全文获取类型
收费全文 | 49928篇 |
免费 | 4768篇 |
国内免费 | 2372篇 |
专业分类
电工技术 | 2960篇 |
技术理论 | 2篇 |
综合类 | 2851篇 |
化学工业 | 8601篇 |
金属工艺 | 3082篇 |
机械仪表 | 3341篇 |
建筑科学 | 3535篇 |
矿业工程 | 1497篇 |
能源动力 | 1465篇 |
轻工业 | 3164篇 |
水利工程 | 801篇 |
石油天然气 | 2815篇 |
武器工业 | 428篇 |
无线电 | 6126篇 |
一般工业技术 | 6624篇 |
冶金工业 | 2729篇 |
原子能技术 | 584篇 |
自动化技术 | 6463篇 |
出版年
2024年 | 293篇 |
2023年 | 1034篇 |
2022年 | 1788篇 |
2021年 | 2522篇 |
2020年 | 1852篇 |
2019年 | 1650篇 |
2018年 | 1706篇 |
2017年 | 1753篇 |
2016年 | 1688篇 |
2015年 | 2229篇 |
2014年 | 2664篇 |
2013年 | 3082篇 |
2012年 | 3199篇 |
2011年 | 3615篇 |
2010年 | 2862篇 |
2009年 | 2773篇 |
2008年 | 2795篇 |
2007年 | 2465篇 |
2006年 | 2600篇 |
2005年 | 2081篇 |
2004年 | 1495篇 |
2003年 | 1351篇 |
2002年 | 1223篇 |
2001年 | 1087篇 |
2000年 | 1063篇 |
1999年 | 1106篇 |
1998年 | 927篇 |
1997年 | 779篇 |
1996年 | 684篇 |
1995年 | 574篇 |
1994年 | 453篇 |
1993年 | 291篇 |
1992年 | 252篇 |
1991年 | 223篇 |
1990年 | 173篇 |
1989年 | 163篇 |
1988年 | 105篇 |
1987年 | 91篇 |
1986年 | 57篇 |
1985年 | 53篇 |
1984年 | 38篇 |
1983年 | 38篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
�غ���ܿ���ǿ�ȼ��㼰�ֳ�Ӧ�� 总被引:6,自引:1,他引:5
对于套管挤毁问题较为严重的油气水井,采用非API标准的特厚壁套管来提高其抗挤强度,是今后预防套管挤毁的重要发展方向。目前,特厚壁套管的抗挤强度计算和尺寸系列尚未形成工业标准,文章提出特厚壁套管的抗挤强度计算方法和尺寸系列,供设计者和厂家参考。API/ISO套管挤毁工作组曾对本文公式进行了测评,结果曼示具有较高的计算精度。大量计算表明,特厚壁套管的抗挤强度大大提高,约为加厚前原套管抗挤强度的1.5~4倍,甚至6倍。最后还介绍了特厚壁套管在中原油田的现场应用情况。 相似文献
62.
采用SE 3 0为固定液进行色谱柱分离 ,用外标定量法测定泥土中的微量六氯环戊二烯 ,结果最小检知量为 0 .18× 10 - 6 ,相关系数为 0 .99992。 相似文献
63.
Onishi K. Rino Choi Chang Seok Kang Hag-Ju Cho Young Hee Kim Nieh R.E. Jeong Han Krishnan S.A. Akbar M.S. Lee J.C. 《Electron Devices, IEEE Transactions on》2003,50(6):1517-1524
Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs. 相似文献
64.
65.
Wei-Hua Guo Yong-Zhen Huang Chun-Lin Han Li-Juan Yu 《Quantum Electronics, IEEE Journal of》2003,39(6):716-721
To improve the accuracy of measured gain spectra, which is usually limited by the resolution of the optical spectrum analyzer (OSA), a deconvolution process based on the measured spectrum of a narrow linewidth semiconductor laser is applied in the Fourier transform method. The numerical simulation shows that practical gain spectra can be resumed by the Fourier transform method with the deconvolution process. Taking the OSA resolution to be 0.06, 0.1, and 0.2 nm, the gain-reflectivity product spectra with the difference of about 2% are obtained for a 1550-nm semiconductor laser with the cavity length of 720 /spl mu/m. The spectra obtained by the Fourier transform method without the deconvolution process and the Hakki-Paoli method are presented and compared. The simulation also shows that the Fourier transform method has less sensitivity to noise than the Hakki-Paoli method. 相似文献
66.
67.
贵金属及其合金铆钉型复合电触点除了应考核其冷态复合强度之外,还必须增加在热态下复合强度的考核,只有这样才能满足用户在产际运行时对复合触点复合强度的要求。 相似文献
68.
Seung-Hwan Kim Seung-Bok Choi Sung-Ryong Hong M.-S.Moon-Sik Han 《International Journal of Mechanical Sciences》2004,46(1):269-157
This paper presents vibration control of a flexible beam structure using a hybrid mount which consists of elastic rubber and piezoelectric stack actuator. After identifying stiffness and damping properties of the rubber and piezoelectric elements, a mechanical model of the hybrid mount is established. The mount model is then incorporated with the beam structure, and the governing equation of motion is obtained in a state space. A sliding mode controller is designed in order to actively attenuate the vibration of the beam structure subjected to high-frequency and small magnitude excitations. The controller is experimentally realized and measured control responses such as acceleration of the beam structure and force transmission through the hybrid mount are evaluated and presented in both frequency and time domains. 相似文献
69.
70.
Obtaining shorter regular expressions from finite-state automata 总被引:1,自引:0,他引:1
We consider the use of state elimination to construct shorter regular expressions from finite-state automata (FAs). Although state elimination is an intuitive method for computing regular expressions from FAs, the resulting regular expressions are often very long and complicated. We examine the minimization of FAs to obtain shorter expressions first. Then, we introduce vertical chopping based on bridge states and horizontal chopping based on the structural properties of given FAs. We prove that we should not eliminate bridge states until we eliminate all non-bridge states to obtain shorter regular expressions. In addition, we suggest heuristics for state elimination that leads to shorter regular expressions based on vertical chopping and horizontal chopping. 相似文献