全文获取类型
收费全文 | 37079篇 |
免费 | 4843篇 |
国内免费 | 2429篇 |
专业分类
电工技术 | 3400篇 |
技术理论 | 3篇 |
综合类 | 2752篇 |
化学工业 | 5118篇 |
金属工艺 | 2033篇 |
机械仪表 | 2612篇 |
建筑科学 | 2637篇 |
矿业工程 | 1440篇 |
能源动力 | 1051篇 |
轻工业 | 3188篇 |
水利工程 | 1056篇 |
石油天然气 | 1530篇 |
武器工业 | 484篇 |
无线电 | 4515篇 |
一般工业技术 | 3893篇 |
冶金工业 | 2727篇 |
原子能技术 | 475篇 |
自动化技术 | 5437篇 |
出版年
2024年 | 263篇 |
2023年 | 845篇 |
2022年 | 1835篇 |
2021年 | 2384篇 |
2020年 | 1783篇 |
2019年 | 1321篇 |
2018年 | 1483篇 |
2017年 | 1816篇 |
2016年 | 1498篇 |
2015年 | 2167篇 |
2014年 | 2596篇 |
2013年 | 2874篇 |
2012年 | 3226篇 |
2011年 | 3206篇 |
2010年 | 2639篇 |
2009年 | 2237篇 |
2008年 | 2181篇 |
2007年 | 1850篇 |
2006年 | 1440篇 |
2005年 | 1146篇 |
2004年 | 787篇 |
2003年 | 625篇 |
2002年 | 618篇 |
2001年 | 517篇 |
2000年 | 364篇 |
1999年 | 285篇 |
1998年 | 546篇 |
1997年 | 395篇 |
1996年 | 272篇 |
1995年 | 189篇 |
1994年 | 173篇 |
1993年 | 138篇 |
1992年 | 84篇 |
1991年 | 56篇 |
1990年 | 50篇 |
1989年 | 66篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 40篇 |
1985年 | 30篇 |
1984年 | 9篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 29篇 |
1976年 | 73篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Uncertainties existing in the acoustic metamaterial may strongly affect its unusual properties. Aiming at this actuality, the interval model is introduced to treat with uncertainties existing in the acoustic metamaterial with Helmholtz resonators. Frequency intervals in which the sound intensity transmission coefficients are certainly less than the required value and the effective bulk moduli are certainly negative are defined as conservative approximations. Frequency intervals in which the sound intensity transmission coefficients may be less than the required value and the effective bulk moduli may be negative are defined as unsafe approximations. The proportion of the conservative approximation and the unsafe approximation is defined as an approximate precision. Based on the quantification of uncertainties of the sound intensity transmission coefficients and the negative effective bulk moduli, an optimization model for the interval acoustic metamaterial with Helmholtz resonators is constructed. Numerical results showed that even suffering from effects of interval parameters, unusual properties of the optimized acoustic metamaterial (such as the bandgap of the sound transmission and the negative effective bulk modulus) could be improved. 相似文献
102.
A hybrid remotely operated underwater vehicle (HROV) capable of working to the full ocean depth has been developed. In order for the vehicle to achieve a certain survivability level, a self-repairing control system (SRCS) has been designed. It consists of two basic technologies, fault diagnosis and isolation (FDI) and reconfigurable control. For F'DI, a model-based hierarchical fault diagnosis system is designed for the HROV. Then, control strategies which reconfigure the control system at intervals according to information from the FDI system are presented. Combining the two technologies, it can obtain the fundamental frame of SRCS for the HROV. Considering the hazardous underwater environment at the limiting depth and the hybrid operating modes, an assessment of the HROV' s survivability is vitally needed before it enters operational service. This paper presents a new definition of survivability for underwater vehicles and develops a simple survivability model for the SRCS. As a result of survivability assessment for the SRCS, we are able to figure out the survivability of SRCS and make further optimization about it. The methodology developed herein is also applicable to other types of underwater vehicles. 相似文献
103.
104.
介绍了未确知有理数的概念,分析了未确知有理数与随机数的关系,给出了未确知有理数的加减运算。以齿轮模数的测定研究了未确知有理数在机械工程中的应用。 相似文献
105.
106.
107.
108.
YJS-02型液压实验系统的PLC改造 总被引:1,自引:0,他引:1
本文主要介绍了YJS-02型液压实验系统的PLC改造及其系统设计。 相似文献
109.
Using capacitance measurement and Mott-Schottky analysis, the semiconducting properties of passive films formed on chromium within the passive potential range under different conditions were investigated. The study reveals a p-type behavior of the passive layers. Two semiconductive parameters, i.e., the acceptor density (NA) and the flatband potential (EFB), which are mainly related to composition and surface charges of the passive films, have been measured. The effect of film formation potential, passivation time, pH and composition of solutions on the parameters are discussed. NA increases either with lowering film formation potentials or with prolonging passivation times. This is attributed to the transformation of a less hydrated oxide film into a more hydrated form. The changes of EFB are discussed as a function of adsorptive anions and pH values of electrolyte solution. 相似文献
110.
结合滹沱河防洪综合整治工程,对钠基膨润土防水毯建立试验模型,着重研究不同试验水头、外界环境条件(温度、风力等因素)对钠基膨润土防水毯的渗水量、水分蒸发量和渗透系数的变化规律。研究结果表明:试验水头与渗透系数成非线性关系,且渗水量随水位的增加而增加,渗透系数随水位的增加而减小。通过模型试验验证了钠基膨润土防水毯高密实、高防水等特点,为类似的防洪综合整治工程提供了技术支撑。 相似文献