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   572篇
  免费   56篇
林业   35篇
农学   7篇
  97篇
综合类   52篇
农作物   24篇
水产渔业   34篇
畜牧兽医   324篇
园艺   4篇
植物保护   51篇
  2024年   2篇
  2023年   10篇
  2022年   9篇
  2021年   25篇
  2020年   30篇
  2019年   25篇
  2018年   23篇
  2017年   17篇
  2016年   21篇
  2015年   16篇
  2014年   24篇
  2013年   29篇
  2012年   43篇
  2011年   49篇
  2010年   19篇
  2009年   27篇
  2008年   43篇
  2007年   38篇
  2006年   35篇
  2005年   34篇
  2004年   27篇
  2003年   25篇
  2002年   18篇
  2001年   6篇
  2000年   4篇
  1999年   2篇
  1998年   2篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1985年   1篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
  1978年   2篇
  1976年   1篇
  1974年   2篇
  1969年   1篇
  1948年   1篇
  1947年   2篇
  1946年   1篇
  1944年   1篇
  1940年   1篇
排序方式: 共有628条查询结果,搜索用时 31 毫秒
371.
Canine serum samples were fractionated on DEAE cellulose using a continuous gradient system to establish a representative chromatographic pattern for normal dog serum. Serum samples were separated using decreasing pH (8.4–4.5) and increasing molarity (0.01–0.3 m) phosphate gradient and the elution pattern was obtained by spectrophotometric (280 nm) analysis of fractions. In preparative separations individual fractions were also analyzed by immunoelectrophoresis to determine the content of IgG immunoglobulins, transferrin and albumin. The results demonstrate a distinctly different chromatographic pattern from that of human serum. The size of the first eluting peak and the position of subsequent peaks of canine serum differ from human serum chromatograms. Fraction analyses demonstrate that this difference is due in part to the content of the various peaks and indicates a difference in electrophoretic mobility of corresponding serum proteins. In addition, canine IgGa was separated free of other immunoglobulins by rechromatographing the first peak using this gradient system.  相似文献   
372.
Three-dimensional (3D) printing, also called rapid prototyping or additive manufacturing, transforms digital images into 3D printed objects, typically by layering consecutive thin films of material. This technology has become increasingly accessible to the public, prompting applications in veterinary surgery. Three-dimensional prints provide direct visualization of complex 3D structures and also haptic feedback relevant to surgery. The main objective of this review is to report current applications of 3D printing in small-animal surgery, including surgical education, preoperative planning, and treatment of tissue defects. The reported uses of 3D prints, their proposed advantages, and current limitations are discussed considering published evidence. Aspects of the manufacturing process specific to each application are described, along with current practices in veterinary surgery.  相似文献   
373.
Two new coumarins, 7-methoxy-5-prenylcoumarin (isocedrelopsin) (1) and 3',4'-dihydrobraylin (2), were isolated from the trunk bark of Cedrelopsis grevei, along with five known coumarins, microfolicoumarin (6,7-dimethoxy-5-prenylcoumarin, (3), obliquin (4), 8-methoxyobliquin (5), aesculetin (6), cedrelopsin (7) and scoparone (8).  相似文献   
374.
The current paper analyses the potential for prescribed burning techniques for mitigating carbon dioxide (CO2) emissions from forest fires and attempts to show quantitatively that it can be a means of achieving a net reduction of carbon emissions in the context of the Kyoto Protocol. The limited number of available studies suggests that significant reductions in CO2 emissions can be obtained and that prescribed burning can be a viable option for mitigating emissions in fire-prone countries. The present analysis shows that the potential reduction attained by prescribed burning as a percentage of the reduction in emissions required by the Kyoto Protocol varies from country to country. Out of the 33 European countries investigated, only in one the requirements of the Kyoto Protocol could potentially be achieved by applying prescribed burning, while three other nations showed a potential net CO2 emissions reduction of about 4–8% of the Kyoto requirements and the majority showed a reduction of less than 2%. This implies that prescribed burning can only make a significant contribution in those countries with high wildland fire occurrence. Over a 5-year period the emissions from wildfires in the European region were estimated to be approximately 11 million tonnes of CO2 per year, while with prescribed burning application this was estimated to be 6 million tonnes, a potential reduction of almost 50%. This means that for countries in the Mediterranean region it may be worthwhile to account for the reduction in emissions obtained when such techniques are applied.  相似文献   
375.
This study presents data on the biomass and net aerial primaryproductivity (NAPP) of two contrasting East Anglian salt marshes.One site was at Tollesbury, Essex where the marshes are of theestuarine type and are subject to marsh degradation and erosionwhile the other site was 130 km to the north at Stiffkey, Norfolkwhere the barrier-type marshes are still actively developing withno signs of erosion. The NAPP was determined by the method ofSmalley with quadrats being harvested monthly with replacement.At the lowest levels at Tollesbury there was Pioneer Marshwhich was dominated by a mixture of Salicornia spp. and Astertripolium. At higher levels at Tollesbury there was LowerMarsh which was dominated by a mixture of Atriplex portulacoides andPuccinellia maritima. Over the four years of the studyPuccinellia became the dominant species following a markeddecrease in the extent and vigour of Atriplex. At Stiffkey theMiddle Marsh was at a much higher level and the vegetation waspredominantly a short dense sward with Atriplex portulacoides,Puccinellia maritima and Limonium vulgare together with smallerquantities of Armeria maritima and Plantago maritima. The meanNAPPs over three years of the Pioneer and Lower Marsh atTollesbury (467 & 519 g m-2 yr-1respectively) were similar butin 1993 the NAPPs recorded at Tollesbury were higher than thoserecorded at Stiffkey (625 & 583 compared with 458 g m-2yr-1).Smalleys method is difficult to apply to communities wherespecies dominance is variable, especially when dominance isshared between species with markedly different growth patterns.The results for NAPP obtained from the salt marshes at Tollesburyand Stiffkey are discussed in relation to results obtained byother workers from comparable areas in England and theNetherlands. Attention is also drawn to the possibly largerbelow-ground component of production that is frequentlyoverlooked. The importance of salt marshes in relation to othercoastal communities lies in the export of a proportion of theorganic matter produced and this mainly depends on theabove-ground production.  相似文献   
376.
377.
Isolated fractures of the proximal tubercle of the talus and the medial trochlear ridge of the talus have been reported in the equine literature. A comminuted, intra-articular fracture of the plantar medial trochlear ridge and proximal tubercle of the talus has not been previously reported. The current case report describes this unique comminuted fracture in a 6-week-old Thoroughbred foal with acute onset lameness. The diagnosis was achieved by a combination of radiography, ultrasonography and computed tomography (CT) followed by CT arthrography. Surgical removal of the fracture fragments was recommended; the intra-articular fracture fragments were removed under arthroscopic visualisation of the plantar pouch of the tarsocrural joint; due to ligamentous attachments and partial extra-articular nature, the fracture fragment of the proximal tubercle of the talus was removed via an arthrotomy extension of the medial arthroscopy portal. On follow-up examination 12 months post-operatively, the yearling showed no clinical evidence of lameness or radiographic evidence of secondary degenerative joint disease.  相似文献   
378.
The prevalence of deafness is high in cat populations in which the dominant white gene is segregating. The objective of this study was to investigate whether there is a gene that is responsible for deafness as well as for blue eyes and to establish a plausible mode of inheritance. For this purpose, data from an experimental colony with deaf cats were analyzed. The hearing status was determined by acoustically evoked brain stem responses (BAER). Complex segregation analyses were conducted to find out the most probable mode of inheritance using maximum likelihood procedures. The prevalence of deafness and partial hearing in the experimental colony was 67% and 29%, respectively. The results of the bivariate segregation analysis support the hypothesis of a pleiotropic major gene segregating for deafness and blue iris colour. The high heritability coefficients for both traits, 0.55 and 0.75 respectively, indicate that beside the major gene there is an important influence of polygenic effects.  相似文献   
379.
380.
Tropical Animal Health and Production - The objective of this study was to compare the use of an external marker titanium dioxide (TiO2) as an alternative to chromic oxide (Cr2O3) in dairy cows....  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