全文获取类型
收费全文 | 161155篇 |
免费 | 8481篇 |
国内免费 | 74篇 |
专业分类
林业 | 9665篇 |
农学 | 6395篇 |
基础科学 | 1111篇 |
20453篇 | |
综合类 | 23852篇 |
农作物 | 7460篇 |
水产渔业 | 9305篇 |
畜牧兽医 | 77536篇 |
园艺 | 2790篇 |
植物保护 | 11143篇 |
出版年
2019年 | 1348篇 |
2018年 | 4659篇 |
2017年 | 4938篇 |
2016年 | 3393篇 |
2015年 | 2050篇 |
2014年 | 2436篇 |
2013年 | 5842篇 |
2012年 | 4995篇 |
2011年 | 7034篇 |
2010年 | 5297篇 |
2009年 | 4537篇 |
2008年 | 6281篇 |
2007年 | 6187篇 |
2006年 | 4616篇 |
2005年 | 4189篇 |
2004年 | 4022篇 |
2003年 | 4195篇 |
2002年 | 3735篇 |
2001年 | 4911篇 |
2000年 | 4822篇 |
1999年 | 3787篇 |
1998年 | 1536篇 |
1997年 | 1623篇 |
1996年 | 1428篇 |
1995年 | 1685篇 |
1994年 | 1466篇 |
1993年 | 1467篇 |
1992年 | 2965篇 |
1991年 | 3157篇 |
1990年 | 3088篇 |
1989年 | 3097篇 |
1988年 | 2781篇 |
1987年 | 2754篇 |
1986年 | 2857篇 |
1985年 | 2654篇 |
1984年 | 2267篇 |
1983年 | 1934篇 |
1979年 | 2057篇 |
1978年 | 1571篇 |
1977年 | 1398篇 |
1976年 | 1376篇 |
1975年 | 1518篇 |
1974年 | 1785篇 |
1973年 | 1794篇 |
1972年 | 1689篇 |
1971年 | 1618篇 |
1970年 | 1591篇 |
1969年 | 1546篇 |
1968年 | 1370篇 |
1967年 | 1447篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Robyn S. HETEM Duncan MITCHELL Brenda A. DE WITT Linda G. FICK Shane K. MALONEY Leith C. R. MEYER Andrea FULLER 《Integrative zoology》2019,14(1):30-47
As one of the few felids that is predominantly diurnal, cheetahs (Acinonyx jubatus) can be exposed to high heat loads in their natural habitat. Little is known about long‐term patterns of body temperature and activity (including hunting) in cheetahs because long‐term concurrent measurements of body temperature and activity have never been reported for cheetahs, or, indeed, for any free‐living felid. We report here body temperature and locomotor activity measured with implanted data loggers over 7 months in 5 free‐living cheetahs in Namibia. Air temperature ranged from a maximum of 39 °C in summer to ?2 °C in winter. Cheetahs had higher (~0.4 °C) maximum 24‐h body temperatures, later acrophase (~1 h), with larger fluctuations in the range of the 24‐h body temperature rhythm (approximately 0.4 °C) during a hot‐dry period than during a cool‐dry period, but maintained homeothermy irrespective of the climatic conditions. As ambient temperatures increased, the cheetahs shifted from a diurnal to a crepuscular activity pattern, with reduced activity between 900 and 1500 hours and increased nocturnal activity. The timing of hunts followed the general pattern of activity; the cheetahs hunted when they were on the move. Cheetahs hunted if an opportunity presented itself; on occasion they hunted in the midday heat or in total darkness (new moon). Biologging revealed insights into cheetah biology that are not accessible by traditional observer‐based techniques. 相似文献
972.
973.
Abdel-Hamid Tamer M. El-Tarabany Mahmoud S. 《Tropical animal health and production》2019,51(8):2421-2429
Tropical Animal Health and Production - The aim was to evaluate the effect of bee pollen (BP) on performance, blood parameters, and metabolic hormones in New Zealand White (NZW) and Rex (RX)... 相似文献
974.
Molini Umberto Aikukutu Gottlieb Khaiseb Siegfried Kahler Barbara Van der Westhuizen Jolandie Cattoli Giovanni Dundon William G. 《Tropical animal health and production》2019,51(7):2105-2108
Between July and August 2018, two outbreaks of infectious laryngotracheitis caused the death of over 116,000 commercial poultry (layers and broilers) near the city of Windhoek, Namibia. A third outbreak occurred in September 2018 in the north of the country approximately 800 km from the original outbreaks. Sample collection and molecular epidemiological analyses revealed that the outbreaks were most likely caused by poor vaccination practices leading to the reversion to virulence of an ILT vaccine strain. The analyses also indicate that inaccurate declarations were made by one of the farms involved and that illegal movement of animals most likely occurred.
相似文献975.
976.
S. Purdy 《Equine Veterinary Education》2019,31(4):199-202
977.
978.
Soto-Navarro SA Encinias AM Bauer ML Lardy GP Caton JS 《Journal of animal science》2012,90(2):585-591
Three studies were conducted to evaluate the feasibility of field peas as a protein source in diets for beef cattle. In the first study, 4 cultivars of field pea were incubated in situ to determine rate and extent of CP disappearance. Results indicate that field pea cultivars vary in CP content (22.6, 26.1, 22.6, and 19.4%, DM basis for Profi, Arvika, Carneval, and Trapper, respectively). Soluble protein fraction ranged from 34.9% for Trapper to 54.9% for Profi. Degradable CP fraction was greater (P = 0.01) for Trapper compared with the other cultivars, and no differences (P ≥ 0.25) were observed among Profi, Arvika, and Carneval. Rate of CP degradation differed (P ≤ 0.03) for all cultivars, with Profi being the greatest and Trapper the smallest (10.8, 10.0, 8.1, and 6.3 ± 1.4%/h for Profi, Carneval, Arvika, and Trapper, respectively). Estimated RDP was not different (P = 0.21) for all 4 cultivars. In the second study, 30 crossbred beef steers (301 ± 15 kg) were individually fed and used to evaluate effects of field pea processing (whole, rolled, or ground) on steer performance. Diets contained 40% field pea grain. Growing steers consuming whole field pea had greater ADG (P = 0.08) than those consuming processed field pea (1.69, 1.52, and 1.63 ± 0.05 kg/d, for whole, rolled, and ground, respectively). However, DMI (kg/d and as % of BW) and G:F were not different (P ≥ 0.24). In the third study, 35 individually fed gestating beef cows (694 ± 17 kg) were used to evaluate the use of field pea as a protein supplement for medium quality grass hay (9.3% CP). Treatments consisted of whole field peas at 1) 0 g (CON), 2) 680 g (FP680), 3) 1,360 g (FP1360), and 4) 2,040 g (FP2040), and 5) 1,360 g of 74% barley and 26% canola meal (BCM). Total intake (forage + supplement) of gestating beef cows increased with increasing field pea level (linear, P = 0.01; supplemented vs. nonsupplemented, P = 0.01). In summary, protein quantity and rate of ruminal protein degradation vary across sources of field peas used in this study. Additionally, because of source variability, nutrient analysis and animal requirements should be considered when field pea is incorporated into beef cattle diets. Processing field pea does not improve performance of growing steers. Supplementation of field pea to gestating cows consuming medium-quality grass hay increased total DMI. Overall, our data indicate field pea can be used in a wide variety of beef cattle diets. 相似文献
979.
Caspe SG Moore DP Leunda MR Cano DB Lischinsky L Regidor-Cerrillo J Alvarez-García G Echaide IG Bacigalupe D Ortega Mora LM Odeón AC Campero CM 《Veterinary parasitology》2012,189(2-4):171-181
The Nc-Spain 7 isolate of Neospora caninum, which was newly obtained from an asymptomatic congenitally infected calf, demonstrated a similar virulence as Nc-1 strain in mouse models. The aim of this study was to characterize the pathogenesis of Nc-Spain 7 isolate in cattle after experimental infection at 65 days of gestation. For this purpose, thirteen pregnant heifers were divided into three groups as follows: group A: 7 heifers inoculated with 1×10(8) tachyzoites of Nc-Spain 7 isolate; group B: 4 heifers inoculated with 1×10(8) tachyzoites of Nc 1 strain; and group C: 2 heifers received PBS. Serum samples were collected weekly and heparinized blood samples were collected three times (0, 28 and 42 days after inoculation) by jugular venipuncture. Placenta and fetal tissue samples were collected at time of necropsy. Specific antibody response in the dams was tested by IFAT, indirect ELISA, and rNcGRA7 and rNcSAG4 based-ELISA. Specific antibody response in fetal fluids was tested by IFAT. IFN-γ production was measured after in vitro culture of PBMC and the supernatant was assessed using a commercial kit (BOVIGAM). A significant increase in N. caninum antibody responses was detected in groups A and B by IFAT and by i-ELISA from day 14 after inoculation onwards. Besides, antibody response against rNCGra7 protein was also detected in all inoculated heifers by rNcGra7-based ELISA. Four fetuses from group A and one from group B were aborted between 3 and 5 weeks after infection. In the recovered fetuses, only 3 out of 4 fetal fluids from fetuses of group A and 1 out of 3 of group B were seropositive by IFAT, but all of them were positive by PCR. Transplacental transmission could be determined in all fetuses from groups A and B by PCR and/or IHC. Heifers of group C and their fetuses remained negative by all techniques. The results of this study demonstrate that the NC-Spain 7 isolate could be transmitted transplacentally, and produced fetal death and abortion in cattle. 相似文献
980.
This study aimed to investigate the distribution of Malassezia species yeasts on the skin of healthy horses. Acetate tape samples were obtained from the lip, axilla, interbulbar region, groin and anus of 12 healthy horses. The samples were stained and examined microscopically and sites harbouring yeast-like organisms were identified. Contact plates were applied to the skin at these sites and cultured at 26 degrees C and 32 degrees C. No growth was obtained on horse blood, Sabouraud's dextrose or modified Dixon's agar. A pure growth of a Malassezia-type organism was obtained on Sabouraud's dextrose agar enriched with oleic acid when it was incubated at 30 degrees C. It was identified by 26S ribosomal DNA D1/D2 sequence analysis as a member of the genus Malassezia, and most closely related to Malassezia sympodialis. However, the level of sequence divergence indicated that it was a novel species. 相似文献