全文获取类型
收费全文 | 69636篇 |
免费 | 7268篇 |
国内免费 | 3740篇 |
专业分类
电工技术 | 4991篇 |
技术理论 | 4篇 |
综合类 | 6071篇 |
化学工业 | 4693篇 |
金属工艺 | 3201篇 |
机械仪表 | 5566篇 |
建筑科学 | 1460篇 |
矿业工程 | 2029篇 |
能源动力 | 692篇 |
轻工业 | 5719篇 |
水利工程 | 498篇 |
石油天然气 | 1926篇 |
武器工业 | 1376篇 |
无线电 | 15290篇 |
一般工业技术 | 5170篇 |
冶金工业 | 2243篇 |
原子能技术 | 607篇 |
自动化技术 | 19108篇 |
出版年
2024年 | 162篇 |
2023年 | 941篇 |
2022年 | 1425篇 |
2021年 | 1940篇 |
2020年 | 1888篇 |
2019年 | 1384篇 |
2018年 | 1366篇 |
2017年 | 1952篇 |
2016年 | 2195篇 |
2015年 | 2661篇 |
2014年 | 3898篇 |
2013年 | 3760篇 |
2012年 | 4912篇 |
2011年 | 5477篇 |
2010年 | 3990篇 |
2009年 | 4038篇 |
2008年 | 4182篇 |
2007年 | 5181篇 |
2006年 | 4516篇 |
2005年 | 4069篇 |
2004年 | 3394篇 |
2003年 | 2951篇 |
2002年 | 2399篇 |
2001年 | 1937篇 |
2000年 | 1692篇 |
1999年 | 1337篇 |
1998年 | 1134篇 |
1997年 | 1002篇 |
1996年 | 832篇 |
1995年 | 680篇 |
1994年 | 630篇 |
1993年 | 534篇 |
1992年 | 410篇 |
1991年 | 324篇 |
1990年 | 289篇 |
1989年 | 251篇 |
1988年 | 179篇 |
1987年 | 101篇 |
1986年 | 77篇 |
1985年 | 107篇 |
1984年 | 70篇 |
1983年 | 94篇 |
1982年 | 62篇 |
1981年 | 46篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 19篇 |
1977年 | 26篇 |
1976年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 812 毫秒
61.
In this paper, we proposed a robust discrete-time controller. This control system, which is derived from the idea of the normalized plant, does not include plant parameters. Thus, we obtain a control system independent of plant parameters and that has the same structure as a conventional optimal servo control system. Simulation and experimental results show that the proposed method is fairly robust to plant parameter variations and external disturbances. 相似文献
62.
针对行星齿轮箱中各部件所激起的振动成分混叠、早期故障特征经常被较强的各级齿轮谐波成分以及环境噪声所湮没的问题,提出一种多共振分量融合卷积神经网络(multi-resonance component fusion based convolutional neural network,简称MRCF-CNN)的行星齿轮箱故障诊断方法。首先,对振动信号进行共振稀疏分解,得到包含齿轮谐波成分的高共振分量和可能包含轴承故障冲击成分的低共振分量;其次,构建多共振分量融合卷积神经网络,将得到的高、低共振分量和原始振动信号进行自适应的特征级融合,通过有监督的方式训练模型并进行行星齿轮箱故障诊断。对行星齿轮箱实验数据的分析结果表明,该方法能够有效分类行星齿轮箱中滚动轴承和齿轮的故障,成功对行星齿轮箱故障进行诊断,同时能够进一步增强卷积神经网络对振动信号所蕴含的故障信息的辨识能力。 相似文献
63.
64.
The present study focuses on experimental investigation of through the thickness displacement and strain field in thin adhesive layer in single sided (unsymmetrical) patch repaired CFRP (carbon fiber reinforced polymer) panel under tensile load. Digital image correlation (DIC) technique is employed to acquire the displacement and strain (longitudinal, peel and shear) field. Experimental determination of shear transfer length based on shear strain field obtained from DIC is introduced to estimate the optimum overlap length which is an essential parameter in patch design for the repair of CFRP structures. Further, DIC experiment with magnified optics is performed to get an insight into complex and localized strain field over thin adhesive layer especially at critical zones leading to damage initiation. The failure mechanism, load displacement behavior, damage initiation and propagation are closely monitored using DIC. The influence of patch edge tapering on strain distribution in adhesive layer is also investigated. The DIC successfully captures the global and localized strain field at critical zones over thin adhesive layer and further helps in monitoring the damage based on strain anomalies. Strains are found to have maximum magnitude at the patch overlap edge and the shear strain level in adhesive layer is higher than the peel strain. Normal tapering increases the peel strain and has negligible influence on shear strain level in adhesive layer. The recommended overlap length is found to be consistent with the recommendation in the literature. Whole field strain pattern and the overlap length obtained from experiment are further compared with the finite element analysis results and they appear to be in good coherence. 相似文献
65.
1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm2 is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm2 array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall Vmin of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances. 相似文献
66.
《Ceramics International》2020,46(5):5602-5609
SiC fibers can be obtained by the spinning, curing, and heat treatment of polycarbosilane (PCS); however, the properties of the PCS precursor must be considered to set the correct spinning conditions. Although many studies have focused on the synthesis conditions, the characterization (in particular, the structural characteristics) of PCS fibers, and the polymer itself has limitations. In this study, PCS was prepared in two steps, and the growth of the polymer with respect to the reaction conditions was analyzed. We found that PCS is formed and grown by the rearrangement and subsequent condensation reactions of polydimethylsilane (PDMS). Further, fiber formation was affected by the reaction temperature, time, and pressure. Three types of PCS were obtained under different synthetic conditions, and they were all characterized. Regardless of the structural similarity of the PCS fibers (based on the spectroscopic analysis), the polymers showed different thermal and rheological properties. Our findings will be important in improving the production of PCS fibers (and subsequent SiC fibers) with finely controlled properties. 相似文献
67.
智能型电子式变频电动执行器及其应用 总被引:2,自引:0,他引:2
针对原有电动执行器只有以低速运行,通过极强的微调才能修正微小偏差这一缺点,提出智能型电动执行器与各种阀体譬合,利用数字化变频技术,改造目前采用模拟技术的电动执行器,使之具有变速运行、动态响应块,调节定位精度高、稳定性好,故障率低、使用寿命长和应用场合广泛的特点。 相似文献
68.
GIS在深圳市三防指挥信息系统中的应用 总被引:1,自引:0,他引:1
深圳市三防指挥信息系统利用GIS技术,结合水利(水务)、防汛、抗旱的具体业务,建立了水情遥测数据处 理分系统、工况监测数据处理分系统、水务行业三防信息管理分系统、决策支持分系统、水源优化调度分 系统,提高了现代化管理水平。 相似文献
69.
70.
关于我省数字化城市建设的几点思考 总被引:3,自引:0,他引:3
通过对国内外数字化城市建设现状的分析 ,结合我省实际情况 ,提出我省建设数字化城市的对策及建设内容和原则 ,强调政府的组织行为 ,发挥社会各界的积极性 ,充分利用现有资源 ,以建设数字化城市门户网站为先导 ,快速启动全省数字化城市建设。 相似文献