全文获取类型
收费全文 | 302815篇 |
免费 | 16472篇 |
国内免费 | 689篇 |
专业分类
林业 | 28318篇 |
农学 | 15595篇 |
基础科学 | 3146篇 |
50030篇 | |
综合类 | 31556篇 |
农作物 | 19829篇 |
水产渔业 | 19835篇 |
畜牧兽医 | 117021篇 |
园艺 | 7423篇 |
植物保护 | 27223篇 |
出版年
2021年 | 2707篇 |
2020年 | 3121篇 |
2019年 | 3891篇 |
2018年 | 7135篇 |
2017年 | 7567篇 |
2016年 | 6362篇 |
2015年 | 4691篇 |
2014年 | 6078篇 |
2013年 | 16731篇 |
2012年 | 8732篇 |
2011年 | 12223篇 |
2010年 | 10261篇 |
2009年 | 9969篇 |
2008年 | 10864篇 |
2007年 | 10251篇 |
2006年 | 8778篇 |
2005年 | 8158篇 |
2004年 | 7864篇 |
2003年 | 7734篇 |
2002年 | 6786篇 |
2001年 | 7173篇 |
2000年 | 6961篇 |
1999年 | 6232篇 |
1998年 | 4250篇 |
1997年 | 4303篇 |
1996年 | 4015篇 |
1995年 | 4676篇 |
1994年 | 4031篇 |
1993年 | 3731篇 |
1992年 | 4889篇 |
1991年 | 5034篇 |
1990年 | 4728篇 |
1989年 | 4726篇 |
1988年 | 4178篇 |
1987年 | 4205篇 |
1986年 | 4204篇 |
1985年 | 4444篇 |
1984年 | 4017篇 |
1983年 | 3724篇 |
1982年 | 3029篇 |
1981年 | 2879篇 |
1980年 | 2877篇 |
1979年 | 3574篇 |
1978年 | 3127篇 |
1977年 | 2867篇 |
1976年 | 2745篇 |
1975年 | 2655篇 |
1974年 | 2854篇 |
1973年 | 2827篇 |
1972年 | 2477篇 |
排序方式: 共有10000条查询结果,搜索用时 570 毫秒
31.
Soil protection for a sustainable future: options for a soil monitoring network for Ireland 下载免费PDF全文
The increased recognition of the importance of soil is reflected in the UN Post‐2015 Development Agenda with sustainable development goals that directly and indirectly relate to soil quality and protection. Despite a lack of legally binding legislation for soil protection, the European Commission remains committed to the objective of soil protection. However, the achievement of a legally binding framework for soil protection relies on the implementation of a soil monitoring network (SMN) that can detect changes to soil quality over time. As beneficiaries do not pay for the provision of soil information, the options for soil monitoring are limited. The use of existing data sets should be considered first. Using Ireland as an example, this research explored the opportunities for a SMN for Ireland considering three existing national data sets. The options for a SMN are considered in terms of their spatial and stratified distribution, the parameters to be measured and an economic analysis of the options proposed. This research finds that for Ireland, either a 10 or a 16 km2 grid interval stratified by land use and drainage class offers the best potential in relation to the spatial distribution of existing data sets to reflect local data at a national level. With existing data, the stratified SIS data using the 16 km2 grid offers the best value for money, with baseline costs for analysis, excluding field costs, of between €706 481 and €2.8 million. Acknowledging the impossibility of measuring all parameters with ideal frequency, this study proposes a two‐tier system for optimized monitoring frequency. Parameters must anticipate future policy requirements. Finally, the implementation of a SMN must be accompanied by standardized methods, defined thresholds and action mandates to maintain soil quality within allowable limits. 相似文献
32.
33.
34.
K A Hahn D W Knapp R C Richardson C L Matlock 《Journal of the American Veterinary Medical Association》1992,200(3):355-357
In 11 dogs with nasal adenocarcinoma, IV treatment with 2 to 8 cycles of cisplatin at a dosage of 60 mg/m2 of body surface, given at 3-week intervals, resulted in a survival time of 8 to 128 weeks (mean, 32.7 weeks; median, 20 weeks). Radiography revealed complete remission in 2 dogs and partial remission in 1 dog, for an overall response rate of 27%. Clinical problems such as nasal discharge (n = 11), sneezing (n = 6), and epistaxis (n = 4) resolved in 1 to 2 weeks in all dogs after beginning chemotherapy. 相似文献
35.
The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility. 相似文献
36.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem. 相似文献
37.
V J Rapp-Gabrielson D A Gabrielson G J Schamber 《American journal of veterinary research》1992,53(6):987-994
Reference strains for Haemophilus parasuis serovars 1 to 7 were examined for virulence by inoculation of guinea pigs. Guinea pig response to intraperitoneal inoculation was similar for the 7 reference strains. However, apparent differences in virulence were detected after intratracheal inoculation. Cells of the references strains for serovars 1 and 5 were most invasive, causing moribundity or death at higher doses and a persistent septicemia at lower doses. Haemophilus parasuis could be isolated from respiratory and systemic sites; purulent bronchopneumonia, pericarditis, and pleuritis were apparent in infected guinea pigs. Inoculation of cells of the reference strains for serovars 2 and 6 also resulted in bronchopneumonia and moribundity or death in some guinea pigs; however, reisolation of H parasuis and microscopic lesions at necropsy were less pronounced than those observed with serovars 1 and 5. Inoculation of cells of serovars 3, 4 and 7 induced only transient clinical signs and minimal evidence of H parasuis infection at necropsy. The data from intratracheal inoculation of guinea pigs are similar to data from other investigations in swine, indicating differences in the pathogenic potential of H parasuis strains. Thus, guinea pigs may be useful as a laboratory animal model for examining cellular factors associated with virulence and immunogenicity of H parasuis. 相似文献
38.
39.
The progressive autolytic changes of atrial specific granules (ASGS) up to 24 hours after death were studied electron microscopically. Tissue samples taken from the left auricular myocardium of four pig hearts at 0, 0.5, 1.5, 3.5, 6, 12 and 24 hours post mortem were fixed for 24 hours by immersion in 2.5 per cent cacodylate buffered glutaraldehyde (pH 7.4). Two pig hearts were kept at 20 degrees C and two at 4 degrees C. Although typical autolytic changes were seen in many organelles, no remarkable modifications in aspect, distribution, content and diameter of ASGS were observed in all samples. The results of this study indicate that ASGS are not morphologically affected by the autolytic processes, at least during the first 24 hours. Hence, the electron microscopic evaluation of ASGS does not need a particular fixation method such as perfusion. This may eliminate technical problems when slaughterhouse material is used. 相似文献
40.
Four experiments with 270, 44, 432 and 66800 Leghorn hens were carried out to investigate the influence of various Mn additions to diets differed in mineral or Ca contents on egg shell quality. The addition of 300 mg Mn/kg diet improved significantly egg shell breaking strength by 4 N over one year. The supply of 50-500 mg Mn/kg diet for 10-24 weeks of the second half of laying year did not influence the egg shell quality. Addition of mineral mixture or Ca grit to layer rations with adequate or higher Mn levels did not influence egg shell strength. High mineral content in a low manganese diet increased number of cracks by 3%. Strength, weight and ash content of tibia were significantly reduced by feeding a low mineral level. Addition of 50-150 mg Mn per kg low mineral diet normalized partially tibia stability in young hens. It was concluded that supplied dietary Manganese influences calcification positively only in young hens. High levels of Ca did not influence the effects of Mn. 50 mg Mn per kg layers mixture have been considered as an essential supply. 相似文献