全文获取类型
收费全文 | 91420篇 |
免费 | 5127篇 |
国内免费 | 324篇 |
专业分类
林业 | 4478篇 |
农学 | 3328篇 |
基础科学 | 640篇 |
12337篇 | |
综合类 | 11952篇 |
农作物 | 3453篇 |
水产渔业 | 4771篇 |
畜牧兽医 | 49089篇 |
园艺 | 1150篇 |
植物保护 | 5673篇 |
出版年
2020年 | 818篇 |
2019年 | 949篇 |
2018年 | 1624篇 |
2017年 | 1733篇 |
2016年 | 1610篇 |
2015年 | 1402篇 |
2014年 | 1682篇 |
2013年 | 3899篇 |
2012年 | 2925篇 |
2011年 | 3508篇 |
2010年 | 2335篇 |
2009年 | 2310篇 |
2008年 | 3265篇 |
2007年 | 3139篇 |
2006年 | 3008篇 |
2005年 | 2685篇 |
2004年 | 2569篇 |
2003年 | 2560篇 |
2002年 | 2370篇 |
2001年 | 3260篇 |
2000年 | 3139篇 |
1999年 | 2431篇 |
1998年 | 998篇 |
1997年 | 957篇 |
1996年 | 892篇 |
1995年 | 1004篇 |
1994年 | 866篇 |
1993年 | 811篇 |
1992年 | 1791篇 |
1991年 | 2024篇 |
1990年 | 1999篇 |
1989年 | 1924篇 |
1988年 | 1775篇 |
1987年 | 1745篇 |
1986年 | 1718篇 |
1985年 | 1580篇 |
1984年 | 1319篇 |
1983年 | 1076篇 |
1979年 | 1266篇 |
1978年 | 999篇 |
1977年 | 795篇 |
1976年 | 847篇 |
1975年 | 866篇 |
1974年 | 1036篇 |
1973年 | 1028篇 |
1972年 | 1035篇 |
1971年 | 901篇 |
1970年 | 924篇 |
1969年 | 896篇 |
1967年 | 819篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment. 相似文献
12.
13.
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.
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
19.
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
20.
Abstract. The Pan‐European Soil Erosion Risk Assessment (pesera ) model was evaluated using existing soil erosion data collected under various types of climate, vegetation, landscape and soil conditions. The data used represent a variety of typical Mediterranean land uses such as winter wheat, vines, olives and bare, stony land prevailing in hilly areas. Using this data, the model was calibrated for sediment transport by overland flow and results compared to measured soil erosion values from runoff plots and a watershed on a monthly basis. The performance of the model was assessed statistically, showing that it can be satisfactorily used for predicting soil erosion rates under the conditions included in the study. The overall model estimate including all the available experimental data was 0.69 t ha?1 yr?1 with a maximum error of 1.49 t ha?1 yr?1. After validation, the model was applied to a small watershed (60 ha) of great ecological importance for the sea turtle Caretta caretta. For this purpose, soil and vegetation maps were compiled from all the necessary data for applying the model. The model was run for three years using daily data from an existing nearby meteorological station. The predicted and measured soil erosion rates for a 7‐month period were 0.31 t and 0.18 t, respectively. Application of the model to each mapping unit showed the over‐riding importance of land use for sediment generation under the given climatic conditions. Bare land, occupying 5.5% of the watershed area, generated up to 69% of the total sediments estimated for the watershed. It is concluded that the pesera model can be used as a regional diagnostic tool under a range of soil, topographic and climatic conditions for identifying the best land use type and vegetation cover to protect hilly areas from soil erosion. The calculated overall root mean square error for the model is 0.06 t ha?1 yr?1, compared to a soil erosion rate of 0.04 t ha?1 yr?1, which can be tolerated for protecting the area for the sea turtle. 相似文献