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   16191篇
  免费   762篇
  国内免费   1600篇
林业   1773篇
农学   2093篇
基础科学   1181篇
  2426篇
综合类   5298篇
农作物   1044篇
水产渔业   668篇
畜牧兽医   2393篇
园艺   629篇
植物保护   1048篇
  2024年   83篇
  2023年   230篇
  2022年   559篇
  2021年   708篇
  2020年   688篇
  2019年   637篇
  2018年   425篇
  2017年   625篇
  2016年   512篇
  2015年   682篇
  2014年   681篇
  2013年   752篇
  2012年   993篇
  2011年   1126篇
  2010年   963篇
  2009年   958篇
  2008年   866篇
  2007年   813篇
  2006年   734篇
  2005年   681篇
  2004年   350篇
  2003年   289篇
  2002年   280篇
  2001年   277篇
  2000年   344篇
  1999年   462篇
  1998年   387篇
  1997年   345篇
  1996年   315篇
  1995年   263篇
  1994年   305篇
  1993年   246篇
  1992年   202篇
  1991年   180篇
  1990年   147篇
  1989年   139篇
  1988年   84篇
  1987年   64篇
  1986年   34篇
  1985年   24篇
  1984年   18篇
  1983年   14篇
  1982年   14篇
  1981年   10篇
  1980年   8篇
  1979年   7篇
  1975年   4篇
  1964年   3篇
  1963年   3篇
  1956年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Objective— To evaluate the accuracy of numerical rating (NRS) and visual analogue (VAS) scoring scales compared with force plate gait analysis and agreement between observers for each scoring scale.
Study Design— Experimental study.
Animals— Mixed breed dogs (n=21) with a right limb tibial osteotomy repaired with an external fixator.
Methods— Three small-animal veterinarians with orthopedic training scored lameness using NRS and VAS before surgery, and at 4 and 8 weeks after surgery. Peak force and impulse were determined at the same time points using a force plate. Agreement between observers and with force plate data was assessed. Significance was set at P ≤.05.
Results— Agreement was generally low among observers for both NRS and VAS scores. When evaluated at each time point, an acceptable level of agreement was present only at 4 weeks after surgery. Only impulse had a significant relationship with some of the observers' subjective scores. No significant relationships between any observer's scores and force plate data existed if very lame dogs were omitted.
Conclusions— Subjective scoring scales do not replace force plate gait analysis. Agreement is low unless lameness is severe, and each observer uses an individually unique scale. Subjective scoring scales most accurately reflect force plate gait analysis when lameness is severe.
Clinical Relevance— Subjective lameness scoring scales may not accurately reflect lameness and do not replace force plate gait analysis. Observers must stay the same during the duration of a study for accurate analyses.  相似文献   
82.
对未经检疫的畜禽不能在运输环节进行补免和补检,要强化产地免疫和检疫;要在法规上加以明确,禁止逃避检疫行为;同时完善配套的公路动物防疫检查站留验场所和标准规定。  相似文献   
83.
芦苇(Phragmites australis)是较好的造纸材料,其纤维素含量高低直接影响造纸的价值,纤维素越高,制浆、漂白工艺越简单,成纸紧度、透明度越高。为研究造纸废水灌溉对芦苇纤维素含量的作用效果,以灌溉造纸废水的芦苇茎和叶为试验对象,测定不同灌溉期和不同浓度废水下芦苇茎和叶的纤维素含量。结果表明,1)灌溉300mg·L-1浓度废水对芦苇纤维素含量影响最大,出苗期芦苇茎纤维素含量表现为:300mg·L-1(36.39%)175mg·L-1(35.39%)50mg·L-1(34.73%)0(33.45%);2)在快速生长期灌溉废水最利于芦苇纤维素的积累,如浓度为300mg·L-1时芦苇茎纤维素含量变化量表现为快速生长期(11.75%)抽穗期(9.64%)成熟期(9.6%)展叶期(7.68%)出苗期(3.64%);3)芦苇纤维素含量总体表现为茎叶,如在出苗期灌溉浓度为300mg·L-1的废水,芦苇纤维素含量表现为茎(33.45%)叶(22.11%);4)废水浓度(X)对芦苇纤维素含量(Y)有显著影响(P0.05),二者的回归方程分别为Y茎=0.012 X+0.379 8,Y叶=0.008 X+0.249 2。  相似文献   
84.
测定了家蚕夏芳、长灰A和大造各品种血液、消化液中酸性核糖核酸酶及家蚕秋白、夏芳、长灰A和大造各品种天冬酰胺酶性变化。结果表明:各品种血液、消化液中酸性核糖核酸酶、天冬酰胺酶活性变化随发育呈现较强的规律性,血液中,4龄第3d、5龄第3d这两种酶均出现峰值,4龄眠前活性较低,消化液中,5龄第3d这两种酶活性均较高,不同品种这两种酶活性峰值出现时间有差异;各品种血液中酸性核糖核酸酶、天冬酰胺酶性均明显高于相应品种消化液中这两种酶活性;各品种之间血液、消化液中这两种酶活性有明显差异。  相似文献   
85.
陈萍  鲁成  朱勇  向仲怀 《蚕业科学》2002,28(1):31-34
研究结果表明 :在RH 6 0 %状态下 ,控制性比的温度和下限时间负相关达到显著水平 ;控制性比的高温处理适于干燥状态下进行 ;处理后雌蚕孵化整齐度明显低于雄蚕孵化整齐度 ,雌雄蚕孵化整齐度均随处理温度的升高而下降 ,尤以雌蚕更为明显。由此提出了在RH 6 0 %状态下sch单养雄蚕品种控制性比的起点温度及温度、时间范围。认为高温催青用下限温度配合 1日收蚁法效果好 ,高温处理以后的胚胎适于在RH 80 %~ 85 %的湿度中保护  相似文献   
86.
不同断奶日龄仔猪血清代谢物水平的变化   总被引:6,自引:0,他引:6  
本试验研究了不同断奶日龄仔猪血清代谢物水平的变化。试验设17日龄断奶、21日龄断奶、28日龄断奶、35日龄断奶4个处理组,每个处理3个重复,每个重复1窝,定时采血。结果表明,17、21日龄断奶组仔猪血糖浓度显著低于35日龄断奶组(P〈0.05),在断奶后2~3周时间内,以17日龄断奶组仔猪血糖浓度波动最大;4个不同断奶日龄组之间仔猪血清尿素氮浓度没有显著差异;与35日龄断奶组比,17日龄断奶仔猪血  相似文献   
87.
基因探针和PCR对鲤吉陶单极虫的检测   总被引:3,自引:1,他引:3  
采用液氮冷冻研磨法破碎吉陶单极虫(Thelohaneluskitauei)孢子,按常规法提取其基因组DNA。取DNAEcoRI消化产物,采用低熔点琼脂糖回收法制备大(3.0~15.0kb)、小(0.5~3.0kb)片段,将其克隆于pBluescriptksEcoRI位点,经α-互补现象、酶切鉴定和虫体DNA生物素标记探针筛选,构建了含23个克隆的基因文库,克隆片段介于0.9~6.8kb之间;经阳性克隆标记筛选及特性分析,制备了长度为0.9kb(19号质粒克隆片段)的探针,该探针具有较强的敏感性和特异性。对该探针两端DNA序列进行分析,设计出1对引物。上游引物序列为:5′TTTCGAACCCGCACAACAAG3′,下游引物序列为:5′TGAGTGGATAG-TATCGCTGC3′。应用该对引物对虫体进行了检测  相似文献   
88.
酸与胆汁耐性芽孢益生菌的筛选   总被引:1,自引:2,他引:1  
曹钰  孙玲玲  陆健 《饲料研究》2006,(12):31-34
试验选用允许直接饲喂的安全微生物中的芽孢杆菌,按照益生菌的特定要求,考察各菌株对低pH和高胆盐的耐受性及产酶特性。筛选获得的凝结芽孢杆菌AHU1366,耐受性优良,并能产生淀粉酶和蛋白酶,是一株比较理想的饲用益生菌。  相似文献   
89.
The objective of this study was to investigate the effect of storage temperatures and time on discoloration and oxidation of prepared chicken breast with paprika oleoresin. Freshly prepared chicken breast containing paprika oleoresin was stored at ?2, ?10, ?18°C, and an oscillating temperature between ?10 and ?18°C (?10/?18°C). A significant decrease in redness was detected at ?2, ?10, and ?10/?18°C. The lowest TBARS values and carbonyl contents were observed in the samples stored at ?18°C for 5 weeks. Also, the values of sulfhydryl groups gradually decreased with the increase in storage temperatures and duration. The results suggest a positive correlation between the loss of redness and oxidation in all samples. The findings indicated that the discoloration and oxidation of prepared chicken breast added with paprika oleoresin were inhibited significantly when stored at ?18°C.  相似文献   
90.
Lu H  Castro AE 《Avian diseases》2004,48(2):263-270
The H7N2 subtype of avian influenza virus (AIV) field isolate (H7N2/chicken/PA/3779-2/97), which caused the 1997-98 AIV outbreak in Pennsylvania, was evaluated for its infectivity, length of infection, and immune response in specific-pathogen-free (SPF) chickens. The composite findings of three clinical trials with various concentrations of virus indicated that this H7N2 subtype contained minimal pathogenicity for chickens. The concentration of the virus in the inoculum proved critical in the establishment of a productive infection in a chicken. Seven-day-old SPF chickens were not infected when inoculated with 10(0.7-2.0) mean embryo lethal dose (ELD50) of the H7N2 virus per bird. At this dose level, the immune response to this virus was not detected by the hemagglutination-inhibition (HI) test. Nonetheless, chickens at ages of 5 and 23 wk old tested were successfully infected when exposed to 10(4.7-5.7) ELD50 of H7N2 infectious doses per bird by various routes of administration and also by direct contact. Infected birds started shedding virus as early as 2 days postinoculation, and the period of virus shedding occurred mostly within 1 or 2 wk postinoculation (WPI). This H7N2 subtype of AIV induced a measurable immune response in all birds within 2 wk after virus exposure. Antibody titers were associated with AIV infectious doses and age of exposure of birds. Challenge of these infected birds with the same H7N2 virus at 5 and 10 WPI indicated the infective virus was recoverable from cloacal swabs at 3 days postchallenge and disappeared thereafter. In these challenged birds, the antibody levels as measured by the HI test spiked within 1-2 wk.  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