全文获取类型
收费全文 | 2011篇 |
免费 | 116篇 |
国内免费 | 120篇 |
专业分类
林业 | 68篇 |
农学 | 130篇 |
基础科学 | 19篇 |
478篇 | |
综合类 | 655篇 |
农作物 | 80篇 |
水产渔业 | 146篇 |
畜牧兽医 | 498篇 |
园艺 | 98篇 |
植物保护 | 75篇 |
出版年
2024年 | 8篇 |
2023年 | 36篇 |
2022年 | 64篇 |
2021年 | 74篇 |
2020年 | 72篇 |
2019年 | 90篇 |
2018年 | 53篇 |
2017年 | 89篇 |
2016年 | 105篇 |
2015年 | 67篇 |
2014年 | 104篇 |
2013年 | 186篇 |
2012年 | 158篇 |
2011年 | 130篇 |
2010年 | 109篇 |
2009年 | 85篇 |
2008年 | 93篇 |
2007年 | 108篇 |
2006年 | 80篇 |
2005年 | 84篇 |
2004年 | 48篇 |
2003年 | 36篇 |
2002年 | 35篇 |
2001年 | 39篇 |
2000年 | 36篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 28篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1962年 | 2篇 |
排序方式: 共有2247条查询结果,搜索用时 29 毫秒
141.
The stress response of grass carp to salinity was evaluated assessing the levels of hematocrit, leucocrit, plasma glucose, sodium, potassium and calcium. Mean hematocrit values increased following exposure to salinity. Mean leucocrit values elevated after exposure to salinity for 24 h, then decreased. Mean plasma glucose increased during saline exposure for 48 h and then decreased to normal values. Plasma sodium and chloride levels were increased to their highest values after 48 h. While plasma potassium value increased with the exposure time, plasma calcium values were not affected by salinity exposure. 相似文献
142.
Calcium ions(Ca2+) act as an intracellular second messenger and affect nearly all aspects of cellular life. They are functioned by interacting with polar auxin transport, and the negative phototropism of plant roots is caused by the transport of auxin from the irradiated side to the shaded side of the roots. To clarify the role of calcium signaling in the modulation of rice root negative phototropism, as well as the relationship between polar auxin transport and calcium signaling, calcium signaling reagents were used to treat rice seminal roots which were cultivated in hydroculture and unilaterally illuminated at an intensity of 100–200 μmol/(m2·s) for 24 h. Negative phototropism curvature and growth rate of rice roots were both promoted by exogenous CaCl2 lower than 100 μmol/L, but inhibited by calcium channel blockers(verapamil and LaCl3), calcineurin inhibitor(chlorpromazine, CPZ), and polar auxin transport inhibitor(N-1-naphthylphthalamic acid, NPA). Roots stopped growing and negative phototropism disappeared when the concentrations increased to 100 μmol/L verapamil, 12.500 μmol/L LaCl3, 60 μmol/L CPZ, and 6 μmol/L NPA. Moreover, 100 μmol/L CaCl2 could relieve the inhibition of LaCl3, verapamil and NPA. The enhanced negative phototropism curvature was caused by the transportation of more auxin from the irradiated side to the shaded side in the presence of exogenous Ca2+. Calcium signaling plays a key role as a second messenger in the process of light signal regulation of rice root growth and negative phototropism. 相似文献
143.
144.
145.
Ragab Abdelmohsen E-Mergawi ;Khalid Naser Al-Redhaiman ;Hussein F. Abouziena 《农业科学与技术》2014,(7):597-604
The effect of N levels and sources on the antioxidant components in vegetable is not completely understood. Therefore, greenhouse experiments were conducted to determine the changes in antioxidant capacity diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP), total phenolics, ascorbic acid, total carotene and lycopene contents in edible portions of lettuce, onion and tomato due to different nitrogen levels and sources. The experiment included three N levels (20, 40 and 60 kg/ha for lettuce trial and 60, 120 and 180 kg/ha for either onion or tomato) and four nitrogen sources (calcium nitrate, ammonium sulphate, ammonium nitrate and urea). The antioxidant capacity and phenolic contents in lettuce was enhanced under low nitrogen level, while the antioxidant capacities, phenolics, carotenoids and lycopene in tomato fruits were not significantly affected by the nitrogen dose applied. Application of calcium nitrate caused 50% increase in DPPH and 20% in FRAP of lettuce compared to other nitrogen forms. Tomato treated with calcium nitrate or ammonium sulphate had higher phenolic and ascorbic acid contents than treated plants with ammonium nitrate or urea. Antioxidant tested parameters of onion were not significantly affected by the nitrogen treatments. Nitrogen concentration in tomato fruits significantly correlated with FRAP antioxidant capacity, phenolics, ascorbic acid, carotene and lycopene contents. 相似文献
146.
147.
维生素D(VD)是一种脂溶性维生素,是动物体内不可缺少的,其在促进骨骼发育和钙磷吸收、改善动物肉品质及免疫细胞的形成等方面都起到重要的作用,虽然VD在动物体内可以合成,但其需要量较大,仍需要从食物中获得,饲料中添加的VD量过多或过少都会影响动物的生产性能、钙和磷的代谢和骨代谢等。因此,适宜的VD添加量具有重要的生物学意义。文章综述了家禽VD的需要量、影响因素及其生理功能。 相似文献
148.
采用盆栽试验,对广东省10 个主栽花生品种进行施钙和施磷处理,利用JMP7.0 对花生的7 个主要农
艺性状进行相关分析和主成分分析。相关分析结果表明院在施磷条件下,单株产量和单株荚果数呈极显著正相关;在
施钙条件下,各性状之间的相关关系更为紧密,有多对性状的相关关系达到显著或者极显著水平。主成分分析表明院
在施磷的条件下,生长势因子为第一主成分,贡献率达43.56%;在施钙条件下,产量因子为第一主成分,贡献率达
46.22%。进行磷效率品种选择时,重点考虑的性状是主茎高、侧枝长和分枝数;进行钙效率品种筛选时,重点考虑的
性状是单株产量、百果重和百仁重。 相似文献
149.
A 10-week feeding experiment was performed in hybrid catfish (Clarias macrocephalus (Gunther) × C. gariepinus (Burchell, 1822) with initial average weight of 1.17 g, in glass aquaria of 200-L capacity. The experiment comprised seven treatments with three replicates each. Ascorbyl phosphate calcium (APCa) was included at 30, 75, 150, 300 and 1000 mg kg−1 feed and compared with one with ascorbyl polyphosphate (APP) at 36 mg kg−1 feed and one without vitamin C supplementation. Fish fed APCa-supplemented feed showed better growth, feed conversion ratio, survival rate and protein utilization compared with those without such supplementation. Ascorbate concentrations in liver and head kidneys were correlated closely with dietary APCa levels. Vertebral collagen and hydroxyproline contents were significantly lower in the fish group without ascorbate supplementation. Red blood cell and white blood cell counts showed no correlation with vitamin C supplementation. Serum protein level was lowest in the group fed feed without vitamin C supplementation and this was lower than those fed feed with APCa and APP supplementation. The fish fed APCa- and APP-supplemented feed showed no difference in serum protein levels. External scorbutic symptoms and histopathological changes of gill tissue were noted in fish fed feed without APCa supplementation. The study indicates that 12.6 mg kg−1 of ascorbic acid molar equivalent supplied as APCa (30 mg kg−1) provided maximum growth and no gross signs as well as histological changes resulting from vitamin C deficiency. 相似文献
150.
S Adhikari 《Aquaculture Research》2003,34(12):975-980
Four experiments were conducted to evaluate the effects of calcium and magnesium hardness on the acute toxicity of copper sulphate to Indian major carp, rohu (Labeo rohita, Hamilton) fingerlings and juvenile catfish (Channa punctatus, Bloch) in medium alkalinity experiments. A preliminary bioassay determined the 96 h LC50 of copper sulphate to be 0.56 mg L?1 for L. rohita fingerlings and 11.78 mg L?1 for juvenile C. punctatus placed in water with calcium hardness and total alkalinity set at 100 mg L?1 CaCO3. In the first experiment, rohu were exposed to 0.56 mg L?1 copper sulphate in environments where calcium hardness was varied from 50 to 350 mg L?1 CaCO3 and total alkalinity was 100 mg L?1 CaCO3. As calcium hardness increased, copper‐induced rohu mortalities decreased significantly from 90% at 50 mg L?1 CaCO3 to 7% at 350 mg L?1 CaCO3. In the second experiment, rohu were exposed to 0.56 mg L?1 copper sulphate in environments where magnesium hardness was varied from 50 to 350 mg L?1 CaCO3 with total alkalinity set at 100 mg L?1 CaCO3. Hundred percent mortality was observed in magnesium‐based hardness treatments. In the third experiment, catfish were exposed to 11.78 mg L?1 copper sulphate in environments where calcium hardness was varied from 50 to 400 mg L?1 and total alkalinity was 100 mg L?1 CaCO3. As calcium hardness increased, copper‐induced catfish mortalities decreased significantly from 90% at 50 mg L?1 CaCO3 to 4% at 400 mg L?1 CaCO3. In the fourth experiment, catfish were exposed to 11.78 mg L?1 copper sulphate in environments where magnesium hardness was varied from 50 to 400 mg L?1 CaCO3, with total alkalinity set at 100 mg L?1 CaCO3. In this case, 100% mortality was also observed in magnesium‐based treatments. Mortality rates in magnesium hardness treatments were consistent with those in the second experiment. These data suggest a calcium‐specific mechanism with respect to acute copper toxicity both in rohu and catfish. 相似文献