全文获取类型
收费全文 | 2274篇 |
免费 | 112篇 |
专业分类
林业 | 127篇 |
农学 | 59篇 |
基础科学 | 14篇 |
307篇 | |
综合类 | 377篇 |
农作物 | 54篇 |
水产渔业 | 170篇 |
畜牧兽医 | 1131篇 |
园艺 | 43篇 |
植物保护 | 104篇 |
出版年
2021年 | 33篇 |
2020年 | 34篇 |
2019年 | 25篇 |
2018年 | 38篇 |
2017年 | 39篇 |
2016年 | 44篇 |
2015年 | 33篇 |
2014年 | 38篇 |
2013年 | 70篇 |
2012年 | 106篇 |
2011年 | 125篇 |
2010年 | 69篇 |
2009年 | 76篇 |
2008年 | 125篇 |
2007年 | 140篇 |
2006年 | 130篇 |
2005年 | 144篇 |
2004年 | 105篇 |
2003年 | 107篇 |
2002年 | 124篇 |
2001年 | 46篇 |
2000年 | 64篇 |
1999年 | 47篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 28篇 |
1993年 | 17篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 30篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1974年 | 19篇 |
1973年 | 13篇 |
1972年 | 14篇 |
1970年 | 13篇 |
1969年 | 15篇 |
1967年 | 9篇 |
排序方式: 共有2386条查询结果,搜索用时 31 毫秒
11.
应用绵羊粪便的近红外光谱方程评定其日粮的可消化有机物 总被引:1,自引:0,他引:1
利用近红外光谱法 (NIRS)对绵羊粪便的扫描值和日粮的体内测定值来建立定标方程式。以绵羊为试验动物 ,日粮主要由各种牧草、作物秸秆和棉花籽壳组成 ,试验动物日粮设计了 78个蛋白水平。在 2 0 0 2年和 2 0 0 3年分别用 15只和 2 0只成熟母羊 (体重为 5 5± 2 .4kg)进行了为期 7周的实验。体内收粪法测定出的日粮可消化有机物(DOM)水平为 5 2 .4 %至 75 .8% ,日粮的可消化有机物的定标方程式决定系数r2 =0 .80 ,定标标准误差SEC =1.5 1。随机选取 2 0 0 3年试验第 3周第 7d的 10个粪便样品利用可消化有机物定标方程预测其日粮的可消化有机物 ,其结果是决定系数r2 =0 .94 5 ,预测标准误差SEP =0 .5 5 2 ,斜率Slope =1.0 83,表明利用近红外光谱法 (NIRS)对粪便的扫描值可以有效预测绵羊日粮的可消化有机物 相似文献
12.
Carlos R Sanchez Suzan Murray Richard J Montali Lucy H Spelman 《Journal of zoo and wildlife medicine》2004,35(3):397-399
A 37-yr-old female Asian elephant (Elephas maximus) presented with anorexia, restlessness, and dark-colored urine. Urinalyses showed hematuria, leukocyturia, isosthenuria, proteinuria, granular casts, and no calcium oxalate crystals. Bloodwork revealed azotemia. Urine culture revealed a pure growth of Streptococcus zooepidemicus resistant to sulfamethoxazole-trimethoprim but susceptible to cephalosporins. A presumptive diagnosis of pyelonephritis was made based on bloodwork, urinalysis, and urine culture. The animal was treated with intravenous ceftiofur, and intravenous and per rectum fluids were given for hydration. The elephant's attitude and appetite returned to normal, the abnormal blood parameters resolved, and urinary calcium oxalate crystals reappeared after treatment, supporting presumptive diagnosis. Follow-up ultrasonography revealed an abnormal outline of both kidneys with parenchymal hyperechogenicity and multiple uterine leiomyomas. 相似文献
13.
14.
15.
16.
A survey of northern Victorian dairy farmers to investigate dairy calf management: colostrum feeding and management 下载免费PDF全文
Objectives
To describe colostrum management practices carried out in northern Victorian dairy herds and to identify weaknesses in these areas that may affect calf health and welfare by comparing the results with the current industry recommendationsMethods
A questionnaire to obtain information about colostrum management and calf‐rearing practices was sent to commercial dairy farming clients of Rochester Veterinary Practice between June and September 2013. The questionnaire consisted of a general herd overview and colostrum harvesting practices.Results
The response rate was 39% (58/150). Many dairy producers were not meeting the current industry recommendations in the following areas: (1) time of removal calf from the dam, (2) relying on calf suckling colostrum from the dam to achieve adequate passive transfer, (3) failing to supplement calves with colostrum, (4) feeding inadequate volumes of colostrum, (5) delayed colostrum harvesting, (6) pooling of colostrum, (7) failing to objectively assess colostrum quality or relying on visual assessment and (8) storing colostrum for a prolonged periods of time at ambient temperatures.Conclusion
The results from this survey highlight the need for greater awareness of industry standards for colostrum management and feeding hygiene.17.
Paula de Aguiar Silva Gleidson Giordano Pinto de Carvalho Aureliano José Vieira Pires Stefanie Alvarenga Santos Douglas dos Santos Pina Robério Rodrigues Silva Carlindo Santos Rodrigues Luis Henrique Almeida de Matos Carlos Emanuel Eiras Daiane Novais-Eiras Wilson Souza Nunes 《Tropical animal health and production》2018,50(4):721-726
In this study, we evaluated the effects of including cassava wastewater in the diet on the feeding behavior of feedlot lambs in 35 male uncastrated Santa Inês × Dorper crossbred lambs at an approximate age of 3 months, with an average live weight of 20.0?±?3.4 kg. Diets were formulated with hay of cassava shoots (roughage) and a concentrate based on corn and soybean, with a roughage:concentrate ratio of 50:50, plus inclusion of cassava wastewater at the levels of 0, 12, 24, 36, or 48 g/kg of the total diet. Feeding behavior was evaluated between the 46th and 52nd days of the experiment. Increasing cassava wastewater levels in the diet reduced (P?<?0.05) the intakes (kg/day) of dry matter and neutral detergent fiber as well as the efficiency of rumination (g/cud and g/h) of dry matter and neutral detergent fiber. The other behavioral parameters were not affected by wastewater inclusion in the diet. Therefore, the inclusion of up to 48 g/kg of cassava wastewater on fresh matter of diets is not recommended for feedlot lambs. 相似文献
18.
Huimin Yang Murray Unkovich Ann McNeill Xianzhi Wang 《Biology and Fertility of Soils》2011,47(4):377-385
Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil
mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in
an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18
permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3− by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year.
We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher
than that of non-N2 fixing species examined. 相似文献
19.
20.
Rachel J Sorensen James S Drouillard Teresa L Douthit Qinghong Ran Douglas G Marthaler Qing Kang Christopher I Vahl James M Lattimer 《Journal of animal science》2021,99(1)
The effect of hay type on the microbiome of the equine gastrointestinal tract is relatively unexplored. Our objective was to characterize the cecal and fecal microbiome of mature horses consuming alfalfa or Smooth Bromegrass (brome) hay. Six cecally cannulated horses were used in a split-plot design run as a crossover in two periods. The whole plot treatment was ad libitum access to brome or alfalfa hay fed over two 21-d acclimation periods with subplots of sampling location (cecum and rectum) and sampling hour. Each acclimation period was followed by a 24-h collection period where cecal and fecal samples were collected every 3 h for analysis of pH and volatile fatty acids (VFA). Fecal and cecal samples were pooled and sent to a commercial lab (MR DNA, Shallowater, TX) for the amplification of the V4 region of the 16S rRNA gene and sequenced using Illumina HiSeq. The main effects of hay on VFA, pH, and taxonomic abundances were analyzed using the MIXED procedure of SAS 9.4 with fixed effects of hay, hour, location, period, and all possible interactions and random effect of horse. Alpha and beta diversities were analyzed using the R Dame package. Horses fed alfalfa had greater fecal than cecal pH (P ≤ 0.05), whereas horses fed brome had greater cecal than fecal pH (P ≤ 0.05). Regardless of hay type, total VFA concentrations were greater (P ≤ 0.05) in the cecum than in feces, and alfalfa resulted in greater (P ≤ 0.05) VFA concentrations than brome in both sampling locations. Alpha diversity was greater (P ≤ 0.05) in fecal compared with cecal samples. Microbial community structure within each sampling location and hay type differed from one another (P ≤ 0.05). Bacteroidetes were greater (P ≤ 0.05) in the cecum compared with the rectum, regardless of hay type. Firmicutes and Firmicutes:Bacteroidetes were greater (P ≤ 0.05) in the feces compared with cecal samples of alfalfa-fed horses. In all, fermentation parameters and bacterial abundances were impacted by hay type and sampling location in the hindgut. 相似文献