全文获取类型
收费全文 | 101411篇 |
免费 | 9469篇 |
国内免费 | 5517篇 |
专业分类
电工技术 | 6959篇 |
技术理论 | 4篇 |
综合类 | 7579篇 |
化学工业 | 15758篇 |
金属工艺 | 6078篇 |
机械仪表 | 6772篇 |
建筑科学 | 8272篇 |
矿业工程 | 3370篇 |
能源动力 | 2720篇 |
轻工业 | 6472篇 |
水利工程 | 2078篇 |
石油天然气 | 5462篇 |
武器工业 | 978篇 |
无线电 | 12158篇 |
一般工业技术 | 11598篇 |
冶金工业 | 4357篇 |
原子能技术 | 1164篇 |
自动化技术 | 14618篇 |
出版年
2024年 | 440篇 |
2023年 | 1465篇 |
2022年 | 2983篇 |
2021年 | 4110篇 |
2020年 | 3049篇 |
2019年 | 2543篇 |
2018年 | 2810篇 |
2017年 | 3149篇 |
2016年 | 2893篇 |
2015年 | 4330篇 |
2014年 | 5235篇 |
2013年 | 6218篇 |
2012年 | 7094篇 |
2011年 | 7590篇 |
2010年 | 6996篇 |
2009年 | 6947篇 |
2008年 | 6648篇 |
2007年 | 6443篇 |
2006年 | 6009篇 |
2005年 | 5160篇 |
2004年 | 3463篇 |
2003年 | 2958篇 |
2002年 | 2733篇 |
2001年 | 2386篇 |
2000年 | 2134篇 |
1999年 | 2073篇 |
1998年 | 1492篇 |
1997年 | 1354篇 |
1996年 | 1201篇 |
1995年 | 1012篇 |
1994年 | 795篇 |
1993年 | 599篇 |
1992年 | 466篇 |
1991年 | 340篇 |
1990年 | 308篇 |
1989年 | 274篇 |
1988年 | 203篇 |
1987年 | 116篇 |
1986年 | 101篇 |
1985年 | 55篇 |
1984年 | 47篇 |
1983年 | 21篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 28篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1959年 | 6篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
茅金根 ,梁秀文 ,杨午阳 ,冯有奎 .等偏移距自动初至静校正 .石油地球物理勘探 ,2 0 0 2 ,37(5 ) :4 6 9~ 4 72 本文提出一种自动计算静校正量的新方法。它首先在等偏移距道集内对相邻道的初至波采用高精度相关构建一个关于炮、检时差的超大矩阵方程 ,然后采用优化统计迭代算法求解炮点和检波点的静校正量 ,并用概率分布函数确定精确的炮、检静校正量 ,最后用误差校正函数消除炮、检静校正误差。实际资料处理结果表明 ,本方法自动、省时、精度高。 相似文献
22.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
23.
Carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN) has often been used to improve the toughness of cyanate ester (CE) resin while sacrificing modulus and thermostability. In this paper, the addition of the appropriate amount of epoxy resin (EP) to the CE/CTBN system is shown to not only increase the modulus and thermostability of the blend, but also improve the toughness. The values of impact strength showed a maximum for the CE/CTBN/EP 100/5/5 blend. The temperature of 10 % weight loss (T10) improves from 376 °C for CE/CTBN 100/5 to 407 °C for the CE/CTBN/EP 100/5/2.5 blend. It is proposed that addition of the appropriate amount of EP can decrease the mobility and increase the stability of CTBN via the reaction between the terminal carboxyl group of CTBN and the hydroxyl group of EP. But a very high EP concentration will decrease the crosslinking density of CE, consequently reducing the mechanical properties and thermostability of the blends. Copyright © 2004 Society of Chemical Industry 相似文献
24.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。 相似文献
25.
Most algorithms on receiver autonomous integrity monitoring (RAIM) are under the assumption of a single-satellite fault, because there is an extremely small probability that significant simultaneous multiple-satellite faults may occur. However, after the implementation of the Galileo system in a few years, there will be more satellites in view for the user to utilise together with GPS satellites, and a combination of them will bring better performance for RAIM. On the other hand, with the help of wide area augmentation system and the use of dual-frequency operation, pseudo-range errors will be reduced greatly. Thus, tighter alert limits are required for RAIM, and formerly `small' errors should not be neglected. All of those factors make it necessary to consider simultaneous multiple-satellite faults. A detailed theoretical analysis of RAIM under the condition of two-satellite faults for both vertical and horizontal directions is presented. The characteristic/max slopes for every pair of satellites are then deduced in order to calculate the tighter vertical/horizontal protection level for RAIM 相似文献
26.
27.
28.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
29.
An efficient algorithm for the random packing of spheres can significantly save the cost of the preparation of an initial configuration often required in discrete element simulations. It is not trivial to generate such random packing at a large scale, particularly when spheres of various sizes and geometric domains of different shapes are present. Motivated by the idea of compression complemented by an efficient physical process to increase packing density, shaking, a new approach, termed compression algorithm, is proposed in this work to randomly fill any arbitrary polyhedral or cylindrical domains with spheres of various sizes. The algorithm features both simplicity and high efficiency. Tests show that it takes 181 s on a 1.4-GHz PC to complete the filling of a cylindrical domain with a total number of 26,787 spheres, achieving a packing density of 52.89%. 相似文献
30.