全文获取类型
收费全文 | 22060篇 |
免费 | 1284篇 |
国内免费 | 1705篇 |
专业分类
林业 | 1835篇 |
农学 | 1941篇 |
基础科学 | 891篇 |
2690篇 | |
综合类 | 7493篇 |
农作物 | 1451篇 |
水产渔业 | 1080篇 |
畜牧兽医 | 5182篇 |
园艺 | 1280篇 |
植物保护 | 1206篇 |
出版年
2024年 | 57篇 |
2023年 | 230篇 |
2022年 | 538篇 |
2021年 | 634篇 |
2020年 | 638篇 |
2019年 | 636篇 |
2018年 | 516篇 |
2017年 | 723篇 |
2016年 | 640篇 |
2015年 | 797篇 |
2014年 | 866篇 |
2013年 | 1203篇 |
2012年 | 1495篇 |
2011年 | 1637篇 |
2010年 | 1476篇 |
2009年 | 1309篇 |
2008年 | 1312篇 |
2007年 | 1175篇 |
2006年 | 1241篇 |
2005年 | 1035篇 |
2004年 | 662篇 |
2003年 | 681篇 |
2002年 | 854篇 |
2001年 | 714篇 |
2000年 | 614篇 |
1999年 | 425篇 |
1998年 | 259篇 |
1997年 | 217篇 |
1996年 | 183篇 |
1995年 | 169篇 |
1994年 | 174篇 |
1993年 | 152篇 |
1992年 | 176篇 |
1991年 | 155篇 |
1990年 | 142篇 |
1989年 | 137篇 |
1988年 | 78篇 |
1987年 | 82篇 |
1986年 | 59篇 |
1985年 | 64篇 |
1984年 | 69篇 |
1983年 | 56篇 |
1982年 | 58篇 |
1979年 | 44篇 |
1978年 | 48篇 |
1977年 | 44篇 |
1976年 | 43篇 |
1974年 | 42篇 |
1972年 | 36篇 |
1969年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 923 毫秒
21.
22.
23.
24.
戴晓红 《安徽农业大学学报》2005,(6):67-69
财务总监制度的设立,是现代企业制度发展的要求,一般说来,财务总监的监督分为事前监督和事后监督。本文分析和探讨了财务总监的事前监督和事后监督机制,认为,应该将事前监督和事后监督机制配合运用,并辅之以切实可行的制衡手段,抑制经理人的机会主义行为,以保障所有者权益。 相似文献
25.
Kyungmin Han Inge Geurden Paul Van der Meeren Sungchul C. Bai Patrick Sorgeloos 《Journal of the World Aquaculture Society》2005,36(2):196-202
The present study examined the distribution of particle sizes in two experimental standardized lipid emulsions (distributed by ICES, International Council for the Exploration of the Sea) as a function of the preparation method (hand shaking or ultrasonic blending) and as a function of storage time. A 24-h enrichment trial compared the incorporated HUFA levels in the nauplii of Artemia franciscana .
The emulsion droplets in the 50% HUFA emulsion (ICES 50, ethyl ester based) were much smaller than in the 30% HUFA emulsion (ICES 30, triacylglycerol-based) in which 90% of the droplets had a diameter below 12.3 μm as compared to 1.3 pn in ICES 50. The blending method highly affected particle sizes. High-shear blending instead of the classical hand shaking of the emulsion of both ICES 30 and 50 reduced the mean particle size from 5.06 to 1.07 μm and from 0.38 to 0.11 μm, respectively. The particle size distributions remained stable during the 1-wk storage, suggesting the absence of agglomeration or bacterial development. The fatty acid composition of 24-h enriched Artemia reflected differences in the HUFA profile of the emulsions, but was independent of observed differences in the size of the particles. 相似文献
The emulsion droplets in the 50% HUFA emulsion (ICES 50, ethyl ester based) were much smaller than in the 30% HUFA emulsion (ICES 30, triacylglycerol-based) in which 90% of the droplets had a diameter below 12.3 μm as compared to 1.3 pn in ICES 50. The blending method highly affected particle sizes. High-shear blending instead of the classical hand shaking of the emulsion of both ICES 30 and 50 reduced the mean particle size from 5.06 to 1.07 μm and from 0.38 to 0.11 μm, respectively. The particle size distributions remained stable during the 1-wk storage, suggesting the absence of agglomeration or bacterial development. The fatty acid composition of 24-h enriched Artemia reflected differences in the HUFA profile of the emulsions, but was independent of observed differences in the size of the particles. 相似文献
26.
27.
Techniques for in vitro production of embryos have been developed world-wide in different species, with promising results in human and ruminants. Thousands of human IVF-babies have been born during the last 20 years and thousands of in vitro -produced calves have been born since the late 1980s. With current methods for bovine in vitro fertilization, about 30–40% of in vitro -fertilized bovine oocytes develop further to the blastocyst stage and can be used for transfer. A proper evaluation of blastocyst quality remains however, an important challenge for every researcher involved in embryology and for every clinician who wants to select the best embryos for transfer. This review attempts to summarize the different methods available for estimation of blastocyst quality with a special emphasis upon differential staining. 相似文献
28.
Deborah R. Van Pelt DVM MS Wayne E. Wingfield MS DVM Timothy B. Hackett DVM Linda G Martin DVM 《Journal of Veterinary Emergency and Critical Care》1993,3(2):63-70
Over the past several decades, recognition of acute respiratory failure as the cause of death in patients suffering from various clinical conditions has prompted aggressiv investigation into the area of respiratory physiology and supportive respiratory care. With the evolution of emergency medicine and critical care services in both human and veterinary medicine, many patients previously considered unsalvageable due to the severity of their underlying disease are now being resuscitated and successfully supported, creating a new population of critically ill patients. Where only a decade ago these patients would have succumbed to their underlying disease, they now survive long enough to manifest the complications of shock and tissue injury in the form of acute respiratory failure. Investigation into the pathophysiology and treatment of this acute respiratory distress syndrom (ARDS) has facilitated increased clinical application of respiratory theerapy and machanical ventilation.1 The purpose of this paper is to provide a basic review of respiratory mechanics and the pathophysiology of hypoxemia as they relate to airway pressure therapy in veterinary patients and to review the use of airway pressure therapy in veterinary patients This paper is divided into two parts; part I reviews respiratory mechanics and hypoxemia as they apply to respiratory therapy, while part II deals specifically with airway pressure therapy andits use in clinical cases. 相似文献
29.
苜蓿施用污泥效果的研究Ⅰ对苜蓿生长及元素含量的影响 总被引:5,自引:2,他引:3
将兰州市七里河污水处理厂生活污泥施用于人工种植的新疆大叶苜蓿草地,探讨了不同施用量对苜蓿生长及各元素含量的影响。研究结果表明,施用1.0-2.0kg/m^2污泥,苜蓿地上生物量显著增加,第一年增产23%-31%,第二年增产15%-31%。施用污泥苜蓿地上和地下部组织中N,P,Ca,Mg和Mn的含量总体呈增加趋势,Fe含量显著增加,而K和重金属元素Ni、Pb、As和Hg的含量与对照无显著差异,Zn和Cu的积累增多,但地上部组织中重金属元素均未超过植物中的平均含量,施用污泥未对新疆大叶苜蓿造成重金属污染。 相似文献
30.
Epidemiological study of enzootic pneumonia in dairy calves in Saskatchewan. 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J Van Donkersgoed C S Ribble L G Boyer H G Townsend 《Canadian journal of veterinary research》1993,57(4):247-254
A field study involving 325 calves from 17 dairy herds in Saskatchewan was conducted to determine the risk of enzootic pneumonia and to assess its association with a number of factors. Two different case definitions of pneumonia were used in the analyses: the first was based on producers' treatment risk (CASE1) and the second was based on semimonthly clinical examinations of calves by the research veterinarian (CASE2). The risk of pneumonia based on CASE1 was 39% and on CASE2 was 29%. The measure of agreement between CASE1 and CASE2 at the calf level of analysis was poor (kappa = 0.24, SE = 0.02) and at the herd level of analysis was moderate (kappa = 0.40, SE = 0.12). The mortality risk from pneumonia was 1.8% and a variety of infectious organisms were isolated from pneumonic lungs. Twenty-seven percent of the calves had inadequate (total IgG < or = 800 mg/dL) levels of passively acquired antibodies as measured by radial immunodiffusion. The proportion of seropositive titers in calves within the first two weeks of age was 94% to parainfluenza 3 virus (PI3V) and bovine respiratory syncytial virus (BRSV), 73% to Pasteurella haemolytica (Ph), 68% to bovine viral diarrhea virus (BVDV), 67% to infectious bovine rhinotracheitis virus (IBRV), 46% to Mycoplasma dispar (Md), 44% to Haemophilus somnus (Hs), and 21% to Mycoplasma bovis (Mb). At the calf level of analysis and after adjusting for clustering, there was a negative association (p = 0.10) between the diagnosis of pneumonia based on CASE2 and total IgG levels and Ph titers (rPh).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献