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   1676篇
  免费   110篇
林业   98篇
农学   29篇
基础科学   11篇
  255篇
综合类   357篇
农作物   58篇
水产渔业   105篇
畜牧兽医   772篇
园艺   36篇
植物保护   65篇
  2023年   16篇
  2022年   20篇
  2021年   41篇
  2020年   49篇
  2019年   51篇
  2018年   37篇
  2017年   35篇
  2016年   47篇
  2015年   24篇
  2014年   43篇
  2013年   65篇
  2012年   103篇
  2011年   121篇
  2010年   68篇
  2009年   50篇
  2008年   115篇
  2007年   90篇
  2006年   95篇
  2005年   72篇
  2004年   56篇
  2003年   72篇
  2002年   70篇
  2001年   17篇
  2000年   13篇
  1999年   14篇
  1996年   13篇
  1994年   11篇
  1993年   8篇
  1992年   15篇
  1991年   13篇
  1990年   10篇
  1989年   10篇
  1988年   8篇
  1987年   10篇
  1986年   18篇
  1985年   15篇
  1984年   10篇
  1983年   9篇
  1979年   11篇
  1978年   12篇
  1977年   10篇
  1976年   9篇
  1975年   10篇
  1974年   10篇
  1973年   12篇
  1972年   7篇
  1971年   13篇
  1969年   12篇
  1968年   7篇
  1967年   13篇
排序方式: 共有1786条查询结果,搜索用时 203 毫秒
101.
Conclusions  
–  •In intensive animal production, a considerable proportion of the livestock population must be expected to receive animal pharmaceuticals.
–  •The administration of pharmacologically-active feed additives has been influenced through the revocation of approval for some individual substances over the last few years. Aside from the substitution of these forbidden substances, further reductions in the use of antibiotic growth promotors can be expected primarily because of economic reasons.
–  •Animal pharmaceuticals frequently consist of so-called older preparations whose ecotoxicological potentials have only been investigated inadequately.
–  •High elimination rates of the active substances and their stability during storage, which could be demonstrated for tetracyclines, might also lead to a significant incorporation of these substances into the soil even when they are employed correctly. In the future, ecotoxicological investigations should be demanded in cases where the EMEA/CVMP trigger values (which are substantially lower) have been exceeded, a procedure which is currently only required for the newly approved agents.
–  •There is presently a considerable need for research into the environmental fate of these older preparations and their ecotoxicological effects. Here, it will be especially important to take the degradation and transformation processes in the soil into account, as well as especially considering the consequences on the microbiological impacts affecting the soil.
–  •Improved transparency in the application of these substances, in the sense of a quantitative’registration of the animal pharmaceuticals (especially the older preparations) which are employed, as well as the environmental monitoring of animal pharmaceuticals (e.g. in groundwater and surface water), would considerably improve the significance of the basic data for future appraisals.
German federal research plan from the German Federal Ministry for the Environment, Wildlife Conservation and Nuclear Safety - Treatment and utilization of wastes. Research report 297 33 911 - UBA-FB 000074. Original title: Charakterisierung und Verwertung von Abf?llen aus der Massentierhaltung unter Berücksichtigung verschiedener B?den. Stoffeintrag in B?den durch Tierarzneimittel und pharmakologisch wirksame Futterzusatzstoffe unter besonderer Berücksichtigung von Tetrazyklinen. A research article on this topic follows in JSS No. 2. DOI: http://dx.doi.org/10.1065/jss2001.02.006. By courtesy of the German Federal Environmental Agency (Umweltbundesamt - UBA). The complete research report is available as UBA-TEXTE 44/00 (ISSN 0722-186X) by payment of DM 20,00 (Euro 10,26), account no. 4327 65-104, Postbank Berlin (BLZ 10010010), Fa. Werbung und Vertrieb, Ahornstra?e 1-2, D-10787 Berlin, Germany  相似文献   
102.
A fully automated rain exclusion canopy system has been designed and constructed to study the impact of simulated acid rain on the growth and yield of agricultural crops. The system consists of three, mobile greenhouse shelters which exclude ambient rainfall and apply simulated acid rain (SAR) treatments to crops established in field plots. All aspects of the field system are controlled by a microcomputer and data acquisition system. In addition, elevated ambient levels of gaseous pollutants (e.g. O3, SO2, NOx) are reduced in field plots via an air exclusion system consisting of large blowers, potassium permanganate-treated alumina filters and perforated polyethylene tubes. Gaseous pollutants can be injected into the treatment plots via the blowers.  相似文献   
103.
104.
105.
Neuron activity related to short-term memory   总被引:39,自引:0,他引:39  
Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory  相似文献   
106.
We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics.  相似文献   
107.
108.
109.
110.
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