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   356篇
  免费   17篇
林业   21篇
农学   14篇
  110篇
综合类   18篇
农作物   31篇
水产渔业   51篇
畜牧兽医   83篇
园艺   9篇
植物保护   36篇
  2023年   3篇
  2022年   8篇
  2021年   16篇
  2020年   10篇
  2019年   15篇
  2018年   6篇
  2017年   14篇
  2016年   11篇
  2015年   16篇
  2014年   14篇
  2013年   19篇
  2012年   29篇
  2011年   36篇
  2010年   14篇
  2009年   13篇
  2008年   15篇
  2007年   27篇
  2006年   21篇
  2005年   20篇
  2004年   17篇
  2003年   12篇
  2002年   17篇
  2001年   1篇
  2000年   3篇
  1999年   1篇
  1998年   1篇
  1997年   4篇
  1996年   2篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
排序方式: 共有373条查询结果,搜索用时 406 毫秒
101.
The crude methanolic extract of Zuccagnia punctata was active toward the fungal pathogens of soybean Phomopsis longicolla and Colletotrichum truncatum. Assay guided fractionation led to the isolation of two chalcones, one flavanone and a new caffeoyl ester derivative as the compounds responsible for the antifungal activity. Another new caffeoyl ester derivative was isolated from the antifungal chloroform extract but proved to be inactive against the soybean infecting fungi up to 50 microg/mL  相似文献   
102.
The behavior of volatile compounds according to two enzymatic treatments applied during the manufacture of fruit juice is described. More than 80 compounds were detected of a wide range of chemical families (alcohols, aldehydes, ketones, terpenoids, esters, norisoprenoids, ...). Theaspirane and alpha-isophoron were tentatively identified for the first time in apricot and peach fruits. The enzymes used, for extraction or clarification of fruit juices, modified the polysaccharides separated by molecular weight and the content of soluble polysaccharides. This could indicate differences in the fruit juice matrix, which could be related to observed changes in the volatile profile. In apricot, the enzymes enhanced the juice in terpenes and norisoprenoids as varietal compounds. In peach and pear, the enzymes used did not favor the amount of lactones and decadienoate esters, the character impact compounds, respectively.  相似文献   
103.
A HS-SPME method coupled to GC-MS was developed and applied for the qualitative and semiquantitative characterization of distilled gin volatile fraction. Sampling, chromatographic conditions, and method performances were evaluated, and the developed method was applied as a comparative study of some of the most popular commercial London Dry Gins and other gins with geographic denominations. During this study, 70 components of the gins' volatile fraction were isolated, tentatively identified or identified by reference compounds. They were mainly represented by mono- and sesquiterpenic compounds, which were quantitatively determined. The comparative study of London Dry Gins and gins with geographical indication permitted clear differentiation between the gins with geographical indication and one of the London Dry Gins tested.  相似文献   
104.
105.
The focus of this review is on the regulatory mechanisms and the mode of action of GH in salmonids. To stimulate further research, it aims at highlighting areas where numerous important breakthroughs have recently been made, as well as where data are currently lacking. The regulation of GH secretion is under complex hypothalamic control, as well as under negative feedback control by GH and IGF-I. Further, the recently characterized ghrelin is a potent GH secretagogue, and may prove to be a link between feed intake and growth regulation. GH plasma profiles show indications of diurnal changes, but whether salmonids have true pulsatile GH secretion remains to be elucidated. The recent cloning and characterization of the salmon GH receptor (GHR) is a major research break-through which will give new insights into the mechanisms of GH action. It should also stimulate research into circulating GH-binding proteins (GHBPs), as they appear to be a soluble form of the GHR. The salmonid GHR sequences show evolutionary divergence from other fish species, but with a high degree of identity within the salmonid group. Radioreceptorassay studies have found GHR present in all tissues examined, which is in line with the highly pleiotropic action of GH. Data are currently scarce on the plasma dynamics of GH in salmonids, and further studies on GHR and GHBPs dynamics coupled to assessments of GH clearance rates and pathways are needed. The direct versus indirect nature of GH action remains to be clarified, but GH appears to act both locally at the target tissue level to stimulate the autocrine/paracrine action of IGF-I, as well as on the liver to increase plasma IGF-I levels. In addition, GH interacts with other hormones such as cortisol, thyroid hormones, insulin, and reproductive hormones, generating a wide range of physiological effects. GH may act both peripherally and directly at the level of the central nervous system to modify behavior, probably by altering the dopaminergic activity in the brain.  相似文献   
106.
  1. The protection of evolutionary processes and maintenance of genetic diversity is necessary for the persistence of biodiversity and ecosystem resilience. The importance of genetic diversity has been reflected in a range of marine policy mechanisms, and the genetic ‘toolbox’ has great potential to support marine protection and marine spatial planning (MSP) at multiple scales. Despite scientific advances in the application of genetics in marine protection and management, systematic integration of genetic information has been generally lacking, primarily due to a knowledge and communication disconnect between geneticists and the marine policy and management community.
  2. To meet these outstanding needs, a ‘geospatial genetics’ approach to spatially map species-specific genetic data and associated information in a way that can be readily integrated by practitioners into marine protection and MSP decisions was developed. Techniques to derive geospatial genetic data layers, which can be viewed and mapped alongside other kinds of spatial data commonly used by conservation practitioners, hold promise for increasing the accessibility of genetic data to support policy decisions more fully.
  3. While applicable to many mobile and sessile taxa, an initial focus was placed on marine mammals, and the approach was developed and refined through a series of international meetings and published papers, as well as the development of interactive, expert-reviewed case studies hosted on the MSP tool SeaSketch.
  4. Outcomes of the work to date are currently serving in the policy arena by informing the identification of Important Marine Mammal Areas, an initiative led by the IUCN Marine Mammal Protected Areas Task Force to apply criteria to identify marine mammal habitats across the world's ocean, seas and relevant inland waters through a standardized process.
  5. It has become clear that geospatial genetics has great potential to foster increased collaboration among an intersectional community of geneticists, spatial ecologists, and practitioners. This increased opportunity for dialogue and cooperation will help ensure that evolutionary processes are factored into marine protection and MSP processes, and potentially for freshwater and terrestrial systems.
  相似文献   
107.
Presumed hybrids between Haliotis rufescens and H. fulgens abalones, produced in a commercial abalone laboratory, were evaluated for progeny viability, gonad characteristics and for their ‘true’ status as hybrids by means of allozyme and microsatellite analyses. Four out of 10 evaluated allozyme loci proved to be useful for the genetic certification of hybrids, Gpi, Mdh‐1, Mdh‐2 and Sod, as they had exclusive alleles for each of the abalone reference species from which the presumed hybrids were produced. Three microsatellite loci were also evaluated for their usefulness in abalone hybrid certification. Two were not useful for hybrid certification as the reference abalone species shared some of the same alleles. The third loci (Hka 56) also had shared alleles between the two species, but at very different frequencies. Therefore, this permitted a presumptive certification of hybrids, which, however, was not error‐proof as two allozyme certified hybrids were wrongly classified as H. rufescens rather than as hybrids. Progeny viability of the only female certified to be a hybrid was significantly lower compared with one viability of the other females spawned, which were certified as H. rufescens. However, the number of eggs spawned by the only certified hybrid female was as large as those spawned by females certified as H. rufescens. Gonads of abalones sampled for the macroscopic appearance of sterility indicated that in the absence of any gonad development, no distinctive difference allows for hybrid identification, as there were undifferentiated individuals that were both hybrid and non‐hybrid. On the other hand, two certified hybrid males were characterized by spermatocytes being the most abundant gamete type, although one had some spermatozoa present, indicating only partial sterility. Among the two female hybrids found, vitellogenesis was observed to proceed up to vitellogenic oocytes.  相似文献   
108.
A multicolumn solid-phase extraction cleanup for the determination of organophosphorus (OP) and organochlorine (OC) pesticides plus PCB congeners in virgin olive oil is presented. The method involves dissolution of the olive oil in hexane, followed by a cleanup system using a diatomaceous earth column (Extrelut-QE) with reversed (C(18)) and normal (alumina) phase SPE columns. Determination of OPs was by GC-NPD, while the OCs and PCBs were analyzed using GC-ECD. Recovery assays for OPs varied from 81.7% to 105.3%, for OCs ranged between 74.3% and 99.4%, while for PCBs were from 60.1% to 119.2%. Quantitation limits ranged from 10 to 25 microg/kg olive oil for OPs, and from 1 to 6 microg/kg olive oil for OCs and PCBs. In the case of positive samples, the confirmation of pesticide identity was performed by ion-trap GC-MS/MS. The applicability of the method was assayed with 19 virgin olive oil samples collected from different olive mills of Aragón (Spain). Only one OP pesticide (acephate) was detected in one sample at a concentration of 10 microg/kg. Organochlorine pesticides were found in 5-47% of samples at very low levels ranging from 1.5 to 5.2 microg/kg. PCBs were found in 20-90% of samples, showing concentrations between 2.3 and 17.3 microg/kg.  相似文献   
109.
The influence of fatty acids (free and bound as ethyl esters) on wine foaming was studied in different white wines and the corresponding sparkling wines. Moreover, from three of these wines the foam formed by CO(2) injection was separated, and two fractions were then obtained: foam wine (FW) and remainder wine (RW). In these fractions and the sparkling wines produced from them, foam properties and fatty acids were also determined. The free fatty acids C8, C10, and C12 were negatively correlated with foamability (HM), whereas the ethyl esters of hexanoic, octanoic, and decanoic acids were positively related to HM. The value of HM was directly proportional to the ratio of esterified to unesterified fatty acids. This was confirmed by the changes that occur in the esterification ratio during the second fermentation and aging. No influence was observed on either the Bikerman coefficient or the stability time of foam.  相似文献   
110.
This retrospective study evaluated the efficacy and side effects of palatal sclerotherapy in standardbred racehorses suspected to have intermittent dorsal displacement of the soft palate (IDDSP). Fifty-one horses were treated with multiple endoscopically guided injections of 3% sodium tetradecyl sulfate in the soft palate. Two groups were identified: those that had respiratory noises during exercise (n = 27) and those that did not (n = 24). Treatment was well-tolerated. Furthermore, horses significantly reduced their racing times for the last 400 m compared with their times before treatment and even when their times were compared to the mean times for horses in the same race. In conclusion, palatal sclerotherapy appears to be a suitable alternative therapeutic option for horses suspected to have IDDSP.  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