首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7233篇
  免费   793篇
  国内免费   393篇
林业   477篇
农学   636篇
基础科学   281篇
  1262篇
综合类   1595篇
农作物   345篇
水产渔业   594篇
畜牧兽医   2336篇
园艺   263篇
植物保护   630篇
  2024年   26篇
  2023年   126篇
  2022年   185篇
  2021年   239篇
  2020年   252篇
  2019年   262篇
  2018年   348篇
  2017年   403篇
  2016年   305篇
  2015年   356篇
  2014年   387篇
  2013年   477篇
  2012年   517篇
  2011年   556篇
  2010年   477篇
  2009年   402篇
  2008年   427篇
  2007年   375篇
  2006年   311篇
  2005年   295篇
  2004年   199篇
  2003年   182篇
  2002年   112篇
  2001年   182篇
  2000年   189篇
  1999年   127篇
  1998年   61篇
  1997年   61篇
  1996年   52篇
  1995年   40篇
  1994年   25篇
  1993年   20篇
  1992年   48篇
  1991年   50篇
  1990年   50篇
  1989年   32篇
  1988年   36篇
  1987年   27篇
  1986年   21篇
  1985年   15篇
  1984年   10篇
  1983年   12篇
  1982年   8篇
  1979年   9篇
  1978年   7篇
  1971年   6篇
  1966年   7篇
  1963年   5篇
  1956年   7篇
  1892年   7篇
排序方式: 共有8419条查询结果,搜索用时 359 毫秒
991.
1. The objective of the study was to investigate the susceptibility of young and older laying hens to fatty liver-haemorrhagic syndrome (FLHS) and to evaluate the reliability of different blood lipid fractions for predicting or diagnosing FLHS.

2. Forty young hens and 40 older hens were caged individually. Each group of hens was randomly allotted to four treatments for 21 days: either a control, an oestradiol group, a high energy-low protein diet (HELPD) group or a HELPD + oestradiol group. Blood levels of oestradiol, triglyceride (TG), cholesterol (CHOL), high density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C), liver total lipids, hepatic haemorrhagic scores and productive performance were assessed.

3. In older hens, β-oestradiol increased (P < 0.05) liver total lipids, hepatic haemorrhagic scores and the incidence of FLHS but reduced (P < 0.05) productive performance; however, such changes were not observed in young hens.

4. In two groups of hens, serum TG, CHOL and HDL-C levels were increased (P < 0.001) by β-oestradiol. Hens with FLHS had higher serum TG, CHOL and HDL-C (P < 0.001) than non-FLHS birds in the older layer group of hens.

5. An interaction (β-oestradiol × HELPD) (P < 0.05) for LDL-C levels was observed in both groups of hens. In young hens, β-oestradiol induced a decrease (P = 0.004) in serum LDL-C levels but the effect was attenuated by HELPD. In older hens, HELPD caused an increase (P = 0.02) in serum LDL-C although the effect depended on the presence of β-oestradiol.

6. In conclusion, older layers were more susceptible to FLHS than young layers after oestradiol treatment. Blood TG, CHOL and HDL-C rather than LDL-C levels can be used as a prediction tool for the overall susceptibility to FLHS in older rather than young layers. There were interactions between oestradiol and HELPD on blood LDL-C levels in laying hens.  相似文献   

992.
993.
This is the first of a series of capsule reviews published by the World Small Animal Veterinary Association ‐ Global Pain Council (WSAVA‐GPC). Each of these short articles provides a brisk assessment of the scientific evidence in specific aspects of pain management, including analgesic techniques, recommendations and controversies surrounding their use. In this first capsule review, the scientific evidence available on the long‐term use of non‐steroidal anti‐inflammatory drugs in cats with concomitant chronic pain and chronic kidney disease is discussed.  相似文献   
994.
995.
This thematic review examines the literature regarding the relationship between domestic violence (DV) and pet abuse (PA) particularly in the veterinary clinical and educational contexts. It examines the significance of this relationship for the veterinary profession including the veterinarian’s role and associated legal and ethical obligations, and relevant current veterinary education standards, to identify future clinical and educational directions. Articles were sourced from online databases by searching the keywords without date restrictions. Overall, 70 articles were retrieved and reviewed.

Pet abuse has been identified as a potential risk factor for DV, and DV perpetrators may harm or kill a pet to exert physical, psychological or emotional control over an intimate partner. Given that victims of DV often seek veterinary aid for their pets, veterinarians may act as frontline professionals in the recognition of the link between PA and DV. Veterinarians must assess individual cases for diagnostic indicators of non-accidental injury and consider demographic factors to identify suspected PA and DV. Despite existing legal and ethical obligations of the veterinarian relating to suspected PA and victims of DV, veterinarians have uncertainty and unpreparedness in addressing PA and DV in a clinical context. Many factors may contribute to the lack of veterinary intervention in suspected cases of PA and DV including concern for animal welfare, confusion about the reporting process and uncertainty in differentiating accidental versus non-accidental injuries in pets. Specific published guidelines regarding the recognition and reporting of PA and DV in the veterinary clinical context are required. Limited published evidence exists examining the implementation and success of veterinary training regarding the relationship between DV and PA. Ultimately, veterinary student education is needed to prepare veterinarians for their response to PA and DV in practice. Further research is required to examine the effects of the delivery of content regarding the link between PA and DV in the veterinary curriculum on veterinary student knowledge and attitudes.  相似文献   

996.
997.
为阐明青海省森林生态系统林下草本层化学计量特征和碳密度分布格局,基于2011年青海森林资源野外样方调查和室内分析,评估了青海省7个优势种(白桦、白杨、红桦、青杄、山杨、圆柏、云杉)林下草本层的化学计量特征(C、N、P;C∶N、C∶P、N∶P)以及碳密度的差异。同时,估算了青海省7个优势种林下草本层碳储量大小。结果表明,草本层地上碳含量圆柏林[(419.9±1.44) g·kg-1]显著高于其他林型,但是地下碳含量[(364.6±8.33) g·kg-1]显著低于其他林型;氮含量均表现出圆柏和云杉林显著高于其他林型;磷含量在不同林型间差异不显著。圆柏林和云杉林林下草本层C∶N、C∶P显著低于其他林型,而N∶P显著高于其他林型。此外,林下草本层地上和地下生物量、碳密度均表现出圆柏林显著高于其他林型。根据青海省7种优势树种化学计量特征与碳密度的相关性分析,发现草本层碳密度与其化学计量特征有相关性,可以根据碳含量推算碳密度。将海拔作为环境因子考虑,发现圆柏和云杉林下草本层碳密度分布于较高海拔,其他树种则分布于较低海拔。因此,理解养分元素在草本层“地上-地下部分”之间的生态化学计量特征,以及估算草本层的碳储量,对于揭示青海省森林生态系统的养分状况和生物化学循环过程极为重要。  相似文献   
998.
ABSTRACT Pasteuria penetrans is a bacterial parasite of root-knot nematodes that shows great potential as a biocontrol agent. Scanning and transmission electron microscopy were used to study the ultrastructure, morphology, and sporogenesis of four isolates of P. penetrans. The effects of different Meloidogyne spp. and tobacco cultivars on sporangium size and morphology of endospores attached to the cuticle of second-stage juveniles (J2) of root-knot nematodes also were investigated. The P. penetrans isolates and their origins were P-20 from M. arenaria race 1 in Levy County, FL; P-100 from Meloidogyne sp. in Pasco County, FL; B-4 from Pratylenchus scribneri in Seminole County, FL; and P-120 from Meloidogyne spp. in Alachua County, FL. Sporangia of the four isolates were identical morphologically and similar in their dimensions, ranging from 2.39 to 3.42 mum in diameter and from 1.38 to 2.38 mum in height. Different Meloidogyne spp. and tobacco cultivars had no effect on sporangium size. Endospores attached to J2 were visualized in three forms: endospores retaining the sporangium wall, endospores covered with a thin exosporium, and endospores without covering. Sporogenesis of P. penetrans was similar to that of other gram-positive bacteria and generally matched the seven-stage scheme reported for Bacillus thuringiensis.  相似文献   
999.
1000.
In the recent years, USUTU virus (USUV), a flavivirus of the Japanese encephalitis virus complex, has been reported in Central Europe. As part of a systematic surveillance programme to monitor possible entrance and/or circulation of vector-borne viruses, since 2001, sentinel-chicken flocks were placed throughout the Italian territory nearby areas considered at risk of virus introduction. They have been periodically checked for the presence of antibodies against flaviviruses by indirect ELISA, plaque reduction neutralization test for USUTU, West Nile and tick-borne encephalitis viruses. In July 2007, a sentinel chicken in a flock of 20 animals located within the Ravenna province seroconverted to USUV reaching neutralizing titres up to 1:5120. A second chicken seroconverted to the same virus 2 months later. Although no virus was rescued from these animals and from wild or farm birds sampled in the area, these results still provided evidence of the circulation of USUV in north-eastern Italy.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号