首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3850篇
  免费   678篇
  国内免费   493篇
电工技术   162篇
综合类   501篇
化学工业   515篇
金属工艺   176篇
机械仪表   118篇
建筑科学   94篇
矿业工程   70篇
能源动力   85篇
轻工业   75篇
水利工程   43篇
石油天然气   141篇
武器工业   34篇
无线电   724篇
一般工业技术   408篇
冶金工业   140篇
原子能技术   15篇
自动化技术   1720篇
  2024年   3篇
  2023年   38篇
  2022年   85篇
  2021年   121篇
  2020年   157篇
  2019年   142篇
  2018年   107篇
  2017年   156篇
  2016年   160篇
  2015年   183篇
  2014年   275篇
  2013年   282篇
  2012年   359篇
  2011年   315篇
  2010年   247篇
  2009年   279篇
  2008年   254篇
  2007年   269篇
  2006年   225篇
  2005年   200篇
  2004年   144篇
  2003年   130篇
  2002年   120篇
  2001年   123篇
  2000年   82篇
  1999年   85篇
  1998年   54篇
  1997年   71篇
  1996年   66篇
  1995年   43篇
  1994年   39篇
  1993年   33篇
  1992年   28篇
  1991年   17篇
  1990年   23篇
  1989年   12篇
  1988年   14篇
  1987年   8篇
  1986年   10篇
  1985年   7篇
  1984年   12篇
  1983年   6篇
  1982年   7篇
  1981年   4篇
  1980年   5篇
  1979年   6篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1973年   4篇
排序方式: 共有5021条查询结果,搜索用时 15 毫秒
1.
基于网络流理论的停机位实时再分配模型   总被引:1,自引:0,他引:1  
针对机场停机位再分配的延时性和乘客满意度不高的问题,采用二值整数多商品网络流模型,将不同停机位映射为不同商品,建立了以燃油消耗成本和对乘客舒适度影响最小的双目标停机位实时再分配优化模型.以某大型机场某一天的时刻表为例,模拟两种不同规模停机位实时分配方案.结果表明,二值整数多商品流停机位实时再分配模型在两种规模仿真实验中,停机位再分配时间最长为4. 187 5 s,机位最多调整个数为2,该模型具有良好的时效性和乘客满意度.  相似文献   
2.
The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, DAB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect DAB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, DAB,exp, by nonlinear regression. For Re < 600, the DAB,exp errors relative to DAB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the DAB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate DAB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.  相似文献   
3.
张航  翁建华  崔晓钰 《化工学报》2019,70(3):874-882
研究了10%(质量分数)LiCl吸湿性盐溶液作为工质的振荡热管传热特性。测试了在45%~90%充液率、10~100 W加热功率下振荡热管蒸发端温度及热阻的变化,并与去离子水工质的实验数据进行了对比。结果表明:在45%、55%的低充液率下,加热功率达到50 W以上时,LiCl溶液振荡热管的热阻明显比去离子水振荡热管低,能有效延迟烧干现象的发生。在62%的中等充液率,35W加热功率以上,LiCl溶液振荡热管的蒸发端温度较离子水振荡热管振荡频率快,幅度小且热阻低。在80%、90%的高充液率下,两种工质振荡热管的蒸发端温度曲线在平均温度、振荡频率、振荡幅度上都较为相似,热阻也比较接近。  相似文献   
4.
In theory, the combination of inorganic materials and polymers may provide a synergistic performance for mixed‐matrix membranes (MMMs); however, the filler dispersion into the MMMs is a crucial technical parameter for obtaining compelling MMMs. The effect of the filler distribution on the gas separation performance of the MMMs based on Matrimid®‐PEG 200 and ZIF‐8 nanoparticles is demonstrated. The MMMs were prepared by two different membrane preparation procedures, namely, the traditional method and non‐dried metal‐organic framework (MOF) method. In CO2/CH4 binary mixtures, the MMMs were tested under fixed conditions and characterized by various methods. Finally, regardless of the MMM preparation procedure, the incorporation of 30 wt % ZIF‐8 nanoparticles allowed to increase the CO2 permeability in MMMs. The ZIF‐8 dispersion influenced significantly the separation factor.  相似文献   
5.
为了解决当前模糊测试技术中变异存在一定的盲目性以及变异生成的样本大多经过相同的高频路径的问题,提出并实现了一种基于轻量级程序分析技术的二进制程序模糊测试方法。首先对目标二进制程序进行静态分析来筛选在模糊测试过程中阻碍样本文件深入程序内部的比较指令;随后对目标文件进行插桩来获取比较指令中操作数的具体值,并根据该具体值为比较指令建立实时的比较进度信息,通过比较进度衡量样本的重要程度;然后基于模糊测试过程中实时的路径覆盖信息为经过稀有路径的样本增加其被挑选进行变异的概率;最后根据比较进度信息并结合启发式策略有针对性地对样本文件进行变异,通过变异引导提高模糊测试中生成能够绕过程序规约检查的有效样本的效率。实验结果表明,所提方法发现crash及发现新路径的能力均优于模糊测试工具AFL-Dyninst。  相似文献   
6.
This article presents a metaheuristic approach, the binary whale optimization algorithm (BWOA), to solve complex, constrained, non-convex, binary-nature profit-based unit commitment (PBUC) optimization problems of a price-taking generation company (GenCo) in the electricity market. To simulate the binary-nature PBUC problem, the continuous, real-value whale position/location is mapped into binary search space through various transfer functions. This article introduces three variants of BWOA using tangential hyperbolic, inverse tangent (arctan) and sigmoidal transfer functions. The effectiveness of the BWOA approaches is examined in test systems with different market mechanisms, i.e. an energy-only market, and energy and reserve market participation with different reserve payment methods. The simulation results are presented, discussed and compared with other existing approaches. The convergence characteristics, solution quality and consistency of the results across different BWOA variants are discussed. The superiority and statistical significance of the proposed approaches with respect to existing approaches is also presented.  相似文献   
7.
Multi-tag collision imposes a vital detrimental effect on reading performance of an RFID system. In order to ameliorate such collision problem and to improve the reading performance, this paper proposes an efficient tag identification algorithm termed as the Enhanced Adaptive Tree Slotted Aloha (EATSA). The key novelty of EATSA is to identify the tags using grouping strategy. Specifically, the whole tag set is divided into groups by a frame of size F. In cases multiple tags fall into a group, the tags of the group are recognized by the improved binary splitting (IBS) method whereas the rest tags are waiting in the pipeline. In addition, an early observation mechanism is introduced to update the frame size to an optimum value fitting the number of tags. Theoretical analysis and simulation results show that the system throughput of our proposed algorithm can reach as much as 0.46, outperforming the prior Aloha-based protocols.  相似文献   
8.
针对SIFT描述子实时性差和传统二进制描述子对尺度、旋转和视角变化鲁棒性差的问题,本文通过优化采样模式和添加灰度差分不变量比较测试进行改进,提出了一种鲁棒性更高的二进制描述子。首先,设计了一种尺度关联、编号标记的采样模式;然后,旋转采样模式中各采样点到特定位置,确保描述子尺度、旋转不变性;接着,分析了采样点点对模式对描述子的影响,选择使用机器学习训练后的128对采样点对;最后,选择灰度值比较测试及梯度绝对值和比较测试构建二进制描述子。实验中采用DoG检测图像关键点,结果表明:本文提出的描述子在描述子构建和描述子匹配上比SIFT描述子分别快84%和67%;在有视角变化的图像匹配上,准确率比传统的二进制描述子高3%~5%,召回率平均要高30%以上。本文提出的特征点描述方法适用于时间要求高的图像匹配领域。  相似文献   
9.
《Ceramics International》2020,46(17):26548-26556
Introducing high-performance compounds for hydrogen sorption is of interest because of their advantages for substantial applications such as energy storage. Here, the role of copper addition on hydrogen storage capability and Coulombic efficiency of CeO2 nanostructure (fabricated by an easy and surfactant-free sonochemical pathway) was examined, for the first time. Nanostructured oxides were fabricated with loading various percentages of copper (4 wt% and 40 wt%) inside CeO2. Nanostructured copper-ceria binary oxides were checked by diverse analyses. The hydrogen storage performance as well as Coulombic efficiency of the nanostructured copper-ceria binary oxides and the net CeO2 were checked through chronopotentiometry charge−discharge pathway in the alkaline medium. The outcomes exhibited that the hydrogen storage capacity of CeO2 nanostructure could be enhanced with adding the proper dosage of copper as a beneficial low-cost solution. Self-assembled copper-doped CeO2 hierarchical nanostructures could display the most appropriate performance than the net CeO2 and nanostructured Cu2O–CeO2. The discharge capacity for the self-assembled copper-doped CeO2 hierarchical nanostructures (fabricated by adding 4 wt% copper) could rise to 5070 mAh/g at 22nd cycle. Appropriate porosity, special architecture and unique morphology as well as convenient surface area of the self-assembled copper-doped CeO2 hierarchical nanostructures render they can be very beneficial compounds in the energy storage.  相似文献   
10.
实物期权法是对项目决策中的灵活性价值进行定量评估的一种方法,是对传统经济评价方法净现值法的修正补充。采用实物期权理论和方法,分析煤层气利用项目可研建设阶段和生产运营阶段的期权特征,确定出煤层气利用项目总价值为现金流量净现值与项目灵活性价值之和。采用二叉树期权定价方法,构建基于实物期权的煤层气利用项目投资评价方法和模型。并结合煤层气脱氧制液化天然气项目实例,在确定评价参数的基础上,分别用净现值法、基于实物期权的延迟期权方法、扩张期权方法及复合期权方法,计算煤层气项目投资价值,同时对评价方法主要影响参数进行敏感性分析。结果表明:实物期权法评价出的煤层气利用项目价值明显高于传统经济评价方法计算出的项目价值,而且组合期权能有效增加项目的价值;标的资产价值和期权执行价格对煤层气利用项目期权价值的影响最大。   相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号