全文获取类型
收费全文 | 155040篇 |
免费 | 19596篇 |
国内免费 | 9227篇 |
专业分类
电工技术 | 52266篇 |
技术理论 | 7篇 |
综合类 | 13617篇 |
化学工业 | 14966篇 |
金属工艺 | 4475篇 |
机械仪表 | 8368篇 |
建筑科学 | 6889篇 |
矿业工程 | 3837篇 |
能源动力 | 13078篇 |
轻工业 | 3991篇 |
水利工程 | 8037篇 |
石油天然气 | 5211篇 |
武器工业 | 1382篇 |
无线电 | 15096篇 |
一般工业技术 | 8734篇 |
冶金工业 | 4618篇 |
原子能技术 | 3482篇 |
自动化技术 | 15809篇 |
出版年
2024年 | 337篇 |
2023年 | 2155篇 |
2022年 | 4054篇 |
2021年 | 4826篇 |
2020年 | 5302篇 |
2019年 | 4480篇 |
2018年 | 4033篇 |
2017年 | 5602篇 |
2016年 | 6051篇 |
2015年 | 6636篇 |
2014年 | 10528篇 |
2013年 | 9785篇 |
2012年 | 12117篇 |
2011年 | 13257篇 |
2010年 | 9573篇 |
2009年 | 9869篇 |
2008年 | 9402篇 |
2007年 | 11097篇 |
2006年 | 9957篇 |
2005年 | 8305篇 |
2004年 | 6746篇 |
2003年 | 5716篇 |
2002年 | 4458篇 |
2001年 | 3775篇 |
2000年 | 3226篇 |
1999年 | 2504篇 |
1998年 | 1747篇 |
1997年 | 1397篇 |
1996年 | 1372篇 |
1995年 | 1175篇 |
1994年 | 1020篇 |
1993年 | 709篇 |
1992年 | 609篇 |
1991年 | 378篇 |
1990年 | 362篇 |
1989年 | 283篇 |
1988年 | 201篇 |
1987年 | 148篇 |
1986年 | 103篇 |
1985年 | 72篇 |
1984年 | 111篇 |
1983年 | 81篇 |
1982年 | 72篇 |
1981年 | 35篇 |
1980年 | 28篇 |
1979年 | 32篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1959年 | 32篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
采用基于计算流体力学方法的全尺度数值模拟计算,建立了适用于潮流能水轮机模拟的剪切来流环境,通过数值计算结果,对潮流能水轮机随时间变化的宏观力和流场特征进行了系统分析,探索水轮机在复杂工况下的水动力特性规律。结果表明,水轮机整个叶轮的总体平均受力在剪切流工况中未受到明显影响; 单个叶片的瞬态轴向力系数和瞬态轴向扭矩系数在旋转周期内出现了明显的周期性变化,且周期性变化幅值随转速增大而增大; 非定常的瞬时轴向扭矩和力的周期性振荡容易引起单个叶片的结构性振动,可能对水轮机的机械结构造成影响。 相似文献
92.
Wax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively. 相似文献
93.
针对齿轮故障特征微弱,在强背景噪声下难以有效提取的问题,提出了一种改进奇异谱分解(ISSD)结合奇异值分解(SVD)的齿轮故障特征提取方法。针对奇异谱分解(SSD)算法中模态参数需凭经验选取的缺陷,基于散布熵优化算法对SSD算法进行了改进,在得到既定的一组奇异谱分量的基础上,根据峭度值最大准则筛选出了最佳奇异谱分量并进行了SVD处理,采用奇异值能量标准谱自适应地确定了信号重构阶数以还原信号和提高降噪效果。最后对信号进行包络解调以提取齿轮故障特征,将所提方法运用到仿真信号和齿轮实测信号中,并同传统包络谱、SSD包络谱以及经验模态分解结合SVD(EMD-SVD)方法进行了对比分析,结果表明,所提方法的降噪和特征提取效果更佳,能够更加有效地实现齿轮故障的判别。 相似文献
94.
《Food Control》2015
A diverse range of genetic elements has been used to develop genetically modified organisms (GMOs) over the last 18 years. Screening methods that target few elements, such as the Cauliflower Mosaic Virus 35S promoter (P-35S) and Agrobacterium tumefaciens nopaline terminator (T-nos), are not sufficient to screen GMOs. In the present study, a multiplex PCR system for all globally commercialized GM soybean events was developed to easily trace the events. For this purpose, screening elements of 24 GM soybean events were investigated and 9 screening targets were selected and divided into three individual triplex PCR systems: P-35S, ribulose-1,5-bisphosphate carboxylase small subunit promoter of Arabidopsis thaliana, T-nos, T-35S, pea E9 terminator, open reading frame 23 terminator of A. tumefaciens, proteinase inhibitor II terminator of potato, acetohydroxy acid synthase large subunit terminator of A. thaliana, and the revealed 3′ flanking sequences of DP-305423-1. The specificity of the assays was confirmed using thirteen GM soybean events as the respective positive/negative controls. The limit of detection of each multiplex set, as determined using certified reference materials of specific GM events, ranged from 0.03 to 0.5%, depending upon target. Furthermore, 26 food samples that contained soybean ingredients, which were purchased from the USA, China, Japan, and Korea, were analyzed, 17 of which contained one or more GM soybean events. These results suggest that the developed screening method can be used to efficiently track and identify 24 GM soybean events in food and feed. 相似文献
95.
96.
97.
《International Journal of Hydrogen Energy》2020,45(8):5367-5374
High-entropy alloys (HEAs), as a new class of metallic materials, have received more and more attention due to its excellent mechanical properties. In this study, the hydrogen absorption properties, such as hydrogen absorption capacity, thermodynamics, kinetics and cyclic properties, as well as the hydride structure of a newly designed TiZrNbTa HEA were investigated. The results showed that multiple hydrides including ε-ZrH2, ε-TiH2 and β-(Nb,Ta)H were found in the TiZrNbTa HEA after hydrogenation. With the increase of temperature from 293 K to 493 K, the maximum hydrogen absorption capacity decreased from 1.67 wt% to 1.25 wt% and the plateau pressure related with β-(Nb,Ta)H hydrides increased from 1.6 kPa to 14.8 kPa. The formation enthalpy of β-(Nb,Ta)H hydride was determined to be −6.4 kJ/mol, which was less stable than that of NbH and TaH hydrides. The results also showed that the TiZrNbTa HEA exhibited a rapid hydrogen absorption kinetic even at the room temperature with a short incubation time, and the hydrogen absorption mechanism was determined to be the nucleation and growth mechanism. Moreover, the hydrogen absorption capacity at 293 K decreased slowly with the cycle numbers, and remained 86% capacity after 10 cycles. Cracking occurred after hydrogen absorption and became worse with cycles. 相似文献
98.
浮选机矿化器是用于浮选矿浆预处理的重要设备,其性能的优劣直接影响到浮选机的工作效果。文章通过流体力学仿真软件FLUENT对XJM-KS型浮选机矿化器的内部流场进行数值仿真,重点研究了聚焦式喷嘴布置所带来的流场特征。模拟结果表明,高速的矿浆射流能够在混合室内产生-2.43×10Pa的负压区,从而吸入大量的空气,实现空气与矿浆的有效混合与预矿化,与传统的机械搅拌式矿浆预处理装置相比,该矿化器能够大幅度提高预矿化效果。 相似文献
99.
Biocatalysis offers a broad spectrum of possible ecological and economic advantages over conventional chemical catalysis processes, e.g., lower energy consumption and high enantio selectivity. The focus of this work is on gas-liquid reactions. These are of great importance in the chemical and biochemical industry and subject of current research since they are often limited by mass transfer or show low selectivity. Different suitable biocatalytically gas-liquid reaction systems were tested in capillary reactor designs in order to obtain information about the interaction between reaction and fluid mechanics. Furthermore, an optical measuring method was established. The experiments were performed in batch mode in a glass beaker with a flow cuvette for UV/Vis measurement of product concentration. 相似文献
100.
《International Journal of Hydrogen Energy》2020,45(16):9803-9810
High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm−2 are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm−2, which is stable during 200 charge-discharge cycles. 相似文献