全文获取类型
收费全文 | 4062篇 |
免费 | 404篇 |
国内免费 | 147篇 |
学科分类
工业技术 | 4613篇 |
出版年
2024年 | 31篇 |
2023年 | 92篇 |
2022年 | 149篇 |
2021年 | 193篇 |
2020年 | 168篇 |
2019年 | 160篇 |
2018年 | 146篇 |
2017年 | 161篇 |
2016年 | 156篇 |
2015年 | 192篇 |
2014年 | 211篇 |
2013年 | 245篇 |
2012年 | 261篇 |
2011年 | 264篇 |
2010年 | 238篇 |
2009年 | 184篇 |
2008年 | 175篇 |
2007年 | 194篇 |
2006年 | 196篇 |
2005年 | 178篇 |
2004年 | 111篇 |
2003年 | 102篇 |
2002年 | 95篇 |
2001年 | 83篇 |
2000年 | 102篇 |
1999年 | 105篇 |
1998年 | 82篇 |
1997年 | 67篇 |
1996年 | 77篇 |
1995年 | 41篇 |
1994年 | 36篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有4613条查询结果,搜索用时 15 毫秒
1.
云南丽江旅游的发展与大研古镇的发展方向问题 总被引:7,自引:0,他引:7
一、发展过程与现状 (一)古城和雪山完美地结合,特点突出,古镇拉动效应明显 丽江有丰富的旅游资源,如独特的东巴文化、古城、雪山等等。经过一段时间发展,丽江旅游产品也形成几个比较突出的亮点,如古城-雪山产品,古城如此完整,雪山的风貌如此突出,而且古城和雪山在不大的地理范围内集中到一起,这在国内是很难得的。古城被评为世界文化遗产后还形成了一个显著的市场拉动效应。 相似文献
2.
SHS法陶瓷衬管的研究现状及应用前景 总被引:2,自引:0,他引:2
回顾了自蔓延高温合成陶瓷衬管的发展历史,对国内外的研究现状进行归纳总结,介绍了离心SHS法生产陶瓷衬管的工艺特点及产品性能,展望了离心SHS陶瓷衬管的应用前景。 相似文献
3.
J. A. Xia H. T. Ren P. R. Munroe Y. Zhao H. K. Liu C. Andrikidis S. X. Dou 《Journal of Superconductivity and Novel Magnetism》1994,7(6):947-950
Silver has been previously added to the melt-textured YBa2Cu3O7?x in order to increase the critical current density (J c ) of these materials. However, the effect of this addition on theJ c is presently unclear. The purpose of this study is to investigate the effect of silver on both critical current density and the microstructure of the melt-textured YBa2Cu3O7?x superconductors by means of X-ray diffraction, optical polarized microscopy, and transmission electron microscopy (TEM). TheJ c of the MTG YBCO/Ag samples is more than 104A/cm2 under the 5 kOe magnetic field. It has been shown that as the concentration of silver increases, the fraction of the 211 phase dispersed within the 123 matrix decreases. Therefore, theJ c slightly decreases. These results, together with the effect of the 211 phase, dislocations, and other structure defects on flux pinning, are described in this paper. 相似文献
4.
针对天铁板坯连铸机一年多来发生的漏钢事故,分析了产生的原因,提出了预防改进的措施,对今后的生产有很好的指导意义。 相似文献
5.
Van Vo N. Shi Xue Dou Hua Kun Liu 《Applied Superconductivity, IEEE Transactions on》1996,6(2):102-105
High temperature superconducting (HTSC) multifilamentary (MT) Bi(Pb)-2223/Ag tapes with reproducible critical current density of between 15000 and 20000 A/cm2 at 77 K in self field have been achieved using the standard flat-rolling method as the intermediate deformation between sintering periods. Long lengths of Bi(Pb)-2223/Ag MT tapes up to 43 m prepared by the conventional method of powder-in-tube (PIT) have been successfully produced on a laboratory scale. Several coils have been fabricated from sections of the long length tape, using the co-wound wind-and-react (W&R) procedure for the pancake-shaped and the singly-wound W&R as well as R&W procedure for the solenoidal coils. A novel W&R solenoidal coil (reaching ~973 ampere-turns) wound on an alumina ceramic tube generates a DC field of ~19 mT at 77 K and has been fabricated together with five pancake-shaped coils, each generating an average of ~5 mT at 77 K. These are destined for magnet construction with a possible combined calculated field of ~0.04 T at 77 K (with liquid nitrogen as a coolant) 相似文献
6.
7.
8.
9.
10.
Zeolite beta with a low SiO2/Al2O3 ratio was synthesized by a novel two-step process.The synthesized sample was characterized with XRD,SEM,FTIR,and N2 adsorption-desorption and solid-state MAS NMR.The results showed that aluminium species were inserted into the framework of zeolite beta.The BET surface area,volume,and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio.Our process was proved an efficient route to synthesize zeolite beta with a low SiO2/Al2O3 ratio. 相似文献