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   668篇
  免费   64篇
林业   130篇
农学   26篇
基础科学   2篇
  182篇
综合类   16篇
农作物   52篇
水产渔业   73篇
畜牧兽医   150篇
园艺   23篇
植物保护   78篇
  2023年   8篇
  2022年   9篇
  2021年   17篇
  2020年   18篇
  2019年   25篇
  2018年   50篇
  2017年   59篇
  2016年   65篇
  2015年   24篇
  2014年   41篇
  2013年   49篇
  2012年   43篇
  2011年   57篇
  2010年   38篇
  2009年   33篇
  2008年   22篇
  2007年   26篇
  2006年   16篇
  2005年   8篇
  2004年   7篇
  2003年   7篇
  2002年   7篇
  2001年   6篇
  2000年   8篇
  1999年   6篇
  1998年   8篇
  1997年   3篇
  1996年   4篇
  1995年   3篇
  1994年   2篇
  1992年   2篇
  1991年   2篇
  1989年   2篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1985年   3篇
  1982年   2篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1973年   2篇
  1970年   2篇
  1969年   2篇
  1968年   3篇
  1965年   2篇
  1958年   2篇
  1957年   2篇
排序方式: 共有732条查询结果,搜索用时 15 毫秒
641.
The microbial diversity of culturable intestinal microflora of wild freshwater salmonid fishes salmon Salmo salar and sea trout Salmo trutta trutta juveniles (0+ years old) from the same environmental conditions were investigated by means of molecular identification techniques and analysis of diet. Significant differences in the intestinal microbial diversity were observed in different fish species. The predominant group in the intestinal tract of the salmon comprised representatives of the Enterobacteriaceae family (23%), Plesiomonas (19.2%) and Carnobacterium (15.3%). Predominant microbiota in sea trout intestinal tract were Enterobacteriaceae (52%), Aeromonas (22%) and Pseudomonas (14%). The results show that Enterobacteriaceae were predominant in the intestinal tract of the salmon and the sea trout juveniles raised on diets of different compositions. However, molecular identification of the intestinal microbiota at the species or genus level revealed differences in these fish species. Bacteria in the hindgut of salmon included Pragia and Serratia. However, bacteria in the gut contents of sea trout from the Enterobacteriaceae family were Buttiauxella, Enterobacter, Moellerella, Pantoea, Rahnella and Tiedjeia arctica. A novel phylotype of T. arctica is harbored in the intestinal tract of wild salmon, and may correspond to a previously undescribed species.  相似文献   
642.
  • 1. Crucian carp Carassius carassius, which is native to south‐east England, has received little previous study in Britain but is threatened by introductions of goldfish Carassius auratus through hybridization and by frequent mis‐identification of brown goldfish as crucian carp. The present study provides the first data on back‐calculated growth, morphology and age‐at‐maturity of crucian carp in Britain.
  • 2. The youngest mature crucian were female (age 2+), the smallest mature crucian were male (age 3+), with almost all fish mature at age 3+. Sex dimorphism in back‐calculated standard length at age was not observed except at age 2+ (juveniles longest). Shifts in morphological characters often associated with maturation (dorsal and ventral fin length, dorsal and anal fin depth, pre‐dorsal distance, body width) were observed between ages 4+ and 7+, which (in contrast to the relatively abrupt shift in maturity) suggests that age and size at maturation may not reflect the size and age of active (i.e. real) spawning.
  • 3. Back‐calculated standard lengths at age for crucian carp were intermediate relative to other European populations, indicating that environmental conditions in England appear to be well suited to the species despite being at the westernmost extent of the species' native European range. The management of ornamental ponds specifically for crucian carp is discussed.
© Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.  相似文献   
643.
A simple and accurate flow-through system was developed for toxicity evaluation of biodegradable substances, wastewaters, and surface waters. The chronic toxicity of phenol to the daphnid Daphnia magna was studied during a 21 d exposure period, first using a semi-static and later a flow-through test. The flow- through system was advantageous especially when lower concentrations of phenol were examined. Its use provided a constant concentration of phenol in all tested samples. Exposure to phenol showed a similar influence on both survival and reproduction of daphnids; the IC25 value was 3.18 mg L-1.  相似文献   
644.
In Europe, during the 1960s, mainly two-rowed spring barley was used for malting. Traditionally, spring malting barley was produced in regions with moderate temperatures and adequate rainfall throughout the growing season. Winter malting barley, on the other hand, was mostly grown in the milder arid and semiarid parts of Europe. Due to global climatic changes and its higher yield, winter malting barley is now increasing in acreage in the traditional spring barley regions. Our study included a comparative analysis of several grain and malt characters of the winter and spring malting barley grown under the agroecological conditions of the Vojvodina Province, Yugoslavia. One thousand grain weight was shown to be approximately the same for both growth habits, whereas winter malting barley proved to have a higher hectoliter mass than the spring one. In those years that were less favorable for spring barley production, winter malting barley had better quality characters, namely a higher fine extract content, a better malt modification, and a lower malt protein content. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
645.
The aim of small-site experiments carried out in the area of the foothills of the ?umava Mts. was to determine the etiological agent of the disease of meadow peavine (Lathyrus pratensis L.). The experimental locality (Kaplice-Chuchelec) was situated in an altitude of 655?m a.s.l. The investigation was accomplished in the years 2004–2005. During the vegetation period we observed whitish to grey-white soft cover of mycelium on the leaves of meadow peavine. These characteristic symptoms of powdery mildew (Erysiphe trifolii Grev.) were found on the plants in the observed area at the end of summer and in autumn. In the area of interest with permanent grassland we evaluated the following variants: first M – mulched stands (mulched once), second L – fallow stands, third K – mown stands (mowing once to three times), and fourth P – pasture stands (grazed by cattle twice to four times). The observed stands were managed in different ways from 2000, and in relation to the ways and intensity of management we observed the changes and coverage of creeping legumes including Lathyrus pratensis. Phytopathological analysis of plants with the symptoms of Erysiphe fungi attack was accomplished in all variants and repetitions during the whole vegetation period. The observation of particular variants was carried out in four repetitions, the size of the sites being 30?m2 (4?×?30?m2), and we evaluated the total number of Lathyrus pratensis plants as well as the number of the plants attacked by powdery mildew. Powdery mildew occurrence on Lathyrus pratensis at different management methods of grass stands was statistically processed (in STATISTICA program). The three-year investigation of Lathyrus pratensis L. yielded statistical evidence that the most significant growth of fungal disease Erysiphe trifolii Grev. was recorded in fallow stands. On the other hand, the least occurrence of the disease was found in the pasture stands, which were grazed by the cattle.  相似文献   
646.
Journal of Plant Diseases and Protection - The aim of this work was to explore the species composition and abundance of mites and insects in grain residues in an empty grain store. Sampling was...  相似文献   
647.
Peniciadametizine A (1); a new dithiodiketopiperazine derivative possessing a unique spiro[furan-2,7''-pyrazino[1,2-b][1,2]oxazine] skeleton, together with a highly oxygenated new analogue, peniciadametizine B (2); as well as two known compounds, brasiliamide A (3); and viridicatumtoxin (4), were isolated and identified from Penicillium adametzioides AS-53, a fungus obtained from an unidentified marine sponge. The unambiguous assignment of the relative and absolute configuration for the spiro center C-2 of compound 1 was solved by the combination of NMR and ECD measurements with Density-Functional Theory (DFT) conformational analysis and Time-Dependent Density-Functional Theory-Electronic Circular Dichroism (TDDFT-ECD) calculations. The spiro[furan-2,7''-pyrazino[1,2-b][1,2]oxazine] skeleton of 1 has not been reported yet among natural products and the biosynthetic pathway for 1 and 2 was discussed. Compounds 1 and 2 showed inhibitory activity against the pathogenic fungus Alternaria brassicae.  相似文献   
648.
Eight aphid species were determined as new records for Serbia as a result of the evaluation of the specimens caught by yellow water traps used for monitoring vector activities in seed potato crops during the 4 years 2007–2010. The invasive aphid species Macrosiphum albifrons Essig 1911; and the new species Acyrthosiphon cyparissiae (Koch 1855), Ctenocallis setosus (Kaltenbach 1846), Myzodium modestum (Hottes 1926), Myzocallis castanicola Baker 1917, Myzocallis occidentalis Remaudiè et Nieto Nafria 1974, Tinocallis platani (Kaltenbach 1843) and Wahlgreniella ossiannilssoni Hille Ris Lambers 1949. M. modestum is very difficult to detect, as it lives hidden in moss. All species are presented with characteristic morphological information of alatae and line drawings.  相似文献   
649.
Slovenia has no history of health problems related to proliferative kidney disease (PKD) either in farmed or in wild fish. However, due to the past molecular evidence for the presence of Tetracapsuloides bryosalmonae DNA in tissues of some fish from open waters, a survey was conducted on wild salmonids that were primarily sampled for other purposes. In winter 2010–2011, specimens from a total of 244 rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., from 30 bodies of fresh water were examined for T. bryosalmonae using a PCR method. The sampled fish showed no clinical signs or gross pathological lesions characteristic of PKD. Nineteen (7.8%) fish from seven (23.3%) fresh waters were positive for T. bryosalmonae. The identity of PCR amplicons was confirmed by sequencing. With one exception, all the positive fish were found in waters from the regions where the average yearly temperatures and the environmental pollution are higher. This preliminary countrywide survey provided the first insight into the situation regarding T. bryosalmonae infection of wild salmonids in Slovenia.  相似文献   
650.
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