全文获取类型
收费全文 | 136700篇 |
免费 | 3693篇 |
国内免费 | 601篇 |
专业分类
电工技术 | 1608篇 |
综合类 | 2398篇 |
化学工业 | 21306篇 |
金属工艺 | 6532篇 |
机械仪表 | 5675篇 |
建筑科学 | 3353篇 |
矿业工程 | 607篇 |
能源动力 | 3237篇 |
轻工业 | 7453篇 |
水利工程 | 1504篇 |
石油天然气 | 551篇 |
武器工业 | 1篇 |
无线电 | 18896篇 |
一般工业技术 | 27140篇 |
冶金工业 | 8274篇 |
原子能技术 | 880篇 |
自动化技术 | 31579篇 |
出版年
2023年 | 505篇 |
2022年 | 625篇 |
2021年 | 1398篇 |
2020年 | 992篇 |
2019年 | 1011篇 |
2018年 | 15406篇 |
2017年 | 14320篇 |
2016年 | 11305篇 |
2015年 | 1888篇 |
2014年 | 2244篇 |
2013年 | 3656篇 |
2012年 | 6173篇 |
2011年 | 12866篇 |
2010年 | 10848篇 |
2009年 | 8484篇 |
2008年 | 9396篇 |
2007年 | 9943篇 |
2006年 | 2346篇 |
2005年 | 3074篇 |
2004年 | 2927篇 |
2003年 | 2811篇 |
2002年 | 2156篇 |
2001年 | 1382篇 |
2000年 | 1375篇 |
1999年 | 1234篇 |
1998年 | 2242篇 |
1997年 | 1462篇 |
1996年 | 1245篇 |
1995年 | 969篇 |
1994年 | 735篇 |
1993年 | 691篇 |
1992年 | 501篇 |
1991年 | 516篇 |
1990年 | 417篇 |
1989年 | 404篇 |
1988年 | 330篇 |
1987年 | 275篇 |
1986年 | 254篇 |
1985年 | 231篇 |
1984年 | 199篇 |
1983年 | 151篇 |
1982年 | 152篇 |
1981年 | 130篇 |
1980年 | 128篇 |
1979年 | 102篇 |
1978年 | 94篇 |
1977年 | 123篇 |
1976年 | 158篇 |
1975年 | 80篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A wide variety of speech recognition distortion measures have been proposed and tested, including some especially effective ones. It is shown that there is a general framework, based on the concepts of information theory, linking most of these measures. The distortion measure between any two speech spectra can be defined in terms of the distortions between the associated probability distributions. This general framework defines three broad families of distortion measures for speech recognition and provides a consistent way of combining the energy and the spectral information of a phonetic event. In addition, the cepstral-domain representation for several distortion measures is derived, allowing comparison of these measures in a domain that also yields convenient equations for their practical implementation 相似文献
952.
Numerical prediction of the wind flow and pollutant dispersion over two-dimensional hilly terrain is presented. The wind tunnel
experiments are conducted to validate the numerical results of the flow field. Measured mean velocity profiles, turbulence
characteristics, and surface pressure distributions show good agreement with the numerical predictions. The hypothesis of
Reynolds number independency for an atmospheric boundary layer flow over aerodynamically rough terrain is numerically confirmed.
The linear theory provides generally good prediction of speed-up characteristics for gently sloped low hills. The effect of
two-dimensional double hills on the dispersion of pollutants from continuously or temporally released line source of different
emission heights and locations is also investigated. The ground-level concentrations are considerably reduced as emission
heights are increased. The variances of ground-level concentration with respect to time from a temporally released source
are strongly influenced by the flow separation. 相似文献
953.
954.
Beckwith-Wiedemann syndrome (BWS) comprises of a number of childhood abnormalities, often associated with one or more tumors. Thirty-eight patients were investigated to determine clinical and/or biological signs associated with a tumor presence. Our patients exhibited a higher incidence of tumor development (21%) than that previously reported, underlying the care with which such patients should be followed, when particular clinical features are observed: visceromegaly affecting three organs (liver, kidney, spleen), and also family history with sign of BWS such as macroglossia, omphalocele, hemihypertrophy, embryonic tumor), high body weight at birth (> or = +2 standard deviations and diastasis recti. 相似文献
955.
Chih-Chun Hsieh Tao-Chih Chang Dong-Yih Lin Ming-Che Chen Weite Wu 《Metals and Materials International》2007,13(5):411-416
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel
welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition
of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD),
scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS),
respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless
steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding.
The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in
the fusion zone of the third pass welds during multi-pass welding. 相似文献
956.
Marielle Montginoul 《Water Resources Management》2007,21(5):861-871
This paper presents the results of a 2003 national survey of urban water pricing structure implemented by 429 district level
water utilities. After providing some background elements on the diversity of existing water pricing structures, the paper
shows how each structure can be used to achieve different management objectives (water allocation efficiency, costs recovery,
and equity). It then describes the structures adopted by French water utilities, showing that flat rate are rarely adopted;
declining blocks frequently used; and increasing blocks pricing which should be used to promote water use efficiency remain
extremely rare. A statistical clustering is then conducted and a typology of situations elaborated. The paper concludes with
highlighting that current pricing structures are influenced by past practices and that the dominant objective of water utilities
is to cover costs. 相似文献
957.
Bong-Un Lee Hwa-Suk Oh Ja-Young Kang 《Journal of Mechanical Science and Technology》2007,21(3):436-447
The geometric singularity problem is one of principal difficulty when using single-gimbal control moment gyros as spacecraft
attitude control devices. To overcome singularity, new steering logics are suggested in this paper which results in a reduction
in the difficulty of generating gimbal rates around a singular state. One of the suggested steering laws presented is the
reduced dimensional singular value decomposition steering law, which adopts the singular value decomposition in reduced dimensional
forms. Two other steering laws make use of the least square method in reduced dimensional forms. All of the suggested steering
laws have been generated for the compensation of the torque insufficiency. These logics are verified mathematically and simulations
at a singular condition and non-singular condition are performed to see how well they work. 相似文献
958.
To ensure the core status can meet the requirements of thermal limits, stability and other constraints during the power ascension process of a nuclear power plant, operators usually gradually increase power based on onsite measurements and experience. To reduce the operator’s burden, this research develops a method to find an optimal power ascension path that can be followed by operators. The power ascension path is formulated as a multiobjective optimization problem with the following constraints: power ascension time, thermal limits, core stability and maximum rod line. A genetic algorithm is adopted to obtain the optimal power ascension path. The results show that using our approach full power can be achieved quickly, while maintaining reasonable margins of thermal limit and stability, in addition to satisfying maximum rod line criteria. 相似文献
959.
The purpose of this study was to analyze the symbolization of colors as cultural codes, based on costume colors. In order to study the significance of colors in cultural changes, we carried out a quantitative analysis and interpreted it from the perspective of cultural semiotics. The range of this study was focused on Korean costume colors, over diverse diachronic stages of Korean culture. For this study 1535 color samples were collected, measured with a spectrophotometer, and analyzed quantitatively according their diachronic stages of origin. As a result, red, blue, and yellow were found to be the most frequently used colors during the Chosun Dynasty, a period based on Confucianism. These colors acted as cultural codes with cultural significance. During the Modern times pink, light blue, and black increased in frequency and represented the reception of western culture, the changing sex role of women in society, and utilitarianism. In these days, neutral colors and grayish tones of all colors are the most significant colors of high frequency. The use of such colors is closely related to industrialization, mechanization, functionalism, and the changes of women's sex roles in the societies. They are used as cultural codes, especially to emphasize a rational and masculine image rather than a feminine image. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 71–79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20290 相似文献
960.
A review of the development of the gel pond technology is presented. First, the emergence and growth of solar pond technology since the 1950's is described. The inherent problems encountered with the conventional salt gradient ponds are discussed, leading to the concept of the solar gel pond in which the salt gradient layer in the former is replaced by a transparent polymer gel. The major work in the first phase dealt with the experimental development of a polymer gel which met certain selection criteria. The criteria considered included transmissivity, stability of physical and chemical properties, high viscosity and other physical and optical properties. The gradual development of the polymer gel through an alternating process of testing and elimination and evaluation of relevant properties of the gel has been described. Modeling and optimization studies of the solar gel pond have been presented. Bansal and Kaushik's model for a salt gradient pond has been modified for a solar gel pond, and the results of the simulation are presented in a graphical form to serve as a quick reference for estimation of pond surface area, depth and flow rate for heat extraction depending on the extreme temperature required in the storage zone and the required heat load. Then, a cost-benefit economic analysis compares the economics of a solar gel pond with a conventional salt gradient pond. The construction of an experimental gel pond (18 m2) at The University of New Mexico is described, and the results of the study are summarized. Information on commercial scale ponds at Chamberino, New Mexico (110 m2), and in Albuquerque, New Mexico (400 m2), is provided. The review of the technology demonstrates the immense potential of the gel pond as a source of alternate energy for the years ahead. 相似文献