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   139篇
  免费   12篇
林业   10篇
农学   12篇
基础科学   4篇
  16篇
综合类   13篇
农作物   19篇
水产渔业   19篇
畜牧兽医   47篇
园艺   1篇
植物保护   10篇
  2023年   1篇
  2022年   3篇
  2021年   4篇
  2020年   7篇
  2019年   3篇
  2018年   8篇
  2017年   1篇
  2016年   4篇
  2015年   4篇
  2014年   5篇
  2013年   5篇
  2012年   3篇
  2011年   15篇
  2010年   4篇
  2009年   6篇
  2008年   7篇
  2007年   3篇
  2006年   9篇
  2005年   2篇
  2004年   3篇
  2003年   3篇
  2002年   9篇
  2001年   3篇
  2000年   2篇
  1999年   3篇
  1998年   3篇
  1997年   1篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1992年   5篇
  1991年   1篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1986年   1篇
  1985年   1篇
  1983年   2篇
  1981年   1篇
  1980年   1篇
  1973年   1篇
  1968年   1篇
  1964年   2篇
  1963年   2篇
  1948年   1篇
排序方式: 共有151条查询结果,搜索用时 15 毫秒
101.
The major uncertainty in the climate change impact study inherits from applying the predictions of General Circulation Models (GCMs). Different results might be obtained by using various GCMs’ predictions, which causes difficulties on the decision making of water resources management. This study proposed an integrated hydrological simulations and optimization framework, consisting of a fuzzy linear programming model with interval numbers, a streamflow simulation model, and agricultural water demand projections, to evaluate the impacts of climate change on reservoir active storage. The reservoir inflows are simulated by the WatBal model, while agricultural water demands are predicted based on the projected change of potential evapotranspiration. Inflows and water demands are used to formulate an interval number fuzzy linear programming model. Fuzzy relationships are used to describe tolerable deficits of water resources, and the interval number is employed to indicate ranges of possible inflows and water demands. This systematic framework is applied to study the Tsengwen reservoir watershed to provide an optimal interval of active storage. The results further indicate the higher tolerable deficit, the smaller difference between superior and inferior active storage.  相似文献   
102.
Critical thermal minima (CTMin) were determined for subadults of Penaeus merguiensis acclimated at 15, 18, 21 and 24 °C for 3 weeks. The effect of cooling rate on CTMin was also investigated. The CTMin of prawns from these respective acclimation groups were 5.3, 6.0, 7.4, 9.0 and 4.7, 5.4, 6.0, 7.3 °C at the cooling rate of 1 °C h?1 and 3 °C h?1 respectively. Both acclimation temperature and cooling rate had a significant effect (P < 0.01) on the CTMin. Observation during the acclimation period showed that the growth rate of prawns acclimated at 24 °C was much higher than those acclimated at 21, 18 and 15 °C. The results indicate that P. merguiensis can overwinter in aquaculture ponds in south‐east Queensland, Australia, or other subtropical areas and attain good growth if simple overwintering facilities are available.  相似文献   
103.
The combined effects of temperature (23 and 27 °C), light intensity (1100 and 2 lux or ≈ 21.5 and 0.04 μEinst m?2 s respectively) and photoperiod (10 h light/14 h dark and 14 h light/10 h dark) on ovarian maturation and spawning performance of ablated pond‐reared Penaeus merguiensis were investigated in a 51‐day experiment. The results showed that temperature was the most influential factor, followed by light intensity, whereas the effect of photoperiod was minor. As the maturation process progressed, the effects of temperature and light intensity became stronger while that of photoperiod became less significant. Temperature significantly affected all the reproductive parameters assessed. Prawns in the 27 °C treatments outperformed those in the 23 °C treatments (P < 0.05). The effect of light intensity was found to have a significant effect (P < 0.05) only on the proportion of spawners (prawns that spawned) and spawning rate. More prawns spawned at a higher rate under dim light (2 lux) than under strong light (1100 lux). Photoperiod affected only the proportion of prawns reaching stage III of ovarian development (P < 0.05). There were interactions between temperature and light intensity affecting the proportion of prawns reaching stage III and, although not significantly, the proportion of spawners (P = 0.177), fecundity (P = 0.134) and survival (P = 0.061). Overall, it is recommended that a combination of 27 °C, 2 lux and 10 h light/14 h dark is suitable for the maturation of pond‐reared P. merguiensis. There were indications that temperature can be used to control the rate of ovarian maturation. Also, it is possible to increase light intensity up to 1100 lux in P. merguiensis hatcheries if prawns are ablated.  相似文献   
104.
This study evaluated the use of live and frozen copepods collected from shrimp ponds for rearing juveniles of the spotted seahorse Hippocampus kuda. Protein and HUFA contents in frozen copepods were all higher than in Artemia nauplii, the conventional live food for seahorse juveniles. The results of this study showed that copepods can be used as feed for rearing seahorse fry and juvenile. The spotted seahorse showed obvious preference for live copepods and rarely fed on dead copepods on the tank bottom. Furthermore, the combination of frozen copepods and live Artemia nauplii resulted in highest growth and highest survival of the experimental seahorses. Further research on possible effects of DHA:EPA ratio on survival and growth of young H. kuda is recommended.  相似文献   
105.
The arrangement of land use substantially affects outdoor human comfort. The purposes of this study were to develop a spatial optimization procedure that involves combining simulated annealing algorithm with a microclimate model (ENVI-met) and to identify the relationship between the spatial pattern of the major cooling source and human comfort. The procedure is an assessment tool for appropriately designing living space on a community scale. The physiological equivalent temperature (PET) was used as the index of human comfort, and the objective of optimization was to minimize the difference in the PET to 23 °C within the study area. Four types of land use, namely buildings, paddies, parks, and ponds, were considered. Given the types of land use and the land areas, the procedure is used to determine the optimal layout that provides the most comfortable environment. The results revealed that the optimal design effectively improved the homogeneity of human comfort quantitatively and spatially in summer. Human comfort in the entire area was improved when the prevailing wind first passes through cooling sources, such as the paddies, and the walkways are easier to cool when the cooling sources are located nearby. The results of the spatial optimization procedure can further be applied to determine the relationship between the spatial pattern of land use and human comfort, and the relationship can be used as a reference for future research on community design.  相似文献   
106.
107.
Adverse outcome pathway (AOP)-based computational models provide state-of-the-art prediction for human skin sensitizers and are promising alternatives to animal testing. However, little is known about their applicability to pesticides due to scarce pesticide data for evaluation. Moreover, pesticides traditionally have been tested on animals without human data, making validation difficult. Direct application of AOP-based models to pesticides may be inappropriate since their original applicability domains were designed to maximize reliability for human response prediction on diverse chemicals but not pesticides. This study proposed to identify a consensus chemical space with concordant human responses predicted by the SkinSensPred online tool and animal testing data to reduce animal testing. The identified consensus chemical space for non-sensitizers achieved high concordance of 85% and 100% for the cross-validation and independent test, respectively. The reconfigured SkinSensPred can be applied as the first-tier tool for identifying non-sensitizers to reduce. animal testing for pesticides by 19.6%.  相似文献   
108.
据1962—1963年两年的研究,桃小食心虫在乐陵棗区一年发生1—2代。第二代发生数量多少与当年整个发生期的早晚有密切的关系。桃小食心虫以老熟幼虫結“越冬茧”在土內越冬,其垂直分布深度限于离土表4寸范围內,平面分布愈近树干密度愈大。越冬幼虫自6月中旬开始出土,一直延續到8月上、中旬結束,盛期在7月中旬左右。越冬幼虫出土与降雨有密切关系。在室內越冬幼虫出土及第一代老熟幼虫脫果后至成虫羽化历期,分别平均为10.4天及10.8天。成虫白天不活动,夜間11—1时之間交尾。产卵前期平均为2.5—2.7天,产卵期間平均为1.3—2.1天。雌虫平均产卵量为27.9粒(越冬代)和40.5粒(第一代),最多可产154粒。在田間,卵绝大多数产在叶片背面基部(72.6%),产在果实梗洼(27.4%)和胴部较少,其它部位尚未发现。田間卵自7月中、下旬开始发生,至8月下旬或9月初結束。第一、二代卵期分別平均为6.8和8.4天,孵化率分別为92.3%和89.5%。幼虫扎果从7月末 (或8月初) 起至9月中、下旬棗采收,前后达50天左右。幼虫脫果从8月中旬起,至9月中、下旬棗采收后尚未結束。果內幼虫期最短9天,最长28天,平均16.8天左右。地面药剂处理应該在6月中、下旬越冬幼虫出土前,这是第一个防治关鍵时期;在第一、二代卵盛期(7月下旬及8月中旬左右),噴药两次是防治桃小食心虫的第二个关鍵时期。地面药剂处理,3%666粉剂与3%666颗粒剂效果差不多。树上喷药可用25%DDT乳剂250倍液加用0.01%“拉开粉”或0.1%水胶,可以提高防治效果。  相似文献   
109.
Oriented polypropylene (OPP) and coated OPP (acrylic/OPP/PVDC) films were printed with two commercially available inks to investigate the influence of inks on water vapor and oxygen transmission rates. The permeation of an aroma compound (d-limonene) through coated OPP film printed with these inks was also evaluated at 35 degrees C and 100% relative humidity. The water vapor transmission rate increased significantly through OPP film printed with nitrocellulose-based ink. The oxygen transmission rate was significantly lower through both OPP and coated OPP films printed with the nitrocellulose ink. The effect of inks on limonene permeation was minor compared to the marked increase in permeation measured when the PVDC side of the coated film was exposed to the aroma, compared to the acrylic side. Scanning electron micrographs of coated film cross sections revealed changes in film structure upon exposure to limonene vapors, which were most pronounced when the PVDC side was exposed to limonene.  相似文献   
110.
Eurasian Soil Science - We investigate the key predictors that influence the soil organic matter (SOM) content in higher altitude plantations. This is to study the potential of carbon sequestration...  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