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   474篇
  免费   15篇
林业   135篇
农学   12篇
  103篇
综合类   36篇
农作物   16篇
水产渔业   37篇
畜牧兽医   123篇
园艺   7篇
植物保护   20篇
  2020年   7篇
  2019年   6篇
  2018年   8篇
  2017年   6篇
  2016年   10篇
  2015年   8篇
  2014年   12篇
  2013年   11篇
  2012年   18篇
  2011年   30篇
  2010年   10篇
  2009年   15篇
  2008年   28篇
  2007年   20篇
  2006年   22篇
  2005年   17篇
  2004年   19篇
  2003年   22篇
  2002年   12篇
  2001年   7篇
  2000年   7篇
  1997年   4篇
  1992年   4篇
  1989年   4篇
  1986年   3篇
  1984年   5篇
  1983年   4篇
  1982年   4篇
  1977年   4篇
  1975年   3篇
  1974年   5篇
  1972年   6篇
  1969年   3篇
  1968年   3篇
  1967年   5篇
  1966年   3篇
  1965年   4篇
  1962年   3篇
  1956年   4篇
  1948年   7篇
  1941年   3篇
  1934年   3篇
  1933年   3篇
  1932年   12篇
  1927年   7篇
  1919年   6篇
  1918年   5篇
  1915年   4篇
  1904年   5篇
  1902年   3篇
排序方式: 共有489条查询结果,搜索用时 15 毫秒
441.
Zusammenfassung Nach kurzer Darstellung der bekannten bionomischen Tatsachen wird die Abh?ngigkeit der Fra?menge von der Temperatur geprüft und eine Steigerung bei zunehmender W?rme nachgewiesen. Die weite Verbreitung des Schildk?fers in den Minzefeldern der Moore bei München h?ngt mit dem Vorkommen einer ursprünglichen Wirtspflanze (Mentha aquatica) zusammen. Eine gef?hrliche Massenvermehrung, die nach den Ern?hrungsverh?ltnissen zu erwarten w?re, wird durch starke Parasitierung und besonders durch zwei- bis dreimalige Ernte mit gleichzeitiger Vernichtung der meisten Tiere vermieden. z. Zt. im Felde Mit 6 Abbildungen  相似文献   
442.
Rye is a multi-purpose cereal crop grown in Central and Eastern Europe as well as in Western Canada. Fusarium head blight (FHB) is one of the diseases that have a severe negative impact on rye, but knowledge about FHB resistance at the genomic level is totally missing in rye. The objective of this study was to elucidate the genetic architecture of FHB resistance in winter rye using genome-wide association (GWA) mapping complemented by genomic prediction (GP) in comparison with marker-assisted selection (MAS). Additionally, plant height and heading stage were analysed. A panel of 465 S1-inbred lines of winter rye was phenotyped in three environments (location–year combinations) for FHB resistance by inoculation with Fusarium culmorum and genotyped with a 15k SNP array. Significant genotypic variation and high heritabilities were found for FHB resistance, heading stage and plant height. FHB did not correlate with heading stage, but was moderately correlated with plant height (r = −.52, p < .001) caused by some susceptible short inbred lines. The GWA scan identified 15 QTL for FHB resistance that jointly explained 74% of the genotypic variance. In addition, we detected 11 QTL for heading stage and 8 QTL for plant height, explaining 26% and 14% of the genotypic variance, respectively. A genome-wide prediction approach resulted in 44% higher prediction abilities than marker-assisted selection for FHB resistance. In conclusion, genomic approaches appear promising to improve and accelerate breeding for complex traits in winter rye.  相似文献   
443.
Chilled storage of zebrafish embryos is possible for up to 33 h at 8 °C without a loss in viability. In the present study, higher chilling temperatures in the range of 10–16 °C were tested to extend the storage periods to 65 h. It was also investigated whether prevention of microbiological growth with antibiotics and iodine, and stabilization of the quality of the storage solution by regular changes and constant aeration had an effect on the embryo and larvae viability. At incubation temperatures of 10 and 12 °C, the embryo development was completely arrested; at 14 and 16 °C, it proceeded slowly. At 10 °C, the percentage of embryos developing to the long‐pec stage was significantly lower than those at 12, 14 and 16 °C and in the control. At 10 and 12 °C, the percentage of embryos developing to the long‐pec stage decreased with increasing chilling period, while it remained constant at 14 and 16 °C. All chilling treatments resulted in low hatching rates <25% and many larvae showed malformations. Supplementation of storage solutions with antibiotics and iodine had no effect on the embryo and larvae viability, similar to regular solution changes and constant aeration.  相似文献   
444.
Automobile traffic pollutes roadside environments with a range of contaminants. In this study, we investigate the distribution patterns of different contaminant classes in topsoils across a highway-forest interface north-east of Vienna, Austria, in order to assess spatial pollutant distribution and evaluate the filtering effect of roadside forests. We collected soil samples along transects perpendicular to the highway, and analyzed the soils for road salt residues (Na), total and mobile heavy metals (Pb, Cd, Cu, Zn, Ni, Cr) as well as polycyclic aromatic hydrocarbons (PAHs). Roadside soil pollution was highly heterogeneous. All contaminants followed an exponential-like decrease with distance from the road, reaching background levels at 5 to 10 m from the road curb. Traffic-born heavy metals in the immediate roadside zone tended to be more mobile than heavy metals of predominantly geogenic origin at greater distances from the road; the presence of road salt residues could have contributed to the elevated heavy metal mobility near the road. The forest vegetation acted as filter for PAHs shown by a sharp concentration increase at the forest edge. PAHs are likely transported with airborne soot particles that are scavenged by the wax-coated coniferous needles at our study site.  相似文献   
445.
Walleye pollock (Gadus chalcogrammus) supports one of the largest commercial fisheries in the world. Juvenile pollock are important forage fish in the eastern Bering Sea (EBS) ecosystem, often representing the largest fraction in the diets of major Bering Sea piscivores. Large variability in the EBS pollock stock biomass in recent years has been attributed primarily to fluctuations in recruitment. It has been hypothesized that predation rates on forage fishes increase when the cold pool (a body of cold water < 2°C) is extensive and covers much of the middle continental shelf, which tends to concentrate larger predatory fishes in the outer shelf and slope regions. In contrast, young pollock appear to tolerate colder temperatures than older fish and can stay in the cold pool, thereby reducing predation. We used a multispecies modeling approach to examine the effects of the cold pool size on predation of juvenile pollock. We found that predation on age‐1 pollock by age‐3+ pollock decreased, and predation on age‐1 and age‐2 pollock by arrowtooth flounder increased with increasing bottom temperature, which was used as a proxy for the cold pool size. These results suggest that the cold pool creates spatial separation between juvenile pollock and arrowtooth flounder, but not between adult and juvenile pollock. The model developed in this study could be used to examine the effects of other covariates on interspecific interactions, help explain observed changes in fish communities, and understand implications of climate change on ecosystems and their productivity.  相似文献   
446.
In Europe, rabies in bats is caused by European Bat Lyssavirus (EBLV) type 1 (EBLV-1) or type 2 (EBLV-2) which form two distinct genotypes (gt 5 and 6) within the genus Lyssavirus of the family of Rhadoviridae. Spill-over infections of EBLV in humans have caused fatal rabies encephalitis and highlighted the relevance of this wildlife disease for public health. The vast majority of the 831 European bat rabies cases reported between 1977 and 2006 were identified as EBLV-1. Only few virus isolates originating from Switzerland, The Netherlands and the United Kingdom were characterized as EBLV-2. Here we report the first EBLV-2 case detected in Germany in a Daubenton's bat (Myotis daubentonii) in August 2007. The bat showed clinical signs of disorders of the central nervous system and subsequently tested positive for rabies. The virus was isolated and characterized as EBLV-2 based on its antigen pattern and by nucleotide sequencing. Phylogenetic analysis indicated an association to EBLV-2 isolates from Switzerland which correlates with the origin of the bat close to the Swiss border.  相似文献   
447.
    
Ohne Zusammenfassung  相似文献   
448.
    
Ohne Zusammenfassung  相似文献   
449.
    
Ohne Zusammenfassung  相似文献   
450.
Ohne Zusammenfassung  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