全文获取类型
| 收费全文 | 3513篇 |
| 免费 | 241篇 |
| 国内免费 | 667篇 |
专业分类
| 林业 | 330篇 |
| 农学 | 574篇 |
| 基础科学 | 300篇 |
| 642篇 | |
| 综合类 | 1359篇 |
| 农作物 | 131篇 |
| 水产渔业 | 115篇 |
| 畜牧兽医 | 704篇 |
| 园艺 | 123篇 |
| 植物保护 | 143篇 |
出版年
| 2024年 | 28篇 |
| 2023年 | 73篇 |
| 2022年 | 129篇 |
| 2021年 | 155篇 |
| 2020年 | 151篇 |
| 2019年 | 197篇 |
| 2018年 | 134篇 |
| 2017年 | 210篇 |
| 2016年 | 233篇 |
| 2015年 | 167篇 |
| 2014年 | 229篇 |
| 2013年 | 219篇 |
| 2012年 | 276篇 |
| 2011年 | 287篇 |
| 2010年 | 201篇 |
| 2009年 | 186篇 |
| 2008年 | 145篇 |
| 2007年 | 161篇 |
| 2006年 | 175篇 |
| 2005年 | 135篇 |
| 2004年 | 100篇 |
| 2003年 | 93篇 |
| 2002年 | 86篇 |
| 2001年 | 91篇 |
| 2000年 | 83篇 |
| 1999年 | 79篇 |
| 1998年 | 59篇 |
| 1997年 | 51篇 |
| 1996年 | 39篇 |
| 1995年 | 30篇 |
| 1994年 | 35篇 |
| 1993年 | 36篇 |
| 1992年 | 34篇 |
| 1991年 | 33篇 |
| 1990年 | 20篇 |
| 1989年 | 23篇 |
| 1988年 | 15篇 |
| 1987年 | 10篇 |
| 1986年 | 6篇 |
| 1985年 | 2篇 |
| 1984年 | 2篇 |
| 1982年 | 2篇 |
| 1979年 | 1篇 |
排序方式： 共有4421条查询结果，搜索用时 15 毫秒
61.
With the development of circulating fluidized bed boiler(CFB),the study field of external heat exchanger(EHE) is greater in extent and degree.In order to research the working process of EHE,the model which deals with flow and heat transfer of EHE for 300MW CFB of Dong Fang Boiler Grou PCo.Ltd.is presented.Based on the cell modeling theory,the EHE is divided into several chamber by heating surfaces.The mass and energy conservation equations of each cell have been developed according to some reasonable assumption.The complete mathematical model has been compiled by Fortran and solved by classical Algorithm of Runge-Kutta.The static test and perturbation experiment of simulating model has been performed.The simulation results show that the model has been reached the steady state rapidly,the dynamic responses are reasonable and the modeling presented in the paper is reliable and appropriate. 相似文献
62.
The exact three di me nsional temperatu re distribution and thermal analysiS to inte-grated circuit substrates have been presen ted by means of numerical method of a fin ite difference.Thismethed.which will overcome the di fficuItv of mathematical deduction mav be consltieredas an analytical way aided by com puters for thermal design of electron ic compon ents. 相似文献
63.
Li Yourong Jin Mingcong Tang Jingwen 《保鲜与加工》1993,(6):46-50
The concept of loss rate of available energy was introduced for evaluating heat exchanger performance. At the same time, the general expression of loss rate of available energy was obtained for heat exchangers of several typical. And NL criteria was recommended for evaluation of the loss rate of available energy of heat exchanger. Then. the influences of inlet temperatures ratio, heat capacity ratio of fluids, the number of heat transfer units and flow patterns of heat exchanger on ,VL criteria were also discussed. 相似文献
64.
65.
66.
67.
68.
Load dynamic matching of supply and demand side based on the utilization of urban sewage heat energy
Flowing dynamic characteristics and its temperature dynamic characteristics of a three-level sewage pipe network in Chongqing were analyzed. A mall's building whole year load was simulated. In the adverse condition of wastewater flow, the market construction peak discharge heat was compared with the sewage heat load, the balance between the most adverse flow and the building demand was found. Explored supply and demand matching method between urban sewage and city building load in flow adverse condition to take full advantage of the urban sewage cold and hot resources. the composite system was adeptcd to make up the most unfavorable flow time of sewage average heat load and the construction load difference; it also puts forward principle of load sharing and control strategy aimed at compound system. 相似文献
69.
70.
地源热泵技术在中国温室设施中的应用探讨 总被引：3，自引：2，他引：3
当前在中国温室设施中应用和推广地源热泵技术尚存在诸多不利因素,大大限制了该项技术在设施农业领域中的发展。为探寻合理的解决途径,对地源热泵空调系统的关键技术和其在中国的发展概况进行了相关的阐述和分析,并以中国农业大学上庄实验站已经建成使用的地下水式温室地源热泵空调系统为实例,介绍该系统的组成、工作流程、性能参数和使用情况,探讨温室地源热泵空调系统在推广和使用中可能出现的投资较高,长时间运行性能不稳定等问题,分析其原因并提出相应的对策建议。 相似文献