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   14194篇
  免费   1001篇
  国内免费   12篇
林业   1145篇
农学   517篇
基础科学   71篇
  2805篇
综合类   618篇
农作物   573篇
水产渔业   1352篇
畜牧兽医   6579篇
园艺   238篇
植物保护   1309篇
  2023年   117篇
  2022年   148篇
  2021年   341篇
  2020年   359篇
  2019年   320篇
  2018年   610篇
  2017年   633篇
  2016年   598篇
  2015年   455篇
  2014年   564篇
  2013年   818篇
  2012年   935篇
  2011年   901篇
  2010年   480篇
  2009年   464篇
  2008年   692篇
  2007年   641篇
  2006年   534篇
  2005年   551篇
  2004年   466篇
  2003年   455篇
  2002年   404篇
  2001年   326篇
  2000年   316篇
  1999年   248篇
  1998年   71篇
  1997年   54篇
  1996年   62篇
  1992年   155篇
  1991年   132篇
  1990年   132篇
  1989年   146篇
  1988年   146篇
  1987年   147篇
  1986年   135篇
  1985年   126篇
  1984年   90篇
  1983年   90篇
  1982年   49篇
  1981年   65篇
  1980年   60篇
  1979年   121篇
  1978年   109篇
  1977年   91篇
  1976年   61篇
  1975年   58篇
  1974年   106篇
  1973年   87篇
  1972年   99篇
  1971年   94篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of...  相似文献   
2.
拉丁美洲和加勒比地区是世界主要的竹资源分布区,以瓜多竹为代表的560多竹种资源占全球竹种的33%,其中巴西、哥伦比亚、秘鲁、厄瓜多尔、墨西哥等国竹林面积和竹种数量位居该地区前列。与亚洲相比,拉丁美洲和加勒比地区现代竹产业发展起步较晚,规模和效益有限。面向未来,该区竹资源主要分布国家的政府正在制定和实施相关政策和战略,助力竹区发展经济、缓解贫困和保护环境。  相似文献   
3.
Landscape Ecology - Landscape resistance surfaces are often used to address questions related to movement, dispersal, or population connectivity. However, modeling landscape resistance is...  相似文献   
4.
5.
Water, Air, & Soil Pollution - The treatment efficiency of Chlorella sorokiniana and Scenedesmus species, immobilized in sodium alginate, was evaluated for removing nitrate from groundwater....  相似文献   
6.
Journal of Crop Science and Biotechnology - The cultivation of sweet corn is expanding in Brazil, but there are serious constraints about the availability of commercial cultivars. The selection of...  相似文献   
7.
Integrated crop–livestock–forest is a promising strategy to improve soil quality. It comprises four different integrated farming systems: crop–livestock, crop–forest, forest–livestock and crop–livestock–forest. This work systematically reviewed studies about integrated crop–livestock–forest systems and soil quality. A total of 92 papers were retrieved from the Web of Science—Clarivate Analytics platform, and the following information was analysed: publication year, institution, region of the studied site, type of integrated system, soil type, tillage system, maximum soil depth and the soil quality indicators assessed. Most studies were published in the second half of the 2010s. Brazil is a prominent focus of research about soil quality and integrated crop–livestock–forest systems, with significant contribution from its central and southern regions. The Embrapa was the main publishing institution, present in over one‐third of the studies. Crop–livestock was the most common integrated system, Ferralsols was the most common soil group, and most of the studied soils were clayey. No tillage was the main tillage system. Most studies focused on the topsoil, assessing physical and/or chemical soil quality indicators. More emphasis on biological indicators of soil quality is required, as well as assessments integrating biological, physical and chemical indicators of soil quality. Future works should compare different integrated systems, including assessments deeper in the soil profile, especially in systems with the forest component, and also in sandy and silty soils. Soil quality indicators that have been rarely used should be further tested. Novel indicators should be added to better understand the promotion of soil quality by integrated crop–livestock–forest systems.  相似文献   
8.
9.
Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.  相似文献   
10.
Phytotherapy can replace antibiotic administration as an alternative to control Aeromonas hydrophila, one of the main bacteria involved in the aetiology of farmed fish diseases. Given that plants of the Lippia spp. genus show biological potential for antimicrobial activity, this study evaluated the chemical composition of essential oils extracted from Lippia alba, Lippia origanoides and Lippia sidoides and their activity against A. hydrophila. The oils were obtained by steam distillation in a Clevenger‐type apparatus and their composition determined by gas chromatography and mass spectrometry (CG/MS). Antibacterial activity was assessed by calculating the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using broth microdilution method. The main compounds identified were geranial (25.4%) and neral (16.6%) in L. alba oil, carvacrol (40.4%) and p‐cymene (11.4%) in L. origanoides oil and thymol (76.6%) and ortho‐cymene (6.3%) in L. sidoides oil. The three Lippia species showed bacteriostatic and bactericidal action against A. hydrophila, with MICs and MBCs ranging from 1250 to 5000 μg mL?1. Of the species tested, the best performance was obtained with essential oil of L. sidoides.  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