全文获取类型
收费全文 | 38010篇 |
免费 | 4072篇 |
国内免费 | 2492篇 |
专业分类
电工技术 | 2934篇 |
技术理论 | 2篇 |
综合类 | 5898篇 |
化学工业 | 2743篇 |
金属工艺 | 1244篇 |
机械仪表 | 2110篇 |
建筑科学 | 2287篇 |
矿业工程 | 1174篇 |
能源动力 | 1204篇 |
轻工业 | 1083篇 |
水利工程 | 1725篇 |
石油天然气 | 2992篇 |
武器工业 | 862篇 |
无线电 | 5454篇 |
一般工业技术 | 6342篇 |
冶金工业 | 759篇 |
原子能技术 | 668篇 |
自动化技术 | 5093篇 |
出版年
2024年 | 119篇 |
2023年 | 395篇 |
2022年 | 828篇 |
2021年 | 894篇 |
2020年 | 924篇 |
2019年 | 925篇 |
2018年 | 949篇 |
2017年 | 1061篇 |
2016年 | 1240篇 |
2015年 | 1202篇 |
2014年 | 1894篇 |
2013年 | 2206篇 |
2012年 | 2565篇 |
2011年 | 2728篇 |
2010年 | 2165篇 |
2009年 | 2243篇 |
2008年 | 2095篇 |
2007年 | 2546篇 |
2006年 | 2463篇 |
2005年 | 1978篇 |
2004年 | 1733篇 |
2003年 | 1624篇 |
2002年 | 1277篇 |
2001年 | 1083篇 |
2000年 | 1088篇 |
1999年 | 1000篇 |
1998年 | 848篇 |
1997年 | 729篇 |
1996年 | 674篇 |
1995年 | 614篇 |
1994年 | 504篇 |
1993年 | 437篇 |
1992年 | 359篇 |
1991年 | 284篇 |
1990年 | 250篇 |
1989年 | 196篇 |
1988年 | 145篇 |
1987年 | 75篇 |
1986年 | 51篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 20篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A damage identification technique for CF/EP composite laminates using distributed piezoelectric transducers 总被引:8,自引:0,他引:8
In this study, a damage identification approach was developed for carbon fibre/epoxy composite laminates with localized internal delamination. Propagation of the Lamb wave in laminates and its interaction with the delamination were examined. The fundamental symmetric Lamb wave mode, S0, and the lowest order shear wave mode, S0′, were chosen to predict damage location. A real-time active diagnosis system was therefore established. This technique uses distributed piezoelectric transducers to generate and monitor the ultrasonic Lamb wave with narrowband frequency. The two-way switches were employed to minimize the number of transducers. A signal-processing scheme based on the time–frequency spectrographic analysis was utilised to extract useful diagnostic information. Also, an optimal identification method was applied on damage searching procedure to reduce errors and obtain the diagnostic results promptly. Experiments were conducted on [0/−45/45/90]s CF/EP laminates to verify this diagnosis system. The results obtained show that satisfactory detection accuracy could be achieved. 相似文献
92.
本文将等效介电常数近似分析方法在应用范围和处理方法上进行了一些改进.发展为双等效介电常数近似分析法,然后用它来分析矩形介质波导阵列.推得两个一维周期的耦合特征方程。如果将Macatili方法应用范围扩展用来研究该波导阵列也会得到同样的结果,它们都能在二维平面上较准确地反应出通带和阻带等主要周期特性。 相似文献
93.
The effect of the charge fluctuation of dust particles on ion acoustic wave (IAW) excited through ionization instability was investigated. The hydrodynamic equations and linear time-dependent perturbation theory served as the starting point of theory, by which the dispersion relation and growth rate of the IAW were given. By comparing the results with the case of constant dust charges, it was found that the charge fluctuation of dust particles reduces the instability of the wave mode. 相似文献
95.
Rahul Sarpeshkar Richard F. Lyon Carver Mead 《Analog Integrated Circuits and Signal Processing》1998,16(3):245-274
Low-power wide-dynamic-range systems are extremely hard to build. The biological cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts. In this paper, we describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, and that dissipates 0.5 mW. This 117-stage, 100 Hz to 10 KHz cochlea has the widest dynamic range of any artificial cochlea built to date. The wide dynamic range is attained through the use of a wide-linear-range transconductance amplifier, of a low-noise filter topology, of dynamic gain control (AGC) at each cochlear stage, and of an architecture that we refer to as overlapping cochlear cascades. The operation of the cochlea is made robust through the use of automatic offset-compensation circuitry. A BiCMOS circuit approach helps us to attain nearly scale-invariant behavior and good matching at all frequencies. The synthesis and analysis of our artificial cochlea yields insight into why the human cochlea uses an active traveling-wave mechanism to sense sounds, instead of using bandpass filters. The low power, wide dynamic range, and biological realism make our cochlea well suited as a front end for cochlear implants. 相似文献
96.
本文应用声波时差测井资料判别划分地层压实异常段,并结合其它测井资料对盖层进行质量评估,寻找油气有利聚集带(段),为勘探提供有利区域和评价依据。 相似文献
97.
98.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a. 相似文献
99.
A two-dimensional plane strain finite element model with absorbing boundary condition has been developed to investigate the ultrasonic wave propagation in isotropic and orthotropic media. It is capable of simulating the experimental pulse echo technique to obtain A-scan data, when a short duration pulse is transmitted into a domain with or without a flaw. The flaw can either be a crack or an inclusion of different material such as a Teflon insert or a resin rich zone. After performing FFT on the A-scan data, frequency domain feature analysis is done. The study provides a guideline regarding the suitability of certain harmonics sensitive to certain types of flaw. The simulation shows other important artifacts of wave propagation such as mode conversion and scattering due to the presence of flaws. 相似文献
100.
耦合腔行波管慢波结构的工作模式及其特性 总被引:1,自引:0,他引:1
耦合腔行波管慢波结构可工作于三种不同模式:正常模、简并模和反向模。应用改进的等效电路法计算了正常模腔通带和槽通带。求得的简并模耦合槽张角与实验值相符。最后讨论了反向模耦合腔行波管诱人的特点。 相似文献