全文获取类型
收费全文 | 6674篇 |
免费 | 547篇 |
国内免费 | 109篇 |
专业分类
林业 | 652篇 |
农学 | 296篇 |
基础科学 | 71篇 |
1800篇 | |
综合类 | 369篇 |
农作物 | 396篇 |
水产渔业 | 824篇 |
畜牧兽医 | 2175篇 |
园艺 | 143篇 |
植物保护 | 604篇 |
出版年
2024年 | 11篇 |
2023年 | 51篇 |
2022年 | 89篇 |
2021年 | 164篇 |
2020年 | 209篇 |
2019年 | 228篇 |
2018年 | 291篇 |
2017年 | 327篇 |
2016年 | 312篇 |
2015年 | 244篇 |
2014年 | 286篇 |
2013年 | 462篇 |
2012年 | 557篇 |
2011年 | 576篇 |
2010年 | 381篇 |
2009年 | 315篇 |
2008年 | 390篇 |
2007年 | 367篇 |
2006年 | 305篇 |
2005年 | 314篇 |
2004年 | 258篇 |
2003年 | 253篇 |
2002年 | 207篇 |
2001年 | 147篇 |
2000年 | 133篇 |
1999年 | 95篇 |
1998年 | 43篇 |
1997年 | 44篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1969年 | 3篇 |
1918年 | 5篇 |
1863年 | 2篇 |
排序方式: 共有7330条查询结果,搜索用时 15 毫秒
91.
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
92.
Evaluation of shrimp polyculture system in Thailand based on stable carbon and nitrogen isotope ratios 总被引:1,自引:0,他引:1
HISASHI YOKOYAMA JUNYA HIGANO a KUMIKO ADACHI YUKA ISHIHI YOSHIHIRO YAMADA b 《Fisheries Science》2002,68(4):745-750
ABSTRACT: To quantify the contribution by cocultured animals to waste assimilation in an intensive shrimp farm in Thailand, the food web structures of the macrobenthos in a reservoir pond, a shrimp culture pond and water treatment ponds were examined using the stable C and N isotope ratio technique. Seawater for aquaculture was drawn from a creek, and stored in a reservoir pond, used for farming the banana prawn Fenneropenaeus merguiensis in culture ponds, and then recycled through treatment ponds where the green mussel Perna viridis was cultured to remove organic wastes discharged from the farming. The clam worm Nereididae sp. and the mud creeper Cerithideopsilla cingulata in the culture pond had δ 13 C values of −21.0‰ and −18.4‰, respectively, suggesting that shrimp feed (mean δ 13 C = −20.7‰) was the main food source for these species. The δ 13 C analysis also suggested that sediments (−23.7‰) in the reservoir pond and particulate organic matter (POM) (−24.0‰) and/or sediments (−25.0‰) in the treatment pond supplied carbon for most macrobenthic animals. However, green mussels in the treatment pond had a mean δ 13 C value of −20.5‰, suggesting that shrimp feed was the main food source for this species. 相似文献
93.
94.
95.
Rocío González Jesús Domingo Celada José Manuel Carral Vanesa García María Sáez‐Royuela Álvaro González 《Aquaculture Research》2011,42(9):1385-1392
Recent advances in crayfish feeding have enabled the development of size grading studies from the start of first‐feeding. A 180‐day experiment aimed at intensive rearing of Pacifastacus leniusculus was carried out under controlled conditions, evaluating the effects of size grading at two different periods from the onset of exogenous feeding. Stage 2 juveniles were stocked in fibreglass tanks at a density of 100 m2, and fed a dry diet for salmonids combined with restricted amounts of Artemia cysts. Five groups were tested: no grading, grading at 60 days (large and small size) and grading at 100 days (large and small size). After 6 months, no significant differences were found in the survival among groups (mean: 73.06%). The highest final growth (pooled results from upper and lower classes: 17.39 mm carapace length, 1.43 g weight) was achieved by the crayfish sorted at 60 days, showing significant differences from the ungraded group. Smaller crayfish graded at 60 days grew significantly faster than smaller crayfish graded at 100 days. The food conversion ratio was lower in the graded groups (mean: 2.64), showing significant differences from the ungraded group (3.23). This study shows that size grading allows a better performance and an improved feeding efficiency. 相似文献
96.
Juana Durán Elena Pastor Amalia Grau José María Valencia 《Aquaculture Research》2012,43(12):1777-1786
The Mediterranean spider crab, Maja squinado, is depleted due to overfishing. The crab has virtually disappeared from areas where it was abundant, such as the Balearic Islands and the Catalan coast. Maja squinado, is economically and ecologically very valuable, and it is essential to obtain information on its biology and rearing conditions to attempt to repopulate the damaged stocks of the species in the Mediterranean basin. Herein, we describe the first successful rearing of M. squinado under laboratory conditions. Our results show that M. squinado is an excellent candidate for restocking using cultured juveniles. Two consecutive broods with a 1–4 day interbrood period were observed in the laboratory in wild‐caught females, the maximum observed duration of embryonic development of the egg mass being 32 days at 18.4 ± 0.9°C, and went through four different stages. The complete larval and first juvenile development was studied in laboratory cultures fed enriched Artemia metanauplius. At 19.6 ± 0.6°C, development from hatching to first crab moult took 17 days, and it comprised two zoeae stages and one megalopa stage. The survival rate at the different stages was monitored, and 7.13 ± 2.3% was achieved at the first crab instar. 相似文献
97.
Francisco J Magallón Barajas Rosalía Servín Villegas Guillermo Portillo Clark & Berenice López Moreno 《Aquaculture Research》2006,37(5):492-499
Transport of post‐larvae shrimp used in aquaculture is an important element of successful cultivation because of the potential for stress during stocking procedures. To find optimum transport conditions, several bioassays were performed in the laboratory to evaluate survival of whiteleg shrimp Litopenaeus vannamei 5–30‐day‐old postlarvae under conditions similar to those encountered during transport from the hatchery to nursery and shrimp ponds. Postlarvae were exposed for 4 h to different temperatures and pH levels ammonia concentrations. Survival was significantly reduced after a 4 h exposure to pH 9 and was inversely related to temperature with or without 7 mg L?1 of ammonia. The 15‐ and 20‐day‐old postlarvae had higher survival rates than other ages. The lowest survival occurred in alkali conditions (pH 9), with 7 mg L?1ammonia at 30 and 32°C. To assure optimal survival of postlarvae during transfer from the hatchery to the nursery and shrimp ponds, we recommend temperatures below 28°C, pH no higher than 8, no ammonia and post‐larval age at least 15 days. 相似文献
98.
99.
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
100.
Dalila F. Canizales-Rodríguez Víctor M. Ocaño-Higuera Enrique Marquez-Rios Abril Z. Graciano-Verdugo Jose L. Cárdenas-López María S. Yepiz-Gómez 《Journal Of Aquatic Food Product Technology》2013,22(3):259-269
Postmortem changes in blue shrimp (Litopenaeus stylirostris) muscle were studied on the basis of biochemical, chemical, physical, and microbiological changes during an 18 day storage period at 0°C. Adenosine 5′-triphosphate (ATP) content, breakdown products, K-value, pH, trimethylamine nitrogen (TMA-N), total volatile basic nitrogen (TVB-N), water holding capacity (WHC), color, and texture (shear force) changes were examined. Also, total mesophilic and psychrophilic bacterial counts were measured. K-value increased linearly (r2 = 0.98) from an initial value of 1.37 ± 0.59 to 59.42 ± 6.05% at Day 18. Spoilage indicators TVB-N and TMA-N increased from 29.56 ± 1.33 and 0.69 ± 0.25 to 39.04 and 2.04 ± 0.59 mg of N/100 g at Day 18, respectively; meanwhile, the total viable counts of mesophilic and psychrophilic bacteria increased from 3.48 ± 0.44 and 2.61 ± 0.29 log CFU/g to 6.27 ± 0.21 and 7.14 ± 0.39 log CFU/g, respectively, which indicated spoilage at the end of the storage period. The pH, texture, WHC, and color were affected (p < 0.05) during the storage period. Overall, results indicate that blue shrimp muscle quality was maintained for 12 days of storage in ice. 相似文献