全文获取类型
收费全文 | 197580篇 |
免费 | 25162篇 |
国内免费 | 8276篇 |
专业分类
电工技术 | 10534篇 |
技术理论 | 2篇 |
综合类 | 12872篇 |
化学工业 | 40648篇 |
金属工艺 | 9225篇 |
机械仪表 | 10428篇 |
建筑科学 | 13405篇 |
矿业工程 | 3563篇 |
能源动力 | 5344篇 |
轻工业 | 20112篇 |
水利工程 | 3545篇 |
石油天然气 | 6734篇 |
武器工业 | 1227篇 |
无线电 | 26563篇 |
一般工业技术 | 28961篇 |
冶金工业 | 8238篇 |
原子能技术 | 2023篇 |
自动化技术 | 27594篇 |
出版年
2024年 | 601篇 |
2023年 | 2140篇 |
2022年 | 4081篇 |
2021年 | 5890篇 |
2020年 | 5424篇 |
2019年 | 6341篇 |
2018年 | 6664篇 |
2017年 | 7646篇 |
2016年 | 7661篇 |
2015年 | 9408篇 |
2014年 | 11278篇 |
2013年 | 14149篇 |
2012年 | 13302篇 |
2011年 | 14085篇 |
2010年 | 13186篇 |
2009年 | 12782篇 |
2008年 | 12307篇 |
2007年 | 11781篇 |
2006年 | 11235篇 |
2005年 | 9306篇 |
2004年 | 7252篇 |
2003年 | 6493篇 |
2002年 | 7057篇 |
2001年 | 6123篇 |
2000年 | 4970篇 |
1999年 | 3817篇 |
1998年 | 2803篇 |
1997年 | 2389篇 |
1996年 | 2137篇 |
1995年 | 1803篇 |
1994年 | 1389篇 |
1993年 | 1106篇 |
1992年 | 888篇 |
1991年 | 684篇 |
1990年 | 568篇 |
1989年 | 408篇 |
1988年 | 358篇 |
1987年 | 262篇 |
1986年 | 191篇 |
1985年 | 193篇 |
1984年 | 143篇 |
1983年 | 112篇 |
1982年 | 87篇 |
1981年 | 80篇 |
1980年 | 71篇 |
1979年 | 49篇 |
1978年 | 41篇 |
1977年 | 44篇 |
1976年 | 72篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
AutoCAD 下非结构网格自动生成 总被引:1,自引:1,他引:0
在AutoCAD环境下,从背景网格生成和数据结构两方面对推进阵面法进行修正。采用修理后的方法,使得在流场、泥沙输移和床面冲淤数值计算的前处理过程中无须精心预设内部控制点而只需给边界一个尺度,就能自动生成适应任意复杂边界的非结构网格,从而提高网格生成、优化的效率和通用性。 相似文献
93.
94.
The Synthesis of Sulfated Titanium Oxide Nanotubes 总被引:1,自引:0,他引:1
Chiu-Hsun Lin Shu-Hua Chien Jiunn-Hsing Chao Chyi-Yang Sheu Yu-Cheng Cheng Ya-Jean Huang Chih-Hsiang Tsai 《Catalysis Letters》2002,80(3-4):153-159
TiO2 nanotubes can be prepared in gram quantities by treating anatase TiO2 powder with concentrated NaOH solution. These TiO2 nanotubes acquired strong acidity after being impregnated with sulfuric acid solution and calcined at 300 °C. The anatase TiO2 powder used to prepare the nanotube did not catalyze the esterification between cyclohexanol and acetic acid, while sulfated TiO2 nanotubes were very reactive toward the esterification reaction. 相似文献
95.
96.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
97.
In this paper, the influence of viewing distance on subjective assessment of the impairment in video sequences is investigated. Subjective tests using the double-stimulus impairment scale variant II (DSIS II) method have been conducted at viewing distances of 5H (where H stands for the screen height) and 3H, respectively. Several statistical measures have been used to analyze the influence, including correlations and ANOVA (analysis of variance) tests. The results reveal that there is a very high correlation between the subjective scores, the variances are similar under the two viewing distances, the means of subjective data at these two viewing distances are the same, and there is no interaction between the viewing distance and the other two factors, i.e., the codec system and the source sequence. Throughout the tests, there is no evidence that a closer viewing distance such as 3H will vary the subjective test result statistically significantly. 相似文献
98.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
99.
Qin‐Tao Liu Malcolm R Clench Judith L Kinderlerer 《Journal of the science of food and agriculture》2002,82(5):553-558
Structural isomers of monoacylglycerols (monoglycerides, MAGs) were identified and compared after degradation of butter oil by two strains of Penicillium roquefortii and a commercial lipase from P roquefortii (EC 3.1.1.3) at pH 7.0 and 10 °C. The conditions were selected as they were comparable with those used in the manufacture of blue mould‐ripened cheese. The commercial lipase was selected to compare with the fungal strains in terms of acyl migration. Results showed that the main isomers formed by lipolysis with the commercial lipase were sn‐2 MAGs (64 mol%), whilst spores and emerging mycelia of P roquefortii produced mainly sn‐1(3) MAGs (83–90 mol%). The work reported here may lead to further assessment of different MAG structural isomers as natural preservatives in foods and dairy products. © 2002 Society of Chemical Industry 相似文献
100.
舰船水声隐身技术(二) 总被引:2,自引:0,他引:2
本文探讨了水声隐身性能对舰船战技术性能的影响 ,舰船水噪声的主要噪声源、水噪声的治理措施及其展望。 相似文献