全文获取类型
收费全文 | 518301篇 |
免费 | 5203篇 |
国内免费 | 1572篇 |
专业分类
电工技术 | 8846篇 |
综合类 | 677篇 |
化学工业 | 77477篇 |
金属工艺 | 27680篇 |
机械仪表 | 18694篇 |
建筑科学 | 10855篇 |
矿业工程 | 4940篇 |
能源动力 | 10616篇 |
轻工业 | 31142篇 |
水利工程 | 7097篇 |
石油天然气 | 16509篇 |
武器工业 | 68篇 |
无线电 | 53039篇 |
一般工业技术 | 116922篇 |
冶金工业 | 79090篇 |
原子能技术 | 16043篇 |
自动化技术 | 45381篇 |
出版年
2021年 | 4364篇 |
2019年 | 4214篇 |
2018年 | 12754篇 |
2017年 | 13134篇 |
2016年 | 11654篇 |
2015年 | 5227篇 |
2014年 | 8566篇 |
2013年 | 20108篇 |
2012年 | 14358篇 |
2011年 | 21653篇 |
2010年 | 18109篇 |
2009年 | 18855篇 |
2008年 | 19530篇 |
2007年 | 20462篇 |
2006年 | 12905篇 |
2005年 | 13512篇 |
2004年 | 12706篇 |
2003年 | 12381篇 |
2002年 | 11353篇 |
2001年 | 10866篇 |
2000年 | 10538篇 |
1999年 | 10178篇 |
1998年 | 22044篇 |
1997年 | 16257篇 |
1996年 | 12464篇 |
1995年 | 9805篇 |
1994年 | 8822篇 |
1993年 | 8975篇 |
1992年 | 6974篇 |
1991年 | 6915篇 |
1990年 | 6807篇 |
1989年 | 6704篇 |
1988年 | 6345篇 |
1987年 | 5916篇 |
1986年 | 5839篇 |
1985年 | 6344篇 |
1984年 | 5961篇 |
1983年 | 5669篇 |
1982年 | 5271篇 |
1981年 | 5423篇 |
1980年 | 5401篇 |
1979年 | 5353篇 |
1978年 | 5554篇 |
1977年 | 5879篇 |
1976年 | 7167篇 |
1975年 | 4912篇 |
1974年 | 4968篇 |
1973年 | 5014篇 |
1972年 | 4350篇 |
1971年 | 3945篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Joel Kuula Heino Kuuluvainen Jarkko V. Niemi Erkka Saukko Harri Portin Anu Kousa 《Aerosol science and technology》2020,54(2):190-202
AbstractLung deposited surface area (LDSA) is a relatively new metric that has been argued to be more accurate at predicting health effects from aerosol exposure. For typical atmospheric aerosol, the LDSA concentration depends mainly on the concentration of ultrafine particles (e.g. vehicular exhaust emissions and residential wood combustion) and therefore optical methods cannot be used to measure and quantify it. The objective of this study was to investigate and describe typical characteristics of LDSA under different urban environments and evaluate how a diffusion charging-based Pegasor AQ Urban sensor (Pegasor Ltd., Finland) can be used as an alternative to optical sensors when assessing local combustion emissions and respective LDSA concentrations. Long-term (12?months) sensor measurements of LDSA were carried out at three distinctly different measurement sites (four sensor nodes) in the Helsinki metropolitan area, Finland. The sites were affected mainly by vehicular exhaust emission (street canyon and urban background stations) and by residential wood combustion (two detached housing area stations). The results showed that the accuracy of the AQ Urban was good (R2 = 0.90) for the measurement of LDSA when compared to differential mobility particle sizer. The mean concentrations of LDSA were more than twice as high at the street canyon (mean 22 µm2 cm?3) site when compared to the urban background site (mean 9.4 µm2 cm?3). In the detached housing area, the mean concentrations were 12 µm2 cm?3, and wood combustion typically caused high LDSA peaks in the evenings. High correlations and similar diurnal cycles were observed for the LDSA and black carbon at street canyon and urban background stations. The utilization of a small-scale sensor network (four nodes) showed that the cross-station variability in hourly LDSA concentrations was significant in every site, even within the same detached housing area (distance between the two sites ~670?m). 相似文献
72.
Bankov S. E. Vesnik M. V. Kravchenko V. F. 《Journal of Communications Technology and Electronics》2020,65(4):398-405
Journal of Communications Technology and Electronics - Abstract—The article presents a rigorous numerical solution, using the Wiener–Hopf method, to the problem of plane wave... 相似文献
73.
Traditionally, in supervised machine learning, (a significant) part of the available data (usually 50%-80%) is used for training and the rest—for validation. In many problems, however, the data are highly imbalanced in regard to different classes or does not have good coverage of the feasible data space which, in turn, creates problems in validation and usage phase. In this paper, we propose a technique for synthesizing feasible and likely data to help balance the classes as well as to boost the performance in terms of confusion matrix as well as overall. The idea, in a nutshell, is to synthesize data samples in close vicinity to the actual data samples specifically for the less represented (minority) classes. This has also implications to the so-called fairness of machine learning. In this paper, we propose a specific method for synthesizing data in a way to balance the classes and boost the performance, especially of the minority classes. It is generic and can be applied to different base algorithms, for example, support vector machines, k-nearest neighbour classifiers deep neural, rule-based classifiers, decision trees, and so forth. The results demonstrated that (a) a significantly more balanced (and fair) classification results can be achieved and (b) that the overall performance as well as the performance per class measured by confusion matrix can be boosted. In addition, this approach can be very valuable for the cases when the number of actual available labelled data is small which itself is one of the problems of the contemporary machine learning. 相似文献
74.
Dorofeyev V. Yu. Sviridova A. N. Svistun L. I. 《Russian Journal of Non-Ferrous Metals》2020,61(3):354-361
Russian Journal of Non-Ferrous Metals - Rolling bearing rings comprise a large reserve for expanding powder metallurgy production. This reserve is being incompletely implemented. The hot forging of... 相似文献
75.
Journal of Communications Technology and Electronics - Abstract—The two-dimensional diffraction problem of a plane polarized TM-wave on two identical solid silver nanocylinders is considered.... 相似文献
76.
Wireless Personal Communications - The rapid development of Information and Communication Technology and the growing number of devices connected to the Internet make the Internet of Things (IoT) as... 相似文献
77.
Metallurgical and Materials Transactions B - The process of obtaining titanium tetrachloride (TiCl4) from the quartz-leucoxene concentrate (QLC) from the Yaregskoe oil-titanium field was studied.... 相似文献
78.
Wesley P. Chan Hiroto Mizohana Xiangyu Chen Yasuto Shiigi Yoshiyuki Yamanoue Masaki Nagatsuka Masayuki Inaba 《野外机器人技术杂志》2019,36(1):17-33
The use of field robots can greatly decrease the amount of time, effort, and associated risk compared to if human workers were to carryout certain tasks such as disaster response. However, transportability and reliability remain two main issues for most current robot systems. To address the issue of transportability, we have developed a lightweight modularizable platform named AeroArm. To address the issue of reliability, we utilize a multimodal sensing approach, combining the use of multiple sensors and sensor types, and the use of different detection algorithms, as well as active continuous closed‐loop feedback to accurately estimate the state of the robot with respect to the environment. We used Challenge 2 of the 2017 Mohammed Bin Zayed International Robotics Competition as an example outdoor manipulation task, demonstrating the capabilities of our robot system and approach in achieving reliable performance in the fields, and ranked fifth place internationally in the competition. 相似文献
79.
80.