全文获取类型
收费全文 | 82843篇 |
免费 | 10750篇 |
国内免费 | 12046篇 |
专业分类
系统科学 | 4593篇 |
丛书文集 | 1822篇 |
教育与普及 | 369篇 |
理论与方法论 | 234篇 |
现状及发展 | 609篇 |
研究方法 | 31篇 |
综合类 | 97978篇 |
自然研究 | 3篇 |
出版年
2024年 | 259篇 |
2023年 | 535篇 |
2022年 | 1103篇 |
2021年 | 1501篇 |
2020年 | 1865篇 |
2019年 | 3992篇 |
2018年 | 4133篇 |
2017年 | 4509篇 |
2016年 | 4754篇 |
2015年 | 5269篇 |
2014年 | 6182篇 |
2013年 | 5863篇 |
2012年 | 5794篇 |
2011年 | 5754篇 |
2010年 | 6053篇 |
2009年 | 5791篇 |
2008年 | 5473篇 |
2007年 | 5686篇 |
2006年 | 4796篇 |
2005年 | 4220篇 |
2004年 | 4006篇 |
2003年 | 3070篇 |
2002年 | 3119篇 |
2001年 | 2497篇 |
2000年 | 1999篇 |
1999年 | 1254篇 |
1998年 | 691篇 |
1997年 | 703篇 |
1996年 | 486篇 |
1995年 | 384篇 |
1994年 | 441篇 |
1993年 | 581篇 |
1992年 | 529篇 |
1991年 | 541篇 |
1990年 | 380篇 |
1989年 | 277篇 |
1988年 | 339篇 |
1987年 | 183篇 |
1986年 | 213篇 |
1985年 | 96篇 |
1984年 | 47篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1977年 | 23篇 |
1972年 | 67篇 |
1969年 | 10篇 |
1968年 | 11篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
利用有限元软件ANSYS/DYNA,模拟了悬臂和简支钢管混凝土构件的侧向冲击数值,计算了动塑性极限弯矩。 相似文献
192.
唐嫦燕 《科技情报开发与经济》2007,17(5):90-92
从国家信息化战略目标、信息政策、信息文化、信息技术、信息伦理道德5个因素入手,分别探讨了它们对信息化法制建设的支撑作用。 相似文献
193.
孙雪姣 《烟台师范学院学报(自然科学版)》2007,23(1):45-49
提出了动车段信息化管理系统的概念,阐述了建设该系统的意义,并对动车段信息化管理系统的框架进行了分析,详细介绍了各个功能模块的设计思路和实现的业务方案。 相似文献
194.
195.
文章利用现代化的教学理念构建以提高学生科学素养为宗旨,以培养学生的创新能力为主线,创设了大学化学实验教学新体系.并对大学化学实验教学活动如何以学生为中心,重视学科间联系,加强科学、技术与社会相统一,实验的绿色化和实验及教学的评价等问题提出了建议,总结了实践经验。 相似文献
196.
A theoretical model for mid-and low-latitude ionospheric electric fields in realistic geomagnetic fields 总被引:1,自引:1,他引:0
The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere. 相似文献
197.
Dot pattern is a type of pattern defined by specific spatial relationship among some dots. As a compensation for concrete and meaningful visual stimuli, meaningless dot pattern can be used as stimuli in learning tasks. We performed an experiment for exploring the perceptual learning process of dot pattern against random-dot background. Participants were required to learn two types of dot patterns (9-dot and 11-dot). They were assigned to two groups: participants in Group 1 learned 9-dot pattern first and 11-dot pattern later, while those in Group 2 learned 11-dot pattern first and 9-dot pattern later. The results showed that participants could acquire the spatial relationship of dot pattern through perceptual learning in relatively short learning time. In comparison with 9-dot pattern, learning time of 11-dot pattern was slightly longer and its accuracy rate lower, but there was significant positive transfer effect from 11-dot pattern learning to 9-dot learning. 相似文献
198.
A New Discipline of Science-The Study of Open Complex Giant System and Its Methodology 总被引:2,自引:0,他引:2
Qian XuesenChina Association for Science Technology Beijing ChinaYu JingyuanBeijing Institute of Information Control P.O.Box Beijing ChinaDai RuweiInstitute of Automation Chinese Academy of Sciences Beijing China 《系统工程与电子技术(英文版)》1993,(2)
This paper introduces the conception of open complex giant system and the methodology for dealing with the system, with stress on its profound significance in development of science and technology. The authors conclude that the reductionism underlying the exact science is not suitable to open complex giant system, and the only feasible alternative is the meta-synthetic engineering from the qualitative to the quantitative. 相似文献
199.
王文超 《系统工程与电子技术》1992,(9)
固体导弹由于测压、安全、关机与点火等的需要,采用的管路系统越来越多、越来越复杂,本文讨论了避免采用管路系统的重要性、可能性与具体方案,提出应严格制定并不断完善研制规范、加强管路系统的地面试验。 相似文献
200.
A. Farina A. ProtopapaRadar Dpt Selenia S. p. A. Via Tiburtina Km. - Rome Italy 《系统工程与电子技术(英文版)》1992,(3)
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems. 相似文献