全文获取类型
收费全文 | 3221篇 |
免费 | 39篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 273篇 |
金属工艺 | 35篇 |
机械仪表 | 40篇 |
建筑科学 | 94篇 |
矿业工程 | 113篇 |
能源动力 | 18篇 |
轻工业 | 160篇 |
水利工程 | 16篇 |
石油天然气 | 5篇 |
无线电 | 160篇 |
一般工业技术 | 278篇 |
冶金工业 | 1796篇 |
原子能技术 | 22篇 |
自动化技术 | 225篇 |
出版年
2021年 | 13篇 |
2020年 | 19篇 |
2019年 | 28篇 |
2018年 | 31篇 |
2017年 | 30篇 |
2016年 | 34篇 |
2015年 | 23篇 |
2014年 | 46篇 |
2013年 | 118篇 |
2012年 | 48篇 |
2011年 | 79篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 55篇 |
2007年 | 59篇 |
2006年 | 61篇 |
2005年 | 40篇 |
2004年 | 57篇 |
2003年 | 45篇 |
2002年 | 57篇 |
2001年 | 42篇 |
2000年 | 37篇 |
1999年 | 69篇 |
1998年 | 518篇 |
1997年 | 275篇 |
1996年 | 211篇 |
1995年 | 120篇 |
1994年 | 110篇 |
1993年 | 125篇 |
1992年 | 36篇 |
1991年 | 46篇 |
1990年 | 43篇 |
1989年 | 47篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 35篇 |
1985年 | 39篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 34篇 |
1980年 | 35篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 58篇 |
1976年 | 122篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1972年 | 14篇 |
1970年 | 6篇 |
排序方式: 共有3260条查询结果,搜索用时 0 毫秒
81.
The potential for community-led local sustainability initiatives to play a key role in a transition towards a low-carbon economy has been acknowledged by both policymakers and researchers. To date, such initiatives have predominantly been established through the efforts of volunteers, resulting in a scattered uptake across towns, cities and other communities in the UK and further afield. In a context where local and national Government are increasingly seeking to deliver local action on climate change in partnership with community organisations, is it possible or desirable for Government and other publicly funded bodies to successfully set up these grassroots initiatives “from the outside” where none exist already? This paper describes a project which explored this question through the provision of a 2-year programme of support for local action on climate change in a sub-region of the UK. Community development strategies were employed with a view to establishing new grassroots climate change initiatives in a range of different communities. The results indicate some potential for the strategy to meet with success, with several new groups and small-scale projects being established as a result. However, the short lifespan of many of the organisations set up and the relatively low impact on carbon emission reduction of their activities raises questions about the effectiveness of grassroots initiatives and how support of their activities can be delivered most effectively to maximise impact and improve cost effectiveness. 相似文献
82.
H.M. Higgins S.E. Golding J. Mouncey I. Nanjiani A.J.C. Cook 《Journal of dairy science》2017,100(4):2909-2916
In the United Kingdom, blanket antibiotic dry cow therapy (BDCT) is commonly prescribed. An alternate strategy is selective dry cow therapy (SDCT) whereby a teat sealant is given instead of an antibiotic to cows with a low probability of infection. Switching from BDCT to SDCT can significantly reduce antibiotic use. The aims of this study were to explore how veterinarians (vets) rationalized their prescribing decisions for mammary treatments at drying off, and the barriers and motivators they perceived to implementing SDCT. Face-to-face interviews were conducted with 20 purposively recruited vets from 6 practices in England, United Kingdom. The data were analyzed qualitatively using an inductive thematic analysis. The majority of participants stated a personal preference for SDCT because it constitutes more responsible antibiotic use. On the majority of farms, the prescribing decision was taken by a senior veterinarian and BDCT was prescribed. Less experienced vets expressed a desire to be more involved in the decision-making process. The first theme, prioritizing responsible antimicrobial prescribing, encapsulated the difficulties vets expressed engaging with farmers, conflicts of interest, and vets’ determination to take action. The second theme, the effect of a vet's experience on their ability to influence farmers, focused on the specific challenges faced by less experienced vets and the importance of vets being both trusted by farmers and being knowledgeable. The third theme, vets’ perceptions about the risk and complexity of implementing SDCT, revealed markedly different levels of concern and fears about adverse outcomes with teat sealants versus antibiotics. The results also showed differences in perceptions about how difficult SDCT is to implement in practice. The last theme, vets’ suggestions for facilitating the introduction of SDCT, was wide ranging and provided useful insight from a veterinary perspective into ways to facilitate SDCT. Initiatives that seek to alter vets’ perceptions of the risks associated with switching to using SDCT are likely to prove useful in facilitating change. Our results also suggest that it is vital for senior vets to take a leading role in facilitating farms to implement SDCT. Less experienced colleagues may benefit from more help from senior vets to gain the trust of farmers and to become involved more quickly in herd-level preventive medicine. Vets must work together and take a united approach to reduce antimicrobial use. 相似文献
83.
We describe a reduction from temporal property verification to a program analysis problem. First we present a proof system that, unlike the standard formulation, is more amenable to reasoning about infinite-state systems: disjunction is treated by partitioning, rather than enumerating, the state space and temporal operators are characterized with special sets of states called frontiers. We then describe a transformation that, with the use of procedures and nondeterminism, enables off-the-shelf program analysis tools to naturally perform the reasoning necessary for proving temporal properties (e.g. backtracking, eventuality checking, tree counterexamples for branching-time properties, abstraction refinement, etc.). Using examples drawn from the PostgreSQL database server, Apache web server, and Windows OS kernel, we demonstrate the practical viability of our work. 相似文献
84.
85.
86.
87.
88.
Differential effects of air conditioning type on residential endotoxin levels in a semi‐arid climate
下载免费PDF全文
![点击此处可从《Indoor air》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J. D. Johnston B. A. Kruman M. C. Nelson R. M. Merrill R. J. Graul T. G. Hoybjerg S. C. Tuttle S. J. Myers R. B. Cook K. S. Weber 《Indoor air》2017,27(5):946-954
Residential endotoxin exposure is associated with protective and pathogenic health outcomes. Evaporative coolers, an energy‐efficient type of air conditioner used in dry climates, are a potential source of indoor endotoxins; however, this association is largely unstudied. We collected settled dust biannually from four locations in homes with evaporative coolers (n=18) and central air conditioners (n=22) in Utah County, Utah (USA), during winter (Jan‐Apr) and summer (Aug‐Sept), 2014. Dust samples (n=281) were analyzed by the Limulus amebocyte lysate test. Housing factors were measured by survey, and indoor temperature and relative humidity measures were collected during both seasons. Endotoxin concentrations (EU/mg) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons. Endotoxin surface loads (EU/m2) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons and in upholstered furniture during winter. For the nine significant season‐by‐location comparisons, EU/mg and EU/m2 were approximately three to six times greater in homes using evaporative coolers. A plausible explanation for these findings is that evaporative coolers serve as a reservoir and distribution system for Gram‐negative bacteria or their cell wall components in homes. 相似文献
89.
90.