全文获取类型
收费全文 | 18127篇 |
免费 | 793篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 215篇 |
综合类 | 18篇 |
化学工业 | 3803篇 |
金属工艺 | 323篇 |
机械仪表 | 403篇 |
建筑科学 | 1008篇 |
矿业工程 | 49篇 |
能源动力 | 502篇 |
轻工业 | 1719篇 |
水利工程 | 120篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1585篇 |
一般工业技术 | 3064篇 |
冶金工业 | 3034篇 |
原子能技术 | 190篇 |
自动化技术 | 2851篇 |
出版年
2023年 | 158篇 |
2022年 | 297篇 |
2021年 | 462篇 |
2020年 | 342篇 |
2019年 | 366篇 |
2018年 | 425篇 |
2017年 | 388篇 |
2016年 | 494篇 |
2015年 | 424篇 |
2014年 | 522篇 |
2013年 | 1075篇 |
2012年 | 858篇 |
2011年 | 1117篇 |
2010年 | 768篇 |
2009年 | 823篇 |
2008年 | 863篇 |
2007年 | 756篇 |
2006年 | 705篇 |
2005年 | 592篇 |
2004年 | 486篇 |
2003年 | 442篇 |
2002年 | 422篇 |
2001年 | 297篇 |
2000年 | 321篇 |
1999年 | 352篇 |
1998年 | 730篇 |
1997年 | 479篇 |
1996年 | 396篇 |
1995年 | 290篇 |
1994年 | 269篇 |
1993年 | 266篇 |
1992年 | 185篇 |
1991年 | 155篇 |
1990年 | 135篇 |
1989年 | 135篇 |
1988年 | 124篇 |
1987年 | 118篇 |
1986年 | 118篇 |
1985年 | 139篇 |
1984年 | 132篇 |
1983年 | 116篇 |
1982年 | 89篇 |
1981年 | 101篇 |
1980年 | 85篇 |
1979年 | 96篇 |
1978年 | 87篇 |
1977年 | 115篇 |
1976年 | 137篇 |
1975年 | 79篇 |
1974年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Joannie W. Chin Eric Byrd Ned Embree Jonathan Martin J. D. Tate 《Journal of Coatings Technology》2002,74(929):39-44
Laboratory ultraviolet (UV) chambers are widely used to obtain weathering data for a wide range of commercial polymer products
including coatings, textiles, elastomers, plastics, and polymeric composites. Although numerous improvements have been made
in the design of UV chambers over the last 80 years, the reproducibility of the exposure results from these chambers has remained
elusive. This lack of reproducibility is attributed to systematic errors in their design, operation, and control which prevent
direct comparisons of the performance of materials exposed in the same environment, comparisons of the performance of the
same material exposed in different laboratories, and the comparison of field and laboratory results. This paper describes
an innovative UV chamber design based on integrating sphere technology that greatly reduces the magnitude of these errors,
as well as provides additional experimental capabilities.
Presented at the 79th Annual Meeting of the Federation of Societies for Coatings Technology, on November 4–7, 2001, in Atlanta,
GA.
Building Materials Division. Gaithersburg, MD.
Freeport, TX. 相似文献
102.
Grard J Martin Doubou Danho Claude Vallet 《Journal of the science of food and agriculture》1991,56(4):419-434
More than 500 carbohydrate samples have been characterised by hydrogen, carbon and oxygen isotopic parameters measured on ethanol and water resulting from controlled fermentation. Different chemical states of the carbohydrate pool have been considered: polysaccharides from cereals, tubers and leguminosae (maize, sorghum, rice, wheat, barley, potato, bean), glucose, fructose and sucrose from fruits (pineapple, citrus, apple, soft fruits), sucrose from sugar plants (beet, cane). The overall carbon-13 content of ethanol and the deuterium and oxygen-18 contents of water before fermentation were determined by mass spectrometry of isotope ratios whereas the investigation of site-specific natural isotope fractionation by deuterium NMR has provided access to the deuterium contents in the methyl (I) and methylene (II) sites of ethanol. The results have been analysed in the multidimensional space of these isotopic variables. Hierarchical clustering, principal component and discriminant analyses have been performed. Among fruits, for example, the pineapple group exhibits a 100% discrimination with respect to the apple and citrus groups which are themselves well distinguished. A still higher discrimination is reached between the three groups, citrus, cane and beet, and the addition of 10% exogenous cane or beet sucrose to citrus juice is unambiguously detected. 相似文献
103.
An adaptive analog continuous-time biquadratic filter is realized in a 2-μm digital CMOS process for operation at 300 kHz. The biquad implements the notch, bandpass and low-pass transfer functions. The only parameter adapted is the resonant frequency of the biquad, which is identical to the notch frequency and the bandpass center frequency. The update method is based on a least-means-square algorithm which adapts the notch frequency to minimize the power at the notch filter output. The actual update is modified to reduce the circuit complexity to one biquad and one correlator. When the filter is tracking a sinusoid, this update generates a ripple-free gradient that decreases tracking error. Applications include phase-frequency detectors, FM demodulators (linear and frequency shift keying), clock extractors, and frequency acquisition aids for phase-locked loops and Costas loops. Measured results from experimental prototypes are presented. Nonidealities of an all-analog implementation are discussed, along with suggestions to improve performance 相似文献
104.
Chang C.-R. Steer M.B. Martin S. Reese E. Jr. 《Microwave Theory and Techniques》1991,39(10):1735-1745
The authors present a newly developed free-running steady-state oscillator analysis algorithm suited to large-signal oscillator analysis. Kurokawa's oscillation condition is coupled with the modified nodal admittance form of the circuit equations to avoid degenerate solutions. The algorithm was implemented by using both harmonic balance and frequency-domain spectral balance techniques. It was used in the simulation of monolithically integrated varactor-tuned MESFET oscillator. Good agreement between simulated power and oscillation frequency results was obtained 相似文献
105.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
106.
Martin J. Beckmann 《The Annals of Regional Science》1992,26(3):199-207
The question explored in this paper is whether the center attracts more spending by all agents in a spatial economy than do peripheral locations, and why this might be so. This is the macroeconomics pendant to the microeconomic concern with accessibility.This paper is the result of discussions on the subject of time and space in economics with my good friend, Tonu Puu. I dedicate it to the memory of another dear friend, Claude Ponsard. 相似文献
107.
H.W. Choi C.W. Jeon M.D. Dawson P.R. Edwards R.W. Martin 《Photonics Technology Letters, IEEE》2003,15(4):510-512
High-performance, two-dimensional arrays of parallel-addressed InGaN blue micro-light-emitting diodes (LEDs) with individual element diameters of 8, 12, and 20 /spl mu/m, respectively, and overall dimensions 490 /spl times/490 /spl mu/m, have been fabricated. In order to overcome the difficulty of interconnecting multiple device elements with sufficient step-height coverage for contact metallization, a novel scheme involving the etching of sloped-sidewalls has been developed. The devices have current-voltage (I-V) characteristics approaching those of broad-area reference LEDs fabricated from the same wafer, and give comparable (3-mW) light output in the forward direction to the reference LEDs, despite much lower active area. The external efficiencies of the micro-LED arrays improve as the dimensions of the individual elements are scaled down. This is attributed to scattering at the etched sidewalls of in-plane propagating photons into the forward direction. 相似文献
108.
109.
Signal classification through multifractal analysis and complex domain neural networks 总被引:1,自引:0,他引:1
W. Kinsner Vincent Cheung K. Cannons J. Pear T. Martin 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2006,36(2):196-203
This paper describes a system capable of classifying stochastic self-affine nonstationary signals produced by nonlinear systems. The classification and the analysis of these signals are important because these are generated by many real-world processes. The first stage of the signal classification process entails the transformation of the signal into the multifractal dimension domain, through the computation of the variance fractal dimension trajectory (VFDT). Features can then be extracted from the VFDT using a Kohonen self-organizing feature map. The second stage involves the use of a complex domain neural network and a probabilistic neural network to determine the class of a signal based on these extracted features. The results of this paper show that these techniques can be successful in creating a classification system which can obtain correct classification rates of about 87% when performing classification of such signals without knowing the number of classes. 相似文献
110.
Reaction-induced phase separation (RIPS) of miscible blends of poly(?-caprolactone) (PCL) and an epoxy resin based on poly(propylene oxide) (PPO) was used to prepare thermoplastic vulcanizates (TPVs) with fine rubber dispersions. Scanning electron microscopy (SEM) confirmed the formation of cross-linked rubber particles dispersed in the thermoplastic matrix at PCL contents ≥20 wt%. The morphology development during phase separation was studied by optical microscopy (OM) and time-resolved small-angle light scattering (SALS). It was shown that higher curing temperatures lead to a decrease in rubber particle size, but at the same time lead to an increase in the extent of particle connectivity. In some cases, gelation of the PPO-rich phase limits full structure development, which leads to extensive connectivity between the dispersed rubber particles and a strong deterioration in tensile properties. 相似文献