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   1524篇
  免费   104篇
  国内免费   4篇
林业   64篇
农学   27篇
基础科学   16篇
  243篇
综合类   261篇
农作物   48篇
水产渔业   82篇
畜牧兽医   714篇
园艺   40篇
植物保护   137篇
  2023年   7篇
  2022年   8篇
  2021年   17篇
  2020年   32篇
  2019年   26篇
  2018年   22篇
  2017年   25篇
  2016年   29篇
  2015年   30篇
  2014年   29篇
  2013年   82篇
  2012年   82篇
  2011年   105篇
  2010年   73篇
  2009年   46篇
  2008年   106篇
  2007年   110篇
  2006年   100篇
  2005年   97篇
  2004年   86篇
  2003年   81篇
  2002年   105篇
  2001年   20篇
  2000年   21篇
  1999年   15篇
  1998年   30篇
  1997年   18篇
  1996年   26篇
  1995年   7篇
  1994年   14篇
  1993年   14篇
  1992年   13篇
  1991年   9篇
  1990年   10篇
  1989年   17篇
  1988年   4篇
  1987年   12篇
  1986年   7篇
  1985年   4篇
  1984年   9篇
  1983年   12篇
  1980年   4篇
  1979年   4篇
  1978年   7篇
  1977年   8篇
  1976年   3篇
  1974年   5篇
  1971年   3篇
  1968年   3篇
  1962年   3篇
排序方式: 共有1632条查询结果,搜索用时 15 毫秒
21.

BACKGROUND

Monitoring is an integral component of integrated pest management (IPM) programmes used to inform crop management decisions. Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), continues to cause economically significant losses in horticultural crops due to an inability to reliably detect the presence of this species before crop damage occurs. To improve vine weevil monitoring we investigated the behavioural responses of adult vine weevils to visual (monitoring tool shade/colour, height and diameter as well as the effect of monitoring tool and plant density) and olfactory (host plant and conspecifics) cues under glasshouse conditions.

RESULTS

Monitoring tool shade, height and diameter all influenced monitoring tool efficacy, with individuals exhibiting a preference for black, tall and wide monitoring tools. The total number of individuals recorded in monitoring tools increased with monitoring tool density. By contrast, plant density did not influence the number of individuals recorded in monitoring tools. Yew-baited monitoring tools retained a larger number of individuals compared to unbaited ones. Similarly, more vine weevils were recorded in monitoring tools baited with yew and conspecifics than in unbaited monitoring tools or those baited with only yew. Baiting monitoring tools with conspecifics alone did not enhance the number of vine weevils recorded in monitoring tools.

CONCLUSIONS

Our study confirms that visual and olfactory cues influence vine weevil behaviour. This provides information on key factors that influence vine weevil monitoring tool efficacy and can be used to inform the development of a new monitoring tool for this pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
22.
Evaluation of brain disease in veterinary patients uses a wide variety of MRI sequences. A shortened protocol that maintains consistency of interpretation would reduce radiologist reporting time, patient anesthetic time, and client cost. The aims of this retrospective, methods comparison, observer agreement study were to evaluate whether abbreviated MRI protocols alter differential diagnoses and recommendations compared to our institution's standard protocol; evaluate interobserver agreement on standard brain MRIs; and assess whether differential diagnoses change after postcontrast images. Normal and pathologic canine and feline brain MRIs were retrieved from hospital archives. Three protocols were created from each: a 5-sequence noncontrast enhanced Fast Brain Protocol 1 (FBP1); a 6-sequence contrast-enhanced Fast Brain Protocol 2 (FBP2); and an 11-sequence standard brain protocol (SBP). Three blinded veterinary radiologists interpreted FBP images for 98 cases (1 reader/case) and SBP images for 20 cases (3 readers/case). A fourth observer compared these interpretations to the original MRI reports (OMR). Overall agreement between FBPs and OMR was good (k = 0.75) and comparable to interobserver agreement for multiple reviews of SBP cases. Postcontrast images substantially altered conclusions in 17/97 cases (17.5%), as well as improved interobserver agreement compared to noncontrast studies. The conclusions reached with shortened brain protocols were comparable to those of a full brain study. The findings supported the use of a 6-sequence brain MRI protocol (sagittal T2-weighted [T2w] TSE; transverse T2w turbo spin echo fluid-attenuated inversion recovery, T2*-weighted gradient recalled echo, T1-weighted spin echo, and diffusion weighted imaging/apparent diffusion coefficient; and postcontrast transverse T1-weighted spin echo) for dogs and cats with suspected intracranial disease.  相似文献   
23.
The centre of origin of the globally distributed wheat pathogen Parastagonospora nodorum has remained uncertain because only a small number of isolates from the Fertile Crescent were included in earlier population genetic and phylogeographic studies. We isolated and genetically analysed 193 P. nodorum strains from three naturally infected wheat fields distributed across Iran using 11 neutral microsatellite loci. Compared to previous studies that included populations from North America, Europe, Africa, Australia, and China, the populations from Iran had the highest genetic diversity globally and also exhibited greater population structure over smaller spatial scales, patterns typically associated with the centre of origin of a species. Genes encoding the necrotrophic effectors SnToxA, SnTox1, and SnTox3 were found at a high frequency in the Iranian population. By sequencing 96 randomly chosen Iranian strains, we detected new alleles for all three effector genes. Analysis of allele diversity showed that all three effector genes had higher diversity in Iran than in any population included in previous studies, with Iran acting as a hub for the effector diversity that was found in other global populations. Taken together, these findings support the hypothesis that P. nodorum originated either within or nearby the Fertile Crescent with a genome that already encoded all three necrotrophic effectors during its emergence as a pathogen on wheat. Our findings also suggest that P. nodorum was the original source of the ToxA genes discovered in the wheat pathogens Phaeosphaeria avenaria f. sp. tritici 1, Pyrenophora tritici-repentis, and Bipolaris sorokiniana.  相似文献   
24.
谈到粪便管理,人们总是较多地注意氮和磷。然而,铜和锌也可造成环境污染。  相似文献   
25.
We have assessed the fatty acid profiles of the livers from seven shark species (Carcharias taurus (raggedtooth/grey nurse), Carcharhinus limbatus (blacktip), Carcharhinus obscurus (dusky), Carcharhinus leucas (Zambezi/bull), Sphyrna lewini (scalloped hammerhead), Carcharhinus brevipinna (spinner), and Galeocerdo cuvieri (tiger)) found off the east coast of South Africa. While there was generally little variation between the species, Carcharias taurus showed fatty acid profiles that would be most favourable in human nutrition, in that it showed both low saturated (SFA) (37.1%) and high polyunsaturated fatty acid (PUFA) (26.6%) levels. However, all species showed profiles rich in PUFA, thus utilising the liver oil from sharks caught as part of the bycatch when fishing for teleost species would avoid unnecessary wastage of a potentially valuable resource. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
26.
Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panulirus cygnus, were held at ambient temperatures (15.6 °C to 23.1 °C; mean 19.0 ± 0.07 °C) or at 23 °C, and fed the same ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, to determine whether elevated temperatures and multiple feeds per night would stimulate growth through increased metabolism and feed utilisation without significant negative impacts on survival. Survival of post-pueruli (mean 63%) did not differ between ambient and 23 °C. Survival of year 1 and 2 juveniles was higher at ambient temperatures (p < 0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 °C: 57% and 74%, respectively). Feeding frequency did not affect survival of post-pueruli and year 2 juveniles (mean 63%, 81% respectively), but survival was 9% higher for year 1 juveniles fed three times per night (58% versus 67%; p < 0.01). All lobsters grew faster at 23 °C than at ambient temperatures (p < 0.05), with the growth of post-pueruli almost doubled at 23 °C (weight gain at 23 °C versus ambient: post-pueruli, 18 438 % versus 9 915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influence the growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feed frequency on post-pueruli where weight and carapace length were significantly higher at ambient temperatures when post-pueruli were fed three times a day, whereas at 23 °C weight and carapace length were significantly greater when fed once per day (p < 0.05). Feed intake (g pellet dry matter lobster− 1 day− 1) of pellet was higher at 23 °C for all lobsters (p < 0.05), but was the same between lobsters fed 3 times per night versus once per night. This study has shown that increasing temperatures to 23 °C significantly improved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growth rates exhibited by year 1 and 2 juveniles at 23 °C may potentially offset their lower survival by significantly reducing culture period. There is no benefit of feeding P. cygnus multiple times at night in terms of growth and survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 °C during the entire growout period, with due care taken to minimise mortalities through adequate provision of food and shelter. Feeding P. cygnus once daily to excess just prior to dusk to co-incide with nocturnal feeding behaviour is recommended.  相似文献   
27.
Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is 13C, and especially 15N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil organic matter. We developed a new approach to determine the natural abundance C and N isotope composition of the microbial biomass across a broad range of soil types, vegetation, and climates. We found consistently that the soil microbial biomass was 15N-enriched relative to the total (3.2 ‰) and extractable N pools (3.7 ‰), and 13C-enriched relative to the extractable C pool (2.5 ‰). The microbial biomass was also 13C-enriched relative to total C for soils that exhibited a C3-plant signature (1.6 ‰), but 13C-depleted for soils with a C4 signature (−1.1 ‰). The latter was probably associated with an increase of annual C3 forbs in C4 grasslands after an extreme drought. These findings are in agreement with the proposed contribution of microbial products to the stabilized soil organic matter and may help explain the shift in isotope composition during soil organic matter formation.  相似文献   
28.
A water soluble storage albumin from Inca peanut (IPA) accounted for approximately 25% (w/w) of defatted seed flour weight, representing 31% of the total seed protein. IPA is a 3S storage protein composed of two glycosylated polypeptides, with estimated molecular weights (MW) of 32800 and 34800 Da, respectively. IPA has an estimated sugar content of 4.8% +/- 0.92% (n = 6). IPA is a basic protein (pI of approximately 9.4) and contains all of the essential amino acids in adequate amounts when compared to the FAO/WHO recommended pattern for a human adult. The tryptophan content of IPA is unusually high (44 mg/g of protein), whereas the phenylalanine content is low (9 mg/g of protein). IPA is a highly digestible protein in vitro.  相似文献   
29.
Satellite and research vessel observations of sea surface temperature during the southwest monsoon of 1979 show the development of large wedge-shaped areas of cold water along the Somali coast at both 5 degrees and 10 degrees N during June and July. The cold water associated with the large northern and southern Somali eddy systems could be traced several hundred kilometers offshore. By late August the cold wedge at 5 degrees N translated northeastward as far as 10 degrees N at speeds of 15 to 30 centimeters per second, indicating a coalescence of the systems.  相似文献   
30.
植物促生菌及其促生机理 (续)   总被引:10,自引:0,他引:10  
3 植物促生菌的促生长机理 3.1 产生嗜铁素 铁是生命的基本物质.不论是动、植物还是微生物,均需含铁蛋白来参与呼吸等一系列生理活动.尽管地球表面矿物含铁丰富,但土壤中能够直接为植物和微生物利用的铁却不多.土壤中铁主要以三价铁(Fe3+)状态存在,在pH值为7.4时其溶解度为10-18mol/L,此浓度下的铁一般无法满足土壤微生物繁衍和植物生长发育的需要.然而,某些细菌和植物分泌一种专门结合铁的小分子蛋白(siderophores)可从土壤中收集铁,这种物质被称之为嗜铁素.铁一旦与嗜铁素相结合则形成可溶性铁-嗜铁素复合体,并可通过植物和微生物细胞膜的特殊通道进入生物体内.氧化铁在体内还原后被释放并参与生物代谢活动.产生嗜铁素被认为是植物促生菌最主要的直接和间接促进植物生长的有效途径之一.植物促生菌产生的嗜铁素一般都具有高度的铁亲合性和专一性,含有各种能鳌合铁的结构基团(如邻二苯酚结构、羧基结构和乙二胺结构等)来摄取土壤中的铁,这种嗜铁素具有极强的吸收铁的能力,可在铁有效性极低时收集土壤中微量的移动性铁,从而使土壤中可用的铁降低至更为缺乏的程度.  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