全文获取类型
收费全文 | 58032篇 |
免费 | 5915篇 |
国内免费 | 2918篇 |
专业分类
电工技术 | 4228篇 |
技术理论 | 2篇 |
综合类 | 4030篇 |
化学工业 | 9158篇 |
金属工艺 | 3232篇 |
机械仪表 | 3807篇 |
建筑科学 | 4476篇 |
矿业工程 | 1818篇 |
能源动力 | 1775篇 |
轻工业 | 4497篇 |
水利工程 | 1126篇 |
石油天然气 | 2623篇 |
武器工业 | 515篇 |
无线电 | 7260篇 |
一般工业技术 | 6543篇 |
冶金工业 | 2647篇 |
原子能技术 | 714篇 |
自动化技术 | 8414篇 |
出版年
2024年 | 277篇 |
2023年 | 1021篇 |
2022年 | 2042篇 |
2021年 | 2707篇 |
2020年 | 2058篇 |
2019年 | 1665篇 |
2018年 | 1865篇 |
2017年 | 2147篇 |
2016年 | 1982篇 |
2015年 | 2880篇 |
2014年 | 3523篇 |
2013年 | 4049篇 |
2012年 | 4364篇 |
2011年 | 4633篇 |
2010年 | 3941篇 |
2009年 | 3680篇 |
2008年 | 3490篇 |
2007年 | 3202篇 |
2006年 | 3136篇 |
2005年 | 2590篇 |
2004年 | 1871篇 |
2003年 | 1426篇 |
2002年 | 1341篇 |
2001年 | 1011篇 |
2000年 | 925篇 |
1999年 | 901篇 |
1998年 | 773篇 |
1997年 | 615篇 |
1996年 | 601篇 |
1995年 | 462篇 |
1994年 | 362篇 |
1993年 | 259篇 |
1992年 | 241篇 |
1991年 | 158篇 |
1990年 | 123篇 |
1989年 | 112篇 |
1988年 | 104篇 |
1987年 | 58篇 |
1986年 | 47篇 |
1985年 | 29篇 |
1984年 | 35篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1965年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
生态用水和社会经济用水的竞争状况使得研究水资源短缺地区流域“三生”用水系统演化状况,以及有效进行流域“三生”用水系统的调控十分必要。从宏观角度出发,本文提出了构建流域主要指标为状态变量下的“三生”用水系统演化模拟模型,并利用模型进行演化趋势预测的分析思路。以蓟运河流域为例,构建了人口数量、人均GDP、生态系统指数以及生态用水比例为状态变量的“三生”用水系统演化模型。通过定量模拟,表明若不加以调控,该流域最终将走向生态失衡、经济停滞的恶性局面。由参数设置对调控方案进行分析,提出了提高生态用水比例、控制经济增长速度、提高用水效率和积极进行生态建设对策,为实现蓟运河流域的“三生”用水系统可持续发展服务。 相似文献
122.
分析了千兆以太网体系结构,给出了符合IEEE 802.3z标准中1000BASE-X规范的发送器电路结构,并采用TSMC 0.25 μm CMOS 混合信号工艺设计了符合该规范的高速复接电路和锁相环时钟倍频电路.芯片核心电路面积分别为(0.3×0.26)mm2和(0.22×0.12)mm2.工作电压2.5 V时,芯片核心电路功耗分别为120 mW和100 mW.时钟倍频电路的10倍频输出时钟信号频率为1.25 GHz,其偏离中心频率1MHz处的单边带相位噪声仅为-109.7 dBc/Hz.在驱动50 Ω输出负载的条件下,1.25 Gbit/s的高速输出数据信号摆幅可达到410 mV. 相似文献
123.
Fei Hu Ankur Teredesai 《Pervasive Computing, IEEE》2007,6(1):88-91
Today, there's an urgent need for well-trained pervasive computing engineers and scientists. Pervasive computing has evolved into a critical field, influencing a broad range of industries from healthcare to manufacturing to defense. However, most computer engineering and computer science programs pay marginal attention, at best, to the field. In this issue, the authors of the Rochester Institute of Technology describes a set of courses on pervasive computing topics and a supporting laboratory designed for both computer engineering and computer science students 相似文献
124.
介绍湛江东兴炼油厂的重整装置由200kt/a扩能至300kt/a中有关催化重整反应动力学模拟计算软件的应用、反应工艺技术的改造、装置标定的情况。结合装置实际情况,采用两段装填、两段混氢技术提升了装置的技术水平。标定结果表明,改造后的装置达到了预期目的。 相似文献
125.
The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride. 相似文献
126.
The testing and quality assurance of the Motif 1.0 graphical user-interface software are described. The testing goals, which fell into three general categories (code coverage, defect-density, and defect-arrival rate), and a deliverable formal test suite are examined. The three phases of the testing process-evaluation, test development, and regression testing-and the tools used in testing are discussed 相似文献
127.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
128.
CHING-HUA Su YI-GAO Sha S. L Lehoczky F. R Szofran D. C Gillies S. D Cobb R. N Scripa 《Journal of Materials Science》1997,32(14):3765-3768
A series of Hg0.84Zn0.16 Te crystal ingots have been grown from pseudobinary melts by the Bridgmam–Stockbarger type directional solidification using
a Marshall Space Flight Center/Space Science Laboratory heat-pipe furnace and the ground control experiment laboratory furnace
of the crystal growth furnace which was flown on the first United States Microgravity Mission. A number of translation rates
and a series of hot- and cold-zone temperatures were employed to assess the influence of growth parameters on the crystal
properties for the purpose of optimizing the in-flight growth conditions.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
129.
Han-Bin Lin Jung-Young Su Yu-Pin Liao Way-Seen Wang 《Quantum Electronics, IEEE Journal of》1995,31(6):1131-1139
By using micro-prisms, improved three-dimensional (3-D) bends of the embedded and buried waveguides of step-index profile are proposed. A simple phase compensation rule for the optimal design of the micro-prism is also presented. Through the simulation of 3-D semivectorial finite-difference beam propagation method, the transmission characteristics of the improved bends are shown to have been enhanced dramatically as compared with those of the conventional ones. Even for a bend angle of as large as 10°, the normalized transmitted power can still be greater than 95%. These results of 3-D bends are then compared with those of the two-dimensional (2-D) ones which are simplified from 3-D structures by the effective index method, and physical explanation of the discrepancy between the 3-D and 2-D results is introduced. The influences of waveguide structures and prism parameters on the transmission characteristics are discussed in detail. Some criteria for the design of large-angle low-loss 3-D improved bends are also accessed 相似文献
130.