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   6814篇
  免费   531篇
  国内免费   429篇
电工技术   374篇
技术理论   5篇
综合类   798篇
化学工业   549篇
金属工艺   142篇
机械仪表   416篇
建筑科学   693篇
矿业工程   135篇
能源动力   244篇
轻工业   182篇
水利工程   259篇
石油天然气   147篇
武器工业   51篇
无线电   472篇
一般工业技术   929篇
冶金工业   381篇
原子能技术   51篇
自动化技术   1946篇
  2023年   79篇
  2022年   90篇
  2021年   129篇
  2020年   171篇
  2019年   192篇
  2018年   173篇
  2017年   212篇
  2016年   223篇
  2015年   255篇
  2014年   355篇
  2013年   498篇
  2012年   401篇
  2011年   523篇
  2010年   401篇
  2009年   437篇
  2008年   418篇
  2007年   482篇
  2006年   440篇
  2005年   357篇
  2004年   316篇
  2003年   278篇
  2002年   237篇
  2001年   178篇
  2000年   147篇
  1999年   123篇
  1998年   103篇
  1997年   78篇
  1996年   82篇
  1995年   65篇
  1994年   53篇
  1993年   37篇
  1992年   50篇
  1991年   29篇
  1990年   29篇
  1989年   21篇
  1988年   14篇
  1987年   9篇
  1986年   11篇
  1985年   7篇
  1984年   9篇
  1983年   3篇
  1982年   7篇
  1978年   3篇
  1964年   3篇
  1960年   3篇
  1958年   3篇
  1957年   6篇
  1956年   2篇
  1955年   4篇
  1954年   3篇
排序方式: 共有7774条查询结果,搜索用时 15 毫秒
1.
随着乙烷产品价值的进一步提升,国内各大油田正大力开展天然气乙烷回收,以提高油田的综合收益。以克拉美丽气田天然气乙烷回收工艺为例,基于序贯模块法建立了天然气乙烷回收系统模型;求解得到该系统的模拟顺序后,采用HYSYS软件建立了计算模型,分析了乙烷回收工艺中各关键参数的影响,并基于?分析方法对该乙烷回收系统进行了评价;最后,以乙烷产品最小比功耗为目标函数,采用序列二次规划(SQP)优化方法对乙烷回收工艺参数进行了优化。结果表明:采用序贯模块法模拟天然气乙烷回收系统具有较好的适用性;经参数优化后,乙烷收率由92.62%提高到97.01%,乙烷产品比功耗降低了约5.4%。  相似文献   
2.
AgNbO3 lead free AFE ceramics are considered as one of the promising alternatives to energy storage applications. In the majority of studies concerning the preparation of AgNbO3 AFE ceramics, an oxygen atmosphere is required to achieve high performance, increasing the complexity of the fabrication process. Herein, a facile approach to preparing AgNbO3 ceramics in the ambient air was reported, in which the AgNbO3 ultrafine powder with stable perovskite structure was synthesized by hydrothermal method instead of the conventional ball milling process, leading to a lower temperature of phase formation and thus smaller grain size. The resulting ceramics sintered at 940 °C displayed high breakdown strength (216 kV/cm) and a recoverable energy density of 3.26 J/cm3 with efficiency of 53.5 %. Also, the high thermal stability of recoverable energy density (with minimal variation of ≤20 %) and efficiency (≤ 10 %) over 30–150℃, enables AgNbO3 ceramics achieved to be a promising candidate for energy storage applications.  相似文献   
3.
作为一种基于项目的协同过滤推荐算法,Slope One算法易于实现且高效。但由于Slope One算法未考虑用户相似性,导致其在处理涉及用户关系的个性化推荐任务时性能不高。针对以上问题,提出了改进的Slope One算法。提出一种均衡接近度灰关联分析方法计算用户之间的均衡接近度,利用均衡接近度度量用户间的相似程度,然后将均衡接近度值融入到Slope One算法中进行评分预测,在MovieLens和Epinions数据集下的对比实验表明,该算法具有更低的平均绝对误差(MAE)和均方根误差(RMSE),提高了预测的准确度和推荐质量。  相似文献   
4.
以去离子水为溶剂,低成本工业硅溶胶为硅源,在纯水体系下制备低成本的SiO2纳米多孔材料,使用酸碱两步法催化,添加表面活性剂来降低溶剂的表面张力,从而减少样品在干燥过程中的开裂。最后经过常压老化干燥制备得到 SiO2纳米多孔材料。制备得到的SiO2块体密度为150~400mg/cm3,室内热导率约为0.04~0.07W/(m.K)。这种方法制备的SiO2纳米多孔材料大幅缩减制备成本,采用HCl作为酸性催化剂提高了工业生产安全,将很大程度上推动纳米多孔材料的工业化生产和应用。  相似文献   
5.
Information and Communication Technology for Development (ICT4D) projects have shown a great promises in recent years. However, simply materializing of ICT4D projects is not enough for minimizing the prevalent digital divide in rural areas in developing countries. For the success of an Information and Communication Technology (ICT) intervention, it is important to consider the capabilities of users, who are responsible for converting ICT resources into outcome. While most of the ICT-related studies are focused on the adoption of actual technologies and influences of different internal and external factors on intervention outcomes, very few studies are focused on evaluating intervention outcomes and redesigning intervention strategies. In this study, I opted for using a conceptual framework following the Capability Approach that simultaneously identifies the influence factors for intervention outcome as well as evaluates the outcome based on Noble Laureate Amartya Sen’s five freedoms concept. A qualitative technique has been chosen to conduct the study. As part of the impact evaluation of an ICT4D intervention, a project known as Union Digital Centres (UDCs) in Bangladesh was selected. A total of ten themes are identified indicating that the outcome of the intervention is contributing to socio-economic and human development. However, the study has revealed that lack of capabilities of users (e.g. prior knowledge and financial inability) bar the UDC programs to fulfill their goals at highest level. This study would practically help the UDC policy makers to adjust the UDC intervention design by addressing the shortcomings of the users to yield higher UDC program outcome. Additionally, this study theoretically contributes in ICT adoption literature by showing that there is a mutual influence between users’ capabilities and ICT-related project outcomes. Finally, using specific case study (ICT4D project in Bangladesh), this study contextualizes Amartya Sen’s five freedoms concept in the ICT-specific context.  相似文献   
6.
Hydrogen gas production was investigated by electrohydrolysis of food waste due to its high organic content. Different voltages generated by DC power supply were applied to food waste in order to produce hydrogen gas. Effects of the DC voltage, reaction time and initial solid content on cumulative hydrogen gas production, hydrogen gas content in the gas phase and total organic carbon (TOC) removal were investigated by using a Box-Behnken statistical experiment design approach. The most suitable voltage/reaction time/solid content values resulting in the highest hydrogen gas content (99%), the highest cumulative hydrogen gas formation (7000 mL) and total organic carbon removal (33%) were determined as 5 V/75 h/20%. The results indicated that food wastes constitute a good source for H2 gas production by electrohydrolysis. Hydrogen gas produced by electrohydrolysis of food waste can be directly used in fuel cells due to its high putrity.  相似文献   
7.
为了反映织物内部纱线的空间构型和微观几何结构,针对在织物建模过程中,因忽略纤维间的相互作用而引起的纱线截面形状变化的问题,基于数字单元法理论,提出了一种计算纤维间摩擦力的方法。通过纱线纤维化离散,用数值模拟和仿真方法模拟三维正交织物成型过程,建立了5种精度递进的微观几何结构数值模型。5种模型中的每根纱线分别由4、7、12、19和37根数字纤维表征。研究结果表明:随着纱线纤维化离散程度的提高,仿真时间延长,织物厚度减小,纤维体积分数增大,节点平均作用力下降速度变缓,势能变小;当每根纱线由19根数字纤维组成时,所建织物的微观几何结构数值模型与真实织物样本在显微镜下的内部切片图像较为吻合。  相似文献   
8.
路东兴 《世界有色金属》2020,(2):223-223,225
伴随着人类社会的向前推进,信息技术已经渗透到我们生活的方方面面,深刻地改变了教育事业,慕课就是在信息时代下诞生的一种新兴教学工具。但是,如何利用好这一工具却仍然是个值得研究的课题。本文从慕课的内涵出发,分析了将混合式教学模式应用于慕课这一教学平台的重要意义。并且,就混合式教学模式在慕课平台中的应用进行了分析。希望能够给相关工作者以一定的启发。  相似文献   
9.
A novel mixing principle utilising oscillating liquid columns was analysed numerically with regard to particle dispersion characteristics. For producing fluid oscillations a pipe (diameter 100 mm) was immersed centrally into a vessel (diameter 450 mm) filled with liquid (filling height 700 mm) and periodically pressurised (frequency 1.2 Hz). The outlet geometry of the central pipe, just ending near the vessel bottom, has a strong effect on mixing and was optimised in this study. The principle of a FPR-mixer does not require rotating stirrers and in the turbulent regime it has power numbers comparable to propellers. The numerical calculations were conducted by a Euler/Lagrange approach neglecting two-way coupling as well as inter-particle collisions for clarity in order to only focus on the effect of interfacial forces on particle dispersion. The continuous phase was calculated in an unsteady way based on the Reynolds-averaged equations combined with the k-ω-SST (shear stress transport) turbulence model. Lagrangian tracking was conducted considering all relevant forces; drag, gravity/buoyancy, fluid inertia, added mass, Basset force and transverse lift forces due to shear and particle rotation. The importance of these forces was analysed with respect to the turbulent particle Stokes number (considered range 0.004 < St < 10.0) and particle/liquid density ratio (i.e. 1.05, 1.5 and 2.5). Finally, the significance of Basset force and shear-rotation lift force (i.e. Magnus effect) on the dispersion process was quantified by mixing parameters.  相似文献   
10.
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