全文获取类型
收费全文 | 8055篇 |
免费 | 387篇 |
国内免费 | 264篇 |
专业分类
电工技术 | 560篇 |
综合类 | 974篇 |
化学工业 | 419篇 |
金属工艺 | 153篇 |
机械仪表 | 352篇 |
建筑科学 | 2249篇 |
矿业工程 | 395篇 |
能源动力 | 194篇 |
轻工业 | 306篇 |
水利工程 | 469篇 |
石油天然气 | 253篇 |
武器工业 | 62篇 |
无线电 | 339篇 |
一般工业技术 | 335篇 |
冶金工业 | 642篇 |
原子能技术 | 40篇 |
自动化技术 | 964篇 |
出版年
2024年 | 11篇 |
2023年 | 33篇 |
2022年 | 82篇 |
2021年 | 149篇 |
2020年 | 167篇 |
2019年 | 106篇 |
2018年 | 105篇 |
2017年 | 131篇 |
2016年 | 181篇 |
2015年 | 193篇 |
2014年 | 423篇 |
2013年 | 393篇 |
2012年 | 471篇 |
2011年 | 611篇 |
2010年 | 519篇 |
2009年 | 551篇 |
2008年 | 476篇 |
2007年 | 673篇 |
2006年 | 629篇 |
2005年 | 460篇 |
2004年 | 410篇 |
2003年 | 367篇 |
2002年 | 352篇 |
2001年 | 251篇 |
2000年 | 210篇 |
1999年 | 171篇 |
1998年 | 70篇 |
1997年 | 75篇 |
1996年 | 88篇 |
1995年 | 59篇 |
1994年 | 53篇 |
1993年 | 31篇 |
1992年 | 37篇 |
1991年 | 32篇 |
1990年 | 19篇 |
1989年 | 7篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1982年 | 3篇 |
1966年 | 4篇 |
1965年 | 4篇 |
1964年 | 8篇 |
1963年 | 6篇 |
1961年 | 6篇 |
1960年 | 7篇 |
1959年 | 7篇 |
1956年 | 4篇 |
1955年 | 6篇 |
排序方式: 共有8706条查询结果,搜索用时 625 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(51):21613-21633
When planning large-scale 100% renewable energy systems (RES) for the year 2050, the system capacity is usually oversized for better supply-demand matching of electrical energy since solar and wind resources are highly intermittent. This causes excessive excess energy that is typically dissipated, curtailed, or sold directly. The public literature shows a lack of studies on the feasibility of using this excess for country-scale co-generation. This study presents the first investigation of utilizing this excess to generate green hydrogen gas. The concept is demonstrated for Jordan using three solar photovoltaic (PV), wind, and hybrid PV-wind RESs, all equipped with Lithium-Ion battery energy storage systems (ESSs), for hydrogen production using a polymer electrolyte membrane (PEM) system. The results show that the PV-based system has the highest demand-supply fraction (>99%). However, the wind-based system is more favorable economically, with installed RES, ESS, and PEM capacities of only 23.88 GW, 2542 GWh, and 20.66 GW. It also shows the highest hydrogen annual production rate (172.1 × 103 tons) and the lowest hydrogen cost (1.082 USD/kg). The three systems were a better option than selling excess energy directly, where they ensure annual incomes up to 2.68 billion USD while having payback periods of as low as 1.78 years. Furthermore, the hydrogen cost does not exceed 2.03 USD/kg, which is significantly lower than the expected cost of hydrogen (3 USD/kg) produced using energy from fossil fuel-based systems in 2050. 相似文献
2.
《Journal of dairy science》2022,105(4):3176-3191
Milk concentrates are used in the manufacturing of dairy products such as yogurt and cheese or are processed into milk powder. Processes for the nonthermal separation of water and valuable milk ingredients are becoming increasingly widespread at farm level. The technical barriers to using farm-manufactured milk concentrate in dairies are minimal, hence the suspicion that the practice of on-farm raw milk concentration is still fairly uncommon for economic reasons. This study, therefore, set out to investigate farmers' potential willingness to adopt a raw milk concentration plant. The empirical analysis was based on discrete choice experiments with 75 German dairy farmers to identify preferences and the possible adoption of on-farm raw milk concentration. The results showed that, in particular, farmers who deemed the current milk price to be insufficient viewed on-farm concentration using membrane technology as an option for diversifying their milk sales. We found no indication that adoption would be impeded by a lack of trustworthy information on milk processing technologies or capital. 相似文献
3.
Based on the multi-item Food Choice Questionnaire (FCQ) originally developed by Steptoe and colleagues (1995), the current study developed a single-item FCQ that provides an acceptable balance between practical needs and psychometric concerns. Studies 1 (N = 1851) and 2 (2a (N = 3290), 2b (N = 4723), 2c (N = 270)) showed that the single-item FCQ scale has good convergent and discriminant validity. Generally, the results showed the highest correlations with the related multi-item dimensions (>0.40). Study 2 refined the scale. Only the items for convenience (Study 2a), sensory appeal (Study 2b) and mood (Study 2c) needed to be revised (as Study 1 showed a correlation between the multi-item and the single-item below the threshold of 0.60). The results also showed comparable predictive validity. Both methods revealed similar association patterns between food motives and consumption behaviours (Fisher’s z tests revealed agreements of 86.2% for Study 1, 92.9% for Study 2a and 100% for Studies 2b and 2c). Study 3 (N = 6062) showed an example of the added value of a context-specific application for the single-item FCQ. Different motives were shown to be relevant across contexts, and the context-specific motives had additional explained variance beyond the general multi-item FCQ. Studies 2b and 3 also showed the performance of the single-item FCQ in an international context. In sum, the results indicate that the single-item FCQ can be used as a flexible and short substitute for the multi-item FCQ. The study also discusses the conditions that should be considered when using the single-item scale. 相似文献
4.
Meat is deeply associated with masculine identity. As such, it is unsurprising that women are more likely than men are to become vegetarian. Given the gendered nature of vegetarianism, might men and women who become vegetarian express distinct identities around their diets? Through two highly powered preregistered studies (Ns = 890 and 1775) of self-identified vegetarians, combining both frequentist and Bayesian approaches, I found that men and women differ along two dimensions of vegetarian identity: (1) dietary motivation and (2) dietary adherence. Compared to vegetarian men, vegetarian women reported that they are more prosocially motivated to follow their diet and adhere to their diet more strictly (i.e., are less likely to cheat and eat meat). By considering differences in how men and women construe vegetarian dieting, investigators can generate deeper insights into the gendered nature of eating behavior. 相似文献
5.
In line with findings on post-purchase food-choice regret, one can expect that pre-purchase anticipated regret with respect to forgone (non-chosen) alternatives has an impact on consumer food choices, especially when the choice is considered to be important. The traditional Random Utility Maximization (RUM) models for discrete choices may not fully capture this impact. This study investigates the usefulness and potential in the food domain of a discrete choice model that follows the regret minimization principle, the Random Regret Minimization (RRM) model, as an alternative and complement to existing RUM models. The two models are applied to consumer stated choices of cheese in a choice experiment. The study also investigates whether and to what extent a number of personality traits determine whether particular consumers rather choose according to utility-maximization, or regret-minimization principles. Results show that at the aggregate level the two models have a similar goodness of fit to the data and prediction ability. Still, each of them shows better fit for particular subgroups of consumers, based on personality traits. Hence, the present study reveals a potential for the RRM model applications in the food domain, and adds to the empirical literature supporting previous findings on the RRM model found in other contexts. Further research is needed to explore in which situations and for which consumer segments the RRM model is the most useful model. 相似文献
6.
Adaptive decision making requires that contingencies between decision options and their relative assets be assessed accurately and quickly. The present research addresses the challenging notion that contingencies may be more visible from small than from large samples of observations. An algorithmic account for such a seemingly paradoxical effect is offered within a satisficing-choice framework. Accordingly, a choice is only made when the sample contingency describing the relative evaluation of the 2 options exceeds a critical threshold. Small samples, because of the high dispersion of their sampling distribution, facilitate above-threshold contingencies. Across a broad range of parameters, the resulting small-sample advantage in terms of hits is stronger than their disadvantage in false alarms. Computer simulations and experiments support the model predictions. The relative advantage of small samples is most apparent when information loss is low, when the threshold is high relative to the ecological contingency, and when the sampling process is self-truncated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
织金电视台通过对有线电视网络进行双向改造,为Internet宽带接入、数字电视、VOD等多媒体应用提供了运行平台,介绍织金县城区HFC双向网络设计方案。 相似文献
8.
9.
中国未来电力需求与核能 总被引:5,自引:0,他引:5
本文介绍了我国未来电力需求和能源结构,阐述了核能是我国满足经济发达地区电力需求的合理选择,并提出了我国“九五”核电计划和中期目标,以及发展核电中面临的问题和基本对策。 相似文献
10.
简述国内磷酸二铵的建设情况及不同的生产工艺、原有磷酸二铵装置改造选用的工艺及生产情况 ,重点介绍 Incro工艺在云南红河州磷肥厂年产 12万吨磷铵装置中的改造情况 ,经过比较认为原采用预中和槽流程磷酸二铵装置增产改造时选用 Incro工艺比较合适 相似文献