全文获取类型
收费全文 | 101366篇 |
免费 | 10844篇 |
国内免费 | 6006篇 |
专业分类
电工技术 | 7538篇 |
技术理论 | 7篇 |
综合类 | 7542篇 |
化学工业 | 15096篇 |
金属工艺 | 6050篇 |
机械仪表 | 6960篇 |
建筑科学 | 8447篇 |
矿业工程 | 3543篇 |
能源动力 | 2930篇 |
轻工业 | 7021篇 |
水利工程 | 2319篇 |
石油天然气 | 5442篇 |
武器工业 | 1132篇 |
无线电 | 12421篇 |
一般工业技术 | 10846篇 |
冶金工业 | 4290篇 |
原子能技术 | 1355篇 |
自动化技术 | 15277篇 |
出版年
2024年 | 576篇 |
2023年 | 1909篇 |
2022年 | 3761篇 |
2021年 | 5266篇 |
2020年 | 4036篇 |
2019年 | 3011篇 |
2018年 | 3446篇 |
2017年 | 3763篇 |
2016年 | 3343篇 |
2015年 | 4864篇 |
2014年 | 6062篇 |
2013年 | 7093篇 |
2012年 | 8187篇 |
2011年 | 8412篇 |
2010年 | 7530篇 |
2009年 | 7037篇 |
2008年 | 6616篇 |
2007年 | 6025篇 |
2006年 | 5462篇 |
2005年 | 4416篇 |
2004年 | 2864篇 |
2003年 | 2141篇 |
2002年 | 1929篇 |
2001年 | 1519篇 |
2000年 | 1424篇 |
1999年 | 1480篇 |
1998年 | 1112篇 |
1997年 | 985篇 |
1996年 | 872篇 |
1995年 | 727篇 |
1994年 | 567篇 |
1993年 | 408篇 |
1992年 | 300篇 |
1991年 | 256篇 |
1990年 | 179篇 |
1989年 | 148篇 |
1988年 | 128篇 |
1987年 | 78篇 |
1986年 | 72篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 22篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 14篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
Zhijiang Li Yingping Zheng Liqin Cao Lei Jiao Yanfei Zhong Caiyi Zhang 《Color research and application》2020,45(4):656-670
Image color clustering is a basic technique in image processing and computer vision, which is often applied in image segmentation, color transfer, contrast enhancement, object detection, skin color capture, and so forth. Various clustering algorithms have been employed for image color clustering in recent years. However, most of the algorithms require a large amount of memory or a predetermined number of clusters. In addition, some of the existing algorithms are sensitive to the parameter configurations. In order to tackle the above problems, we propose an image color clustering method named Student's t-based density peaks clustering with superpixel segmentation (tDPCSS), which can automatically obtain clustering results, without requiring a large amount of memory, and is not dependent on the parameters of the algorithm or the number of clusters. In tDPCSS, superpixels are obtained based on automatic and constrained simple non-iterative clustering, to automatically decrease the image data volume. A Student's t kernel function and a cluster center selection method are adopted to eliminate the dependence of the density peak clustering on parameters and the number of clusters, respectively. The experiments undertaken in this study confirmed that the proposed approach outperforms k-means, fuzzy c-means, mean-shift clustering, and density peak clustering with superpixel segmentation in the accuracy of the cluster centers and the validity of the clustering results. 相似文献
34.
分析了20号无缝钢管的室温和低温力学性能,结合显微组织观察、晶粒度统计和断口分析,发现低温低应力工况下服役后20号无缝钢管的力学性能完全符合冷库用液氨管道的使用要求。 相似文献
35.
为解决共享交通下的共乘用户群体发现效率低、准确率不高问题,依据R-树原理建立GeoOD-Tree索引,并在此基础上提出以最大化共乘率为目标的群体发现策略。首先,对原始时空轨迹数据进行特征提取与标定处理,挖掘有效出行起讫点(OD)轨迹;其次,针对用户起讫点轨迹的特征,建立GeoOD-Tree索引进行有效的存储管理;最后,给出以最大化共乘行程为目标的群体发现模型,并运用K最近邻(KNN)查询对搜索空间剪枝压缩,提高群体发现效率。采用西安市近12000辆出租车营运轨迹数据,选取动态时间规整(DTW)等典型算法与所提算法在查询效率与准确率上进行性能对比分析。与DTW算法相比,所提算法的准确率提高了10.12%,查询效率提高了约15倍。实验结果表明提出的群体发现策略能有效提高共乘用户群体发现的准确率和效率,可有效提升共乘出行方式的出行率。 相似文献
36.
38.
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
39.
40.
Mohamad A.A. Attia Roberto Orrù Francesco Delogu Selena Montinaro Sebastiano Garroni Emad M.M. Ewais Giacomo Cao 《Journal of the American Ceramic Society》2015,98(5):1453-1459
The effects produced by annealing Y2O3 nanopowders on their spark plasma sintering (SPS) behavior are systematically investigated in this work. It is found that the annealed powders display higher sinterability with respect to the as‐received ones. Indeed, the maximum densification level reached from pristine powders is about 97.5%, whereas density decreases when further increasing either the sintering temperature or the dwell time. In contrast, the density of SPS products obtained from pretreated powder monotonically increases with temperature and processing time, thus leading to fully dense materials in 30 min at 1050°C and 60 MPa. Correspondingly, it is found that the annealing treatment markedly inhibits grain coarsening during SPS. Thus, dense translucent samples with grain size below 100 nm can be attained from annealed powders. On the other hand, white‐opaque specimens with significantly coarser microstructures (up to 1‐μm‐sized grains) are obtained when pristine powders are directly processed under the same sintering conditions. Furthermore, it is observed that the annealing treatment of SPS samples in air allows for graphite contamination removal, whereas no improvement in term of light transmittance is produced. 相似文献