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   326篇
  免费   14篇
林业   32篇
农学   17篇
  86篇
综合类   14篇
农作物   18篇
水产渔业   40篇
畜牧兽医   70篇
园艺   17篇
植物保护   46篇
  2024年   3篇
  2023年   3篇
  2022年   1篇
  2021年   7篇
  2020年   11篇
  2019年   10篇
  2018年   13篇
  2017年   15篇
  2016年   19篇
  2015年   11篇
  2014年   11篇
  2013年   21篇
  2012年   24篇
  2011年   26篇
  2010年   14篇
  2009年   12篇
  2008年   15篇
  2007年   17篇
  2006年   15篇
  2005年   15篇
  2004年   6篇
  2003年   9篇
  2002年   14篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1997年   5篇
  1996年   3篇
  1993年   3篇
  1992年   3篇
  1991年   2篇
  1990年   6篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1974年   3篇
排序方式: 共有340条查询结果,搜索用时 30 毫秒
21.
With data from 33 nations, we illustrate the differences between cultures that are tight (have many strong norms and a low tolerance of deviant behavior) versus loose (have weak social norms and a high tolerance of deviant behavior). Tightness-looseness is part of a complex, loosely integrated multilevel system that comprises distal ecological and historical threats (e.g., high population density, resource scarcity, a history of territorial conflict, and disease and environmental threats), broad versus narrow socialization in societal institutions (e.g., autocracy, media regulations), the strength of everyday recurring situations, and micro-level psychological affordances (e.g., prevention self-guides, high regulatory strength, need for structure). This research advances knowledge that can foster cross-cultural understanding in a world of increasing global interdependence and has implications for modeling cultural change.  相似文献   
22.
Journal of Plant Diseases and Protection - The importance of herbal plants is evident in the prevalent use as flavoring ingredients in food. However, meeting the growing demand for organic grown...  相似文献   
23.
The effects of Hg, As, Pb, Cu, Cd, and Cr (1, 2, and 5 mg L?1 each) on Azolla pinnata R. Br. were analyzed. The treatments (2 and 5 mg L?1) of the heavy metal pollutants decreased Hill activity, chlorophyll, protein and dry wt, and increased tissue permeability over control values. The effects were most pronounced with the treatment of 5 mg L?1. The harmful effects of the metals were, in general, found by the treatments in the order: Cd 〉 Hg 〉 Cu 〉 As 〉 Pb 〉 Cr. There was no significant change in these parameters at 1 mg L?1 of the metals over control. Thus Azolla pinnata shows tolerance to the heavy metals tested up to 1 mg L?1 each.  相似文献   
24.
The influence of Al3+ on the mineral content of mycorrhizal fungi was studied in vitro. Amanita muscaria (L. ex Fr.) Pers. ex Hooker whose growth is reduced and Lactarius piperatus (L. ex Fr.) S.F. Gray whose growth is stimulated by Al3+ where chosen for the experiments. 0, 0.1, 1, and 10mM A3+ were added as Al2(SO4)3 · 18H2O to modified M-40 medium. Al3+ drastically affected the mineral contents of the mycelia of both fungi: the Al, Ca, and Na contents increased while P, Mg, and K decreased with the increasing Al3+ concentrations in the media. On the other hand, some important differences between the two mycelia were detected. In the mycelia of Lacterius piperatus grown on the control media, there was about twice as much Ca content and a three times lower P content than in the Amanita muscaria mycelia. The Al3+ content in the mycelia of Lactarius piperatus grown on 10mM Al3+ was six times higher than in Amanita muscaria at the same concentration.  相似文献   
25.
Rhizoctonia solani is an important soil-borne pathogen causing diseases in numerous economically important crops. The pathogen R. solani can be responsible for relevant yield losses as well as on lettuce and potato. To develop a biocontrol strategy, two bacterial strains, Pseudomonas fluorescens L13–6-12 and Serratia plymuthica 3Re4–18 were evaluated against R. solani causing black scurf in potato and bottom rot in lettuce. The disease suppression effect of the two antagonists was tested as well as in a climate chamber and in the field during two vegetation periods. The results of the climate chamber experiments showed, that R. solani can significantly reduced the lettuce growth. The dry mass losses on lettuce and the disease severity on potato sprouts were significantly limited through bacterization. The antagonist L13–6-12 showed best disease suppression effect in climate chamber experiments on both crops. A significant lower disease severity was to observed in treatments with bacterial antagonists as well as on lettuce plants and harvested potato tubers during both vegetation periods. Also the dry mass losses on lettuce were clear reduced in treatments with bacterial antagonists, whereas only a partly limitation of yield losses on potato was to achieved. In summary, the results supported that the use of bacterial antagonists can be part of a control strategy against R. solani.  相似文献   
26.
The effect of thermal energy intensity (TEI) on the rate of nitrogen (N) accumulation by maize from a Hamerly clay loam soil (Aerie Calciaquoll) was examined with and without supplemental irrigation. Soil- and air-TEI expressed as cumulative growing degree days (GDD) was determined from hourly temperature measurements taken within each plot at soil depths of 0.05-, 0.15-, and 0.3-m and at a height of 1.2-m above ground surface. A daily mean TEI (GDD per day) was calculated for each growth period. Estimates of time coefficient(s), k, in uni- and diphasic tanh[k(time)] functions, plotted against mean TEI for the periods; 1) planting to emergence, 2) emergence to eighth leaf, 3) eighth leaf to time(s) of maximum N accumulation rate, (t0), 4) planting to t0, 5) emergence to t0, 6) first diphasic maximum accumulation rate (t01) to 50 % silking, and 7) silking to second diphasic maximum accumulation rate t02 showed several linear relationships. Uniphasic time coefficients were modelled as functions of air-TEI. The first diphasic time coefficient, k1 was modelled as a function of pre- and post-emergent soil-TEI. Attempts to model k2, the second time coefficient of the diphasic model were unsuccessful; however, this time coefficient was linearly related to TEI for the growth period ‘t01, to 50 % silking’ and curvilinearly related to k1.  相似文献   
27.
Hypogammaglobulinemia as a result of failure of transfer of passive immunity (FTPI) is an important risk factor for infectious disease in neonatal foals. The current gold standard for determining serum immunoglobulin concentrations is radial immunodiffusion (RID). The purpose of this study was to compare immunoglobulin concentrations measured by RID with those determined by an automated turbidimetric immunoassay (TIA), which has a much shorter turnaround time. Immunoglobulin concentrations were measured by both RID and TIA in serum collected from 84 neonatal foals. Sixty-seven foals had results within the linear range for both assays. Sensitivity and specificity of TIA for diagnosis of FTPI with IgG < or = 800 mg/dL were 0.81 (95% CI 0.70-0.88) and 0.86 (95% CI 0.76-0.93) and with IgG < or = 400 mg/dL were 0.63 (95% CI 0.35-0.86) and 0.92 (95% CI 0.87-0.95), respectively. A significant linear relationship was found between IgG concentrations determined by TIA and RID (TIA = 0.9511RID + 8.4354; R2 = .59, P < .0001). The coefficients of variation for between-run and within-run precision for the TIA were 2.5 and 3%, respectively. Storage of samples from 10 foals at -20 degrees C for 10-12 months resulted in a reduction in TIA-measured serum IgG concentration of -17.6% (SD = 3.7%), indicating that long-term storage of samples at -20 degrees C should be avoided. The results of this study indicate that measurement of serum IgG by TIA can be used to evaluate foals for FTPI.  相似文献   
28.
The aim of the study was to evaluate the influence of low dose (LOEL - lowest observed effect level) of zearalenone (200 microg/kg b.w.), applied per os for 7 days (short-term intoxication), on sexual behavior, concentration of the examined xenobiotic and its metabolite and selected estrogens in sexually immature gilts: ovariohysterectomised (group D1) and intact (group D2) animals. Clinical signs of oestrus (reddening, oedema and hyperaemia of the vulva and serorhoea from the reproductive tract--lack of standing reflex) were obserwed in group D1 on day 6 and in group D2 on day 4 of the experiment. Laboratory analyses of blood plasma were carried out determine the presence of zearalenone and alpha-zearalenole. They revealed an increase in the level of alpha-zearalenol before the oestrus, decrease in total amount of both examined substances on day when the oestrus appeared and increase in the level of both examined xenobiotics in the post oestrus period together with the higher share of zearalenone. Medium concentrations of estrone and estradiol within the borders of method determination in the majority of periods examined. Higher levels of estrone (32.0 pg/ml) were found on day 4, in the group D2 and estradiol (6.5 pg/ml) on day 6 in the D2 group. The presents study revealed that zearalenone applied per os at LOEL dose causes the incidence of apparent sexual readiness (without standing reflex) in sexually immature gilts with the somatically immature reproductive system.  相似文献   
29.
30.
We describe the morphological, biological, and molecular characteristics of Cryptosporidium pig genotype II and propose the species name Cryptosporidium scrofarum n. sp. to reflect its prevalence in adult pigs worldwide. Oocysts of C. scrofarum are morphologically indistinguishable from C. parvum, measuring 4.81–5.96 μm (mean = 5.16) × 4.23–5.29 μm (mean = 4.83) with a length to width ratio of 1.07 ± 0.06 (n = 400). Oocysts of C. scrofarum obtained from a naturally infected pig were infectious for 8-week-old pigs but not 4-week-old pigs. The prepatent period in 8-week-old Cryptosporidium-naive pigs was 4–6 days and the patent period was longer than 30 days. The infection intensity of C. scrofarum in pigs was generally low, in the range 250–4000 oocysts per gram of feces. Infected pigs showed no clinical signs of cryptosporidiosis and no pathology was detected. Cryptosporidium scrofarum was not infectious for adult SCID mice, adult BALB/c mice, Mongolian gerbils (Meriones unguiculatus), southern multimammate mice (Mastomys coucha), yellow-necked mice (Apodemus flavicollis), or guinea pigs (Cavia porcellus). Phylogenetic analyses based on small subunit rRNA, actin, and heat shock protein 70 gene sequences revealed that C. scrofarum is genetically distinct from all known Cryptosporidium species.  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