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   589篇
  免费   30篇
林业   15篇
农学   5篇
  60篇
综合类   91篇
农作物   56篇
水产渔业   18篇
畜牧兽医   323篇
园艺   18篇
植物保护   33篇
  2020年   4篇
  2019年   13篇
  2018年   10篇
  2016年   9篇
  2015年   11篇
  2014年   10篇
  2013年   33篇
  2012年   25篇
  2011年   24篇
  2010年   19篇
  2009年   21篇
  2008年   22篇
  2007年   21篇
  2006年   15篇
  2005年   25篇
  2004年   12篇
  2003年   13篇
  2002年   15篇
  2001年   11篇
  2000年   19篇
  1999年   14篇
  1998年   12篇
  1997年   7篇
  1996年   4篇
  1995年   8篇
  1993年   9篇
  1992年   7篇
  1991年   11篇
  1990年   19篇
  1989年   8篇
  1988年   10篇
  1987年   9篇
  1985年   10篇
  1984年   12篇
  1983年   10篇
  1982年   4篇
  1981年   6篇
  1980年   10篇
  1979年   12篇
  1978年   7篇
  1977年   5篇
  1976年   5篇
  1975年   5篇
  1974年   6篇
  1973年   6篇
  1972年   9篇
  1971年   4篇
  1970年   6篇
  1967年   7篇
  1955年   4篇
排序方式: 共有619条查询结果,搜索用时 31 毫秒
1.
High-resolution computed tomography (HRCT) was performed in 21 isolated animal lungs, from 4 mammalian species (pigs, rabbits, dogs, sheep). Gross and subgross central and peripheral lung morphology was determined by HRCT. Three distinct types of lungs can be identified, principally based on the extent of interlobular septal development; the relationship of major vessels to airways; and the thickness of the visceral pleura. Type-I lung is found in pigs, sheep, and cattle; type-II lung is found in rabbits, dogs, cats, and monkeys; and type-III lung is found in human beings and horses. These mammalian lungs were compared with human lungs. The potential use of HRCT to investigate specific human lung diseases in the aforementioned species also was considered.  相似文献   
2.
3.
Oral squamous cell carcinoma (OSCC) is the most common oral epithelial malignancy in dogs. It exhibits locally aggressive biological behaviour with the potential to metastasize, and a reported 1-year survival rate of 0% when left untreated. Expression studies suggest that aberrant MAPK signalling plays a key role in canine OSCC tumorigenesis, which is consistent with BRAF and HRAS MAPK-activating mutations reported in some tumours. Several morphological subtypes of canine OSCC have been described, with papillary, conventional, and basaloid as the most common patterns. We hypothesized that mutational differences may underlie these phenotypic variations. In this study, targeted Sanger sequencing and restriction fragment length polymorphism assays demonstrate that up to 85.7% of canine papillary OSCC (n = 14) harbour a BRAF p.V595E mutation. Assessment of neoplastic epithelial cell proliferation using Ki67 immunolabelling (n = 10) confirmed a relatively high proliferation activity, consistent with their known aggressive clinical behaviour. These findings underscore a consistent genetic feature of canine papillary OSCC and provide a basis for the development of novel diagnostic and targeted therapeutic approaches that can improve the quality of veterinary care.  相似文献   
4.
Fasciolosis is an endemic zoonotic parasitic disease with significant impacts on human health and both animal health and production. Early post-infection impacts on the host remain unclear. The objective of this study was to determine the changes, if any, to levels of endotoxin in cattle plasma in response to early-stage infection with Fasciola hepatica. Thirty-six (36) commercial bred cattle were experimentally infected with approximately 400 viable metacercariae. Plasma lipopolysaccharide (endotoxin) levels were examined on 24 occasions from 0 h before infection to 336 h after infection using the Limulus Amoebocyte Lysate chromogenic end point assay and compared with that of six (6) uninfected control animals. Peak lipopolysaccharide levels in infected animals were reached at 52 h after infection and returned to pre-infection levels at time 144 h after infection. Infected animals had significantly elevated lipopolysaccharide levels between 24 and 120 h after infection when compared to uninfected animals. The mean change in endotoxin units (EU)/mL over time after infection was statistically significant in infected animals. Elevations of lipopolysaccharide occurred in all infected animals suggesting a possible repeatable and titratable endotoxemia conducive to therapeutic agent model development.  相似文献   
5.
The robustness of Pacific oyster, Crassostrea gigas (Thunberg), sperm cryopreservation in the context of selective breeding based on family lines was investigated. Irrespective of egg density, high fertilization success was achieved with cryopreserved sperm when sperm:egg ratios of 1000:1 to 10 000:1 were used. Variation among replicate runs on the same oyster batches was minimal, indicating that cryopreservation and larval rearing procedures were repeatable. Twenty independent single male–female crosses were made to assess the utility of cryopreserved sperm in selective breeding. The fertility of unfrozen sperm was generally a poor predictor of cryopreserved sperm fertility. Based on D‐larval yields, 17 of the 20 crosses were likely to yield adequate spat for selective breeding (>105 D‐larvae from 1 million eggs), two were marginal (5 × 104 D‐larvae) and one was inadequate (4 × 103 D‐larvae). An alternative fertilization strategy to improve D‐yield from a given number of sperm was then tested. Fertilizing 10 million eggs at a sperm:egg ratio of 200:1 increased the total D‐yield when compared with fertilizing 1 million eggs at a sperm:egg ratio of 2000:1 for the same male–female pair. We conclude that, despite wide variation in fertility, cryopreserved sperm is useful for family production.  相似文献   
6.
7.
Glyphosate was recently evaluated for its potential to interact with the estrogen, androgen and thyroid (EAT) hormone pathways, including steroidogenesis, under the United States Environmental Protection Agency's (USEPA) Endocrine Disruptor Screening Program (EDSP), then by Germany, the rapporteur Member State who led the European Annex 1 renewal for glyphosate, and then by the European Food Protection Agency (EFSA) also as part of the Annex 1 renewal for glyphosate. Under the EDSP, 11 Tier 1 assays were run following the USEPA's validated 890‐series test guidelines and included five in vitro and six in vivo assays to evaluate the EAT pathways. Steroidogenesis was evaluated as part of the estrogen and androgen pathways. An up‐to‐date critical review has been conducted that considered results from the EDSP Tier 1 battery, guideline regulatory studies and an in‐depth analysis of the literature studies that informed an endocrine assessment. A strength of this evaluation was that it included data across multiple levels of biological organization, and mammalian and nonmammalian test systems. There was strong agreement across the in vitro and in vivo Tier 1 battery, guideline studies and relevant literature studies, demonstrating that glyphosate does not interact with EAT pathways including steroidogenesis. Based on an analysis of the comprehensive toxicology database for glyphosate and the literature, this review has concluded that glyphosate does not have endocrine‐disrupting properties through estrogen, androgen, thyroid and steroidogenic modes of action. © 2020 Society of Chemical Industry  相似文献   
8.
9.
During the investigation of factors affecting fruit size in strawberry, the physical characteristics of the fruiting structure were examined as a possible cause of size limitation in fruit. The greatest total weight of fruit which can be sustained at any one time on an inflorescence appeared to be related to the dimensions of the main peduncle. At this limit the fruit yield may be no more than half the potential fruit yield of the inflorescence, indicating that unless ripe berries are removed development of immature berries may be restricted or stopped.This implies that under conventional management high yields will require frequent picking to achieve full potential. Once-over cropping, as in mechanical harvesting, may entail accepting yields one half or less of those now being obtained by conventional hand picking.It is suggested that if evaporative losses from ripe berries can be reduced, as by cloching, tunnelling, windbreaks, or plant breeding for less permeable cell walls, increased yields might be expected.  相似文献   
10.
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