全文获取类型
收费全文 | 19327篇 |
免费 | 3292篇 |
国内免费 | 1171篇 |
专业分类
电工技术 | 1617篇 |
技术理论 | 6篇 |
综合类 | 1519篇 |
化学工业 | 2231篇 |
金属工艺 | 935篇 |
机械仪表 | 1158篇 |
建筑科学 | 1158篇 |
矿业工程 | 1104篇 |
能源动力 | 1808篇 |
轻工业 | 541篇 |
水利工程 | 243篇 |
石油天然气 | 974篇 |
武器工业 | 379篇 |
无线电 | 3307篇 |
一般工业技术 | 3315篇 |
冶金工业 | 1404篇 |
原子能技术 | 504篇 |
自动化技术 | 1587篇 |
出版年
2024年 | 68篇 |
2023年 | 377篇 |
2022年 | 614篇 |
2021年 | 765篇 |
2020年 | 794篇 |
2019年 | 715篇 |
2018年 | 696篇 |
2017年 | 746篇 |
2016年 | 866篇 |
2015年 | 796篇 |
2014年 | 1330篇 |
2013年 | 1299篇 |
2012年 | 1639篇 |
2011年 | 1827篇 |
2010年 | 1379篇 |
2009年 | 1323篇 |
2008年 | 1079篇 |
2007年 | 1153篇 |
2006年 | 1062篇 |
2005年 | 836篇 |
2004年 | 751篇 |
2003年 | 572篇 |
2002年 | 522篇 |
2001年 | 406篇 |
2000年 | 391篇 |
1999年 | 304篇 |
1998年 | 215篇 |
1997年 | 223篇 |
1996年 | 172篇 |
1995年 | 139篇 |
1994年 | 131篇 |
1993年 | 106篇 |
1992年 | 102篇 |
1991年 | 72篇 |
1990年 | 63篇 |
1989年 | 50篇 |
1988年 | 30篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 38篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1959年 | 3篇 |
1955年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Plastic encapsulated microcircuits (PEMs) are increasingly being used in applications requiring operation at temperatures lower than the manufacturer’s recommended minimum temperature, which is 0°C for commercial grade components and −40°C for industrial and automotive grade components. To characterize the susceptibility of PEMs to delamination at these extreme low temperatures, packages with different geometries, encapsulated in both biphenyl and novolac molding compounds, were subjected to up to 500 thermal cycles with minimum temperatures in the range −40 to −65°C in both the moisture saturated and baked conditions. Scanning acoustic microscopy revealed there was a negligible increase in delamination at the die-to-encapsulant interface after thermal cycling for the 84 lead PQFPs encapsulated in novolac and for both 84 lead PQFPs and 14 lead PDIPs encapsulated in biphenyl molding compound. Only the 14 lead novolac PDIPs exhibited increased delamination. Moisture exposure had a significant effect on the creation of additional delamination. 相似文献
32.
采用声发射(AE)技术,通过测定AE事件数、幅度和持续时间等发射特征参数以及恒载 Felieity效应,对SiC/Al和C/Al两类束丝纤维增强铝昨合在拉伸变形过程中的损失失效特征进行了分析探讨。实验结果表明,纤维种类、界面状况对复合材料损伤过程有着显著的影响,声发射技术是表征这类复合材料损伤特征很有潜力的方法。 相似文献
33.
Guangyan Li W. Ian Hamilton Ged Morrisroe Theresa Clarke 《Cognition, Technology & Work》2006,8(1):30-40
A study was carried out using simulation to investigate driver responses to lineside signals and signs at various approach
speeds. The objectives of the study were: (1) to find out whether train speed would significantly affect signal/sign reading;
(2) to examine at which point certain types of signs or signals could be detected or recognised, and (3) to determine a speed
cut-off level above which certain types of signs or signals are no longer recognisable or detectable. Fifty-seven train drivers
from 12 Train Operating Companies in the UK participated in the trials. Twenty different types of lineside signs and ten types
of signals were tested under six different approach speeds ranging from 100 to 350 km/h (62–218 mph). Driver performance measures
were ‘time remaining to the signal/sign’ at the point of detection or recognition, and reading error rate. The results showed
a significant influence of train speed on driver responses to lineside signals/signs and demonstrated a non-linear relationship
between driver responses to signals/signs and approach speed. This has been used to estimate a maximum approach speed limit
within which a specific signal or sign can be correctly detected or recognised. The findings and implications of the study
are discussed in the paper. 相似文献
34.
Michio Kumagai Kanako Ishikawa Jiao Chunmeng 《Lakes & Reservoirs: Research and Management》2002,7(4):345-348
We have examined two aspects of the dynamics and biogeochemical significance of the physical environment in Lake Biwa. One is the horizontal distribution of cyanobacteria as it relates to the ‘first gyre’ in the north basin of Lake Biwa. We could easily measure the first gyre using a vessel‐mounted acoustic doppler currents profiler. We were able to quantify the dynamics of the horizontal and vertical structure of currents and water temperature of this gyre. The first gyre did not remain at a fixed position; it moved north and south according to the growth of the gyre. This may play a role in the redistribution of cyanobacteria from place to place in the north basin. The second important environmental dynamic we measured was oxygen consumption rates from 1994 to 2000. We found that the minimum oxygen concentration in the hypolimnion has a clear inverse relationship with the apparent oxygen consumption rates in the 80–85 m depth layer. As a reduction in oxygen concentration in the hypolimnion can have a serious impact on benthic organisms, we concluded that the Lake Biwa environment should be monitored carefully and systematically. 相似文献
35.
36.
37.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
38.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
39.
40.
One of the new physical methods that provides much information about the processes going on in a friction contact zone in real time is acoustic emission (AE). Basic experimental results of AE in friction are presented and analysed. Using AE signals we can get an indication about the state of the friction processes, about the quality of solid and liquid layers on the contacting surfaces in real time, sometimes about intensity of wear, changing of wear and friction regimes and so on. The influence of sliding velocity, load, roughness and some physical and mechanical properties of the body on the parameters of AE are also given. Some attention to the practical implementation of these techniques for control of capability for work of friction pairs in real conditions are given. Modern methods and devices enable condition monitoring of sliding and rolling bearings. 相似文献