全文获取类型
收费全文 | 85228篇 |
免费 | 8540篇 |
国内免费 | 4803篇 |
专业分类
电工技术 | 8468篇 |
技术理论 | 7篇 |
综合类 | 10048篇 |
化学工业 | 4457篇 |
金属工艺 | 1280篇 |
机械仪表 | 3848篇 |
建筑科学 | 7111篇 |
矿业工程 | 3412篇 |
能源动力 | 1791篇 |
轻工业 | 6115篇 |
水利工程 | 3587篇 |
石油天然气 | 5491篇 |
武器工业 | 1328篇 |
无线电 | 15090篇 |
一般工业技术 | 4725篇 |
冶金工业 | 2619篇 |
原子能技术 | 409篇 |
自动化技术 | 18785篇 |
出版年
2024年 | 424篇 |
2023年 | 1163篇 |
2022年 | 2148篇 |
2021年 | 2631篇 |
2020年 | 2789篇 |
2019年 | 2170篇 |
2018年 | 2182篇 |
2017年 | 2561篇 |
2016年 | 3092篇 |
2015年 | 3408篇 |
2014年 | 5685篇 |
2013年 | 5152篇 |
2012年 | 6601篇 |
2011年 | 6858篇 |
2010年 | 5071篇 |
2009年 | 4952篇 |
2008年 | 4985篇 |
2007年 | 5764篇 |
2006年 | 5198篇 |
2005年 | 4653篇 |
2004年 | 3802篇 |
2003年 | 3512篇 |
2002年 | 2523篇 |
2001年 | 2164篇 |
2000年 | 1657篇 |
1999年 | 1477篇 |
1998年 | 1040篇 |
1997年 | 953篇 |
1996年 | 810篇 |
1995年 | 685篇 |
1994年 | 550篇 |
1993年 | 375篇 |
1992年 | 244篇 |
1991年 | 207篇 |
1990年 | 146篇 |
1989年 | 162篇 |
1988年 | 103篇 |
1987年 | 57篇 |
1986年 | 64篇 |
1985年 | 47篇 |
1984年 | 64篇 |
1983年 | 53篇 |
1982年 | 47篇 |
1981年 | 28篇 |
1980年 | 19篇 |
1979年 | 27篇 |
1977年 | 24篇 |
1964年 | 18篇 |
1959年 | 19篇 |
1956年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
Xiaofeng Liao Xueming Li Jun Pen Guanrong Chen 《International Journal of Communication Systems》2004,17(5):437-445
In this paper, a simple image secure communication scheme based on the chaotic Chebyshev map and chaos synchronization is proposed. The scheme relies on the excellent correlation property of chaotic sequences, which is very desirable for secure image communication. The results obtained by computer simulation indicate that the transmitted source image can be correctly and reliably recovered using the proposed scheme, even through a noisy channel. Notably, the scheme possesses relatively high security and can be easily implemented. Moreover, the quality of the recovered image is satisfactory, quantified by such common criteria as the bit‐error rate performance. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
94.
小功率行波管可靠性数字仿真的研究 总被引:1,自引:1,他引:0
基于对实际器件的测试数据,采用模糊数学和最可能故障法建立整个器件的可靠性模型.引入可靠性分布密度函数,将实际测试得到的离散数据拟合成随时间变化的连续函数,不仅可得到小功率行波管测试性能的评估,而且还可以对其可靠性进行预测;进一步研究,还可以给出预测的准确度概率.本文主要讨论小功率行波管可靠度评估模型的建立、数据处理与精度分析等,并对预测与准确度的概率给予简要的介绍. 相似文献
95.
Claudio Sacchi Gianluca Gera Carlo S. Regazzoni 《International Journal of Satellite Communications and Networking》2004,22(2):193-215
This paper aims at focusing on the aspects concerning the physical layer design for an innovative satellite communication experiment. Such an experiment, denoted by the acronym DAVID–DCE (Data and Video Interactive Distribution—Data Collection Experiment) is based on the exploitation of the W‐band (75–110 GHz) for high‐bit‐rate satellite transmission. The potential advantages of using of the W‐band are mainly related to the great bandwidth availability, and to the absence of interference. Moreover, an expected result of the experiment is a substantive improvement in the communication system's performances in the presence of meteorological phenomena (e.g. rain) as compared with the more conventional Ka‐band satellite transmission. On the other hand, problems to be faced concern the non‐ideal behaviours of hardware devices employed for high‐frequency digital transmission. In particular, carrier recovery and timing recovery are the most crucial signal‐processing tasks to be carefully considered in the design of the physical level of the system, because they considerably suffer from hardware impairments. The purpose of this work is to illustrate the proposed solutions in terms of the most critical modulation, demodulation and synchronization design issues, together with the effects of non‐ideal behaviours of hardware components on BER performances. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
K. Khalil J. C. Hand M. Mariswamy M. S. Obaidat 《International Journal of Communication Systems》1995,8(2):117-127
Since computer networks play an important role in distributed computing environments, an application's performance depends heavily on the quality of service provided by the communication networks. To ensure a high performance, the characteristics of wide area networks, WANs, must be well understood. This paper presents methodologies to characterize WAN traffic based on real measurements from Bellcore's backbone network that connects remote sites using dedicated T1 links. This paper also suggests some workload models that can be used for wide area network sizing and performance evaluation studies. It is found that the inter-site traffic pattern depends on the time of the day and the day of the week. Furthermore, the traffic between two sites is found to be reasonably symmetric, except for those sites designated as back-up sites. The coefficient of variation is used as a measure for the traffic burstiness and it is found to be 1·5 degree during working hours. The methods presented here are easy to use and cost-effective. 相似文献
97.
移动通信基站在高层建筑天台架设的定向天线,对周围环境的电磁辐射影响水平的监测进行分析,探讨高层建筑天台电磁辐射环境的污染防治对策。 相似文献
98.
Docherty Nancy M.; Cohen Alex S.; Nienow Tasha M.; Dinzeo Thomas J.; Dangelmaier Ruth E. 《Canadian Metallurgical Quarterly》2003,112(3):469
This study examined the degree to which different types of communication disturbances in the speech of 48 schizophrenia patients and 28 controls were variable and state related versus stable and traitlike. Clinically rated formal thought disorder and 5 types of referential disturbance showed substantial stability within participants over time. The sixth type of referential disturbance, the vague reference, was not stable over time. Formal thought disorder was associated with the severity of core psychotic symptoms in patients, whereas referential disturbances showed little or no association with positive or negative symptom severity. Furthermore, changes in psychotic symptoms over time were accompanied by corresponding changes in formal thought disorder but not referential disturbances. These results support the idea that some types of referential disturbances are traitlike and may be reflective of vulnerability as well as manifest illness. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
MCRC��ǻ��չ��ճ�̽ 总被引:1,自引:0,他引:1
本文根据MCRC引进装置的情况,对加拿大Delta公司的MCRC硫回收工艺作了初步探索,介绍了该方法的工艺特征,并评述了引进装置的性能考核结果。文中还结合四川气田建厂的环保要求,评价了MCRC方法的使用价值及意义。 相似文献
100.
作者结合实例,论述了氨罐保冷改造的设计、选材及施工,给出了改造后两年的测试结果,并对测试结果进行了分析。 相似文献