全文获取类型
收费全文 | 97937篇 |
免费 | 9639篇 |
国内免费 | 7108篇 |
专业分类
电工技术 | 3313篇 |
技术理论 | 1篇 |
综合类 | 6146篇 |
化学工业 | 25312篇 |
金属工艺 | 9932篇 |
机械仪表 | 4791篇 |
建筑科学 | 3468篇 |
矿业工程 | 2470篇 |
能源动力 | 2610篇 |
轻工业 | 6489篇 |
水利工程 | 1269篇 |
石油天然气 | 4173篇 |
武器工业 | 783篇 |
无线电 | 11487篇 |
一般工业技术 | 13572篇 |
冶金工业 | 4516篇 |
原子能技术 | 1583篇 |
自动化技术 | 12769篇 |
出版年
2024年 | 188篇 |
2023年 | 1890篇 |
2022年 | 2394篇 |
2021年 | 4053篇 |
2020年 | 3451篇 |
2019年 | 2960篇 |
2018年 | 2554篇 |
2017年 | 3180篇 |
2016年 | 3528篇 |
2015年 | 3572篇 |
2014年 | 5106篇 |
2013年 | 5675篇 |
2012年 | 6470篇 |
2011年 | 8078篇 |
2010年 | 6043篇 |
2009年 | 6770篇 |
2008年 | 6007篇 |
2007年 | 6853篇 |
2006年 | 6206篇 |
2005年 | 5152篇 |
2004年 | 4010篇 |
2003年 | 3601篇 |
2002年 | 2955篇 |
2001年 | 2388篇 |
2000年 | 2161篇 |
1999年 | 1675篇 |
1998年 | 1292篇 |
1997年 | 1061篇 |
1996年 | 989篇 |
1995年 | 835篇 |
1994年 | 754篇 |
1993年 | 594篇 |
1992年 | 479篇 |
1991年 | 373篇 |
1990年 | 290篇 |
1989年 | 212篇 |
1988年 | 141篇 |
1987年 | 126篇 |
1986年 | 122篇 |
1985年 | 80篇 |
1984年 | 64篇 |
1983年 | 50篇 |
1982年 | 58篇 |
1981年 | 42篇 |
1980年 | 54篇 |
1979年 | 33篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
以Ti6Al4V球形粉末为原料,利用激光选区熔化成形方法制备了Ti6Al4V合金试样,采用光学显微镜、扫描电镜及力学性能测试等手段,研究了退火工艺对Ti6Al4V合金室温力学性能及组织的影响规律。结果表明: SLM成形沉积态Ti6Al4V合金室温抗拉强度超过1200 MPa,而平均断后伸长率仅为4.0%;在650 ℃下进行真空退火处理,合金的抗拉强度仍保持在1200 MPa左右,规定塑性延伸强度Rp0.2高于1150 MPa,但试样的断后伸长率<10%;而在750及800 ℃下进行真空退火处理,合金试样的抗拉强度降至1100 MPa左右,规定塑性延伸强度高于1050 MPa,伸长率达到甚至超过10%,材料的综合强韧性得到明显提升。随着真空退火加热温度和保温时间的增加,SLM成形Ti6Al4V合金原始β晶界逐渐变模糊,晶粒趋向于等轴化。与此同时,快速冷却转变的α′针状马氏体未出现明显地粗化。 相似文献
62.
《能源学会志》2020,93(1):152-164
The ignition, injection, and micro-explosion characteristics of aviation fuel (RP-3)/ethanol mixed droplets and biodiesel/ethanol mixed droplets at different proportions under high temperature conditions (420 °C) were compared using an experimental setup. A device for measuring small droplet volumes was designed using an infusion set and different types of needles, and a corresponding equation was established. Mixed droplets suspended on high-temperature resistance nichrome wire with a diameter of 0.2 mm were heated by sending them to a position approximately 2 mm from the forklift preheating plug using a moving rail. SLR and high-speed cameras were used to observe the flame structure as well as the injection and micro-explosion of the mixed droplets during combustion, respectively. Expansion, injection, and micro-explosion were observed in the biodiesel/ethanol mixed droplet experiments when the biodiesel content was 60%. Although the micro-explosion of mixed droplets of aviation fuel/ethanol was not observed, expansion and ejection of the droplets were observed. Image Pro-plus software was used to calculate the diameters at different times in the combustion cycle of the droplets. Through this analysis, the occurrence of micro-explosion was described, and a model for the calculation of micro-explosion strength was established. 相似文献
63.
Improved photocatalytic hydrogen production from methanol/water solution using CuO supported on fluorinated TiO2 下载免费PDF全文
64.
为了提升脑胶质瘤分割精度,提出一种结合注意力机制的3D卷积神经网络算法。输入3个不同尺度的图像块,经过9个卷积层和1个分类层后得到3个不同的分类结果,将分类结果与注意力学习到的权重相乘并逐体素相加得到输出。此外该算法采用了一种混合Dice损失函数与Focal损失函数的超参数损失函数。实验表明,该算法的Dice系数在整体区域、核心区域以及增强区域分别达到了95.31%、80.12%、82.25%。与已有的一种脑胶质瘤分割算法deepmedic相比,整体区域、核心区域以及增强区域的Dice系数分别提升了3%、2%、6%。在脑胶质瘤分割方面,具有重要的临床意义。 相似文献
65.
针对无线网络链路干扰大、误码率高等特点,以及TCP Westwood算法(TCPW)存在估算带宽时过度依赖包的反馈,缺乏区分传输过程中丢包类型的缺点等问题,提出一种TCPW拥塞控制优化算法--TCPW-F。该算法利用发送速率等构建拥塞因子[F]作为判断丢包类型的依据,同时对判定发生噪声丢包时的拥塞窗口进一步调整,避免噪声丢包引起的窗口下降,提高该情况下窗口的发送效率。仿真结果表明,TCPW-F算法在时延性能方面表现更优,单位时间抖动趋于稳定的速度更快。在同一信道带宽下增大包生成速率,改进算法的实时吞吐量明显高于原算法,具备一定的噪声丢包感知能力,无线网络的TCP传输质量获得较大改善。 相似文献
66.
Along with the advent of 5G era, China's transportation industry for intelligent development enters into the fast lane. Based
on the integration of communication technology, Internet of things technology, big data technology, cloud computing technology, ar-
tificial intelligence technology and so on, the whole process and all-round intelligent control are carried out in traffic construction,
traffic management, road transportation, traffic service and so on, so as to ensure smooth and safe travel and to provide good servic-
es to road, railway, civil aviation, water transportation and other transportation networks. It is the important feature of intelligent
transportation in the 5G era. This paper analyses the trend of application and development of 5G network in intelligent transporta-
tion, which is the research basis of perfecting transportation service and the scientific basis of promoting the intelligent and modern
development of transportation in China. 相似文献
67.
Hashim A.
Hashim 《国际强度与非线性控制杂志
》2020,30(10):3848-3870
》2020,30(10):3848-3870
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form. 相似文献
68.
This article presents a design methodology for linearizing GaN HEMT amplifiers based on splitting a large FET into multiple parallel FETs with same total gate periphery and by biasing them individually. By varying the biases, the magnitude and the phase of the IMD3 components at the output of FET changes. A detailed simulation methodology using commercial microwave CAD software is presented. Simulation results show that by biasing one device in Class AB and other(s) in deep Class AB mode, IMD3 components of parallel FETs can be made out of phase to each other leading to cancellation and improvement in linearity. Three prototype circuits were simulated using (a) a single 5 mm FET (1 × 5 mm), (b) two parallel 2.5 mm FETs (2 × 2.5 mm), and (c) four parallel 1.25 mm FETs (4 × 1.25 mm), for a total gate periphery of 5 mm, over the frequency range of 0.8 to 1.0 GHz. IMD3 improvement up to 20 dBc was achieved with the 4 × 1.25 mm circuit when the FET biases were optimized. Measurement results show improvement in linearity up to 20 dBc for 4 × 1.25 mm circuit. The proposed method improves linearity without a substantial penalty on the power consumption and is straightforward to implement. 相似文献
69.
D‐psicose 3‐epimerase secretory overexpression,immobilization, and d‐psicose biotransformation,separation and crystallization 下载免费PDF全文
70.
Radio-Frequency (RF) energy harvesting must cope with the limited availability and high variability of the energy source. In this paper, the modeling of an RF harvester for ultra low power environments is presented. A mathematical model based on theoretical analysis is developed. The model demonstrates that the maximum transferred power point is located in a three-dimensional space defined by the input capacitance, the output voltage, and the load resistance of the rectifier circuit. Moreover, the mathematical model returns results in substantial agreement with the SPICE simulation results, while guaranteeing a remarkable reduction of the required computation time. Furthermore, the paper reports the implementation of a mixed signal system for the 3-D MPPT, to be embedded in an RF harvester, in a 65 nm CMOS technology. The circuit exhibits a simulated power consumption lower than 100 nW, making this solution suitable for ultra low power harvesting. 相似文献