全文获取类型
收费全文 | 144234篇 |
免费 | 22913篇 |
国内免费 | 6355篇 |
专业分类
电工技术 | 8600篇 |
技术理论 | 8篇 |
综合类 | 8310篇 |
化学工业 | 32223篇 |
金属工艺 | 6688篇 |
机械仪表 | 8136篇 |
建筑科学 | 10091篇 |
矿业工程 | 3409篇 |
能源动力 | 3909篇 |
轻工业 | 14715篇 |
水利工程 | 2975篇 |
石油天然气 | 5778篇 |
武器工业 | 1167篇 |
无线电 | 19234篇 |
一般工业技术 | 22013篇 |
冶金工业 | 4761篇 |
原子能技术 | 1431篇 |
自动化技术 | 20054篇 |
出版年
2024年 | 506篇 |
2023年 | 1737篇 |
2022年 | 3433篇 |
2021年 | 4991篇 |
2020年 | 4958篇 |
2019年 | 5876篇 |
2018年 | 6172篇 |
2017年 | 6852篇 |
2016年 | 7004篇 |
2015年 | 8635篇 |
2014年 | 9756篇 |
2013年 | 11765篇 |
2012年 | 10598篇 |
2011年 | 10926篇 |
2010年 | 10271篇 |
2009年 | 9706篇 |
2008年 | 9309篇 |
2007年 | 8740篇 |
2006年 | 7819篇 |
2005年 | 6277篇 |
2004年 | 4800篇 |
2003年 | 4122篇 |
2002年 | 4074篇 |
2001年 | 3495篇 |
2000年 | 3042篇 |
1999年 | 2180篇 |
1998年 | 1237篇 |
1997年 | 1037篇 |
1996年 | 922篇 |
1995年 | 820篇 |
1994年 | 608篇 |
1993年 | 455篇 |
1992年 | 324篇 |
1991年 | 211篇 |
1990年 | 202篇 |
1989年 | 184篇 |
1988年 | 129篇 |
1987年 | 75篇 |
1986年 | 58篇 |
1985年 | 40篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1959年 | 10篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
对甲基丙烯酸三氟乙酰氧乙酯(TFAOEMA)的阴离子聚合及原予转移自由基聚合进行了研究。常用的阴离于引发剂如丁基锂、1,1-二苯基已基锂等很难引发TFAOEMA的阴离子聚合,而碱性较弱的引发剂如三乙基铝却容易引发,且产率较高。以氯化亚铜、五甲基二乙基三胺、溴代丙酸乙酯为引发体系的TFAOEMA的本体原子转移自由基聚合符合活性聚合特征。但在四氢呋喃为溶剂的原子转移自由基聚合中却存在活性中心失活现象。以末端含卤素的聚甲基丙烯酸甲酯为大分子引发剂,引发TFAOEMA的原子转移自由基聚合,得到了含氟双嵌段聚合物。 相似文献
142.
STUDY ON PHASE PERCEPTION IN SPEECH 总被引:4,自引:0,他引:4
Tong Ming Bian Zhengzhong Li Xiaohui Dai Qijun Chen Yanpu 《电子科学学刊(英文版)》2003,20(5):387-392
The perceptual effect of the phase information in speech has been studied by auditory subjective tests. On the condition that the phase spectrum in speech is changed while amplitude spectrum is unchanged, the tests show that: (1) If the envelop of the reconstructed speech signal is unchanged, there is indistinctive auditory perception between the original speech and the reconstructed speech; (2) The auditory perception effect of the reconstructed speech mainly lies on the amplitude of the derivative of the additive phase; (3) td is the maximum relative time shift between different frequency components of the reconstructed speech signal. The speech quality is excellent while td <10ms; good while 10ms< td <20ms; common while 20ms< td <35ms, and poor while td >35ms. 相似文献
143.
In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on. 相似文献
144.
New polyaniline (PANI) asymmetric membranes were fabricated using a phase‐inversion technique with hexane as the coagulation bath. These membranes exhibit a dense structure with macrovoids distributed asymmetrically throughout the cross‐section. A stress–strain study demonstrated that the Young's modulus (1.421 GPa) and strain at break (7.6 %) of the new PANI asymmetric membranes prepared from hexane are approximately 12 and 4 times higher, respectively, than the values reported previously for the PANI integrally skinned asymmetric membranes (ISAMs) (123 MPa Young's modulus and 1.8 % strain at break). Furthermore, monolithic electrochemical actuators based on a single PANI asymmetric membrane were constructed, and a bending movement of up to 20 Hz was experimentally recorded in a hydrochloric acid aqueous solution. A lifetime of over 329 500 cycles was determined for these actuators at a ± 2° angular displacement (5 Hz). The lifetime is limited by a bending fatigue that creates a transversal crack on the PANI membrane at the air–water interface. Control over the actuator movement is also manifested by the linear dependences of the bending angle on the charge and of the angular velocity on the current. These relationships are independent of both the kind of applied electric signal and the frequency used. 相似文献
145.
146.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
147.
148.
随着深亚微米集成电路技术的发展,集成电路的规模越来越大,工作频率越来越高,并正朝着系统集成的方向发展,因而在模拟速度,模拟精度和可模拟的电路规模等各个方面对电路仿真技术提出了新的要求。近年来,各种新的电路仿真方法和仿真系统用相继脱颖百出,并将取代那些传统的,已经无法适应深亚微米技术发展的电路仿真器。 相似文献
149.
钇铁石榴石薄膜材料的光吸收谱及Bi,Al掺入对谱的影响研究 总被引:2,自引:1,他引:1
采用单离子晶场跃迁模型,拟合出钇铁石榴石(YIG)薄膜材料的光吸收谱,与实验谱吻合得较好。从实验和理论上分析了(BIAI)YIG 薄膜材料的光吸收谱,结果表明,Al3+离子的作用如同稀释剂一样,减小了光吸收,Bi3+离子由于其强的自旋轨道耦合作用,增大了跃迁振子强度和跃迁线宽,从而增大了光吸收损耗,在此基础上所作的(BiAl)YIG的理论谱与实验谱符合得较好。 相似文献
150.