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   288篇
  免费   11篇
林业   12篇
农学   16篇
基础科学   1篇
  53篇
综合类   39篇
农作物   18篇
水产渔业   9篇
畜牧兽医   104篇
园艺   9篇
植物保护   38篇
  2023年   2篇
  2022年   3篇
  2021年   7篇
  2020年   4篇
  2019年   8篇
  2018年   3篇
  2017年   13篇
  2016年   8篇
  2015年   6篇
  2014年   15篇
  2013年   19篇
  2012年   17篇
  2011年   9篇
  2010年   7篇
  2009年   11篇
  2008年   17篇
  2007年   12篇
  2006年   9篇
  2005年   10篇
  2004年   8篇
  2003年   11篇
  2002年   10篇
  2001年   8篇
  2000年   4篇
  1999年   7篇
  1998年   7篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1992年   3篇
  1991年   5篇
  1990年   3篇
  1989年   5篇
  1988年   3篇
  1987年   2篇
  1986年   5篇
  1985年   5篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1981年   3篇
  1979年   1篇
  1978年   5篇
  1975年   1篇
  1973年   2篇
  1970年   1篇
  1953年   1篇
  1936年   2篇
排序方式: 共有299条查询结果,搜索用时 593 毫秒
81.
OBJECTIVE: To evaluate the efficacy of cellophane banding of single congenital extrahepatic portosystemic shunts in dogs using transcolonic portal scintigraphy. To investigate the portal circulation of those dogs with elevated postoperative shunt fractions to determine the cause of the persistent shunting. Further, to evaluate whether presenting signs, clinical pathology findings and liver histopathology are predictive of outcome. DESIGN: Prospective study of 16 dogs presenting with single congenital extrahepatic portosystemic shunts. PROCEDURE: Dogs with single extrahepatic portosystemic shunts attenuated by cellophane banding underwent portal scintigraphy and bile acids tolerance testing pre- and post-operatively. Dogs identified with elevated shunt fractions at 10 weeks post-operatively underwent mesenteric portovenography. Qualitative hepatic histopathology from all dogs was reviewed by a veterinary pathologist and assigned a semi-quantitative score to identify any abnormalities that may predict surgical outcome. RESULTS: At 10 weeks post cellophane banding, 10 of 16 cases (63%) had normal shunt fractions, whilst six dogs (37%) had increased shunt fractions and seven dogs (44%) had increased serum bile acids. Of these dogs, mesenteric portovenography revealed incomplete closure of the shunt in three dogs (18.6%) and multiple acquired shunts in three dogs (18.6%). Liver histopathology findings were similar for all dogs, regardless of outcome. CONCLUSIONS: Cellophane banding is an efficacious method for complete gradual occlusion of single extrahepatic shunts when the shunt vessel is attenuated to < or = 3 mm. Transcolonic portal scintigraphy is a reliable method for assessment of shunt attenuation and, unlike serum bile acids, is not influenced by other causes of liver dysfunction.  相似文献   
82.
83.
84.
The effect of colored shade nets with different shade intensities and qualities of irradiation transmittance on pepper powdery mildew was tested in mini-plots and field experiments. Leaf coverage byLeveillula taurica and leaf shedding due to the disease were more severe in the shade, by up to 275% and 70%, respectively, than in the open field. Leaf coverage byL. taurica symptoms and leaf shedding from plants grown under 25% shade black nets were higher, by up to 70% and 180%, respectively, than under 40% shade nets. The color of the shade nets affected the intensity of photosynthetically active (PAR), ultra-violet (UV), blue, red and far red radiations, the UV/blue light ratio, and percent PAR and UV transmitted. The various nets suppressed the disease differently. Black, blue-silver, green and red nets were associated with lower levels of disease in the field experiments. The red net was also superior in the mini-plots. The other results from the mini-plots were not similar to those from the field, probably reflecting more intensive epidemic development in the mini-plots. No interaction between net type and cultivar was found when two cultivars were grown under the nets. Yield was higher under nets than in the open; nevertheless, the yield from plants grown under the 40% shade black net was not higher than that of the plants under the 25% black net, despite the significantly lower levels of disease at the higher shade intensity. B-quality pepper yield was significantly higher in the plots covered by 25% shade. Yield differences between the different colored nets were also not well correlated with disease levels, probably due to factors negating the direct effect of the nets on the plants and their yield. Implementation of either ‘friendly’ (Ampelomyces quisqualis AQ10/Trichoderma harzianum T39/ sulfur/ neem seed extract) or chemical (sulfur/ pyrifenox/ Polyoxin AL/ myclobutanil/ azoxystrobin) spray regimes successfully reduced disease severity under the different nets. There was no interaction between net type and spray regime. Thus, growing sweet pepper under shade nets results in increased yields and also in higher powdery mildew severity. Disease is negatively associated with the rate of shading and is variably affected by the quality of light filtered through the different colored shade nets. http://www.phytoparasitica.org posting May 8, 2007.  相似文献   
85.
BOOK REVIEW     
The 5-MinuteVeterinary Consult: Canine and Feline . 2nd edn. Tilley LP, Smith FWK, Lippincott Williams & Wilkins  相似文献   
86.
The loss of aldicarb sulphoxide was studied in incubation experiments with soil from four plough layers and two deeper layers. The loss during the 111 days of the experiment could be described by first-order kinetics. The half-lives at 15°C ranged from 20 days in a clay loam to 46 days in a peaty sand. The loss of sulphoxide in deeper layers was considerably slower than in the corresponding top layers of a soil profile. In soil from a silty layer at 70–90 cm depth the half-life was about 53 days. In soil from a sand layer at 90–110 cm depth a loss of only about 15% was measured after 111 days of incubation. First-order rate constants for sulphoxide conversion in a clay loam at 6, 15 and 25°C were found to be 0.009, 0.033, and 0.05 day?1 respectively; in a greenhouse soil these rate constants were 0.0052, 0.019 and 0.04 day?1 respectively. The fractions of aldicarb sulphoxide that were oxidised to sulphone at 15°C in soil from plough layers were computed to range from 0.52 to 0.76.  相似文献   
87.
An IgM enzyme-linked immunosorbent assay (IgM-ELISA) for the detection of antibodies to bovine herpesvirus-1 (BHV-1) was developed. Its applicability was examined by serological studies in two calves experimentally infected with virulent BHV-1 over a period of 60 days. IgM antibodies were detected by ELISA on day 6 after infection, and there was an increase in IgG antibodies on day 9. Serum neutralizing (SN) antibodies were detected only on day 13, confirming the higher sensitivity of the ELISAs. A similar study of four calves treated with a commercial inactivated virus vaccine indicated no detectable IgM-ELISA response, and late SN and IgG-ELISA reactivity. Thus IgM-ELISA appears to be of value in assessing recent infection, whereas IgG-ELISA and SN cannot distinguish between infection and vaccination. The possible limitations imposed on the specific IgM-ELISA by the presence of IgM rheumatoid factor (IgM-RF) in bovine serum were examined. IgM-RF levels were determined in bovines of various ages. Elevated values of IgM-RF were found in the sera of older animals; their occurrence may lead to false IgM-positive diagnosis (16%) of BHV-1 infection. This was examined in 113 serum specimens from suspected cases of BHV-1 infection and in 32 bulls at an insemination center. Pretreatment of serum samples with an antibovine IgG serum eliminated false positivity of the IgM-ELISA. It is concluded that IgM-ELISA should be of particular value in the diagnosis of recent infection with BHV-1, mainly in calves.  相似文献   
88.
Aldicarb was incubated in seven soils at 15°C and its loss was well described by first-order kinetics. Rate constants varied between 0.078 day?1 in a peaty sand to 0.35 day?1 in a clay loam. The concentration-time relationships for aldicarb, its sulphoxide and its sulphone were approximated by a computation model which was used to analyse the importance of the various consecutive and simultaneous reactions. It was computed that 91 to 100% of the aldicarb would be oxidised to its sulphoxide.  相似文献   
89.
The use of correlated microscopic techniques, including the scanning electron microscopic modes of backscattered electron imaging and energy dispersive x-ray analysis, aid in defining the process of dispersion of silicon-containing material around silicone rubber (polydimethylsiloxane) prosthetic devices.  相似文献   
90.
Many galaxies have taken on their familiar appearance relatively recently. In the distant Universe, galaxy morphology deviates significantly (and systematically) from that of nearby galaxies at redshifts (z) as low as 0.3. This corresponds to a time approximately 3.5 x 10(9) years in the past, which is only approximately 25% of the present age of the Universe. Beyond z = 0.5 (5 x 10(9) years in the past), spiral arms are less well developed and more chaotic, and barred spiral galaxies may become rarer. At z = 1, around 30% of the galaxy population is sufficiently peculiar that classification on Hubble's traditional "tuning fork" system is meaningless. On the other hand, some characteristics of galaxies have not changed much over time. The space density of luminous disk galaxies has not changed significantly since z = 1, indicating that although the general appearance of these galaxies has continuously changed over time, their overall numbers have been conserved.  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