全文获取类型
收费全文 | 14978篇 |
免费 | 1739篇 |
国内免费 | 1237篇 |
专业分类
电工技术 | 1242篇 |
综合类 | 1934篇 |
化学工业 | 1877篇 |
金属工艺 | 570篇 |
机械仪表 | 777篇 |
建筑科学 | 1396篇 |
矿业工程 | 383篇 |
能源动力 | 489篇 |
轻工业 | 332篇 |
水利工程 | 449篇 |
石油天然气 | 503篇 |
武器工业 | 153篇 |
无线电 | 1815篇 |
一般工业技术 | 2068篇 |
冶金工业 | 317篇 |
原子能技术 | 148篇 |
自动化技术 | 3501篇 |
出版年
2024年 | 41篇 |
2023年 | 210篇 |
2022年 | 317篇 |
2021年 | 402篇 |
2020年 | 431篇 |
2019年 | 398篇 |
2018年 | 365篇 |
2017年 | 465篇 |
2016年 | 505篇 |
2015年 | 570篇 |
2014年 | 819篇 |
2013年 | 910篇 |
2012年 | 1121篇 |
2011年 | 1191篇 |
2010年 | 948篇 |
2009年 | 997篇 |
2008年 | 911篇 |
2007年 | 1099篇 |
2006年 | 949篇 |
2005年 | 824篇 |
2004年 | 719篇 |
2003年 | 626篇 |
2002年 | 529篇 |
2001年 | 497篇 |
2000年 | 369篇 |
1999年 | 284篇 |
1998年 | 235篇 |
1997年 | 200篇 |
1996年 | 182篇 |
1995年 | 148篇 |
1994年 | 129篇 |
1993年 | 82篇 |
1992年 | 76篇 |
1991年 | 83篇 |
1990年 | 67篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1973年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Masatoshi Hasegawa Mari Fujii Junichi Ishii Shinya Yamaguchi Eiichiro Takezawa Takashi Kagayama Atsushi Ishikawa 《Polymer》2014
A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high Tg's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films. 相似文献
992.
Identification and extraction of brain tumor from MRI using local statistics of Zernike moments
下载免费PDF全文
![点击此处可从《International journal of imaging systems and technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kiran Thapaliya Goo‐Rak Kwon 《International journal of imaging systems and technology》2014,24(4):284-292
In this article, a novel method is proposed for the detection of brain tumor in magnetic resonance images (MRIs). The features of Zernike moments are used to analyze the MRIs. The image is divided into two parts from the center of the image based on the average value of the pixel located at the center boundary, and new image vectors are formed to extract the tumor. The local statistics values obtained from the low and high order Zernike moments are used to calculate the appropriate threshold value for efficient tumor extraction. The proposed method successfully analyzes the tumor part of the image on testing with different MRIs. 相似文献
993.
Hiroshige Kumamaru 《Journal of Nuclear Science and Technology》2017,54(2):242-252
Three-dimensional numerical calculations have been performed on the magnetohydrodynamic (MHD) flows through a rectangular channel with sudden expansion, particularly in order to estimate the pressure drop through the sudden expansion. The sudden expansion is in the directions both perpendicular and parallel to the applied magnetic field. The Hartmann number, the Reynolds number and the magnetic Reynolds number are set to ~100, ~1000 and ~0.001, respectively, in simulating laboratory conditions. The continuity equation, the momentum equation and the induction equation were solved numerically by the finite difference method as discretization following the MAC method as solution procedure. On the whole, in the sudden expansion in the direction perpendicular to applied magnetic field, the loss coefficient is estimated to be nearly zero or small. In particular, the loss coefficient becomes negative for small aspect ratios. The reason of negative loss coefficient is attributable to decrease in the induced current just upstream of the expansion. On the other hand, in the sudden expansion in the direction of applied magnetic field, all the cases give positive and large loss coefficients, meaning that the pressure drop through the expansion becomes large. In particular, the loss coefficient becomes considerably large when the Hartmann number increases. 相似文献
994.
多信道共用方式电话线路扩容装置的研究 总被引:2,自引:1,他引:1
为解决电话线路紧张问题,采用多信道共用方式设计研制了电话线路扩容装置,阐述了电话线路扩容装置的工作原理,并分析了采用电话线路扩容装置后的呼损。 相似文献
995.
996.
The technology of pressure relief gas drainage is one of the most effective and economic for preventing gas emissions in underground mines. Based on current understanding of strata breakage and fracture development in overlying strata, the current study divides the overlying strata into the following three longitudinal zones in terms of the state of gas flow: a turbulent channel zone, a transitional circulation channel zone and a seepage channel zone. According to the key strata discrimination theory of controlling the overlying strata, the calculation method establishes that the step-type expansion of the mining gas channel corresponds to the advancing distance of working face, and this research also confirms the expanding rule that the mining gas channel in overlying strata follows the advancing distance of mining working face. Based on the geological conditions of Xinjing Coal Mine of Yangquan, this paper researches the expanding rule of mining gas channel as well as the control action of the channel acting on the pressure relief flow under the condition of the remote protective layer, and got the distance using inversion that the step-type expanding of mining gas channel is corresponding to the advancing distance of working face, which verifies the accuracy and feasibility of theoretical calculation method proposed in this study. The research provides the theoretical basis for choosing the technology of pressure relief gas drainage and designing the parameters of construction. 相似文献
997.
998.
严永仙 《杭州应用工程技术学院学报》2010,(3):164-169
从不等式的特点出发,应用实际范例给出了泰勒公式中展开点选取的几种情况:区间的中点,已知区间的两端点,函数的极值点或最值点,已知区间的任意点。同时对各种情况的运用范围和特点作了说明,以便更好地运用泰勒中值定理证明不等式。 相似文献
999.
1000.
Tapatee Kundu Roy Abhijit Ghosh Debasis Bhowmick Dirtha Sanyal Soumyajit Koley Alok Chakrabarti 《Ceramics International》2011,37(7):2679-2687
The ability of silica (SiO2) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO2 acts as a sintering inhibitor in the ZnO–SiO2 system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO2 to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO2 addition. It has been observed that SiO2 incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO2 doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO2 addition to ZnO. 相似文献