全文获取类型
收费全文 | 17925篇 |
免费 | 1999篇 |
国内免费 | 722篇 |
专业分类
电工技术 | 675篇 |
综合类 | 870篇 |
化学工业 | 5065篇 |
金属工艺 | 1141篇 |
机械仪表 | 586篇 |
建筑科学 | 644篇 |
矿业工程 | 255篇 |
能源动力 | 1304篇 |
轻工业 | 613篇 |
水利工程 | 166篇 |
石油天然气 | 429篇 |
武器工业 | 75篇 |
无线电 | 2091篇 |
一般工业技术 | 4659篇 |
冶金工业 | 574篇 |
原子能技术 | 148篇 |
自动化技术 | 1351篇 |
出版年
2024年 | 78篇 |
2023年 | 652篇 |
2022年 | 519篇 |
2021年 | 800篇 |
2020年 | 800篇 |
2019年 | 767篇 |
2018年 | 751篇 |
2017年 | 825篇 |
2016年 | 712篇 |
2015年 | 673篇 |
2014年 | 958篇 |
2013年 | 1093篇 |
2012年 | 1077篇 |
2011年 | 1378篇 |
2010年 | 929篇 |
2009年 | 972篇 |
2008年 | 820篇 |
2007年 | 964篇 |
2006年 | 865篇 |
2005年 | 717篇 |
2004年 | 599篇 |
2003年 | 539篇 |
2002年 | 448篇 |
2001年 | 379篇 |
2000年 | 341篇 |
1999年 | 287篇 |
1998年 | 284篇 |
1997年 | 236篇 |
1996年 | 169篇 |
1995年 | 167篇 |
1994年 | 128篇 |
1993年 | 90篇 |
1992年 | 94篇 |
1991年 | 110篇 |
1990年 | 79篇 |
1989年 | 69篇 |
1988年 | 49篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 27篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 507 毫秒
81.
E. Stenitzer H. Diestel Th. Zenker R. Schwartengräber 《Water Resources Management》2007,21(9):1567-1584
The performance of the water balance and crop growth model SIMWASER to estimate the water supply of a lawn by capillary rise
from shallow ground water was investigated by using lysimeter measurements with a sandy and a clayey soil. Moreover the robustness
of the model was evaluated by running it either with measured hydraulic soil parameters or with estimated pedotransfer functions
(PTFs) derived from texture and bulk density. Simulations were performed for the years 1996–1998 with input data from the
lysimeter station Berlin-Dahlem (Germany) for lysimeters containing undisturbed sandy or clayey soil monoliths, with groundwater
at 135 cm depth. Simulated evapotranspiration and percolation/capillary rise were in good agreement with the measured data
for all variants, while simulated soil water storage was acceptable only for the variants using hydraulic soil data based
on laboratory measurements or using PTFs derived from known soil class and bulk density. PTFs based on mean total pore volume
of the respective soil classes yielded soil water storages which were evidently too high; therefore they should be used with
care and must be avoided at all in simulating the soil water balance of arid sites with shallow groundwater. 相似文献
82.
Computer models of the lubrication of piston-rings in internal combustion engines normally present an estimate of the minimum oil-film thickness between ring and cylinder wall as a function of crank angle. As a consequence, experimental measurements of film thickness play a critical role in the verification of theoretical models of piston-ring lubrication. A review is presented of the wide range of techniques that have been used to measure this important variable. The strengths and weaknesses of particular techniques are identified and a number of ways in which the techniques could be developed further are proposed 相似文献
83.
84.
水性聚氨酯电导率与聚沉值的研究 总被引:4,自引:0,他引:4
研究了软(硬)段含羧基的水性阴离子纳米聚氨酯体系的n(NCO)/n(OH)比值,COOH的质量分类,反离子各类,合成方法与电导率关系及产生的原因;探讨了该体系的n(NCO)/n(OH)值,COOH的质量分数,合成方法与临界聚沉值(Cc.c)的关系和规律。并分析,比较了软(硬)段含羧基的水性阴离子聚氨酯体系电导率与Cc.c二者关系,得出了随COOH的质量分数升高,二者变化相同,随n(NCO)/n(OH)比值升高,二者变化相反的结论。 相似文献
85.
86.
Rubina H. Shreiner 《Journal of research of the National Institute of Standards and Technology》2002,107(5):393-399
The stability of solutions having an electrolytic conductivity, κ, of 5 μS/cm to 100 000 μS/cm packaged in glass screw-cap bottles, glass serum bottles, and glass ampoules was monitored for 1 year to 2 years. The conductivity was determined by measuring the ac resistance of the solution. Mass loss was also monitored for solutions packaged in bottles. The solutions were prepared using KCl in water (κ ≥100 μS/cm) or KCl in 30 % (by mass) n-propanol 70 % (by mass) water (κ ≤ 15 μS/cm). The conductivity changes were compared by packaging type and by nominal κ. The main causes of the κ changes are evaporation (screw-cap bottles) and leaching (screw-cap bottles, serum bottles, and ampoules). Evaporation is determined from mass loss data; leaching occurs from the glass container with no change in mass. The choice of optimal packaging, which depends on the conductivity level, is the packaging in which κ changes the least with time. Ampoules are the most suitable packaging for standards having nominal κ values of 500 μS/cm to 100 000 μS/cm. Screw-cap bottles are most suitable for standards having a nominal κ of 5 μS/cm to 100 μS/cm. 相似文献
87.
Ran-Rong Lee 《Journal of the American Ceramic Society》1991,74(9):2242-2249
AIN ceramics with densities varying from 3.18 to 3.30 g/cm3 and room-temperature thermal conductivities varying from 88 to 193 W/m K were produced. Different sintering conditions, packing powders, AIN powder sources, carbon additive, and sintering times were evaluated, and the key processing parameters which cause the differences in density and thermal conductivity were identified. SEM, TEM, and EDS were used to characterize the correlation between thermal conductivity, microstructure, and processing parameters. The important parameters which control the thermal conductivity of AIN ceramics are discussed. 相似文献
88.
复合轴控制系统应用研究 总被引:18,自引:3,他引:15
复合轴控制是提高光电跟踪系统精度和控制带宽的一种有效手段,尤其在光束定向器系统中,不仅要求系统要稳定地跟踪上动态目标,而且必须将光束涣定在目标的某一点上,这对控制系统的要求是非常高的,必须采用双或三复合轴控制方式。 相似文献
89.
90.
聚氧化乙烯—聚磷酸钠共混物的钠离子导电性 总被引:1,自引:0,他引:1
研究了聚氧化乙烯-聚磷酸钠共混物的钠离子导电性和低分子量多缩乙二醇对共混物导电性的改进作用。结果表明,降低多缩乙二醇的分子量以及增加其含量都有利于提高共混物的离子导电率。增塑剂改进共混物导电性的实质是提高共混物的非晶相含量,共混物内钠离子传导发生在非晶区,聚合物链段运动是离子传导的主要推动力。 相似文献