全文获取类型
收费全文 | 420篇 |
免费 | 19篇 |
专业分类
林业 | 2篇 |
农学 | 9篇 |
27篇 | |
综合类 | 59篇 |
农作物 | 47篇 |
水产渔业 | 40篇 |
畜牧兽医 | 231篇 |
园艺 | 13篇 |
植物保护 | 11篇 |
出版年
2020年 | 13篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2008年 | 20篇 |
2007年 | 12篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 19篇 |
1999年 | 11篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 5篇 |
1974年 | 11篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1969年 | 3篇 |
1968年 | 8篇 |
1966年 | 5篇 |
1953年 | 3篇 |
1939年 | 3篇 |
1937年 | 3篇 |
1936年 | 5篇 |
1935年 | 5篇 |
1934年 | 5篇 |
1930年 | 3篇 |
1926年 | 3篇 |
1925年 | 3篇 |
1924年 | 6篇 |
排序方式: 共有439条查询结果,搜索用时 15 毫秒
101.
Walter G. Whitford Diana W. Freckman Ned Z. Elkins Lawrence W. Parker Rob Parmalee Janice Phillips Suzanne Tucker 《Soil biology & biochemistry》1981,13(5):417-425
Diurnal patterns of microarthropod abundance in surface leaf litter were related to its moisture content. Leaf litter moisture was nearly 7% by weight at 0800h but fell to less than 1% by mid-day. Oribatid and tydeid mites moved into litter in the early morning and back into the soil before mid-day. There were no significant differences in numbers of nematodes in litter or soil and 78–98% of the nematodes were anhydrobiotic (coiled) in soil and litter at all times sampled.Following simulated rainfall there were fewer microarthropods in litter at mid-day in the absence of marked decreases in soil and litter moisture content. During drying, there were gradual reductions in numbers and species diversity of litter microarthropods. Nematode numbers did not change as litter dried. Anhydrobiotic nematodes in the soil increased from 14% on day 1 to 85% on day 4. Between 24 and 36 h after simulated rainfall, the proportion of anhydrobiotic litter nematodes increased from 35 to 80%,.Within 1 h after simulated rainfall, there were marked increases in numbers and diversity of microarthropods in surface litter. No collembolans were extracted from dry litter controls but the wet litter was dominated by isotomid, sminthurid and onychiurid collembolans. There were increases in numbers and diversity of oribatid, tydeid and gamasid mites in the wet surface litter within l h after wetting compared to controls. 相似文献
102.
Colbourne JK Pfrender ME Gilbert D Thomas WK Tucker A Oakley TH Tokishita S Aerts A Arnold GJ Basu MK Bauer DJ Cáceres CE Carmel L Casola C Choi JH Detter JC Dong Q Dusheyko S Eads BD Fröhlich T Geiler-Samerotte KA Gerlach D Hatcher P Jogdeo S Krijgsveld J Kriventseva EV Kültz D Laforsch C Lindquist E Lopez J Manak JR Muller J Pangilinan J Patwardhan RP Pitluck S Pritham EJ Rechtsteiner A Rho M Rogozin IB Sakarya O Salamov A Schaack S Shapiro H Shiga Y Skalitzky C Smith Z Souvorov A Sung W 《Science (New York, N.Y.)》2011,331(6017):555-561
We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges. 相似文献
103.
D K Beede G T Schelling G E Mitchell R E Tucker W W Gill S E Koenig T O Lindsey 《Journal of animal science》1986,62(3):857-863
Two digestion and metabolism experiments were conducted to determine effects of monensin in low-protein diets. Monensin supplementation (27 mg/kg of diet dry matter) of steers (303 kg) fed 8.7% crude protein increased (P less than .01) apparent N digestibility and N retention and decreased (P less than .01) percentage of N apparently absorbed lost in urine. Apparent digestibilities of dry matter, gross energy and acid detergent lignin were increased (P less than .05). Digestibilities of neutral detergent and acid detergent fibers were not affected by monensin. In growing wether goats (15 kg) fed 8.5% crude protein, monensin (23 mg/kg of diet dry matter) improved (P less than .01) apparent N digestibility and apparent N absorption. However, urinary N excretion also increased (P less than .05), resulting in no difference in N retention. Monensin did not affect digestibilities of dry matter or gross energy. Efficiency of feed conversion and average daily gain were improved with monensin supplementation of growing goats fed a low-protein, high-roughage diet. Monensin resulted in typical shift of acetate-to-propionate ratio in both experiments. Results suggest that improved N utilization may account for some benefits of feeding monensin. 相似文献
104.
David O. Wallin Clive C. H. Elliott Herman H. Shugart Compton J. Tucker Friedrich Wilhelmi 《Landscape Ecology》1992,7(2):87-99
Data derived from the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA series of operational, polar orbiting,
meteorological satellites have previously been shown to be quite useful for monitoring vegetation dynamics at scales ranging
from regional (104 km2) to global. In this report, we demonstrate that these same data can be used to monitor potential breeding habitat for a highly
mobile, granivorous African weaver-bird, the red-billed quelea (Quelea quelea). This species is often considered to be an agricultural pest, affecting cereal production throughout sub-Saharan Africa.
The temporal resolution and very large (continental) spatial coverage provided by these data can provide a unique context
within which to examine species distribution and abundance patterns. 相似文献
105.
Effects of photoperiod on growth, eating patterns and clearance rate, secretion rate and half-life of growth hormone in serum were assessed in Holstein heifers. Sixty-four prepubertal heifers (avg body wt 102 kg) were blocked by weight into four groups of 16. Within block, each animal was randomly assigned to one of four photoperiod treatments: 16 h of cool-white fluorescent light:8 h dark (CW-16L:8D), CW-8L:16D, CW-6L:8D:2L:8D or 16 h of VitaLite fluorescent light:8D (V-16L:8D). Animals were fed ad libitum a complete mixed diet formulated for heifers to gain approximately .9 kg/d. Average daily body weight gains were .93, .96, .98 and 1.0 kg/d during 112 d of exposure to CW-8L:16D, CW-6L:8D:2L:8D, CW-16L:8D and V-16L:8D, respectively. Heifers exposed to V16L:8D and CW-16L:8D gained more weight (112 and 110 kg; P less than .05 and P less than .08, respectively) than heifers exposed to CW-8L:16D (104 kg). Body weight gain was not different (P greater than .10) between heifers exposed to CW-6L:8D:2L:8D (108 kg) or CW-8L:16D, or between heifers exposed to CW-16L:8D or V-16L:8D. Total number of eating events in 30 h and percentage of total events in the lighted period were 549 and 96% and 523 and 50% in heifers exposed to CW-16L:8D and CW-8L:16D, respectively. Clearance rates (620 vs 636 ml/min), secretion rates (3.0 vs 3.8 micrograms/min) and half lives (17.2 vs 17.9 min) of growth hormone in serum were similar in heifers exposed to CW-16L:8D and CW-8L:16D.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
106.
Russell L. Tucker DVM Gregory B. Daniel DVM MS Sandra L. Daniel DVM MS PhD Theresa Buckman AHT 《Veterinary radiology & ultrasound》1992,33(4):241-246
Technetium-99m hexamethylpropyleneamine oxine (99m Tc-HMPAO) and Indium-111 oxine (111 In-oxine) labeled canine gramulocytes were evaluated in vitro over a six hour period. Labeling efficiency for 99m TC-HMPAO and 111 In-oxine labeled granulocytes was 39.6%± 8.0% and 60.6%± 17.6% (mean ± SD) respectively. The mean in vitro elution of the radiolabel ranged from 8.7-14.0% for the 99m Tc-HMPAO grannulocytes and from 6.1-9.0% for the 111 In-oxine granulocytes. Mean cell viability, for the 99m Tc-HMPAO, 111 In-oxine and non-radiolabeled control granulocytes ranged from 97.8-99.4%, 96.4-98.5% and 98.2-99.0%, respectively. The phagocytic ability of the 99m Tc-HMPAO, 111 In-oxine and control granulocytes ranged from 47.5-54.1%, 38.9-56.2% and 46.6-57.8% respectively over the six hour study period. Although labeling efficiency using 111 In-oxine was significantly (P=0.05) better than 99m Tc-HMPAO, there was no significant difference in label retention of the two radiolabels. There was no significant difference in viability or phagocytic function during the six hour study period. Considering the potential cost advantage and the superior imaging qualities of Technetium-99m relative to Indium-111, 99m Tc-HMPAO appears to be a good alternative to 111 In-oxine as a granulocyte label. 相似文献
107.
108.
Birkenheuer AJ Le JA Valenzisi AM Tucker MD Levy MG Breitschwerdt EB 《Journal of the American Veterinary Medical Association》2006,228(4):568-571
OBJECTIVE: To describe the demographic and clinical characteristics of feline cytauxzoonosis in the mid-Atlantic states and compare the Cytauxzoon felis 18S rRNA gene sequences from affected cats with sequences reported from affected cats in other regions. DESIGN: Retrospective case series. ANIMALS: 34 cats with C. felis infection. PROCEDURE: Medical records of cats in which C. felis infection was diagnosed from May 1998 through June 2004 were reviewed; data collected included signalment, month of diagnosis, geographic location, clinicopathologic abnormalities, medical treatments, outcome, and necropsy findings when applicable. Cytauxzoon felis DNA was amplified, cloned, and sequenced from 4 of these cats and compared with previously reported C. felis DNA sequences. RESULTS: Of 34 C. felis-infected cats, 28 resided in North Carolina, 3 resided in South Carolina, and 3 resided in Virginia; in 32 cats, a diagnosis of C. felis infection was made in April through September. Pancytopenia and icterus were the most common clinicopathologic abnormalities. Thirty-two cats either died or were euthanatized, and 2 cats survived. At 5 veterinary hospitals, multiple cases were identified, and 4 multicat households had > 1 cat infected with C. felis. The 18S rRNA gene sequences characterized in organisms obtained from 4 cats were nearly identical to C. felis DNA sequences reported from other US regions. CONCLUSIONS AND CLINICAL RELEVANCE: Data indicate that veterinarians in the mid-Atlantic region of the United States should consider C. felis infection in cats that become ill with fever, icterus, and pancytopenia or bicytopenia, especially in the spring and summer months. 相似文献
109.
110.