全文获取类型
收费全文 | 4400篇 |
免费 | 397篇 |
国内免费 | 449篇 |
专业分类
林业 | 609篇 |
农学 | 281篇 |
基础科学 | 211篇 |
842篇 | |
综合类 | 1852篇 |
农作物 | 77篇 |
水产渔业 | 575篇 |
畜牧兽医 | 323篇 |
园艺 | 61篇 |
植物保护 | 415篇 |
出版年
2024年 | 36篇 |
2023年 | 134篇 |
2022年 | 163篇 |
2021年 | 183篇 |
2020年 | 235篇 |
2019年 | 239篇 |
2018年 | 155篇 |
2017年 | 210篇 |
2016年 | 216篇 |
2015年 | 202篇 |
2014年 | 260篇 |
2013年 | 278篇 |
2012年 | 347篇 |
2011年 | 317篇 |
2010年 | 265篇 |
2009年 | 278篇 |
2008年 | 215篇 |
2007年 | 270篇 |
2006年 | 219篇 |
2005年 | 183篇 |
2004年 | 162篇 |
2003年 | 119篇 |
2002年 | 112篇 |
2001年 | 78篇 |
2000年 | 70篇 |
1999年 | 49篇 |
1998年 | 44篇 |
1997年 | 27篇 |
1996年 | 26篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 11篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有5246条查询结果,搜索用时 31 毫秒
101.
生物大分子标记物是指生物体内的一些对外界环境变化敏感并能产生一些可检测变化的大分子物质,这些大分子物质能够反映环境变化对生物体的影响。随着社会对环境保护的日益重视和分子生物学技术的发展,将生物大分子标记物的检测应用到环境监测中已经成为一种趋势。生物大分子标记物检测由于其测定指标全面、准确、系统且具有特异性等优点,近十几年来作为污染物暴露和毒性效应的早期预警工具已被广泛应用于环境评价中。本文对一些主要的生物大分子标记物及其检测技术在环境监测中的应用状况及应用前景进行综述,旨在为生物大分子标记技术在环境检测实际操作中的应用提供参考依据。 相似文献
102.
The hypothesis that the presence of fish farming zones affects the water quality and plankton communities was investigated in an Aegean Sea fish farm during February, June, September and January 2000–2001. In the spatial coverage, a total of 12 stations were sampled; three of them were reference stations. A variance analysis was applied to the measurements made at the stations near the fish farms and at the control stations. While no significant differences in concentrations of nutrients, chlorophyll a, particulate organic carbon and particulate organic nitrogen were detected between the stations and the control sites within one season, significant differences were detected between the parameter values measured except for total dissolved phosphorus and dissolved organic phosphorus at different seasons. The seasonal differences were also significant with regard to the biodiversity. Together with these temporal differences in general, there was a higher diversity of species at the control site as compared with the other stations in September, which was the key season to detection of significant changes. The most important consideration is that it is not sufficient to take the instantaneous values for the physico‐chemical variables; rather, it is necessary to monitor the biological parameters in order to define the differences in the ecosystem. 相似文献
103.
广州精通教育基地校园二期环境设计,延续与强化校区总体规划设计精神,充分结合校区的地形地貌,以人为本,因地制宜,抓住校园文化内涵,将校园精神贯穿于环境设计的各个部分,形成极近自然的校园景观环境。 相似文献
104.
105.
以盐碱化湖泊和池塘水进行凡纳滨对虾(Litopenaeus vannamei Boone,1931)幼虾生长试验,探讨碱水环境对虾体重生长速度与Ca2 、Mg2 、Ca2 Mg2 质量浓度及(1/2Ca2 )/(1/2 Mg2 )的关系,为碱水水域养殖提供科学依据.结果表明,在碱度为10.32~38.50 mmol/L、盐度1.02~3.34g/L、pH 8.5~9.5的水环境中,体长为10~20 mm的幼虾饲养27 d的体重生长速度为(0.95 0.18)mg/d,存活率(47.5±14.5)%.不同水环境存活率差异显著(P<0.01),体重生长速度差别不明显(P>0.05).体重生长速度与环境因子问的相关性不明显.通过驯化提高幼虾对水环境的综合适应能力,是碱水水域养殖对虾的重要途径. 相似文献
106.
107.
Processes of collating a European fisheries database to meet the objectives of the European Union Water Framework Directive 总被引:1,自引:0,他引:1
U. BEIER & E. DEGERMAN A. MELCHER C. ROGERS H. WIRLÖF 《Fisheries Management and Ecology》2007,14(6):407-416
Abstract FIsh Database of European Streams, a common database for the FAME project, was merged using existing data on electric fishing and environmental data. FIsh Database of European Stream is a relational database with eight tables. Metrics based on classification of fish species into guilds were calculated, and provided in separate tables. FIsh Database of European Stream contained information about 150 freshwater fish species, from 12 countries, 17 ecoregions, 40 main river regions, 2651 rivers and 8228 sites. Examples of data coverage and use are given. Relationships between environmental variables were illustrated using principal component analysis, which resulted in three environmental components – latitude, size and altitude. Environmental component scores were correlated with fish metrics used in the European Fish Index. Results exemplify how fish guilds reflect gradients in environmental variation. Benefits and problems concerning standardisation and data availability at the global level are discussed. 相似文献
108.
Abstract – Temperature fluctuation has been shown to affect somatic growth rates and metabolic functions of fish, but little is known about the effects of fluctuating temperatures on life-history traits. We examined these effects on female Japanese medaka ( Oryzias latipes ) reared from hatch to maturity at two mean temperatures (27 and 30 °C) with diel temperatures either held constant or allowed to fluctuate ±5 °C. Feeding regimes were manipulated to equilibrate medaka growth rates in all treatments. Age and length at maturity decreased as a result of thermal fluctuation, whereas there was no effect of temperature fluctuation on the proportion of fish attaining maturity or on the number of eggs produced by a mature female. We hypothesise that short-term high temperatures associated with temperature fluctuation decreases development time, whereas reduced energy conversion efficiency at higher temperatures does not allow for increased egg production. 相似文献
109.
110.