全文获取类型
收费全文 | 2020篇 |
免费 | 69篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 17篇 |
综合类 | 2篇 |
化学工业 | 688篇 |
金属工艺 | 62篇 |
机械仪表 | 33篇 |
建筑科学 | 47篇 |
能源动力 | 123篇 |
轻工业 | 138篇 |
水利工程 | 13篇 |
石油天然气 | 7篇 |
无线电 | 136篇 |
一般工业技术 | 403篇 |
冶金工业 | 134篇 |
原子能技术 | 25篇 |
自动化技术 | 267篇 |
出版年
2024年 | 9篇 |
2023年 | 26篇 |
2022年 | 56篇 |
2021年 | 78篇 |
2020年 | 57篇 |
2019年 | 56篇 |
2018年 | 95篇 |
2017年 | 81篇 |
2016年 | 89篇 |
2015年 | 26篇 |
2014年 | 71篇 |
2013年 | 150篇 |
2012年 | 99篇 |
2011年 | 134篇 |
2010年 | 91篇 |
2009年 | 81篇 |
2008年 | 97篇 |
2007年 | 75篇 |
2006年 | 77篇 |
2005年 | 53篇 |
2004年 | 37篇 |
2003年 | 28篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 19篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 27篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1970年 | 3篇 |
排序方式: 共有2095条查询结果,搜索用时 0 毫秒
171.
Suprabha Nayar Sharmistha P. Sagar Avijit Guha 《Journal of materials science. Materials in medicine》2010,21(4):1099-1102
Hydroxyapatite-poly (vinyl) alcohol nanocomposite powder was synthesized using varying poly (vinyl) alcohol concentrations. The dried powder was compacted into micro-porous disks at a load of 4 tons. The disks were sintered at 1200°C to evolve porous nanocomposites. Size and shape of the pores observed in the scanning electron micrographs were quantified by using image processing software. Ultrasound velocity measurements were done to evaluate mechanical properties non-destructively. 相似文献
172.
Anil Kumar Mandeep Kaur Rajeev Kumar Pinaki Ranjan Sengupta Vasantha Raman Gopal Bhatia Kedar Nath Sood 《Journal of Materials Science》2010,45(5):1393-1400
Carbon–copper composites with varying copper to carbon ratio of 0.66–1.5 (by weight) were developed from coal-tar-pitch-derived green coke (as such or modified with natural graphite) as carbon source and electrolytic grade copper powder at different heat treatment temperatures (HTTs) of 1000–1400 °C. The physical, mechanical, and electrical properties differ depending upon the HTT and also on copper to carbon ratio (Cu/C). The composites prepared at HTT of 1100 °C having Cu/C ratio of 0.66 and 0.9 exhibited a high bending strength of 150 and 140 MPa, bulk density of 2.63 and 2.81 gm/cm3, electrical resistivity of 1.6 and 0.96 m Ω cm and shore hardness of 88 and 84, respectively, in spite of well-known inadequate wettability between copper and carbon. Increasing the temperature from 1100 °C for processing of the composites deteriorated the properties mainly due to the loss of copper through melting above 1100 °C as revealed by X-ray, scanning electron microscopy, thermal analysis and EDAX studies. 相似文献
173.
This paper emphasizes on establishment of traceability for the strain measuring data acquisition system in terms of voltage. If this amplifier’s output voltage is not calibrated then traceability chain breaks. To complete the traceability chain, the amplifier’s output voltage has been calibrated for corresponding strain. The sensitivity is calculated using calibration results and further used to feed in data acquisition system to display the result in terms of force/strain. 相似文献
174.
R. Vidya Sagar B. K. Raghu Prasad B. L. Karihaloo 《International Journal of Fracture》2010,161(2):121-129
Notched three-point bend specimens (TPB) were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and the entire fracture process was simulated using a regular triangular two-dimensional lattice network only over the expected fracture process zone width. The rest of the beam specimen was discretised by a coarse triangular finite element mesh. The discrete grain structure of the concrete was generated assuming the grains to be spherical. The load versus CMOD plots thus simulated agreed reasonably well with the experimental results. Moreover, acoustic emission (AE) hits were recorded during the test and compared with the number of fractured lattice elements. It was found that the cumulative AE hits correlated well with the cumulative fractured lattice elements at all load levels thus providing a useful means for predicting when the micro-cracks form during the fracturing process, both in the pre-peak and in the post-peak regimes. 相似文献
175.
176.
R. Vidya Sagar B.K. Raghu Prasad S. Shantha Kumar 《Cement and Concrete Research》2012,42(8):1094-1104
Notched three point bend (TPB) specimens made with plain concrete and cement mortar were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and simultaneously acoustic emissions (AE) released were recorded during the experiments. Amplitude distribution analysis of AE released during concrete was carried out to study the development of fracture process in concrete and mortar specimens. The slope of the log-linear frequency–amplitude distribution of AE is known as the AE based b-value. The AE based b-value was computed in terms of physical process of time varying applied load using cumulative frequency distribution (Gutenberg–Richter relationship) and discrete frequency distribution (Aki's method) of AE released during concrete fracture. AE characteristics of plain concrete and cement mortar were studied and discussed and it was observed that the AE based b-value analysis serves as a tool to identify the damage in concrete structural members. 相似文献
177.
Anil G. Panda Malhari D. Bhor Sunil S. Ekbote Bhalchandra M. Bhanage 《Catalysis Letters》2009,131(3-4):649-655
Polyethylene glycol based diphosphinite ligands and their Wilkinson type Rh-polymeric carbonyl complexes were prepared for homogeneous hydroformylation of styrenes. The effect of reaction variables such as temperature, pressure, P/Rh ratio, Substrate/Rh ratio, phosphine and phosphinite ligands on the activity and selectivity performance were discussed in detail. The catalyst showed a high rate of reaction, TON and tunable regioselectivity depending upon reaction conditions as compared to conventional Rh-phosphine based catalysts. 相似文献
178.
The influence of gel and molecular weight on the properties of natural rubber has been described. Crystallization, stress relaxation and orientation properties of different samples have been studied. Samples having different gel contents but similar molecular weights and samples having the same gel content with varying molecular weights have been prepared by extracting whole natural rubber. The gel content was varied from 1.5 to 29% and molecular weight from 1 × 105 to 9.9 × 105 g mol−1. The gels reduce the overall crystallinity measured by differential scanning calorimetric experiments after freezing the samples for different time periods at −15°C. They also have a stiffening effect on the tensile relaxation modulus and decrease the rate of relaxation significantly. Birefringence, which measures the orientation and stress-induced crystallization, increases with time at high elongation for samples containing gels. At lower elongation, however, the birefringence of unvulcanized samples decreases with time. This decrease is less for gel samples. Natural rubbers of high molecular weight behave similarly in the above properties when compared to low molecular weight samples. The effect of gel is more predominant than that of molecular weight. 相似文献
179.
180.
S.P. Nehra M.K. Jangid Subodh Srivastava Anil Kumar Balram Tripathi M. Singh Y.K. Vijay 《International Journal of Hydrogen Energy》2009,34(17):7306
Bilayer thin films of diluted magnetic semiconductor CdTe/Mn have been prepared using vacuum thermal evaporation method at pressure of 10−5 torr. Annealing of bilayer thin films has been performed in atmospheric condition at constant temperature 400 °C for 1 hour. Hydrogenation of as-grown and annealed bilayer thin films has been performed by keeping these in hydrogenation cell. Structural characteristics of as-grown and heat treated thin films have been performed by X-ray diffractometer. Current–voltage characteristics of both as-grown hydrogenated and annealed hydrogenated bilayer thin films have been studied to find out the effect of hydrogenation. Surface topography of as-grown and annealed bilayer thin films has been confirmed by optical microscopy. 相似文献