全文获取类型
收费全文 | 7941篇 |
免费 | 956篇 |
国内免费 | 568篇 |
专业分类
电工技术 | 574篇 |
综合类 | 620篇 |
化学工业 | 1100篇 |
金属工艺 | 757篇 |
机械仪表 | 638篇 |
建筑科学 | 576篇 |
矿业工程 | 281篇 |
能源动力 | 271篇 |
轻工业 | 680篇 |
水利工程 | 246篇 |
石油天然气 | 390篇 |
武器工业 | 73篇 |
无线电 | 919篇 |
一般工业技术 | 704篇 |
冶金工业 | 422篇 |
原子能技术 | 120篇 |
自动化技术 | 1094篇 |
出版年
2024年 | 54篇 |
2023年 | 96篇 |
2022年 | 297篇 |
2021年 | 376篇 |
2020年 | 268篇 |
2019年 | 203篇 |
2018年 | 219篇 |
2017年 | 215篇 |
2016年 | 190篇 |
2015年 | 317篇 |
2014年 | 399篇 |
2013年 | 489篇 |
2012年 | 578篇 |
2011年 | 595篇 |
2010年 | 583篇 |
2009年 | 575篇 |
2008年 | 589篇 |
2007年 | 554篇 |
2006年 | 539篇 |
2005年 | 443篇 |
2004年 | 314篇 |
2003年 | 228篇 |
2002年 | 243篇 |
2001年 | 232篇 |
2000年 | 154篇 |
1999年 | 177篇 |
1998年 | 98篇 |
1997年 | 110篇 |
1996年 | 88篇 |
1995年 | 60篇 |
1994年 | 56篇 |
1993年 | 39篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有9465条查询结果,搜索用时 0 毫秒
31.
从我国磷矿资源以中低品位磷矿居多,低浓度磷肥本身含有作物所需中微量元素,低浓度磷肥制造成本低及我国农民长期的使用习惯,论述低浓度磷肥在我国存在的必要性。过磷酸钙企业目前存在规模小、分散、生产技术落后、污染严重、废弃物利用率低等问题,提出过磷酸钙生产的技改方向,如无熟化造粒技术,采用浓酸矿浆法并同时采用集散微机自控技术,主要设备实行定型化、系列化等,以增强企业的竞争力。 相似文献
32.
In upstream transmission of the DOCSIS (data over cable service interface specification) 1.0/1.1 and the TDMA mode of DOCSIS 2.0 standard, a packet begins with a preamble, the length and value of which are programmable by the headend. The acquisition process includes packet detection, symbol timing estimation, carrier frequency offset estimation and carrier phase estimation by means of the preamble so that the following information packet can be correctly demodulated. Methods to solve these tasks are not subject to standardization and are left to the system designer. However, they have a great impact on the system performance and thus are key elements for implementation. We present dedicated algorithms. A specific preamble is created and the corresponding scheme for packet acquisition is described in some detail. The packet detecting algorithm is independent of the carrier and symbol timing. The symbol timing estimate is obtained by using the minimum mean square algorithm regardless of the carrier frequency deviation and carrier phase. Algorithms for estimating the carrier frequency offset and carrier phase are proposed. Computer simulation results are given for all algorithms presented. 相似文献
33.
34.
An experimental study for the pathologic changes of the canine tracheal mucosa under YAG:Nd laser ablation was performed in order to master the appropriate parameters for the clinical treatment of YAG:Nd laser. 6 male and female Mongolia dogs weighing 13-18 kg were received 20W YAG:Nd laser treatment and their pathologic changes were examined instantly and 3, 7, 14 and 28 days after ablation. 相似文献
35.
1. Introduction Seismic physical modeling technology is an important method for the research on seismic exploration theory and methods. In seismic physical experiments, the earth, mantle or field site are scaled down to physical models according to the similarity principle, and then the seismic field and its variation are observed in the laboratory for the research work on the theories and methods of the earth structure, earthquake forecasting, energy and mineral resource exploration, and engi… 相似文献
36.
37.
A new efficient numerical method and the dynamic analysis of composite laminates with piezoelectric layers 总被引:1,自引:0,他引:1
Firstly, a numerical method for the inversion of Laplace transform is developed and its accuracy is shown through examples. Then, a state-vector equation for the dynamic problems of piezoelectric plates is deduced directly from a modified mixed variational principle for piezoelectric bodies and its exact solution for the dynamic problems of simply supported rectangle piezoelectric plate is simply given. For multilayered hybrid plates, we derive the solution in terms of the propagator matrices. The techniques accounts for the compatibility of generalized displacements and generalized stresses on the interface both the elastic layers and piezoelectric layers, and the transverse shear deformation and the rotary inertia of laminate are also considered in the global algebraic equation of structure. Meanwhile, there is no restriction on the thickness and the number of layers. As an application of the numerical inversion of Laplace transform presented in this paper, typical numerical examples of the harmonic vibration and transient response are proposed and discussed. Since the highly accurate numerical results, they can serve as benchmarks to test various thick plate theories and various numerical methods, such as the finite and boundary element methods for transient response problems. 相似文献
38.
产品创新是企业生存和发展的基础。分析了武钢钢铁产品的市场需求,找出了武钢企业外部环境的机会与威胁和企业内部的优势与劣势,提出了产品创新的战略措施。 相似文献
39.
简述了涟钢铁水喷镁脱硫技术的设备概况、工艺流程和试生产情况。重点介绍处理过程的反应机理和控制方法,通过调整和改造,解决了钢水回硫的问题,实现了铁水脱硫-转炉-RH精炼炉-CSP的匹配。 相似文献
40.
“两步法”求取双目视觉传感器中摄象机位置关系 总被引:2,自引:1,他引:1
根据平行线“消隐点”理论,提出了用于双目视觉传感器自标定的“两步法”。该方法仅需4对消隐点象面坐标便可线性求解出旋转矩阵,再用2个空间点坐标便可线性求解出平移矢量。 相似文献