全文获取类型
收费全文 | 185886篇 |
免费 | 15635篇 |
国内免费 | 8398篇 |
专业分类
电工技术 | 11307篇 |
技术理论 | 18篇 |
综合类 | 13750篇 |
化学工业 | 30296篇 |
金属工艺 | 10271篇 |
机械仪表 | 11735篇 |
建筑科学 | 14778篇 |
矿业工程 | 4668篇 |
能源动力 | 5258篇 |
轻工业 | 15037篇 |
水利工程 | 3505篇 |
石油天然气 | 9450篇 |
武器工业 | 1500篇 |
无线电 | 21072篇 |
一般工业技术 | 21495篇 |
冶金工业 | 8279篇 |
原子能技术 | 1910篇 |
自动化技术 | 25590篇 |
出版年
2024年 | 540篇 |
2023年 | 2814篇 |
2022年 | 4775篇 |
2021年 | 7174篇 |
2020年 | 5486篇 |
2019年 | 4506篇 |
2018年 | 4951篇 |
2017年 | 5662篇 |
2016年 | 5097篇 |
2015年 | 7113篇 |
2014年 | 9424篇 |
2013年 | 11326篇 |
2012年 | 12646篇 |
2011年 | 13676篇 |
2010年 | 12232篇 |
2009年 | 11670篇 |
2008年 | 11378篇 |
2007年 | 10873篇 |
2006年 | 10794篇 |
2005年 | 9028篇 |
2004年 | 6283篇 |
2003年 | 5442篇 |
2002年 | 5190篇 |
2001年 | 4556篇 |
2000年 | 4370篇 |
1999年 | 4349篇 |
1998年 | 3655篇 |
1997年 | 2856篇 |
1996年 | 2613篇 |
1995年 | 2094篇 |
1994年 | 1748篇 |
1993年 | 1235篇 |
1992年 | 969篇 |
1991年 | 776篇 |
1990年 | 558篇 |
1989年 | 502篇 |
1988年 | 391篇 |
1987年 | 232篇 |
1986年 | 202篇 |
1985年 | 125篇 |
1984年 | 106篇 |
1983年 | 79篇 |
1982年 | 77篇 |
1981年 | 72篇 |
1980年 | 69篇 |
1979年 | 41篇 |
1978年 | 15篇 |
1977年 | 34篇 |
1976年 | 18篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Baofeng Hou Hong He Ruixiu Jia Meilong Fu Yanbin Cao Shaoqun He Liwen Luo Youqing Huang 《应用聚合物科学杂志》2019,136(10):47161
The synthesis and performance of a novel temperature-tolerant foamed resin for enhanced oil recovery were investigated using various methods, including infrared, NMR, scanning electron microscopy (SEM), and displacement experiments. Polycondensation of furfuryl alcohol prepolymers was confirmed by the infrared and NMR results. The poor temperature tolerance of furfuryl alcohol prepolymers after gelation at high temperatures is mainly due to the fracture of furan rings. The addition of ester additives is an effective method of increasing the temperature tolerance of the prepared foamed resins and can effectively reduce the weight-loss rate of the polycondensation products. The SEM results show that the skeleton structure of the foamed resin remains intact after high-temperature treatment. Thus, the novel plugging agent system has excellent thermal stability and still has a high strength (>0.8 MPa) after high-temperature aging treatment for 40 days, giving the prepared foamed resin a good plugging performance (plugging rate > 91%) at 250 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47161. 相似文献
92.
Ionomics is a novel multidisciplinary field that uses advanced techniques to investigate the composition and distribution of all minerals and trace elements in a living organism and their variations under diverse physiological and pathological conditions. It involves both high-throughput elemental profiling technologies and bioinformatic methods, providing opportunities to study the molecular mechanism underlying the metabolism, homeostasis, and cross-talk of these elements. While much effort has been made in exploring the ionomic traits relating to plant physiology and nutrition, the use of ionomics in the research of serious diseases is still in progress. In recent years, a number of ionomic studies have been carried out for a variety of complex diseases, which offer theoretical and practical insights into the etiology, early diagnosis, prognosis, and therapy of them. This review aims to give an overview of recent applications of ionomics in the study of complex diseases and discuss the latest advances and future trends in this area. Overall, disease ionomics may provide substantial information for systematic understanding of the properties of the elements and the dynamic network of elements involved in the onset and development of diseases. 相似文献
93.
94.
Wai-Ching Liu Huey-Yuan Wang Lung-Chien Chen Shih-Wei Huang Chengtie Wu Ren-Jei Chung 《Ceramics International》2019,45(5):5668-5679
Tricalcium silicate (C3S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C3S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C3S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C3S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C3S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C3S. Lastly, HAp/C3S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C3S biocompatibility with this new composites HAp/C3S. C-75 (75% C3S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers. 相似文献
95.
96.
97.
98.
目前网络上的服装图像数量增长迅猛,对于大量服装图像实现智能分类的需求日益增加。将基于区域的全卷积网络(Region-Based Fully Convolutional Networks,R-FCN)引入到服装图像识别中,针对服装图像分类中网络训练时间长、形变服装图像识别率低的问题,提出一种新颖的改进框架HSR-FCN。新框架将R-FCN中的区域建议网络和HyperNet网络相融合,改变图片特征学习方式,使得HSR-FCN可以在更短的训练时间内达到更高的准确率。在模型中引入了空间转换网络,对输入服装图像和特征图进行了空间变换及对齐,加强了对多角度服装和形变服装的特征学习。实验结果表明,改进后的HSR-FCN模型有效地加强了对形变服装图像的学习,且在训练时间更短的情况下,比原来的网络模型R-FCN平均准确率提高了大约3个百分点,达到96.69%。 相似文献
99.
100.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献