全文获取类型
收费全文 | 4480篇 |
免费 | 228篇 |
国内免费 | 13篇 |
专业分类
林业 | 310篇 |
农学 | 195篇 |
基础科学 | 39篇 |
890篇 | |
综合类 | 671篇 |
农作物 | 272篇 |
水产渔业 | 433篇 |
畜牧兽医 | 1417篇 |
园艺 | 140篇 |
植物保护 | 354篇 |
出版年
2023年 | 45篇 |
2022年 | 33篇 |
2021年 | 98篇 |
2020年 | 105篇 |
2019年 | 118篇 |
2018年 | 104篇 |
2017年 | 102篇 |
2016年 | 113篇 |
2015年 | 70篇 |
2014年 | 117篇 |
2013年 | 228篇 |
2012年 | 260篇 |
2011年 | 297篇 |
2010年 | 198篇 |
2009年 | 164篇 |
2008年 | 252篇 |
2007年 | 267篇 |
2006年 | 238篇 |
2005年 | 239篇 |
2004年 | 235篇 |
2003年 | 217篇 |
2002年 | 204篇 |
2001年 | 67篇 |
2000年 | 54篇 |
1999年 | 61篇 |
1998年 | 40篇 |
1997年 | 31篇 |
1996年 | 39篇 |
1995年 | 31篇 |
1994年 | 36篇 |
1993年 | 48篇 |
1992年 | 30篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 42篇 |
1988年 | 37篇 |
1987年 | 26篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有4721条查询结果,搜索用时 31 毫秒
991.
992.
Ohne Zusammenfassung
Mit 2 Abbildungen 相似文献
993.
Fujio Kasamatsu Paul Ensor Gerald G. Joyce & Noritugu Kimura 《Fisheries Oceanography》2000,9(3):214-223
The relationship between the distribution of minke whales ( Balaenoptera acutorostrata ) in the Bellingshausen and Amundsen Seas (longitude between 60°W and 120°W), and environmental and physiographic variables (sea-surface temperature, sea-ice extension, and sea-floor-slope type), was studied to determine whether these environmental and physical factors affect the distribution and density of minke whales. The analysis was based on sightings data obtained from the 1989/90 and 1982/83 IWC/IDCR cruises. The mean sea-surface temperatures for comparable areas were significantly higher in 1989/90 (2.04°C) than in 1982/83 (1.12°C), and the area where the sea-surface temperature was greater than 1°C in the 1989/90 study was approximately twice that of the 1982/83 study. Additionally, during the surveys, the extent of the sea ice in 1989/90 was less than that in 1982/83, with the mean ice edge about 92.6 km (50 nautical miles; 1 nautical mile ≈1.852 km) farther south in 1989/90 than in 1982/83. This is consistent with the sea ice extent observed in winter, when the sea ice extent was less in 1989 than in 1982. The distribution of minke whales was substantially different between the two surveys, with the density and abundance of minke whales being greater in 1982/83 than in 1989/90. The warmer sea-surface temperatures, fewer cold-water intrusions, and the smaller extent of sea ice in 1989/90 may be related to the difference in distribution of minke whales from 1982/83, possibly owing to the shift in availability of prey. 相似文献
994.
Ali Al‐Hisnawi Ana Rodiles Mark D. Rawling Mathieu Castex Paul Waines Georgia Gioacchini Oliana Carnevali Daniel L. Merrifield 《Journal of the World Aquaculture Society》2019,50(6):1133-1151
A study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 106 CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p < .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout. 相似文献
995.
Leah Beesley Paul G. Close Daniel C. Gwinn Matthew Long Michael Moroz Wayne M. Koster Timothy Storer 《Ecology of Freshwater Fish》2019,28(3):434-445
Movement and migration of fish are critical for sustaining riverine fish populations. Water resource development alters natural flow regimes and can disconnect habitats and interfere with hydrological cues for fish movement. Environmental flow releases can counter these impacts, but to be effective they must be based on quantitative flow–biota relationships. We used radio‐telemetry to investigate the association between flow and movement of Tandanus bostocki, a plotosid fish endemic to south‐western Australia. Movement was assessed for 15 adult fish at three temporal scales: weekly, daily and bihourly to reveal seasonal patterns in movement, movement around individual flow pulses, and to describe changes in home range respectively. We used a predictive modelling approach to assess the importance of discharge and other covariates on the directional distance travelled or linear home range size. Our seasonal and flow pulse study revealed that T. bostocki undertook larger downstream movements during higher flows and smaller upstream movements during lower flows. Daily movements tended to be downstream on the ascending limb of flow pulses and upstream on the descending limb. Flow‐dependent movements at weekly or daily time scales were relatively modest (typically hundreds of metres) and were moderated by time of year and gender; however, fish underwent a synchronised 1‐km movement upstream during the known reproductive period in October. The home range study revealed that T. bostocki had larger home ranges (night‐time foraging) when baseflow was elevated. These results can assist the design of customised environmental flows in the study river and other flow‐regulated rivers. 相似文献
996.
S. M. Paul KHURANA K.S. Bhargava 《The Journal of Horticultural Science and Biotechnology》2013,88(2):209-211
Seven aphids were tested for their ability to transmit 3 viruses of papaya. Mild mosaic virus (MMV) was transmitted by Aphis craccivora, A. gossypii and Myzus persicae. Distortion ringspot virus (DRV) was transmitted by A. nerii, Lipaphis pseudobrassicae and M. persicae. Ringspot virus (RSV) was transmitted only by M. persicae. Specificity of transmission by the aphid vectors of MMV and DRV was demonstrated. A. craccivora, A. nerii and L. pseudobrassicae are reported as new vectors of these viruses. 相似文献
997.
998.
Subrata Kumar Shil Md. Mahiuddin Zahangir Bhajan Chandra Das Mohammad Mahbubur Rahman Saroj Kumar Yadav Md. Manzoorul Kibria AMAM Zonaed Siddiki 《Anatomia, histologia, embryologia》2023,52(2):180-189
Ganges River dolphins (Platanista gangetica spp. gangetica) are air-breathing, warm-blooded mammals endemic to the Ganges and Karnaphuli rivers of the Indian subcontinent. Nevertheless, very little basic histomorphological research has been conducted on this endangered species. Therefore, this study aimed to describe the morphological features of different organs of P. gangetica. Despite becoming aquatic animals, they showed similarities with terrestrial mammals, such as the pair of lungs and an apical bronchus in the respiratory system, which are pretty standard in ruminants and pigs. However, unlike the terrestrial animal, the tracheobronchial tree was stiffer due to circularly arranged anastomosing plates of the hyaline cartilaginous ring in the trachea, cartilaginous plates in the bronchiole, and thick alveolar septa. The digestive system showed a three-chambered mechanical and glandular stomach similar to the artiodactyles. However, the intestine showed smaller caecum like the monogastric mammal. The urogenital system showed lobulated kidneys, a urinary bladder, a fibroelastic penis with sigmoid flexure, and a long urethral process similar to some terrestrial ruminants. Considering the aquatic environment, all those modifications, unlike terrestrial mammals, are necessary for their adaptation. Thus, this research will broadly help our clinicians and conservationist to take further steps toward disease diagnosis and monitoring of marine health of this endangered species. 相似文献
999.
Probal Jyoti Doley Kabita Sarma Pranab Chandra Kalita Ranjana Goswami Arup Kalita Rupan Sarkar Chethan Gollahalli Eregowda Parimal Roychoudhary Om Prakash Choudhary 《Anatomia, histologia, embryologia》2023,52(2):223-233
The present study was undertaken to characterize the ultrastructural morphology of the blood cells of commonly reared chickens in the state of Mizoram, India under backyard poultry farming. For this study, 2 ml of whole blood was aseptically collected from the wings veins of 12 chickens of three different breeds namely the Zoar, Aseel and Rhode Island Red and processed for ultrastructural imaging under standard protocols. Under scanning electron microscopy (SEM) the matured erythrocytes of Zoar, Aseel and Rhode Island Red appeared elliptical in shape while the leukocytes and thrombocytes appeared round in shape with variable surface modifications. Under transmission electron microscopy (TEM) the granules of the heterophils of Zoar, Aseel and Rhode Island Red appeared predominantly fusiform in shape, the granules of the eosinophils appeared round in shape and that of the basophils appeared pleomorphic in shape. The cytoplasm of the monocytes, medium-to-large lymphocytes and thrombocytes of Zoar, Aseel and Rhode Island Red under TEM appeared to be vacuolated and granular while that of the small lymphocytes appeared to be granular but non-vacuolated. The study concluded that the ultrastructural characteristics of the blood cells of the three breeds of chicken studied were almost similar to the blood cells of other birds reported earlier. 相似文献
1000.
A field study was conducted to investigate the fate of 15N-labelled nitrate applied at 20 kg N ha−1 in a wet summer to microplots installed in areas under different residue management regimes in second-rotation hoop pine (Araucaria cunninghamii) plantations aged 1–3 years in south-east Queensland, Australia. PVC microplots of 235 mm diameter and 300 mm long were driven into 250 mm soil. There were three replications of each of eight treatments. These were areas just under and between 1-year-old windrows (ca. 2–3 m in width) of harvesting residues spaced 15 m apart, and with and without incorporated foliage residues (20 t DM ha−1); the areas just under and between 2- or 3-year-old windrows spaced 10 m apart. Only 7–29% of the added 15N was recovered from the top 750 mm of the soil profile with the leaching loss estimated to be 70–86% over the 34-day period. The 15N loss via denitrification was 3.7–6.3% by directly measuring the 15N gases emitted. The microplots with the incorporated residues at the 1-year-old site had the highest 15N loss (6.3%) as compared with the other treatments. The 15N mass balance method together with the use of bromide (Br) tracer applied at 100 kg Br ha−1 failed to obtain a reliable estimate of the denitrification loss. The microplots at the 1-year-old site had higher 15N immobilisation rate (7.5–24.7%) compared with those at 2- and 3-year-old sites (2.1–3.6%). Incorporating the residues resulted in an increase in 15N immobilisation rate (24.5–24.7%) compared with the control without the incorporated residues (8.4–14.3%). These findings suggest that climatic conditions played important roles in controlling the 15N transformations in the wet summer season and that the residue management regimes could also significantly influence the 15N transformations. Most of the 15N loss occurred through leaching, but a considerable amount of the 15N was lost through denitrification. Bromide proved to be an unsuitable tracer for monitoring the 15N leaching and movement under the wet summer conditions. 相似文献