全文获取类型
收费全文 | 13650篇 |
免费 | 1029篇 |
国内免费 | 197篇 |
专业分类
电工技术 | 28篇 |
技术理论 | 1篇 |
综合类 | 747篇 |
化学工业 | 1257篇 |
金属工艺 | 41篇 |
机械仪表 | 126篇 |
建筑科学 | 113篇 |
矿业工程 | 20篇 |
能源动力 | 172篇 |
轻工业 | 10691篇 |
水利工程 | 99篇 |
石油天然气 | 196篇 |
无线电 | 67篇 |
一般工业技术 | 918篇 |
冶金工业 | 197篇 |
原子能技术 | 39篇 |
自动化技术 | 164篇 |
出版年
2024年 | 140篇 |
2023年 | 396篇 |
2022年 | 539篇 |
2021年 | 788篇 |
2020年 | 770篇 |
2019年 | 723篇 |
2018年 | 655篇 |
2017年 | 584篇 |
2016年 | 602篇 |
2015年 | 562篇 |
2014年 | 769篇 |
2013年 | 1018篇 |
2012年 | 865篇 |
2011年 | 828篇 |
2010年 | 544篇 |
2009年 | 473篇 |
2008年 | 394篇 |
2007年 | 629篇 |
2006年 | 628篇 |
2005年 | 490篇 |
2004年 | 387篇 |
2003年 | 377篇 |
2002年 | 298篇 |
2001年 | 190篇 |
2000年 | 212篇 |
1999年 | 171篇 |
1998年 | 131篇 |
1997年 | 113篇 |
1996年 | 84篇 |
1995年 | 77篇 |
1994年 | 73篇 |
1993年 | 61篇 |
1992年 | 57篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 25篇 |
1986年 | 23篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1980年 | 6篇 |
1966年 | 2篇 |
1964年 | 4篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1955年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
101.
针对保健食品企业监管效率低以及管理模式的不健全, 提出一种基于Android平台的移动监管系统模式. 智能终端设备通过连接3G、4G等无线网络, 使监管人员在执法现场将采集的信息数据直接上传至服务器, 同时增设数据同步代理机制, 实时监听用户的离线和在线状态, 防止数据丢失, 再利用蓝牙无线通信技术实现监管数据的后台打印功能, 进一步简化执法流程. 本系统的应用实现了移动监管和移动办公的模式, 具有实际应用价值. 相似文献
102.
Alisher Mirzabaev Dawit Guta Jann Goedecke Varun Gaur Jan Börner Detlef Virchow 《国际水》2015,40(5-6):772-790
This article provides a review of trade-offs and synergies of bioenergy within the water–energy–food security nexus, with emphasis on developing countries. It explores the links of bioenergy with food security, poverty reduction, environmental sustainability, health, and gender equity. It concludes that applying the nexus perspective to analyses of bioenergy widens the scope for achieving multiple-win outcomes along the above aspects. 相似文献
103.
Water–energy–food nexus in a transboundary context: the Euphrates–Tigris river basin as a case study
The interlinkage between water, energy and food security and its transboundary relevance is becoming increasingly important. The paper analyses the evolution of transboundary water resources management in the Euphrates–Tigris basin with specific reference to interlinkages between water, food and energy policies at national and transboundary levels, and it explores how the policy shifts at the highest decision-making level have served to produce synergies for cooperation among the riparians or vice versa. 相似文献
104.
The purpose of this study is to analyze the political economy of food-water security in the water-scarce Middle East and North Africa region. The study deploys the lens of virtual water trade to determine how the region's economies have met their rising food-water requirements over the past three decades. It is shown that the region's water and food security currently depend to a considerable extent on water from outside the region, ‘embedded’ in food imports and accessed through trade. The analysis includes blue (surface and groundwater) and green water resources. 相似文献
105.
《Information Security Journal: A Global Perspective》2013,22(1-3):68-82
ABSTRACTRobust security measures are integrated into new release versions of operating systems (OSs) to ensure that users have a more secure and reliable environment in which to run their daily tasks. In this article, through extensive practical experiments, we evaluate and compare the resilience of popular versions of Microsoft Windows OSs and Apple Mac OS X against Address Resolution Protocol (ARP) cache poisoning attack in a local area network (LAN). The experimental results demonstrate clearly that all tested versions of Windows OSs and Apple Mac OS X are vulnerable to the ARP cache poisoning attack, and do not deploy built-in efficient security features to prevent success of this attack. In addition, the experimental results directly contradict the common belief that Windows OSs are always less secure than Apple OSs. On the other hand, the article analyzes the efforts that have been made and the different methods that have been applied to detect and prevent ARP cache poisoning attacks. The article shows that none of these efforts and methods has been able to give satisfactory results. 相似文献
106.
107.
Two high‐head dams on the Elwha River in Washington State (USA) have changed the migratory patterns of resident and anadromous fish, limiting Pacific salmon to the lower 7.9 km of a river that historically supported large Pacific salmon runs. To document the effects of the dams prior to their removal, we measured carbon and nitrogen stable isotope ratios of primary producers, benthic macroinvertebrates, and fish, and water chemistry above, between and below the dams. We found that δ15N was significantly higher in fish, stoneflies, black flies, periphyton and macroalgae where salmon still have access. Fish and chloroperlid stoneflies were enriched in δ13C, but the values were more variable than in δ15N. For some taxa, there were also differences between the two river sections that lack salmon, suggesting that factors other than marine‐derived nutrients are structuring longitudinal isotopic profiles. Consistent with trophic theory, macroalgae had the lowest δ15N, followed by periphyton, macroinvertebrates and fish, with a range of 6.9, 6.2 and 7.7‰ below, between, and above the dams, respectively. Water chemistry analyses confirmed earlier reports that the river is oligotrophic. Phosphorous levels in the Elwha were lower than those found in other regional rivers, with significant differences among regulated, unregulated and reference sections. The removal of these dams, among the largest of such projects ever attempted, is expected to facilitate the return of salmon and their marine‐derived nutrients (MDN) throughout the watershed, possibly altering the food web structure, nutrient levels and stable isotope values that we documented. Published in 2010 by John Wiley & Sons, Ltd. 相似文献
108.
食品是人类最直接、最重要的消费品。食品安全状况是衡量一个国家经济发展水平和人民生活质量的重要指标。随着我国进口食品的数量和品种逐年增加,我国进口食品安全问题也日益突出。根据国家质检总局统计数据显示:2008年查获的不合格的食品和化妆品共3162批次,2009年共1591批次,2010年共1645批次,2010年前两个月共252批次。不断发生的进口食品安全问题凸显了我国食品安全监管法律制度的漏洞。为确保我国进口食品安全和保护我国消费者食品安全消费需求,完善我国进口食品安全监管法律制度,构建科学合理的进口食品安全监管体系是当务之急。 相似文献
109.
Caspar Schweigman 《International Transactions in Operational Research》2008,15(2):173-193
For many years, the author has been involved in teaching and research in the use of Operations Research as a tool of analysis to study food security problems in sub‐Saharan Africa, in particular, grass root problems of poor farmers. The paper presents an introduction to the way Operations Research methods have been applied in case studies and research projects, and discusses in retrospect the author's views on the strengths and limitations of the application of Operations Research. The paper has in particular been written for people who are not familiar with applications of Operations Research in agriculture, and are interested to learn about its potential usefulness in practice. The retrospective part is largely based on food security studies in e.g. Tanzania, Burkina Faso, Bénin, Togo and Eritrea and on participation in several interdisciplinary research programmes in Africa. 相似文献
110.
基于手机短信的订餐系统设计与开发 总被引:1,自引:0,他引:1
手机的普及为移动电子商务的开展创造了条件.介绍了利用手机开展移动电子商务的3种主要模式,结合具体应用提出了一种构建在手机短信平台上的移动订餐系统.该系统利用J2ME和XML技术实现了订餐短信的自动生成,利用GSMModem实现了移动短信平台与计算机系统的集成,同时实现了订餐短信的自动分发路由.与其它基于手机短信的商业应用不同,该系统不依赖于通信运营商的端口,相对自主.短信订餐相对传统订餐方式有明显优势. 相似文献