全文获取类型
收费全文 | 7717篇 |
免费 | 239篇 |
国内免费 | 45篇 |
专业分类
电工技术 | 133篇 |
综合类 | 24篇 |
化学工业 | 839篇 |
金属工艺 | 110篇 |
机械仪表 | 198篇 |
建筑科学 | 347篇 |
矿业工程 | 3篇 |
能源动力 | 148篇 |
轻工业 | 302篇 |
水利工程 | 23篇 |
石油天然气 | 25篇 |
武器工业 | 3篇 |
无线电 | 1473篇 |
一般工业技术 | 1028篇 |
冶金工业 | 2281篇 |
原子能技术 | 33篇 |
自动化技术 | 1031篇 |
出版年
2023年 | 40篇 |
2022年 | 76篇 |
2021年 | 92篇 |
2020年 | 58篇 |
2019年 | 72篇 |
2018年 | 106篇 |
2017年 | 81篇 |
2016年 | 135篇 |
2015年 | 113篇 |
2014年 | 134篇 |
2013年 | 319篇 |
2012年 | 306篇 |
2011年 | 323篇 |
2010年 | 238篇 |
2009年 | 298篇 |
2008年 | 328篇 |
2007年 | 317篇 |
2006年 | 307篇 |
2005年 | 255篇 |
2004年 | 207篇 |
2003年 | 215篇 |
2002年 | 158篇 |
2001年 | 172篇 |
2000年 | 167篇 |
1999年 | 227篇 |
1998年 | 840篇 |
1997年 | 482篇 |
1996年 | 354篇 |
1995年 | 239篇 |
1994年 | 168篇 |
1993年 | 194篇 |
1992年 | 88篇 |
1991年 | 74篇 |
1990年 | 66篇 |
1989年 | 65篇 |
1988年 | 72篇 |
1987年 | 57篇 |
1986年 | 48篇 |
1985年 | 76篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 42篇 |
1981年 | 40篇 |
1980年 | 36篇 |
1979年 | 24篇 |
1978年 | 19篇 |
1977年 | 38篇 |
1976年 | 101篇 |
1975年 | 18篇 |
1973年 | 19篇 |
排序方式: 共有8001条查询结果,搜索用时 15 毫秒
51.
Anabaena sp. strain PCC 7120 adapts to deprivation of fixed nitrogen by undergoing physiological and genetic changes that include formation of N2-fixing heterocysts. Whether or not certain of the genes involved are interdependently expressed has been studied. 相似文献
52.
A microprocessor clock generator based on an analog phase-locked loop (PLL) is described for deskewing the internal logic control lock to an external system lock. This PLL is fully generated onto a 1.2-million-transistor microprocessor in 0.8-μm CMOS technology without the need for external components. It operates with a lock range from 5 to 110 MHz. The clock skew is less than 0.1 ns, with a peak-to-peak jitter of less than 0.3 ns for a 50-MHz system clock frequency 相似文献
53.
54.
Degradation Behaviors of Metal-Induced Laterally Crystallized n-Type Polycrystalline Silicon Thin-Film Transistors Under DC Bias Stresses 总被引:1,自引:0,他引:1
Min Xue Mingxiang Wang Zhen Zhu Dongli Zhang Man Wong 《Electron Devices, IEEE Transactions on》2007,54(2):225-232
Device degradation behaviors of typical-sized n-type metal-induced laterally crystallized polycrystalline silicon thin-film transistors were investigated in detail under two kinds of dc bias stresses: hot-carrier (HC) stress and self-heating (SH) stress. Under HC stress, device degradation is the consequence of HC induced defect generation locally at the drain side. Under a unified model that postulates, the establishment of a potential barrier at the drain side due to carrier transport near trap states, device degradation behavior such as asymmetric on current recovery and threshold voltage degradation can be understood. Under SH stress, a general degradation in subthreshold characteristic was observed. Device degradation is the consequence of deep state generation along the entire channel. Device degradation behaviors were compared in low Vd-stress and in high Vd-stress condition. Defect generation distribution along the channel appears to be different in two cases. In both cases of SH degradation, asymmetric on current recovery was observed. This observation, when in low Vd-stress condition, is tentatively explained by dehydrogenation (hydrogenation) effect at the drain (source) side during stress 相似文献
55.
Dasgupta U. Wooi Gan Yeoh Chun Geik Tan Sheng Jau Wong Mori H. Singh R. Itoh M. 《Microwave Theory and Techniques》2002,50(11):2443-2452
An implementation of the IF section of WCDMA mobile transceivers with a set of two chips fabricated in an inexpensive 0.35-/spl mu/m two-poly three-metal CMOS process is presented. The transmit/receive chip set integrates quadrature modulators and demodulators, wide dynamic range automatic gain control (AGC) amplifiers, with linear-in-decibel gain control, and associated circuitry. This paper describes the problems encountered and the solutions envisaged to meet stringent specifications, with process and temperature variations, thus overcoming the limitations of CMOS devices, while operating at frequencies in the range of 100 MHz-1 GHz. Detailed measurement results corroborating successful application of the new techniques are reported. A receive AGC dynamic range of 73 dB with linearity error of less than /spl plusmn/2 dB and spread of less than 5 dB for a temperature range of -30/spl deg/C to +85/spl deg/C in the gain control characteristic has been measured. The modulator measurement shows a carrier suppression of 35 dB and sideband/third harmonic suppression of over 46 dB. The core die area of each chip is 1.5 mm/sup 2/. 相似文献
56.
57.
Kin-Lu Wong Tzung-Wern Chiou 《Antennas and Propagation, IEEE Transactions on》2002,50(3):346-351
Designs of broadband dual-polarized patch antennas fed by promising feed structures of a capacitively coupled feed and a slot-coupled feed (antenna A), two capacitively coupled feeds of a 180° phase shift and a slot-coupled feed (antenna B), and two capacitively coupled feeds of a 180° phase shift and two slot-coupled feeds (antenna C) are proposed and experimentally studied. The first two feed designs are for the excitation of a single-element broadband patch antenna, while the last design is for a two-element broadband patch antenna. These proposed patch antennas have a thick air substrate, and the 10 dB return-loss impedance bandwidths obtained for the two polarizations are all greater than 13%. High isolation (<-30 dB for antenna A, <-32 dB for antenna B, <-35 dB for antenna C) between the two feeding ports for the entire impedance bandwidth of the proposed antennas can be obtained. Also, improved cross-polarization levels (>20 dB) in both E and H plane patterns for the two polarizations of antennas B and C are achieved 相似文献
58.
59.
60.
Neonatally induced microgyric lesions produce defects in rapid auditory processing in adult male rats. Given that females across species are less susceptible to the deleterious effects of neural injury and that treatment with neuroprotective agents at the time of injury can reduce neural damage, the authors tested the effects of sex and neuroprotectant exposure on the behavioral consequences of microgyric lesions in rats. Results showed that sham but not microgyric males were able to perform the task at the fastest rate of stimulus presentation. Microgyric females, in contrast, discriminated at all stimulus conditions and did not differ from female shams. Microgyric males treated with MK-801 had reduced cortical damage and performed the discrimination at the fastest condition. Results suggest that females are less susceptible to the behavioral effects of neocortical microgyria and that MK-801 may ameliorate the behavioral consequences of these lesions in male rats. 相似文献