全文获取类型
收费全文 | 5207篇 |
免费 | 673篇 |
国内免费 | 287篇 |
专业分类
电工技术 | 446篇 |
技术理论 | 1篇 |
综合类 | 265篇 |
化学工业 | 859篇 |
金属工艺 | 366篇 |
机械仪表 | 399篇 |
建筑科学 | 581篇 |
矿业工程 | 136篇 |
能源动力 | 163篇 |
轻工业 | 261篇 |
水利工程 | 107篇 |
石油天然气 | 323篇 |
武器工业 | 52篇 |
无线电 | 582篇 |
一般工业技术 | 680篇 |
冶金工业 | 177篇 |
原子能技术 | 69篇 |
自动化技术 | 700篇 |
出版年
2024年 | 40篇 |
2023年 | 113篇 |
2022年 | 212篇 |
2021年 | 379篇 |
2020年 | 266篇 |
2019年 | 179篇 |
2018年 | 182篇 |
2017年 | 239篇 |
2016年 | 181篇 |
2015年 | 252篇 |
2014年 | 270篇 |
2013年 | 323篇 |
2012年 | 360篇 |
2011年 | 362篇 |
2010年 | 331篇 |
2009年 | 324篇 |
2008年 | 286篇 |
2007年 | 248篇 |
2006年 | 266篇 |
2005年 | 199篇 |
2004年 | 175篇 |
2003年 | 118篇 |
2002年 | 110篇 |
2001年 | 105篇 |
2000年 | 105篇 |
1999年 | 120篇 |
1998年 | 86篇 |
1997年 | 82篇 |
1996年 | 55篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1959年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有6167条查询结果,搜索用时 15 毫秒
1.
低轨互联网星座是当前全球研究和发展的热点,互联网星座支持随遇接入遥感卫星和信息在轨直接处理的应用前景备受期待,但由于轨道高度不同会产生双向高动态异构星座的接入互联问题。首先,通过设定低轨卫星互联网星座在不同轨道特性、不同卫星数量情况下的随遇接入仿真场景,重点探讨了时空非连续可视性和多普勒频移问题对遥感卫星接入性能的影响;其次,基于遥感卫星随遇接入互联网星座场景的特点,分析了不同时延性在轨处理任务的流程及其星地功能分配;最后,对当前在轨智能处理算法存在的问题和未来研究重点进行阐述,为未来低轨互联网星座及遥感卫星的发展和联合组网应用提供可靠的理论支撑。 相似文献
2.
Nan Wu Xiaodong Li Mu Zhang Yi Ren Qi Zhu Haijun Peng Hongqiang Ru Xudong Sun 《Journal of the European Ceramic Society》2021,41(4):2898-2907
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density. 相似文献
3.
双检合并技术在海底电缆地震资料处理中被广泛应用,可衰减电缆鬼波的影响。传统方式以水、陆检记录的波场记录相同为假设,电缆鬼波压制效果差,合并效果并不理想。在分析交叉鬼波化双检合并技术基本原理的基础上,综合利用水检资料与陆检鬼波褶积的结果和陆检资料与水检鬼波褶积的结果求取刻度算子,同时在地震资料处理中利用陆检资料标定水检资料,从而优化了交叉鬼波化双检合并技术。实际资料处理结果表明,改进后的技术可有效衰减电缆鬼波,分离出上行波场,大幅度拓宽地震资料频带,提高地震资料分辨率,从而提供更丰富的构造细节信息。 相似文献
4.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
5.
Novel lamellar mesostructured hydroxyapatites have firstly been synthesized by template-assisted technique. The mild and nontoxic surfactant, phosphoric acid monododecyl ester (MAP), is used to act as a structure-directing template. The structure of sample was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscope and Transmission electron microscopy. The results indicate that the obtained sample is a well-organized lamellar mesostructured hydroxyapatite with a uniform layer spacing of 3.64 nm. 相似文献
6.
In this paper, we propose a new face recognition algorithm based on a single frontal-view image for each face subject, which considers the effect of the face manifold structure. To compare two near-frontal face images, each face is considered a combination of a sequence of local image blocks. Each of the image blocks of one image can be reconstructed according to the corresponding local image block of the other face image. Then an elastic local reconstruction (ELR) method is proposed to measure the similarities between the image block pairs in order to measure the difference between the two face images. Our algorithm not only benefits from the face manifold structure, in terms of being robust to various image variations, but also is computationally simple because there is no need to build the face manifold. We evaluate the performance of our proposed face recognition algorithm with the use of different databases, which are produced under various conditions, e.g. lightings, expressions, perspectives, with/without glasses and occlusions. Consistent and promising experimental results were obtained, which show that our algorithm can greatly improve the recognition rates under all the different conditions. 相似文献
7.
利用Altera公司的Stratix系列芯片内部的ROM实现了一种基于查找表结构的有限冲击响应(FIR)数字滤波器,从而将卷积运算变换成一种查表后的加法运算,提高了运算速度,节省了逻辑单元;并且利用Altera公司的FPGA开发软件QuartusⅡ与MathWorks公司的MATLAB软件实现电子设计自动化(EDA)应用中的联合仿真,从而提高了现场可编程门阵列(FPGA)设计的效率,使得QuartusⅡ的波形仿真功能更加强大;利用最新版本的QuartusⅡ3.0还可以将波形文件转换成Testbench文件导入到专业仿真软件例如ModelSim中进行仿真. 相似文献
8.
介绍了国内首次研制的光缆CATV用1.3μmDFB激光器组件。组件工作频带达到1GHz,带内起伏〈1dB,组件的RIN〈-153dB/Hz;出纤光功率〉2mW,载噪比CNR〉50dB。首次实现用低反射尖锥端光纤的DFB激光器耦合。 相似文献
9.
10.
教育是一项公益性事业,追求公共利益是发展教育事业的基本目标,教育的公益性并不取决于办学形式,教育的公益性也不反对追求教育的功利价值和效率价值.教育的公共利益中也包含物质利益,其公益性是以市场经济为基础的。 相似文献