全文获取类型
收费全文 | 207031篇 |
免费 | 15544篇 |
国内免费 | 7875篇 |
专业分类
电工技术 | 11367篇 |
技术理论 | 14篇 |
综合类 | 11286篇 |
化学工业 | 35939篇 |
金属工艺 | 10604篇 |
机械仪表 | 12109篇 |
建筑科学 | 16474篇 |
矿业工程 | 4970篇 |
能源动力 | 5888篇 |
轻工业 | 12829篇 |
水利工程 | 3256篇 |
石油天然气 | 11217篇 |
武器工业 | 1352篇 |
无线电 | 25578篇 |
一般工业技术 | 26832篇 |
冶金工业 | 10983篇 |
原子能技术 | 2141篇 |
自动化技术 | 27611篇 |
出版年
2024年 | 892篇 |
2023年 | 3301篇 |
2022年 | 5894篇 |
2021年 | 8002篇 |
2020年 | 5859篇 |
2019年 | 5054篇 |
2018年 | 5467篇 |
2017年 | 6247篇 |
2016年 | 5727篇 |
2015年 | 7356篇 |
2014年 | 9592篇 |
2013年 | 12361篇 |
2012年 | 12324篇 |
2011年 | 13983篇 |
2010年 | 11702篇 |
2009年 | 11542篇 |
2008年 | 10954篇 |
2007年 | 10515篇 |
2006年 | 10923篇 |
2005年 | 9672篇 |
2004年 | 6604篇 |
2003年 | 5815篇 |
2002年 | 5270篇 |
2001年 | 4749篇 |
2000年 | 4894篇 |
1999年 | 5663篇 |
1998年 | 5303篇 |
1997年 | 4369篇 |
1996年 | 3967篇 |
1995年 | 3322篇 |
1994年 | 2770篇 |
1993年 | 2189篇 |
1992年 | 1703篇 |
1991年 | 1278篇 |
1990年 | 1019篇 |
1989年 | 877篇 |
1988年 | 681篇 |
1987年 | 499篇 |
1986年 | 394篇 |
1985年 | 335篇 |
1984年 | 212篇 |
1983年 | 198篇 |
1982年 | 163篇 |
1981年 | 145篇 |
1980年 | 132篇 |
1979年 | 97篇 |
1978年 | 63篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
针对电信运营商在构建内部数据通信网(DCN)时遇到的各应用系统的隔离问题,详细介绍了目前几种主流的虚拟专用网(VPN)技术,并进行分析比较,最后提出了运营商内部数据通信网的VPN解决方案。 相似文献
34.
Chih-Ming Chen Hahn-Ming Lee Chia-Chen Tan 《Engineering Applications of Artificial Intelligence》2006,19(8):967-978
The explosion of on-line information has given rise to many manually constructed topic hierarchies (such as Yahoo!!). But with the current growth rate in the amount of information, manual classification in topic hierarchies results in an immense information bottleneck. Therefore, developing an automatic classifier is an urgent need. However, classifiers suffer from enormous dimensionality, since the dimensionality is determined by the number of distinct keywords in a document corpus. More seriously, most classifiers are either working slowly or they are constructed subjectively without any learning ability. In this paper, we address these problems with a fair feature-subset selection (FFSS) algorithm and an adaptive fuzzy learning network (AFLN) for classification. The FFSS algorithm is used to reduce the enormous dimensionality. It not only gives fair treatment to each category but also has ability to identify useful features, including both positive and negative features. On the other hand, the AFLN provides extremely fast learning ability to model the uncertain behavior for classification so as to correct the fuzzy matrix automatically. Experimental results show that both FFSS algorithm and the AFLN lead to a significant improvement in document classification, compared to alternative approaches. 相似文献
35.
36.
Chun-Yuan Chen Shiou-Ying Cheng Wen-Hui Chiou Hung-Ming Chuang Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(3):126-128
A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications. 相似文献
37.
38.
Hao Wang Ying Lin Biao Chen 《Signal Processing, IEEE Transactions on》2003,51(10):2613-2623
We investigate non data-aided channel estimation for cyclically prefixed orthogonal frequency division multiplexing (OFDM) systems. By exploiting channel diversity using only two receive antennas, a blind deterministic algorithm is proposed. Identifiability conditions are derived that guarantee the perfect channel retrieval in the absence of noise. In the presence of noise, the proposed method has the desired property of being data efficient-only a single OFDM block is needed to achieve good estimation performance for a wide range of SNR values. The algorithm is also robust to input symbols as it does not have any restriction on the input symbols with regard to their constellation or their statistical properties. In addition, this diversity-based algorithm is computationally efficient, and its performance compares favorably to most existing blind algorithms. 相似文献
39.
40.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献