全文获取类型
收费全文 | 2128篇 |
免费 | 87篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 10篇 |
综合类 | 1篇 |
化学工业 | 399篇 |
金属工艺 | 28篇 |
机械仪表 | 29篇 |
建筑科学 | 134篇 |
矿业工程 | 3篇 |
能源动力 | 35篇 |
轻工业 | 250篇 |
水利工程 | 26篇 |
石油天然气 | 11篇 |
无线电 | 150篇 |
一般工业技术 | 342篇 |
冶金工业 | 543篇 |
原子能技术 | 7篇 |
自动化技术 | 251篇 |
出版年
2023年 | 23篇 |
2022年 | 42篇 |
2021年 | 67篇 |
2020年 | 34篇 |
2019年 | 56篇 |
2018年 | 35篇 |
2017年 | 52篇 |
2016年 | 59篇 |
2015年 | 52篇 |
2014年 | 67篇 |
2013年 | 135篇 |
2012年 | 83篇 |
2011年 | 131篇 |
2010年 | 109篇 |
2009年 | 99篇 |
2008年 | 108篇 |
2007年 | 79篇 |
2006年 | 78篇 |
2005年 | 80篇 |
2004年 | 56篇 |
2003年 | 71篇 |
2002年 | 58篇 |
2001年 | 34篇 |
2000年 | 28篇 |
1999年 | 33篇 |
1998年 | 80篇 |
1997年 | 49篇 |
1996年 | 47篇 |
1995年 | 28篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有2219条查询结果,搜索用时 21 毫秒
1.
2.
3.
4.
William W. Bowerman Amy S. Roe Michael J. Gilbertson David A. Best James G. Sikarskie Rachel S. Mitchell Cheryl L. Summer 《Lakes & Reservoirs: Research and Management》2002,7(3):183-187
The bald eagle (Haliaeetus leucocephalus) is one of the most studied birds of North America, and a great amount of natural life‐history information, including the response of various stressors on the eagles' ability to reproduce, are well known. In Michigan, the eagle has been chosen to track the trends of bioaccumulative compounds of concern across watersheds in the state. The state has been divided into major watersheds, and 20% of these are surveyed each year. A control area in northern Minnesota, Voyageurs National Park, is also sampled annually. We report here on the methods used, the preliminary results of the 1999 field season, and how differences in mercury concentrations varied over a 10‐year period. Mercury in feathers of nestling eagles declined over time only in Lakes Michigan and Huron, but have not decreased among other subpopulations in Michigan. Concentrations of polychlorinated biphenyls (PCBs) and 4,4′‐DDE in blood plasma from nestling eagles have declined over time for most subpopulations; however, they remain greater for breeding areas associated with the Great Lakes' food web. Sea eagles of the genus Haliaeetus are a good sentinel species to track trends in bioaccumulative compounds in aquatic systems. 相似文献
5.
This article argues that an iconic event in the history of helping research--the story of the 38 witnesses who remained inactive during the murder of Kitty Genovese--is not supported by the available evidence. Using archive material, the authors show that there is no evidence for the presence of 38 witnesses, or that witnesses observed the murder, or that witnesses remained inactive. Drawing a distinction between the robust bystander research tradition and the story of the 38 witnesses, the authors explore the consequences of the story for the discipline of psychology. They argue that the story itself plays a key role in psychology textbooks. They also suggest that the story marks a new way of conceptualizing the dangers of immersion in social groups. Finally, they suggest that the story itself has become a modern parable, the telling of which has served to limit the scope of inquiry into emergency helping. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
7.
This article examines the determinants of first-time use durations of the injectable contraceptive Depo Medroxy Progesterone Acetate (DMPA) for rural Bangladeshi women. The method's side effects were defined by 200 first-time users in Matlab district during lengthy, open-ended interviews. Women with many children used the method longer than did women of low parity. Those who experienced side effects had shorter use durations than those who did not, and those who cited heavy bleeding as their main problem discontinued use soonest. Women whose husbands approved of family planning had significantly longer use durations than those whose husbands disapproved. Respondents who adopted DMPA because of perceived positive aspects of the drug used it longer than those who chose it for other reasons. Results of the study underscore the importance of viewing side effects in a specific social and cultural context. Expanded side-effects counseling for women and their husbands is needed. 相似文献
8.
Text search is a type of strategic reading that involves locating specific goal-relevant information. Previous research has indicated that college and high school students often exhibit inefficient or unsuccessful text-search performance. Consequently, the effects of 2 manipulations on text-search performance were investigated: (1) the presence of indexed terms in a text-search task and (2) the use of a planning prompt before beginning a task. 34 college students engaged in 6 text-search tasks. Half of these tasks contained terms that could be used in an index; half required that a search term be generated. Half of the subjects were randomly assigned to a prompt condition in which they were prompted to plan their search before beginning each task. The results indicated that a planning prompt raised the success level of search performance, as did the presence of terms that were searchable in the textbook's index. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
Riley William T.; Schumann Mary F.; Forman-Hoffman Valerie L.; Mihm Patricia; Applegate Bradford W.; Asif Ofer 《Canadian Metallurgical Quarterly》2007,38(1):44
Increased adoption of empirically supported treatments (ESTs) has been hindered in part by inadequate and inconvenient access to EST information and training. To improve diffusion of ESTs, the authors developed a Web application to provide practitioners with concise information by disorder on ESTs. The resulting site, therapyadvisor.com, was evaluated by 239 practicing psychologists to assess the usefulness of the site and explore possible interactions of EST attitudes on ratings of usefulness and impact. Two thirds of participants indicated using ESTs in practice, and limited time and resources were cited as primary barriers to EST adoption. The Web application was rated positively by most participants and was reported to increase awareness of and commitment to try ESTs among approximately 60% of participants. The results of this project support the feasibility of a Web application to increase diffusion and promote further adoption of ESTs. Technological and e-learning advances are promising directions for encouraging the adoption of ESTs specifically and evidence-based practice generally, particularly among busy practitioners who have inadequate time and resources for more traditional forms of dissemination and training. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Abstract: Environmental justice advocates have recently focused attention on cumulative exposure in minority neighborhoods due to multiple sources of pollution. This article uses U.S. EPA's National Air Toxics Assessment (NATA) for 1996 to examine environmental inequality in California, a state that has been a recent innovator in environmental justice policy. We first estimate potential lifetime cancer risks from mobile and stationary sources. We then consider the distribution of these risks using both simple comparisons and a multivariate model in which we control for income, land use, and other explanatory factors, as well as spatial correlation. We find large racial disparities in California's “riskscape” as well as inequalities by other factors and suggest several implications for environmental and land use policy. 相似文献