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   1521篇
  免费   169篇
  国内免费   161篇
  2024年   9篇
  2023年   42篇
  2022年   62篇
  2021年   78篇
  2020年   88篇
  2019年   102篇
  2018年   116篇
  2017年   102篇
  2016年   93篇
  2015年   90篇
  2014年   93篇
  2013年   230篇
  2012年   110篇
  2011年   59篇
  2010年   48篇
  2009年   67篇
  2008年   60篇
  2007年   71篇
  2006年   64篇
  2005年   41篇
  2004年   28篇
  2003年   30篇
  2002年   20篇
  2001年   19篇
  2000年   14篇
  1999年   18篇
  1998年   18篇
  1997年   13篇
  1996年   12篇
  1995年   6篇
  1994年   9篇
  1993年   5篇
  1992年   6篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   1篇
  1987年   4篇
  1986年   3篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1977年   1篇
  1976年   2篇
  1970年   1篇
排序方式: 共有1851条查询结果,搜索用时 147 毫秒
121.
Recent environmental trends, including (1) an expansion of existing command and control directives, (2) the introduction of market‐based policy instruments, and (3) the adoption of extended producer responsibility, have created a need for new tools to help managerial decision‐making. To address this need, we develop a nonlinear mathematical programming model from a profit‐maximizing firm's perspective, which can be tailored as a decision‐support tool for firms facing environmental goals and constraints. We typify our approach using the specific context of diesel engine manufacturing and remanufacturing. Our model constructs are based on detailed interviews with top managers from two leading competitors in the medium and heavy‐duty diesel engine industry. The approach allows the incorporation of traditional operations‐planning considerations—in particular, capacity, production, and inventory—together with environmental considerations that range from product design through production to product end of life. A current hurdle to implementing such a model is the availability of input data. We therefore highlight the need not only to involve all departments within businesses but also for industrial ecologists and business managers to work together to implement meaningful decision models that are based on accurate and timely data and can have positive economic and environmental impact.  相似文献   
122.
This article elaborates an integrated policy framework, including policy features and specific measures that can be implemented to mitigate the barriers to eco‐innovations. We claim that factors inhibiting the development and uptake of eco‐innovations are multifaceted and stem from different sources. This systems view, which highlights the multilayered conception of the obstacles to eco‐innovation, calls for a combination of environmental and technology policies adapted to the different barriers and characteristics of the technologies. Drawing on evolutionary economics, the article sheds light on the appropriate combinations of framework conditions and instruments that are most effective to promote eco‐innovation, considering different barriers and eco‐innovation types (process/product, mature/immature, and radical/incremental).  相似文献   
123.
124.
Abstract: State wildlife agencies often use input obtained through public meetings to develop management policies. Because public meetings can be dominated by single stakeholder groups, these policies may not reflect the attitudes of new wildlife stakeholders. In 2000 the Utah Wildlife Board, after a series of public meetings, adopted a statewide policy for winter-feeding mule deer (Odocoileus hemionus). The policy was implemented by the Utah Division of Wildlife Resources from 2001 to 2007 in Cache County of northern Utah, USA. In 2007, we surveyed Utah households representing metropolitan, nonmetropolitan, and Cache County residents (n = 1,800) to evaluate whether the winter-feeding policy reflected the attitudes of all wildlife stakeholders. Survey respondents, regardless of residence strata, believed winterfeeding programs were essential for managing mule deer in Utah (χ26 = 7.02, P = 0.32). However, most respondents were reluctant to support feeding programs at the expense of habitat restoration projects (χ26 = 11.64, P = 0.07). Our results suggest that the winter-feeding policy represented the attitudes of the Utah residents surveyed, though few had participated in its development. Respondents' strong utilitarian attitudes toward wildlife (e.g., strong support for hunting and feeding) influenced those respondents' perceptions of the policy. Given the effects of increased urbanization on utilitarian attitudes toward wildlife in many parts of the United States, coupled with decreasing numbers of traditional wildlife stakeholders, state wildlife agencies should continually reevaluate their public involvement processes to ensure new wildlife stakeholders' attitudes and concerns are represented.  相似文献   
125.
To know the prevalence of Enterobius vermicularis infection and what are the most important risk factors, we evaluated the incidence and risk factors of enterobiasis among children attended in kindergartens in Busan metropolitan city, Republic of Korea. A total of 1,674 children from 21 kindergartens in 11 of 16 autonomous districts of Busan were evaluated for E. vermicularis infection by the cellotape anal swab technique. The overall egg-positive rate for E. vermicularis was 10.7% (179/1,674), and the prevalence of enterobiasis in each kindergarten ranged between 0% and 32.4%. There was an increasing tendency of the egg positive rate according to the population density; the higher the population density communities had, the higher egg-positive rate for E. vermicularis was detected (P = 0.001). Among personal hygiene factors involving children, thumb-sucking (P = 0.036) and fingernail-trimming (P = 0.024) were highly associated with enterobiasis. In addition, taking anthelmintic medications against E. vermicularis infection was strongly associated with enterobiasis (P = 0.014). Moreover, parents'' knowledge of enterobiasis was correlated significantly with the incidence of enterobiasis of their children (P = 0.006). In conclusion, we need to consider not only personal hygiene but also parents'' knowledge about enterobiasis as a factor in order to develop new strategies for elimination or to complete reduction of enterobiasis in Korea.  相似文献   
126.
In this article, I highlight the challenges, tensions, and affinities between Latino educational anthropology and diaspora studies. Some of the urgent questions include attention to new Latino destinations, transnationalism, and Latino diversity. It concludes by suggesting future pathways through Latina feminist thought.  相似文献   
127.
Medical students, subject to unique challenges and stressors, frequently engage in misconduct. In this observational study, carried out in a medical school in Colombia, we developed a survey to explore the association between misconduct and stress, potential stressors and other possible contributing factors, such as sex, age and academic year. Of the 433 students that responded to our survey, 97.9% did not fully disagree with at least one of the mentioned misconducts and 99.8% admitted to at least one transgression. Based on a scale we developed, 61.4% of the students consistently agreed with misconduct and 44.9% frequently engaged in misconduct. A logistic regression model suggests that being male (OR 1.90, CI 95% 1.27–2.84) and stress (OR 1.04, CI 95% 1.01–1.06) may increase the likelihood of misconduct. In a subgroup of students, excluding those in their last year of studies, higher academic semester (OR 1.25, CI 95%: 1.10–1.42) may also be a risk factor for misconduct. Most of the observed variation in the data, however, is not explained by these factors. Other modifiers, such as student personality and sub‐culture, may play a greater role in determining misconduct. The proportion of medical students that engage in misconduct is very high and warrants the attention of the medical education community.  相似文献   
128.
In this work, it is shown that in a deterministic context, a threshold policy can induce cyclic behavior in an otherwise exploited stable population. These dynamics ensue as a result of the combination of the degree of harvesting pressure and more protective threshold densities. Virtual equilibrium in variable structure systems plays a determinant role in this dynamical outcome.  相似文献   
129.
Rogers W  Ballantyne A  Draper H 《Bioethics》2007,21(9):520-524
In this paper we argue that sex-selective abortion (SSA) cannot be morally justified and that it should be prohibited. We present two main arguments against SSA. First, we present reasons why the decision for a woman to seek SSA in cultures with strong son-preference cannot be regarded as autonomous on either a narrow or a broad account of autonomy. Second, we identify serious harms associated with SSA including perpetuation of discrimination against women, disruption to social and familial networks, and increased violence against women. For these reasons, SSA should be prohibited by law, and such laws should be enforced. Finally, we describe additional strategies for decreasing son-preference. Some of these strategies rely upon highlighting the disadvantages of women becoming scarce, such as lack of brides and daughters-in-law to care for elderly parents. We should, however, be cautious not to perpetuate the view that the purpose of women is to be the consorts for, and carers of, men, and the providers of children. Arguments against SSA should be located within a concerted effort to ensure greater, deeper social and cultural equality between the sexes.  相似文献   
130.
Two important human action selection processes are the choice by citizens of parties to support in elections and the choice by party leaders of policy 'packages' offered to citizens in order to attract this support. Having reviewed approaches analysing these choices and the reasons for doing this using the methodology of agent-based modelling, we extend a recent agent-based model of party competition to treat the number and identity of political parties as an output of, rather than an input to, the process of party competition. Party birth is modelled as an endogenous change of agent type from citizen to party leader, which requires describing citizen dissatisfaction with the history of the system. Endogenous birth and death of parties transforms into a dynamic system even in an environment where all agents have otherwise non-responsive adaptive rules. A key parameter is the survival threshold, with lower thresholds leaving citizens on average less dissatisfied. Paradoxically, the adaptive rule most successful for party leaders in winning votes makes citizens on average less happy than under other policy-selection rules.  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