全文获取类型
收费全文 | 42919篇 |
免费 | 3776篇 |
国内免费 | 2103篇 |
专业分类
电工技术 | 2563篇 |
技术理论 | 5篇 |
综合类 | 3526篇 |
化学工业 | 7041篇 |
金属工艺 | 2211篇 |
机械仪表 | 2568篇 |
建筑科学 | 3515篇 |
矿业工程 | 1011篇 |
能源动力 | 1138篇 |
轻工业 | 4652篇 |
水利工程 | 901篇 |
石油天然气 | 1982篇 |
武器工业 | 400篇 |
无线电 | 4697篇 |
一般工业技术 | 4532篇 |
冶金工业 | 1620篇 |
原子能技术 | 541篇 |
自动化技术 | 5895篇 |
出版年
2024年 | 133篇 |
2023年 | 625篇 |
2022年 | 1085篇 |
2021年 | 1638篇 |
2020年 | 1269篇 |
2019年 | 1020篇 |
2018年 | 1206篇 |
2017年 | 1291篇 |
2016年 | 1205篇 |
2015年 | 1723篇 |
2014年 | 2167篇 |
2013年 | 2641篇 |
2012年 | 3073篇 |
2011年 | 3346篇 |
2010年 | 2958篇 |
2009年 | 2885篇 |
2008年 | 2925篇 |
2007年 | 2645篇 |
2006年 | 2536篇 |
2005年 | 2176篇 |
2004年 | 1502篇 |
2003年 | 1154篇 |
2002年 | 1117篇 |
2001年 | 931篇 |
2000年 | 874篇 |
1999年 | 899篇 |
1998年 | 724篇 |
1997年 | 601篇 |
1996年 | 516篇 |
1995年 | 459篇 |
1994年 | 330篇 |
1993年 | 249篇 |
1992年 | 216篇 |
1991年 | 158篇 |
1990年 | 110篇 |
1989年 | 99篇 |
1988年 | 84篇 |
1987年 | 39篇 |
1986年 | 54篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
111.
In this paper, we study the minimum cross-entropy optimization problem subject to a general class of convex constraints. Using a simple geometric inequality and the conjugate inequality we demonstrate how to directly construct a "partial" geometric dual program which allows us to apply the dual perturbation method to derive the strong duality theorem and a dual-to-primal conversion formula. This approach generalizes the previous results of linearly, quadratically, and entropically constrained cross-entropy optimization problems and provides a platform for using general purpose optimizers to generate ε-optimal solution pair to the problem. 相似文献
112.
进行了PAA(PolyacrylicAcid)-PSF(Polysulfone)交联复合膜的制备,研究了交联剂、添加剂对膜性能的影响,并通过扫描电镜观察了膜的断面结构.研究了PAA-PSF交联复合膜对低浓度有机醇类水溶液反渗透分离性能.发现对于1000×10-6乙醇水溶液截留率达到66.2%,透过流束可达0.9×10-6(m3·m-2·s-1).随醇的分子量的增加,截留率不断上升,对戊醇的截留率达94.3%,而透过流束则保持相对稳定.对不同结构醇类的分离性能研究表明,截留率存在有:tert->sec->iso->n-的规律. 相似文献
113.
The formation mechanism of the synthesis of MoO3 -doped YSr2 Cu3 O y powders using the citrate process was investigated. It was shown that the precursor phase (Sr1- x Y x )14 Cu24 O41 played a crucial role in forming the superconducting phase. It was found that the precursor phase (Sr1- x Y x )14 Cu24 O41 interacted with water and decomposed when it was heavily milled and heated. 相似文献
114.
From January 1987 to December 1993, 426 patients with lung cancer were operated in our hospital, among which 159 patients were diagnosed postoperatively to be N2 disease by pathology including 81 central type and 78 peripheral type lung cancer. Radical operations were performed on 135 cases, palliative operations on 24 cases. Follow up study: one-year survival rate was 71.7%, three-year survival rate 29.0% and five-year survival rate 21.7%. The main factors affecting operative results are tumor cell type, the number and location of metastatic lymph nodes and the thoroughness of dissection. Tumor staging, except T4 tumor is not a main factor influencing prognosis. The indications of operation performed on N2 lung cancer and the necessity of extensive nodal exenteration are also discussed in this article. We consider extensive hilar and mediastinal nodal exenteration necessary in order to achieve radical resection and good prognosis. 相似文献
115.
116.
ATM局域网仿真体系结构的研究 总被引:4,自引:0,他引:4
本文在简要叙述了基于ATM技术进行局域网仿真的原理后,对局域网仿真体系结构作了一些探讨。考虑的重点是无连接服务和群播功能的实现 相似文献
117.
本文综述了广义谱域导抗法,直线法及直线法的快速算法,全波离散镜象法等主要方法,并对各种方法的特点进行了比较,这些方法可有效地处理平面分层介质结构问题,文中包括作者近期的研究成果。 相似文献
118.
Hong-Sheng Fang Chung-Biau Tsay 《International Journal of Machine Tools and Manufacture》1996,36(10):1123-1135
A mathematical model for a ZE-type worm gear set is proposed. The characteristics of a ZE-type worm gear cut with an oversize hob cutter are investigated. Bearing contacts and kinematic errors in the ZE-type worm gear set due to regrinding of oversize hob cutters are also studied. Bearing contacts in the worm gear set were obtained using surface separation topology techniques and tooth contact analysis. It was found that bearing contact locations are sensitive to the hob cutter setting angle and setting distance. Kinematic error minimization was achieved modifying worm normal tooth angle. By applying the optimization theorem and computer simulation programs, optimum hob cutter settings and worm normal tooth angle were determined to improve bearing contact location and minimize the worm gear set kinematic errors. A numerical example is given to demonstrate the results of the investigation. The developed computer-aided manufacture program has successfully been applied to the worm gear manufacture and hob cutter design. 相似文献
119.
Tzong-Yow Tsai Zhi-Cheng Lee Jong-Rong Chen Chi-Chung Chen Yen-Cheng Fang Ming-Hong Cha 《Quantum Electronics, IEEE Journal of》2005,41(5):741-746
A novel ultracompact 2/spl times/2 wavelength division multiplexer (WDM) for 1.55-/spl mu/m operation based on highly dispersive two-mode interference (TMI) was designed, theoretically modeled, and verified using a finite-difference-time-domain (FDTD) method. A two-moded waveguide assisted with a dispersive tooth-shaped grating provided a mode-dependent reflection band of central wavelength at 1.55 /spl mu/m. The wavelengths of 1538 and 1572 nm that were at the band edges and had the lowest reflection losses and relatively high dispersion were selected for wavelength multiplexing. The result showed that the wavelengths were separated by grating dispersion in a coupler length of 75 /spl mu/m which was much shorter than the required length of 1.1 mm in a regular TMI multiplexer of no grating. Insertion loss of about 1.7 dB and channel contrast of about 12 dB were achieved. 相似文献
120.