全文获取类型
收费全文 | 309594篇 |
免费 | 3999篇 |
国内免费 | 715篇 |
专业分类
电工技术 | 6195篇 |
综合类 | 560篇 |
化学工业 | 46746篇 |
金属工艺 | 10329篇 |
机械仪表 | 8829篇 |
建筑科学 | 7904篇 |
矿业工程 | 862篇 |
能源动力 | 8573篇 |
轻工业 | 31104篇 |
水利工程 | 2533篇 |
石油天然气 | 3669篇 |
武器工业 | 8篇 |
无线电 | 39698篇 |
一般工业技术 | 58488篇 |
冶金工业 | 56632篇 |
原子能技术 | 5461篇 |
自动化技术 | 26717篇 |
出版年
2021年 | 2278篇 |
2019年 | 2141篇 |
2018年 | 3610篇 |
2017年 | 3453篇 |
2016年 | 3542篇 |
2015年 | 2542篇 |
2014年 | 4444篇 |
2013年 | 14324篇 |
2012年 | 7367篇 |
2011年 | 10116篇 |
2010年 | 7903篇 |
2009年 | 9133篇 |
2008年 | 9600篇 |
2007年 | 9581篇 |
2006年 | 8507篇 |
2005年 | 7888篇 |
2004年 | 7760篇 |
2003年 | 7497篇 |
2002年 | 7333篇 |
2001年 | 7544篇 |
2000年 | 7206篇 |
1999年 | 7546篇 |
1998年 | 17655篇 |
1997年 | 12842篇 |
1996年 | 10097篇 |
1995年 | 7872篇 |
1994年 | 7203篇 |
1993年 | 6906篇 |
1992年 | 5287篇 |
1991年 | 5066篇 |
1990年 | 4934篇 |
1989年 | 4781篇 |
1988年 | 4673篇 |
1987年 | 3887篇 |
1986年 | 4007篇 |
1985年 | 4717篇 |
1984年 | 4276篇 |
1983年 | 4021篇 |
1982年 | 3602篇 |
1981年 | 3761篇 |
1980年 | 3456篇 |
1979年 | 3419篇 |
1978年 | 3226篇 |
1977年 | 3814篇 |
1976年 | 4847篇 |
1975年 | 2780篇 |
1974年 | 2660篇 |
1973年 | 2675篇 |
1972年 | 2215篇 |
1971年 | 1963篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Verbovitskii Yu. V. Denis R. V. Shtender V. V. Zavalii I. Yu. 《Powder Metallurgy and Metal Ceramics》2015,54(3-4):220-226
Powder Metallurgy and Metal Ceramics - Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray... 相似文献
32.
33.
34.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
35.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
36.
Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
37.
38.
39.
40.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献