全文获取类型
收费全文 | 13546篇 |
免费 | 108篇 |
国内免费 | 109篇 |
专业分类
林业 | 421篇 |
农学 | 109篇 |
基础科学 | 27篇 |
1631篇 | |
综合类 | 4420篇 |
农作物 | 371篇 |
水产渔业 | 128篇 |
畜牧兽医 | 6233篇 |
园艺 | 73篇 |
植物保护 | 350篇 |
出版年
2013年 | 26篇 |
2012年 | 983篇 |
2011年 | 1184篇 |
2010年 | 242篇 |
2009年 | 164篇 |
2008年 | 1050篇 |
2007年 | 1033篇 |
2006年 | 966篇 |
2005年 | 1015篇 |
2004年 | 820篇 |
2003年 | 828篇 |
2002年 | 774篇 |
2001年 | 542篇 |
2000年 | 699篇 |
1999年 | 257篇 |
1998年 | 33篇 |
1997年 | 40篇 |
1996年 | 36篇 |
1995年 | 52篇 |
1994年 | 72篇 |
1993年 | 98篇 |
1992年 | 124篇 |
1991年 | 111篇 |
1990年 | 96篇 |
1989年 | 109篇 |
1988年 | 131篇 |
1987年 | 133篇 |
1986年 | 118篇 |
1985年 | 95篇 |
1984年 | 121篇 |
1983年 | 138篇 |
1982年 | 115篇 |
1981年 | 128篇 |
1980年 | 87篇 |
1979年 | 82篇 |
1978年 | 32篇 |
1977年 | 33篇 |
1972年 | 30篇 |
1970年 | 32篇 |
1967年 | 32篇 |
1966年 | 47篇 |
1963年 | 85篇 |
1960年 | 35篇 |
1958年 | 29篇 |
1957年 | 30篇 |
1956年 | 29篇 |
1955年 | 26篇 |
1954年 | 30篇 |
1953年 | 28篇 |
1948年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
OBJECTIVES: To describe the clinical signs, clinicopathological abnormalities and outcome of metaldehyde intoxication in dogs. METHODS: Medical records of dogs presenting between 1989 and 2005 with a diagnosis of metaldehyde toxicity were reviewed retrospectively. Data obtained from the medical record included signalment, history, clinical signs, laboratory tests results, hospitalisation period length, treatments and outcome. RESULTS: Eighteen dogs fulfilled the inclusion criteria. The most prevalent clinical signs were seizures, hyperthermia, tachycardia and muscle tremors. Serum biochemistry abnormalities included increased serum muscle enzymes activities, acidaemia (six dogs) and decreased blood bicarbonate (eight dogs). Treatment was symptomatic and supportive. Hyperbilirubinaemia was observed in two dogs. Diazepam was the most commonly used anticonvulsant followed by phenobarbitone and pentobarbital. General inhalant anaesthesia was required in nine of 18 dogs with seizures unresponsive to anticonvulsants. The survival was 83 per cent (15 of 18 dogs). CLINICAL SIGNIFICANCE: This clinical study recorded, for the first time in the veterinary literature, several clinicopathological abnormalities from severely intoxicated dogs. Metabolic acidosis was common, while acute or delayed hepatotoxicity was an uncommon complication. 相似文献
162.
163.
E Yong BIAN Wei SHAN Dexin ZHANG Di FU Chunlei 《东北农业大学学报(英文版)》2006,13(2):149-152
Sludge is produced wherever sewage purification takes place. The amount of municipal dry sludge in China is more than 5.0×106 t per year. There are lots of soil nutrients, such as nitrogen, phosphorus and or- ganic matters contained in sludge, but heavy … 相似文献
164.
饲养策略是针对整个猪群,这必然会导致自然资源的低效利用,甚至可能会扩大猪在屠宰时的个体差异。通过管理猪群均匀度做到精准饲喂有助于提高动物生产系统的效率。这个解决办法依赖于对营养供给与动物生产性能之间的精准预测、生产性能的持续监测和调节营养供给的饲喂系统。 相似文献
165.
Laurence E. D. SMITH 《农业科学与工程前沿(英文版)》2020,7(1):90-97
Farmers are the key agents who manage land and water. Agriculture Green Development (AGD) requires a transformation in farming from high resource consumption and environmental cost to sustainable intensification with high productivity, high resource use efficiency and low environmental risk. This paper analyzes the public policy challenge of AGD and makes the case for a location-sensitive policy mix made up of regulation, advice provision, voluntarism and targeted incentives. The public agricultural extension service in China is a key resource, but one that requires reorientation and reform with the aim of better balancing high farm productivity with environmental protection. 相似文献
166.
Izquierdo MS Robaina L Juárez-Carrillo E Oliva V Hernández-Cruz CM Afonso JM 《Fish physiology and biochemistry》2008,34(2):117-127
The Δ6 and Δ5 desaturases and elongases show only very limited activity in marine fish, and little is known of the possibility
of enhancing Δ6 desaturase gene expression in these fish. The use of plant oils in marine fish diets is limited by their lack
of n−3 highly unsaturated fatty acids (HUFA) despite an abundant content of the 18C fatty acid precursor linoleic and α-linolenic
acids. The objective of the present study was to determine the ability of larval gilthead seabream to utilize vegetable oils
and assess the nutritional regulation of Δ6 desaturase gene expression. Seventeen-day-old gilthead seabream larvae were fed
during a 17-day period with one of four different microdiets formulated with either sardine fish oil (FO), soybean, rapeseed
or linseed oils, respectively, or a fifth diet containing defatted squid meal and linseed oil. Good larval survival and growth,
both in terms of total length and body weight, were obtained by feeding the larvae either rapeseed, soybean or linseed oils.
The presence of vegetable oils in the diet increased the levels of 20:2n−9 and 20:2n−6, 18:2n−9, 18:3n−6, 20:3n−6 and 20:4n−6, in larvae fed rapeseed and soybean oils in comparison to those fed FO. In addition, a sixfold increase in the relative
expression of Δ6 desaturase-like gene was found in larvae fed rapeseed and soybean oils, denoting the nutritional regulation
of desaturase activity through its gene expression in this fish species. However, feeding linseed oil did not increase the
expression of the Δ6 desaturase gene to such a high extent. 相似文献
167.
Vikingstad E Andersson E Norberg B Mayer I Klenke U Zohar Y Stefansson SO Taranger GL 《Fish physiology and biochemistry》2008,34(3):289-298
Atlantic salmon (Salmo salar L.) females (2 SW), maturing for the first time, were reared under one of three temperature regimes (high: 14.3 ± 0.5°C;
natural: 10.6 ± 1.0°C; and cold: 6.9 ± 1.0°C) in combination with one of two experimental treatments; an injection of GnRH
analogue (GnRHa) contained in biodegradable microspheres, or a sham injection (microspheres only). The six experimental groups
were then reared under simulated natural photoperiod for 4 weeks. Blood samples were drawn for analysis of plasma steroid
levels and the fish were inspected for ovulation weekly. Batches of stripped eggs were incubated in triplicate incubators
in raceways until the eyed stage. Treatment with GnRHa resulted in a substantial advancement and synchronization of ovulation
at all temperatures, while exposure to cold water also appeared to advance ovulation slightly. While 75% (warm and cold) to
90% (natural) of GnRHa fish ovulated during the 4-week trial, only 30% of sham-treated females exposed to cold water, and
none of the sham-treated fish held at higher temperatures, ovulated during this period. Survival rates of embryos to the eyed-stage
were significantly higher for broodstock exposed to cold water. Plasma levels of testosterone (T), 17β-oestradiol (E2), and 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP) were all significantly affected by treatment with GnRHa and, to a lesser
extent, temperature. The efficiency of GnRHa in counteracting the negative effects of high temperature on ovulation and the
associated changes in circulating sex steroids suggest that temperature inhibition operates at least in part at the brain
or pituitary. 相似文献
168.
该研究通过一系列的土柱实验研究土壤中硅和重金属的反应机制。土柱实验在可溶性镉、铜、镍和铅酸盐的情况下,用各种活性硅(硅藻土,沸石,无定形二氧化硅,浓缩单硅酸)处理灰森林土。所有富硅物质都用电子显微镜测试分析过。富硅物质对土壤中重金属的钝化试验结果表明:硅藻土和浓缩单硅酸比沸石和无定形二氧化硅更能降低重金属的移动性。重金属移动性的降低是由土壤溶液中单硅酸和重金属的反应,以及富硅物质表面对重金属的吸附实现的。重金属在土壤中移动的强度与自身种类有关。施用富硅物质可明显降低镉和镍的移动性,对铜和铅的效果不明显。 相似文献
169.
据Arny等(1966)报道,用遗传抗性有效地控制大麦黄矮病毒(BYDV)已经成功地在大麦上得到了证实.然而在小麦对BYDV的抗性遗传方面的报道却极为有限.尽管Qualset等(1973)不少人对某些抗性资源作过报道,但没有发现免疫性,也没有见到主基因控制的抗性.Topcn(1975)研究了Anza(抗)×Bluebird(感)和Anza(抗)×CA63121(抗)这两个春小麦杂交组合后代群体的抗性遗传行为,发现该两组合的F_2资料呈现连续性 相似文献
170.
乌龙茶种质资源种群遗传多样性AFLP评价 总被引:18,自引:1,他引:18
以银染法AFLP分子标记技术用5对引物组合对来自福建武夷山市、安溪县、台湾省和广东潮安县45份乌龙茶品种资源进行遗传多样性分析。结果表明,5对引物扩增出208条多态性条带,多态性为92.03%;最大遗传距离为0.481,最小遗传距离为0.124,种质资源间遗传多样性估值较高,达0.311。按照地理分布分组分析表明,种群内遗传多样性以武夷山最高,其次为安溪乌龙茶种质资源,以台湾的乌龙茶种质资源遗传多样性最小;种群间遗传相似性,以武夷山与安溪种群间最高,达0.9505,以台湾和潮安县类型间的相似性最低,相似性系数为0.77。构建的种间和种群间进化树表明,可将45份乌龙茶品种划分为二大类型,福建类型和广东潮安类型。结合种群间相似系数,提出乌龙茶种质资源与其加工工艺的演化路径是一致的,也是由武夷山向安溪再向台湾传播。 相似文献