首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1564篇
  免费   145篇
  国内免费   65篇
电工技术   13篇
综合类   119篇
化学工业   247篇
金属工艺   9篇
机械仪表   32篇
建筑科学   139篇
矿业工程   13篇
能源动力   163篇
轻工业   158篇
水利工程   641篇
石油天然气   9篇
无线电   15篇
一般工业技术   41篇
冶金工业   19篇
原子能技术   4篇
自动化技术   152篇
  2024年   5篇
  2023年   37篇
  2022年   118篇
  2021年   115篇
  2020年   59篇
  2019年   51篇
  2018年   62篇
  2017年   58篇
  2016年   85篇
  2015年   71篇
  2014年   91篇
  2013年   103篇
  2012年   91篇
  2011年   118篇
  2010年   85篇
  2009年   76篇
  2008年   68篇
  2007年   65篇
  2006年   67篇
  2005年   60篇
  2004年   46篇
  2003年   50篇
  2002年   37篇
  2001年   19篇
  2000年   23篇
  1999年   23篇
  1998年   20篇
  1997年   19篇
  1996年   5篇
  1995年   12篇
  1994年   5篇
  1993年   7篇
  1992年   4篇
  1991年   5篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
排序方式: 共有1774条查询结果,搜索用时 31 毫秒
71.
In this paper we argue that insights from feminist perspectives, particularly in the form of an ethics of care, have a number of advantages when used as a lens through which to consider questions relevant to the governance of emerging technologies. We highlight how an emphasis on central themes of importance in feminist theory and care ethics such as relationality, contextuality, dependence, power, affect, and narrative can shine a light on a number of salient issues that are typically missed by the dominant and largely consequentialist risk assessment frame. We argue that the care ethics lens is a better fit when technologies are understood not simply as devices designed to create a certain end experience for a user but as transformative systems that smuggle in numerous social and political interests. The advantages of these care ethics themes for emerging technologies are illustrated through a detailed consideration of agricultural biotechnology. We show how the feminist care ethics lens might have anticipated the very questions that have proved themselves to be the sticking points for this technology. We therefore suggest that applying a care ethics lens can significantly broaden the frame of appraisal processes used for the governance of emerging technologies and usefully grant legitimacy to questions and concerns that are prominent in public discourse but typically left out of practices of risk assessment.  相似文献   
72.
This study sought to quantify and characterize cassava waste as fuel. The wastes from three cultivars were collected to study and were divided into three distinct parts of the cassava plant: seed stem, thick stalks, and thin stalks. Physical and chemical analyzes were carried out to determine the elemental composition of the waste: volatile matter; fixed carbon; ash; moisture; lignin; cellulose; hemicellulose; ash composition and higher heating value were determined. We conducted a thermogravimetric analysis in oxidizing and inert atmospheres to study the behavior of the waste as fuel. The root productivity obtained ranged from 7.7 to 13.0 t ha−1 yr−1 on a dry basis (db), and the ratio between waste and roots varied from 0.36 to 0.91. The physical and chemical properties of cassava waste are analogous to those of woody biomass regarding the elemental composition, the higher heating value, and thermogravimetric analysis. Ash content varied from 2.5% to 3.5%, reaching around 6.0% in samples unwashed. Approximately 60% of the ashes are alkali oxides, especially P2O5, K2O, and CaO, which have low melting points. The alkali index calculated suggests that there is a strong tendency that the combustion process leads to ash fouling and the formation of ash deposits.  相似文献   
73.
Mislabelling of seafood products has been documented in numerous countries for over three-quarters of a century. With a trend towards increased consumption of seafood, the informed consumer demands accurately labelled products that provide full disclosure of composition. DNA barcoding can be used to accurately identify a seafood product to species based on its genetic signature, and so provides a means to test the authenticity and accuracy of seafood labelling. This can be especially useful for products such as fillets which have few or no unambiguous identifying characters, and can easily be mislabelled. We investigated labelling accuracy in seafood retailers in Tasmania, Australia. Thirty-eight seafood products were obtained from seafood retailers, sequenced for the barcoding gene region cytochrome oxidase subunit 1(CO1), and subsequently identified to species level by querying GenBank and Barcode of Life Data Systems (BOLD) DNA sequence records. Results were compared with standard fish names (SFN) prescribed under the Australian Fish Names Standard (AFNS) and FishBase. Of the 38 samples, none were deemed to have been mislabelled under Australian regulation, although in some cases naming discrepancies and ambiguity may cause confusion for some consumers. Our work, while reflecting high standards in Tasmanian seafood, highlights the need for mandatory standard labelling across all seafood products so as to eliminate any possible misrepresentation.  相似文献   
74.
Livestock and poultry husbandry is a major source of agricultural pollution in China. Thus far, national-scale approaches to estimating pollutant loads from livestock and poultry rearing remain limited. This impedes effective water quality assessment and relevant policy making. Applying unit load and export coefficient modelling, we estimated pollutant loads from livestock and poultry raising from 2000 to 2010. Results show that the total annual pollutant loads generated from the faeces and urine of livestock and poultry in 2010 had a chemical oxygen demand of 78.2?million metric tonnes; biochemical oxygen demand of 72.7?million tonnes; ammonia nitrogen of 7.4?million tonnes; total phosphorus of 6.0?million tonnes; and total nitrogen of 18.0?million tonnes. Livestock and poultry husbandry has been one of the main pollution sources in China. The significant contributors are pigs and cattle. In particular, pollution from livestock and poultry raising in China spatially overlaps with industrial and domestic pollution. South eastern regions face the difficult challenge of controlling and managing agricultural, industrial and domestic pollution.  相似文献   
75.
In this research a new heterogeneous catalyst has been prepared for biodiesel production. The catalyst was prepared by sulfonating industrial sugar waste. Unlike homogeneous catalysts, which require further purification and separation from the biodiesel production reaction media, this inexpensive synthetic catalyst does not need to go through an additional separation process. This advantage consequently minimizes the total application costs. The catalyst was prepared by partially carbonizing sugar beet pulp at 400 °C. The carbonization product was then sulfonated with concentrated H2SO4 vapor in order to produce a solid catalyst. The prepared catalyst was used in the esterification reaction between palm fatty acid distillate (PFAD) and methanol. The effects of the temperature, methanol/PFAD ratio, reaction time and catalyst dosage on the efficiency of the production were individually investigated. The optimum biodiesel production occurred at 85 °C, a reaction time of 300 min, catalyst dosage of 3 g and methanol/PFAD ratio of 5:1 (mol/mol), lowering the acid value from 198 to 13.1 (mg KOH/g oil) or the equivalent, with a fatty acid methyl ester yield of around 92 %. The results suggest that the synthesized inexpensive catalyst is useful for biodiesel production from PFAD.  相似文献   
76.
77.
农业灌溉用水量约占全国总用水量的60%,客观测算农田灌溉用水量是落实最严格水资源制度的重要抓手,综合运用数据库管理手段实现农业用水复核工作的流程化和规范性成为迫切需求.深入剖析农田灌溉用水量客观测算的原理与方法,梳理测算业务的数据流程,基于合理的数据分类提出测算模型数据需求.分析各类数据特性及数据间的关联特性,明确数据...  相似文献   
78.
Drought and salinity stresses are significant abiotic factors that limit rice yield. Exploring the co-response mechanism to drought and salt stress will be conducive to future rice breeding. A total of 1748 drought and salt co-responsive genes were screened, most of which are enriched in plant hormone signal transduction, protein processing in the endoplasmic reticulum, and the MAPK signaling pathways. We performed gene-coding sequence haplotype (gcHap) network analysis on nine important genes out of the total amount, which showed significant differences between the Xian/indica and Geng/japonica population. These genes were combined with related pathways, resulting in an interesting mechanistic draft called the ‘gcHap-network pathway’. Meanwhile, we collected a lot of drought and salt breeding varieties, especially the introgression lines (ILs) with HHZ as the parent, which contained the above-mentioned nine genes. This might imply that these ILs have the potential to improve the tolerance to drought and salt. In this paper, we focus on the relationship of drought and salt co-response gene gcHaps and their related pathways using a novel angle. The haplotype network will be helpful to explore the desired haplotypes that can be implemented in haplotype-based breeding programs.  相似文献   
79.
80.
林晓丹 《中国园林》2022,38(12):121-126
旱涝共存压力下黄土台塬传统聚落形成了“围池而居”的形态,以及可识别的地域景观特征。首先,基于多次田野调查、文献查阅、历史卫星地图分析、口述史等研究方法,解析水池与传统聚落空间建构之间的关系,从“池-巷”组成的蓄水排涝体系及“池-庙”形成的地方社会场景两方面,总结归纳水池所塑造的风土聚落景观特征,并挖掘其中的生存智慧。其次,将“池-巷”蓄水排涝体系归纳为“多池联动”“分巷汇水”与“边缘拦蓄”3种模式,总结“池-庙”地方社会场景赋予水池及其周边公共建筑基础服务设施之外的文化景观作用。最后,总结传统蓄水池进出水口及配套设施的设置方式,并通过口述史记录总结水池的地方营造技艺。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号