全文获取类型
收费全文 | 253992篇 |
免费 | 3001篇 |
国内免费 | 868篇 |
专业分类
电工技术 | 4836篇 |
综合类 | 197篇 |
化学工业 | 36502篇 |
金属工艺 | 9536篇 |
机械仪表 | 7570篇 |
建筑科学 | 6134篇 |
矿业工程 | 885篇 |
能源动力 | 7249篇 |
轻工业 | 21297篇 |
水利工程 | 2204篇 |
石油天然气 | 3231篇 |
武器工业 | 15篇 |
无线电 | 34363篇 |
一般工业技术 | 50170篇 |
冶金工业 | 48721篇 |
原子能技术 | 5081篇 |
自动化技术 | 19870篇 |
出版年
2021年 | 2191篇 |
2020年 | 1571篇 |
2019年 | 1928篇 |
2018年 | 3295篇 |
2017年 | 3326篇 |
2016年 | 3425篇 |
2015年 | 2243篇 |
2014年 | 3993篇 |
2013年 | 11545篇 |
2012年 | 6280篇 |
2011年 | 8632篇 |
2010年 | 6933篇 |
2009年 | 7925篇 |
2008年 | 8442篇 |
2007年 | 8344篇 |
2006年 | 7417篇 |
2005年 | 6522篇 |
2004年 | 6306篇 |
2003年 | 6578篇 |
2002年 | 6068篇 |
2001年 | 6535篇 |
2000年 | 5989篇 |
1999年 | 6409篇 |
1998年 | 16528篇 |
1997年 | 11429篇 |
1996年 | 8810篇 |
1995年 | 6629篇 |
1994年 | 5919篇 |
1993年 | 5866篇 |
1992年 | 4150篇 |
1991年 | 4033篇 |
1990年 | 3871篇 |
1989年 | 3660篇 |
1988年 | 3577篇 |
1987年 | 3036篇 |
1986年 | 2955篇 |
1985年 | 3220篇 |
1984年 | 2938篇 |
1983年 | 2844篇 |
1982年 | 2646篇 |
1981年 | 2551篇 |
1980年 | 2483篇 |
1979年 | 2317篇 |
1978年 | 2118篇 |
1977年 | 2614篇 |
1976年 | 3583篇 |
1975年 | 1780篇 |
1974年 | 1742篇 |
1973年 | 1672篇 |
1972年 | 1478篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
241.
Summary The equilibrium water contents of linear poly(acrylic acid) sodium salts with different degrees of neutralisation were found to be dependent on temperature and relative humidity. An octahedral model for the primary hydration of poly(acrylic acid) sodium salts (HIRAOKA and YOKOYAMA 1980) was critically evaluated in the light of these findings and an anomaly in the water uptake versus neutralisation curve at approximately 33% neutralisation was explained by the counterion condensation theory. (MANNING 1979). 相似文献
242.
Bounds on the number of samples needed for neural learning. 总被引:1,自引:0,他引:1
The relationship between the number of hidden nodes in a neural network, the complexity of a multiclass discrimination problem, and the number of samples needed for effect learning are discussed. Bounds for the number of samples needed for effect learning are given. It is shown that Omega(min (d,n) M) boundary samples are required for successful classification of M clusters of samples using a two-hidden-layer neural network with d-dimensional inputs and n nodes in the first hidden layer. 相似文献
243.
An audio recording/playback head using an amorphous (Fe-Co-Ru-Cr) 75(Si-B)25 alloy was developed. Compared with a commercial Sendust head, three excellent features were observed. The wear of the amorphous alloy head when used with γ-Fe2O 3 is two-thirds that of the Sendust head. The output level at high-frequency (14 kHz) is 5 dB higher than that of the Sendust head. The bias current for the amorphous alloy head is half that of the Sendust head 相似文献
244.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 97–100, August, 1989. 相似文献
245.
246.
247.
We report on the Langmuir-Blodgett film deposition and plasma etching of cadmium distearate on n-Gao.47Ino.53As to form a high-barrier-height Schottky barrier. Using this technique to form the gate electrode, we fabricated a 1?m-gate-length inverted InP-GalnAs modulation-doped field-effect transistor (MODFET) with an extrinsic transconductance of 170mS/mm and a cutoff frequencyfT of 19 GHz. 相似文献
248.
R. Breil T. Fries J. Garnaes J. Haycocks D. Hüser J. Joergensen W. Kautek L. Koenders N. Kofod K. R. Koops R. Korntner B. Lindner W. Mirand A. Neubauer J. Peltonen G. B. Picotto M. Pisani H. Rothe M. Sahre M. Stedman G. Wilkening 《Precision Engineering》2002,26(3)
Comparison measurements on reference standards are reported in which 13 partners with different instruments took part. A set of prototype standards which had been produced and calibrated within a European project were used for the measurements. Here, results of measurements on a 240 nm step height standard and a two-dimensional lateral standard with a nominal pitch of 1 μm are reported. 相似文献
249.
Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (Tg). melting points (Tm) and crystallisation temperatures (Tc) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in Tg, Tm and Tc. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation. 相似文献
250.
Steroidal glycoalkaloids, found in species of the Solanaceae, elicit bursting activity in galeal and tarsal chemosensilla of adult Colorado potato beetles. The effect has an average latency of 6–12 sec, depending on the sensillum/alkaloid combination. A 20-sec alkaloid treatment is often suffficient to render galeal sensilla unresponsive to gamma-aminobutyric acid, normally an effective stimulant. The alkaloids have similar effects on galeal sensilla of larval Colorado potato beetles and on labellar chemosensilla of the blowfly. It is concluded that these compounds act independently of any specialized chemoreceptor in the Colorado potato beetle, and that association of the Colorado potato beetle with solanaceous plants has not led to evolution of a specific receptor forSolanum glycoalkaloids. 相似文献