全文获取类型
收费全文 | 13286篇 |
免费 | 491篇 |
国内免费 | 218篇 |
专业分类
电工技术 | 443篇 |
技术理论 | 2篇 |
综合类 | 1376篇 |
化学工业 | 861篇 |
金属工艺 | 363篇 |
机械仪表 | 908篇 |
建筑科学 | 3243篇 |
矿业工程 | 606篇 |
能源动力 | 445篇 |
轻工业 | 469篇 |
水利工程 | 293篇 |
石油天然气 | 358篇 |
武器工业 | 38篇 |
无线电 | 1051篇 |
一般工业技术 | 681篇 |
冶金工业 | 466篇 |
原子能技术 | 130篇 |
自动化技术 | 2262篇 |
出版年
2024年 | 26篇 |
2023年 | 70篇 |
2022年 | 150篇 |
2021年 | 190篇 |
2020年 | 235篇 |
2019年 | 164篇 |
2018年 | 174篇 |
2017年 | 241篇 |
2016年 | 408篇 |
2015年 | 409篇 |
2014年 | 1294篇 |
2013年 | 786篇 |
2012年 | 828篇 |
2011年 | 970篇 |
2010年 | 844篇 |
2009年 | 700篇 |
2008年 | 574篇 |
2007年 | 945篇 |
2006年 | 867篇 |
2005年 | 776篇 |
2004年 | 619篇 |
2003年 | 489篇 |
2002年 | 352篇 |
2001年 | 274篇 |
2000年 | 244篇 |
1999年 | 215篇 |
1998年 | 172篇 |
1997年 | 143篇 |
1996年 | 138篇 |
1995年 | 150篇 |
1994年 | 111篇 |
1993年 | 67篇 |
1992年 | 52篇 |
1991年 | 60篇 |
1990年 | 27篇 |
1989年 | 57篇 |
1988年 | 41篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1963年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
High dimensionality in real-world multi-reservoir systems greatly hinders the application and popularity of evolutionary algorithms, especially for systems with heterogeneous units. An efficient hierarchical optimization framework is presented for search space reduction, determining the best water distributions, not only between cascade reservoirs, but also among different types of hydropower units. The framework is applied to the Three Gorges Project (TGP) system and the results demonstrate that the difficulties of multi-reservoir optimization caused by high dimensionality can be effectively solved by the proposed hierarchical method. For the day studied, power output could be increased by 6.79 GWh using an optimal decision with the same amount of water actually used; while the same amount of power could be generated with 2.59 × 107 m3 less water compared to the historical policy. The methodology proposed is general in that it can be used for other reservoir systems and other types of heterogeneous unit generators. 相似文献
3.
随着我国石油需求量不断增加,致密油藏的开发也愈发重要。如何高效开发致密油藏是一项重点难点,其中致密油藏注天然气提高采收率是一个极具潜力的研究方向。因此,本文着重介绍以天然气作为能量补充介质在国内外的研究现状和应用现状,并且从两相特征等方面总结了理论研究中的一些机理,对致密油藏注天然气提高采收率的发展前景进行了一定的展望。 相似文献
4.
In this paper, limiting factors for increased use of biomethane as a transportation fuel are studied. The aim of this research is to recognize and estimate the limiting factors for biomethane utilization in the transportation sector. The limiting factors are studied by using calculation models from Life cycle perspective and literature reviews. According to the results, the main limiting factors can be classified into the following categories: production potential, technology, economy or policy. For biomethane utilization in Finland, the main limiting factors seem to be the lack of distribution infrastructure in northern parts of the country and the uncertain economical feasibility for agricultural biomass producers and for vehicle owners. From the political perspective, the external costs for petrol operated vehicles are higher than for biomethane operated vehicles. Reductions from the external costs could be used by political decisions as a base to support the growth of biomethane in the transportation sector which could lead to GHG emission reductions. A similar systematic approach can also be used to study limiting factors for other transportation energy systems. 相似文献
5.
《Energy Policy》2015
Electric vehicles (EVs) are considered alternatives to internal combustion engines due to their energy efficiency and contribution to CO2 mitigation. The adoption of EVs depends on consumer preferences, including cost, social status and driving habits, although it is agreed that current and expected costs play a major role. We use a partial equilibrium model that minimizes total energy system costs to assess whether EVs can be a cost-effective option for the consumers of each EU27 member state up to 2050, focusing on the impact of different vehicle investment costs and CO2 mitigation targets. We found that for an EU-wide greenhouse gas emission reduction cap of 40% and 70% by 2050 vis-à-vis 1990 emissions, battery electric vehicles (BEVs) are cost-effective in the EU only by 2030 and only if their costs are 30% lower than currently expected. At the EU level, vehicle costs and the capability to deliver both short- and long-distance mobility are the main drivers of BEV deployment. Other drivers include each state’s national mobility patterns and the cost-effectiveness of alternative mitigation options, both in the transport sector, such as plug-in hybrid electric vehicles (PHEVs) or biofuels, and in other sectors, such as renewable electricity. 相似文献
6.
《Energy Policy》2015
The low price of lead-acid, the most popular battery, is often used in setting cost targets for emerging energy storage technologies. Future cost reductions in lead acid batteries could increase investment and time scales needed for emerging storage technologies to reach cost-parity. In this paper the first documented model of cost reductions for lead-acid batteries is developed. Regression to a standard experience curve using 1989–2012 data yield a poor fit, with R2 values of 0.17 for small batteries and 0.05 for larger systems. To address this problem, battery costs are separated into material and residual costs, and experience curves developed for residual costs. Depending on the year, residual costs account for 41–86% of total battery cost. Using running-time averages to address volatility in material costs, a 4-year time average experience curve for residual costs yield much higher R2, 0.78 for small and 0.74 for large lead-acid batteries. The learning rate for residual costs in lead-acid batteries is 20%, a discovery with policy implications. Neglecting to consider cost reductions in lead-acid batteries could result in failure of energy storage start-ups and public policy programs. Generalizing this result, learning in incumbent technologies must be understood to assess the potential of emerging ones. 相似文献
7.
论文比较详细地阐述了涉密网主机系统所面临的安全隐患,提出了涉密网主机安全防护所要解决的几个技术问题,并就可能实现的技术方法进行了探讨和比较。 相似文献
8.
国产风机盘管空调系统常见问题分析 总被引:2,自引:1,他引:1
分析了国产风机盘管使用中常见的问题,指出机组因风量不足、冷量风量匹配不合理以及风机盘管某些设备故障,导致了风机盘管精度低、舒适性差、能耗高等一系列问题。指出应引起空调设计和运行维护人员的注意。 相似文献
9.
提出在县市级广电宽带数据网络的建设过程中,要着眼业务发展,突出高扩展性,构建基于标准、扩展灵活的主干网,实现网络建设的可持续性发展,并结合实际,从核心设备、端口、中继带宽、网络业务4个方面对扩展能力进行了阐述. 相似文献
10.
三峡水库减淤增容调度方式研究——多汛限水位调度方案 总被引:8,自引:0,他引:8
本文建议在汛期中小流量时(Q<35000m3/s),将坝前水位维持在148~151m;出现汛情且流量更较大后,将坝前水位降低到143m;入库流量大于35000m3/s且短期预报将出现大于十年一遇洪水时,预泄洪水到135m.按这一调度,汛期约80%时间可以维持在较高水位,一般洪水期。汛限水位143m不影响坝区通航,135m水位迎洪可大量增加防洪库客。到100年后可减淤30亿m3,增加防洪库容约40亿m3.变动回水区减淤40%,优化了坝区水沙搭配,可改善通航条件。降低库区洪水位,缓解防洪与移民的矛盾。可对发电带来较大好处:提高发电效益,减少粗沙过机。初期水库排沙比大于原方案,可减轻下游冲刷。同时,可减小三峡汛初泄水与鄱阳湖防洪的矛盾。 相似文献