全文获取类型
收费全文 | 545111篇 |
免费 | 25532篇 |
国内免费 | 12663篇 |
专业分类
电工技术 | 20689篇 |
技术理论 | 35篇 |
综合类 | 18550篇 |
化学工业 | 91554篇 |
金属工艺 | 27280篇 |
机械仪表 | 25953篇 |
建筑科学 | 29323篇 |
矿业工程 | 11167篇 |
能源动力 | 13373篇 |
轻工业 | 42246篇 |
水利工程 | 7644篇 |
石油天然气 | 26077篇 |
武器工业 | 2471篇 |
无线电 | 58571篇 |
一般工业技术 | 82086篇 |
冶金工业 | 61900篇 |
原子能技术 | 8395篇 |
自动化技术 | 55992篇 |
出版年
2023年 | 5155篇 |
2022年 | 9336篇 |
2021年 | 13846篇 |
2020年 | 10110篇 |
2019年 | 9304篇 |
2018年 | 11409篇 |
2017年 | 12455篇 |
2016年 | 11568篇 |
2015年 | 13816篇 |
2014年 | 18149篇 |
2013年 | 27409篇 |
2012年 | 25125篇 |
2011年 | 29222篇 |
2010年 | 24551篇 |
2009年 | 24244篇 |
2008年 | 24597篇 |
2007年 | 24340篇 |
2006年 | 24128篇 |
2005年 | 21338篇 |
2004年 | 15520篇 |
2003年 | 13964篇 |
2002年 | 13369篇 |
2001年 | 12660篇 |
2000年 | 12870篇 |
1999年 | 14243篇 |
1998年 | 19507篇 |
1997年 | 15224篇 |
1996年 | 12607篇 |
1995年 | 9952篇 |
1994年 | 8767篇 |
1993年 | 7523篇 |
1992年 | 6049篇 |
1991年 | 5321篇 |
1990年 | 4977篇 |
1989年 | 4684篇 |
1988年 | 4279篇 |
1987年 | 3533篇 |
1986年 | 3433篇 |
1985年 | 3667篇 |
1984年 | 3498篇 |
1983年 | 3188篇 |
1982年 | 2826篇 |
1981年 | 2987篇 |
1980年 | 2712篇 |
1979年 | 2863篇 |
1978年 | 2738篇 |
1977年 | 2841篇 |
1976年 | 3693篇 |
1975年 | 2457篇 |
1973年 | 2320篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
介绍一种基于变频调速控制的全自动定量包装机,结构简单,组态灵活,性价比高,可广泛应用于食品饲料等行业,现场运行实践证明其通用性好,准确度和可靠性高、速度快、稳定性好。并论述变频器控制系统的设计及使用中的注意问题。 相似文献
12.
At the present time, organic solid wastes from industries and agricultural activities are considered to be promising substrates for biogas production via anaerobic digestion. Moreover solids stabilisation is required before reutilization or disposal. Slaughterhouses are among the most important industries in Uruguay and produce 150,000 tons of ruminal content (RC) and 30,000 tons of blood per year. In order to determine the influence of the solids and blood contents, the ammonia inhibition and the inoculum adaptation co-digestion batch tests were performed. A set of experiences with TS concentration of 2.5%, 5% and 7.5% and different ratios of RC/blood were carried out using an inoculum from an UASB reactor. In all experiences fast blood hydrolisation was observed. A higher methane production was detected in the experiences with higher TS content. However, the fraction of solids degradation was lower in these experiences. A plateau in the biogas production was found. The free ammonia level, which was above the reported inhibitory levels, could explain this behaviour. After the inhibition period the biogas production restarted probably due to the biomass acclimatisation to the ammonia. In order to determine the inoculum adaptation a new experiment was performed. The inoculum used was the sludge coming from the first set of experiences. Based upon batch tests a 3.5 m3 pilot reactor was designed and started up. Ammonia inhibition was avoided by the start-up strategy and in two weeks the biogas production was 3.5 m3/d. The VS stabilisation with a solid retention time of 20 days was of 43%. The pilot reactor working at steady state had a TS concentration of 3-4% with a ratio of RC/blood of 10:1 at the entrance. 相似文献
13.
14.
抽油机变频调速的若干现象 总被引:2,自引:0,他引:2
变频器产生的最初用途是速度控制,但它还有显著的节能作用.应用变频调速,可以大大提高电机转速的控制精度.使电机在最节能的转速下运行.遗对作为能耗大国的中国来说至关重要,应用前景广阔。从本期开始.“变频器与节能”专栏将陆续邀请国内外知名专家反厂商向广大读者介绍变频器节能的原理和具体应用.希望使更多读者认识和了解变频器在节能方面发挥的重要作用。[编者按] 相似文献
15.
Stormwater quality simulation models are useful tools for the design and management of sewer systems. Modelling results are highly sensitive to experimental data used for calibration. This sensitivity is examined for three modelling approaches of various complexities (site mean concentration approach, event mean concentration approach and build-up, washoff and transport modelling approach) applied to a typical case study (design of a dry detention tank), accounting for the variability of calibration data and their effect on simulation results. Calibrated models with different calibration data sets were used to simulate 3 years of rainfall with different retention tank specific volumes. Annual pollutant load interception efficiencies were determined. Simulations results revealed (i) that there is no advantage in using the EMC model compared to the SMC model and (ii) that the BWT model resulted in higher design ratios than those given by the SMC/hydraulic approach. For both EMC and BWT models, using an increasing number n of events for calibration leads to narrower confidence intervals for the design ratios. It is crucial for design ratios to account for successive storm events in chronological order and to account for the maximum allowable flow to be transferred to the downstream WWTP. 相似文献
16.
无刷同步电机的励磁系统对励磁电流的测量是制约该励磁方式发展的一大障碍。设计了一个射频系统可以用来解决同步电机的励磁电流的测量问题。该系统可以方便地检测到同步电机励磁机的整流二极管的工作状态并且可以动态地显示励磁电流,极大地方便了运行人员做出判断,而且结构简单、方便实用。 相似文献
17.
L. Gao P. Hrter Ch. Linsmeier J. Gstttner R. Emling D. Schmitt-Landsiedel 《Materials Science in Semiconductor Processing》2004,7(4-6):331
Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt3)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO2/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO2/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO2 substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas. 相似文献
18.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
19.
为了提高注入剖面测井的准确性,研制了一种新型注入剖面组合测井仪。该仪器由流量处理单元、伽马处理单元、井温处理单元、磁性定位处理单元、调制式传输、电源电路六部分组成。一次下井可同时测取流量、伽马、井温、磁性定位四组参数。具有测取资料精度高、单芯电缆传输、流量可单点测量也可连续测量以厦现场监测和维修方便等特点。 相似文献
20.