全文获取类型
收费全文 | 106668篇 |
免费 | 8980篇 |
国内免费 | 4684篇 |
专业分类
电工技术 | 5454篇 |
技术理论 | 8篇 |
综合类 | 9570篇 |
化学工业 | 18808篇 |
金属工艺 | 2177篇 |
机械仪表 | 2682篇 |
建筑科学 | 16447篇 |
矿业工程 | 5917篇 |
能源动力 | 6853篇 |
轻工业 | 6415篇 |
水利工程 | 19246篇 |
石油天然气 | 8524篇 |
武器工业 | 303篇 |
无线电 | 2420篇 |
一般工业技术 | 5570篇 |
冶金工业 | 4955篇 |
原子能技术 | 1152篇 |
自动化技术 | 3831篇 |
出版年
2024年 | 352篇 |
2023年 | 1227篇 |
2022年 | 2451篇 |
2021年 | 2956篇 |
2020年 | 3210篇 |
2019年 | 2654篇 |
2018年 | 2599篇 |
2017年 | 3199篇 |
2016年 | 3625篇 |
2015年 | 3581篇 |
2014年 | 6706篇 |
2013年 | 6568篇 |
2012年 | 8226篇 |
2011年 | 8276篇 |
2010年 | 6106篇 |
2009年 | 6325篇 |
2008年 | 5571篇 |
2007年 | 7169篇 |
2006年 | 6505篇 |
2005年 | 5934篇 |
2004年 | 4657篇 |
2003年 | 4230篇 |
2002年 | 3655篇 |
2001年 | 2982篇 |
2000年 | 2494篇 |
1999年 | 1894篇 |
1998年 | 1412篇 |
1997年 | 1158篇 |
1996年 | 906篇 |
1995年 | 809篇 |
1994年 | 584篇 |
1993年 | 453篇 |
1992年 | 372篇 |
1991年 | 287篇 |
1990年 | 203篇 |
1989年 | 213篇 |
1988年 | 139篇 |
1987年 | 142篇 |
1986年 | 106篇 |
1985年 | 107篇 |
1984年 | 98篇 |
1983年 | 62篇 |
1982年 | 41篇 |
1981年 | 10篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
This research investigates the utility of passive microwave remote sensing instruments to accurately determine snow water equivalent (SWE) over large spatial extents. Three existing Special Sensor Microwave Imager (SSM/I) snow water equivalent algorithms produced by Chang, Tait and Goodison were evaluated for their ability to determine snow water equivalent in a snowpack containing substantial depth hoar, large faceted snow crystals. The Kuparuk River Watershed (8140 km2) test site on the North Slope of Alaska was chosen for its snowpack containing a think depth hoar layer and long history of ground truth data. A new regional snow water equivalent algorithm was developed to determine if it could produce better results than the existing algorithms in an area known to contain significant depth hoar. The four algorithms were tested to see how well they could determine snow water equivalent: (1) on a per pixel basis, (2) across swath-averaged spatial bands of approximately 850 km2, and (3) on a watershed scale. The algorithms were evaluated to see if they captured the annual spatial distribution in snow water equivalent over the watershed. Results show that the algorithms developed by Chang and from this research are generally within 3 cm of the spatially averaged snow water equivalents over the entire watershed. The algorithms produced by Chang, Tait, and in this research were able to predict the basin-wide ground measured snow water equivalent value within a percent error range from −32.4% to 24.4% in the years with a typical snowpack. None of the algorithms produce accurate results on a pixel-by-pixel scale, with errors ranging from −26% to 308%. 相似文献
72.
金沙江防洪(库容)规划的探讨 总被引:1,自引:0,他引:1
在分析长江灾害洪水特征的基础上,全面深入地研究了全沙江水库的防洪库客、防洪目标、防洪特点和调度原则,并对防洪库容的作用进行了估算和分析。从多方面比较了虎跳峡高坝方案与低坝方案,结果表明:高坝方案的效益明显高于低坝方案,而两者所需付出的代价相差不大。 相似文献
73.
Yun‐Hwei Shen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(5):581-586
A novel strategy of sweep coagulation to treat low turbidity water is presented herein. Study findings demonstrated that an Na+‐saturated bentonite with medium cation exchange capacity (CEC) resulted in significant turbidity removal at a bentonite dosage of 30 mg dm?3. Bentonite dispersion with fully delaminated platelets tended to undergo a more porous type of coagulation with intense face‐to‐face interactions of platelets and effectively entrapped TiO2 particles in band‐type structures. This type of coagulation usually results in a large volume of settled flocs with a fluffy structure and excellent turbidity removal efficiency for sweep coagulation. The sign and magnitude of electrical charge on TiO2 particles has a minor effect on the efficiency of sweep coagulation. Copyright © 2005 Society of Chemical Industry 相似文献
74.
In this paper we present some preliminary results about the coupling of shallow water equations for free surface flows and Darcy equation for groundwater flows. A suitable set of interface conditions is discussed: the Beavers and Joseph formula for the bottom stress is used. An iterative algorithm to solve the coupled problem is proposed and some numerical results are presented. 相似文献
75.
介绍了天铁炼钢厂中间包水模实验原理和过程,分析了斜、直、圆三种型式挡渣墙模拟结果,提出了合理的挡渣控流方案,在生产实践中使用效果良好。 相似文献
76.
对两种煤代油方式——水煤浆和煤制混合煤气进行了燃料价格、设备投资及运行费用的分析对比。结果表明,两种代油方法均有可观的经济效益,燃料费用可分别节约52.4%和45.2%。如果原燃油工业炉窑由于工艺需要已装有除尘设备而又可用产生的蒸汽做雾化剂时,则水煤浆代油更具有经济优势。 相似文献
77.
78.
Catherine J. Harrison Yann A. Le Gouellec Robert C. Cheng Amy E. Childress 《Canadian Metallurgical Quarterly》2007,133(11):1004-1014
A dual-staged nanofiltration process is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. Investigation of this system at the bench-scale level focused on membrane surface characterization, ion rejection (including boron, bromide, and iodide rejection), and flux decline. Results from this study showed that two commercially available nanofiltration membranes can effectively desalinate seawater. Although fouling was apparent—and resulted in approximately 20% flux decline over 3 days—a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on the polarization modulus, and hence on membrane performance. 相似文献
79.
This paper describes the elastic response of a block sample of compressible Chicago glacial clay under a variety of stresses and its relationship with the deformation characteristics at relatively large strains. The elastic shear stiffness was obtained from bender element tests during consolidation and shearing in drained triaxial stress probe tests. An empirical correlation was established based on the elastic shear stiffness in a preyield condition. By comparing the empirical correlation with the measured elastic shear stiffness in the stress region during probing, the changes of elastic shear stiffness were investigated. The departure of elastic shear stiffness from values computed by the empirical relation based on K0 loading directly relates to the yielding characteristics of the clay. The large-scale change of soil structure at yielding alters the well-established relationship between the elastic shear stiffness and stresses in the preyield condition. The mechanical yielding response of clays can be detected based on the systematic analysis of the elastic shear wave velocities. 相似文献
80.