全文获取类型
收费全文 | 1156篇 |
免费 | 73篇 |
国内免费 | 3篇 |
专业分类
林业 | 56篇 |
农学 | 24篇 |
基础科学 | 5篇 |
132篇 | |
综合类 | 191篇 |
农作物 | 39篇 |
水产渔业 | 159篇 |
畜牧兽医 | 574篇 |
园艺 | 26篇 |
植物保护 | 26篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 32篇 |
2018年 | 27篇 |
2017年 | 33篇 |
2016年 | 31篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 52篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 46篇 |
2009年 | 38篇 |
2008年 | 59篇 |
2007年 | 66篇 |
2006年 | 81篇 |
2005年 | 60篇 |
2004年 | 59篇 |
2003年 | 55篇 |
2002年 | 63篇 |
2001年 | 26篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1972年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1936年 | 3篇 |
1902年 | 2篇 |
排序方式: 共有1232条查询结果,搜索用时 15 毫秒
1.
Twelve nonlactating dairy cows, free of signs of liver disease and with normal serum activities of liver-derived enzymes and normal liver biopsy tissue, were examined over a 72-hour period for serum total bile acid concentrations. The cattle were fed hay twice daily, and blood samples were obtained every hour for 24 hours, every other hour for 24 hours, then every hour for 24 hours. After 3 weeks, the study was repeated on 6 of the cattle, thus providing data for eighteen 72-hour periods. Serum bile acid concentration varied greatly over the 72 hours, with the range being from one third to 3 times the median. There were variations by as much as 60 mumol/L from 1 hour to the next. After another 3 weeks, 8 of the cattle were deprived of hay for 48 hours and then fed hay morning and afternoon of the third (last) day of the study. There was no significant reduction in bile acid concentration after withholding the hay, but the variability was reduced (P = 0.02) during the last 20 hours of the hay-deprivation period. In 3 ancillary studies, serum bile acid concentrations were examined over a 48-hour period in 2 cows in early lactation, 3 cows in midlactation, and two 6-month-old heifers. The cows were fed hay and grain twice daily, and the heifers were fed only hay twice daily. In comparison with values for the 12 nonlactating cows fed hay twice daily, mean serum bile acid concentration in the recently freshened cows was significantly (P < 0.002) higher (62.9 vs 22.0 mumol/L).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
2.
Chloroform-methanol (2:1 v/v), absolute methanol, and 90% acetone were evaluated for their effectiveness as extractants of chlorophyll a from samples of phytoplankton communities collected from catfish ponds. Chloroform-methanol consistently extracted more chlorophyll a than either 90% acetone or methanol. Precision for the methanol extraction was also unacceptably low, with an average coefficient of variation of 17%. Average coefficients of variation for the chloroform-methanol and 90% acetone extraction procedures were 6 and 5%, respectively. Filtered samples should be steeped in chloroform-methanol for at least 4 h to obtain maximum chlorophyll extraction, and the addition of MgCO3 to the extractant as a buffer is not necessary. 相似文献
3.
The dietary lysine requirement of juvenile red drum Sciaenops ocellatus was reevaluated in two separate experiments. In the first experiment, lyophilized red drum muscle was combined with an L-form crystalline amino acid premix to yield diets containing approximately 35% protein on a dry-matter basis. Gradations (0.25%) of L-lysine HCl were added to the basal diet containing approximately 1.0% lysine. Each diet was fed to triplicate groups of juvenile red drum initially weighing 6–7 g for 8 weeks. Based on growth and feed efficiency data, the lysine requirement (±SE) was determined to be 1.55% (±0.079%) of dry diet or 4.430% of dietary protein. In a second experiment, the lysine requirement of red drum was investigated with diets containing 35% intact protein from zein and red drum muscle. Each of the zein-based diets containing incremental levels of lysine was fed to triplicate groups of juvenile red drum initially weighing 1–2 g for 8 weeks. A crystalline amino acid test diet serving as a control in this experiment significantly outperformed the zein-based diets, and palatability of those diets was questionable due to an obvious change in feeding behavior of the fish. Due to the inferior performance of the fish fed the zein-based diets, the authors were not successful in determining a requirement with these diets. Thus, a lysine requirement of 1.55% of dry diet (4.43% of dietary protein) as determined in the first experiment is recommended for juvenile red drum. 相似文献
4.
5.
Corinna Kashuba Charlie Hsu Aric Krogstad Craig Franklin 《Veterinary Clinics of North America: Exotic Animal Practice》2005,8(1):107-122
Most viral infections in small mammals are transient and rarely produce clinical signs. When clinical signs do appear, they are often of a multifactorial etiology such as respiratory infection with Sendai virus and the bacteria M. pulmonis in rodents. Diagnosis is generally made based on clinical signs, while therapy involves treatment for concurrent bacterial infections and supportive care. Small mammals may carry zoonotic viruses such as LCMV, but natural infections are uncommon. Viral diseases are rare (or largely unknown) for hedgehogs, chinchillas, and prairie dogs, while no known naturally occurring, clinically relevant viral diseases exist for gerbils and sugar gliders. This article is intended to aid the clinician in identifying viral infections in small mammals and to help determine the significance each virus has during clinical disease. 相似文献
6.
Fritz Hervé Saïd Sonia Renaud Pierre-Cyril Mutake Snoden Coid Craig Monicat François 《Landscape Ecology》2003,18(3):293-302
After the eradication of the Tse-Tse fly in the Mid-Zambezi valley, human settlements and fields extended mainly along the main rivers. In order to investigate the consequences of this human development on wildlife diversity we monitored three rivers of the Mid-Zambezi valley in Zimbabwe: Angwa, Manyame and Kadzi. The rivers were divided in segments of 200 m which were checked for spoors in order to assess the number of species and the number of individuals that used the segments. Human settlements were also recorded. We used a GIS to define the spatial characteristics of the fields present along the rivers, and related them to the distribution and abundance of wild species spoors in the river beds and banks. Our results show that the number of species in one segment of the river decreased with the increasing size of the field area bordering the segment. For all the major ungulate species, the numbers of individuals recorded per segment decreased with increasing field area. A similar trend was observed for small and medium-sized carnivores, though they were in lower numbers when present. Our analyses thus confirm that the extension of human agriculture in wildlife areas has an impact on most wild species, but we also define some threshold value of field size above which there seem to be an acceleration of the decrease in wildlife density and diversity: 3.2 ha for medium and small herbivores and carnivores; only the elephant seem to tolerate larger field area with a threshold value of 32 ha.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
7.
8.
Hamish M Aiken Nathan J Bott Ivona Mladineo Francisco E Montero Barbara F Nowak & Craig J Hayward 《Fish and Fisheries》2007,8(3):167-180
Global distribution of platyhelminth parasites and their host specificities are not well known. Our hypothesis was that platyhelminth parasites of large pelagic fishes are common around the world. We analysed molecular variation in three different taxa of platyhelminth parasites infecting four species of tunas: yellowfin tuna (Thunnus albacares, Scombridae) from Western Australia, southern bluefin tuna (Thunnus maccoyii, Scombridae) from South Australia, Pacific bluefin tuna (Thunnus orientalis, Scombridae) from Pacific Mexico and northern bluefin tuna (T. thynnus, Scombridae) from two localities in the Mediterranean (Spain and Croatia). Comparisons of ITS2 and partial 28S rDNA demonstrated two congeneric species of blood flukes (Digenea: Sanguinicolidae) from multiple hosts and localities: Cardicola forsteri from southern bluefin and northern bluefin tunas, and Cardicola sp. from Pacific bluefin and northern bluefin tunas; and a gill fluke, Hexostoma thynni (Polyopisthocotylea: Hexostomatidae), from yellowfin, southern bluefin and northern bluefin tunas. Partial 28S rDNA indicates that a second type of fluke on the gills, Capsala sp. (Monopisthocotylea: Capsalidae), occurs on both southern bluefin and Pacific bluefin tunas. This appears to be the first report of conspecific platyhelminth parasites of teleosts with a wide‐ranging geographical distribution that has been confirmed through molecular approaches. Given the brevity of the free‐living larval stage of both taxa of flukes on the gills (H. thynni and Capsala sp.), we conclude that the only feasible hypothesis for the cosmopolitan distribution of these flatworms is migrations of host tunas. Host migration also seems likely to be responsible for the widespread occurrence of the two species of blood flukes (Cardicola spp.), although it is also possible that these were translocated recently by the spread of infected intermediate hosts. 相似文献
9.
通过饲喂使用一种独特的可持续生产的,有机认证的蛋白原料的无鱼粉日粮,海虾在一个生长季节可以增重高达23克。这一生产系统包括低饲养密度,自然手段调控微生物食物链,改善环境和动物福利。生产成本显著降低,生产的有机产品的价值提高。 相似文献
10.