全文获取类型
收费全文 | 7414篇 |
免费 | 706篇 |
国内免费 | 333篇 |
学科分类
工业技术 | 8453篇 |
出版年
2024年 | 25篇 |
2023年 | 143篇 |
2022年 | 253篇 |
2021年 | 393篇 |
2020年 | 317篇 |
2019年 | 239篇 |
2018年 | 222篇 |
2017年 | 257篇 |
2016年 | 233篇 |
2015年 | 277篇 |
2014年 | 321篇 |
2013年 | 400篇 |
2012年 | 448篇 |
2011年 | 434篇 |
2010年 | 442篇 |
2009年 | 413篇 |
2008年 | 414篇 |
2007年 | 401篇 |
2006年 | 398篇 |
2005年 | 313篇 |
2004年 | 209篇 |
2003年 | 187篇 |
2002年 | 199篇 |
2001年 | 148篇 |
2000年 | 189篇 |
1999年 | 180篇 |
1998年 | 144篇 |
1997年 | 151篇 |
1996年 | 117篇 |
1995年 | 109篇 |
1994年 | 91篇 |
1993年 | 93篇 |
1992年 | 71篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有8453条查询结果,搜索用时 31 毫秒
71.
Iterative computation is pervasive in many applications such as data mining, web ranking, graph analysis, online social network
analysis, and so on. These iterative applications typically involve massive data sets containing millions or billions of data
records. This poses demand of distributed computing frameworks for processing massive data sets on a cluster of machines.
MapReduce is an example of such a framework. However, MapReduce lacks built-in support for iterative process that requires
to parse data sets iteratively. Besides specifying MapReduce jobs, users have to write a driver program that submits a series
of jobs and performs convergence testing at the client. This paper presents iMapReduce, a distributed framework that supports
iterative processing. iMapReduce allows users to specify the iterative computation with the separated map and reduce functions,
and provides the support of automatic iterative processing within a single job. More importantly, iMapReduce significantly
improves the performance of iterative implementations by (1) reducing the overhead of creating new MapReduce jobs repeatedly,
(2) eliminating the shuffling of static data, and (3) allowing asynchronous execution of map tasks. We implement an iMapReduce
prototype based on Apache Hadoop, and show that iMapReduce can achieve up to 5 times speedup over Hadoop for implementing
iterative algorithms. 相似文献
72.
随着计算机技术及多媒体技术的发展,多媒体在教学中的应用越来越广泛,多媒体有着传统教学媒体不具备的独特优势,但在实际教学中也有不足之处,在教学中必须根据实际情况灵活运用多媒体才能取得理想的教学效果。 相似文献
73.
Zhuang Xuezeng 《电子科学学刊(英文版)》1985,2(2):162-175
A technique of symmetry analysis for modal characteristics in uniform waveguides or resonators with ferrite rods is presented
here. Symmetry analysis can provide basic information concerning modal characteristics. After summarizing the basic principles
of symmetry analysis, some points concerning symmetry operations are discussed. Then the process of symmetry analysis is applied
to structures, i.e. uniform wave guides withC
n
symmetry or
symmetry and resonators withD
nh
symmetry in which exist longitudinally magnetized ferrite rods. Finally, results of the symmetry analysis are given in four
tables. 相似文献
74.
在外界电磁波的干扰下,线缆会在车辆内部产生很强的耦合电流和电压,严重影响车辆正常工作,一般需要采用屏蔽线缆来减少干扰. 屏蔽线缆抑制电磁干扰的能力,不仅和线缆本身的屏蔽层有关,还须选择正确的接地方式. 着重对线缆的多种接地方式进行仿真研究,分析不同接地位置和数目对线缆抗干扰性能的影响,为实际车辆线缆防护提供参考. 相似文献
75.
Yixing Wang Liheng Dai Kai Qu Lu Qin Linzhou Zhuang Hu Yang Zhi Xu 《Frontiers of Chemical Science and Engineering》2021,15(4):892
Photocatalytic membranes have received increasing attention due to their excellent separation and photodegradation of organic contaminants in wastewater. Herein, we bound Ag-AgBr nanoparticles onto a synthesized polyacrylonitrile-ethanolamine (PAN-ETA) membrane with the aid of a chitosan (CS)-TiO2 layer via vacuum filtration and in-situ partial reduction. The introduction of the CS-TiO2 layer improved surface hydrophilicity and provided attachment sites for the Ag-AgBr nanoparticles. The PAN-ETA/CS-TiO2/Ag-AgBr photocatalytic membranes showed a relatively high water permeation flux (~ 47 L·m–2·h–1·bar–1) and dyes rejection (methyl orange: 88.22%; congo red: 95%; methyl blue: 97.41%; rose bengal: 99.98%). Additionally, the composite membranes exhibited potential long-term stability for dye/salt separation (dye rejection: ~97%; salt rejection: ~6.5%). Moreover, the methylene blue and rhodamine B solutions (20 mL, 10 mg·L−1) were degraded approximately 90.75% and 96.81% in batch mode via the synthesized photocatalytic membranes under visible light irradiation for 30 min. This study provides a feasible method for the combination of polymeric membranes and inorganic catalytic materials. 相似文献
76.
盐雾环境下的污秽物具有较高的可溶盐含量,可造成绝缘子绝缘性能下降,进而危及电力系统的安全运行.以XWP2-160型瓷双伞绝缘子和FXBW-110/120-2型复合绝缘子为研究对象,基于场致荷电机理,利用多物理场耦合软件COMSOL对其积污特性进行数值模拟,探索了盐密ESDD的计算方法,并验证了其合理性.利用该方法研究了盐雾环境下风速、雾滴粒径、电压类型对瓷及复合绝缘子积污特性的影响,分析了污秽沿绝缘子伞裙的分布规律.结果表明:复合绝缘子的积污量大于同条件下瓷双伞绝缘子积污量,盐雾环境频发地区可优先考虑瓷双伞绝缘子;直流电压下,瓷及复合绝缘子的积污量增长趋势均与风速、粒径呈正相关;复合绝缘子积污量沿伞裙近似呈U型分布,瓷双伞绝缘子积污量沿伞裙近似呈M型分布,且风速越大分布趋势越明显. 相似文献
77.
Cells employ proteins to perform metabolic functions and maintain active physiological state through charge transfer and energy conversion. These processes are carried out in a narrow space precisely and rapidly, which, no doubt, bring great difficulty for their detection and dissection. Fortunately, in recent years, the development and expansion of single-molecule technique in protein research make monitoring the dynamical changes of protein at single-molecule level a reality, which also provides a powerful tool for the further exploration of new phenomena and new mechanisms of life activities. This paper aims to summarize the working principle and essential achievements of single-molecule technique in protein research in recent five years. We focus on not only dissecting the difference of nanopores, atomic force microscope, scanning tunneling microscope, and optical tweezers technique, but also discussing the great significance of these single-molecule techniques in investigating intramolecular and intermolecular interactions, electron transport, and conformational changes. Finally, the opportunities and challenges of the single-molecule technique in protein research are discussed, which provide a new door for single-molecule protein research. 相似文献
78.
Long Tang Jianchun Jiang Guoqiang Song Yajing Wang Ziheng Zhuang Ying Tan Yan Xia Xianfeng Huang Xiaoqing Feng 《International journal of molecular sciences》2021,22(11)
Urolithins (hydroxylated 6H-benzo[c]chromen-6-ones) are the main bioavailable metabolites of ellagic acid (EA), which was shown to be a cognitive enhancer in the treatment of neurodegenerative diseases. As part of this research, a series of alkoxylated 6H-benzo[c]chromen-6-one derivatives were designed and synthesized. Furthermore, their biological activities were evaluated as potential PDE2 inhibitors, and the alkoxylated 6H-benzo[c]chromen-6-one derivative 1f was found to have the optimal inhibitory potential (IC50: 3.67 ± 0.47 μM). It also exhibited comparable activity in comparison to that of BAY 60-7550 in vitro cell level studies. 相似文献
79.
Fiber-based hygroresponsive torsional actuators provide desirable merits, such as light weight and shapeability, for developing smart systems to harvest energy from moisture which is a ubiquitous natural resource. A key challenge in this development is to realize moisture-triggered actuation combining large actuation and rapid responses. Here, a multiscale design strategy is explored to create high-performance hygroresponsive torsional actuators consisting of chitosan and multiwalled carbon nanotubes (MWCNTs). The superior actuation performance arises from the synergism of contributing factors at different scales, including 1) MWNCTs accelerate the water transport in primary twisted fibers (PTFs), fostering the rotation of PTFs upon moisture stimuli; 2) in situ-formed hierarchically-assembled twists realize cascade amplification of moisture-triggered actuation. Specifically, PTFs are self-twisted to generate secondary helical yarns, that are subsequently over-twisted to yield tertiary coiled yarn. The resultant yarn actuator can reach a maximum rotation speed of 11 400 rpm in 5 s, output gravitational potential energy of 2.4 J kg−1 and gravitational potential power of 0.053 W kg−1 during contraction. This work represents the first design of fiber-based actuators by virtue of moisture-triggered in situ formation of yarns. The established principles of multiscale design will enable high-performance fiber-based hygroresponsive actuators toward advanced intelligent textile and soft robotics. 相似文献
80.