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   147686篇
  免费   10673篇
  国内免费   71篇
林业   5782篇
农学   4979篇
基础科学   896篇
  17434篇
综合类   25686篇
农作物   5762篇
水产渔业   8972篇
畜牧兽医   76832篇
园艺   1771篇
植物保护   10316篇
  2020年   1412篇
  2019年   2137篇
  2018年   2492篇
  2017年   2790篇
  2016年   2672篇
  2015年   2357篇
  2014年   2697篇
  2013年   6221篇
  2012年   4288篇
  2011年   5020篇
  2010年   3556篇
  2009年   3298篇
  2008年   4841篇
  2007年   4531篇
  2006年   4266篇
  2005年   4075篇
  2004年   3855篇
  2003年   3901篇
  2002年   3596篇
  2001年   4463篇
  2000年   4239篇
  1999年   3416篇
  1998年   1424篇
  1997年   1426篇
  1995年   1626篇
  1994年   1416篇
  1993年   1425篇
  1992年   2897篇
  1991年   3047篇
  1990年   2959篇
  1989年   3017篇
  1988年   2743篇
  1987年   2786篇
  1986年   2927篇
  1985年   2793篇
  1984年   2299篇
  1983年   2030篇
  1982年   1444篇
  1979年   2073篇
  1978年   1633篇
  1977年   1471篇
  1976年   1402篇
  1975年   1511篇
  1974年   1861篇
  1973年   1928篇
  1972年   1846篇
  1971年   1758篇
  1970年   1662篇
  1969年   1574篇
  1967年   1404篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
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.
Holothuria scabra (sandfish) and Babylonia areolata were trialed in two large‐scale co‐culture experiments. Experiment 1 assessed co‐culture in 4 × 400 m2 earthen ponds where Babylonia were cultured in a central pen at a density of 400 individuals/m2 with sandfish occupying the remaining pond space at 1.1 individuals/m2. Sandfish grew from 18.20 ± 6.67 g to 119.03 ± 17.74 g in 92 days and Babylonia (fed trash fish in both experiments) grew from 0.90 ± 0.38 g to 4.93 ± 1.44 g, but Babylonia growth was not increased in co‐culture compared to monoculture. Water and sediment quality varied between co‐culture and monoculture ponds. Neither showed clear improvement due to sandfish culture. Experiment 2 compared non‐segregated sandfish‐Babylonia co‐culture with Babylonia monoculture in 20 m2 concrete raceways. Sandfish were cultured at 2 individuals/m2 and Babylonia at 300 individuals/m2. Sandfish grew up to 1.91 g.day?1 with 100% survival. Babylonia weight gain was significantly greater in co‐culture raceways (3.35 ± 0.64 g over 61 days), which was double that of Babylonia in monoculture. Substrate total N was reduced by 20% in co‐culture compared with monoculture (p = .032). This provisional study of commercial scale sandfish‐Babylonia co‐culture demonstrates culture compatibility, providing a basis for further system development.  相似文献   
9.
Drought severely limits crop yield of peanut. Yet cultivars with enhanced root development enable the exploration of a greater volume of soil for water and nutrients, helping the plant survive. Root distribution patterns of three genotypes (ICGV 98305, ICGV 98324 and Tifton‐8) were compared when grown in well‐watered rhizoboxes and when grown in rhizoboxes where an early‐season drought was imposed using rain‐exclusion shelters. The treatments were arranged in a completely randomized design with three replications, and the experiment was conducted during two seasons at the Field Crop Research Station of Khon Kaen University, in Khon Kaen, Thailand. The root system of ICGV 98305, when grown under drought, had a significantly higher root length in the 30–110 cm deep soil layers and less roots in the 0–30 cm soil layers when under drought than when grown under well‐watered conditions. Roots of Tifton‐8 had the largest reductions in root length in upper soil layer and reduced in most soil layers. Tifton‐8 grown under drought was smaller than under well‐watered control for all root traits, showing negative response to drought. The peanut genotypes with high root traits in deeper soil layer under early‐season drought might contribute to drought avoidance mechanism.  相似文献   
10.
Increasingly, weeds have been taking on global distributions. With the proliferation of invasive weeds has come the challenge of managing these species over broad geographical regions, with diverse habitats and political jurisdictions. Here, we review the management of Mikania micrantha Kunth (Asteraceae; mile‐a‐minute) throughout its invaded range, extending through most of the Pacific islands and southern and south‐east Asia. Context matters when determining the best course of action for managing M. micrantha, as it has invaded a large variety of agricultural and natural systems. In Queensland, Australia and Florida, USA, M. micrantha has been targeted in relatively successful eradication campaigns, highlighting the importance of early detection and rapid response methods, while elsewhere in its invaded range, populations are either still increasing or showing limited signs of decline. An inter‐regional approach to research and management should incorporate successful management strategies employed throughout the invaded range including, but not limited to, chemical and cultural control practices, manual and mechanical control, classical biological control using the rust fungus Puccinia spegazzinii, plant–plant competition and integrated approaches utilising two or more control methods concurrently. Additional knowledge of M. micrantha genetics is required to determine if management approaches could be fine‐tuned for particular populations. Countries bordering the Mekong River formed a network in 2011 to co‐ordinate the management of invasive species such as M. micrantha. Expanding such a collaborative approach to other regions could further reduce populations of M. micrantha and limit its spread.  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