全文获取类型
收费全文 | 5222篇 |
免费 | 93篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 241篇 |
综合类 | 7篇 |
化学工业 | 1012篇 |
金属工艺 | 128篇 |
机械仪表 | 149篇 |
建筑科学 | 57篇 |
矿业工程 | 1篇 |
能源动力 | 174篇 |
轻工业 | 294篇 |
水利工程 | 25篇 |
石油天然气 | 4篇 |
无线电 | 587篇 |
一般工业技术 | 787篇 |
冶金工业 | 1327篇 |
原子能技术 | 188篇 |
自动化技术 | 351篇 |
出版年
2023年 | 19篇 |
2022年 | 54篇 |
2021年 | 76篇 |
2020年 | 38篇 |
2019年 | 46篇 |
2018年 | 61篇 |
2017年 | 61篇 |
2016年 | 72篇 |
2015年 | 59篇 |
2014年 | 101篇 |
2013年 | 247篇 |
2012年 | 159篇 |
2011年 | 206篇 |
2010年 | 146篇 |
2009年 | 178篇 |
2008年 | 221篇 |
2007年 | 156篇 |
2006年 | 168篇 |
2005年 | 156篇 |
2004年 | 122篇 |
2003年 | 134篇 |
2002年 | 123篇 |
2001年 | 106篇 |
2000年 | 109篇 |
1999年 | 144篇 |
1998年 | 537篇 |
1997年 | 319篇 |
1996年 | 224篇 |
1995年 | 150篇 |
1994年 | 131篇 |
1993年 | 133篇 |
1992年 | 53篇 |
1991年 | 56篇 |
1990年 | 47篇 |
1989年 | 46篇 |
1988年 | 50篇 |
1987年 | 43篇 |
1986年 | 59篇 |
1985年 | 42篇 |
1984年 | 57篇 |
1983年 | 48篇 |
1982年 | 55篇 |
1981年 | 45篇 |
1980年 | 48篇 |
1979年 | 19篇 |
1978年 | 42篇 |
1977年 | 35篇 |
1976年 | 62篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有5332条查询结果,搜索用时 15 毫秒
81.
Masaki Yamamoto 《Theory of Computing Systems》2006,39(5):723-742
A test instance generator (an instance generator for short) for MAX2SAT is a procedure that produces, given a number n of
variables, a 2-CNF formula F of n variables (randomly chosen from some reasonably large domain), and simultaneously provides
one of the optimal solutions for F. We propose an outline to design an instance generator using an expanding graph of a certain
type, called here an "exact 1/2-enlarger". We first show a simple algorithm for constructing an exact 1/2-enlarger, thereby
deriving one concrete polynomial-time instance generator GEN. We also show that an exact 1/2-enlarger can be obtained with
high probability
from graphs randomly constructed. From this fact, we propose another type of instance generator RGEN; it produces a 2-CNF
formula with a solution which is optimal for the formula with high probability. However, RGEN produces less structured formulas
and a much larger class of formulas than GEN. In fact, we prove the NP-hardness of MAX2SAT over the set of 2-CNF formulas
produced by RGEN. 相似文献
82.
Summary Dehalogenation polycondensations of 2,7-dibromo-9,10-dihydrophenanthrene with isolated zero-valent nickel complex and electrochemically generated zero-valent nickel complex afford -conjugated poly(9,10-dihydrophenanthrene-2,7-diyl). The electrochemically synthesized polymer is obtained as a thin film on electrode, and shows a reversible electrochemically doping-undoping cycle in an oxidation region. The polymer has essentially the same -conjugation system as that of poly(p-phenylene). 相似文献
83.
Suppression of sidelobe levels for guided-wave acousto-optic tunable filters using weighted coupling
Yamamoto Y Tsai CS Esteghamat K Nishimoto H 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1993,40(6):814-818
An analysis of guided-wave acousto-optic tunable filters (AOTFs) that employ simple acousto-optic (AO) weighted coupling techniques for sidelobe reduction and the calculated and experimental results from a specific example that involves only variation of the width of a surface acoustic wave (SAW) slot waveguide are presented. The calculations on single- and multi-stage AOTFs consisting of an optical channel waveguide and a SAW slot waveguide in LiNbO(3) substrate show that waveguide width weighting using generalized Hamming functions would provide significant improvement in sidelobe suppression. Calculated results together with the design, fabrication, and measured performance characteristics of a single-stage AOTF that utilizes a weighted-aperture SAW slot waveguide in YX-LiNbO(3) substrate at the optical wavelength of 1.55 mum and the acoustic center frequency of 175 MHz are reported. The measured sidelobe level is -13.6 dB and the measured FWHM bandwidth is 26 A, as compared to the theoretical values of -15.0 dB and 15 A, respectively. The RF drive power was measured to be 1.0 W at a mode-conversion efficiency of 100% 相似文献
84.
Haijme Yamamoto Shinji Okamoto Satoe Mitsumine 《Journal of the Society for Information Display》2000,8(3):241-245
Abstract— A red‐emitting phosphor, SrTiO3:Pr3+, for low‐voltage‐type FEDs and VFDs was developed by Futaba Corporation in 1996. The addition of Al or Ga is essential in the preparation of this phosphor because it improves the luminescence efficiency dramatically. For this impurity effect, Futaba Corporation proposed a charge‐compensation mechanism, which was supported by a recent observation of emission lines due to Al3+‐Pr3+ pairs. In addition, it was found that Al also works as a scavenger of planar defects, presumably SrO thin layers interleaved in the SrTiO3 lattice, by forming strontium aluminates. The latter mechanism suggests the possibility that a similar impurity effect can be found in materials with crystal structures, including alkaline‐earth oxide layers (Ruddlesden‐Popper phases). 相似文献
85.
86.
87.
Research on machine recognition of handprinted characters 总被引:5,自引:0,他引:5
Mori S Yamamoto K Yasuda M 《IEEE transactions on pattern analysis and machine intelligence》1984,(4):386-405
Machine recognition of handprinted Chinese characters has recently become very active in Japan. Both from the practical and the academic point of view, very encouraging results are reported. The work is described systematically and analyzed in terms of so-called feature matching, which is likely to be the mainstream of the research and development of machine recognition of handprinted Chinese characters. A database, ETL8 (881 Kanji, 71 hirakana, and 160 variations for each category), is explained, on which many experiments were performed. Recognition rates reported using this database can be compared, and so somewhat qualitative evaluation of these methods is described. Based on the comparative study, the merits and demerits of both feature and structural matching are discussed and some future directions are mentioned. 相似文献
88.
89.
S Asari T Satoh M Sakurai Y Yamamoto K Sadamoto 《Canadian Metallurgical Quarterly》1981,33(12):1201-1206
In this paper, the authors report biplane computed cerebral angiotomographic findings in 5 cases of Moyamoya disease. The specific features of Moyamoya disease on the CT image were as follows: On the axial plane, the linear structures of the anterior half of the circle of Willis and the proximal portion of the middle cerebral arteries disappeared, and instead of these normal structures, irregular, tortuous or patchy high-density areas just like a "caterpillar" were shown in the basal cistern and medial Sylvian fissures. On the modified coronal plane, the supraclinoid internal carotid arteries and the carotid fork could be identified only with a difficulty, and abnormal, "nebular" high-density areas consisting of irregular, tortuous or patchy high-density vascular components became visible in the basal cistern extending to the basal ganglia. A modified coronal plane and intravenous minimum dose bolus injection method seemed to be more useful for the visualization of these specific features on the CT image. Even before carotid angiography, we can suspect Moyamoya disease for finding these specific features on the CT image. Carotid angiography has been the only method of diagnosing Moyamoya disease. Instead of this invasive examination, computed cerebral angiotomography is useful in detecting Moyamoya disease conveniently and non-invasively. Therefore, we may conclude that computed cerebral angiotomography is very useful method for screening and follow up study of Moyamoya disease. 相似文献
90.
Yasuhiro Kodera Takeshi Yamamoto Naoki Toyofuku Manshi Ohyanagi Zuhair A. Munir 《Journal of Materials Science》2006,41(3):727-732
The ordering of stacking-disordered silicon carbide prepared from the elements by high energy ball milling was investigated
during sintering. A sharp increase in density in the temperature region 1700–1800°C was associated with a decrease in the
disorder. Samples which had low disorder density showed a more continuous sintering behavior with temperature. Highly dense
(up to 99% relative density) SiC can be obtained at 1900°C under a pressure of 70 MPa with no hold time. Similar results were
observed for structurally disordered carbon with 10 at% of boron. The sintering behavior exhibited an abrupt density increase
in the narrow temperature region of 1450–1600°C and was associated with disorder-order transformation. 相似文献