全文获取类型
收费全文 | 23969篇 |
免费 | 1157篇 |
国内免费 | 2415篇 |
专业分类
林业 | 841篇 |
农学 | 3486篇 |
基础科学 | 1016篇 |
4528篇 | |
综合类 | 10652篇 |
农作物 | 2961篇 |
水产渔业 | 187篇 |
畜牧兽医 | 1824篇 |
园艺 | 747篇 |
植物保护 | 1299篇 |
出版年
2024年 | 93篇 |
2023年 | 538篇 |
2022年 | 862篇 |
2021年 | 1047篇 |
2020年 | 1067篇 |
2019年 | 1037篇 |
2018年 | 859篇 |
2017年 | 1288篇 |
2016年 | 1425篇 |
2015年 | 1100篇 |
2014年 | 1466篇 |
2013年 | 1629篇 |
2012年 | 1930篇 |
2011年 | 1755篇 |
2010年 | 1388篇 |
2009年 | 1216篇 |
2008年 | 1032篇 |
2007年 | 1062篇 |
2006年 | 909篇 |
2005年 | 829篇 |
2004年 | 601篇 |
2003年 | 538篇 |
2002年 | 373篇 |
2001年 | 428篇 |
2000年 | 348篇 |
1999年 | 341篇 |
1998年 | 279篇 |
1997年 | 273篇 |
1996年 | 246篇 |
1995年 | 266篇 |
1994年 | 187篇 |
1993年 | 199篇 |
1992年 | 180篇 |
1991年 | 165篇 |
1990年 | 132篇 |
1989年 | 105篇 |
1988年 | 84篇 |
1987年 | 82篇 |
1986年 | 52篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1962年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
长丰3号苦瓜是汕头市白沙蔬菜原种研究所用C99-01A作母本、C01-03B作父本配制而成的杂交一代组合。果实长圆锥形,瓜长25~30cm,横径6~8cm,皮绿色,单瓜质量300~600g。中抗白粉病、枯萎病,耐热、耐寒、耐涝性强,适应性广。早熟,播种至初收春季为75天,夏秋直播后52天始收,每667m2产量3000~4000kg。 相似文献
92.
A study was conducted to estimate the record keeping, genetic selection, educational, and farm management effects on average
milk yield per cow (AYC), milk fat percentage, bacterial score, and bulk tank somatic cell count (BTSCC) of dairy farms in
the central region of Thailand. Farms were located in the provinces of Saraburi and Nakhon Ratchisima and were members of
the Muaklek dairy cooperative. Records from individual animals were unavailable. Thus, farm records of milk yield, milk fat
percentage, bacterial score, and BTCCC were collected from July 1, 2003 through June 30, 2006. Additional record keeping,
genetic selection, education, and farm management information was collected through a questionnaire in May of 2006. Data from
the Muaklek dairy cooperative and the questionnaire were then merged by a farm identification number. A single trait mixed
model was used to analyze AYC, milk fat percentage, and BTSCC, while a log linear model was used to analyze bacterial score.
Results showed that farms that kept records on individual animals had higher (P < 0.05) milk fat percentages and lower bacterial scores than farms that did not. Farms that used genetic information (EBV)
and phenotypes when selecting sires were higher (P < 0.05) for milk fat percentage than farms that used only phenotypes and personal opinion. Farms milking cows with a single
unit milking machine and by hand, had higher (P < 0.05) bacterial scores and BTSCC than farms using only a single or multi unit machine. Overall farms that kept individual
animal records, used EBV when selecting sires, used a single method for collecting milk, and used family labor achieved higher
performance from their herds than farms that did not. 相似文献
93.
Eighteen multiparous Zebu cows in their third lactation and their calves were randomly allocated to three suckling periods, up to 3, 4 or 5 months of age of the calf. The cows were individually fed natural hay, cottonseed cake and molasses. At 2 months of age, all calves were separated from their mothers, and were offered cottonseed cake mixed with molasses and Mucuna hay individually. The calves stimulated milk ejection by suckling 30 seconds and suckled the residual milk for 45 minutes after milking. The dry matter intake of cows (3.68, 3.29 and 3.31% of body weight) and calves (2.88, 2.80 and 2.55% of body weight) for suckling up 3, 4 and 5 months of age, respectively, was not significantly affected by treatment and neither was the growth rate of the calves (178, 157 and 149 g/d for 3, 4 or 5 months suckling period, respectively). Cows suckling their calves up to 5 months had significantly higher milk yield and higher amount of saleable milk (1.97, 2.93 and 3.69 kg/cow/d for 3, 4 and 5 months suckling period, respectively). The fat content of the milk decreased with increasing length of the suckling period while the protein content was not affected. In conclusion, a suckling period of 5 months resulted in higher total milk production and higher amount of saleable milk but did not seem to have any effect on calf growth when the calves were supplemented. 相似文献
94.
Amory JR Barker ZE Wright JL Mason SA Blowey RW Green LE 《Preventive veterinary medicine》2008,83(3-4):381-391
The milk yields of 1824 cows were used to investigate the effect of lesion-specific causes of lameness, based on farmer treatment and diagnosis of lame cows, on milk yield. A three-level hierarchical model of repeated test day yields within cows within herds was used to investigate the impact of lesion-specific causes of lameness (sole ulcer, white line disease, digital dermatitis and other causes) on milk yield before and after treatment compared with unaffected cows. Cattle which developed sole ulcer (SU) and white line disease (WLD) were higher yielding cattle before they were diagnosed. Their milk production fell to below that of the mean of unaffected cows before diagnosis and remained low after diagnosis. In cattle which developed digital dermatitis (DD) there was no significant difference in milk yield before treatment and a slightly raised milk yield immediately after treatment. The estimated milk loss attributable to SU and WLD was approximately 570 and 370 kg, respectively. These results highlight that specific types of lameness vary by herds and within herds they are associated with higher yielding cattle. Consequently lesion-specific lameness reduction programmes targeting the cow and farm specific causes of lameness might be more effective than generic recommendations. They also highlight the importance of milk loss when estimating the economic impact of SU and WLD on the farms profitability. 相似文献
95.
在家兔饲料中添加4种优良牧草对肉兔生产应用效果进行了多重比较试验,探索不同牧草在单独和配合使用的情况下对肉兔生产能力和饲喂效果的差异性和显著性。试验证明,4种牧草中黑麦草饲喂效果最好,其次为聚合草。牧草混合饲喂的效果好于单独饲喂,其中黑麦草与白三叶混合饲喂效果最好。 相似文献
96.
分级指数与相对值在奶牛用粗饲料品质评定上的比较研究 总被引:4,自引:2,他引:2
本文在测定江西奶牛养殖常用的6种粗饲料(串叶松香草、桂牧1号杂交象草、矮象草、黑麦草、墨西哥玉米与鸭茅)的常规成分基础上,实测了奶牛对这6种粗饲料的干物质随意采食量(DMI),并采用相关模型计算出这6种粗饲料的分级指数(GI)与相对值(RFV)。分别应用单项指标粗蛋白(CP)、中性洗涤纤维(NDF)、干物质随意采食量(DMI)以及综合指标RFV、GI对试验用6种粗饲料品质的分级进行了比较。研究表明:单一指标都难以正确地评定粗饲料品质,必须使用综合的整体指标。GI是首个将粗饲料的可利用能、CP、NDF与家畜的DMI综合起来考虑的一个粗饲料综合评定指数,对粗饲料的分级比RFV更精确。 相似文献
97.
98.
99.
100.
微量元素对黑麦草产量和品质的影响 总被引:5,自引:1,他引:4
在N、P、K肥料的基础上,采用Fe、Cu、Zn、Mn、B、Mo 6种微肥对黑麦草Lolium multiflorum进行叶面喷施,研究不同用量对黑麦草产量和品质的影响。试验表明:喷施Fe 0.05%、Cu 0.07%、Zn 0.40%、Mn 0.10%、B 0.60% 和Mo 0.20%与对照组相比增产差异显著(P<0.05)。适度的Fe、Cu、Mn、B和Mo能提高黑麦草的粗蛋白、粗纤维和粗灰分含量,粗蛋白提高3.72%~6.67%,无氮浸出物含量呈降低趋势,喷施Zn肥降低了粗蛋白含量,喷施B肥提高了粗脂肪含量。黑麦草中Cu、B、Mo的含量随喷肥量的提高而增加,喷施Cu 0.1%、B 1%和Mo 0.3%时,黑麦草中的含量最高,与对照组差异显著(P<0.05)。喷施Zn 0.40%、Mn 0.1%、Fe 0.05%时牧草中相应的微量元素最高,与对照组差异显著(P<0.05)。 相似文献