全文获取类型
收费全文 | 491篇 |
免费 | 21篇 |
专业分类
林业 | 12篇 |
农学 | 9篇 |
基础科学 | 6篇 |
69篇 | |
综合类 | 154篇 |
农作物 | 13篇 |
水产渔业 | 24篇 |
畜牧兽医 | 187篇 |
园艺 | 9篇 |
植物保护 | 29篇 |
出版年
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 21篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1997年 | 5篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1974年 | 14篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 11篇 |
1968年 | 5篇 |
1967年 | 4篇 |
1930年 | 5篇 |
1920年 | 4篇 |
1904年 | 4篇 |
1901年 | 3篇 |
排序方式: 共有512条查询结果,搜索用时 31 毫秒
1.
C A Osborne T D O'Brien H K Ghobrial L Meihak J B Stevens 《Veterinary Clinics of North America: Small Animal Practice》1986,16(1):45-65
Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis. 相似文献
2.
Abstract. Soil samples from a 32-year grassland field experiment were taken from 0–5, 5–10, and 10–15 cm soil depths in February 2002. Plots received annual treatments of unamended control, mineral fertilizer, three rates of pig slurry and three rates of cow slurry, each with six replicates. Samples were analysed for cation exchange capacity (CEC), exchangeable cations (Na+ , K+ , Ca2+ , Mg2+ ), pH and Olsen P. Exchangeable sodium percentage (ESP) was calculated as a sodicity indicator. Mean ESP was generally greater for slurry treatments than the control, with a trend of increasing ESP with application rate. This was particularly marked for cow slurry. At 0–5 cm depth ESP increased from 1.18 in the control to 1.75 at the highest rate of pig slurry and 5.60 at the highest rate of cow slurry. Similar trends were shown for CEC, exchangeable Na+ , K+ and Mg2+ , Ca2+ and Olsen P. The build-up of soil P due to slurry applications, together with this combination of physical and chemical factors, may increase the risk of P loss to surface waters, particularly from soils receiving high rates of cow slurry. 相似文献
3.
Hill D Correa MT Stevens JB 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1994,23(3):73-75
Azostix-reagent-tests(R) strips (Ames, Miles, Inc., Diagnostic Division, Elkhart, IN) were used to measure blood urea nitrogen values in blood samples from 125 dogs and cats at the North Carolina State University, College of Veterinary Medicine. Results of the tests were compared with standard serum urea nitrogen results. Sensitivity, specificity, and negative predictive values were high (86.4, 90.3, and 96.5%, respectively). Positive predictive value was low, 65.5% of the dogs and cats with elevated blood urea nitrogen values were correctly classified as abnormal The test performs well when the prevalence of abnormal values is near 50%. 相似文献
4.
Singleton Megan P. Thode Andrea E. Sánchez Meador Andrew J. Iniguez Jose M. Stevens Jens T. 《Landscape Ecology》2021,36(12):3429-3449
Landscape Ecology - Spatial patterns of high-severity wildfire in forests affect vegetation recovery pathways, watershed dynamics, and wildlife habitat across landscapes. Yet, less is known about... 相似文献
5.
Stevens R Buret M Garchery C Carretero Y Causse M 《Journal of agricultural and food chemistry》2006,54(17):6159-6165
We present a technique for easy, rapid analysis of both total and reduced forms of vitamin C in fruits using microplates and a plate reader. This technique has been compared with a spectrofluorometric technique classically used for assaying vitamin C in fresh tomato. We have applied these methods to a population of 118 tomato mutant lines and controls in search of variability for this trait. Six lines, identified as having high vitamin C levels, and four lines having low vitamin C levels have been chosen for further study. The vitamin C levels have been compared with sugar concentration, dry matter content, fruit weight, titratable acidity, and firmness. The correlations that often exist in tomato varieties between sugar and vitamin C content (positive correlation) or fruit weight and vitamin C content (negative correlation) can be uncoupled in the lines selected for further analysis. 相似文献
6.
7.
The importance of predicting grass N yield lies in its controlling influence on grass DM output and thus on animal production. Results from 88 experiments studying the use of fertilizer N on cut grass swards show that the major part (97%) of the variation in grass N yield could be explained in terms of fertilizer N rate, an estimate of soil N and an interaction between the two. From this, it appears that high fertilizer N recovery is associated with a high uptake of soil N and vice versa. 相似文献
8.
The development of resistance is the main threat to the long-term use of toxins from Bacillus thuringiensis (Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene, Caenorhabditis elegans bre-5, which encodes a putative beta-1,3-galactosyltransferase. Lack of bre-5 in the intestine led to resistance to the Bt toxin Cry5B. Wild-type but not bre-5 mutant animals were found to uptake toxin into their gut cells, consistent with bre-5 mutants lacking toxin-binding sites on their apical gut. bre-5 mutants displayed resistance to Cry14A, a Bt toxin lethal to both nematodes and insects; this indicates that resistance by loss of carbohydrate modification is relevant to multiple Bt toxins. 相似文献
9.
Distribution and properties of geographically distinct isolates of sugar beet yellowing viruses 总被引:1,自引:0,他引:1
M. Stevens N. J. Patron ‡ C. A. Dolby R. Weekes § P. B. Hallsworth O. Lemaire H. G. Smith 《Plant pathology》2005,54(2):100-107
From a total of 261 yellow sugarbeet leaves collected from 10 countries representing three continents, the incidence and distribution of strains of Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV) and Beet yellows virus (BYV) were analysed using serological and molecular methods. BMYV was found in all countries except Greece, and more frequently in the northern and western areas of Europe, whereas BYV predominated in Turkey, Spain, Greece, the USA and Chile. BChV, originally found in the USA and the UK in 1989, was identified in France, Spain, the Netherlands and Chile. Nine sugar beet poleroviruses, plus a reference isolate of Turnip yellows virus (TuYV, syn. Beet western yellows virus ), were further characterized and compared. Isolates obtained from sugar beet infected this species, but not oilseed rape or lettuce; all isolates except one infected Capsella bursa-pastoris . The coat-protein sequences of these isolates were highly similar, with the consensus sequence representing 89% of nucleotide residues. Within the coat-protein gene, two regions were identified that could represent specific epitopes to which monoclonal antibody BYDV-PAV-IL-1 could bind; this antibody is used to distinguish beet poleroviruses in ELISA. Comparison of the sequences at the 5' end showed that sequence homology existed only between isolates with the same host range. The first sequence data of polerovirus isolates from Chile are presented, showing that the coat protein and the 5' end of their genomes are highly similar to those of BMYV isolates found in Europe. Chilean polerovirus isolates may have been imported from the northern hemisphere in sugar beet breeding material. 相似文献
10.
Lisa L Farina Darryl J Heard Dana M LeBlanc Jeffery O Hall Gary Stevens James F X Wellehan Carol J Detrisac 《Journal of zoo and wildlife medicine》2005,36(2):212-221
This study evaluated the relationship between blood iron parameters and hepatic iron concentrations, and correlation of histologic findings with hepatic iron concentrations in a captive population of Egyptian fruit bats (Rousettus aegyptiacus) and island flying foxes (Pteropus hypomelanus). Blood samples were collected for complete blood counts, plasma biochemical profiles, serum iron concentrations, total iron-binding capacity, whole-blood lead concentrations, and plasma ferritin assays. Liver samples obtained by laparotomy were divided, with one half processed for histologic examination and the other half frozen and submitted for tissue mineral analysis. The histologic sections were scored by two blinded observers for iron deposition, necrosis, and fibrosis. The Egyptian fruit bats had significantly higher liver iron (mean = 3,669 +/- 1,823 ppm) and lead (mean = 8.9 +/- 5.8 ppm) concentrations than the island flying foxes (mean [Fe] = 174 +/- 173 ppm, mean [Pb] = 1.9 +/- 0.5 ppm). Hepatic iron concentrations significantly correlated with tissue lead concentrations, histologic grading for iron and necrosis, serum iron, transferrin saturation, and plasma ferritin (P < 0.001). Blood lead concentrations negatively correlated with tissue lead concentrations (P < 0.001). When the product of transferrin saturation and serum iron was greater than 51, an individual animal had a high probability of having iron overload. When the product of these two variables was greater than 90, there was a high probability that the animal had hemochromatosis. On the basis of this study, it appears that evaluation of serum iron, transferrin saturation, and plasma ferritin are useful and noninvasive methods for diagnosis of hemochromatosis in Egyptian fruit bats. 相似文献