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   2633篇
  免费   263篇
  国内免费   118篇
林业   290篇
农学   105篇
基础科学   148篇
  185篇
综合类   1145篇
农作物   46篇
水产渔业   884篇
畜牧兽医   118篇
园艺   33篇
植物保护   60篇
  2024年   10篇
  2023年   47篇
  2022年   49篇
  2021年   93篇
  2020年   98篇
  2019年   146篇
  2018年   71篇
  2017年   105篇
  2016年   101篇
  2015年   84篇
  2014年   150篇
  2013年   126篇
  2012年   164篇
  2011年   195篇
  2010年   159篇
  2009年   166篇
  2008年   148篇
  2007年   152篇
  2006年   128篇
  2005年   136篇
  2004年   111篇
  2003年   99篇
  2002年   72篇
  2001年   97篇
  2000年   70篇
  1999年   38篇
  1998年   44篇
  1997年   18篇
  1996年   27篇
  1995年   16篇
  1994年   30篇
  1993年   15篇
  1992年   19篇
  1991年   9篇
  1990年   5篇
  1989年   6篇
  1988年   5篇
  1987年   5篇
排序方式: 共有3014条查询结果,搜索用时 15 毫秒
101.
食用菌产业的发展具有极大的发展前景,对于食用菌生产也提出了越来越严格的要求。食用菌产业的发展在为农民提供了谋生的途径的同时,还需要加强食用菌菌种监督与管理,层层把关。  相似文献   
102.
以欧亚种酿酒葡萄"赤霞珠"为试材,采用分光光度法,系统比较了金沙江流域和澜沧江流域不同海拔"赤霞珠"葡萄果实品质差异及其发育期品质指标的积累规律,以期为香格里拉及世界其它高海拔产区优质和特色葡萄与葡萄酒的生产提供参考。结果表明:较长的日照时长、较强的紫外辐射及较大的温差使得位于海拔2 121m的溜筒江生产的"赤霞珠"葡萄果实还原糖含量最高(265.16g·L-1),总酸最低(4.01g·L-1)。另外,位于海拔2 238m的达日生产的"赤霞珠"葡萄果实总酚、单宁和果皮总花色苷含量最高(分别为8.58mg·g-1、11.54mg·g-1和160.53A520·g-1)。金沙江和澜沧江流域各产地发育期葡萄果实可溶性固形物和还原糖含量均呈升高趋势,总酸均呈先增加后降低趋势。金沙江流域(瓦卡和达日)比澜沧江流域(西当、斯农和阿东)葡萄果实还原糖快速积累期和总酸快速下降期普遍提前2周左右。金沙江流域和澜沧江流域各产地在海拔2 000~2 250m范围内,成熟期葡萄果实中总酚、单宁和果皮总花色苷含量随着葡萄园海拔升高而升高,并均在各流域2 250m附近的葡萄园达最高。随着葡萄园海拔再度升高,到海拔最高的阿东(2 602m),其葡萄果实中总酚和单宁的含量又有所下降,但是果皮总花色苷没有显著变化。金沙江流域2个产地葡萄果实总酚和单宁含量在整个发育期内的积累规律与澜沧江流域4个产地不同,且达到最大值的时期也不同。可能是由于澜沧江流域溜筒江产地的风土条件与金沙江流域类似,其发育期内品质指标,特别是还原糖和总酸含量的变化与金沙江流域具有类似的模式。  相似文献   
103.
农业是一切非物质生产部门存在与发展的必要条件,重农固本是安民之基、兴国之要。但在农业生产发展过程中,部分农资生产、经营主体及农户为谋求更大的经济效益,忽视农产品质量安全问题,严重影响了我国农业的健康持续发展。基于此,加强农产品质量安全监管与农业行政执法就显得尤为重要。本文主要分析了柳州市农产品质量安全生产的现状,论述了农业执法在农产品质量安全监管中的作用,提出了合理化的改善建议,以期推动当地农业的可持续发展。  相似文献   
104.
本文在介绍新西兰《1993年公司法》关于董事义务规定的基础上指出:其特点是将原属普通法中董事义务成文化,其目的看起来是要脱离普通法,但实际上,在公司法施行中.在对有关公司法的案件处理的过程中,仍然需要靠普通法对董事的义务进一步解释和完善。  相似文献   
105.
黄硕琳 《水产学报》1990,14(1):72-78
一、新海洋法中的渔业规则 (一)1982年海洋法公约中的渔业规则在国际法中的地位 联合国第三次海洋法会议于1978年底召开,经过长期协商,于1982年4月23日通过了《海洋法公约》,公约于1982年12月10日开始签字,有119个国家立即签了字。到1985年11月为止,共有159  相似文献   
106.
Non-commercial invertebrate discards in an experimental trammel net fishery   总被引:1,自引:0,他引:1  
Abstract  Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relation to selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a 1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm) outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m−1 of net) of non-commercial invertebrates were discarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Within non-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata (Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus (Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echinoderms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter, respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were not related to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impacts on benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m).  相似文献   
107.
Abstract  The tremendous loss of life and assets resulting from the 2004 tsunami dealt a devastating blow to the coastal communities of Aceh Province, Indonesia. An assessment of the fishing fleet structure pre- and post-tsunami, including associated pattern in boat aid, in 15 coastal communities was conducted and compared with data on boat relief efforts over 17 districts of the Province. Aid was found to be not proportionally allocated to losses incurred by communities and was in many cases below what could be seen as a trend toward overcapacity. The distribution of aid appeared to be done without consideration of the former structure of the fleet, which changed significantly over time (pre- and post-tsunami), and resulted in a new fleet of reduced diversity with a strong focus on the smaller boat categories. If this situation perpetuates after the initial post-disaster period, it may further exacerbate the pre-existing economic and geographic marginalisation of some remote communities, and reduce the capacities of the fleets to diversify and develop multi-species harvesting strategies; thus, increasing the risk of ecologically unsustainable exploitation in near shore areas.  相似文献   
108.
Irish Sea fisheries have undergone considerable change in recent years following the decline of commercially important finfish stocks and their slow response to management's recovery plans. In 2015, the fishing industry called for a holistic exploration into the impact of environmental change and food web effects to identify the drivers underpinning stock dynamics. In this study, we identify correlations between large‐scale climatic indicators, temperature, primary and secondary productivity, and fish recruitment in the Irish Sea and incorporate them into an Ecopath with Ecosim food web model co‐created by scientists and fishers. Negative correlations were found between the North Atlantic Oscillation winter index (NAOw) and large zooplankton abundance and between the Atlantic Multidecadal Oscillation (AMO) and the recruitment of cod (Gadus morhua) and whiting (Merlangius merlangus). Using correlation analyses to direct the addition of environmental drivers to the Irish Sea ecosystem model improved the models fit against observed biomass and catch data and revealed the indirect impacts of environmental change as mitigated through trophic interactions. Model simulations suggest that historic environmental change suppressed the overall production of commercial finfish, limiting opportunities for the fishing industry, whilst also dampening the rate of stock recovery despite marked reductions in fishing effort. These results suggest that failure to account for ecosystem information may lead to misconceived expectations and flawed fisheries management; therefore, there is a need to operationalize ecosystem information through management procedures to support fisheries advice.  相似文献   
109.
Abstract Global warming is expected to result in considerable changes in northern European freshwater fish populations, fisheries and aquaculture. Shifts towards cyprinid and percid dominance in fish assemblages are expected, together with a decrease and collapse of salmonid and other coldwater fish populations. Most of the evident changes will occur in shallow lakes, where no thermal stratification occurs. The potential ranges of some fish species will shift northwards but pronounced changes will occur in the relative abundance of individual fish species. Total fish production will increase but because of changed composition of fish communities the commercial and recreational value of catches will decrease. Salmonid aquaculture productivity will increase provided that fish farmers adapt to new circumstances and cold, oxygenated water is available in larger quantities during summer.  相似文献   
110.
金厦海域生物资源丰富,曾是厦门和金门渔民传统的生产渔场。近年来随着两地经济的发展,该海域的海洋生态的损害逐步加重,渔业资源严重衰退,海洋生物多样性遭受重大损害。显然,两岸携手进行该海域的海洋生态养护是十分必要的。本文通过分析该海域的海洋生物资源的基本情况及厦门和金门多年来开展的渔业资源养护工作及其效果,提出两岸携手养护厦金海域渔业资源的合作机制,并建议合作开展海洋环境质量调查,渔业生产现状调查,增殖放流,鱼类栖地再造,划设渔业资源保护区等工作。  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