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   289篇
  免费   19篇
  国内免费   8篇
林业   18篇
农学   36篇
  62篇
综合类   44篇
农作物   52篇
水产渔业   5篇
畜牧兽医   74篇
园艺   3篇
植物保护   22篇
  2024年   3篇
  2023年   5篇
  2022年   6篇
  2021年   8篇
  2020年   12篇
  2019年   12篇
  2018年   5篇
  2017年   12篇
  2016年   13篇
  2015年   7篇
  2014年   8篇
  2013年   25篇
  2012年   18篇
  2011年   12篇
  2010年   13篇
  2009年   14篇
  2008年   15篇
  2007年   12篇
  2006年   11篇
  2005年   8篇
  2004年   7篇
  2003年   10篇
  2002年   8篇
  2001年   9篇
  2000年   7篇
  1999年   5篇
  1998年   7篇
  1997年   6篇
  1996年   7篇
  1995年   8篇
  1994年   1篇
  1993年   2篇
  1992年   4篇
  1990年   2篇
  1989年   1篇
  1988年   5篇
  1986年   4篇
  1985年   1篇
  1983年   3篇
排序方式: 共有316条查询结果,搜索用时 15 毫秒
11.
An experiment was conducted to evaluate the effects of different proportions of ‘Au Grazer’ sericea lespedeza [SL, Lespedeza cuneata (Dum. Cours.) G. Don], a legume rich in condensed tannins (CT), on nutrient intake and digestibility, and to estimate methane (CH4) emissions and 13C isotopic composition (δ13CCH4) from beef steers consuming a forage-based diet. Twenty-five Angus-crossbred steers were distributed in a randomized complete block design (344 ± 48 kg initial BW), and randomly assigned to one of five treatments: 0SL, 25SL, 50SL, 75SL, and 100SL, diets containing 0%, 25%, 50%, 75%, and 100% of SL hay, respectively, mixed with ‘Tifton-85’ bermudagrass hay (Cynodon spp.). The study was carried out for two experimental periods of 21-d each. The statistical model included the fixed effect of treatment and random effects of block, experimental period, and their interaction. Apparent total tract digestibility of crude protein, neutral detergent fiber, and acid detergent fiber was linearly decreased (P < 0.001) by the inclusion of SL. No effects were observed for total CH4 emissions per day, nor for CH4 relative to organic matter intake or digestible organic matter with the inclusion of SL. However, emission of CH4 in relation to intake of CT was affected by treatment (P < 0.001). A linear (P < 0.001) decrease and a quadratic effect (P < 0.001) were observed for δ13C of diets and gas, respectively, in which diets and enteric CH4 with greater inclusion of SL were more depleted in 13C. Moreover, the difference in δ13C between diets and gas (Δδ13C) had a linear decrease (P = 0.001) with the inclusion of SL. The model developed to predict the C3 proportions in the enteric CH4 fitted to predicted values (P < 0.0001). Therefore, greater proportions of SL resulted in lesser CH4 emission when CT intake was considered and the isotopic composition from enteric CH4 was able to predict the contribution of SL in the emissions.  相似文献   
12.
豆科植物通过与土壤中的根瘤菌共生发育形成根瘤,在根瘤中根瘤菌可以将空气中氮气转化成植物可以直接利用的铵态氮.共生过程中为了平衡氮素的摄取和能量的损耗,豆科植物形成了地上与地下信号交互的结瘤自调控机制(Auto-regulation of nodulation,AON),进而调节结瘤的数量.本文综述了AON分子调控机制近...  相似文献   
13.
通过监测传统胶园与全周期种植模式胶园土壤的养分差异,探讨全周期种植方式对胶园土壤养分的影响。结果表明,传统胶园内离树越近的位点,土壤养分含量和微生物量碳越低;除速效磷外,全周期胶园内离树越近的位点,土壤养分含量和微生物量碳越高。总体而言,全周期胶园土壤全氮、无机氮和微生物量碳低于传统胶园,但均没有达到显著差异,而其土壤有机质、速效磷和速效钾含量高于传统胶园,其中速效磷含量达显著差异(P<0.05)。与传统胶园相比,全周期种植模式主要影响土壤养分和微生物量碳的分布特征,其中土壤速效磷和速效钾含量亦相对较高,其他指标变化较小。  相似文献   
14.
以间作胶园的土壤为材料,以单作胶园土壤为对照,采用土壤常规分析方法分别测定其中的主要营养成分。结果表明,间作的9种豆科作物均不同程度的降低了胶园土壤的有机质、全氮(除间作凉薯和黎豆的土壤全氮含量略高于不间作土壤外)、全磷、速效磷含量及pH值,不同程度的增加了铵态氮、硝态氮、全钾及速效钾含量。说明成龄胶园间作豆科作物能改善土壤的硝态氮、铵态氮、全钾及速效钾含量,短时期内提高了土壤的供氮、供钾能力,但降低了土壤磷含量和土壤磷的供应能力。由此可见,在成龄胶园内进行间作,必须加强作物施肥,以实现土壤养分的收支平衡,维护土壤功能、保护土壤质量。  相似文献   
15.
Apparent digestibilities (D) of energy and proximate nutrients were determined in rainbow trout, Oncorhynchus mykiss (Walbaum), by stripping faeces and using Cr2O3 as a marker. When wheat gluten + L-lysine-HCl (WG-lys) as sole source of dietary N were increased stepwise from 324 to 941 g·kg?1, replacing 210 g·Kg?1 fish oil (FO) and 407 g·kg?1 gelatinized corn starch (GCS), D of crude protein rose from 96 to 99% and that of FO was always above 96%. D of GCS was 70% at inclusions up to 210 g·kg?1, but only 41 at 407 g·kg?1. Three by-products of poultry slaughtering and three legume seeds replaced WG at levels of 250 and 500 g·kg?1 in a basal diet of WG-lys, minerals and vitamins. Soy beans had been pressure cooked at one of two intensities, and field beans and fields peas were either untreated or had been autoclaved. D of energy and crude protein was hardly affected by dietary proportion in poultry blood mean (84 and 85%), poultry offal meal (80 and 81%) and incompletely pressure cooked soy beans (82 and 90%); increasing dietary proportions from 250 to 500 g·kg?1 reduced the respective values of feather meal (88–81 and 86–83%), raw (43–32 and 76–70%) and autoclaved field beans (67–57 and 89–86%), as well as raw (47–39 and 86–83%) and autoclaved field peas (65–40 and 91–86%). At the higher proportion, D of energy of completely pressure cooked soy beans was reduced from 91 to 86%, but that of crude protein was constant at 94%.  相似文献   
16.
鲁北滨海地区引种豆科牧草的灰色关联度分析   总被引:2,自引:0,他引:2  
试验在鲁北滨海地区对经一般观察后初步入选的14种豆科牧草进行了观察,并采用灰色关联度分析法以干草产量、鲜草产量、繁殖系数、折干率、叶量率、生长速度为主要指标进行综合评价。结果表明:综合性状最好的豆科牧草是草木樨属牧草,其中白花草木樨尤为突出;其次为沙打旺和美国苜蓿,也是适于鲁北滨海地区种植的豆科牧草。  相似文献   
17.
Summary An electrophoretic procedure was developed for storage proteins which can discriminate cultivars of forage legumes, Centrosema macrocarpum, C. pubescens and C. sp.n. Proteins extracted from cotyledons were separated in 10% polyacrylamide gel containing 10% sucrose. Electrophoretic patterns are presented to illustrate the results that can be obtained with the procedure described. Cultivars of all three species were distinguishable based upon the variation in their acid soluble seed proteins.Joint publiccation of the Department of Food Science, University of Manitoba (No 101) and Centro Internacional de Agricultura Tropical-CIAT.  相似文献   
18.
Pea would benefit from the plasticity and adaptability of its cross-incompatible relatives Pisum fulvum and Lathyrus sativus L., and we have tested reciprocal sexual crossings by manually cross-pollinating plants of genotypes of these three species. Studies of in situ germination of pollen grains on stigmata showed that pollen tubes were generally unable to germinate or could not reach the ovary. A few putative hybrid pods were nevertheless harvested, with one grain per pod germinated in vitro, then micropropagated for flow cytometry, isoenzyme, molecular (ribosomal ITS PCR-RFLP) and genomic in situ hybridization (GISH) studies. One such grain was recovered from an inter-generic cross of P. sativum x L. sativus and four from an inter-specific P. sativum x P. fulvumcross. A strong cross-incompatibility was shown between pea and grass pea, where the putative hybrid turned out to be pea. Conversely, with the interspecific, P. sativum x P. fulvum cross, flow cytometry and isoenzymes with leaf tissues strongly suggested hybridity, while molecular approaches and GISH confirmed the production of inter-specific hybrids, and without the need for a wild type P. sativum accession as a bridging cross.  相似文献   
19.
Summary An attempt has been made to estimate quantitatively the amount of N fixed by legume and transferred to the cereal in association in intercropping systems of wheat (Triticum aestivum L.) — gram (Cicer arietinum L.) and maize (Zea mays L.) —cowpea (Vigna unguiculate L.) by labelling soil and fertilizer nitrogen with 15N. The intercropped legumes have been found to fix significantly higher amounts of N as compared with legumes in sole cropping if the intercropped cereal-legume received the same dose of fertilizer N as the sole cereal crop. But when half of the dose of the fertilizer N applied to sole cereal crop was received by intercropped plants, the amount of N fixed by legumes in association with cereals was significantly less than that fixed by sole legumes. Under field conditions 28% of the total N uptake by maize (21.2 kg N ha–1) was of atmospheric origin and was obtained by transfer of fixed N by cowpea grown in association with maize. Under greenhouse conditions gram and summer and monsoon season cowpea have been found to contribute 14%–20%, 16% and 32% of the total N uptake by associated wheat and summer and monsoon maize crops, respectively. Inoculation of cowpea seeds with Rhizobium increased both the amount of N fixed by cowpea and transferred to maize in intercropping system.  相似文献   
20.
小麦与豆科绿肥轮作和合理施用氮肥对黄土高原旱地缺素地区具有特别重要意义.本试验以夏休闲为对照,比较了小麦与绿豆、大豆、秋豆轮作和氮肥水平(0、108、135、162kg/hm2)对小麦产量和籽粒养分的影响.结果表明,小麦与豆科绿肥轮作,在黄土高原早地受水分限制影响,小麦产量降低9.7%~26.6%;同时,与休闲处理相较...  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