全文获取类型
收费全文 | 2697篇 |
免费 | 268篇 |
国内免费 | 253篇 |
专业分类
林业 | 98篇 |
农学 | 55篇 |
基础科学 | 169篇 |
146篇 | |
综合类 | 687篇 |
农作物 | 70篇 |
水产渔业 | 922篇 |
畜牧兽医 | 871篇 |
园艺 | 10篇 |
植物保护 | 190篇 |
出版年
2024年 | 22篇 |
2023年 | 59篇 |
2022年 | 104篇 |
2021年 | 164篇 |
2020年 | 126篇 |
2019年 | 153篇 |
2018年 | 96篇 |
2017年 | 134篇 |
2016年 | 138篇 |
2015年 | 118篇 |
2014年 | 128篇 |
2013年 | 184篇 |
2012年 | 174篇 |
2011年 | 183篇 |
2010年 | 124篇 |
2009年 | 127篇 |
2008年 | 122篇 |
2007年 | 123篇 |
2006年 | 123篇 |
2005年 | 105篇 |
2004年 | 84篇 |
2003年 | 84篇 |
2002年 | 81篇 |
2001年 | 78篇 |
2000年 | 60篇 |
1999年 | 47篇 |
1998年 | 48篇 |
1997年 | 29篇 |
1996年 | 43篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有3218条查询结果,搜索用时 31 毫秒
81.
82.
为研究环境与摄食因素对人工鱼礁区不同体长许氏平鲉分布的影响,采用2017—2018年山东省近岸3处鱼礁区环境和渔业资源的调查数据,利用变异系数CV均值将样本的体长分为10组,每组体长间隔为33 mm,并使用Bray-Curtis相似性指数比较不同海域许氏平鲉体长组成的相似性;运用去趋势对应分析(DCA)、典范对应分析(CCA)分析各环境要素对不同体长组许氏平鲉分布的影响;运用胃含物分析法分析许氏平鲉的食物组成。结果显示,西霞口与长岛鱼礁区样本体长组成相似性指数为70.66%,前三岛鱼礁区与西霞口鱼礁区、长岛鱼礁区的相似性指数较低,分别为54.94%和59.46%;大体长(299~365mm)许氏平鲉的分布与水深、水质指数(WQI)和化学需氧量(COD)相关性较大,喜好水深较深、营养丰富的水域;小体长(35~200 mm)许氏平鲉喜好水深较浅,水质好的水域。大体长(200~365 mm),高龄(2~3龄)的个体主要摄食鱼类、虾类和蟹类,优势饵料为鱼类(IRI为65.94%);小体长(35~200 mm),低龄(0~1龄)的个体主要摄食虾类和蟹类,优势饵料为虾类(IRI为45.69%)。研究表明,在浅水区域投放幼鱼保护型鱼礁,为幼鱼提供庇护所;将捕捞作业集中在深水区,减少对许氏平鲉小体长个体的兼捕,可以达到针对性增殖、保护许氏平鲉资源的目的。 相似文献
83.
鱼类早期发育阶段摄食行为研究现状 总被引:2,自引:0,他引:2
对鱼类早期阶段的摄食行为研究进行了综述。重点阐述了胃含物分析法、饥饿对摄食的影响、摄食器官的形态发育特征与摄食行为的关系、食物选择及其生理生态因子对摄食的作用。初步探讨了仔稚鱼饥饿后的捕食量和捕食速度的变化,并结合食物保障,分析了食物选择性指数I在鱼类摄食行为研究中的应用。 相似文献
84.
85.
Wenresti G Gallardo Myrna N Bautista-Teruel Armando C Fermin & Clarissa L Marte 《Aquaculture Research》2003,34(10):839-842
A method of marking abalone (Haliotis asinina Linne) for sea ranching and stock enhancement purposes was developed. Three‐month‐old abalone juveniles (11.8‐mm shell length, 0.28 g) were fed artificial diets for 1, 2, or 3 weeks. The width of the bluish‐green shell band produced by abalone juveniles was 1.7, 2.6, and 4.2 mm after 1, 2, or 3 weeks of feeding respectively. The growth and survival of juveniles fed artificial diets did not differ from that of juveniles fed the seaweed Gracilariopsis bailinae (control). Feeding the diet‐fed juveniles with the seaweed thereafter produced the natural brownish shell, thus forming a sandwiched bluish‐green band. An experimental release in outdoor tanks with natural growth of seaweeds and diatoms, and in a marine reserve showed that the shell band remained clear and distinct, indicating the usefulness of this shell marking method in sea ranching and stock enhancement of abalone. 相似文献
86.
枸杞岛海藻场角蝾螺夏季摄食选择性及其生态学意义 总被引:2,自引:1,他引:2
于2013年夏季对枸杞岛海藻场螺类优势种角蝾螺进行了稳定同位素、摄食选择性、消化代谢物粒径等系列实验.稳定同位素结果显示,角蝾螺是牧食性生物,在藻场中的营养级为2.12,属初级消费者,底栖海藻是角蝾螺的主要食源,贡献率为94.5%;摄食选择性实验结果显示,角蝾螺具有较宽的摄食选择,能够摄食海带、铜藻、粗枝软骨藻等1 1种大型藻类,其中铜藻及蜈蚣藻是枸杞岛潮下带的重要优势种;消化代谢物实验结果显示,角蝾螺的啃食作用能为藻场碎屑提供增量,角蝾螺对海藻场碎屑的增量为(0.016 ~0.094)g/d,经过啃食及消化作用产生的碎屑主要粒级为1Φ(> 250 μm).稳定同位素分析—摄食选择偏好实验—螺类消化代谢物粒径分析的系列研究表明,角蝾螺在枸杞岛海藻场的群落食物网中,可以起到连接牧食食物链和碎屑食物链的重要作用. 相似文献
87.
Vanesa García José M. Carral María Sáez-Royuela Rocío González Álvaro González 《Journal Of Applied Aquaculture》2013,25(1):57-65
There are no specifically formulated dry foods for tench (Tinca tinca L.), which forces farmers to use diets formulated for other fish species. This has major drawbacks, such as high mortality, slow growth, and body deformities. A 120 day experiment was performed with five-month-old juvenile tench (initial mean weight: 0.388 g; total length: 31.78 mm) to evaluate decapsulated Artemia cysts as a supplement to a dry diet for other fish species. Three treatments, differing in the daily supplement, were tested: 1,800 freshly hatched nauplii, 1,800 cysts, and 300 cysts per g of tench biomass. Final survival ranged between 95.3% and 97.9%. Juvenile tench that received the supplement of 1,800 decapsulated Artemia cysts had a specific growth rate (1.28), weight (1.83 g), and total length (52.30 mm) significantly higher than those with the same amount of nauplii. The lowest supplement (300 cysts/g of fish biomass) allowed significantly lower growth and higher condition coefficient (1.40) than the rest. Animals with body deformities (1.06%) were only recorded in the groups that received the lowest cyst supplement. Results showed Artemia cysts are a suitable dietary supplement for juvenile tench, being an advantageous alternative to live nauplii. 相似文献
88.
The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of
starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns
differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased
to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding
on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized
in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to
increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic
activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding
with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent
changes due to morphological and physiological modifications or diet shift during larval development but that they became
stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned.
Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days
after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding
groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days
after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival
can be obtained in the culture. 相似文献
89.
投喂频率对黄鳝幼鱼摄食、生长及饵料利用效率的影响 总被引:1,自引:0,他引:1
研究了不同投喂频率对黄鳝(Monopterus albus)摄食率、特定生长率、饵料效率、体重分化、鱼体组成的影响。试验共设5组不同投喂频率(2、3、4、12次/d和24次/d),每组3个重复,试验持续30 d。结果显示:投喂频率4次/d组的摄食率显著高于其它各组(P<0.05);特定生长率有不同程度增高,4次/d组达到最高(P<0.05);饲料利用效率4次/d组显著高于2次/d组(P<0.05),与其它组无显著性差异(P>0.05);随着投喂频率增加,各试验组组内个体体重无显著差异(P>0.05),黄鳝的规格趋于整齐。试验各组黄鳝的鱼体成分无显著性差异(P>0.05);饵料蛋白质和能量的表观消化率,在4次/d时达到最高(P<0.05)。试验表明:黄鳝的生长受投喂频率的影响,每天投喂4次是黄鳝养殖的最佳投喂频率。 相似文献
90.
V. C. Rubio F. J. Snchez-Vzquez J. A. Madrid 《Aquaculture (Amsterdam, Netherlands)》2003,220(1-4):697-705
European sea bass exhibits a feeding rhythm with seasonal phase inversions: nocturnal feeding is predominant in winter, and diurnal feeding during the rest of the year. This explains the increased growth of sea bass fed at night during the winter months, but to fully assess such feeding practices, it is important to monitor food-catching efficiency in the dark. To evaluate the influence of nocturnal feeding on pellet-capture efficiency under laboratory conditions, we developed an infrared pellet detector linked to on-line recording with a microcomputer. Feed waste was recorded for eight groups of four sea bass (54.6±15.8 g body weight) fed either diurnal or nocturnal meals with long (>60 s) or short (<20 s) feed availability times. With short feed availability times, food-catching efficiency in complete darkness (0 lx) was reduced to 78.6%, compared to 93.5% in diurnally fed fish. This was confirmed in a second experiment, performed during winter, involving 4000 sea bass in four sea cages (1000 per cage) provided with self-feeders and pellets detectors. Feed waste amounted to less than 13% of the food distributed, but nocturnal demands (29% of total feed demands) were accompanied by higher levels of uneaten pellets (68% of the total feed waste) than diurnal demand. This suggests that if the aim is to reduce feed waste, nocturnal feeding should be restricted in sea cages. 相似文献