全文获取类型
收费全文 | 2367篇 |
免费 | 185篇 |
国内免费 | 153篇 |
专业分类
林业 | 185篇 |
农学 | 189篇 |
基础科学 | 48篇 |
122篇 | |
综合类 | 850篇 |
农作物 | 170篇 |
水产渔业 | 380篇 |
畜牧兽医 | 550篇 |
园艺 | 56篇 |
植物保护 | 155篇 |
出版年
2024年 | 14篇 |
2023年 | 30篇 |
2022年 | 53篇 |
2021年 | 78篇 |
2020年 | 107篇 |
2019年 | 79篇 |
2018年 | 70篇 |
2017年 | 100篇 |
2016年 | 103篇 |
2015年 | 83篇 |
2014年 | 120篇 |
2013年 | 176篇 |
2012年 | 145篇 |
2011年 | 138篇 |
2010年 | 127篇 |
2009年 | 143篇 |
2008年 | 134篇 |
2007年 | 117篇 |
2006年 | 117篇 |
2005年 | 96篇 |
2004年 | 72篇 |
2003年 | 70篇 |
2002年 | 65篇 |
2001年 | 65篇 |
2000年 | 49篇 |
1999年 | 50篇 |
1998年 | 35篇 |
1997年 | 48篇 |
1996年 | 22篇 |
1995年 | 25篇 |
1994年 | 33篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有2705条查询结果,搜索用时 40 毫秒
181.
李宗红 《农业图书情报学刊》2007,19(2):145-147,169
利用美国《数学评论》2004年光盘,对其收录的90余种中国高校学报进行了检索统计.结果表明:2004年总计收录1858条,江苏、山东、北京和上海为入选期刊数最多的省市,收录量列前3住的依次是四川、山东和江苏。其中四川大学学报(0490—6756)收录量最多,为87条,四川师范大学学报自然科学版(1001-8395)收录76条,为师范大学学报收录最多的期刊。 相似文献
182.
H. Stützel W. Aufhammer A. Rautenkranz B. Wagner J. Falfus E. Nalborczyk 《Journal of Agronomy and Crop Science》1993,170(3):177-186
Yield formation and yield components of a conventional and an epigonal genotype of white lupin ( Lupinus albus )
Differences in yield formation and yield structure of two contrasting Lupinus albus growth types, the conventional, freely branching cultivar Kalina and the epigonal. little branching cultivar Ep I were analyzed. Both cultivars were grown in field experiments at Hohenheim in 1987 and 1988 with a combined variation of population density (30–120 plants/m2 ) and plant distribution. In addition, assimilate distribution within the plant was studied using a 14 C-labelling experiment. – The contributions of branches to light interception of the crops during the generative phase were > 90 % in Kalina as compared to about 30 % in Ep 1 . Relative 14 C uptake of branches was in a similar range, but great proportions of the 14 C taken up by branches was translocated to main stems. No genotype x plant density interactions with respect to grain yield were recorded, indicating that yield formation at main stems and branches was affected by cropping conditions similarly in both genotypes. This applies to the conditions of the experiments, where stress effects were absent. Under these conditions, the conventional genotype showed agronomic, but no physiological disadvantages. 相似文献
Differences in yield formation and yield structure of two contrasting Lupinus albus growth types, the conventional, freely branching cultivar Kalina and the epigonal. little branching cultivar Ep I were analyzed. Both cultivars were grown in field experiments at Hohenheim in 1987 and 1988 with a combined variation of population density (30–120 plants/m
183.
昌潍白猪内分泌腺的生长发育规律 总被引:1,自引:0,他引:1
系统研究了1~8月龄昌潍白猪(192头)内分泌腺的性状指标,并由此得出了其内分泌腺的生长发育规律及其与体重变化的回归方程.结果表明,肾上腺在1~3、5~6月龄生长速度最快(P<0.01);甲状腺在1~8月龄有2个生长高峰期,即4月龄和6月龄;胸腺的生长高峰期集中于3~4月龄(P<0.01),颈部胸腺在1~3月龄生长速度显著快于胸部胸腺,胸部胸腺左侧生长发育明显快于右侧;脑垂体在2~6月龄生长速度较快.肾上腺、甲状腺、胸腺、脑垂体随体重变化的回归方程分别是y=0.019 9x+0.801 6(r=0.975 9,P<0.01);y=0.163 4x+1.286 8(r=0.976 1,P<0.01);y=1.760 8x+26.995 0(r=0.946 2,P<0.01);y=0.002 4x+0.062 0(r=0.908 3,P<0.01). 相似文献
184.
毛白杨花粉败育机制的研究 总被引:8,自引:0,他引:8
从细胞遗传学角度较为系统地揭示了毛白杨花粉败育的机制,即主要是毛白杨异质性遗传基础与环境相互作用的结果。(1)在减数分裂中有数目不等的联合程度较差的单价体以及落后染色体出现,这种与异质性相关的染色体行为异常,导致同源染色体向子细胞的不均衡,造成且功能染色体的缺失,从而引起毛白杨一定比率的败育花粉的产生;(2)遗传上的不平衡与温度等环境因子相互作用,进一步引发毛白杨生理乃至结构上的不平衡,花粉母细胞(或孢原细胞)和绒毡层细胞发育异常,从而造成不产粉或产粉较少;环境与基因型互作的差异性导致了花粉败育的年度不稳定性。(3)易位、倒位等染色体结构变异和天然三倍体株系的存在也是造成毛白杨花粉败育的原因。 相似文献
185.
Effect of culture system on the nutrition and growth performance of Pacific white shrimp Litopenaeus vannamei (Boone) fed different diets 总被引:2,自引:0,他引:2
A.G.J. TACON J.J. CODY L.D. CONQUEST S. DIVAKARAN I.P. FORSTER & O.E. DECAMP 《Aquaculture Nutrition》2002,8(2):121-137
Two 8-week feeding trials were conducted with juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) to compare the growth and performance of animals fed a series of experimental and commercial pelleted shrimp and fish feeds and dietary feeding regimes within an indoor running-water culture system and an outdoor zero-water-exchange culture system. The best overall shrimp growth performance was observed for animals fed the experimental shrimp diet and all-day feeding regime under outdoor zero-water-exchange culture conditions. Final body weight and average weekly growth rate under these conditions were 2.8 and 3.4 times greater, respectively, than animals of similar size fed with the same diet under indoor running-water culture conditions. Although direct comparison between indoor and outdoor culture systems is difficult because of the lower indoor water temperatures, and consequently lower mean daily feed intake of animals, it is believed that the higher growth and feed performance of animals reared under outdoor `green-water' culture conditions was primarily due to their ability to obtain additional nutrients from food organisms endogenously produced within the zero-water-exchange culture system. The most promising features of zero-water-exchange culture systems are that they offer increased biosecurity, reduced feed costs and water use for the farmer, and by doing so provide a potential avenue of moving the shrimp culture industry along a path of greater sustainability and environmental compatibility. 相似文献
186.
通过对几种药物及其给药途径对仔猪白痢的疗效分析,说明用新炎清配长效无敌给哺乳母猪一次同肉注射治疗得猪白痢效果确切,方法简便,省时省工,值得推广。 相似文献
187.
This study augments knowledge of bone growth by observing the development of the hyoid bone in the New Zealand White rabbit.
Preserved hyoid bones representing five different age periods, each period including five individuals and the total number
of animals being 25, were fixed in 3.5% formaldehyde solution and 95% ethanol, followed by a pure acetone bath. They were
then stained with an alcian blue–alizarin red combination. The mode of bone formation was intracartilaginous type ossification.
While the basihyoideum and thyrohyoideum were observed to start ossifying first at prenatal stage, indicating that they are
the main skeletal structures of the hyoid apparatus, the ceratohyoideum and lingual process began to ossify in the second
and third periods. The separately occurring primary ossification centres fused completely among themselves in the fifth period.
Because no further ossification centers were observed and the ossified parts continued the development and growth, the research
was terminated after 10 weeks of age. 相似文献
188.
Summary Interspecific hybrids have been obtained in an otherwise incompatible cross betweenBrassica juncea × Brassica hirta through the in vitro culture of hybrid ovules and ovaries. The best response was observed from ovules and ovaries cultured 10–15 and 5–7 days after pollination respectively on a basal medium supplemented with indoleacetic acid, kinetin and casein hydrolysate. In some cases the basal cut end of the ovaries proliferated to form callus and shoots. The in vitro-derived hybrid seeds varied in their colour, size and shape, and the F1 plants in the field showed a large diversity in their morphological traits. The hybrids were sterile, and had an intermediate number of chromosomes (2n=30). 相似文献
189.
A 2-year study of autumn-sown white lupin (Lupinus albus L.) was conducted under rainfed Mediterranean conditions in southern Spain. 108 landraces were evaluated for yield and major
phonological and plant structural characteristics. Path coefficient and Genotype-Trait (GT) biplot analysis were used. Applying
both types of analyses to the multiple trait data revealed that GT biplot graphically displayed the interrelationships among
traits and facilitated visual comparison of accessions and selection. Wide variation was observed for trait phenology (dates
of flowering and maturity), plant structure (plant and first order inflorescence height) and yield characters (first order
branches, first order inflorescence and total yield). It was found that the accessions with the highest yields were the tallest
and the latest to flower, both on the mainstem and on the lowest first order branch, and also were the latest to mature. GT
biplots also had suggested as the accessions have been displayed according to their origins. The results showed that foreign
germplasm may be an important material for improving some yield components such as number of pods and seeds per plant of locally
adapted lupins in Spain.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
190.