全文获取类型
收费全文 | 232543篇 |
免费 | 6652篇 |
国内免费 | 4001篇 |
专业分类
电工技术 | 7237篇 |
技术理论 | 6篇 |
综合类 | 4209篇 |
化学工业 | 28944篇 |
金属工艺 | 15089篇 |
机械仪表 | 12422篇 |
建筑科学 | 7824篇 |
矿业工程 | 2533篇 |
能源动力 | 5349篇 |
轻工业 | 11193篇 |
水利工程 | 2921篇 |
石油天然气 | 4663篇 |
武器工业 | 558篇 |
无线电 | 29257篇 |
一般工业技术 | 47946篇 |
冶金工业 | 33461篇 |
原子能技术 | 3124篇 |
自动化技术 | 26460篇 |
出版年
2024年 | 338篇 |
2023年 | 1251篇 |
2022年 | 2328篇 |
2021年 | 3195篇 |
2020年 | 2350篇 |
2019年 | 2211篇 |
2018年 | 11779篇 |
2017年 | 12587篇 |
2016年 | 7793篇 |
2015年 | 3761篇 |
2014年 | 4321篇 |
2013年 | 7945篇 |
2012年 | 8971篇 |
2011年 | 16293篇 |
2010年 | 15050篇 |
2009年 | 14241篇 |
2008年 | 13980篇 |
2007年 | 15946篇 |
2006年 | 6536篇 |
2005年 | 9403篇 |
2004年 | 6844篇 |
2003年 | 6051篇 |
2002年 | 4760篇 |
2001年 | 4289篇 |
2000年 | 3940篇 |
1999年 | 4214篇 |
1998年 | 10257篇 |
1997年 | 6859篇 |
1996年 | 5424篇 |
1995年 | 3677篇 |
1994年 | 3276篇 |
1993年 | 3064篇 |
1992年 | 1918篇 |
1991年 | 1814篇 |
1990年 | 1664篇 |
1989年 | 1451篇 |
1988年 | 1260篇 |
1987年 | 920篇 |
1986年 | 931篇 |
1985年 | 946篇 |
1984年 | 827篇 |
1983年 | 715篇 |
1982年 | 716篇 |
1981年 | 694篇 |
1980年 | 584篇 |
1979年 | 481篇 |
1978年 | 414篇 |
1977年 | 534篇 |
1976年 | 960篇 |
1975年 | 300篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
O. Perat J. M. Dorkel E. Scheid P. Temple Boyer Y. S. Chung A. Peyre-Lavigne M. Zecri P. Tounsi 《Microelectronics Reliability》2002,42(7):1053-1058
Reliability of thermomechanical simulations is critically linked to the accuracy of the mechanical properties that govern the behaviour of structure, like Young's modulus (E) and coefficient of thermal expansion (CTE). For many cases, the values found in literatures are dealing with bulk properties without detailed information on temperature effects. To address such issues, it is necessary to measure the materials parameters as a function of temperature. The measurement of CTE is usually accomplished by evaluating the thermal deflections of a subjected material layer deposited on a substrate, providing that E is known at a specific temperature of experiment. A bilayer method, based on theory of elasticity, is proposed to determine both E and CTE for a given temperature with a good resolution. This paper presents the theoretical analysis, the design and process of the microsystem test structures, and the main calculation results. 相似文献
102.
This paper analyzes probability of bit-error (Pe) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of Pe analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low Pe (< 10-3) or a prohibitively large computational complexity. The paper presents an alternate method of Pe analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P e performance, user capacity and the accuracy of the proposed method 相似文献
103.
Computing must become much more human centered--for example, by presenting personalized information to users and by respecting personal preferences when controlling multiple devices or invoking various services. Appropriate representation of the information's semantics and of the functionality of devices and services will be critical to such personalized computing. Symbolic artificial intelligence techniques provide the method of choice for the required semantic-representation and reasoning capabilities. 相似文献
104.
Moss C.D. Teixeira F.L. Yang Y.E. Jin Au Kong 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(1):178-186
A three-dimensional (3D) finite-difference time-domain (FDTD) scheme is introduced to model the scattering from objects in continuous random media. FDTD techniques have been previously applied to scattering from random rough surfaces and randomly placed objects in a homogeneous background, but little has been done to simulate continuous random media with embedded objects where volumetric scattering effects are important. In this work, Monte Carlo analysis is used in conjunction with FDTD to study the scattering from perfectly electrically conducting (PEC) objects embedded in continuous random media. The random medium models under consideration are chosen to be inhomogeneous soils with a spatially fluctuating random permittivities and prescribed correlation functions. The ability of frequency averaging techniques to discriminate objects in this scenarion is also briefly investigated. The simulation scheme described in this work can be adapted and used to help in interpreting the scattered field data from targets in random environments such as geophysical media, biological media, or atmospheric turbulence 相似文献
105.
The performance of a home made MIS–p-Si solar cell was experimentally studied under various gamma irradiation doses (up to 500 Mrad). The effect of radiation dose on the I−V and C−V characteristics was investigated in this work. The obtained results showed that all the output parameters of the cells under investigation were degraded with gamma radiation exposure. In addition, the effects of fabrication conditions (metal thickness and adding of antireflection coating) on the cell output parameters were also investigated. 相似文献
106.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
107.
108.
激光熔覆Ni基SiC合金涂层组织与性能的研究 总被引:5,自引:0,他引:5
利用5kWCO2连续波激光器在16Mn钢基材表面对含20%(体积比)SiC陶瓷粉末的镍基自熔性合金粉末进行激光熔覆得到Ni基SiC合金涂层(NiSiC)。研究了合金涂层的组织形貌及相结构,并用单纯的镍基合金涂层(Ni60)进行了显微硬度及滑动磨损性能的对比试验。结果表明,NiSiC合金涂层由γ枝晶及其间的共晶组织组成,主要组成相为γ-Ni,γ-(Ni,Fe)固溶体和(Cr,Fe)7C3,Cr23C6及(Cr,Si)3Ni3Si等化合物。添加SiC的镍基合金涂层NiSiC比单纯的镍基合金涂层Ni60具有较高的硬度和耐磨性。 相似文献
109.
摩托罗拉微控制器(MCU)具有编程语言简单、外围设备齐全、存储器模型用户友好、选择广及供应多、性能价格比高等优点,被设计者评为最容易使用的产品之一。在全球顶级的原始设备制造厂商(OEM)的无数嵌入式系统和用户最终产品中都可找到摩托罗拉的MCU,包括键盘、传呼机、电子游戏机、洗衣机、安全系统及汽车等。 相似文献
110.