全文获取类型
收费全文 | 90484篇 |
免费 | 7788篇 |
国内免费 | 4084篇 |
专业分类
电工技术 | 5688篇 |
技术理论 | 2篇 |
综合类 | 5777篇 |
化学工业 | 14013篇 |
金属工艺 | 4956篇 |
机械仪表 | 5215篇 |
建筑科学 | 6721篇 |
矿业工程 | 1853篇 |
能源动力 | 2647篇 |
轻工业 | 7087篇 |
水利工程 | 1811篇 |
石油天然气 | 3877篇 |
武器工业 | 675篇 |
无线电 | 12040篇 |
一般工业技术 | 11651篇 |
冶金工业 | 4617篇 |
原子能技术 | 1029篇 |
自动化技术 | 12697篇 |
出版年
2024年 | 370篇 |
2023年 | 1371篇 |
2022年 | 2574篇 |
2021年 | 3563篇 |
2020年 | 2502篇 |
2019年 | 2105篇 |
2018年 | 2358篇 |
2017年 | 2801篇 |
2016年 | 2455篇 |
2015年 | 3396篇 |
2014年 | 4445篇 |
2013年 | 5665篇 |
2012年 | 6040篇 |
2011年 | 6751篇 |
2010年 | 5857篇 |
2009年 | 5649篇 |
2008年 | 5585篇 |
2007年 | 5347篇 |
2006年 | 5122篇 |
2005年 | 4178篇 |
2004年 | 2844篇 |
2003年 | 2349篇 |
2002年 | 2370篇 |
2001年 | 2025篇 |
2000年 | 1912篇 |
1999年 | 1939篇 |
1998年 | 1826篇 |
1997年 | 1576篇 |
1996年 | 1411篇 |
1995年 | 1185篇 |
1994年 | 923篇 |
1993年 | 761篇 |
1992年 | 607篇 |
1991年 | 462篇 |
1990年 | 385篇 |
1989年 | 298篇 |
1988年 | 252篇 |
1987年 | 182篇 |
1986年 | 152篇 |
1985年 | 139篇 |
1984年 | 100篇 |
1983年 | 75篇 |
1982年 | 68篇 |
1981年 | 59篇 |
1980年 | 51篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 54篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
印刷术的发明是中国人的骄傲。从1041年毕升发明活字印刷算起,经历了近千年的磨砺。“当代毕升”王选教授研制成功的中国汉字北大方正印前桌面系统,彻底淘汰了热排,淘汰了铅与火,改写了印前排版的历史,成为近代印刷的里程碑。虽然王选先生永远地离开了我们,但他对我国出版印刷事业所作的贡献将飚炳史册,光耀千秋。 相似文献
62.
从做大到做强的主体是PCB企业(集团) 中国PCB工业如何从做大到做强!(6) 总被引:2,自引:2,他引:0
从做大到做强是中国PCB工业的唯一出路.而做强中国PCB工业的主体是中国的PCB企业(集团).只有大多数的中国PCB企业做大并做强了,中国PCB工业才能称得上是PCB强国. 相似文献
63.
64.
The approach to risk management for RF and microwave radiation has been to establish guidelines for maximum permissible levels of exposure. These guidelines are based on evaluations of the relevant scientific literature and, with safety margins to account for uncertainties and gaps in scientific knowledge, offer a significant level of protection against established hazards of RF and microwave radiation for short-term exposures. One can argue, on this basis, that the precautionary principle - specifically, safety factors -have been used to guide the making and promulgation of existing permissible-exposure standards for RF and microwave radiation. Therefore, discussions on the appropriateness of the precautionary principle for RF radiation may be "much ado about nothing". Clearly, this approach to "pre caution" neither has stifled technological development, nor has it helped to enforce the acceptance of zero risk, but it provided a basis for action when science was unable to give a clear answer. 相似文献
65.
This article presents a graph-theoretic method for constructing low-density parity-check (LDPC) codes from connected graphs without the requirement of large girth. This method is based on finding a set of paths in a connected graph, which satisfies the constraint that any two paths in the set are either disjoint or cross each other at one and only one vertex. Two trellis-based algorithms for finding these paths are devised. Good LDPC codes of practical lengths are constructed and they perform well with iterative decoding. 相似文献
66.
Yen-Shin Lai Juo-Chiun Lin 《Power Electronics, IEEE Transactions on》2003,18(5):1211-1219
A new hybrid fuzzy controller for direct torque control (DTC) induction motor drives is presented in this paper. The newly developed hybrid fuzzy control law consists of proportional-integral (PI) control at steady state, PI-type fuzzy logic control at transient state, and a simple switching mechanism between steady and transient states, to achieve satisfied performance under steady and transient conditions. The features of the presented new hybrid fuzzy controller are highlighted by comparing the performance of various control approaches, including PI control, PI-type fuzzy logic control (FLC), proportional-derivative (PD) type FLC, and combination of PD-type FLC and I control, for DTC-based induction motor drives. The pros and cons of these controllers are demonstrated by intensive experimental results. It is shown that the presented induction motor drive is with fast tracking capability, less steady state error, and robust to load disturbance while not resorting to complicated control method or adaptive tuning mechanism. Experimental results derived from a test system are presented confirming the above-mentioned claims. 相似文献
67.
Chun-Tsen Lu Kun-Wei Lin Huey-Ing Chen Hung-Ming Chuang Chun-Yuan Chen Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(6):390-392
A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated. 相似文献
68.
69.
厂内一台B25汽轮机,因振动超差,进行了20个月的分析、计算和试验,最后发现中心孔内有250 g左右的油水化合物,造成转子热弯曲,激发汽轮机出现振动严重超标. 相似文献
70.