全文获取类型
收费全文 | 2648篇 |
免费 | 94篇 |
国内免费 | 146篇 |
专业分类
系统科学 | 96篇 |
丛书文集 | 72篇 |
教育与普及 | 67篇 |
理论与方法论 | 5篇 |
现状及发展 | 98篇 |
研究方法 | 51篇 |
综合类 | 2496篇 |
自然研究 | 3篇 |
出版年
2024年 | 11篇 |
2023年 | 15篇 |
2022年 | 40篇 |
2021年 | 61篇 |
2020年 | 37篇 |
2019年 | 14篇 |
2018年 | 40篇 |
2017年 | 40篇 |
2016年 | 29篇 |
2015年 | 59篇 |
2014年 | 68篇 |
2013年 | 45篇 |
2012年 | 90篇 |
2011年 | 128篇 |
2010年 | 90篇 |
2009年 | 115篇 |
2008年 | 121篇 |
2007年 | 113篇 |
2006年 | 114篇 |
2005年 | 94篇 |
2004年 | 96篇 |
2003年 | 126篇 |
2002年 | 143篇 |
2001年 | 147篇 |
2000年 | 122篇 |
1999年 | 144篇 |
1998年 | 78篇 |
1997年 | 94篇 |
1996年 | 70篇 |
1995年 | 69篇 |
1994年 | 59篇 |
1993年 | 60篇 |
1992年 | 52篇 |
1991年 | 61篇 |
1990年 | 48篇 |
1989年 | 46篇 |
1988年 | 49篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1980年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1965年 | 2篇 |
1958年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有2888条查询结果,搜索用时 15 毫秒
51.
1 Introduction
Over the past several years, the preparation and characterization ofnanoscale magnetic materials, especially one-dimensional (1D) nanostructure, have attracted much attention as the nanomaterials would allow investigating the fundamental aspects of magnetic-ordering phenomena in magnetic materials with reduced dimensions and could lead to new potential applications such as data storage technology[1-6]. 相似文献
52.
53.
As a newly developed precision technology, casting-forging complex near net forming process is utilized to produce complex components with a short lead time, low cost and high precision, thus to accelerate the response speed of the market and enhance the competitive power of products. In this paper, the casting-forging complex near net forming process of alternator claw pole was developed and investigated with a combination of experimental and numerical simulation method. Qualified near net workpiece was manufactured, mechanical parameter and relative field information during the forming process was also obtained. While the alternator claw-pole is processed with this technology, the forming force is small, the process is short and the quality of forgings is perfect. Therefore, the complex casting-forging near net forming process of claw-pole is an energy and material saving technology, which will have a vast developing and application prospect in the future. 相似文献
54.
Fracture toughness is very important when applying Damage Tolerance Design and Assessment Techniques. The traditional testing approach for obtaining fracture toughness values is costly and time consuming. In order to estimate the fracture toughness of ductile metals, the fracture mechanics theory, materials plastic deformation theory and materials constructive relationships are employed here. A series of formulae and a theoretical approach are presented to calculate fracture toughness values of different materials in the plane stress and plane strain conditions. Compared with test results, evaluated values have a good agreement. 相似文献
55.
MAOCheng-ying LUYan-sheng 《武汉大学学报:自然科学英文版》2004,9(5):687-693
As the increasing popularity and complexity of Web applications and the emergence of their new characteristics. the testing and maintenance of large, complex Web applications are becoming more complex and difficult. Web applications generally contain lots of pages and are used by enormous users. Statistical testing is an effective way of ensuring their quality. Web usage can be accurately described by Markov chain which has been proved to be an ideal model for software statistical testing. The results of unit testing can b eutilized in the latter stages, wbich is an important strategy for bottom-to-top integration testing, and the other improvement of extended Markov chain model (FMM) is to present the error type vector which is treated as a part of page node. This paper also proposes the algorithm for generating test cases of usage paths. Finally, optional usage reliability evaluation methods and an incremental usability regression testing model for testing and evaluation are presented. 相似文献
56.
Selective functionalization of mesoporous silica nanospheres (MSNs) is crucial for nanoengineering of MSNs.
Herein, we have combined “surface-protected etching strategy” and “cationic surfactant assisted etching
strategy” to prepare functionalized MSNs with externally attached amino groups. The externally attached NH2
groups endow the catalysts with excellent catalytic performance for nitroaldol reaction between nitromethane
and benzaldehyde. In addition, those NH2-MSNs can also be used to support gold nanoparticles, which display
very good catalytic performance for reduction of 4-nitrophenol. It can be envisioned that the synthesis protocol
developed in this work could also be extended to nanoengineered MSNs, which provides opportunities for nanoreactors
design. 相似文献
57.
一种并发Java程序控制流模型 总被引:1,自引:0,他引:1
研究了并发Java程序控制流模型的建模问题.通过深入分析并发Java程序设计语言的语义以及带抑止弧Petri网的建模能力,提出了一种并发Java程序控制流模型--CJCFM,并给出了从并发Java程序构造该模型的方法.CJCFM以带抑止弧Petri网为基础,简单直观,可模拟程序实际运行过程,对并发程序的理解、分析和测试有很大帮助.通过对现有开源Petri网实验平台PIPE的功能进行扩展,可在该平台中直接构造并执行CJCFM.借助成熟的Petri网理论与算法,可验证CJCFM的各种性质,从而达到对源程序进行分析的目的.实验表明:CJCFM能有效协助理解、分析和测试并发Java程序. 相似文献
58.
摘 要:PID控制器有着广泛的应用,其参数也有多种智能调整方法。本文分析了免疫系统的免疫网络理论,提出了一种用免疫网络理论调整PI控制器的策略,并用于永磁同步电机的直接转矩控制的调速系统,以克服电阻变化引起磁链控制器输出不准确,影响控制精度的问题。该策略计算简单,在永磁同步电机定子电阻变化较大情况下,仍具有高控制精度。仿真结果验证了这一免疫网络理论控制策略的有效性,并与一般PI控制和采用遗传算法的PI控制的效果进行了比较。 相似文献
59.
为进一步研究超高性能混凝土(ultra-high-performance concrete, UHPC)预制板加固钢筋混凝土(reinforced concrete, RC)梁的抗剪性能,开展了3根足尺RC梁的试验研究,包含1根对比梁和2根UHPC预制板加固梁,关注UHPC板及其内嵌CFRP板条对RC梁抗剪性能的影响。试验结果表明:试验梁均发生受剪破坏,但加固梁的承载力、刚度和延性均明显提高,其中,因内嵌CFRP板条提高了UHPC板的抗裂性能,极限荷载及对应位移分别提高了30.8%和28.5%;螺杆力学锚固发挥了侧向约束作用和销栓作用,在一定程度上提高了UHPC板的贡献。同时,通过建立非线性有限元模型对试验梁进行了数值分析,模拟结果与试验结果吻合度高,表明模型所选的本构关系及相关参数合理,可用于预测UHPC板加固RC梁的全过程受力行为。 相似文献
60.
根据TM S320C 5402的特点,提出了采用G.723.1语音编解码算法设计的语音压缩系统.给出了系统的硬件结构和软件流程,及A/D、D/A模块与DSP接口电路的设计方法.该系统具有很强的实时性和实用性. 相似文献