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   6733篇
  免费   551篇
  国内免费   653篇
林业   811篇
农学   436篇
基础科学   305篇
  1039篇
综合类   2847篇
农作物   157篇
水产渔业   800篇
畜牧兽医   809篇
园艺   102篇
植物保护   631篇
  2024年   64篇
  2023年   218篇
  2022年   252篇
  2021年   310篇
  2020年   350篇
  2019年   389篇
  2018年   213篇
  2017年   329篇
  2016年   343篇
  2015年   296篇
  2014年   420篇
  2013年   422篇
  2012年   492篇
  2011年   482篇
  2010年   396篇
  2009年   401篇
  2008年   327篇
  2007年   396篇
  2006年   339篇
  2005年   257篇
  2004年   231篇
  2003年   177篇
  2002年   161篇
  2001年   111篇
  2000年   104篇
  1999年   78篇
  1998年   63篇
  1997年   38篇
  1996年   40篇
  1995年   39篇
  1994年   42篇
  1993年   26篇
  1992年   21篇
  1991年   28篇
  1990年   23篇
  1989年   16篇
  1988年   19篇
  1987年   5篇
  1986年   4篇
  1984年   3篇
  1982年   4篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1976年   1篇
排序方式: 共有7937条查询结果,搜索用时 390 毫秒
41.
过度施用化肥带来的负外部性使棉区土壤面临着棉花增产和保护生态环境的双重挑战。本文在棉花生产的决策主体农户尺度上,利用对新疆重点植棉地区实地问卷调查所得数据,定量化研究了新疆棉农过度施用化肥程度,并通过经济计量模型分析了导致农户过量施用化肥的主要因素。研究结果表明,新疆棉花种植农户的化肥施用量(折纯量)平均达到610.20 kg·hm~(-2),过量施用率占到实际施用量的59.6%。导致农户过量施用化肥的主要因素是缺乏科学施肥培训和避免收入损失的盲目性。研究结果在农户行为学方面做了有益的科学探讨,并为科学引导农户合理施肥提供了科学依据。  相似文献   
42.
羊群行为属于行为经济学的一部分,认为市场主体在信息环境不确定的情况下,其行为易受到其他参与主体的影响,模仿他人决策。基于Hwang和Samlton羊群行为测度方法(HS方法)及EGARCH模型,运用2003年1季度至2014年3季度我国30个省市房地产市场销售价格数据,验证我国房地产市场羊群行为的存在性,并分析购房者羊群行为对中国房地产价格波动的影响。结果表明:我国房地产市场羊群行为显著存在,且购房者羊群行为与房地产价格波动呈正相关关系。  相似文献   
43.
从哈贝马斯公共领域理论出发,提出了微信群与微信公众号已经初步形成了公共领域这一观点,并主要介绍了围绕微信公共领域的社交功能、自媒体传播功能和商业贸易平台功能而产生的失范行为。依法规范微信公共领域,可以从完善依法管理微信公共领域、依法运营微信公共领域、依法使用微信公共领域三个有机联系层面的法治规范展开。  相似文献   
44.
环境污染责任保险因开展经验及历史数据不足致费率难以合理厘定,引入模糊信息粒及综合评价理论,相对传统方法,更能实现费率厘定的公平合理,保障各方利益.本文以化学原料及化学制品制造业为研究对象,首先运用模糊信息粒理论处理历史数据,克服数据模糊不确定性,得出第三者赔偿额的模糊信息粒X~;其次运用传统精算定价方法得出行业基准费率的模糊信息粒p~;最后运用模糊综合评价二级评价理论,综合追溯期、企业规模等影响因素,得出投保企业风险综合评价集B~,以此修正基准费率.  相似文献   
45.
港口原油装船VOCs大气环境影响探讨   总被引:1,自引:0,他引:1  
李鑫  寿幼平 《绿色科技》2015,(3):181-182
收集了原油装船VOCs的估算方法,认为原油装船时VOCs排放量为0.012%,VOCs浓度为0.1kg/m3。采用SCREEN3对其环境影响进行分了析,结果表明:下风向最大浓度出现在400m 处,浓度值7.99mg/m3,直到2700m处,浓度值才小于1mg/m3,直到10000m处,浓度值仍为0.14mg/m3,原油装船VOCs的大气环境影响较大。  相似文献   
46.
利用浙江省67个县市的农业经济截面数据,以环境负荷量为因变量,以肉产量和耕地面积为自变量构建模型,对家畜养殖生产的环境效应进行研究。结果表明,2013年绍兴市区、衢州市区、龙游县和江山县的环境负荷量超过警戒值,金华市区、德清县和淳安县的环境负荷量超过适宜值;家畜养殖生产存在着环境负效应,并受到耕地资源的约束,其环境负荷量与肉产量正相关,与耕地面积负相关。  相似文献   
47.
Animal-assisted interventions (AAIs) have been associated with positive effects on human psychological and physiological health. Although the perception of quality standards in AAIs is high, only few investigations have focused on potential welfare implications for therapy dogs linked to their performance in AAIs. The standardized program “multiprofessional animal-assisted intervention (MTI)” has been carried out in adult mental health care, significantly improving patients' prosocial behaviors. In the present study, we monitored salivary cortisol and behavioral measures in therapy dogs that participated in MTI group therapy sessions in an in-patient substance abuse treatment facility. Work-related activity (lay, sit, stand, walk, and run), behavior (lip licking, yawning, paw lifting, body shake, tail wagging, and panting), response to human action (taking food treats and obeying commands), and salivary cortisol levels were analyzed over the course of 5 subsequent MTI working sessions in experienced therapy dogs (N = 5), aged 5.4 ± 2.8 years (mean ± standard deviation). Salivary cortisol levels decreased from presession to postsession in sessions 1, 2, and 3. However, only in session 4 and 5, postsession cortisol levels were significantly lower than presession levels (P = 0.043). There was no difference between salivary cortisol levels sampled on a nonworking day at home and work-related levels sampled at the therapy site. None of the behavioral parameters varied significantly over the course of the 5 MTI sessions. Both lip licking (P = 0.038) and body shake (P = 0.021) were positively correlated with the decline in cortisol during session 5. The study results suggest that trained dogs are not being stressed by repeated participation in in-patient substance abuse therapy sessions. Further investigation into the effects of animal-assisted therapy on dogs' physiological markers and behavior is warranted.  相似文献   
48.
The objective of this study was to evaluate the response of healthy housebound domestic cats to the simultaneous provision of 2 litterboxes of differing sizes by recording the average daily frequency of urination and defecation in each box. Forty-three households with 74 privately owned cats were each provided with 2 different-sized plastic containers, with the larger box being 86 cm in length, exceeding the size of commercially available litterboxes. Owners were also provided with an unlimited supply of clumping cat litter and a logbook to record daily urine and fecal deposits in the boxes as they were scooped over a 4-week period. The 2 litterboxes were initially placed at opposite sides of the same room in the owner's home. After 2 weeks, the boxes were emptied completely, refilled with clean clumping litter, and replaced in the opposite location. Results were recorded as simple counts of urine and fecal deposits for each day and each household. Over the 28-day period, there were a total of 5031 urine and fecal deposits in the larger boxes and 3239 urine and fecal deposits in the regular boxes. The effects of phase (days 1-14 vs. 15-28) and box size (regular vs. large) on the number of deposits per cat were evaluated using a linear mixed model. In addition to evaluating phase and box size, the effects of number of cats in the house, their average age, and gender were also evaluated. Urine deposits were significantly more frequent than fecal deposits. Large boxes were preferentially selected over regular boxes in both phases, but this difference was greater in phase 1 than phase 2. Further analysis indicated that there was a location preference during the first 2 days in phase 2, and this effect decreased as the study progressed. Results indicate that most cats show a definite preference for a larger litterbox than is typically available to them in homes and that other factors such as box cleanliness and location may have a compounding influence on this choice.  相似文献   
49.
利用博弈论的方法对国防工业发展中已进入国防工业的企业群、待进入国防工业的企业群和政府的对策进行分析,并得出结论:政府首先要指导已进入国防工业的企业群合理定位;其次要考虑制定多大程度的保护政策来保护已进入国防工业企业的发展和利益;最后政府需要对军工企业的诉讼制定合理的支持标准,使已进入国防工业企业始终处于竞争环境良性发展.当然政府作出以上决策的主要依据是在保证本国安全的前提下使国防工业企业的利润实现最大化.  相似文献   
50.
从环境保护的角度出发,重点论述了微生物在这一领域的应用现状与发展前景,指出微生物将会在21世纪的环境保护领域中发挥重要作用。  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