全文获取类型
收费全文 | 4072篇 |
免费 | 124篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 197篇 |
综合类 | 7篇 |
化学工业 | 1030篇 |
金属工艺 | 102篇 |
机械仪表 | 97篇 |
建筑科学 | 87篇 |
能源动力 | 151篇 |
轻工业 | 462篇 |
水利工程 | 17篇 |
石油天然气 | 2篇 |
无线电 | 304篇 |
一般工业技术 | 750篇 |
冶金工业 | 516篇 |
原子能技术 | 150篇 |
自动化技术 | 335篇 |
出版年
2023年 | 28篇 |
2022年 | 65篇 |
2021年 | 95篇 |
2020年 | 35篇 |
2019年 | 50篇 |
2018年 | 91篇 |
2017年 | 70篇 |
2016年 | 125篇 |
2015年 | 64篇 |
2014年 | 114篇 |
2013年 | 225篇 |
2012年 | 179篇 |
2011年 | 250篇 |
2010年 | 180篇 |
2009年 | 205篇 |
2008年 | 230篇 |
2007年 | 183篇 |
2006年 | 129篇 |
2005年 | 133篇 |
2004年 | 125篇 |
2003年 | 113篇 |
2002年 | 116篇 |
2001年 | 84篇 |
2000年 | 72篇 |
1999年 | 77篇 |
1998年 | 189篇 |
1997年 | 153篇 |
1996年 | 114篇 |
1995年 | 67篇 |
1994年 | 74篇 |
1993年 | 67篇 |
1992年 | 39篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 44篇 |
1988年 | 19篇 |
1987年 | 35篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 30篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 30篇 |
1976年 | 28篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有4207条查询结果,搜索用时 15 毫秒
11.
Sakai T. Kobayashi K. Kubota S. Morikura M. Kato S. 《Selected Areas in Communications, IEEE Journal on》1995,13(2):285-290
Diversity combining methods for mobile satellite communication systems employing convolutional encoding and soft-decision Viterbi decoding are evaluated. Computer simulation clarifies that the pre-Viterbi-decoding maximal ratio combining method has better performance than other methods in Rician fading channels. The simulation results agree with the Pe (bit error probability) performance derived from the numerical analysis for slow fading using the approximate Pe performance of Viterbi decoding in AWGN (additive white Gaussian noise) channels and the probability density function of Rician fading. Applying this diversity method to the multi-beam mobile satellite communication systems, a satellite beam diversity reception scheme is proposed. A computer simulation result shows that the proposed scheme decreases the packet error rate of the control signals to less than 1/100 around the satellite beam boundary 相似文献
12.
13.
An inversion relationship is clarified between lightness and brightness, and also between chroma and colorfulness under nonuniform illumination with different illuminance levels (high and low) within the same visual field. Brightness (or colorfulness) of object color with low lightness (or chroma) under high illuminance level is perceived higher than that of another object color with high lightness (or chroma) under low illuminance level. Two color images are given for showing the inversion phenomena on brightness–lightness and colorfulness–chroma between object colors under different illuminance levels. These color images are useful for making researchers on color understand the differences in concept between brightness and lightness, and also between colorfulness and chroma. In particular, the concept of colorfulness is important, but difficult to understand. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 372–377, 2007 相似文献
14.
A novel elastic polymer containing 4,4′-bipyridinium salts with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as part of the main chain was synthesized. The cast film showed persistent and reversible colour changes due to photoinduced electron transfer upon excitation of an ion-pair charge-transfer band (ex >365 nm) in vacuo. The lifetime of the coloured state markedly depended on temperature. The optically written data were stored without decay below 0°C and were erased thermally at elevated temperatures. The colour changes were reversibly repeatable for many times. 相似文献
15.
An analytical expression for conjugate signals is developed for a case where three rectangular pulses with the same center frequency are injected into a two-level system. The Maxwell's equation is solved with the slowly varying envelope approximation and with the perturbative third-order nonlinear polarization expression of a two-level system. Numerical examples are discussed in such a way that the input pulsewidth is changed relative to the energy relaxation and dephasing times. As the optical pulsewidth becomes short, ripples appear in the signal pulse due to the beat between the optical field and the resonant oscillation of the atomic system 相似文献
16.
The integral experiment on beryllium with D-T neutrons for verification of tritium breeding 总被引:1,自引:0,他引:1
Yury Verzilov Satoshi Sato Kentaro Ochiai Masayuki Wada Axel Klix Takeo Nishitani 《Fusion Engineering and Design》2007,82(1):1-9
A clean benchmark experiment on beryllium was performed with D-T neutrons at the FNS facility of the Japan Atomic Energy Agency. The main objective was to verify the integral data related to the tritium production on lithium isotopes. Tritium production rates, as well as activation reaction rates were measured inside the beryllium assembly that was shaped as a pseudo-cylindrical slab with an area-equivalent diameter of 628 mm and a thickness of 355 mm. Experimental results were analyzed with a three-dimensional Monte Carlo transport code MCNP-4C and FENDL/MC-2.0, JENDL-3.2/3.3 neutron transport libraries. Evaluation of reaction rates was based on the cross section data taken from the JENDL Dosimetry File and ENDF B-VI data libraries. Analysis shows that all calculation combinations (transport and activation cross section libraries) used for evaluation of reaction rates give data that is agreeable with measured values within 10%. 相似文献
17.
We clarified the roles of IL-1 beta in peripheral neural regeneration after axotomy in a three-dimensional collagen gel culture system ranging from a single neurone to a dorsal root ganglion (DRG) explant with its associated nerve bundles. Application of 30 U/ml IL-1 beta to the culture systems clearly enhanced neural regeneration. This regeneration was evident in transected nerve terminals of DRG explants with or without associated nerve bundles, but not in dissociated single neurones. Neural survival was not affected by IL-1 beta in any of these culture systems. These results suggest that IL-1 beta stimulates surrounding non-neuronal cells to secrete neurotrophic factors, thus enhancing neurite regeneration from transected nerve terminals in cultured adult DRG explants. 相似文献
18.
BACKGROUND: Foot complications in diabetes incur huge human and medical costs. There is a high incidence of complicated diabetes mellitus in Far North Queensland, particularly in the indigenous communities. METHODS: An audit of 51 patients admitted to Cairns Base Hospital from July 1992 to December 1994 with diabetic foot complications requiring surgical intervention was performed. RESULTS: The majority of surgical procedures were for serious infections in neuropathic feet precipitated by minor trauma. Surgical procedures included debridement/drainage, minor amputation, major amputation and arterial bypass. Half of the patients required more than one procedure and/or multiple admissions. Average length of stay was 48 days. Indigenous patients were overrepresented in this audited group. CONCLUSIONS: Prevention or minimization of diabetic foot complications can be achieved only through improvement in education and vigilance at all levels of the treatment process from community to hospital. Special attention to the needs of indigenous communities with a high incidence of diabetes must be a feature of any future initiatives. 相似文献
19.
T Sakai A Konishi T Nishiyama T Higashizawa H Bito 《Canadian Metallurgical Quarterly》1998,47(8):998-1001
Effectiveness in visualization of the vocal cord during orotracheal intubation with McCoy (McC) compared with Macintosh (Min) and Miller (Mil) blades were investigated. After an institutional review board approval, 117 patients for elective surgery under general anesthesia requiring tracheal intubation were investigated. Five board certified anesthesiologists tried to visualize the vocal cord of a patient three times with the three different types of laryngoscope. Total of 351 intubation attempts were studied. The view obtained at laryngoscopy with each of the three blades was recorded as follows. Grade 1. If most of the glottis is visible. Grade 2. If only the posterior extremity of the glottis is visible. Grade 3. If no part of the glottis can be seen. Grade 4. If not even the epiglottis can be exposed. Eight-two Grade 1 views were obtained with McC, 72 with Mil and 47 with Min, respectively. Thirty-three Grade 2 views were obtained with McC, 36 with Min and 24 with Mil. Two Grade 3 views with McC, 34 with Min and 14 with Mil were obtained. Seven Grade 4 views were obtained with Mil. The grades of laryngeal visualization with McC were significantly lower than those with Min and Mil. 相似文献
20.
Takeshi Kikuchi Yoshizo Kitami Masato Yokoyama Hiroshi Sakai 《Journal of Materials Science》1989,24(12):4275-4278
The phase equilibria in the pseudo-binary system Bi2O3-TeO2 at 600° 950° C in air were examined by solid-state reaction techniques and X-ray powder diffraction method. Four pseudo-binary compounds appeared, i.e., -Bi2O3 type solid solution having a compositional range of (1-x)Bi2O3·xTeO2 wherex=0 0.4 a new compound Bi6Te2O15 which has an orthorhombic cell of a=2.27(4) nm, b=1.06(1) nm and c = 0.539(8) nm, 2Bi2O3 · 3TeO2, and an unidentified phase Bi2O3·2TeO2. The formation of the phase Bi6Te2O15, in which all the Te ions are hexavalent, was confirmed by the thermogravimetry and by the Mössbauer spectra. The liquidus curves for whole system were determined by DTA method. 相似文献