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   912篇
  免费   68篇
  国内免费   2篇
林业   65篇
农学   14篇
基础科学   3篇
  128篇
综合类   180篇
农作物   18篇
水产渔业   106篇
畜牧兽医   371篇
园艺   41篇
植物保护   56篇
  2024年   5篇
  2023年   11篇
  2022年   11篇
  2021年   28篇
  2020年   31篇
  2019年   37篇
  2018年   34篇
  2017年   21篇
  2016年   30篇
  2015年   30篇
  2014年   24篇
  2013年   53篇
  2012年   56篇
  2011年   78篇
  2010年   40篇
  2009年   30篇
  2008年   47篇
  2007年   62篇
  2006年   60篇
  2005年   53篇
  2004年   43篇
  2003年   37篇
  2002年   36篇
  2001年   11篇
  2000年   10篇
  1999年   5篇
  1997年   3篇
  1995年   3篇
  1994年   2篇
  1993年   6篇
  1992年   3篇
  1991年   4篇
  1990年   6篇
  1989年   5篇
  1988年   2篇
  1987年   2篇
  1986年   4篇
  1985年   6篇
  1984年   5篇
  1983年   5篇
  1980年   4篇
  1978年   5篇
  1977年   6篇
  1976年   7篇
  1975年   3篇
  1974年   2篇
  1973年   2篇
  1969年   2篇
  1963年   2篇
  1942年   2篇
排序方式: 共有982条查询结果,搜索用时 15 毫秒
201.
Preparing articulated skeletons of small vertebrates is extremely difficult due to the presence of vast amounts of cartilage and/or the extremely small size of skeletal components. Clearing the tissues surrounding small skeletons and staining the bones in toto reveals the skeletal system without the risk of displacing the bony components. The specimens are first fixed and bleached which renders the tissues preserved and transparent. These specimens may then be exposed to alizarin red S which stains bone a pink to red colour making them visible through the transparent soft tissues. Toluidine blue may also be used to stain cartilage a blue colour. The Spalteholz staining method is cited, though the focus will be on the KOH and glycerine clearing method for macroscopic observation.  相似文献   
202.
203.
204.
205.
The present work aimed to investigate the presence of T. vivax DNA in the semen of experimentally infected goats. Twelve male goats native to the Brazilian Northeast, adults, were randomly assigned to two experimental groups: the infected group consisting of six goats infected intravenously with 0.5 mL of blood containing approximately 1.25?×?105 trypomastigotes of T. vivax, and a control group composed of six uninfected goats. After the infection, clinical examinations aiming to evaluate rectal temperature, parasitemia and hematocrit were performed. Semen samples were collected from goats by electroejaculation on the 7th, 14th and 21st days post-infection (dpi). The recombinant DNA-encoding gene encoding the L-like-specific gene for T. vivax. The infection was characterized by increased rectal temperature, high parasitemia and significant reduction of hematocrit values. Results for T. vivax DNA detection using TviCatL-PCR were positive in all semen samples from the infected group collected on 7th, 14th and 21st dpi. The presence of T. vivax DNA in 7th dpi suggests the early invasion of the parasite in the reproductive organs. Also, the finding of T. vivax DNA in all periods analyzed may suggest the continued elimination of the parasite in the semen, which may increase the chances of sexual transmission. Thus, T. vivax DNA is recorded for the first time in the semen of infected goats. Thus, these data are of great importance, since the detection of the T. vivax genetic material in the semen may point to the possibility that the parasite may be transmitted through the sexual pathway.  相似文献   
206.
An English Bulldog underwent radiation therapy of an intracranial, left lateral ventricle mass. Following resolution of the primary mass, an intraventricular fourth ventricle lesion developed. Subsequently, multiple lesions developed from the cervical central canal and leptomeninges. Serial magnetic resonance imaging documented the propagation of lesions along the cerebrospinal fluid (CSF) pathways, known as “CSF drop metastasis.” Histopathology confirmed multifocal intraventricular and leptomeningeal oligodendroglioma. Oligodendroglioma should be included in the differential diagnosis for an intraventricular tumor exhibiting apparent CSF drop metastasis.  相似文献   
207.
Pentzia incana is one of the most important of all natural pasture plants in the dry interior (Karoo) region of South Africa. This highly aromatic shrub is thought to be responsible for the distinctive flavour of Karoo lamb (a registered geographical indication), yet the essential oil is here characterised for the first time. Leafy twigs are traditionally chewed for relief of stomach ache. Essential oil is associated with numerous small, multicellu- lar glands. Gas chromatography and gas chromatography/mass spectrometry analysis of 17 essential oil samples from five populations showed considerable variation in both yield (0.12% to 0.88% dry weight) and composition. Of interest was the presence of one major biosynthetic group comprising yomogi alcohol (to 38.9%), artemisia alcohol (to 26.1%), artemisia ketone (to 35.0%) and artemisyl acetate (to 9.4%). High levels of fragranol (26.9%) and fragranyl acetate (27.1%) were observed only in a single specimen. Other main compounds were 1,8-cineole (to 16.7%), santolina alcohol (to 11.3%), camphor (to 47.9%), linalyl acetate (to 17.4%) and bicyclogermacrene (to 11.8%). Six of the 10 major compounds were isolated and their identities confirmed by nuclear magnetic resonance. The volatile compounds may possibly be linked to the medicinal use of P. incana, as well as the flavour profile of Karoo lamb.  相似文献   
208.
209.
210.

Management of tropical marine environments calls for interdisciplinary studies and innovative methodologies that consider processes occurring over broad spatial scales. We investigated relationships between landscape structure and reef fish assemblage structure in the US Virgin Islands. Measures of landscape structure were transformed into a reduced set of composite indices using principal component analyses (PCA) to synthesize data on the spatial patterning of the landscape structure of the study reefs. However, composite indices (e.g., habitat diversity) were not particularly informative for predicting reef fish assemblage structure. Rather, relationships were interpreted more easily when functional groups of fishes were related to individual habitat features. In particular, multiple reef fish parameters were strongly associated with reef context. Fishes responded to benthic habitat structure at multiple spatial scales, with various groups of fishes each correlated to a unique suite of variables. Accordingly, future experiments should be designed to test functional relationships based on the ecology of the organisms of interest. Our study demonstrates that landscape-scale habitat features influence reef fish communities, illustrating promise in applying a landscape ecology approach to better understand factors that structure coral reef ecosystems. Furthermore, our findings may prove useful in design of spatially-based conservation approaches such as marine protected areas (MPAs), because landscape-scale metrics may serve as proxies for areas with high species diversity and abundance within the coral reef landscape.

  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