全文获取类型
收费全文 | 9524篇 |
免费 | 1453篇 |
国内免费 | 727篇 |
专业分类
电工技术 | 624篇 |
技术理论 | 1篇 |
综合类 | 847篇 |
化学工业 | 1064篇 |
金属工艺 | 156篇 |
机械仪表 | 646篇 |
建筑科学 | 447篇 |
矿业工程 | 259篇 |
能源动力 | 677篇 |
轻工业 | 299篇 |
水利工程 | 191篇 |
石油天然气 | 259篇 |
武器工业 | 92篇 |
无线电 | 1842篇 |
一般工业技术 | 766篇 |
冶金工业 | 386篇 |
原子能技术 | 183篇 |
自动化技术 | 2965篇 |
出版年
2024年 | 56篇 |
2023年 | 225篇 |
2022年 | 359篇 |
2021年 | 441篇 |
2020年 | 372篇 |
2019年 | 276篇 |
2018年 | 267篇 |
2017年 | 316篇 |
2016年 | 370篇 |
2015年 | 433篇 |
2014年 | 674篇 |
2013年 | 634篇 |
2012年 | 792篇 |
2011年 | 800篇 |
2010年 | 612篇 |
2009年 | 558篇 |
2008年 | 574篇 |
2007年 | 698篇 |
2006年 | 615篇 |
2005年 | 517篇 |
2004年 | 392篇 |
2003年 | 367篇 |
2002年 | 257篇 |
2001年 | 198篇 |
2000年 | 162篇 |
1999年 | 139篇 |
1998年 | 118篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 47篇 |
1994年 | 29篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
综述了单螺杆挤出机内聚合物熔体层流混合机理的研究进展,对提高混合的措施进行了分析总结,指出了进一步强化混合效果的方法。 相似文献
102.
An apparatus was developed for investigating the release rates of pheromone formulations at temperatures and air velocities that correspond with those in the field. Polyurethane foam proved an excellent adsorbent for the recovery of tetradecen-1-ol acetates, allowing high air flows at low differential pressure and without breakthrough of these compounds. The experimental setup and procedures are described. The release rates of all formulations investigated were almost proportional to the square root of air velocity, and their logarithms were proportional to the reciprocal of temperature (K). When temperature is increased from 15°C to 25°C, the release rates increase by about 2-2.5 ×. Both relationships were combined into one equation that allows a reliable estimate to be made of the actual release rates of a formulation, under varying conditions, on the basis of its specific parameters and the relevant meteorological data. 相似文献
103.
In statistical modeling, parameter estimation is an essential and challengeable task. Estimation of the parameters in the Dirichlet mixture model (DMM) is analytically intractable, due to the integral expressions of the gamma function and its corresponding derivatives. We introduce a Bayesian estimation strategy to estimate the posterior distribution of the parameters in DMM. By assuming the gamma distribution as the prior to each parameter, we approximate both the prior and the posterior distribution of the parameters with a product of several mutually independent gamma distributions. The extended factorized approximation method is applied to introduce a single lower-bound to the variational objective function and an analytically tractable estimation solution is derived. Moreover, there is only one function that is maximized during iterations and, therefore, the convergence of the proposed algorithm is theoretically guaranteed. With synthesized data, the proposed method shows the advantages over the EM-based method and the previously proposed Bayesian estimation method. With two important multimedia signal processing applications, the good performance of the proposed Bayesian estimation method is demonstrated. 相似文献
104.
介绍了提高聚合釜生产能力的措施,改变聚合水油比,由原来的1.77降低到1.70,增加投料系数0.16;采用新助剂和密闭投料等新工艺,缩短聚合反应周期2.7h。使30m3聚合釜生产能力从5kt/a提高到6.5kt/a。 相似文献
105.
106.
John H. Cross 《Journal of chemical ecology》1980,6(4):781-787
Chemicals (bp 270–490 °C/1 atm) evaporated from a controlled-release formulation dispenser were carried by an airflow to a collector packed with a polymeric adsorbent. After a set time, the chemicals were recovered by thermally desorbing them onto a gas-liquid chromatograpic column. They were then separated and quantified. The apparatus is described, and the requirements for its successful use are discussed. The soundness of the thermal desorption technique was confirmed by comparison with another technique: solvent elution from the collector. The advantages of the former technique are discussed.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA. 相似文献
107.
北京市雨水收集利用蓄水池容积计算与分析 总被引:1,自引:0,他引:1
基于北京市1984—2013年的日降雨资料,以北京林业大学林业楼及其周边绿地为研究区,设置3种用水情景(冲厕、绿地灌溉及冲厕+绿地灌溉),采用连续模拟法,分别绘制3种用水情景下雨水收集利用工程的雨水截留率、自来水替代率、供水保证率以及效益费用比变化曲线,并通过综合分析这些曲线的变化特征确定雨水蓄水池最佳设计容积(60~82 m3)。同时采用设计暴雨法计算1~5年不同重现期的蓄水池设计容积(77~248 m3)。结果表明,连续模拟法计算过程相对复杂,但可用于综合衡量雨水收集利用工程的雨洪管理效益,以及缓解水资源短缺效益、供水可靠性及经济可行性分析。 相似文献
108.
《Journal of Systems Architecture》2014,60(8):630-643
Maintaining a multi-version index on flash memory could generate a lot of updates and invalid pages. It is important to have an efficient garbage collection mechanism to ensure the flash memory has sufficient number of free blocks for storing new data versions and their index structures. In this paper, we study the important performance issues in using the purging-range query to reclaim the blocks, which are storing old data versions and invalid index entries, to be free blocks. To reduce the cost for processing the purging-range query, we propose the physical block labeling (PBL) scheme to provide a better estimation on the purging version number to be used for purging old data versions. To further enhance the performance of the garbage collection process, and at the same time to maximize the deadspans of data versions and balance the wear levels of the blocks, we propose two schemes called, the sequential placement (SQ) and frequency-based placement (FBP), for placing new data versions into free pages. As illustrated in the performance studies, both SQ and FBP can effectively balance the wear levels of the blocks. The deadspans of data versions are longer under FBP than both SQ and RR, and the page reallocation cost is also lower under FBP especially when the size of flash memory allocated for the database is limited. The experimental results also illustrate that PBL can effectively minimize the number of invocations of the purging-range query to be one to reclaim the required number of blocks in each garbage collection. 相似文献
109.
随着我国经济社会的快速发展,建设坚强智能电网的步伐也越来越快。智能电表作为智能电网的最末端,已开始在农村推广应用。通过分析目前农村智能电表推广应用中存在的问题,提出了在农村智能电表全面推广中应解决的问题和应对措施。 相似文献
110.
当前的人工抄表和计算已很难适应电能统计和结算的要求,致使能够满足电网商业化运营的电量计费系统应运而生。介绍了电能量采集及计费自动化系统的用途、数据流和功能。 相似文献