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   304篇
  免费   10篇
林业   74篇
农学   6篇
基础科学   3篇
  33篇
综合类   28篇
农作物   10篇
水产渔业   25篇
畜牧兽医   112篇
园艺   12篇
植物保护   11篇
  2023年   4篇
  2022年   3篇
  2021年   7篇
  2020年   4篇
  2019年   3篇
  2017年   4篇
  2016年   6篇
  2015年   4篇
  2014年   9篇
  2013年   10篇
  2012年   13篇
  2011年   16篇
  2010年   9篇
  2009年   11篇
  2008年   15篇
  2007年   17篇
  2006年   15篇
  2005年   11篇
  2004年   14篇
  2003年   11篇
  2002年   10篇
  1997年   2篇
  1993年   4篇
  1992年   4篇
  1989年   2篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1981年   2篇
  1977年   2篇
  1975年   3篇
  1970年   5篇
  1969年   2篇
  1955年   2篇
  1954年   2篇
  1948年   3篇
  1944年   2篇
  1943年   3篇
  1942年   2篇
  1941年   2篇
  1940年   3篇
  1938年   7篇
  1936年   8篇
  1935年   4篇
  1934年   4篇
  1931年   7篇
  1930年   3篇
  1928年   3篇
  1896年   2篇
排序方式: 共有314条查询结果,搜索用时 230 毫秒
21.
Zusammenfassung 1. Das Streupulver (Delicia-Ratron-Streupulver) hat sich bis jetzt als ein recht brauchbares Hausrattenmittel gezeigt. wenn es in Verbindung mit geeigneten Ködern den Hausratten einverleibt werden kann.Eine Pulver- oder Köderscheu besteht nicht, dagegen kann von einer anlockenden Wirkung gesprochen werden. Die wiederholte Annahme anderer Giftköder durch Hausratten ist bekannt, diese Köder finden noch bessere Annahme. Bei der Auslage von Brotscheiben kann die unangenehme Verschmutzung der Auslegestelle durch das Pulver durch ein loses Einwickeln der Scheiben in Zeitungspapier verhütet werden.2. Der Zeitpunkt für die Anlage von Schüttungen war günstig. Von Anfang Oktober bis Ende März des nächsten Jahres haben die Hausratten die Winterquartiere bezogen. Ein gewisser, aber nicht durchschlagender Erfolg kann diesen Schüttungen zugesprochen werden, doch steht der Erfolg in keinem Verhältnis zum Aufwand an Material und Arbeitszeit.3. Die Ursache des angeblich gesteigerten Lärmes in den Einschüben der Zimmerdecken bedarf noch der Klärung.4. Das Streupulver war für mich ein neues Rattenmittel, dessen Anwendung und Wirkungsbreite ich durch eigene Versuche kennen lernen wollte. Eine solche Versuchsreihe, die Anlage von Schüttungen, die Suche nach geeignetem Ködermaterial konnte recht gut, im Zuge der pausenlosen Schädlingsbekämpfung, die hier eingeführt ist, erfolgen.  相似文献   
22.
23.

Background

Bovine paratuberculosis is an incurable chronic granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis (MAP). The prevalence of MAP in the Swiss cattle population is hard to estimate, since only a few cases of clinical paratuberculosis are reported to the Swiss Federal Food Safety and Veterinary Office each year.Fecal samples from 1,339 cattle (855 animals from 12 dairy herds, 484 animals from 11 suckling cow herds, all herds with a history of sporadic paratuberculosis) were investigated by culture and real-time polymerase chain reaction (PCR) for shedding of MAP.

Results

By culture, MAP was detected in 62 of 445 fecal pools (13.9%), whereas PCR detected MAP in 9 of 445 pools (2.0%). All 186 samples of the 62 culture-positive pools were reanalyzed individually. By culture, MAP was grown from 59 individual samples (31.7%), whereas PCR detected MAP in 12 individual samples (6.5%), all of which came from animals showing symptoms of paratuberculosis during the study. Overall, MAP was detected in 10 out of 12 dairy herds (83.3%) and in 8 out of 11 suckling cow herds (72.7%).

Conclusions

There is a serious clinically inapparent MAP reservoir in the Swiss cattle population. PCR cannot replace culture to identify individual MAP shedders but is suitable to identify MAP-infected herds, given that the amount of MAP shed in feces is increasing in diseased animals or in animals in the phase of transition to clinical disease.  相似文献   
24.
Avian bornaviruses (ABV) are known to be the causative agent of proventricular dilatation disease (PDD) in parrots and their relatives (Psittaciformes). A broad range of ABV genotypes has been detected not only in psittacine birds, but also in other avian species including canary birds (Serinus canaria forma domestica) and Bengalese finches (Lonchura striata f. dom.), which are both members of the order songbirds (Passeriformes).During this study 286 samples collected from captive and wild birds of various passerine species in different parts of Germany were screened for the presence of ABV. Interestingly, only three ABV-positive samples were identified by RT-PCR. They originated from one yellow-winged pytilia (Pytilia hypogrammica) and two black-rumped waxbills (Estrilda troglodytes) from a flock of captive estrildid finches in Saxony. The ABV isolates detected here were only distantly related to ABV isolates found in passerine species in Germany and Japan and form a new genotype tentatively called ABV-EF (for “estrildid finches”).  相似文献   
25.
Synchronization of estrus and ovulation are of paramount importance in modern livestock improvement programs. These methods are critical for assisted reproduction technologies, including artificial insemination and embryo transfer, that can increase productivity. In the current study, subcutaneous implants containing norgestomet were placed for long (14 days), medium (9 days), and short (5 days) periods of time in 70 crossbred ewes undergoing fixed-time artificial insemination. The resulting effects on estrus synchronization and conception rates were subsequently evaluated. Among the synchronized ewes, 85.7% (60/70) underwent estrus over a period of 72 h after progestagen treatment ceased. The shortest mean interval between withdrawal of the device and onset of estrus (34.2 ± 8.9 h) was observed in the G14 days of P4 group (p < 0.05). The conception rate of the G14 days of P4 group was statistically higher than that of the other groups (83.3% vs. 60.9% vs. 47.8%; p < 0.05). In conclusion, 14 days of norgestomet treatment produced higher conception rates and a greater number of pregnancies at the beginning of the breeding season.  相似文献   
26.
Data on the G.S.I. of adults and appearance of fry indicated a regular lunar spawning cycle of S. rivulatus within a seasonal breeding period. A mass collection technique yielding 5000–7000 fry per day was developed.  相似文献   
27.
    
Ohne Zusammenfassung  相似文献   
28.
Five parents of common vetch (Vicia sativa L.) having orange/beige cotyledon colour, brown/white testa colour, purple/green seedling colour and purple/white flower colour were crossed as a full diallele set. The inheritance patterns of cotyledon, testa or seed coat colour, flower and seedling colour, were studied by analyzing their F1, F2, BC1 and BC2 generations. The segregation pattern in F2, BC1 and BC2, showed that cotyledon colour was governed by a single gene with incomplete dominance and it is proposed that cotyledon colour is controlled by two allelic genes, which have been designated Ct1 and Ct2. Testa colour was governed by a single gene with the brown allele dominant and the recessive allele white. This gene has been given the symbol H. Two complementary genes governed both flower and seedling colours. These flower and seedling colour genes are pleiotropic and the two genes have been given the symbols S and F.  相似文献   
29.
On the cause of the 1930s Dust Bowl   总被引:3,自引:0,他引:3  
During the 1930s, the United States experienced one of the most devastating droughts of the past century. The drought affected almost two-thirds of the country and parts of Mexico and Canada and was infamous for the numerous dust storms that occurred in the southern Great Plains. In this study, we present model results that indicate that the drought was caused by anomalous tropical sea surface temperatures during that decade and that interactions between the atmosphere and the land surface increased its severity. We also contrast the 1930s drought with other North American droughts of the 20th century.  相似文献   
30.
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