全文获取类型
收费全文 | 495486篇 |
免费 | 50762篇 |
国内免费 | 38492篇 |
专业分类
电工技术 | 38138篇 |
技术理论 | 62篇 |
综合类 | 56102篇 |
化学工业 | 68427篇 |
金属工艺 | 20074篇 |
机械仪表 | 30642篇 |
建筑科学 | 48688篇 |
矿业工程 | 17857篇 |
能源动力 | 14396篇 |
轻工业 | 30417篇 |
水利工程 | 16787篇 |
石油天然气 | 16166篇 |
武器工业 | 4912篇 |
无线电 | 49216篇 |
一般工业技术 | 45083篇 |
冶金工业 | 20713篇 |
原子能技术 | 6217篇 |
自动化技术 | 100843篇 |
出版年
2024年 | 920篇 |
2023年 | 5684篇 |
2022年 | 9977篇 |
2021年 | 13292篇 |
2020年 | 13436篇 |
2019年 | 11973篇 |
2018年 | 11120篇 |
2017年 | 14401篇 |
2016年 | 16565篇 |
2015年 | 18859篇 |
2014年 | 26620篇 |
2013年 | 28834篇 |
2012年 | 34771篇 |
2011年 | 38175篇 |
2010年 | 29498篇 |
2009年 | 30282篇 |
2008年 | 30185篇 |
2007年 | 36700篇 |
2006年 | 34634篇 |
2005年 | 30101篇 |
2004年 | 25627篇 |
2003年 | 21966篇 |
2002年 | 17792篇 |
2001年 | 14283篇 |
2000年 | 11718篇 |
1999年 | 9659篇 |
1998年 | 7540篇 |
1997年 | 6456篇 |
1996年 | 5828篇 |
1995年 | 5116篇 |
1994年 | 4420篇 |
1993年 | 3350篇 |
1992年 | 2856篇 |
1991年 | 2184篇 |
1990年 | 1865篇 |
1989年 | 1564篇 |
1988年 | 1212篇 |
1987年 | 817篇 |
1986年 | 633篇 |
1985年 | 633篇 |
1984年 | 572篇 |
1983年 | 446篇 |
1982年 | 442篇 |
1981年 | 282篇 |
1980年 | 238篇 |
1979年 | 164篇 |
1978年 | 92篇 |
1977年 | 113篇 |
1976年 | 88篇 |
1975年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
41.
《Geotextiles and Geomembranes》2022,50(5):910-921
This paper presents a field-scale experimental track over a poor subgrade with an unreinforced section and a geocell-reinforced section subjected to in-situ performance tests. Plate load tests and Benkelman beam tests were carried out distributed in several unreinforced and reinforced layers. The objective was to: (1) examine the variability of the elastic modulus of unbound granular material (UGM) due the influence of its thickness and the presence of poor subgrade in its base, (2) evaluate the modulus improvement factor (MIF) generated by the geocell reinforcement in the UGM and (3) verify the most appropriate condition to apply the MIF to transport infrastructure design. The results showed that there is a significant influence of the thickness of the UGM layer on its elastic modulus when the layer is supported directly over a soft subgrade. The MIF values obtained in field suggest that its determination is mostly related to the UGM maximum elastic modulus rather than its decreased values (by virtue of poor subgrade or reduced thicknesses), and that the analytical formulation presented for MIF calculation has good predictive capability to be applied to pavement design. 相似文献
42.
《Geotextiles and Geomembranes》2022,50(5):994-1003
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
43.
为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成;细菌群落在不同季节有显著差异;地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用;随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。 相似文献
44.
《Ceramics International》2022,48(4):4710-4721
In this study, AA5083 sheets were reinforced with four different hybrid nanoparticles by friction stir processing (FSP) for the development of surface nanocomposites used in advanced engineering applications. The present research focused on improving the properties and tribological behaviour of AA5083 alloy surfaces, including novel hybrid nanoparticles and the intermetallic phase formed during FSP. A tribometer tester with a constant normal load was used to examine the tribological performance of the hybrid composites. After the wear test, a surface profiler inspector was used to analyse the morphology and surface roughness of the examined materials. The Vickers micro-hardness of the base metal and the manufactured composites were measured. During FSP, a new intermetallic phase of AlV3 was successfully formed at 300–400 °C in the hybrid nanocomposites containing VC particles. The reinforcements resulted in additional grain refining than FSP. The AA5083/Ta2C–Al2O3 exhibited the greatest grain refinement, a sixty-fold reduction in grain size compared to that of the base alloy. The results revealed that the hybrid nanocomposites containing VC particles demonstrated the most significant microhardness values inside the stirred zone as a result of the presence of the AlV3 phase, which was increased by 25–30%. Moreover, the mechanical properties were significantly improved for all manufactured nanocomposites. The tensile strength was increased by 28% through the hybridisation of AA5083 using a hybrid of VC-GNPs. The dispersion of Ta2C-GNPs and VC-GNPs in the matrix led to excellent interfacial adhesion, resulting in an enhancement in the mechanical properties. The AA5083/VC-GNPs surface composite outperformed other manufactured composites regarding wear resistance. In addition, due to GNPs soft nature, it reduced the coefficient of friction (COF) of the manufactured composites by 20–25% compared to other reinforcements. 相似文献
45.
Gehad Abo-Lila Taha Sokkar Eman Seisa Emam Omar 《Microscopy research and technique》2022,85(2):667-684
In this article, an adaptive denoising method is suggested to accurate investigate the optical and structural features of polymeric fibers from noisy phase shifting microinterferograms. The mixed class of noise that may produce in the phase-shifting interferometric techniques is established. To our knowledge, this is an early study considered the mixing noises that may occur in microinterferograms. The suggested method utilized the convolution neural networks to detect the noise class and then denoising, it according to its class. Four convolution neural networks (Googlenet, VGG-19, Alexnet, and Alexnet–SVM) are refined to perform the automatic classification process for the noise class in the established data set. The network with the highest validation and testing accuracy of these networks is considered to apply the suggested method on realistic noisy microinterferograms for polymeric fibers, polypropylene and antimicrobial polyethylene terephthalate)/titanium dioxide, recoded using interference microscope. Also, the suggested method is applied on noisy microinterferograms include crazing and nanocomposite material. The demodulated phase maps and the three-dimensional birefringence profiles are calculated for tested fibers according to the suggested method. The obtained results are compared with the published data for these fibers and found to be in good agreements. 相似文献
46.
本文介绍“风险矩阵法”进行风险分级工作的基本思路,结合水泥厂的生产特点通过危险有害因素辨识,获得危险源分布情况,采用风险矩阵法对风险进行评估,按风险值将风险等级划分为重大风险、较大风险、一般风险和低风险,为水泥生产企业的安全风险分级工作提供参考。 相似文献
47.
《中国稀土学报(英文版)》2022,40(11):1751-1762
Metal organic frameworks (MOFs) derivatives represented by quasi-MOFs have excellent physical and chemical properties and can be applied for the catalytic combustion of volatile organic compounds (VOCs). In this work, Pd/quasi-Ce-BTC synthesized by simple one-step N2 pyrolysis was applied to the oxidation of toluene, showing excellent toluene catalytic activity (T90 = 175 °C, 30000 mL/(g·h)). Microscopic analyses indicate the formation and interaction of a carbon matrix composite quasi-MOF structure interface. The results show that the amorphous carbon matrix formed during the partial pyrolysis of Ce-BTC significantly improves the adsorption and activation capacity of toluene in the reaction, and constructs a reductive system to maintain high concentrations of Ce3+ and Pd0, which can facilitate the activation and utilization of oxygen in reaction. Quasi in-situ XPS proves that carbon matrix is indirectly involved in the activation and storage of oxygen, and Pd0 is the crucial active site for the activation of oxygen. Stability and water resistance tests display good stability of Pd/quasi-Ce-BTC. This work provides a potential method for designing quasi-MOF catalysts towards VOCs effective abatement. 相似文献
48.
Reham Alabduljabbar 《计算机系统科学与工程》2022,40(1):1-15
It is a common observation that whenever patients arrives at the front desk of a hospital, outpatient clinic, or other health-associated centers, they have to first queue up in a line and wait to fill in their registration form to get admitted. The long waiting time without any status updates is the most common complaint, concerning health officials. In this paper, UrNext, a location-aware mobile-based solution using Bluetooth low-energy (BLE) technology is presented to solve the problem. Recently, a technology-oriented method, the Internet of Things (IoT), has been gaining popularity in helping to solve some of the healthcare sector’s problems. The implementation of this solution could be illustrated through a simple example of when a patient arrives at a clinic for a consultation. Instead of having to wait in long lines, that patient will be greeted automatically, receive a push notification of an admittance along with an estimated waiting time for a consultation session. This will not only provide the patients with a sense of freedom but would also reduce the uncertainty levels that are generally observed, thus saving both time and money. This work aims to improve the clinics’ quality of services, organize queues and minimize waiting times, leading to patients’ comfort while reducing the burden on nurses and receptionists. The results demonstrate that the presented system is successful in its performance and helps achieves a pleasant and conducive clinic visitation process with higher productivity. 相似文献
49.
Software is a central component in the modern world and vastly affects the environment’s sustainability. The demand for energy and resource requirements is rising when producing hardware and software units. Literature study reveals that many studies focused on green hardware; however, limited efforts were made in the greenness of software products. Green software products are necessary to solve the issues and problems related to the long-term use of software, especially from a sustainability perspective. Without a proper mechanism for measuring the greenness of a particular software product executed in a specific environment, the mentioned benefits will not be attained. Currently, there are not enough works to address this problem, and the green status of software products is uncertain and unsure. This paper aims to identify the green measurements based on sustainable dimensions in a software product. The second objective is to reveal the relationships between the elements and measurements through empirical study. The study is conducted in two phases. The first phase is the theoretical phase, where the main components, measurements and practices that influence the sustainability of a software product are identified. The second phase is the empirical study that involved 103 respondents in Malaysia investigating current practices of green software in the industrial environment and further identifying the main sustainability dimensions and measurements and their impact on achieving green software products. This study has revealed seven green measurements of software product: Productivity, Usability, Cost Reduction, Employee Support, Energy Efficiency, Resource Efficiency and Tool Support. The relationships are statistically significant, with a significance level of less than 0.01 (p = 0.000). Thus, the hypothesised relationships were all accepted. The contributions of this study revolve around the research perspectives of the measurements to attain a green software product. 相似文献