全文获取类型
收费全文 | 155773篇 |
免费 | 6352篇 |
国内免费 | 3228篇 |
专业分类
电工技术 | 4674篇 |
技术理论 | 7篇 |
综合类 | 6629篇 |
化学工业 | 23817篇 |
金属工艺 | 8686篇 |
机械仪表 | 7767篇 |
建筑科学 | 7343篇 |
矿业工程 | 2976篇 |
能源动力 | 3311篇 |
轻工业 | 8252篇 |
水利工程 | 2291篇 |
石油天然气 | 5660篇 |
武器工业 | 466篇 |
无线电 | 16824篇 |
一般工业技术 | 25378篇 |
冶金工业 | 6519篇 |
原子能技术 | 1003篇 |
自动化技术 | 33750篇 |
出版年
2024年 | 303篇 |
2023年 | 1274篇 |
2022年 | 2121篇 |
2021年 | 2936篇 |
2020年 | 2221篇 |
2019年 | 1982篇 |
2018年 | 16335篇 |
2017年 | 15553篇 |
2016年 | 11826篇 |
2015年 | 3296篇 |
2014年 | 3677篇 |
2013年 | 4427篇 |
2012年 | 7469篇 |
2011年 | 14104篇 |
2010年 | 12328篇 |
2009年 | 9386篇 |
2008年 | 10516篇 |
2007年 | 11402篇 |
2006年 | 3926篇 |
2005年 | 4650篇 |
2004年 | 3409篇 |
2003年 | 3257篇 |
2002年 | 2400篇 |
2001年 | 1743篇 |
2000年 | 1981篇 |
1999年 | 2115篇 |
1998年 | 1827篇 |
1997年 | 1463篇 |
1996年 | 1455篇 |
1995年 | 1209篇 |
1994年 | 976篇 |
1993年 | 728篇 |
1992年 | 564篇 |
1991年 | 451篇 |
1990年 | 328篇 |
1989年 | 254篇 |
1988年 | 235篇 |
1987年 | 142篇 |
1986年 | 120篇 |
1985年 | 96篇 |
1984年 | 66篇 |
1983年 | 40篇 |
1982年 | 42篇 |
1968年 | 46篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
本文提出并研究了一种新型的强度反射型光纤温度传感器.根据定容气体温度与压力的线性关系,通过简单的测温元调制光纤中的反射光强,从而得知待测温度.这种传感器结构紧凑,造价低廉.在30~50℃范围内,灵敏度可以达到30mV/℃以上. 相似文献
22.
Although cortico steroids are effective anti-inflammatory agents in ameliorating asthma symptoms and bronchial hperreactivity, their mechanism of action is unknown. Interleukin (IL)-5 is known to play a key role in regulating eosinophil proliferation and activation. Therefore, we examined the changes of IL-5 mRNA expressions in PBMC semi-quantitatively with RT-PCR as well as serum ECP levels and MCH-PC20 values in asthmatics before and after being treated with corticosteroids. The results revealed that there were significant decrease in the level of IL-5 mRNA and serum ECP concentration after therapy (P < 0.05) and there was remarkable improvement in the values of MCH-PC20 and FEV1% (P < 0.05). It was also found that the changes of serum ECP levels or MCH-PC20 values were accompanied by a reduction in IL-5 mRNA expression (r = 0.5426 or 0.4857, P < 0.05). These results suggested that the therapeutic effects of corticosteroids in asthma may result from modulation of IL-5 gene expression with consequent inhibition of eosinophil activation. 相似文献
23.
Jin-Wei Shi Chi-Kuang Sun 《Lightwave Technology, Journal of》2002,20(11):1942-1950
We present the theory and design of a tapered line distributed photodetector (TLDP). In the previously demonstrated velocity-matched distributed photodetector (VMDP), high electrical bandwidth is achieved by proper termination in the input end to absorb reverse traveling waves, sacrificing one-half of the quantum efficiency. By utilizing the tapered line structure and phase matching between optical waves and microwaves in our analyzed structure, a traveling-wave photodetector is more realizable and ultrahigh bandwidth can be attained due to removal of the extra input dummy load that sacrifices one-half of the total quantum efficiency. To investigate the advantages of TLDP over VMDP, we calculate their electrical bandwidth performances by using an analytic photodistributed current model. We adopted low-temperature-grown (LTG) GaAs-based metal-semiconductor-metal (MSM) traveling-wave photodetectors as example unit active devices in the analytic bandwidth calculation for their high-speed and high-power performances. Both VMDP and TLDP in our simulation are assumed to be transferred onto glass substrates, which would achieve high microwave velocity/impedance and make radiation loss negligible. The simulated bandwidth of a properly designed LTG GaAs MSM TLDP is /spl sim/325 GHz, which is higher than the simulated bandwidth of the LTG GaAs MSM VMDP with an open-circuit input end (/spl sim/240 GHz) and is almost comparable to the simulated bandwidth of an input-terminated LTG GaAs MSM VMDP (/spl sim/330 GHz). This proposed method can be applied to the design of high-bandwidth distributed photodetectors for radio-frequency photonic systems and optoelectronic generation of high-power microwaves and millimeter waves. 相似文献
24.
25.
26.
Three interesterified vegetable oils (IVOs) prepared from palm, cottonseed, and olive oil, respectively, have been studied for application to Frankfurters. Beef fat (10%) was replaced by one of the IVOs at 20, 60 or 100%. Fatty acid composition of the lipid fraction in the Frankfurters and saturated/unsaturated ratios were established for all batches. We found that total or partial replacement of beef fat by IVOs did not lead to significant changes in appearance, colour, texture, flavour or sensory score. We conclude that IVOs may be successfully applied as beef fat substitutes in Frankfurters. 相似文献
27.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
28.
STEP-NC是由欧美提出的新的数控接口标准,目的是取代旧的数控标准ISO6983。本文首先分析了STEP-NC的两种应用标准:ISO14649(ARM)和STEPAP238(AIM),并且分析了Part21和Part28的应用领域及Part21文件格式和其中的信息产生方法。然後介绍了ST-Developer环境下ROSEC++颠库编程接口及其应用程序的早、晚编联方式,并且以此为基础设计了整个程序的编程流程,重点介绍了工艺规划设计。最后给出了在C++编程环境下利用ROSE库函数写入形成STEP AP238文件的方法。 相似文献
29.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
30.
Interface characteristics of carbon fibre reinforced copper matrix composites materials with various interface states and their effect on the flexural strength of composites have been studied. Interfacial states are mechanical bonding, dissolution bonding and reaction bonding. To a certain extent, raising the interfacial strength enables an increase in the flexural strength due to prevention of carbon fibre being pulled out under low stress during fracture process of composites. Raising the interfacial bondage strength, causes the brittleness of composites to increase; the fracture surface of composites is converted from a fibre pull-out model to a fibre even model. While strengthening the interface bondage, the extent of chemical reaction and dissolution at the interface must be controlled to avoid degrading the carbon fibre. 相似文献