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   5911篇
  免费   273篇
  国内免费   456篇
林业   830篇
农学   598篇
基础科学   655篇
  760篇
综合类   2724篇
农作物   227篇
水产渔业   136篇
畜牧兽医   411篇
园艺   117篇
植物保护   182篇
  2024年   28篇
  2023年   95篇
  2022年   158篇
  2021年   187篇
  2020年   193篇
  2019年   220篇
  2018年   113篇
  2017年   205篇
  2016年   269篇
  2015年   289篇
  2014年   329篇
  2013年   340篇
  2012年   541篇
  2011年   516篇
  2010年   342篇
  2009年   347篇
  2008年   294篇
  2007年   320篇
  2006年   316篇
  2005年   245篇
  2004年   209篇
  2003年   189篇
  2002年   106篇
  2001年   130篇
  2000年   90篇
  1999年   88篇
  1998年   82篇
  1997年   59篇
  1996年   61篇
  1995年   46篇
  1994年   53篇
  1993年   42篇
  1992年   29篇
  1991年   27篇
  1990年   32篇
  1989年   21篇
  1988年   11篇
  1987年   10篇
  1986年   5篇
  1985年   1篇
  1983年   1篇
  1955年   1篇
排序方式: 共有6640条查询结果,搜索用时 116 毫秒
141.
小菜蛾弯尾姬蜂室内批量繁殖的技术   总被引:7,自引:0,他引:7  
陈宗麒  缪森等 《昆虫天敌》2001,23(4):145-148
报道小菜蛾弯尾姬蜂室内批量繁殖工艺技术。实验室温度:20℃-25℃,光照:L:D12:12,相对温度:65%-70%,40m^2温室面积用于栽培甘蓝。在此条件下,每周可生产2000头-3000头小菜蛾弯尾姬蜂,可田间释放寄生蜂防治小菜蛾15亩-20亩。  相似文献   
142.
水稻主要病虫综合治理效益评估方法   总被引:1,自引:0,他引:1  
水稻主要稻虫综合治理是一个多输入输出的管理系统,作者层次法引入水稻病虫综合防治效益评估研究。采用专家咨询、数学分析等手段建立了水稻病虫综合防治效益评估层次模型,对总目标、亚目标、准则,指层要的权重值进行科学评估,并对指标层各个要素建立定量化方法,从而建立了一整套综合防治效益定量评估方法,通过对4个综合防治点1992-1993年早、晚委的综合防治总体效益进行评估,评估结果基本客观地反映了当前水稻IE  相似文献   
143.
广西草地资源开发利用策略初探   总被引:3,自引:1,他引:2  
蒋建生 《草业科学》1996,13(1):70-72,F003
对广西草地的类型,数量,载畜能力及基本特征进行了论述,提出了合理开发利用草地资源的五条措施。  相似文献   
144.
分析了湖南早稻生产滑坡的原因,并从品种(组合)和栽培技术方面分析了湖南早稻的增产潜力及提出了今后发展的对策。  相似文献   
145.
Vegetables attract high applications of pesticides, and farmers in developing countries use many acutely toxic insecticides to control pests on these crops. With the liberalisation of agricultural markets in developing countries, the number of small-scale farmers growing vegetables for both domestic and export markets is increasing. Demand for supplies of year-round and exotic fruit and vegetables has grown in industrialised countries, but with rising quality standards and traceability requirements it is difficult for small-scale farmers to benefit from this lucrative non-traditional agricultural export trade. The demand is high for vegetables in the expanding cities in developing countries, and farmers in peri-urban areas, or rural areas with good access to the cities, are in a position to find a growing market for their produce. Poor storage facilities will often mean that farmers are forced to sell at peak times when prices are low. Farmers rarely have access to training in pesticide use, and have only limited or no access to advice on the complicated management of pesticides. The Food and Agriculture Organisation of the UN is concerned about high levels of poor quality and adulterated pesticides on sale in developing countries. Surveys repeatedly show that without training, farmers are unable to make good crop decisions: recognition of pests and their predators is generally low, leading to decisions to spray to kill any insect; knowledge of product selection, application rates and timing is poor; different products are often combined in the belief that the effect will be greater; re-entry periods after spraying and essential harvest intervals are not known; and without knowledge of alternatives, farmers will often assume that the only solution to pest problems is to spray more frequently. From a consumer's point of view, few developing countries are able to monitor pesticide residues, particularly for produce grown for home consumption: most countries do not have laboratories for even simple residue testing. Changes in European Maximum Residue Limits means that export crops will be rejected if they contain residues at the Limit of Detection of pesticides not registered in Europe. Season-long field level training in Integrated Pest Management can help farmers to become better decision-makers, and to greatly reduce pesticide use while reducing risks to their own health and environment, producing safer products for consumers, maintaining yields, and increasing incomes.  相似文献   
146.
通过对大量统计资料和典型调查的系统分析,对天津农产品加工业的发展状况进行了深入的系统研究,分析了发展的特点、差距和问题,指出了天津农产品加工业发展的 10个方向  相似文献   
147.
论草地退化   总被引:1,自引:1,他引:1  
在总结草地退化概念的基础上,从草地退化的成因,退化的表现形式和学科角度3个方面剖析了草地退化的内涵;将草地退化过程概括为量变阶段,量变与质变交互阶段和质变阶段3个时期,并阐述了每一退化过程的主要特征;以新疆为例,提出治理退化草地应首先对草地退化阶段进行科学诊断,以生态置换工程为依托,从落实转变思想观念、整合资源等方面从根本上遏止退化源,进而从补偿制度、农牧区畜牧业联营政策及人口政策等方面进行调控,从而推进退化草地治理的进程,达到草地资源的可持续发展。  相似文献   
148.
现代民主政治作为人类政治智慧的结晶和现代文明的标志对和谐社会的构建意义重大。民主政治是程序政治、透明政治、宽容政治、法治政治。它为和谐社会提供了必须的制度基础。改革开放以来,社会主义民主政治建设取得了巨大成就,但在构建和谐社会的今天仍然存在一些问题。我们要把握好解决问题的着眼点,找到解决问题的有效路径。在和谐社会的构建过程中发挥民主政治的重要作用,使民主政治与和谐社会相得益彰。  相似文献   
149.
Exergy, the thermodynamic function that represents the distance of an open system from equilibrium, is proposed as an ecological indicator for summarizing the complex dynamics occurring in a disturbed community during its recovery processes. These complex dynamics can be difficult to capture by using classical indices. In this study, we sampled macrobenthos using the BACI scheme (before versus after; control versus impact) in tidal wetlands of west Chongming Island, China, an area that has been disturbed by ecological engineering measures. Exergy storage is estimated for benthic communities. The control area is proposed as dynamic reference for estimating local exergy storage of the benthic community. Three different methods were used for estimating exergy on the basis of coefficients: (a) taken for taxa groups; (b) estimated from coding genes given for broad taxonomic groups; and (c) estimated from genome size taken as close as possible to the taxonomic level of the species, providing a basis for inferring similarities. We found a decrease of local exergy content in the disturbed area 9 days after the disturbance. Subsequently, the reference exergy of the benthic community increased (i.e. in the surrounding control area) in accordance with the proposed hypothesis regarding the dynamics of exergy storage during a system's development. Estimates of local exergy arrived at using the three methods provided comparable results. Based on this, we then discuss the feasibility of using the more readily available genome size data for estimating exergy. This result may have important implications for broader application of this indicator to biological systems. Moreover, the adjacent control samples seem to represent an appropriate dynamic reference for estimating the local exergy of disturbed communities. We found that exergy was a useful indicator that integrates the processes underlying the recovery of the benthic community after disturbance.  相似文献   
150.
对Botryosphaeria dothidea通过皮孔侵入果实的过程进行了光学显微镜和扫描电镜观察,发现接种后2d分生孢子完成萌发和附着胞形成过程。接种后10d,菌丝体在皮孔表面缓慢生长。从20 ̄30d菌丝体加速扩展并形成几个分枝,通常从皮孔外围侵入果实,但仅限于皮孔表面组织。从40~50d,菌丝体扩展更为繁茂,一些菌丝开始突入皮孔的第2层组织。接种皮孔中可检测到多聚半乳糖醛酸酶(PG),但活性比对照高。皮孔有3层,第1层为含果胶的死组织,易被病菌侵染降解,底部的第3层非常坚固,是阻止病菌侵染的有效屏障。随果实发育,皮孔大小、数目和裂口均有规律地增加。我们的研究结果进一步证实了苹果轮纹病的潜伏侵染特性。  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