全文获取类型
收费全文 | 59580篇 |
免费 | 5681篇 |
国内免费 | 3069篇 |
专业分类
电工技术 | 3879篇 |
技术理论 | 8篇 |
综合类 | 4110篇 |
化学工业 | 9841篇 |
金属工艺 | 3194篇 |
机械仪表 | 3533篇 |
建筑科学 | 4242篇 |
矿业工程 | 1666篇 |
能源动力 | 1885篇 |
轻工业 | 4174篇 |
水利工程 | 1237篇 |
石油天然气 | 3109篇 |
武器工业 | 703篇 |
无线电 | 7369篇 |
一般工业技术 | 7111篇 |
冶金工业 | 3075篇 |
原子能技术 | 776篇 |
自动化技术 | 8418篇 |
出版年
2024年 | 232篇 |
2023年 | 939篇 |
2022年 | 1859篇 |
2021年 | 2655篇 |
2020年 | 1944篇 |
2019年 | 1602篇 |
2018年 | 1796篇 |
2017年 | 1885篇 |
2016年 | 1680篇 |
2015年 | 2481篇 |
2014年 | 2920篇 |
2013年 | 3737篇 |
2012年 | 3957篇 |
2011年 | 4200篇 |
2010年 | 3673篇 |
2009年 | 3568篇 |
2008年 | 3487篇 |
2007年 | 3356篇 |
2006年 | 3300篇 |
2005年 | 2732篇 |
2004年 | 2060篇 |
2003年 | 1751篇 |
2002年 | 1805篇 |
2001年 | 1643篇 |
2000年 | 1417篇 |
1999年 | 1357篇 |
1998年 | 1184篇 |
1997年 | 999篇 |
1996年 | 817篇 |
1995年 | 673篇 |
1994年 | 500篇 |
1993年 | 439篇 |
1992年 | 329篇 |
1991年 | 268篇 |
1990年 | 186篇 |
1989年 | 178篇 |
1988年 | 146篇 |
1987年 | 84篇 |
1986年 | 86篇 |
1985年 | 72篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 37篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
43.
Hechun Cao Hui Zheng Lining Fan Zifeng Cheng Jianwei Zhou Qiong Wu Peng Zheng Liang Zheng Yang Zhang 《International Journal of Applied Ceramic Technology》2020,17(2):813-822
In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). 相似文献
44.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献
45.
Haibo Zhang Guohua Geng Kang Li Cheng Liu Yuqing Hou 《Journal of Modern Optics》2018,65(20):2278-2289
Cone-beam X-ray luminescence computed tomography (CB-XLCT) is an attractive hybrid imaging modality, and it has the potential of monitoring the metabolic processes of nanophosphors-based drugs in vivo. However, the XLCT imaging suffers from a severe ill-posed problem. In this work, a sparse nonconvex Lp (0?p?1) regularization was utilized for the efficient reconstruction for early detection of small tumour in CB-XLCT imaging. Specifically, we transformed the non-convex optimization problem into an iteratively reweighted scheme based on the L1 regularization. Further, an iteratively reweighted split augmented lagrangian shrinkage algorithm (IRW_SALSA-Lp) was proposed to efficiently solve the non-convex Lp (0?p?1) model. We studied eight different non-convex p-values (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8) in both 3D digital mouse experiments and in vivo experiments. The results demonstrate that the proposed non-convex methods outperform L2 and L1 regularization in accurately recovering sparse targets in CB-XLCT. And among all the non-convex p-values, our Lp(1/4?p?1/2) methods give the best performance. 相似文献
46.
The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows. 相似文献
47.
目前,基于因素空间理论的背景基提取算法计算过程复杂,初始化必须依赖各因素极值,基点数量提取冗余等原因,未能在应用中取得很好效果。为此,结合内点判别法和知识可继承、可扩展的思想,提出一种计算简单、初始化独立、基点数量小的改进的背景基提取算法。然后,利用改进的背景基提取算法构造出一种全新的数据分类算法-基点分类算法,基点分类算法以提取每一类样本的背景基为预测模型,再通过新定义的λ-背景基,优化预测模型。数值实验表明:基点分类算法原理简单、构造难度小、分类模型泛化能力强,预测能力准确率高,同时严格的模型限定区域又能为识别新类别提供新方法。 相似文献
48.
49.
Li Jinghang Zhao Zhigang Zhang Shaohui Su Cheng 《Journal of Mechanical Science and Technology》2021,35(10):4727-4735
Journal of Mechanical Science and Technology - A multi-robot collaborative towing system fixed on floating base for high load marine work was established in this paper, and its dynamics and... 相似文献
50.
HEGF中CO井筒流动及扩散规律研究 总被引:2,自引:0,他引:2
目前,高能气体压裂广泛的应用于低渗透油气田,可以有效清除近井地带由于钻井、射孔和各种措施造成的污染和堵塞,达到油气井增产、注水井增注的目的。但最近一些低渗透油气田却出现了频繁的CO气体中毒事件,给油田及员工带来巨大的损失。针对这一现象,运用现场数据以及物理模拟和数学模拟方法首次通过对CO气体流动、扩散等的综合研究,建立了CO井筒流动及大气扩散模型。同时,也考察了井筒压力、气油比、风速、气体泄放速率、大气稳定度等主要因素对CO气体扩散的影响。通过现场实例计算,证实模型具有较高的准确性。此项工作的完成为建立监控系统提供基础技术依据,同时对合理、有效的开发油气田以及煤层气的开发将具有重要的实际意义。 相似文献