全文获取类型
收费全文 | 132058篇 |
免费 | 14446篇 |
国内免费 | 9069篇 |
专业分类
电工技术 | 11320篇 |
技术理论 | 1篇 |
综合类 | 11076篇 |
化学工业 | 18149篇 |
金属工艺 | 8702篇 |
机械仪表 | 9117篇 |
建筑科学 | 10601篇 |
矿业工程 | 4363篇 |
能源动力 | 3352篇 |
轻工业 | 12220篇 |
水利工程 | 3420篇 |
石油天然气 | 5833篇 |
武器工业 | 1332篇 |
无线电 | 15516篇 |
一般工业技术 | 13281篇 |
冶金工业 | 5409篇 |
原子能技术 | 1817篇 |
自动化技术 | 20064篇 |
出版年
2024年 | 708篇 |
2023年 | 2053篇 |
2022年 | 4502篇 |
2021年 | 5869篇 |
2020年 | 4371篇 |
2019年 | 3275篇 |
2018年 | 3530篇 |
2017年 | 4102篇 |
2016年 | 3848篇 |
2015年 | 5804篇 |
2014年 | 7024篇 |
2013年 | 8505篇 |
2012年 | 9964篇 |
2011年 | 10558篇 |
2010年 | 9812篇 |
2009年 | 9760篇 |
2008年 | 9676篇 |
2007年 | 9452篇 |
2006年 | 8444篇 |
2005年 | 7025篇 |
2004年 | 4949篇 |
2003年 | 3796篇 |
2002年 | 3591篇 |
2001年 | 3282篇 |
2000年 | 2712篇 |
1999年 | 1992篇 |
1998年 | 1211篇 |
1997年 | 1102篇 |
1996年 | 923篇 |
1995年 | 759篇 |
1994年 | 626篇 |
1993年 | 473篇 |
1992年 | 361篇 |
1991年 | 298篇 |
1990年 | 265篇 |
1989年 | 205篇 |
1988年 | 170篇 |
1987年 | 136篇 |
1986年 | 101篇 |
1985年 | 50篇 |
1984年 | 44篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 37篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1976年 | 10篇 |
1959年 | 21篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Cheqing Jin Jeffrey Xu Yu Aoying Zhou Feng Cao 《Knowledge and Information Systems》2014,40(3):509-539
Clustering uncertain data streams has recently become one of the most challenging tasks in data management because of the strict space and time requirements of processing tuples arriving at high speed and the difficulty that arises from handling uncertain data. The prior work on clustering data streams focuses on devising complicated synopsis data structures to summarize data streams into a small number of micro-clusters so that important statistics can be computed conveniently, such as Clustering Feature (CF) (Zhang et al. in Proceedings of ACM SIGMOD, pp 103–114, 1996) for deterministic data and Error-based Clustering Feature (ECF) (Aggarwal and Yu in Proceedings of ICDE, 2008) for uncertain data. However, ECF can only handle attribute-level uncertainty, while existential uncertainty, the other kind of uncertainty, has not been addressed yet. In this paper, we propose a novel data structure, Uncertain Feature (UF), to summarize data streams with both kinds of uncertainties: UF is space-efficient, has additive and subtractive properties, and can compute complicated statistics easily. Our first attempt aims at enhancing the previous streaming approaches to handle the sliding-window model by using UF instead of old synopses, inclusive of CluStream (Aggarwal et al. in Proceedings of VLDB, 2003) and UMicro (Aggarwal and Yu in Proceedings of ICDE, 2008). We show that such methods cannot achieve high efficiency. Our second attempt aims at devising a novel algorithm, cluUS , to handle the sliding-window model by using UF structure. Detailed analysis and thorough experimental reports on synthetic and real data sets confirm the advantages of our proposed method. 相似文献
982.
聚烯烃接枝马来酸酐接枝率的测定—聚乙烯接枝 总被引:2,自引:1,他引:2
以非均相化学接枝法和红外光谱法相结合的方法绘制了定量校正曲线,可用于红外光谱法测定聚乙烯接枝马来酸酐的接枝率。该方法简便快速,准确可靠,重复性好。 相似文献
983.
Zhengyu Su Jian Sun Xianfeng Gu Feng Luo Shing-Tung Yau 《Engineering with Computers》2014,30(4):475-486
In geometric modeling, surface parameterization plays an important role for converting triangle meshes to spline surfaces. Parameterization will introduce distortions. Conventional parameterization methods emphasize on angle-preservation, which may induce huge area distortions and cause large spline fitting errors and trigger numerical instabilities.To overcome this difficulty, this work proposes a novel area-preserving parameterization method, which is based on an optimal mass transport theory and convex geometry. Optimal mass transport mapping is measure-preserving and minimizes the transportation cost. According to Brenier’s theorem, for quadratic distance transportation costs, the optimal mass transport map is the gradient of a convex function. The graph of the convex function is a convex polyhedron with prescribed normal and areas. The existence and the uniqueness of such a polyhedron have been proved by the Minkowski-Alexandrov theorem in convex geometry. This work gives an explicit method to construct such a polyhedron based on the variational principle, and formulates the solution to the optimal transport map as the unique optimum of a convex energy. In practice, the energy optimization can be carried out using Newton’s method, and each iteration constructs a power Voronoi diagram dynamically. We tested the proposal algorithms on 3D surfaces scanned from real life. Experimental results demonstrate the efficiency and efficacy of the proposed variational approach for the optimal transport map. 相似文献
984.
Poly(vinyl pyrrolidone‐co‐isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP–POSS) were synthesized by one‐step polymerization and characterized using FTIR, high‐resolution 1H‐NMR, solid‐state 13C‐NMR, 29Si‐NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The Tg of the PVP–POSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self‐association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low POSS content, the role as diluent dominates, resulting in a decrease in Tg. At a relatively high POSS content, the last two factors dominate and result in Tg increase of the PVP–POSS hybrid. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2208–2215, 2004 相似文献
985.
Quanxi Feng Sanyang Liu Jianke Zhang Guoping Yang Longquan Yong 《Applied Intelligence》2014,41(2):563-581
Biogeography-based optimization (BBO) is a new emerging population-based algorithm that has been shown to be competitive with other evolutionary algorithms. However, there are some insufficiencies in solving complex problems, such as poor population diversity and slow convergence speed in the later stage. To overcome these shortcomings, we propose an improved BBO (IBBO) algorithm integrating a new improved migration operator, Gaussian mutation operator, and self-adaptive clear duplicate operator. The improved migration operator simultaneously adopts more information from other habitats, maintains population diversity, and preserves exploitation ability. The self-adaptive clear duplicate operator can clear duplicate or almost identical habitats, while also preserving population diversity through a self-adaptation threshold within the evolution process. Simulation results and comparisons from the experimental tests conducted on 23 benchmark functions show that IBBO achieves excellent performance in solving complex problems compared with other variants of the BBO algorithm and other evolutionary algorithms. The performance of the improved migration operator is also discussed. 相似文献
986.
987.
为提高四角喷燃液态排渣锅炉运行的安全性和经济性,从锅炉原理和实际运行情况对锅炉高温受热面的积灰与结焦问题进行了分析,并提出了解决办法,同时提出了一种基于热力学模型的受热面积灰状态实时监测方法。 相似文献
988.
Ping-Hua Xiang Xian-Lin Dong Chu-De Feng Yong-Ling Wang 《Journal of the American Ceramic Society》2003,86(9):1631-1634
NiO nanoparticle-coated lead zirconate titanate (PZT) powders are successfully fabricated by the heterogeneous precipitation method using PZT, Ni(NO3 )2 ·6H2 O, and NH4 HCO3 as the starting materials. The amorphous NiCO3 ·2Ni(OH)2 ·2H2 O are uniformly coated on the surface of PZT particles. XRD analysis and the selected-area diffraction (SAD) pattern indicate that the amorphous coating layer is crystallized to NiO after being calcined at 400°C for 2 h. TEM images show that the NiO particles of ∼8 nm are spherical and weakly agglomerated. The thickness of the nanocrystalline NiO coating layer on the surface of PZT particle is ∼30 nm. 相似文献
989.
990.
High‐temperature vulcanized silicone rubber was prepared by using allyl‐capped carbosilane dendrimers, in which the core molecules were Si(CH2CH?CH2)4 and Ph2Si(CH2CH?CH2)2 as crosslinker and nanoscale reinforcing filler, respectively. Allyl‐capped carbosilane dendrimers improved the mechanical properties of silicone rubber. The optimum tensile strength and tear strength were 9.6 MPa and 31.0 kN/m, respectively, when using SiGn(allyl)m as the crosslinker and 10.1 MPa and 32.0 kN/m, respectively, when using Ph2SiGn(allyl)m as the crosslinker. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1772–1775, 2006 相似文献