全文获取类型
收费全文 | 43910篇 |
免费 | 6758篇 |
国内免费 | 4711篇 |
专业分类
化学 | 23292篇 |
晶体学 | 408篇 |
力学 | 2033篇 |
综合类 | 264篇 |
数学 | 3599篇 |
物理学 | 11484篇 |
无线电 | 14299篇 |
出版年
2024年 | 199篇 |
2023年 | 1061篇 |
2022年 | 1371篇 |
2021年 | 1613篇 |
2020年 | 1601篇 |
2019年 | 1628篇 |
2018年 | 1318篇 |
2017年 | 1386篇 |
2016年 | 1762篇 |
2015年 | 2003篇 |
2014年 | 2465篇 |
2013年 | 3079篇 |
2012年 | 3716篇 |
2011年 | 3788篇 |
2010年 | 2696篇 |
2009年 | 2697篇 |
2008年 | 2883篇 |
2007年 | 2711篇 |
2006年 | 2459篇 |
2005年 | 2037篇 |
2004年 | 1547篇 |
2003年 | 1328篇 |
2002年 | 1302篇 |
2001年 | 1136篇 |
2000年 | 962篇 |
1999年 | 859篇 |
1998年 | 706篇 |
1997年 | 646篇 |
1996年 | 661篇 |
1995年 | 528篇 |
1994年 | 485篇 |
1993年 | 375篇 |
1992年 | 370篇 |
1991年 | 338篇 |
1990年 | 263篇 |
1989年 | 223篇 |
1988年 | 152篇 |
1987年 | 124篇 |
1986年 | 143篇 |
1985年 | 117篇 |
1984年 | 95篇 |
1983年 | 69篇 |
1982年 | 46篇 |
1981年 | 43篇 |
1980年 | 37篇 |
1979年 | 31篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1974年 | 29篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A new integrated magnetic full wave DC/DC power converter that provides flexible transformer design by incorporating an independent output inductor winding is introduced. The transformer is implemented on a traditional three-leg magnetic core. The inductor winding can be separately designed to control the output current ripple. The cross-sectional area of the inductor core leg can be reduced dramatically. The operation and performance of the proposed circuit are verified on a 100 W prototype converter. 相似文献
102.
103.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
104.
105.
Chongyu Mei Junqiao Ding Bing Yao Yanxiang Cheng Zhiyuan Xie Yanhou Geng Lixiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1746-1757
Two orange phosphorescent iridium complex monomers, 9‐hexyl‐9‐(iridium (III)bis(2‐(4′‐fluorophenyl)‐4‐phenylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐PIr) and 9‐hexyl‐9‐(iridium(III)bis(2‐(4′‐fluorophenyl)‐4‐methylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐MIr), were successfully synthesized. The Suzuki polycondensation of 2,7‐bis(trimethylene boronate)‐9,9‐dioctylfluorene with 2,7‐dibromo‐9,9‐dioctylfluorene and Br‐PIr or Br‐MIr afforded two series of copolymers, PIrPFs and MIrPFs, in good yields, in which the concentrations of the phosphorescent moieties were kept small (0.5–3 mol % feed ratio) to realize incomplete energy transfer. The photoluminescence (PL) of the copolymers showed blue‐ and orange‐emission peaks. A white‐light‐emitting diode with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/PIr05PF (0.5 mol % feed ratio of Br‐PIr)/Ca/Al exhibited a luminous efficiency of 4.49 cd/A and a power efficiency of 2.35 lm/W at 6.0 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.46, 0.33). The CIE coordinates were improved to (0.34, 0.33) when copolymer MIr10PF (1.0 mol % feed ratio of Br‐MIr) was employed as the white‐emissive layer. The strong orange emission in the electroluminescence spectra in comparison with PL for these kinds of polymers was attributed to the additional contribution of charge trapping in the phosphorescent dopants. © 2007 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 45: 1746–1757, 2007 相似文献
106.
107.
A configurable nonlinear filter generator is proposed. The nonlinear function employed is key controllable. By changing the key, a different sequence will be obtained. Simulated results show that an optimal linear complexity profile of the sequence can be generated 相似文献
108.
本文介绍了可在微机上实现大规模电信网践模拟的实用化软件SIMUNET,及基所采用的无时钟事件追踪法。该软件可用规划中的电信网络和实际网路的模拟及性能评价,也可用于不同流量控制算法的评价。文中给出一个评价实例。 相似文献
109.
An adaptive morphological filter for image processing 总被引:6,自引:0,他引:6
Novel types of opening operator (NOP) and closing operator (NCP) are proposed. An adaptive morphological filter is then constructed on the basis of the NOP and NCP. The filter can remove any details consisting of fewer pixels than a given number N, while preserving the other details. Efficient algorithms are also developed for the implementation of the NOP and NCP. 相似文献
110.
The general volume equivalence theorem for bianisotropic scatterers is presented, where the equivalent electric and magnetic currents are determined by a pair of coupled vector integral equations. Moreover, using the general volume equivalence theorem and conventional image principle, image theory is developed for a bianisotropic body over an infinite perfect electric or magnetic conducting ground plane. 相似文献