumine, have been synthesized. Only two of them were found to be able to undergo the Diels-Alder reaction. The stereochemistry of the reaction product has also been examined. 相似文献
97.
Wang K.C. Asbeck P.M. Chang M.F. Sullivan G.J. Miller D.L. Basit H.F. 《Electronics letters》1989,25(17):1111-1112
The authors report a novel noninterfering and simple approach for evaluation of circuits implemented with AlGaAs/GaAs heterojunction bipolar transistors (HBTs). This method makes use of radiative recombination in the base region of current-carrying HBTs. The infrared radiation emitted is 'visible' to the closed-circuit TV (CCTV) cameras. Therefore, one can view the operation of the HBT circuit under test at normal biases with a TV monitor. This method can be used to determine logic states of gates, as well as collector current of individual HBTs within integrated circuits.<> 相似文献
98.
99.
Anchoring Properties of Nematic Liquid Crystals Studied Using the Attenuated Total Reflection Method
By using the attenuated total reflection method associated with the excitation of surface plasmons, the tilt angle of the liquid crystal director and its gradient at the surface are measured in a planar nematic cell as a function of the applied voltage. The surface anchoring anisotropy δπ of the liquid crystal and the surface elastic constant ks, are found to be δπ = 0.288 erg/cm and ks, = 9·12 × 10-11 erg, respectively, when the boundary condition suggested by Barbero et al is used. The theoretical and experimental values obtained with this boundary condition and that of Mada are discussed. The results show that the boundary condition proposed by Barbero et al is in better agreement with the experiment. 相似文献
100.
多任务调度算法在单片机控制系统中的应用 总被引:1,自引:1,他引:0
为了满足单片机控制系统的复杂要求 ,提出了多任务调度算法 ,通过与单任务程序结构的对比和分析 ,详细说明了多任务调度算法的实现 ,指出了应用该算法的必要性 ,并且以科研生产的实例说明其具体应用。 相似文献