全文获取类型
收费全文 | 103485篇 |
免费 | 5615篇 |
国内免费 | 69篇 |
专业分类
林业 | 5420篇 |
农学 | 3559篇 |
基础科学 | 549篇 |
12615篇 | |
综合类 | 15970篇 |
农作物 | 3867篇 |
水产渔业 | 5221篇 |
畜牧兽医 | 54636篇 |
园艺 | 1233篇 |
植物保护 | 6099篇 |
出版年
2019年 | 888篇 |
2018年 | 1571篇 |
2017年 | 1699篇 |
2016年 | 1597篇 |
2015年 | 1410篇 |
2014年 | 1688篇 |
2013年 | 3896篇 |
2012年 | 3087篇 |
2011年 | 3607篇 |
2010年 | 2358篇 |
2009年 | 2382篇 |
2008年 | 3420篇 |
2007年 | 3453篇 |
2006年 | 3246篇 |
2005年 | 3053篇 |
2004年 | 2861篇 |
2003年 | 2833篇 |
2002年 | 2652篇 |
2001年 | 3598篇 |
2000年 | 3420篇 |
1999年 | 2756篇 |
1998年 | 1072篇 |
1997年 | 1039篇 |
1996年 | 1018篇 |
1995年 | 1133篇 |
1994年 | 977篇 |
1993年 | 982篇 |
1992年 | 2043篇 |
1991年 | 2173篇 |
1990年 | 2223篇 |
1989年 | 2093篇 |
1988年 | 1983篇 |
1987年 | 1997篇 |
1986年 | 1950篇 |
1985年 | 1894篇 |
1984年 | 1561篇 |
1983年 | 1304篇 |
1982年 | 918篇 |
1979年 | 1379篇 |
1978年 | 1083篇 |
1977年 | 882篇 |
1976年 | 927篇 |
1975年 | 952篇 |
1974年 | 1247篇 |
1973年 | 1157篇 |
1972年 | 1242篇 |
1971年 | 1207篇 |
1970年 | 1121篇 |
1969年 | 1074篇 |
1967年 | 961篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection. 相似文献
14.
29 samples of commonly used surfaces were tested for their water characteristics (litre weight, water capacity, water binding, water evaporation) and their contribution to airborne fungal spores (dust formation, dust setting). The results are discussed in comparison to the literature with regard to the environment. The results are: 1. Any surface--no matter of what material--eventually causes air pollution with fungal spores and dust. 2. Correct watering prevents air pollution by any surface. 3. Artificial products have no advantage over natural materials in the parameters tested. 4. The question of proper disposal of old surface material has to be clarified before purchase. The results show that a mixture of sand and wood shavings should be recommended as a surface for indoor arenas, especially in regard to environmental protection and proper disposal. 相似文献
15.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils. 相似文献
16.
The study describes plumage modifications and specific feather malformations, as related to the domestication process of different poultry species. The modifications include naked necks, leg feathering, frizzle feathering, silky feathering, fat quills, and feather abnormalities caused by behavioural hypertrophies. Most of these plumage modifications correspond to the breed standard for exhibition poultry fancy. However, they impair the normal function of these animals. The negative influences comprise disorders in social behaviour, loss of typical plumage functions and disabilities of normal mobility, as well as genetic defects and pathogenic predispositions. 相似文献
17.
Anthony S. Moore BVSc MVSc Gregory K. Ogilvie David M. Vail 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(5):343-344
Twenty-five dogs with malignant lymphoma refractory to chemotherapy were treated with actinomycin D at a median dose of 0.7 mg/m2 (range, 0.5 to 0.9 mg/m2 ) every 3 weeks. The dogs treated had received between 2 and 8 chemotherapeutic agents (median 7), for a median of 266 days before being treated with actinomycin D. For 23 of the 25 dogs, previous chemotherapy included doxorubicin. No dog responded to actinomycin D chemotherapy. 相似文献
18.
The anthelmintic efficacy of abamectin (avermectin B1) was evaluated against gastrointestinal nematodes, including Ostertagia ostertagi inhibited larvae and lungworm, in yearling crossbred beef heifers during late spring. The calves were grazed on contaminated pasture for 10 weeks and then held under conditions free of nematode infection for 3 weeks prior to allotment and treatment on 5 June. Thirteen calves were randomly assigned to two groups of six by restricted randomization on body weights; the extra lightest calf was assigned to the non-treated control group. Group 1 calves were treated with abamectin at 200 micrograms kg-1 body weight by s.c. injection and Group 2 calves were not treated; all were killed at 14 days after treatment. Ostertagia ostertagi was present in all controls; arithmetic mean numbers of adults, developing fourth stage larvae (L4) and inhibited EL4 were 7683, 605 and 36,102, respectively. Other nematode genera present in controls in sufficient numbers for the experiment were Haemonchus placei adults, Trichostrongylus axei adults, Cooperia spp. adults, Oesophagostomum radiatum adults, Bunostomum phlebotomum adults, Dictyocaulus viviparus adults and E5 (immature adults). Abamectin was highly effective (consistently greater than 99% efficacy and P less than 0.05) in removing all nematodes present in treated calves as represented in non-treated controls, including the primary target of Ostertagia ostertagi inhibited EL4. The lowest efficacy was 93.8%, against D. viviparus E5. 相似文献
19.
N Machida T Nakamura K Kiryu S Haramaki K Too 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(6):1213-1216
A 20-year-old pony mare with persistent ventricular tachycardia (VT) was examined cardiopathologically. At necropsy, the heart was enlarged and rounded with both ventricular dilatation. In a longitudinal section of the ventricular septum, a large grayish white patchy lesion (5 x 25 mm) was detected in the relatively higher portion. Microscopically, the lesion was extensive myocardial fibrosis located in the vicinity of the proximal part of the left bundle branch. Partially the fibrotic lesion was in contact with the branch. Such a lesion might play an important role in creating a suitable background for the development of VT via automaticity or reentry mechanism. 相似文献
20.
Abstract – Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis , were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius , as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch. 相似文献