全文获取类型
收费全文 | 5415篇 |
免费 | 443篇 |
国内免费 | 175篇 |
专业分类
电工技术 | 223篇 |
综合类 | 241篇 |
化学工业 | 993篇 |
金属工艺 | 89篇 |
机械仪表 | 234篇 |
建筑科学 | 238篇 |
矿业工程 | 131篇 |
能源动力 | 121篇 |
轻工业 | 502篇 |
水利工程 | 70篇 |
石油天然气 | 96篇 |
武器工业 | 37篇 |
无线电 | 922篇 |
一般工业技术 | 858篇 |
冶金工业 | 509篇 |
原子能技术 | 142篇 |
自动化技术 | 627篇 |
出版年
2024年 | 8篇 |
2023年 | 51篇 |
2022年 | 98篇 |
2021年 | 200篇 |
2020年 | 123篇 |
2019年 | 128篇 |
2018年 | 148篇 |
2017年 | 169篇 |
2016年 | 160篇 |
2015年 | 175篇 |
2014年 | 265篇 |
2013年 | 355篇 |
2012年 | 351篇 |
2011年 | 431篇 |
2010年 | 339篇 |
2009年 | 307篇 |
2008年 | 294篇 |
2007年 | 269篇 |
2006年 | 242篇 |
2005年 | 203篇 |
2004年 | 155篇 |
2003年 | 159篇 |
2002年 | 141篇 |
2001年 | 124篇 |
2000年 | 101篇 |
1999年 | 112篇 |
1998年 | 171篇 |
1997年 | 119篇 |
1996年 | 86篇 |
1995年 | 62篇 |
1994年 | 69篇 |
1993年 | 44篇 |
1992年 | 35篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 36篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 21篇 |
1976年 | 30篇 |
1974年 | 14篇 |
1973年 | 8篇 |
排序方式: 共有6033条查询结果,搜索用时 46 毫秒
31.
This study has explored the potential energy surface on the chemical reaction of CH2OH with NO by using ab initio calculation. We have found the new reaction pathway producing N-hydroxy formamide, which can further decompose to generate isocyanic acid as a reducing agent of hydrocarbons selective catalytic reduction. 相似文献
32.
33.
用DSC研究了熔融温度对不同类型成核剂成核PP的异相成核作用的稳定性的影响。观察到随熔融温度提高,纯PP的成核作用稳定,降温结晶温度基本不变。而有机磷酸盐类成核剂成核PP的结果温度比纯PP的高,而且异相成核作用受熔融温度的影响也很小。但山梨醇类成核剂成核PP的异相成核作用随熔融温度提高,结晶温度逐步降低明显,表明其异相成核作用对热不稳定。 相似文献
34.
I-shaped slots will fit entirely on the rectangular waveguide narrow wall without wrapping onto the broad wall. This slot type is suitable for single plane scan-phased arrays where element spacing, in the scan plane, is equal to or less than one-half wavelength. The method of moments solution for the I-slot is presented. Comparison of computed results with measured data illustrates the validity of this solution. To facilitate future designs, the waveguide scattering parameters and the radiation characteristics of I-slots are included 相似文献
35.
用微机计算电子衍射径向分布函数 总被引:1,自引:0,他引:1
本文介绍用微机计算非晶态高聚物电子衍射径向分布函数(RDF)。运用二次样条函数分段拟合及傅氏积分的数学方法,通过 BASIC 程序,只要输入初始实验数据即可自动解算且连续得到与各运算阶段相应的曲线图及其运算结果. 相似文献
36.
D. Li A. F. Yee I. -W. Chen S. -C. Chang K. Takahashi 《Journal of Materials Science》1994,29(8):2205-2215
The fracture toughness and uniaxial tensile yield strengths of unmodified and CTBN-rubber-modified epoxies were measured under hydrostatic pressure. The purpose of these experiments was to learn how suppressing cavitation in rubber particles affects the deformation mechanisms and the fracture toughness of rubber-modified epoxy. It was found that the cavitation of CTBN-rubber could be suppressed at a relatively low pressure (between 30 and 38 M Pa). With cavitation suppressed, the rubber particles are unable to induce massive shearyielding in the epoxy matrix, and the fracture toughness of the rubber-modified epoxy is no higher than that of the unmodified epoxy in the pressure range studied. Unmodified epoxy shows a brittle-to-ductile transition in fracture toughness test. The reason for this transition is the postponement of the cracking process by applied pressure.Work performed while on a sabbatical leave at the University of Michigan. 相似文献
37.
A trade-off analysis on the cost and system packaging metrics of an electronic product aimed at the commercial/retail industry has been carried out. By comparing the system cost and packaging metrics with those of comparable consumer products, we have determined that there is opportunity for significant cost, size, and weight reduction of the overall electronics packaging system. These include the use of fine pitch IC packages, smaller discrete components, denser PCB wiring technology, double sided IC package surface mount, surface mount connectors, and improved plastics for the product housing. The analysis concluded that PCB area reduction of 40%, using a single PCB instead of three boards, reduction in board cost of over 50% and product weight reduction of over 28% are possible using available technologies. 相似文献
38.
39.
The article is to introduce author's research results in recent years in the field of leadership behavior. The main researches conducted in this field include competency model of senior executives in communication industry and family firms; transformational leadership and its relationship with leadership effectiveness, the impact of supervisor's feedback on employees' behavior and the cross-culture study of supervisor's feedback. Theoretical and practical contributions of these researches are explained. Directions for future research are discussed. 相似文献
40.
A modification to the time-domain finite-difference method (TDFDM) that uses a variable step size is investigated. The entire computational volume is divided into a coarse grid with a large step size. A fine grid with a small step size is introduced only around discontinuities. The corresponding time increments are related to the spatial increments with the same ratio in order to minimize the numerical dispersion. The fields within the coarse and fine grids are found using the TDFDM, while an interpolation in space and time is utilized to calculate the tangential electric field on the coarse-fine grid boundary. This subgridding decreases the required computer memory and therefore expands the capability of the TDFDM. The technique is shown to be numerically stable and does not entail any extra numerical error. The method is applied to the calculation of waveguides and microstrips 相似文献