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   456篇
  免费   43篇
林业   9篇
农学   39篇
基础科学   3篇
  33篇
综合类   87篇
农作物   16篇
水产渔业   17篇
畜牧兽医   267篇
园艺   1篇
植物保护   27篇
  2022年   4篇
  2021年   4篇
  2020年   18篇
  2019年   11篇
  2018年   9篇
  2017年   13篇
  2016年   11篇
  2015年   7篇
  2014年   10篇
  2013年   14篇
  2012年   17篇
  2011年   30篇
  2010年   14篇
  2009年   14篇
  2008年   19篇
  2007年   21篇
  2006年   19篇
  2005年   13篇
  2004年   16篇
  2003年   7篇
  2002年   8篇
  2001年   7篇
  2000年   9篇
  1999年   14篇
  1998年   6篇
  1997年   6篇
  1996年   6篇
  1993年   4篇
  1992年   10篇
  1991年   5篇
  1989年   5篇
  1988年   5篇
  1987年   7篇
  1986年   4篇
  1985年   5篇
  1984年   12篇
  1983年   7篇
  1982年   7篇
  1980年   3篇
  1979年   8篇
  1978年   5篇
  1977年   4篇
  1975年   8篇
  1974年   5篇
  1973年   3篇
  1972年   5篇
  1970年   6篇
  1968年   4篇
  1967年   4篇
  1966年   5篇
排序方式: 共有499条查询结果,搜索用时 46 毫秒
181.
182.
SUMMARY: Correlated responses in pituitary gland weight and growth hormone (GH) concentration in the serum and pituitary were studied in lines of mice selected for growth rate, and in controls. The selection criteria were weight gain between 28 and 38 days on an ad libitum feed intake (EPA line), or on intake restricted to 80% of the control mice (EPR line), and weight gain between 48 and 58 days under the above two feeding regimes (LPA and LPR lines). The control line was maintained by random breeding. In generation 13, pituitary weight and growth hormone levels were determined at 38 days in lines EPA, EPR and the control and at 58 days in lines LPA, LPR and the control. Pituitary weight, corrected for body weight gain, was smaller in the EPA line than in the control line at 38 days and was greater in the LPR line than in the control line at 58 days. There were large differences in serum GH concentrations between the selected lines and the control; the differences were statistically significant at 38 days, with the EPA and EPR lines having lower levels than the controls. ZUSAMMENFASSUNG: Ver?nderung von Wachstumshormonspiegel bei Selektion für Zuwachs bei M?usen Ver?nderungen im Hypophysengewicht und Wachstumshormon-(GH)-Konzentrationen im Serum und in der Hypophyse wurden bei Wachstumsselektionslinien und bei Kontrollm?usen untersucht. Selektionskriterien waren Zuwachs zwischen 28 und 38 Tagen bei ad libitum Futteraufnahme (EPA Linie) oder bei Linien, wo Futteraufnahme auf 80% derjenigen der Kontrollm?use (EPR Linie) begrenzt wurde und Zuwachs zwischen 48 und 58 Tagen unter beiden Futterweisen (LPA und LPR Linie). Die Kontrollinie wurde durch Zufallspaarung fortgepflanzt. In Generation 13 wurden Hypophysengewicht und Wachstumshormonspiegel im Alter von 38 Tagen in Linien EPA, EPR und in Kontrollen und bei 58 Tagen in Linien LPA und LPR und Kontrollen bestimmt. Hypophysengewicht, korrigiert für Zuwachs, war geringer in der LPA Linie als in der Kontrolle bei 38 Tagen Alter und gr??er in der LPR Linie als in der Kontrolle bei 58 Tagen. Zwischen GH Konzentrationen selektierter und Kontrollinien waren erhebliche Differenzen, die bei 38 Tagen signifikant waren, wobei EPA und EPR Linien geringere Werte als die Kontrollen aufwiesen.  相似文献   
183.
ABSTRACT A beta-glucuronidase (GUS) reporter gene and a hygromycin B (hygB) phosphotransferase gene were integrated separately into the Trichoderma harzianum strain 1295-22 genome, using biolistic transformation. The mycelial growth and biocontrol ability of the transformed strains did not differ from that of the original strain. The transformed Gus(+)-kanamycin-resistant (Gus(+)Kan(R)) strains were used to monitor growth and interactions with Rhizoctonia solani on creeping bentgrass plants. The hygB-resistant (hygB(R)) strains were used to selectively recover strain 1295-22 from the rhizosphere soil and phylloplane of creeping bentgrass after spray applications. The population levels of two hygB(R) strains and the original strain were very similar for all treatments. All three strains persisted for the duration of the experiment (28 days) in both the rhizosphere soil and on leaves, although population levels declined somewhat over the course of the experiment in unautoclaved soils. In this study, the results demonstrated that hygB(R) strains remained dominant over time when assayed on Trichoderma-selective medium containing hygB. The hygB(R) strains were not displaced by strains that colonized untreated plants. Microscopic observation showed that the Gus(+)Kan(R) strains colonized the rhizoplane, seed coat, and phylloplane of creeping bentgrass. These results supported our earlier observation that strain 1295-22 was rhizosphere and phyllo-plane competent. Interactions between T. harzianum and R. solani were readily observed in situ and changed over time. Two types of reactions were found in these experiments. In the first type, sections of hyphae of R. solani near the hyphae of T. harzianum appeared damaged, and the pathogen appeared necrotic when viewed with a microscope. The second type, observed less frequently than the first type, was typical of myco-parasitism. The findings in this study provide new insight into the interactions between R. solani and T. harzianum, providing a basis for future research.  相似文献   
184.
185.
The toxicity of fenbendazole, an anthelmintic for use in swine, was tested by feeding 8 growing pigs 2,000 mg of fenbendazole/kg of body weight daily for 14 days. A transient leukopenia developed on day 6, but values returned to base line on day 18, 4 days after discontinuation of dosing. Sorbitol dehydrogenase values were significantly (P less than 0.05) increased from day 4 and returned to base line on day 20. Marked gross or histopathologic lesions were not found.  相似文献   
186.
Hyperviscosity syndrome was associated with increased plasma content of monoclonal immunoglobulin (IgA or IgM) in 3 dogs with lymphocytic leukemia. The diagnosis of lymphocytic leukemia was based on the finding of a large number of mature lymphocytes in the blood and bone marrow. The clinical signs included weakness, lethargy, depression, and coughing due to congestive heart failure. Consistent physical findings were splenomegaly, with or without peripheral lymphadenopathy, and funduscopic abnormalities. Of the 2 dogs treated successfully with chlorambucil, 1 remains in remission after withdrawal of the drug for over 1 year.  相似文献   
187.
188.
1. A study was conducted to compare apparent and true digestibility of amino acids in a high protein experimental diet between young ostriches (7 months of age) and cockerels.

2. A mean value for true digestibility of amino acids (TAAD) of 0.837 ± 0.0073 (range 0.780 to 0.862) was derived for ostriches, compared with a mean value of 0.795 ± 0.0258 (range 0.723 to 0.825) for cockerels.

3. True retention of dietary protein was 0.646 ±0.0114 and 0.609 ±0.0643 for ostriches and cockerels respectively.

4. Results in the present study produced evidence that the method for determining metabolisable energy values of ingredients for ostriches is also suitable for measuring the digestibility of amino acids.

5. It was concluded that accurate diet formulation for ostriches requires the assessment of amino acid digestibilities for individual ingredients, because values derived from poultry would underestimate digestibilities for ostriches.  相似文献   

189.
Tuberculosis (TB), due to infection with Mycobacterium bovis was diagnosed in a flock of alpaca in Ireland in 2004. An epidemiological investigation was conducted to identify the risk of TB for farmed alpaca where TB is endemic, the origin of the infection, the potential for alpaca-to-alpaca transmission and appropriate control measures. The investigation focused on the alpaca flock (including the farm, animal movements and breeding, feeding and flock health practice), the disease episode (including animal disease events and subsequent control measures) and TB infection risk in the locality. The TB risk to alpaca is high in areas where infection is endemic in cattle and badgers and where biosecurity is inadequate. It is most likely that the source of infection for the alpaca was a local strain of M. bovis, present in cattle in this area since at least 2001. Genotyping of isolates identified a single variable number tandem repeat (VNTR) profile in both cattle and alpaca in this region. Although a tuberculous badger was also removed from the vicinity, bacterial isolation was not attempted. On this farm, infection in alpaca was probably derived from a common source. Alpaca-to-alpaca transmission seems unlikely. Two broad control strategies were implemented, aimed at the rapid removal of infected (and potentially infectious) animals and the implementation of measures to limit transmission. Tests that proved useful in detecting potentially-infected animals included measurement of the albumin-to-globulin ratio and regular body condition scoring. Skin testing was time consuming and unproductive, and early detection of infected animals remains a challenge. The flock was managed as a series of separate groupings, based on perceived infection risk. No further TB cases have been detected.  相似文献   
190.
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