全文获取类型
收费全文 | 1435篇 |
免费 | 143篇 |
专业分类
林业 | 112篇 |
农学 | 40篇 |
基础科学 | 5篇 |
366篇 | |
综合类 | 104篇 |
农作物 | 56篇 |
水产渔业 | 133篇 |
畜牧兽医 | 595篇 |
园艺 | 43篇 |
植物保护 | 124篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 22篇 |
2021年 | 38篇 |
2020年 | 42篇 |
2019年 | 33篇 |
2018年 | 57篇 |
2017年 | 42篇 |
2016年 | 45篇 |
2015年 | 44篇 |
2014年 | 67篇 |
2013年 | 102篇 |
2012年 | 104篇 |
2011年 | 141篇 |
2010年 | 65篇 |
2009年 | 63篇 |
2008年 | 121篇 |
2007年 | 83篇 |
2006年 | 62篇 |
2005年 | 73篇 |
2004年 | 68篇 |
2003年 | 56篇 |
2002年 | 46篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1578条查询结果,搜索用时 31 毫秒
31.
P. Jiménez O. Ortiz D. Tarrasón M. Ginovart M. Bonmatí 《Biology and Fertility of Soils》2007,44(2):393-398
This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity,
total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone
quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS
were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with
no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied
soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect
decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control.
The rank order of the initial stimulating effect was soil–TDS ≥ soil–DS ≥ soil–CDS, and probably, this order depended on the
proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO2) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were
the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase
activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils. 相似文献
32.
Marongiu B Piras A Porcedda S Tuveri E Sanjust E Meli M Sollai F Zucca P Rescigno A 《Journal of agricultural and food chemistry》2007,55(24):10022-10027
The volatile oil of the bark of Cinnamomum zeylanicum was extracted by means of supercritical CO2 fluid extraction in different conditions of pressure and temperature. Its chemical composition was characterized by GC-MS analysis. Nineteen compounds, which in the supercritical extract represented >95% of the oil, were identified. (E)-Cinnamaldehyde (77.1%), (E)-beta-caryophyllene (6.0%), alpha-terpineol (4.4%), and eugenol (3.0%) were found to be the major constituents. The SFE oil of cinnamon was screened for its biological activity about the formation of melanin in vitro. The extract showed antityrosinase activity and was able to reduce the formation of insoluble flakes of melanin from tyrosine. The oil also delayed the browning effect in apple homogenate. (E)-Cinnamaldehyde and eugenol were found to be mainly responsible of this inhibition effect. 相似文献
33.
Kyriakos C. Prousis Stefanos Kikionis Efstathia Ioannou Silvia Morgana Marco Faimali Veronica Piazza Theodora Calogeropoulou Vassilios Roussis 《Marine drugs》2022,20(1)
Marine biofouling is an epibiotic biological process that affects almost any kind of submerged surface, causing globally significant economic problems mainly for the shipping industry and aquaculture companies, and its prevention so far has been associated with adverse environmental effects for non-target organisms. Previously, we have identified bromosphaerol (1), a brominated diterpene isolated from the red alga Sphaerococcus coronopifolius, as a promising agent with significant antifouling activity, exerting strong anti-settlement activity against larvae of Amphibalanus (Balanus) amphitrite and very low toxicity. The significant antifouling activity and low toxicity of bromosphaerol (1) motivated us to explore its chemistry, aiming to optimize its antifouling potential through the preparation of a number of analogs. Following different synthetic routes, we successfully synthesized 15 structural analogs (2–16) of bromosphaerol (1), decorated with different functional groups. The anti-settlement activity (EC50) and the degree of toxicity (LC50) of the bromosphaerol derivatives were evaluated using cyprids and nauplii of the cirriped crustacean A. amphitrite as a model organism. Derivatives 2, 4, and 6–16 showed diverse levels of antifouling activity. Among them, compounds 9 and 13 can be considered as well-performing antifoulants, exerting their activity through a non-toxic mechanism. 相似文献
34.
Faridy Juárez-Chairez Milagros Stephanie Cid-Gallegos María Gabriela Meza-Márquez Ofelia Cristian Jiménez-Martínez 《Plant foods for human nutrition (Dordrecht, Netherlands)》2020,75(2):142-153
Plant Foods for Human Nutrition - Chickpea is one of the most consumed legumes worldwide. Among their benefits are the high protein concentration that reflects not only at the nutritional level but... 相似文献
35.
Landscape Ecology - The majority of remaining tropical forests exist as fragments embedded in a matrix of agricultural production. Understanding the effects of these agricultural landscapes on... 相似文献
36.
Silva Silviany Angelica Fernandes Silva Fláive Loyze Baldassarini Ribas Alessandra Ferreira de Souza Silvia Graciele Hülse dos Santos Tiago Benedito 《Journal of Crop Science and Biotechnology》2020,23(3):241-251
Journal of Crop Science and Biotechnology - Superoxide dismutases (SODs) are a group of enzymes that play essential roles in catalyzing the dismutation of superoxide radicals to protect cells from... 相似文献
37.
NaCl胁迫对黄瓜种子萌发的影响 总被引:7,自引:0,他引:7
采用培养皿发芽法研究了NaCl胁迫处理对黄瓜种子萌发的影响。结果表明:NaCl胁迫浸种、水环境下发芽对黄瓜种子萌发的影响较小,只有在高浓度NaCl胁迫下,才对种子萌发起抑制作用。不同浓度的NaCl胁迫对黄瓜种子发芽的影响有显著差异;随着NaCl胁迫浓度的增大。对发芽的抑制作用明显增强。种子活力指数、发芽指数、胚根一级侧根数比发芽率对NaCl胁迫的反应更敏感。在225mmol/L NaCl胁迫下,黄瓜种子萌发对外源Ca^2 反应较为敏感,适量的外源Ca^2 (10mmol/L CaCl2)对盐胁迫有一定的缓解效应,浓度过高对发芽起抑制作用。适当时间的吸湿-回干处理能缓解NaCl胁迫对黄瓜种子萌发的抑制作用。 相似文献
38.
森林虫害监测是森林经营管理中的一个重要内容,为此作者利用陆地卫星第5号的主题成图仪数据,在加拿大不列颠哥伦比亚省卡奇河试验区对花旗松林被云杉茅卷蛾危害的状况进行了监测。试验表明,在直方均衡的基础上进行比值处理和最大概似分类,其图象处理效果比较理想。利用直升飞机航空目视调查所勾绘的虫害分布图进行对照检验,其位置和形状基本吻合,面积也达到一定的精度。这种分析方法所取得的结果,可作为虫害防治的依据。 相似文献
39.
Brown shrimp (Farfantepenaeus aztecus) density distribution in the Northern Gulf of Mexico: an approach using boosted regression trees
下载免费PDF全文
![点击此处可从《Fisheries Oceanography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jose T. Montero Tanya A. Chesney Jennifer R. Bauer John T. Froeschke Jim Graham 《Fisheries Oceanography》2016,25(3):337-348
The estuarine‐dependent brown shrimp, Farfantepenaeus aztecus, is a significant commercial fishery and important species in the Gulf of Mexico (GOM) ecosystem as well as being a key component in energy transfer between benthic and pelagic food web systems. Because of the economical and ecological importance of brown shrimp, we developed a spatial population model to identify places of high shrimp density under a set of spatial, environmental and temporal variables in the Northern Gulf of Mexico (NGOM). We used fisheries‐independent data collected by the Southeast Area Monitoring and Assessment Program (SEAMAP) from 1992 to 2007 (summer and fall seasons). The relationship between the predictor variables and shrimp density was modeled using Boosted Regression Trees (BRT). Within the environmental variables included in the model, bottom type and depth of the water column were the most important predictors of shrimp density in the NGOM. Spatial predictions performed using the trained BRT model for summer and fall seasons showed a spatial segregation of shrimp density. During the summer, higher densities were predicted near the Texas and Louisiana coast and during the fall, higher densities were predicted further offshore. The model performed well and allowed successful prediction of brown shrimp hot spots in the NGOM. Model results allow fisheries managers to evaluate the potential impact from fisheries on the resource and to develop future fisheries management strategies, understand the biology of brown shrimp as well as assess the potential impacts of oil spills or climate change. 相似文献
40.
Mattana Efisio Peguero Brígido Di Sacco Alice Agramonte Wilvin Encarnación Castillo Wilkin Rafael Jiménez Francisco Clase Teodoro Pritchard Hugh W. Gómez-Barreiro Pablo Castillo-Lorenzo Elena Terrero Encarnación Marianny Way Michael J. García Ricardo Ulian Tiziana 《New Forests》2020,51(4):705-721
New Forests - Native trees from the Caribbean were tested for seed desiccation responses, by adapting the “100-seed test” protocol. Ninety-seven seed lots of 91 species were collected... 相似文献