全文获取类型
收费全文 | 118020篇 |
免费 | 12389篇 |
国内免费 | 7412篇 |
专业分类
电工技术 | 8756篇 |
技术理论 | 9篇 |
综合类 | 12544篇 |
化学工业 | 5613篇 |
金属工艺 | 2811篇 |
机械仪表 | 6338篇 |
建筑科学 | 13841篇 |
矿业工程 | 3285篇 |
能源动力 | 1798篇 |
轻工业 | 13286篇 |
水利工程 | 4737篇 |
石油天然气 | 4805篇 |
武器工业 | 1071篇 |
无线电 | 12235篇 |
一般工业技术 | 6100篇 |
冶金工业 | 4330篇 |
原子能技术 | 946篇 |
自动化技术 | 35316篇 |
出版年
2024年 | 276篇 |
2023年 | 1581篇 |
2022年 | 2969篇 |
2021年 | 3858篇 |
2020年 | 3864篇 |
2019年 | 3122篇 |
2018年 | 2832篇 |
2017年 | 3460篇 |
2016年 | 3815篇 |
2015年 | 4435篇 |
2014年 | 8252篇 |
2013年 | 6966篇 |
2012年 | 8634篇 |
2011年 | 9280篇 |
2010年 | 7215篇 |
2009年 | 7429篇 |
2008年 | 7472篇 |
2007年 | 8708篇 |
2006年 | 7567篇 |
2005年 | 6545篇 |
2004年 | 5670篇 |
2003年 | 4931篇 |
2002年 | 4085篇 |
2001年 | 3038篇 |
2000年 | 2528篇 |
1999年 | 1886篇 |
1998年 | 1331篇 |
1997年 | 1109篇 |
1996年 | 925篇 |
1995年 | 830篇 |
1994年 | 630篇 |
1993年 | 471篇 |
1992年 | 372篇 |
1991年 | 294篇 |
1990年 | 222篇 |
1989年 | 192篇 |
1988年 | 151篇 |
1987年 | 123篇 |
1986年 | 89篇 |
1985年 | 122篇 |
1984年 | 85篇 |
1983年 | 88篇 |
1982年 | 78篇 |
1981年 | 48篇 |
1980年 | 39篇 |
1979年 | 41篇 |
1978年 | 16篇 |
1977年 | 26篇 |
1976年 | 15篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
To benefit from recent advances in modeling and computational algorithms,as well as the availability of new covariance data,sensitivity and uncertainty analyses are needed to quantify the impact of uncertain sources on the design parameters of small prismatic high-temperature gas-cooled reactors(HTGRs).In particular,the contribution of nuclear data to the keff uncertainty is an important part of the uncertainty analysis of small-sized HTGR physical calculations.In this study,a small-sized HTGR designed by China Nuclear Power Engineering Co.,Ltd.was selected for keff uncertainty analysis during full lifetime burnup calculations.Models of the cold zero power(CZP)condition and full lifetime burnup process were constructed using the Reactor Monte Carlo Code RMC for neutron transport calculation,depletion calculation,and sensitivity and uncertainty analysis.For the sensitivity analysis,the Contribution-Linked eigenvalue sensitivity/Uncertainty estimation via Track length importance Characterization(CLUTCH)method was applied to obtain sensitive infor-mation,and the"sandwich"method was used to quantify the keff uncertainty.We also compared the keff uncertainties to other typical reactors.Our results show that 235U is the largest contributor to keff uncertainty for both the CZP and depletion conditions,while the contribution of 239Pu is not very significant because of the design of low discharge burnup.It is worth noting that the radioactive capture reaction of 28Si significantly contributes to the keff uncer-tainty owing to its specific fuel design.However,the keff uncertainty during the full lifetime depletion process was relatively stable,only increasing by 1.12%owing to the low discharge burnup design of small-sized HTGRs.These numerical results are beneficial for neutronics design and core parameters optimization in further uncertainty prop-agation and quantification study for small-sized HTGR. 相似文献
2.
3.
4.
This paper analyses the perception of Artificial Intelligence (AI) by individuals in Spain and the factors associated with it. It uses data from 6308 individuals from a 2018 Spanish survey. A binary logit regression model is formulated and estimated for the attitude towards robots and AI and its possible determinants. As main results are that a gender gap is detected, and that people have a negative attitude if they are not interested in scientific discoveries and technological developments and if AI and robots are not useful at work. 相似文献
5.
Yujie Chen Yiping Song Zhen Zhang Yali Chen Qiliang Deng Shuo Wang 《Advanced functional materials》2021,31(41):2104885
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs. 相似文献
6.
7.
The ways in which environmental priorities are framed are varied and influenced by political forces. One technological advance--the proliferation of government open data portals (ODPs)--has the potential to improve governance through facilitating access to data. Yet it is also known that the data hosted on ODPs may simply reflect the goals and interests of multiple levels of political power. In this article, I use traditional statistical correlation and regression techniques along with newer natural language processing and machine learning algorithms to analyze the corpus of datasets hosted on government ODPs (total: 49,066) to extract patterns that relate scales of governance and political liberalism/conservatism to the priorities and meaning attached to environmental issues. I find that state-level and municipal-level ODPs host different categories of environmental datasets, with municipal-level ODPs generally hosting more datasets pertaining to services and amenities and state-level ODPs hosting more datasets pertaining to resource protection and extraction. Stronger trends were observed for the influences of political conservatism/liberalism among state-level ODPs than for municipal-level ODPs. 相似文献
8.
9.
10.
Sylwia Judycka Joanna Nynca Piotr Hliwa Andrzej Ciereszko 《International journal of molecular sciences》2021,22(2)
Sex reversal has been used as a breeding strategy by salmonid fish to produce genetically and phenotypically single sex populations. Production of all-female fish has great importance for the creation of monosex female triploids of salmonid fish, which are valued for their sterility, lack of female maturation, and larger commercial size. Among salmonids, the majority of rainbow trout (Oncorhynchus mykiss) production is based on all-female production with a high proportion of all-female triploid production in Europe. The main aim of this review is to present the recent knowledge regarding sex-reversed females (SRFs) of salmonid fish. We discuss the methods of sex reversal as well as their effects on the morphology and histology of the reproductive tract. We focus on the characteristics of SRF semen as well as the factors determining semen quality. The lower quality of SRF sperm compared to that of normal males has resulted in the need for the artificial maturation of semen. Most importantly, methods of semen storage—both short-term and long-term (cryopreservation)—that can improve hatchery operations are presented with the special emphasis on recent progress in development of efficient cryopreservation procedures and use of cryopreserved semen in hatchery practice. Moreover, we also address the emerging knowledge concerning the proteomic investigations of salmonid sperm, focusing primarily on the proteomic comparison of normal male and SRF testicular semen and presenting changes in SRF rainbow trout sperm proteome after in vitro incubation in artificial seminal plasma. 相似文献