全文获取类型
收费全文 | 67821篇 |
免费 | 6486篇 |
国内免费 | 3332篇 |
专业分类
电工技术 | 4314篇 |
技术理论 | 8篇 |
综合类 | 4789篇 |
化学工业 | 11594篇 |
金属工艺 | 3549篇 |
机械仪表 | 3994篇 |
建筑科学 | 4965篇 |
矿业工程 | 1846篇 |
能源动力 | 2095篇 |
轻工业 | 4887篇 |
水利工程 | 1352篇 |
石油天然气 | 3391篇 |
武器工业 | 736篇 |
无线电 | 8247篇 |
一般工业技术 | 8071篇 |
冶金工业 | 3378篇 |
原子能技术 | 926篇 |
自动化技术 | 9497篇 |
出版年
2024年 | 247篇 |
2023年 | 1076篇 |
2022年 | 2057篇 |
2021年 | 2953篇 |
2020年 | 2195篇 |
2019年 | 1811篇 |
2018年 | 2027篇 |
2017年 | 2168篇 |
2016年 | 1913篇 |
2015年 | 2747篇 |
2014年 | 3380篇 |
2013年 | 4232篇 |
2012年 | 4444篇 |
2011年 | 4775篇 |
2010年 | 4219篇 |
2009年 | 4120篇 |
2008年 | 3966篇 |
2007年 | 3742篇 |
2006年 | 3785篇 |
2005年 | 3217篇 |
2004年 | 2362篇 |
2003年 | 1959篇 |
2002年 | 2090篇 |
2001年 | 1869篇 |
2000年 | 1629篇 |
1999年 | 1552篇 |
1998年 | 1324篇 |
1997年 | 1125篇 |
1996年 | 921篇 |
1995年 | 767篇 |
1994年 | 583篇 |
1993年 | 488篇 |
1992年 | 369篇 |
1991年 | 310篇 |
1990年 | 210篇 |
1989年 | 203篇 |
1988年 | 165篇 |
1987年 | 96篇 |
1986年 | 102篇 |
1985年 | 77篇 |
1984年 | 42篇 |
1983年 | 30篇 |
1982年 | 40篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 25篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1974年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
51.
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
52.
53.
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
54.
四川盆地作为国内页岩气开发的重点区域,通过近几年的不断攻关和实践,机械钻速得到了提高,但由于受地层复杂、可钻性差、非均质性强等地质因素的影响,导致井下钻柱系统不良振动剧烈,容易出现钻头损坏严重、钻速较低等问题,严重影响了钻井时效。为了解决上述难题,以该盆地涪陵工区上二叠统龙潭组—中二叠统茅口组为例,采用井下振动高频测量工具的实测手段,测量了钻头—钻柱系统的动态振动加速度参数,结合地层的岩性和矿物组分分析,研究钻头失效原因与对策,并开展了现场试验。研究结果表明:①在非均质地层中钻进的钻头—钻柱系统产生了大于40 m/s~2的高幅值瞬时冲击振动,高幅值的瞬时冲击是导致钻头先期失效的主要原因;②提出了抑制高幅值的瞬时冲击振动采用"减振+增压"工具组合和避免井下工具共振的钻井参数;③采用钻井新参数的试验井比邻井的高幅值瞬时振动降低了17%,单只钻头进尺增加24%,钻头工作环境得到了较大的改善,钻头使用数量减少。结论认为,该研究成果能够有效地改善钻头—钻柱系统的振动状态,有利于达成延长钻头使用寿命的目标。 相似文献
55.
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
56.
57.
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
58.
59.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
60.
Yu Zhao Zhigang Xu Zongshi Li Weihong Qiao Lubai Cheng 《Petroleum Science and Technology》2006,24(7):821-827
Heavy alkyl benzene sulfonates (HABS) were synthesized, and their interfacial tensions were measured and compared with those of petroleum sulfonates ORS-41. Effects of their coupling with lignosulfonate were also studied. The results showed that HABS exhibited good interfacial activities and the system of HABS blending with LS displayed better interfacial activities than ORS-41 and therefore reduced the prime cost. Their best proportions of synergism were from 3:1 to 4:1. HABS might be a more promising alkali-surfactant-polymer (ASP) flooding agent. 相似文献