全文获取类型
收费全文 | 556543篇 |
免费 | 6794篇 |
国内免费 | 1494篇 |
专业分类
电工技术 | 10440篇 |
综合类 | 554篇 |
化学工业 | 82442篇 |
金属工艺 | 25372篇 |
机械仪表 | 19531篇 |
建筑科学 | 13121篇 |
矿业工程 | 3313篇 |
能源动力 | 12627篇 |
轻工业 | 45025篇 |
水利工程 | 6100篇 |
石油天然气 | 10908篇 |
武器工业 | 83篇 |
无线电 | 64657篇 |
一般工业技术 | 112019篇 |
冶金工业 | 94940篇 |
原子能技术 | 12223篇 |
自动化技术 | 51476篇 |
出版年
2021年 | 3775篇 |
2019年 | 3646篇 |
2018年 | 12976篇 |
2017年 | 13442篇 |
2016年 | 10658篇 |
2015年 | 4833篇 |
2014年 | 7602篇 |
2013年 | 21503篇 |
2012年 | 14117篇 |
2011年 | 23016篇 |
2010年 | 19553篇 |
2009年 | 20358篇 |
2008年 | 21063篇 |
2007年 | 22507篇 |
2006年 | 14215篇 |
2005年 | 15806篇 |
2004年 | 13921篇 |
2003年 | 13362篇 |
2002年 | 12431篇 |
2001年 | 11799篇 |
2000年 | 11313篇 |
1999年 | 11344篇 |
1998年 | 26625篇 |
1997年 | 19469篇 |
1996年 | 15365篇 |
1995年 | 11832篇 |
1994年 | 10647篇 |
1993年 | 10476篇 |
1992年 | 8235篇 |
1991年 | 7846篇 |
1990年 | 7522篇 |
1989年 | 7399篇 |
1988年 | 7226篇 |
1987年 | 6217篇 |
1986年 | 6131篇 |
1985年 | 7162篇 |
1984年 | 6766篇 |
1983年 | 6114篇 |
1982年 | 5781篇 |
1981年 | 6013篇 |
1980年 | 5714篇 |
1979年 | 5487篇 |
1978年 | 5446篇 |
1977年 | 6308篇 |
1976年 | 7995篇 |
1975年 | 5009篇 |
1974年 | 4851篇 |
1973年 | 4889篇 |
1972年 | 4095篇 |
1971年 | 3846篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
Young Been Kim Sung Hyeon Jung Dong Su Kim Nishad G. Deshpande Hee Won Suh Hak Hyeon Lee Ji Hoon Choi Ho Seong Lee Hyung Koun Cho 《Advanced functional materials》2021,31(38):2102439
Antimony triselenide (Sb2Se3) nanoflake-based nitrogen dioxide (NO2) sensors exhibit a progressive bifunctional gas-sensing performance, with a rapid alarm for hazardous highly concentrated gases, and an advanced memory-type function for low-concentration (<1 ppm) monitoring repeated under potentially fatal exposure. Rectangular and cuboid shaped Sb2Se3 nanoflakes, comprising van der Waals planes with large surface areas and covalent bond planes with small areas, can rapidly detect a wide range of NO2 gas concentrations from 0.1 to 100 ppm. These Sb2Se3 nanoflakes are found to be suitable for physisorption-based gas sensing owing to their anisotropic quasi-2D crystal structure with extremely enlarged van der Waals planes, where they are humidity-insensitive and consequently exhibit an extremely stable baseline current. The Sb2Se3 nanoflake sensor exhibits a room-temperature/low-voltage operation, which is noticeable owing to its low energy consumption and rapid response even under a NO2 gas flow of only 1 ppm. As a result, the Sb2Se3 nanoflake sensor is suitable for the development of a rapid alarm system. Furthermore, the persistent gas-sensing conductivity of the sensor with a slow decaying current can enable the development of a progressive memory-type sensor that retains the previous signal under irregular gas injection at low concentrations. 相似文献
42.
Chemical and Petroleum Engineering - The processes of separation of impurities of particles of different sizes are analyzed under conditions of irregularity of structural and kinematic parameters... 相似文献
43.
Ivashchuk O. A. Ivashchuk O. D. Fedorov V. I. Shtana A. I. 《Russian Engineering Research》2020,40(11):970-972
Russian Engineering Research - Models based on regression analysis for predicting the operational efficiency of high-pressure roller crushers are considered. A systematized and structured... 相似文献
44.
Popov N. N. Presnyakov D. V. Lar’kin V. F. 《Journal of Machinery Manufacture and Reliability》2020,49(3):232-236
Journal of Machinery Manufacture and Reliability - A device based on smart alloys has been designed for use in machine building items, in particular, in nuclear engineering, for preventing... 相似文献
45.
Klimis?S.?NtalianisEmail author Anastasios?D.?Doulamis Nikolaos?D.?Doulamis Nikos?E.?Mastorakis Athanasios?S.?Drigas 《Journal of Signal Processing Systems》2015,80(2):153-161
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation. 相似文献
46.
47.
48.
49.
Christoph Gottschalk Aiko Huckauf Arne Dübecke Florian Kaltner Matthias Zimmermann Ines Rahaus 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2018,35(7):1366-1383
The contamination of honey with hepatotoxic pyrrolizidine alkaloids (PAs) is a well-known hazard for food safety. While management strategies and controls of the honey industry aim to reduce the PA levels, uncertainties remain with regard to the safety of regionally produced and marketed honey. In addition, a previous study showed large differences of results obtained after various periods of storage and apparent differences between the analytical results of different laboratories. Therefore, this study aimed at examining these uncertainties by monitoring the impact of storage on the PA and PA N-oxide (PANO) content of two freshly harvested honeys and on possible demixing effects caused by pollen settling. Additionally, three analytical approaches – target analysis with matrix-matched calibration or standard addition and a sum parameter method – were applied for a comparative analysis of 20 honeys harvested in summer 2016. All samples originated from Schleswig-Holstein in Northern Germany where the PA plant Jacobaea vulgaris is currently observed on a massive scale. The results of the time series analyses showed that PANO levels markedly decreased within a few weeks and practically reached the LOD 16 weeks after harvest. Tertiary PAs, by contrast, remained stable and did not increase as a consequence of PANO decrease. The experiments on a putative demixing, which may result in a heterogeneous distribution of PAs/PANOs, revealed that there was no such effect during storage of up to 12 weeks. A comparison of the PA/PANO levels obtained by different analytical approaches showed that in some cases the sum parameter method yielded much higher levels than the target approaches, whereas in other cases, the target analysis with standard addition found higher levels than the other two methods. In summary, the results of this study highlight uncertainties regarding the validity and comparability of analytical results and consequently regarding health risk assessment. 相似文献
50.