全文获取类型
收费全文 | 1543篇 |
免费 | 89篇 |
国内免费 | 3篇 |
专业分类
林业 | 58篇 |
农学 | 33篇 |
基础科学 | 5篇 |
157篇 | |
综合类 | 250篇 |
农作物 | 86篇 |
水产渔业 | 168篇 |
畜牧兽医 | 803篇 |
园艺 | 39篇 |
植物保护 | 36篇 |
出版年
2021年 | 28篇 |
2020年 | 34篇 |
2019年 | 34篇 |
2018年 | 32篇 |
2017年 | 39篇 |
2016年 | 38篇 |
2015年 | 28篇 |
2014年 | 30篇 |
2013年 | 69篇 |
2012年 | 81篇 |
2011年 | 87篇 |
2010年 | 47篇 |
2009年 | 38篇 |
2008年 | 78篇 |
2007年 | 77篇 |
2006年 | 97篇 |
2005年 | 67篇 |
2004年 | 71篇 |
2003年 | 62篇 |
2002年 | 68篇 |
2001年 | 45篇 |
2000年 | 14篇 |
1999年 | 23篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1974年 | 13篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1968年 | 12篇 |
1967年 | 6篇 |
1966年 | 7篇 |
1936年 | 8篇 |
1935年 | 7篇 |
1924年 | 6篇 |
排序方式: 共有1635条查询结果,搜索用时 74 毫秒
51.
Allison D Tuttle Mark Papich Gregory A Lewbart Shane Christian Conny Gunkel Craig A Harms 《Journal of zoo and wildlife medicine》2006,37(4):567-570
The nonsteroidal antiinflammatory drug ketoprofen (KTP) is a commonly used antiinflammatory and analgesic agent in reptile medicine, but no studies documenting its pharmacokinetics in this species have been published. Ketoprofen was administered as a racemic mixture to green iguanas (Iguana iguana) intravenously (i.v.) and intramuscularly (i.m.) at 2 mg/kg. Pharmacokinetic analyses were performed and indicated that ketoprofen in iguanas administered by the intravenous route has a classical two-compartmental distribution pattern, a slow clearance (67 ml/ kg/hr) and a long terminal half-life (31 hr) compared to ketoprofen studies reported in mammals. When delivered by the intramuscular route, bioavailability was 78%. These data indicate the daily dosing that is generally recommended for reptile patients, as an extrapolation from mammalian data, may be more frequent than necessary. 相似文献
52.
Amanda B McLaughlin Jonathan H Epstein Vibhu Prakash Craig S Smith Peter Daszak Hume E Field Andrew A Cunningham 《Journal of zoo and wildlife medicine》2007,38(3):446-452
Although bats of the genus Pteropus are important ecologically as pollinators and natural hosts for zoonotic pathogens, little is known about their basic physiology. Hematology and plasma biochemistries were determined from wild-caught flying foxes (Pteropus giganteus) in northern India (n=41). Mean lymphocyte differential count was higher for juveniles than adults. Mean platelet count was lower than previously reported. No hemoparasites were observed. No differences were observed between plasma biochemistry values of male and female bats, juveniles and adults, or lactating and nonlactating females. Variation in aspartate aminotransferase (AST) was seen based on body condition score. Blood urea nitrogen and cholesterol concentrations were lower in P. giganteus than other mammalian groups, but were consistent with those reported from other Pteropus species. Alanine aminotransferase and AST concentrations were higher than those reported for Pteropus vampyrus, a closely related species. This study provides basic physiologic information that can be used in future health and disease studies of Indian flying foxes. 相似文献
53.
Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability 总被引:1,自引:2,他引:1
While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts
to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber
harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial
private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily
for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of
forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends
were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest
types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the
average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes
decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased
while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity
of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners.
The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns
for forest sustainability. 相似文献
54.
FACIAL FIBROSARCOMA IN TWO COWS 总被引:1,自引:0,他引:1
Lisa G. Britt DVM MS Ohn R. Middleton DVM Reginlad A. Valdez DVM MS Russell L. Tucker DVM Steven M. Parish DVM Jeff W. Tyler DVM PhD 《Veterinary radiology & ultrasound》1998,39(1):18-21
Fibrosarcoma is a common tumor affecting bone, but is uncommon in cows, Reported here are two bovine cases of facial fibrosarcoma that were very invasive. 相似文献
55.
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
56.
Quantity and characteristics of microorganisms associated with ruminal fluid or particles 总被引:4,自引:0,他引:4
An experiment was conducted to 1) determine quantity of microbial CP and DM associated with undigested feed particles, 2) quantify the amount of microorganisms removed from ruminally incubated forages and 3) compare forage disappearances (D) corrected for microbial contamination, using diaminopimelic acid (DAPA) ratios obtained from particle-associated or fluid-associated microorganisms. Samples of alfalfa hay, bermudagrass hay and orchardgrass hay placed in dacron bags were incubated via ruminal cannula for 6 and 12 h. Whole ruminal contents (WRC) were sampled at the time of bag removal and partitioned into fluid- and particle-associated microorganisms. Particle-associated microorganisms were further divided into loosely-associated (LA) and firmly associated (FA) microorganisms. Percentage microbial CP and DAPA, quantities of OM, CP (mg) and DAPA (micrograms), microbial contamination and microbial contribution to ruminal contents were not affected by time (P greater than .05). The highest concentrations of CP and DAPA were found in fluid and LA, respectively (P less than .01). The total amount (content) of OM, CP and DAPA were highest in FA and lowest in microbes in the fluid fraction. Firmly-associated microorganisms constituted 54.1% of the particle-associated population. Corrected DMD were higher (P less than .01) based on FA than on fluid and LA microbe compositions. Corrected CPD were similar (P greater than .10) between populations except at 6 h, when LA corrected CPD were lower. Theoretically, using FA microorganisms should give the most accurate correction for microbial contamination. However, results indicate that, although the three populations differed in composition, fluid and FA corrected CPD were similar. Corrections based on composition of any of these three populations will yield higher estimates of disappearance compared with uncorrected values. 相似文献
57.
David J. Wise Phillip H. Klesius Craig A. Shoemaker William R. Wolters 《Journal of the World Aquaculture Society》2000,31(2):206-212
These studies were conducted to evaluate the efficacy of a live attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish. In one study channel catfish fingerlings (72 d of age post hatch) were immersed for 30 min in water containing E. ictaluri RE-33 at dosages of 1 × 106 , 1 × 107 and 2 × 107 CFU/ML of water. No mortalities were observed following vaccination. Following exposure to virulent Edwardsiella ictaluri the cumulative mortality of fish vaccinated with dosages of at least 1 × 107 CFU/mL were significantly lower than that of non-vacccinated fish in both laboratory and field challenges. Vaccination with 1 × 106 CFU RE-33mL provided some protection during the laboratory challenge but failed to protect fish under field conditions. In a second study, vaccination of 6 full-sib families of channel catfish at a vaccine dosage of 1 × 107 CFU/mL resulted in a relative percent survival among families ranging from 67.1 to 100%. Significant differences in mortality were found among families and between vaccinated and unvaccinated groups, but there was no family by vaccine interaction. Families with the highest mortality after vaccination were also shown to have the highest mortality without vaccination (r = 0.82; P = 0.04). 相似文献
58.
The cis and trans isomers of the synthetic pyrethroid resmethrin, labelled with radiocarbon in either the alcohol or acid moiety, were individually administered orally to White Leghorn laying hens at a dosage of 10 mg kg?1. With each isomer and label position, greater than 90% of the radiocarbon was eliminated in the excreta within 24 h after the treatment. Radiocarbon residues in the egg white and yolk fractions were low, with peak levels observed 1 and 4-5 days after treatment in white and yolk, respectively. In birds sacrificed 12 h after treatment, radiocarbon residues in tissues were low; the highest levels were found in the liver and kidney. 相似文献
59.
H. G. Zuckerman C. H. Metzger B. A. Brown W. B. Ward Frank W. Hussey R. W. Donaldson E. E. Isaac Marx Koehnke William H. Martin K. H. Fernow E. V. Hardenburg Robert Schmidt E. M. Gillig E. B. Tussing E. R. Jackman T. E. Odland S. P. Swenson John Tucker 《American Journal of Potato Research》1936,13(8):223-232
60.
Monensin was added at 0 or 23 mg/kg dry matter to low (8.3%) or high (17.5%) crude protein diets (2 X 2 factorial arrangement) that were fed to 28 growing wether goats for 194 to 256 d. Average daily gain increased 24% with monensin and 20% with higher crude protein (P less than .05). Feed conversion was improved by both monensin and higher crude protein (P less than .001). During the experiment, digestion and metabolism trials were conducted twice (Periods I and II) with each goat. Apparent dry matter and gross energy digestibility coefficients were not affected by monensin in either period. Digestibility of dietary N was enhanced 7% by monensin in Period II (P less than .01) and tended to be improved in Period I. Higher dietary protein increased all digestibility coefficients (P less than .001). Nitrogen retention was not affected by monensin but was greater (P less than .001) for high-protein-fed goats. Potential changes in empty body composition were assessed by comparative slaughter balance. No effects of dietary treatments on percentage composition of empty body were noted, except a trend for higher protein in monensin-fed goats compared with controls (P less than .1). Empty body protein gain as a percentage of protein intake improved 41% with monensin and decreased 37% with higher dietary protein content (P less than .05). Monensin increased conversion of dietary energy to body ether extract energy (12%, P less than .05), to protein energy (35%, P less than .001) and to total body energy (23%, P less than .001). Magnitude of improvement tended to be greater with low than high dietary protein treatments, suggesting a protein-sparing effect of monensin as determined by comparative slaughter method. However, N retention, measured by intake-excreta balances, was not affected by monensin, suggesting that these point estimates are less than adequate to evaluate true body protein gain. 相似文献