全文获取类型
收费全文 | 62702篇 |
免费 | 3557篇 |
国内免费 | 45篇 |
专业分类
林业 | 2566篇 |
农学 | 1915篇 |
基础科学 | 310篇 |
7017篇 | |
综合类 | 10600篇 |
农作物 | 2192篇 |
水产渔业 | 3008篇 |
畜牧兽医 | 33987篇 |
园艺 | 767篇 |
植物保护 | 3942篇 |
出版年
2018年 | 945篇 |
2017年 | 981篇 |
2016年 | 877篇 |
2015年 | 823篇 |
2014年 | 904篇 |
2013年 | 2680篇 |
2012年 | 1827篇 |
2011年 | 2187篇 |
2010年 | 1374篇 |
2009年 | 1326篇 |
2008年 | 2029篇 |
2007年 | 2002篇 |
2006年 | 1887篇 |
2005年 | 1733篇 |
2004年 | 1625篇 |
2003年 | 1670篇 |
2002年 | 1599篇 |
2001年 | 1835篇 |
2000年 | 1800篇 |
1999年 | 1484篇 |
1998年 | 641篇 |
1997年 | 633篇 |
1996年 | 562篇 |
1995年 | 666篇 |
1994年 | 619篇 |
1993年 | 582篇 |
1992年 | 1233篇 |
1991年 | 1385篇 |
1990年 | 1272篇 |
1989年 | 1283篇 |
1988年 | 1174篇 |
1987年 | 1147篇 |
1986年 | 1199篇 |
1985年 | 1206篇 |
1984年 | 971篇 |
1983年 | 918篇 |
1982年 | 596篇 |
1979年 | 899篇 |
1978年 | 708篇 |
1977年 | 703篇 |
1976年 | 719篇 |
1975年 | 720篇 |
1974年 | 873篇 |
1973年 | 849篇 |
1972年 | 817篇 |
1971年 | 728篇 |
1970年 | 775篇 |
1969年 | 741篇 |
1968年 | 651篇 |
1967年 | 658篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
A.A. Twaddle B.V.Sc. M.R.C.V.S. 《New Zealand veterinary journal》2013,61(1-2):26-27
Abstract Extract Rural veterinary practice faces difficulties in many parts of the world. Falling farm incomes and increasing costs have sometimes resulted in reduced use of veterinary services. There seems to be widespread agreement that an increased emphasis on preventive medicine would improve the situation for both the farmer and his veterinarian. There appear to be no commonly agreed formal criteria for the development and evaluation of health programmes, either in human or veterinary medicine, but increasing attention is being paid to the problem(1) (12) (14) (15), In some ways the evaluation of animal health programmes should be the easier, for there are fewer ethical problems and economic criteria are of paramount importance in rural practice. 相似文献
142.
T.M. Skerman M.Sc. Ph.D. I.M. Cairney B.V.Sc. M.R.C.V.S. 《New Zealand veterinary journal》2013,61(11):205-211
Extract I have taken as my subject for this address the topic, “Change”, and will deal with two aspects of change, one the challenge of change due to new knowledge and techniques and second the change we must make in our attitude to other agricultural disciplines and ancillary veterinary personnel. 相似文献
143.
In grasses and clovers the highest concentrations of selenium were found in the leaves. The selenium content of different species in spring pastures on the same soil type did not vary widely although the slower growing and more deeply rooting species contained higher levels. The concentration of selenium in a pasture varied with time of the year, the lower levels being usually associated with conditions that stimulated rapid growth of the herbage, although factors other than growth rate were also involved. Lucerne appeared to be unusual in that in some areas it accumulated much higher levels of selenium than was found in other associated species. A very wide variation in levels of selenium in pastures growing on different soils has been observed (3-1500 ng/g). Selenium-responsive unthriftiness in grazing lambs occurred where the selenium content of spring pastures was <20 ng/g. Pastures containing >30 ng/g were apparently adequate while intermediate levels were probably marginally deficient. 相似文献
144.
145.
K.R. Viviano B. VanderWielen 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2013,27(2):250-258
Background
Antioxidant depletion and lipid peroxidation have been correlated with disease severity and associated with poor outcomes.Hypothesis/Objectives
Supplementing dogs with N‐acetylcysteine (NAC) during the first 48 hours of hospitalization will increase cysteine, normalize glutathione concentrations, and decrease the degree of lipid peroxidation associated with illness.Animals
Sixty systemically ill hospitalized client‐owned dogs and 14 healthy control dogs.Methods
Randomized investigator‐blinded, placebo‐controlled prospective study. Dogs were randomized to treatment with NAC (n = 30) versus placebo (n = 30). Antioxidants, urine 8‐isoprostane/creatinine (IP/Cr), and clinical score were determined before and after treatment with NAC. Glutathione, cysteine, and vitamin E concentrations were quantified using high‐performance liquid chromatography. Atomic absorption spectroscopy and enzyme‐linked immunosorbent assays were used to quantify selenium and isoprostane concentrations, respectively.Results
Ill dogs had significantly lower vitamin E concentrations (27 versus 55 μg/mL; P = .0005) as well as elevated IP/Cr ratios (872 versus 399 pg/mg; P = .0007) versus healthy dogs. NAC supplementation significantly increased plasma cysteine (8.67 versus 15.1 μM; P < .0001) while maintaining glutathione concentrations. Dogs in the placebo group experienced a statistically significant decrease in glutathione concentrations (1.49 versus 1.44 mM; P = .0463). Illness severity and survival were unchanged after short duration NAC supplementation.Conclusions
Ill dogs experience systemic oxidative stress. Supplementation with NAC during the first 48 hours of hospitalization stabilized erythrocyte glutathione concentrations. The clinical impact of this supplementation and glutathione concentration stabilization was undetermined. 相似文献146.
J.M. Kelsey B.Sc. 《New Zealand veterinary journal》2013,61(5):109-112
Extract This experiment was designed primarily to compare the efficacy of two heat-concentrated synthetic medium tuberculins, one prepared from strains of Mycobacterium bovis and the other from Mycobacterium tuberculosis, when used in tuberculin testing of cattle. 相似文献
147.
Extract Scouring syndromes constitute a major disease group in dairy calves in New Zealand. 相似文献
148.
D.T. Beakenridge B.V.Sc. 《New Zealand veterinary journal》2013,61(6):166-167
Extract Mange in pigs caused by Sarcoptes scabiei var. suis is reported to be common in New Zealand, but, to the writer's knowledge, no investigation has been made of the number of infested farms in any area. 相似文献
149.
R. Barry Nehring B. Hancock M. Catanese M. E. T. Stinson D. Winkelman J. Wood 《Journal of aquatic animal health》2013,25(3):205-220
Abstract Elucidating the dynamics of a parasitic infection requiring two hosts in a natural ecosystem can be a daunting task. Myxobolus cerebralis (Mc), the myxozoan parasite that causes whirling disease in some salmonids, was detected in the Colorado River upstream of Windy Gap Reservoir (WGR) in 1988. Subsequently, whirling disease was implicated in the decline of wild Rainbow Trout Oncorhynchus mykiss in the river when WGR was identified as a point source of Mc triactinomyxons (TAMs). Between 1997 and 2004, numerous investigations began to elucidate the etiology of Mc in WGR. During this period, Mc TAM production in WGR declined more than 90%. Explanations for the decline have included differences in stream discharge between years, changes in the thermal regime of the lake, severe drought, changes in the fish population structure in WGR, and reductions in the prevalence and severity of Mc infection in salmonids in the Colorado and Fraser rivers upstream of WGR. All of these have been discredited as explanations for the reduced TAM production. In 2005, a new study was conducted to replicate the studies completed in 1998. In this paper, the results of a new real-time polymerase chain reaction assay utilized to quantify the mitochondrial 16S rDNA specific to each of four lineages of Tubifex tubifex in pooled samples of 50 oligochaetes are presented. These results suggest that compared with 1998, the densities of aquatic oligochaetes and T. tubifex have increased, TAM production has been greatly reduced, and the decline is congruent with the dominance of lineages I, V, and VI of T. tubifex—three lineages that are refractory or highly resistant to Mc infection—in the oligochaete population. While it is possible that the resistant lineages function as biofilters that deactivate Mc myxospores, the reason for the decline in TAM production in WGR remains an enigma. Received February 15, 2012; accepted March 17, 2013 相似文献
150.
SILKE HECHT GREGORY B. DANIEL SALLY K. MITCHELL 《Veterinary radiology & ultrasound》2006,47(6):602-608
Diuretic renal scintigraphy is commonly used in human medicine to differentiate obstructive from nonobstructive pyelectasia. In order to determine normal parameters, 99mTc-DTPA renal scintigraphy was performed twice in 20 healthy adult Mongrel dogs. Each dog was injected with either 3.0 mg/kg furosemide or an equivalent volume of saline 4.5 min following injection of the radiopharmaceutical. The following parameters were evaluated: (1) global and individual glomerular filtration rate (GFR); (2) time of peak (TOP) of the time-activity curve (TAC); (3) shape of the TAC; (4) individual kidney excretion half-time (T1/2); (5) proportion of maximum activity measured at end of study (8 min); (6) time of onset; and (7) duration of the effect of the diuretic. Most TAC in the diuretic renography group showed a steep drop in the curve following administration of the diuretic compared with a gradual slope in the saline control group. There was a statistically significant difference in T1/2 between the control renograms (median 10.25 min, range 4.41-18.07 min) and the diuretic renograms (median 4.16 min, range 3.62-5.90 min). There was a statistically significant difference in percentage maximum activity between the control renograms (median 65.25%, range 48.27-93.68%) and the diuretic renograms (median 48.54%, range 35.64-58.76%). Median time of onset of the diuretic effect was 1.10 min (0.20-2.40 min), and median duration was 0.83 min (0.30-2.35 min). 相似文献