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   5594篇
  免费   413篇
  国内免费   329篇
电工技术   108篇
综合类   263篇
化学工业   1059篇
金属工艺   296篇
机械仪表   341篇
建筑科学   219篇
矿业工程   46篇
能源动力   164篇
轻工业   188篇
水利工程   21篇
石油天然气   146篇
武器工业   63篇
无线电   597篇
一般工业技术   1292篇
冶金工业   57篇
原子能技术   68篇
自动化技术   1408篇
  2024年   3篇
  2023年   61篇
  2022年   107篇
  2021年   159篇
  2020年   139篇
  2019年   158篇
  2018年   135篇
  2017年   118篇
  2016年   182篇
  2015年   198篇
  2014年   242篇
  2013年   299篇
  2012年   293篇
  2011年   394篇
  2010年   275篇
  2009年   284篇
  2008年   358篇
  2007年   325篇
  2006年   357篇
  2005年   277篇
  2004年   293篇
  2003年   270篇
  2002年   265篇
  2001年   174篇
  2000年   157篇
  1999年   119篇
  1998年   115篇
  1997年   99篇
  1996年   96篇
  1995年   77篇
  1994年   59篇
  1993年   50篇
  1992年   49篇
  1991年   34篇
  1990年   27篇
  1989年   24篇
  1988年   21篇
  1987年   5篇
  1986年   9篇
  1985年   9篇
  1984年   6篇
  1983年   2篇
  1982年   4篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1973年   1篇
  1972年   1篇
排序方式: 共有6336条查询结果,搜索用时 185 毫秒
1.
A series of large scale direct shear experiments is used to investigate the effect of the geomembrane (GMB) surface roughness, geotextile (GTX) properties, and GTX ageing, on the GMB-GTX interface shear behaviour. Interfaces involving smooth, coextruded textured, and structured surface GMBs underlying four different nonwoven needle-punched staple fibres (GTXs) with mass per unit areas between 200 and 2400 g/m2, and a geocomposite drain (GCD) are examined at normal stresses between 250 and 1000 kPa. The results showed that the interlocking between the GMB and GTX increased with increasing the GMB asperity height and/or decreasing the mass per unit area of the GTX. For the interfaces that involved GTXs preaged prior to the shear box experiments for up to 2 years at 85 °C, it was found that the 2400 g/m2 heat bonded two-layered GTX exhibited internal shear failure at low shear displacements. However, all the highly aged single layered GTXs showed an increase in the peak interface friction angles with the increase in their ageing. For these single layered GTX, the results suggest that assessing the interface friction angles using unaged GTXs for the stability analysis is conservative as long as the GTX remains intact in the field.  相似文献   
2.
Interface shear strength of geosynthetic clay liners (GCL) with the sand particles is predominantly influenced by the surface characteristics of the GCL, size and shape of the sand particles and their interaction mechanisms. This study brings out the quantitative effects of particle shape on the interaction mechanisms and shear strength of GCL-sand interfaces. Interface direct shear tests are conducted on GCL in contact with a natural sand and a manufactured sand of identical gradation, eliminating the particle size effects. Results showed that manufactured sand provides effective particle-fiber interlocking compared to river sand, due to the favorable shape of its grains. Further, the role of particle shape on the hydration of GCL is investigated through interface shear tests on GCL-sand interfaces at different water contents. Bentonite hydration is found to be less in tests with manufactured sand, leading to better interface shear strength. Grain shape parameters of sands, surface changes related to hydration and particle entrapment in GCL are quantified through image analysis on sands and tested GCL surfaces. It is observed that the manufactured sand provides higher interface shear strength and causes lesser hydration related damages to GCL, owing to its angular particles and low permeability.  相似文献   
3.
Geogrid reinforcement can significantly improve the uplift bearing capacity of anchor plates. However, the failure mechanism of anchor plates in reinforced soil and the contribution of geogrids need further investigation. This paper presents an experimental study on the anchor uplift behavior in geogrid-reinforced soil using particle image velocimetry (PIV) and the high-resolution optical frequency domain reflectometry (OFDR). A series of model tests were performed to identify the relationship between the failure mechanism and various factors, such as anchor embedment ratio, number of geogrid layers, and their location. The test results indicate that soil deformation and the uplift resistance of anchor plates are substantially influenced by anchor embedment ratio and location of geogrids, whereas the number of geogrid layers has limited influence. In reinforced soil, increasing the embedment ratio greatly improves the ultimate bearing capacities of anchor plates and affects the interlock between the soil and geogrids. As the embedment depth increases, the failure surfaces gradually change from a vertical slip surface to a bulb-shaped surface that is limited within the soil. The strain monitoring data shows that the deformations of geogrids are symmetrical, and the peak strains of geogrids can characterize the reinforcing effects.  相似文献   
4.
供水管网仿真广泛应用于城市供水输配调度,是城市供水管网监测与维护的重要技术手段。由于在面向城市级的大规模管网中产生了海量的计算数据,因此在一般计算平台上无法满足管网仿真计算的算力需求。为提升城市级供水管网仿真的计算效率,提出一种有效的并行化方案。基于“嵩山”超级计算机系统采用中央处理器+数据缓存单元(CPU+DCU)架构,利用其在密集数据计算方面的优势,对“嵩山”超级计算机进行供水管网仿真。参照可移植性异构计算接口(HIP)异构编程模型,在“嵩山”超级计算机上实现供水管网仿真的异构计算,并结合管道数据分割方案,使用消息传递接口开启多进程以实现DCU加速数据通信传递。通过重定义数据类型解决计算过程中结构体传输问题,实现单节点内多DCU的大规模密集计算。在不同计算平台和多种计算策略仿真上的对比结果表明,与传统x86平台相比,该优化方案在小规模数据与大规模数据上的加速比分别达到5.269、10.760,与采用计算统一设备架构异构编程模型的传统GPU异构平台相比,计算性能有明显提高。  相似文献   
5.
Garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) electrolyte suffers from unstable chemical passivation under air exposure, responsible for the poor interfacial wettability and conductivity with Li metal. Instead of conventional methods to remove surface contaminants by mechanical polishing, acid etching and high temperature reduction, herein we propose a simple strategy of interfacial gas release and detergency to smartly convert Li2CO3 passivation layer into ion-conductive Li3PO4 domains at mild temperature (∼200 ℃). The in-situ formation of PH3 vapor and its phosphorization enables a dramatic decrease of Li/garnet interfacial resistance down to 2 Ω cm2 at room temperature (RT). The improved interfacial wettability and conductivity endow the symmetric cells with ultra-stable galvanostatic cycling over 1500 h and high critical current density of 2.6 mA/cm2. The high coulombic efficiency of Li plating enables a high reversibility of solid-state NCM811/Li cells even under a low N/P ratio (∼4) and high cut-off voltage of 4.5 V at RT. The prototype of fluoride-garnet solid-state batteries are successfully driven as rechargeable system (rather than widely known primary battery) with high conversion capacity (400 ∼ 500 mAh/g) and high-rate performance (251.2 mAh/g at 3 C). This interface infiltration-detergency approach provides a practical solution to the achievement of high-energy solid-state Li metal batteries.  相似文献   
6.
The interfacial oxidation behavior of Cr4Mo4V high-speed steel (HSS) joints undergoing hot-compression bonding was investigated by using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In the heating and holding processes, dispersed rod-like and granular $\delta - {\text{Al}}_{{2}} {\text{O}}_{{3}}$ oxides were formed at the interface and in the matrix near the interface due to the selective oxidation and internal oxidation of Al, while irregular Si–Al–O compounds and spheroidal SiO2 particles were formed at the interface. After the post-holding treatment, SiO2 oxides and Si–Al–O compounds were dissolved into the matrix, and $\delta - {\text{Al}}_{{2}} {\text{O}}_{{3}}$ oxides were transformed into nanoscale $\alpha - {\text{Al}}_{{2}} {\text{O}}_{{3}}$ particles, which did not deteriorate the mechanical properties of the joints. The formation and migration of newly-formed grain boundaries by plastic deformation and post-holding treatment were the main mechanism for interface healing. The tensile test results showed that the strength of the healed joints was comparable to that of the base material, and the in-situ tensile observations proved that the fracture was initiated at the grain boundary of the matrix rather than at the interface. The clarification of interfacial oxides and microstructure is essential for the application of hot-compression bonding of HSSs.  相似文献   
7.
With the development of human–computer interaction technology, brain–computer interface (BCI) has been widely used in medical, entertainment, military, and other fields. Imagined speech is the latest paradigm of BCI and represents the mental process of imagining a word without making a sound or making clear facial movements. Imagined speech allows patients with physical disabilities to communicate with the outside world and use smart devices through imagination. Imagined speech can meet the needs of more complex manipulative tasks considering its more intuitive features. This study proposes a classification method of imagined speech Electroencephalogram (EEG) signals with discrete wavelet transform (DWT) and support vector machine (SVM). An open dataset that consists of 15 subjects imagining speaking six different words, namely, up, down, left, right, backward, and forward, is used. The objective is to improve the classification accuracy of imagined speech BCI system. The features of EEG signals are first extracted by DWT, and the imagined words are classified by SVM with the above features. Experimental results show that the proposed method achieves an average accuracy of 61.69%, which is better than those of existing methods for classifying imagined speech tasks.  相似文献   
8.
Li+ doping is regarded as an effective strategy to enhance the room-temperature hydrogen storage of metal-organic frameworks (MOFs). In this work, Li+ is doped into both MIL-100(Fe) and MIL-100(Fe)/graphene oxide (GO) composite, and it is demonstrated that the hydrogen uptake of Li+ doped MIL-100(Fe)/GO (2.02 wt%) is improved by 135% compared with Li+ doped MIL-100(Fe) (0.86 wt%) at 298 K and 50 bar, which is ascribed to its higher isosteric heat of adsorption (7.33 kJ/mol) resulting from its more accessible adsorption sites provided by doped Li+ ions and ultramicropores. Grand canonical Monte Carlo (GCMC) simulation reveals that Li+ ions distributing in the interface between MIL-100(Fe) and GO within MIL-100(Fe)/GO composite is favorable for hydrogen adsorption owing to the increased number of adsorption sites, thus contributing to the enhanced hydrogen storage capacity. These findings demonstrate that MIL-100(Fe)/GO is a more promising Li+ doping substrate than MIL-100(Fe).  相似文献   
9.
Highly active, low-cost, and durable electrocatalysts toward hydrogen evolution reaction (HER) are crucial for electrochemical water splitting. Herein, a green, facial, and effective strategy was proposed to develop CoP on carbon cloth (CoP/o-CC) as efficient self-supported hydrogen evolution electrodes. The designed CoP/o-CC exhibits superior catalytic activity with overpotentials of 118 mV and 95.45 mV to deliver a current density of 10 mA cm?2 in acidic and alkaline solution, respectively, which is superior to most reported studies. In addition, the designed CoP/o-CC electrode also possesses excellent stability even under a large current density of 100 mA cm?2. The origin of significantly enhanced stability thereby was further systematically investigated. Experimental study reveals that the oxygenated functional groups on carbon cloth play the role to bind the CoP electrocatalysts, forming C-O-Co bonds. Thus, the enhanced electrochemical and structural stability of CoP/o-CC is predominantly caused by the interfacial interaction of the C-O-Co bonds between the CoP active materials and surface oxygenated functional groups of carbon fiber. Therefore, we believe that this work provides an in-depth insight into the role of interfacial interaction between the substrate and the catalysts and offers a new methodology to design durable and efficient electrocatalysts.  相似文献   
10.
泡沫在常规与非常规油气开发、CO2埋存上的应用效果与其稳定性密切相关。以挖掘高盐储层自身潜力为目标,利用盐诱导油酸酰胺丙基甜菜碱(ODAB)构建高稳泡沫,并结合ODAB的表面性质、体相性质以及液膜薄化行为探究主导其稳定性的关键机制。研究结果表明,在低ODAB浓度下(质量分数为0.02%~0.05%),泡沫稳定性由表面扩张黏弹性控制,高盐可降低体相与表面间的分子扩散交换速度,令表面扩张黏弹性增强,泡沫稳定性提高。随着ODAB浓度增加,虽表面扩张黏弹性降低,但高盐可诱导蠕虫状胶束形成、生长并逐渐紧密纠缠,从而促使体相黏弹性增强,液膜薄化特征转变、速度下降。在高ODAB浓度下(质量分数为0.05%~1.00%),体相黏弹性对盐度、ODAB浓度变化的响应与泡沫稳定性完全一致,是ODAB泡沫稳定性改善的决定性因素。  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