全文获取类型
收费全文 | 1674篇 |
免费 | 39篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 58篇 |
综合类 | 1篇 |
化学工业 | 335篇 |
金属工艺 | 32篇 |
机械仪表 | 26篇 |
建筑科学 | 78篇 |
矿业工程 | 2篇 |
能源动力 | 58篇 |
轻工业 | 117篇 |
水利工程 | 11篇 |
石油天然气 | 5篇 |
无线电 | 125篇 |
一般工业技术 | 216篇 |
冶金工业 | 414篇 |
原子能技术 | 20篇 |
自动化技术 | 221篇 |
出版年
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 109篇 |
2012年 | 46篇 |
2011年 | 84篇 |
2010年 | 53篇 |
2009年 | 57篇 |
2008年 | 63篇 |
2007年 | 76篇 |
2006年 | 64篇 |
2005年 | 43篇 |
2004年 | 49篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 21篇 |
2000年 | 24篇 |
1999年 | 31篇 |
1998年 | 84篇 |
1997年 | 46篇 |
1996年 | 44篇 |
1995年 | 37篇 |
1994年 | 20篇 |
1993年 | 33篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 29篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 22篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1973年 | 15篇 |
排序方式: 共有1719条查询结果,搜索用时 0 毫秒
21.
One-order-statistic estimators are derived for the shape parameter K of the limited distribution function F1(x, ?, K) = 1 - (? - x)K and the Pareto distribution function F2(y, ?, K) = 1 - (y - ?)-K, given the location parameters ? and ?, respectively. Similar estimators are derived for the scale parameters v1 and Vn, of the Type II asymptotic distributions of smallest and largest values, F3(w, v1, K) = 1 - exp[-(w/v1)-K] and F4(z, vn K) = exp [-(z/vn)-K], given the shape parameter K and assuming the location parameter is zero. The one-order-statistic estimators are K?|? = -1/Cmn 1n(? - xmn) for the limited distribution, K?|? = 1/Cmn 1n(ymn - ?) for the Pareto distribution, ?1|K = Cmn-1/K Wmn and ?n|K = Cmn-1/K Zn-m+1,n for the Type II distributions of smallest and largest values, where Xmn, Ymn, Wmn, Zmn are the mth order statistics of samples of size n from the respective distributions and Cmn is the coefficient for a one-order-statistic estimator of the scale parameter of an exponential distribution, which has been tabled in an earlier paper. It is shown that exact confidence bounds can be easily derived for these parameters using exact confidence bounds for the scale parameter of the exponential distribution. Use of the estimators is illustrated by numerical examples. 相似文献
22.
A 3D hierarchical computational model of damage and strength of wood is developed. The model takes into account the four scale microstructures of wood, including the microfibril reinforced structure at nanoscale, multilayered cell walls at microscale, hexagon-shape-tube cellular structure at mesoscale and annual rings at the macroscale. With the use of the developed hierarchical model, the influence of the microstructure, including microfibril angle (MFA), the cell shape and the wood density (annual ring structure), differences between earlywood and latewood as well as microstructural arrangements and cellulose strength distributions on the tensile strength of wood is studied numerically. Good agreement of the theoretical results with experimental data has been obtained. 相似文献
23.
Leon A. S. Tam K. W. Shin J. L. Weisner D. Schumacher F. 《Solid-State Circuits, IEEE Journal of》2007,42(1):7-16
This first generation of "Niagara" SPARC processors implements a power-efficient Chip Multi-Threading (CMT) architecture which maximizes overall throughput performance for commercial workloads. The target performance is achieved by exploiting high bandwidth rather than high frequency, thereby reducing hardware complexity and power. The UltraSPARC T1 processor combines eight four-threaded 64-b cores, a floating-point unit, a high-bandwidth interconnect crossbar, a shared 3-MB L2 Cache, four DDR2 DRAM interfaces, and a system interface unit. Power and thermal monitoring techniques further enhance CMT performance benefits, increasing overall chip reliability. The 378-mm2 die is fabricated in Texas Instrument's 90-nm CMOS technology with nine layers of copper interconnect. The chip contains 279 million transistors and consumes a maximum of 63 W at 1.2 GHz and 1.2 V. Key functional units employ special circuit techniques to provide the high bandwidth required by a CMT architecture while optimizing power and silicon area. These include a highly integrated integer register file, a high-bandwidth interconnect crossbar, the shared L2 cache, and the IO subsystem. Key aspects of the physical design methodology are also discussed 相似文献
24.
Jan Mulkens Bob Streefkerk Hans Jasper Jos de Klerk Fred de Jong Leon Levasier Martijn Leenders 《电子工业专用设备》2008,37(3):13-19
论述了第五世代双扫描平台浸液式扫描曝光机的性能和进展。表明了在高速扫描状态下有生产价值的套刻和聚焦性能的实现。浸液式设备更多的关键部分与缺陷有关,而且该机的改进是通过有生产价值的缺陷水平方面来体现的。为了保持这种缺陷水平的改进效果,需要在圆片应用中进行专门稳定的测量。特加是边缘空泡除去(EBR)设计和圆片斜面良流线性是很重要的。 相似文献
25.
The method of moments in the spectral domain is applied to the rigorous full-wave analysis of coupled line microstrip filters fabricated on magnetized ferrites. The results show that the center frequency of the filters can be tuned over a wide range by adjusting the magnitude of the bias magnetic field of the ferrite substrates. However, the filters bandwidth is reduced as the tuning frequency increases. This bandwidth reduction is explained in terms of the behavior of the resonant frequencies and quality factors of the resonators included in the filters. 相似文献
26.
Chakrapani V. Varanasi Leon Chuck Lyle Brunke Jack Burke Andrew D. Chaney Paul N. Barnes 《Journal of Electronic Materials》2007,36(10):1265-1269
A simple testing method is used to compare the yield strengths (YS) of biaxially textured metallic substrates (Ni and its
alloys) presently under development for YBa2Cu3O7−x
coated conductors. This method is based on a retired ASTM D3379 tensile test standard method that was originally recommended
for single filament materials. Several common textured substrates, such as Ni, Ni-3at.%W, and Ni-5at.%W, procured from different
manufacturers, were tested using this method, and the data were compared with the values reported in the literature. A new
alloy substrate (constantan (Cu55-Ni44-Mn1wt.%)) that is biaxially textured in-house was also tested using this method, and
the YS data were compared with those of other substrates. For the substrates used in this study, the data obtained using this
method indicated that Ni substrates have YS of ∼52 MPa, Ni-3at.%W substrates have YS of ∼106 MPa, Ni-5at.%W substrates have
YS 163 MPa, and Cu55-Ni44-Mn1 wt.% substrates have YS of 74 MPa. 相似文献
27.
Changlong Xu Ying-Chang Liang Wing Seng Leon 《Wireless Communications, IEEE Transactions on》2008,7(1):43-47
In this letter, we propose a low complexity algorithm for extended turbo product codes by considering both the encoding and decoding aspects. For the encoding part, a new encoding scheme is presented for which the operations of looking up and fetching error patterns are no longer necessary, and thus the lookup table can be omitted. For the decoder, a new algorithm is proposed to extract the extrinsic information and reduce the redundancy. This new algorithm can reduce decoding complexity greatly and enhance the performance of the decoder. Simulation results are presented to show the effectiveness of the proposed scheme. 相似文献
28.
Alexander ARGYROS Mark STRATON Andrew DOCHERTY Eun Hee MIN Ziyi GE Kok Hou WONG Francois LADOUCEUR Leon POLADIAN 《中国光电子学前沿》2010,3(1)
Circular birefringence is a property of chiral materials. In this work, we consider the use of chiral materials in optical fibres to produce circularly birefringent optical fibres and in fibres where a contrast in circular birefringence contributes to forming the waveguide. (-)-menthyl methacrylate is also investigated as a possible material for the fabrication of such fibres. 相似文献
29.
Leon A. Luxemburg 《Circuits, Systems, and Signal Processing》1990,9(1):3-29
This paper introduces a theory of modulop Laplace andZ-transforms which can adequately analyze any time-varying periodically switching system in frequency domain, in particular, switched-capacitor SC networks with nonideal operational amplifiers. Formulae for inverse and direct modulop transforms are included. Since the regular Laplace andZ-transform fail to be adequate for a nonideal sampled system, this new tool can be effectively used instead. An extremely efficient and fast program is developed based on the general theory. This program has been used by the author for the analysis of SC networks with nonideal operational amplifiers and requires less time for calculations compared with conventional time-domain methods. Furthermore, closed-form solutions for the nonideal transfer functions are given. The presented algorithm permits us to calculate the transfer function in partial fraction form and thus stability can be verified immediately. 相似文献
30.
Gifford HC King MA Wells RG Hawkins WG Narayanan MV Pretorius PH 《IEEE transactions on medical imaging》2000,19(5):463-473
Localization ROC (LROC) observer studies examined whether detector response compensation (DRC) in ordered-subset, expectation-maximization (OSEM) reconstructions helps in the detection and localization of hot tumors. Simulated gallium (Ga-67) images of the thoracic region were used in the study. The projection data modeled the acquisition of attenuated 93- and 185-keV photons with a medium-energy parallel-hole collimator, but scatter was not modeled. Images were reconstructed with five strategies: 1) OSEM with no DRC; 2) OSEM preceded by restoration filtering; 3) OSEM with iterative DRC; 4) OSEM with an ideal DRC; and 5) filtered backprojection (FBP) with no DRC. All strategies included attenuation correction. There were four LROC studies conducted. In a study using a single tumor activity, the ideal DRC offered the best performance, followed by iterative DRC, restoration filtering, OSEM with no DRC, and FBP. Statistical significance at the 5% level was found between all pairs of strategies except for restoration filtering and OSEM with no DRC. A similar ranking was found for a more realistic study using multiple tumor activities. Additional studies considered the effects of OSEM iteration number and tumor activity on the detection improvement that iterative DRC offered with respect to OSEM with no DRC. 相似文献