全文获取类型
收费全文 | 831349篇 |
免费 | 9495篇 |
国内免费 | 2090篇 |
专业分类
电工技术 | 15380篇 |
综合类 | 705篇 |
化学工业 | 127649篇 |
金属工艺 | 33275篇 |
机械仪表 | 26502篇 |
建筑科学 | 18553篇 |
矿业工程 | 5417篇 |
能源动力 | 22462篇 |
轻工业 | 64539篇 |
水利工程 | 9560篇 |
石油天然气 | 18187篇 |
武器工业 | 46篇 |
无线电 | 93111篇 |
一般工业技术 | 168008篇 |
冶金工业 | 149992篇 |
原子能技术 | 19131篇 |
自动化技术 | 70417篇 |
出版年
2021年 | 7672篇 |
2020年 | 5780篇 |
2019年 | 7372篇 |
2018年 | 12566篇 |
2017年 | 12684篇 |
2016年 | 13373篇 |
2015年 | 8573篇 |
2014年 | 14317篇 |
2013年 | 39190篇 |
2012年 | 22539篇 |
2011年 | 30722篇 |
2010年 | 24536篇 |
2009年 | 27554篇 |
2008年 | 28058篇 |
2007年 | 27668篇 |
2006年 | 24250篇 |
2005年 | 21920篇 |
2004年 | 20922篇 |
2003年 | 20689篇 |
2002年 | 19671篇 |
2001年 | 19282篇 |
2000年 | 18301篇 |
1999年 | 18576篇 |
1998年 | 45422篇 |
1997年 | 32210篇 |
1996年 | 25004篇 |
1995年 | 18902篇 |
1994年 | 16911篇 |
1993年 | 16709篇 |
1992年 | 12496篇 |
1991年 | 11896篇 |
1990年 | 11757篇 |
1989年 | 11344篇 |
1988年 | 10779篇 |
1987年 | 9732篇 |
1986年 | 9370篇 |
1985年 | 10697篇 |
1984年 | 9732篇 |
1983年 | 9100篇 |
1982年 | 8276篇 |
1981年 | 8446篇 |
1980年 | 7886篇 |
1979年 | 7955篇 |
1978年 | 7792篇 |
1977年 | 8792篇 |
1976年 | 11174篇 |
1975年 | 6899篇 |
1974年 | 6620篇 |
1973年 | 6725篇 |
1972年 | 5684篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods
and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working
defects on the behavior of structures under standard and emergency conditions.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006. 相似文献
142.
Mobile devices are vulnerable to theft and loss due to their small size and the characteristics of their common usage environment. Since they allow users to work while away from their desk, they are most useful in public locations and while traveling. Unfortunately, this is also where they are most at risk. Existing schemes for securing data either do not protect the device after it is stolen or require bothersome reauthentication. Transient Authentication lifts the burden of authentication from the user by use of a wearable token that constantly attests to the user's presence. When the user departs, the token and device lose contact and the device secures itself. We show how to leverage this authentication framework to secure all the memory and storage locations on a device into which secrets may creep. Our evaluation shows this is done without inconveniencing the user, while imposing a minimal performance overhead 相似文献
143.
144.
du Burck F. Lopez O. El Basri A. 《IEEE transactions on instrumentation and measurement》2003,52(2):288-291
We have developed a narrow-band controller in the MHz range, based on a field-programmable gate array. It is used to control the probe beam intensity in frequency-modulated spectroscopy experiments with an acoustooptic modulator. The residual amplitude modulation at the modulation frequency (2.5 MHz) is reduced by 50 dB. The first-harmonic detection of the signals is operated in saturation spectroscopy of I/sub 2/ at 514.5 nm and 501.7 nm. A reduction of the background noise and a large increase in the signal-to-noise ratio are obtained. 相似文献
145.
Phase equilibria involving spinel solid solutions, delafossite, and hematite in the Fe–Cu–O system are studied by emf measurements in solid-electrolyte galvanic cells. The results demonstrate that, above 1250 K, Fe3O4 and CuFe2O4 form a continuous series of solid solutions. At lower temperatures, the solid solution disproportionates with the formation of delafossite and Fe2O3, and two spinel solid solutions appear: one based on Fe3O4 and the other based on Cu2FeO4. The compositions of the spinel phases in equilibrium with delafossite and Fe2O3 are determined in the range 1100–1250 K. 相似文献
146.
Takauchi H. Tamura H. Matsubara S. Kibune M. Doi Y. Chiba T. Anbutsu H. Yamaguchi H. Mori T. Takatsu M. Gotoh K. Sakai T. Yamamura T. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2094-2100
We describe a CMOS multichannel transceiver that transmits and receives 10 Gb/s per channel over balanced copper media. The transceiver consists of two identical 10-Gb/s modules. Each module operates off a single 1.2-V supply and has a single 5-GHz phase-locked loop to supply a reference clock to two transmitter (Tx) channels and two receiver (Rx) channels. To track the input-signal phase, the Rx channel has a clock recovery unit (CRU), which uses a phase-interpolator-based timing generator and digital loop filter. The CRU can adjust the recovered clock phase with a resolution of 1.56 ps. Two sets of two-channel transceiver units were fabricated in 0.11-/spl mu/m CMOS on a single test chip. The transceiver unit size was 1.6 mm /spl times/ 2.6 mm. The Rx sensitivity was 120-mVp-p differential with a 70-ps phase margin for a common-mode voltage ranging from 0.6 to 1.0 V. The evaluated jitter tolerance curve met the OC-192 specification. 相似文献
147.
148.
149.
Lorenzetto G. Galtarossa A. Palmieri L. Santagiustina M. Someda C.G. Fiorone R. 《Lightwave Technology, Journal of》2003,21(2):424-431
First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled. 相似文献
150.
In order to ascertain the metastable phase relation in the Cr2O3-Fe2O3 system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr2O3-rich (CC) and Fe2O3-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders. 相似文献