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   1114篇
  免费   32篇
  国内免费   105篇
林业   56篇
农学   110篇
基础科学   14篇
  113篇
综合类   476篇
农作物   134篇
水产渔业   41篇
畜牧兽医   237篇
园艺   55篇
植物保护   15篇
  2024年   7篇
  2023年   11篇
  2022年   49篇
  2021年   57篇
  2020年   36篇
  2019年   50篇
  2018年   32篇
  2017年   63篇
  2016年   73篇
  2015年   66篇
  2014年   83篇
  2013年   84篇
  2012年   91篇
  2011年   95篇
  2010年   66篇
  2009年   81篇
  2008年   55篇
  2007年   76篇
  2006年   48篇
  2005年   31篇
  2004年   23篇
  2003年   13篇
  2002年   12篇
  2001年   6篇
  2000年   5篇
  1999年   7篇
  1998年   7篇
  1997年   3篇
  1996年   3篇
  1995年   5篇
  1994年   4篇
  1993年   1篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1981年   1篇
排序方式: 共有1251条查询结果,搜索用时 15 毫秒
61.
超滤膜分离纯化花生壳中水溶性膳食纤维   总被引:1,自引:2,他引:1  
为探索花生壳中水溶性膳食纤维(SDF)的有效分离纯化方法和效果,选择适宜的膜组件,采用不同截留分子量的超滤膜以及优化膜分离过程的操作条件,对SDF提取液进行超滤分离,试验结果表明:选用PS-30聚砜膜,在压力为0.08MPa、料液比为1:75g/mL、温度为30℃时,分离纯化效果最为显著。其中,膜通量达到127.2L/(m2·h)、SDF的得率达到67.56%,非淀粉多糖(NSP)的质量分数由49.85%提高到92.36%,蛋白质量分数从5.53%降到0.92%。与传统的提取法比较,超滤膜分离纯化花生壳水溶性膳食纤维具有生产周期短,成本低,产品纯度高等优点。  相似文献   
62.
Aluminum (Al) is very toxic to many living organisms, including plants, animals and microorganisms. However, despite many studies on Al tolerance in plants, little has been reported concerning these mechanisms in microorganisms. In this study, a red yeast, which could tolerate Al 3+ concentrations as high as 200 mmol L-1 , was isolated from acidic soils, identified as Rhodotorula sp. and designated as RS1. As the medium compositions can greatly affect the responses of microorganisms to Al, two culture mediums, glucose medium (GM) and lysogeny broth medium containing soil extract (S-LBM), were used. During growth of RS1, the pH of medium decreased in GM but increased in S-LBM. These changes in the pH of the media were not induced by Al addition. No or little secretion of organic acids was observed in RS1 growth media. Importantly, the thickness of the cell walls and the ratio of cell wall to biomass of RS1 significantly increased in GM with high Al 3+ concentrations. In the presence of 100 mmol Al L-1 , 78.0% of the total Al of whole cells was present in the thickened cell walls. The Al in cell walls was mostly bound to OH, amide and CO groups of polysaccharides. These results suggest that thickening of the cell wall in response to the high Al 3+ concentrations may play an important role in the high tolerance of RS1 to Al and that pH increase of the medium and chelation of Al ions are not involved in Al tolerance of this organism.  相似文献   
63.
Abstract

An experiment was conducted using 720 one-day-old Arbor Acres broiler chickens to evaluate the effects of Astragalus membranaceus root powder (AMP), Astragalus polysaccharides (APS) on growth performance, carcass characteristics, and antioxidant enzymes, and metabolites of blood and liver in broiler chickens. The six dietary treatments included a control that was a corn–soybean meal basal diet; basal diet supplemented with 120 mg/kg antibiotic; 350 mg/kg APS; or 5000, 10,000, or 15,000 mg/kg diet of AMP. Supplementation of 10,000 mg/kg AMP increased average daily gain and feed conversion rate of broilers in grower period (22–42 d) and over the entire experiment compared to basic diet. Responses of antioxidant status to dietary APS and AMP varied depending on the age of the broilers. Beneficial effects of AMP on growth and feed utilization of broilers could be obtained by inclusion of AMP at the rate of 10,000 mg/kg diet.  相似文献   
64.
为观察姬松茸水溶性粗多糖对镉中毒小鼠血液系统的影响,将60只SPF级雄性健康小白鼠随机分为对照组、模型组、试验组1、试验组2和试验组3共5组,模型组与3个试验组采用同一水平镉染毒,但同时对3个试验组给予不同剂量的姬松茸水溶性粗多糖溶液进行保护,试验日程为5周,试验结束时对各组小鼠采血,检测各项血液指标。结果显示,模型组小鼠的血液指标红细胞数(RBC)、血红蛋白浓度(HGB)、血细胞比容(HCT)、平均红细胞体积(MCV)、平均红细胞血红蛋白含量(MCH)、平均红细胞血色素浓度(MCHC)显著低于对照组的相应指标;与模型组相比,给予高剂量姬松茸水溶性粗多糖的试验组3的血液指标RBC、HGB、HCT、MCV、MCH、MCHC均显著提高,而白细胞数(WBC)、小型白细胞数(Lym)和中型白细胞数(Mid)则显著下降。证实,重金属镉能够损伤小鼠的血液系统,但高剂量姬松茸水溶性粗多糖对镉的损伤具有防止作用。  相似文献   
65.
The aim of the present article is to show the possibilities of chemometric tools and the parallel factor analysis (PARAFAC) model, as well as to understand the complexities of the fluorescence emission-excitation matrix (EEM) of water-soluble organic matter (WSOM) extracted from sewage sludge samples obtained with different origins and stabilization procedures. The variation in the composition of WSOM in the different sewage sludge samples could be correlated with the conditions of stabilization; therefore, the use of fluorescence spectroscopy to monitor these changes can be a useful tool to optimize the management of this residual flux, avoiding environmental pollution. However, the “contour density” EEM maps obtained with fluorescence present continuous spectra with different peaks, valleys, and shoulders where manual peak picking can be complicated and subjective, especially in complex matrixes such as sewage sludge. With the PARAFAC algorithm, it is possible to resolve the emission and excitation spectra of the different fluorescence components present in the samples and their contribution to the total fluorescence. Also, the contribution (scores) of the different fluorophors can be coupled with another chemometric tool to provide an effective classification method using the stabilization conditions of sewage sludge as main criterion. In this study, a wide survey of sewage sludge samples (287) was characterized by fluorescence emission-excitation matrix. The final molecular composition of the sewage sludge samples was not related to the stabilization (aerobic vs anaerobic) treatments. However, a sewage sludge classification based on a combined spectroscopic-chemometric approach was obtained, which could be used for the optimization of sewage sludge use in agriculture, minimizing the environmental risks.  相似文献   
66.
为了促进新型水溶肥的推广应用,以制种玉米LY263为指示作物,在河西绿洲灌区研究了新型水溶肥料、普通肥料和普通水溶肥对制种玉米产量及经济效益的影响。结果表明,在化肥用量较普通肥料减少26.2%的条件下,施用新型水溶肥系列产品玉米高效专用水溶肥Ⅰ型168~240 kg/hm2+Ⅱ型336~480 kg/hm2+Ⅲ型105~150 kg/hm2(70%~100%新型水溶肥),较常规施肥模式制种玉米增产0.5%~7.1%,纯收益增加1470.3~ 2 647.2元/hm2;较普通水溶肥模式增产0.7%~8.8%,纯收益增加1 979.6~3 156.5元/hm2。与普通水溶肥模式相比,施用80%新型水溶肥和100%新型水溶肥可实现制种玉米显著增产,70%新型水溶肥可确保制种玉米不减产,均可在河西灌区应用。  相似文献   
67.
研究了植酸对霍山石斛类原球茎悬浮培养细胞生长、多糖合成和培养基中主要营养成分消耗的影响,并分析了细胞中可溶性还原糖、可溶性蛋白质、丙二醛含量以及过氧化物酶和多酚氧化酶的活性。结果表明,植酸能抑制过氧化物酶和多酚氧化酶的活性,提高细胞活力,从而促进细胞生长和多糖合成,以2.5g/L浓度的植酸效果最好,培养36d时,类原球茎干重为29.4g/L,多糖产量为2.06g/L。动力学分析表明,添加2.5g/L的植酸还有利于碳、氮、磷等营养物质的吸收。  相似文献   
68.
射频辅助提取香菇柄多糖   总被引:2,自引:1,他引:2  
探讨射频技术在香菇柄多糖提取中的应用,优化了射频辅助提取香菇柄多糖的工艺,并与传统水提法、超声波辅助提取法和微波辅助提取法进行了比较。采用Draper-Lin中心组合设计和全因素中心组合设计对影响射频提取的处理时间、料液比、作用温度、预浸泡时间进行了筛选和优化。优化结果为:射频处理5.2min,作用温度(82.6±3)℃,料液比1:40(5g:200mL),预浸泡时间20min。在此条件下,香菇柄多糖提取率达到43.1mg/g。与传统水提法、超声波辅助提取法和微波辅助提取法相比,得率分别提高了94.1%,40.8%和5.38%;与传统水提法相比,多糖纯度有所提高(42.8%→46.7%),提取时间也大大缩短(6h→5.2min)。  相似文献   
69.
为综合利用春砂仁中多种有效成分,该文设计三级提取方案,先除去杂质并回收芳香及呈味成分,然后采用微波-水溶液法提取春砂仁多糖,以前级温和的条件保护后级提取产物(多糖)的特性。通过GC-MS分析得到春砂仁低极性组分中所含的挥发性成分;然后提高提取剂的极性,通过单因素及正交试验分别选择了水溶液提取春砂仁多糖的最佳工艺条件。结果表明:液固比10∶1(V/W),微波功率600 W,提取温度80℃,时间 20 min,春砂仁粗多糖产率为11.33%;纯化粗多糖的条件:Sevag试剂中氯仿与正丁醇的比例为3∶1,萃取3次,所得纯化多糖的产率为50.30%;干燥多糖的条件:温度-49~-56℃,压强24~40 kPa,干燥时间4 h。  相似文献   
70.
不同种植年限大棚菜田土壤水溶性盐分的变化特征   总被引:12,自引:0,他引:12  
采集新乡市不同种植年限大棚菜田、露天菜田及大田土壤共计160个样品,调查分析水溶性盐总量、各盐分离子的变化及土壤pH值。结果表明,大棚土壤在连续种植不同年限后,水溶性盐总量上升幅度与种植年限呈极显著相关(r=0.92**);K+、Na+、Cl-、NO2-、NO3-、SO24-含量与种植年限呈正相关,而Ca2+、Mg2+、HCO3-含量变化与种植年限呈负相关;土壤pH值降低幅度与种植年限呈极显著相关;K+、Na+、Cl-、NO3-、SO42-的含量均与土壤水溶性盐总量呈极显著相关。新乡市大棚菜田土壤中Cl-、NO2-、NO3-含量与pH值变化存在极显著负相关;SO42-含量与pH值变化存在显著负相关;HCO3-与土壤pH值变化存在极显著正相关。新乡市大棚菜田阳离子以K+、Na+为主,阴离子主要以Cl-、NO2-、NO3-、SO42-为主;不同种植年限对大棚土壤盐渍化和酸化有极显著影响,K+、Na+、Cl-、NO2-、NO3-、SO42-则是造成土壤盐渍化的重要原因,Cl-、NO2-、NO3-、SO42-是造成土壤酸化的重要原因。  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