全文获取类型
收费全文 | 92614篇 |
免费 | 7077篇 |
国内免费 | 3336篇 |
专业分类
电工技术 | 4977篇 |
技术理论 | 10篇 |
综合类 | 5152篇 |
化学工业 | 16273篇 |
金属工艺 | 4734篇 |
机械仪表 | 5589篇 |
建筑科学 | 7569篇 |
矿业工程 | 2156篇 |
能源动力 | 2693篇 |
轻工业 | 5611篇 |
水利工程 | 1593篇 |
石油天然气 | 4822篇 |
武器工业 | 578篇 |
无线电 | 11453篇 |
一般工业技术 | 11905篇 |
冶金工业 | 4803篇 |
原子能技术 | 903篇 |
自动化技术 | 12206篇 |
出版年
2024年 | 301篇 |
2023年 | 1428篇 |
2022年 | 2399篇 |
2021年 | 3512篇 |
2020年 | 2608篇 |
2019年 | 2233篇 |
2018年 | 2499篇 |
2017年 | 2777篇 |
2016年 | 2566篇 |
2015年 | 3283篇 |
2014年 | 4450篇 |
2013年 | 5572篇 |
2012年 | 5823篇 |
2011年 | 6109篇 |
2010年 | 5355篇 |
2009年 | 5170篇 |
2008年 | 4894篇 |
2007年 | 4797篇 |
2006年 | 4976篇 |
2005年 | 4391篇 |
2004年 | 2937篇 |
2003年 | 2609篇 |
2002年 | 2309篇 |
2001年 | 2105篇 |
2000年 | 2342篇 |
1999年 | 2637篇 |
1998年 | 2431篇 |
1997年 | 1911篇 |
1996年 | 1771篇 |
1995年 | 1477篇 |
1994年 | 1233篇 |
1993年 | 897篇 |
1992年 | 666篇 |
1991年 | 550篇 |
1990年 | 409篇 |
1989年 | 368篇 |
1988年 | 318篇 |
1987年 | 170篇 |
1986年 | 157篇 |
1985年 | 104篇 |
1984年 | 91篇 |
1983年 | 60篇 |
1982年 | 58篇 |
1981年 | 53篇 |
1980年 | 38篇 |
1979年 | 37篇 |
1978年 | 13篇 |
1977年 | 33篇 |
1976年 | 17篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
在经济全球化的背景下,由于民族文化、区域文化差异性和多样性的存在,日用陶瓷企业在开展国际营销活动时需要一个行之有效的营销策略。本文通过分析民族文化差异,为日用陶瓷企业实施国际文化营销提供一些建议。 相似文献
992.
993.
对PS在疲劳/蠕变复合作用下应变与寿命进行了研究。结果表明:其疲劳/蠕变曲线与纯蠕变曲线十分相似。加载时间周期越短和疲劳载荷变化越频繁。结束普弹应变阶段应变越小,进入延迟弹性变形的平台应变阶段越早。在疲劳/蠕变复合作用下聚苯乙烯存在疲劳和蠕变的交互损伤,其断裂寿命比纯疲劳或纯蠕变的断裂寿命低。断裂寿命减小,疲劳/蠕变的交互损伤程度与温度密切相关,PS在较低温度的疲劳/蠕变交互损伤作用大于较高温度的交互损伤作用。随温度升高,疲劳/蠕变断裂寿命下降是疲劳和蠕变各自的单独损伤增加所致。 相似文献
994.
995.
996.
纤维素衍生物液晶相转变和织态结构 总被引:1,自引:1,他引:1
本文综述了纤维素衍生物液晶态相转变和织态结构。描述了纤维素衍生物从各向同性态向液晶态的转变过程和液晶态的织构特征。讨论了溶液浓度和温度对液晶相织构的影响。探讨了各种因素,如溶剂、取代基含量、外加力场和外加磁场等对液晶相的形成及织态结构的影响。 相似文献
997.
Yurun Yang Yongmin Huang Yonglin Chen Dening Wang Honglai Liu Chunpu Hu 《应用聚合物科学杂志》2004,91(5):2984-2991
A series of polyurethane (PU) films made from toluene diisocyanate (TDI), 1,4‐butanediol (BDO), and hydroxyl‐terminated polybutadiene (HTPB), hydroxyl terminated polybutadiene/styrene (HTBS), or hydroxyl terminated polybutadiene/acrylonitrile (HTBN) was synthesized by solution polymerization. The absorption of benzene vapor was found mainly in the soft phase. The equilibrium adsorption (M∞) was reduced with increasing hard segment content for all the PUs. The values of M∞ were in the sequence of HTBN‐PUs > HTBS‐PUs > HTPB‐PUs, which could be explained by the different interaction parameters between soft segments and benzene. The HTBN‐PU film showed the lowest degree of phase segregation and had more hard segments intermixed in the soft phase, restricting the movement of soft segments, and therefore resulted to non‐Fickian behavior, while the HTPB‐PU is antithetical. FTIR and atomic force microscopy were utilized to identify the hydrogen bonding behavior and morphology change of the PU films before and after the absorption of benzene vapor. The tensile strength of the HTBN‐PUs showed a greater decrease than that of HTBS‐PUs and HTPB‐PUs after absorbing benzene vapor. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2984–2991, 2004 相似文献
998.
A new catalyst (Ni/Mo/MgO) is reported, with which one can synthesize multi-walled carbon nanotube (MWNT) bundles with a yield of more than 45 times the amount of the pristine catalyst, using a methane-hydrogen mixture as precursor. Powder X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis show that the purity of the as-prepared MWNTs is over 97%. The diameter of the carbon nanotubes is 9-20 nm, measured by high-resolution electron microscopy on 421 individual MWNTs. The high purity of the as-prepared MWNTs allows us to omit the usual complex purification process required for carbon nanotubes synthesized by chemical vapor deposition. Because of its durable high activity, the Ni/Mo/MgO catalyst in its pristine state is ideal for mass production of high-quality MWNTs. The synergism of nickel and molybdenum is considered the main reason for the high yield of carbon nanotubes. 相似文献
999.
P.L. Lin P.Y. Huang P.W. Huang H.C. Hsu C.C. Chen 《Computer methods and programs in biomedicine》2014
Teeth segmentation for periapical raidographs is one of the most critical tasks for effective periapical lesion or periodontitis detection, as both types of anomalies usually occur around tooth boundaries and dental radiographs are often subject to noise, low contrast, and uneven illumination. In this paper, we propose an effective scheme to segment each tooth in periapical radiographs. The method consists of four stages: image enhancement using adaptive power law transformation, local singularity analysis using Hölder exponent, tooth recognition using Otsu's thresholding and connected component analysis, and tooth delineation using snake boundary tracking and morphological operations. Experimental results of 28 periapical radiographs containing 106 teeth in total and 75 useful for dental examination demonstrate that 105 teeth are successfully isolated and segmented, and the overall mean segmentation accuracy of all 75 useful teeth in terms of (TP, FP) is (0.8959, 0.0093) with standard deviation (0.0737, 0.0096), respectively. 相似文献
1000.
This paper presents a dynamic compensation concept to grapple with the dynamic defects of a traditional robot arm, especially while performing high-speed endpoint regulations. The proposed high-speed dynamic compensation concept offers a new point of view for cooperating with a traditional manipulator to realize highly dexterous performance of manipulations. The concept is realized through adoption of a high-speed light-weight actuator as well as endpoint closed loop configured high-speed cameras. The dynamic compensation is analyzed experimentally with 1000 Hz visual feedback and a high-speed finger for a robot arm in the case of one degree of freedom. The advantage of the proposed approach is that the modeling for the robot system’s dynamics is not needed, whereas it is necessary and trivial in order to realize high-speed regulations by traditional approaches. Thus, the control issue becomes easier with the proposed approach. As an application for this concept, fast peg-and-hole alignment with large position and attitude uncertainty is studied. The alignment algorithm is based on a visual compliance strategy. Alignment experiments show that with the proposed concept of dynamic compensation as well as visual compliant motion control, robust and fast convergence was realized for most cases. 相似文献