全文获取类型
收费全文 | 3723篇 |
免费 | 216篇 |
国内免费 | 5篇 |
专业分类
林业 | 499篇 |
农学 | 113篇 |
基础科学 | 22篇 |
908篇 | |
综合类 | 394篇 |
农作物 | 133篇 |
水产渔业 | 256篇 |
畜牧兽医 | 1251篇 |
园艺 | 81篇 |
植物保护 | 287篇 |
出版年
2023年 | 21篇 |
2022年 | 45篇 |
2021年 | 76篇 |
2020年 | 72篇 |
2019年 | 82篇 |
2018年 | 96篇 |
2017年 | 114篇 |
2016年 | 107篇 |
2015年 | 89篇 |
2014年 | 108篇 |
2013年 | 245篇 |
2012年 | 217篇 |
2011年 | 227篇 |
2010年 | 148篇 |
2009年 | 154篇 |
2008年 | 227篇 |
2007年 | 199篇 |
2006年 | 172篇 |
2005年 | 161篇 |
2004年 | 137篇 |
2003年 | 141篇 |
2002年 | 142篇 |
2001年 | 75篇 |
2000年 | 57篇 |
1999年 | 52篇 |
1998年 | 35篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 45篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 33篇 |
1991年 | 21篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 21篇 |
1987年 | 22篇 |
1985年 | 24篇 |
1984年 | 16篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1979年 | 16篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1974年 | 16篇 |
1973年 | 19篇 |
1971年 | 13篇 |
1970年 | 23篇 |
1968年 | 14篇 |
排序方式: 共有3944条查询结果,搜索用时 500 毫秒
121.
Müller T Brancq B Milius A Okori N Vaille C Gauvrit C 《Pest management science》2002,58(12):1243-1249
Ethoxylates of rapeseed oil and of methylated rapeseed oil were synthesized and tested as adjuvants for 2,4-D and phenmedipham. Provided they had less than 6 units of ethylene oxide (EO), 1.0 to 10 g litre(-1) ethoxylates in water induced droplet spreading on barley leaves. In an acetone-based medium all derivatives strongly promoted the foliar uptake of 2,4-D, with no clear influence of the ethoxylation degree. In the same medium there was a negative influence of ethoxylate chain length on the foliar uptake of phenmedipham. In a water-based medium, phenmedipham applied with rapeseed oil emulsified with ethoxylated (20 EO) rapeseed oil displayed uptake rates close to a commercial preparation. The same was true for phenmedipham applied with ethoxylated (2 EO) methylated rapeseed oil. In bioassays, phenmedipham prepared with methylated rapeseed oil emulsified with ethoxylated (20 EO) rapeseed oil was as efficacious on barley as a commercial formulation. The same was true for phenmedipham prepared with ethoxylated (2 EO) methylated rapeseed oil. However, neither rapeseed oil nor methylated rapeseed oil emulsified with ethoxylated (2 EO) methylated rapeseed oil conferred good efficacy to phenmedipham. Hence, ethoxylated rapeseed oil derivatives are promising adjuvants or formulants for herbicides. 相似文献
122.
OBJECTIVE: To establish reference values for activated coagulation time (ACT) in cats by use of jugular venipuncture and direct collection of blood into ACT vacuum tubes. ANIMALS: 100 clinically normal cats that were to have elective surgery performed at a private practice. PROCEDURE: Collection of 3 blood samples for ACT measurement was attempted for each cat at the time of elective surgery: sample 1, obtained before sedation; sample 2, tube 1 of 2 consecutive samples obtained from a single venipuncture of the contralateral jugular vein after sedation with acepromazine and ketamine hydrochloride; and sample 3, tube 2 collected immediately following collection of sample 2 without removing the needle from the vein. Venipuncture quality was rated subjectively on a 3-point scale. RESULTS: Median ACT were 95 seconds for each sample group. The middle 95% of values ranged inclusively from 55 to 185 seconds (sample 1), 65 to 135 seconds (sample 2), 45 to 145 seconds (sample 3), and 55 to 165 seconds overall (samples 1, 2, and 3). Significant differences in ACT values were not detected between sample groups. Significant relationships between ACT and venipuncture quality or sex of cat were not detected. CONCLUSIONS AND CLINICAL RELEVANCE: With the ACT protocols used, clinically normal cats had ACT of < 165 seconds. The ACT in cats does not appear to be significantly affected by sex, sedation with acepromazine and ketamine, or by moderately traumatic venipunctures. These results refute widespread statements that ACT should be < 65 seconds in healthy cats. Cats with ACT repeatedly > 165 seconds should be further evaluated for hemostatic disorders. 相似文献
123.
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
124.
Bacterial colonization affects early organ and gastrointestinal growth in the neonate 总被引:1,自引:0,他引:1
R.H. Siggers T. Thymann J.L. Siggers M. Schmidt A.K. Hansen P.T Sangild 《Livestock Science》2007,109(1-3):14-18
Enteral nutrition coupled with bacterial colonization has been shown to have major functional and developmental effects during the postnatal period of neonates. In this study, we developed a highly sensitive premature pig model to elucidate the specific developmental impact of initial bacterial colonization on premature neonates by comparing germ-free and conventionally reared pigs. Thirty-eight preterm pigs (93% gestation) were delivered via caesarean section and reared in either germ-free or conventional isolators for 40–48 h. Pigs were fed either infant milk formula or sow's colostrum. Enteral feeding for two days had trophic effects on gastrointestinal weights, particularly for pancreas, stomach and small intestine (SI). The absence of bacteria in formula fed pigs resulted in a mucosa that appeared more robust and had higher weights for both SI and pancreas, compared to conventional formula fed pigs (P < 0.05). Colostrum fed pigs also had markedly increased mucosal SI proportions, lung and spleen weights compared to conventional formula fed pigs. Colostrum fed pigs and germ-free pigs were similar although stomach, pancreas and distal SI weights were highest for germ-free pigs. The results demonstrate that the initial bacterial colonization interacts with diet to modulate the early neonatal organ development, particularly of the GIT. 相似文献
125.
T. Thymann C. Gudbergsen S. Bresson N.B. Kristensen C.F. Hansen 《Livestock Science》2007,108(1-3):132-136
Suckling pigs were separated from their dam for 24 h on day 21 (1 × 24 h fasting, n = 10) or day 21 and 24 (2 × 24 h fasting, n = 10). Pigs in the control group (n = 10) were not fasted before weaning. All pigs were weaned on day 28 postpartum. Feed intake during the first 4 days post-weaning was higher (P < 0.05) for pigs exposed to 1 × 24 h fasting compared with controls. Water consumption was not affected by fasting prior to weaning. The difference in post-weaning feed uptake was not reflected in any clinical traits, intestinal morphology, or activity of digestive enzymes (maltase, dipeptidylpeptidase IV, aminopeptidases A and N; P > 0.15). In conclusion, a short period of fasting prior to weaning can increase post-weaning feed uptake, although this had no clinical impact under the present experimental conditions. 相似文献
126.
以6个苹果品种为试材,进行苹果的有效负载面积与产量相关性试验.结果表明:在一定条件下,有效负载面积(EBS)越大,产量相应越高.不同纬度对不同品种的EBS和产量的影响不同.土壤中砾石含量对EBS和产量都有影响,但品种和砧木不同,EBS的减少率不同.不同品种对砾石的耐受能力不同. 相似文献
127.
Joseph Aubert Mouen Bedimo Daniel Bieysse Ibrahim Njiayouom Jean Pierre Deumeni Christian Cilas Jean Loup Nottéghem 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(4):391-400
In the high altitude regions of Africa, coffee berry disease (CBD), caused by Colletotrichum kahawae, is the main constraint for arabica coffee (Coffea arabica) production. However, certain agricultural practices can reduce losses caused by the disease and thereby promote optimum
production. On small family farms in Cameroon, mixed cropping with fruit trees, intercropping with food crops and maintenance
pruning of coffee trees are very widespread agricultural practices that can affect CBD epidemics. Consequently, an epidemiological
study was conducted to assess how cultural practices affected the disease in an arabica coffee smallholding in Cameroon. The
disease was monitored on a weekly basis over four successive years (2002–2005) on coffee trees in diverse cultural situations.
Cultural practices likely to reduce losses due to CBD were identified. The infection rate was significantly lower on coffee
trees grown intensively than on coffee trees grown in the traditional manner. Coffee trees located under the shade of fruit
trees were significantly less attacked than those located in full sunlight. In addition, berries on the leafless parts of
branches, near the main trunk of the coffee tree, were less infected than those on leafy sections. These results show that
maintenance pruning, removal of mummified berries, and mixed cropping with shade plants are cultural practices which create
environmental conditions that limit CBD development. 相似文献
128.
129.
130.
Susanne Lier Hansen 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(2):103-109
Some of the chemical changes inside the bulb of onions (Allium cepa L.) and the influence of various harvesting criteria on dry matter content and composition were studied during long-term storage. Onion weight, dry matter content, total N and the non-structural carbohydrates, glucose, fructose, sucrose and total fructans were examined. Significant (P<0.05) interseasonal differences were observed in the weight of the onions, dry matter content, glucose and total non-structural carbohydrates. Furthermore, the dry matter content and composition differed inside the onion bulbs depending on the length of the storage period. The stage of maturation at the time of harvest also significantly influenced the weight of the onions, the dry matter content in individual onions and the fructose content. 相似文献