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   217篇
  免费   24篇
林业   11篇
农学   11篇
  53篇
综合类   10篇
农作物   18篇
水产渔业   18篇
畜牧兽医   98篇
园艺   6篇
植物保护   16篇
  2023年   3篇
  2022年   5篇
  2021年   7篇
  2020年   17篇
  2019年   9篇
  2018年   11篇
  2017年   13篇
  2016年   12篇
  2015年   10篇
  2014年   18篇
  2013年   13篇
  2012年   18篇
  2011年   17篇
  2010年   10篇
  2009年   11篇
  2008年   16篇
  2007年   12篇
  2006年   11篇
  2005年   9篇
  2004年   10篇
  2003年   4篇
  2002年   4篇
  1990年   1篇
排序方式: 共有241条查询结果,搜索用时 15 毫秒
11.
Glyoxal, methylglyoxal, and diacetyl formed as Maillard reaction products in heat-treated food were determined in coffee extracts (coffee brews) obtained from green beans and beans with different degrees of roast. The compounds have been reported to be mutagenic in vitro and genotoxic in experimental animals in a number of papers. More recently, alpha-dicarbonyl compounds have been implicated in the glycation process. Our data show that small amounts of glyoxal and methylglyoxal occur naturally in green coffee beans. Their concentrations increase in the early phases of the roasting process and then decline. Conversely, diacetyl is not found in green beans and forms later in the roasting process. Therefore, light and medium roasted coffees had the highest glyoxal and methylglyoxal content, whereas dark roasted coffee contained smaller amounts of glyoxal, methylglyoxal, and diacetyl. For the determination of coffee alpha-dicarbonyl compounds, a reversed-phase high performance liquid chromatography with a diode array detector (RP-HPLC-DAD) method was devised that involved the elimination of interfering compounds, such as chlorogenic acids, by solid phase extraction (SPE) and their derivatization with 1,2-diaminobenzene to give quinoxaline derivatives. Checks of SPE and derivatization conditions to verify recovery and yield, respectively, resulted in rates of 100%. The results of the validation procedure showed that the proposed method is selective, precise, accurate, and sensitive.  相似文献   
12.
In most European countries, registration and identification of dogs is compulsory. In Italy, the national dog registry is composed of regional dog registries. Although dog registries have been established for many years, the issue related to completeness of data has not been addressed so far. The objective of this study was twofold: first to assess the completeness of data of the dog registry through telephone interview of a sample of dog owners drawn from the dog registry, then to estimate the total owned dog population in 4 boroughs of Rome. For the second objective, a capture–recapture method was applied using data from the dog registry and data from a face-to-face questionnaire submitted to people waiting in the sitting room of 5 points of access for booking and payment of primary and specialist care. Different scenarios are proposed to verify the assumptions of the estimation procedure and potential biases are discussed. The completeness of data of the dog registry was 88.9% (95% CI: 85.8–91.9%) and the owned-dog population was estimated at 26,244 dogs (95% CI: 24,110–28,383). The dog registry is an important source of information especially when it is properly updated and completeness of data is known.  相似文献   
13.
The paper analyses the determinants of regional disparities in per capita gross domestic product (GDP) and their evolution over time in the enlarged European Union (EU). With reference to the literature it groups EU regions on the basis of three different factors—specialisation, socio‐economic features, and innovation. It then analyses regional disparities in per capita GDP (EU‐relative and country‐relative) across groups over 2004–2011 using both non‐parametric tools and traditional regression analysis with spatial effects. The paper finds that EU‐wide convergence actually conceals growing divergence across old member regions and within new members. Coming to the factors that lie at the heart of regional disparities, country factors lose importance for newcomers but become more important for older members, notwithstanding longstanding integration. Socio‐economic factors and innovation instead become increasingly important for all areas, socio‐economic factors lying at the heart of within‐country differences and innovation more of those between regions. Finally, specialisation appears to have a lower explanatory power.  相似文献   
14.
The composition of the essential oil from ripe and unripe berries and leaves of Juniperus oxycedrus L. ssp. oxycedrus, Juniperus phoenicea ssp. turbinata and Juniperus communis ssp. communis was analyzed by GC-MS, and microbiological assays were carried out. Samples were collected in different localities (Sardinia, Italy) and hydro distilled. The yields ranged between 2.54% +/- 0.21 (v\w dried weight) and 0.04% +/- 0.00. A total of 36 components were identified. The major compounds in the essential oils were alpha-pinene, beta-pinene, delta-3-carene, sabinene, myrcene, beta-phellandrene, limonene, and D-germacrene. Both qualitative and quantitative differences between species and between different parts of the plant were observed. The essential oils and their major compounds were tested against Candida albicans, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and the minimum inhibitory concentration and minimum bactericidal concentration were determined. The results obtained led to a nonsignificant inhibitory effect, although all the essential oils from Juniperus phoenicea ssp. turbinata and the essential oil from leaves of Juniperus oxycedrus ssp. oxycedrus exhibited rather good or weak activity against Candida albicans and Staphylococcus aureus.  相似文献   
15.
The possibility of arbitrarily "adding" and "subtracting" single photons to and from a light field may give access to a complete engineering of quantum states and to fundamental quantum phenomena. We experimentally implemented simple alternated sequences of photon creation and annihilation on a thermal field and used quantum tomography to verify the peculiar character of the resulting light states. In particular, as the final states depend on the order in which the two actions are performed, we directly observed the noncommutativity of the creation and annihilation operators, one of the cardinal concepts of quantum mechanics, at the basis of the quantum behavior of light. These results represent a step toward the full quantum control of a field and may provide new resources for quantum information protocols.  相似文献   
16.
A new test method for measuring the antioxidant power of herbal products, based on solid-phase spectrophotometry using tetrabenzo-[b,f,j,n][1,5,9,13]-tetraazacyclohexadecine-Cu(II) complex immobilized on silica gel, is proposed. The absorbance of the modified sorbent (lambda(max) = 712 nm) increases proportionally to the total antioxidant activity of the sample solution. The method represents an attractive alternative to the mostly used radical scavenging capacity assays, because they generally require complex long-lasting stages to be carried out. The proposed test method is simple ("drop and measure" procedure is applied), rapid (10 min/sample), requires only the monitoring of time and absorbance, and provides good statistical parameters (s(r)相似文献   
17.
Penaeid trawling is among the world's least selective fishing methods; a characteristic that has evoked spatial closures being implemented in some fisheries if certain bycatch limits are exceeded. For decades, considerable work has been done to develop modifications to penaeid trawls that reduce unwanted bycatches, with most focussed at the posterior section (i.e. codend). More recently, efforts have examined ways to prevent bycatch entry into trawls entirely—via modifications to anterior components. This study assessed the utility of proactively lowering the headlines of Australian penaeid trawls, using clips at the otter boards, to 68% and 54% of their conventional height, and demonstrated mean total bycatch reductions (by weight) of 69% and 79%, respectively, with no effects on the targeted Metapenaeus macleayi (Haswell). The results provide insights into the location and behaviour of various species in the water column preceding capture, and support a simple and easy method for regional fishers to use in situ to avoid excessive bycatch and associated fishing closures. More broadly, the data support ongoing efforts in other penaeid‐trawl fisheries to reduce bycatches via similar, rapid adjustments to anterior components, depending on species‐specific behaviours during capture.  相似文献   
18.
19.
Use of decision support systems (DSS) has thus far been framed as a social process of adoption or technical process of usability. We analyze the development of a DSS as a process of institutionalization of new as well as drift of existing practices. We write an Actor-Network-Theory (ANT) account, i.e. an interpretive study, that follows the traces left by both human and non-human actors (e.g. technology, methodologies, etc.) to understand how a DSS development project institutionalizes DSS technology in several forest management organizations in the German state of Rheinland Pfalz. The research has an innovative value since it uses ANT in the design of a DSS, hence affecting it, while commonly ANT has been used to understand why networks work or do not. Moreover, we use a new technology (PREZITM, www.prezi.com) for the visualization of the whole actor network coherent to the ANT methodology, i.e. “keeping the social flat.” As a result, the development of the ANT account proposed in the present paper, even if still partial, supports the design of new technologies being introduced in current practice and generates an important learning effect thanks to the underpinning interpretative approach.  相似文献   
20.
There is currently a considerable amount of interest in the benefits of certain dietary elements, and in particular of olive oil, in endothelial function and thus in hypertension. "Orujo" or pomace olive oil is obtained from the residues of the olive by a novel centrifugation process, and it is a good dietary source of triterpenic compounds such as oleanolic and maslinic acid, erythrodiol, and uvaol. Until now, there was no information available regarding the properties of these triterpenoids on the vasculature of hypertensive animals. However, in this in vitro study, we have analyzed the vasorelaxation induced by these triterpenoids in isolated aorta from spontaneously hypertensive rats (SHR). The triterpenoids tested induced concentration-dependent vasorelaxation, mostly involving nitric oxide (NO). Indeed, the responses were attenuated by removal of the endothelium or following pretreatment with the NO synthase inhibitor L-NAME. Furthermore, the differences that were observed in the potency of relaxation, the selectivity, and the dependence on the endothelium were attributed to structural features of the triterpenoids. In conclusion, triterpenic components in pomace olive oil induce vasorelaxation of the aorta from SHR, and this effect generally involves endothelial NO.  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