全文获取类型
收费全文 | 12138篇 |
免费 | 842篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 203篇 |
综合类 | 25篇 |
化学工业 | 2671篇 |
金属工艺 | 338篇 |
机械仪表 | 638篇 |
建筑科学 | 249篇 |
矿业工程 | 12篇 |
能源动力 | 477篇 |
轻工业 | 920篇 |
水利工程 | 45篇 |
石油天然气 | 26篇 |
武器工业 | 2篇 |
无线电 | 2233篇 |
一般工业技术 | 2422篇 |
冶金工业 | 1039篇 |
原子能技术 | 147篇 |
自动化技术 | 1555篇 |
出版年
2023年 | 104篇 |
2022年 | 141篇 |
2021年 | 213篇 |
2020年 | 204篇 |
2019年 | 261篇 |
2018年 | 316篇 |
2017年 | 273篇 |
2016年 | 412篇 |
2015年 | 346篇 |
2014年 | 522篇 |
2013年 | 849篇 |
2012年 | 724篇 |
2011年 | 851篇 |
2010年 | 625篇 |
2009年 | 703篇 |
2008年 | 621篇 |
2007年 | 513篇 |
2006年 | 494篇 |
2005年 | 439篇 |
2004年 | 402篇 |
2003年 | 379篇 |
2002年 | 393篇 |
2001年 | 298篇 |
2000年 | 271篇 |
1999年 | 274篇 |
1998年 | 501篇 |
1997年 | 323篇 |
1996年 | 247篇 |
1995年 | 188篇 |
1994年 | 145篇 |
1993年 | 152篇 |
1992年 | 86篇 |
1991年 | 97篇 |
1990年 | 81篇 |
1989年 | 73篇 |
1988年 | 56篇 |
1987年 | 53篇 |
1986年 | 45篇 |
1985年 | 38篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 19篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 34篇 |
1975年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
M.H. Song B. Park S. Nishimura T. Toyooka I.J. Chung Y. Takanishi K. Ishikawa H. Takezoe 《Advanced functional materials》2006,16(14):1793-1798
A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage. 相似文献
82.
83.
84.
Sung Ho Jeong Joon Jeong Yi Jong Keun Kim Man Yeong Ha 《Journal of Mechanical Science and Technology》1991,5(1):16-21
A computer program to calculate the strip temperature heated in the continuous annealing furnace was developed, using the
zone method for radiative heat transfer analysis with the measured gas temperature in the furnace. Using theF
E Operator, the present study considered the effects of soot and transient species, in addition to the H2O−CO2 gas mixture on the gas radiative heat transfer. The predicted strip temperature distribution forF
E=1.05 represented well the measured data. The maximum difference in the heat flux transfered to the strip from the combustion
gas forF
E=1.0 (without soot and transient species gas radiation) and 1.05 (with soot and transient species gas radiation) was about
15%. The present study also investigated the effects of line speed and thickness variations on the strip temperature, establishing
the bases for the on-line computer model. 相似文献
85.
Summary Cyclic tris(ethylene terephthalate) (CTET) was separated from oligomeric extract of poly(ethylene terephthalate) by the conventional solvent separation method. The structure of CTET was characterized by differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. It is shown that the double melting behavior of meltcrystallized CTET is attributed to the morphological change created by heat-treatment. The effect of the morphological change on the crystal structure of CTET was also examined. 相似文献
86.
The notion of pseudorandomness is the theoretical foundation on which to consider the soundness of a basic structure used in some block ciphers. We examine the pseudorandomness of the block cipher KASUMI, which will be used in the next‐generation cellular phones. First, we prove that the four‐round unbalanced MISTY‐type transformation is pseudorandom in order to illustrate the pseudorandomness of the inside round function FI of KASUMI under an adaptive distinguisher model. Second, we show that the three‐round KASUMI‐like structure is not pseudorandom but the four‐round KASUMI‐like structure is pseudorandom under a non‐adaptive distinguisher model. 相似文献
87.
88.
We address the problem of computing fundamental performance bounds for estimation of object boundaries from noisy measurements in inverse problems, when the boundaries are parameterized by a finite number of unknown variables. Our model applies to multiple unknown objects, each with its own unknown gray level, or color, and boundary parameterization, on an arbitrary known background. While such fundamental bounds on the performance of shape estimation algorithms can in principle be derived from the Cramer-Rao lower bounds, very few results have been reported due to the difficulty of computing the derivatives of a functional with respect to shape deformation. We provide a general formula for computing Cramer-Rao lower bounds in inverse problems where the observations are related to the object by a general linear transform, followed by a possibly nonlinear and noisy measurement system. As an illustration, we derive explicit formulas for computed tomography, Fourier imaging, and deconvolution problems. The bounds reveal that highly accurate parametric reconstructions are possible in these examples, using severely limited and noisy data. 相似文献
89.
Hydrogen is considered to be the most important future energy carrier in many applications reducing significantly greenhouse gas emissions, but the safety issues associated with hydrogen applications need to be investigated and fully understood to be applicable as the carrier. Generally, the locations of hydrogen production and consumption are different. Hydrogen must be transported from the point of production to the point of use. Pipeline delivery is cheaper than all other methods for large quantities of hydrogen. The rupture of a hydrogen pipeline can lead to outcomes that can pose a significant threat to people and property in the immediate vicinity of the failure point. In this work, a simplified equation of hazard analysis is proposed for the pipeline transporting hydrogen, which relates the diameter, the operating pressure and the length of the pipeline to the size of the affected area in the event of a failure of the pipeline. The dominant hazards are thermal radiation from sustained fire and shock pressure from gas cloud explosion. For a transmission pipeline of hydrogen gas, the hazard area from the fire is slightly larger than by the other event. The hazard area is directly proportional to the operating pressure raised to the power one-half, and to the pipeline diameter. This simplified equation to estimate the hazard area will be a useful tool for safety management of hydrogen gas transmission pipelines. 相似文献
90.
STATIONARY AND NON-STATIONARY STATE SPACE MODELS 总被引:1,自引:0,他引:1
Abstract. The concepts of time invariance, stationarity, non-stationarity and immemorial time are considered for state space models (SSMs). Necessary and sufficient conditions for stationarity are given and connected with standard conditions. Expressions are given for the unconditional mean and covariance matrix of the state of a time-immemorial SSM. Application of the results is made to a variety of theoretical and empirical models and the initialization of the Kalman filter in the non-stationary case and for the ARIMA ( p, d, q ) model. 相似文献