全文获取类型
收费全文 | 184566篇 |
免费 | 10133篇 |
国内免费 | 117篇 |
专业分类
林业 | 7768篇 |
农学 | 5972篇 |
基础科学 | 1288篇 |
22102篇 | |
综合类 | 29861篇 |
农作物 | 6846篇 |
水产渔业 | 9492篇 |
畜牧兽医 | 96638篇 |
园艺 | 2319篇 |
植物保护 | 12530篇 |
出版年
2018年 | 2412篇 |
2017年 | 2634篇 |
2016年 | 2525篇 |
2015年 | 2197篇 |
2014年 | 2632篇 |
2013年 | 7019篇 |
2012年 | 4907篇 |
2011年 | 6118篇 |
2010年 | 3903篇 |
2009年 | 3883篇 |
2008年 | 5956篇 |
2007年 | 5744篇 |
2006年 | 5601篇 |
2005年 | 5164篇 |
2004年 | 4992篇 |
2003年 | 5007篇 |
2002年 | 4798篇 |
2001年 | 6067篇 |
2000年 | 5843篇 |
1999年 | 4772篇 |
1998年 | 1907篇 |
1997年 | 1918篇 |
1996年 | 1791篇 |
1995年 | 2159篇 |
1994年 | 1967篇 |
1993年 | 1874篇 |
1992年 | 3931篇 |
1991年 | 4147篇 |
1990年 | 4261篇 |
1989年 | 4150篇 |
1988年 | 3838篇 |
1987年 | 3943篇 |
1986年 | 3968篇 |
1985年 | 3825篇 |
1984年 | 3235篇 |
1983年 | 2789篇 |
1982年 | 1958篇 |
1981年 | 1790篇 |
1980年 | 1736篇 |
1979年 | 2881篇 |
1978年 | 2332篇 |
1977年 | 1961篇 |
1976年 | 1832篇 |
1975年 | 1906篇 |
1974年 | 2529篇 |
1973年 | 2522篇 |
1972年 | 2509篇 |
1971年 | 2265篇 |
1970年 | 2137篇 |
1969年 | 1983篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Newby TJ Stokes CR Huntley J Evans P Bourne FJ 《Veterinary immunology and immunopathology》1979,1(1):37-47
The immune response of pigs fed 200 mg per day of dinitrophenylated bovine gamma globulin has been evaluated in terms of the antibody and lymphocyte responses and of the induction of tolerance and immune exclusion. Although dosing for ten days resulted in a small IgA response as indicated by splenic plaque forming cells, serum antibody could only be detected when dosing was continued for 42 days. secretory antibody was detected at any time. Antigen feeding for two weeks rendered the animals hyporesponsive to subsequent parenteral antigenic challenge but had little effect upon their ability to exclude an oral dose of antigen from the circulation. 相似文献
972.
K. P. Bland 《Veterinary research communications》1979,3(1):125-136
The function and suppression of urine spraying by cats is discussed as also is the source of tom-cat odour. It seems unlikely that tom-cat odour is derived from the lipid in the proximal convoluted tubule of the kidney, however its production by the anal glands has not yet been proven. Although male cats show a flehmen response when sniffing urine, smell seems to play a more important role in reproduction in the female than the male. The available data suggests that valeric acid may function as a female/female pheromone in cats by inducing or facilitating oestrus. Nepetalactone, the active ingredient of catnip, is probably not related to any naturally occurring pheromone in the cat but simply acts as an hallucinogenic drug. 相似文献
973.
Riley JH Lassen ED 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1979,8(1):31-33
The Activated Coagulation Time (ACT) was determined on 10 normal cows. Duplicate samples were taken from each cow. The mean ACT was 145 seconds with a range of 120-180 seconds. Standard deviations were 18 and 13 for the first and second sampling, respectively. Repeatability of the ACT was acceptable. 相似文献
974.
H. A. Van Hoof H. Huttinga A. Knaap H. P. Maas Geesteranus W. H. M. Mosch D. G. J. De Raay-Wieringa 《European journal of plant pathology / European Foundation for Plant Pathology》1979,85(3):87-98
In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten. 相似文献
975.
Concentrations of DDT, TDE, DDE, and sigma DDT were determined in homogenized whole fish samples of 129 northern pike (Esox lucius). These fish were netted between June 1974 and June 1975 in the first 10 km of the Richelieu River flowing in Canadian territory. Two years after the banning of DDT, sigma DDT levels ranged from 0.2 ppm fresh body weight in two-year-old specimens to 1.5 ppm in a six-year-old pike. Residues increased greatly with age, and significant seasonal variations in the sigma DDT levels were found in five- and six-year-old pike. 相似文献
976.
Exposure of Israeli agricultural spray pilots and ground crews to parathion was studied. Measurements were made with personal samplers contianing wet midget impingers; samples were analyzed by gas chromatography. Cockpit air exposure levels during 11-21-minute sampling periods for 12 flights ranged from nearly 0 to 430 microgram/m3. During sampling periods of 30 minutes to 4 hours the threshold limit value (TLV) of 100 microgram/m3 was exceeded in 2 of 19 instances. In seven measurements of ground crew exposures, TLV was not exceeded. Air washing with parathion resulted in airborne contamination of the ground level area at more than three times the TLV. Skin exposure data suggested that this route of exposure was significant for ground crew workers but not for pilots. Calculations based on the present data and standard absorption formula suggested that total daily intake for ground crew, but not for pilots, exceeded the Accepted Daily Intake (ADI) of 5 microgram/kg body weight. Sources of exposure and contamination for ground crew and pilots were identified. Recommended environmental control measures for parathion exposure should include cockpit air filtration, modification in flight patterns, paving landing areas, installation of hosing and drainage, NaOH neutralization point, and separate loading and unloading sites. Personal control measures were suggested as a supplement. 相似文献
977.
The uptake of 2,4,5-T by spines of gorse (Ulex europaeus L.) was limited and not enhanced when picloram was added to the application solution. Translocation of 2,4,5-T in 6-month-old cuttings after treatment of a single spine or lateral branch was poor. The most significant accumulation of translocated herbicide occurred in stem tissue, with lesser amounts detected in root tissues, root nodules, stem apices and flowers. Untreated lateral branches or spines accumulated minimal amounts of herbicide. The pattern and extent of distribution of 2,4,5-T was not increased by addition of picloram. The lack of efficient control of gorse by 2,4,5-T can largely be attributed to its inadequate uptake and lack of true systemic translocation. 相似文献
978.
979.
Culliton BJ 《Science (New York, N.Y.)》1979,204(4392):480-481
980.
The concentration of electrical energy usage in alternating-current motor drives presents an opportunity for substantial conservation. Emerging advances in power semiconductor transistor systems will support a major commerical effort to this end. An alternating-current synthesizer for this purpose may soon be available. The synthesizer produces electricial power of variable and programmable frequency, voltage, and wave form so that performance can be optimized. This technology provides the additional opportunity for fundamental improvements in electrical distribution and usage systems in the longer term. Power processing with semiconductor a-c motor controls is expected to become widespread in the near future. 相似文献