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   823篇
  免费   64篇
林业   28篇
农学   14篇
基础科学   2篇
  88篇
综合类   94篇
农作物   28篇
水产渔业   32篇
畜牧兽医   546篇
园艺   31篇
植物保护   24篇
  2024年   1篇
  2023年   10篇
  2022年   16篇
  2021年   20篇
  2020年   28篇
  2019年   43篇
  2018年   27篇
  2017年   32篇
  2016年   29篇
  2015年   21篇
  2014年   32篇
  2013年   37篇
  2012年   68篇
  2011年   77篇
  2010年   42篇
  2009年   25篇
  2008年   67篇
  2007年   54篇
  2006年   46篇
  2005年   30篇
  2004年   43篇
  2003年   39篇
  2002年   39篇
  2001年   7篇
  2000年   2篇
  1999年   5篇
  1998年   6篇
  1997年   4篇
  1996年   5篇
  1995年   4篇
  1994年   9篇
  1993年   2篇
  1992年   3篇
  1991年   4篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1974年   1篇
  1965年   1篇
排序方式: 共有887条查询结果,搜索用时 183 毫秒
791.
Numerous studies have tried to understand and model bubble growth inside dough. Experimental studies are inconvenienced by the methods’ inability to capture the dynamic phenomena. In this paper, a versatile experimental method was developed to allow for macroscopic expansion of wheat dough. The study evaluates expansion of a dough disk under varying: moisture content (40, 41, 42, 43, and 44% wb), leavening acid concentration (30, 40, and 50% db), pressure schemas, pressurizing gas (compressed air and CO2), and lubrication (Teflon® film coating and Pam® aerosol lubricant). Dough expansion increased 22.6% by increasing moisture content from 40 to 44%. Increased baking powder formulation (40% db) was used to enhance initial growth conditions and CO2 production. ‘Pressure pulse’ and ‘pressure vacuum methods’ added pressurization alternatively with full vacuum. The former method included a rest period before vacuum application, and increased expansion by 10.8%. Teflon® and Pam® reduced friction between the dough and acrylic plate and increased the final expansion by 14.7% compared to no lubricant following the ‘standard pressurization method’. ‘Pressure pulse’ and ‘pressure vacuum’ experiments decreased expansion by 28.4 and 38.2%, respectively compared to ‘standard pressurization’ while using Teflon® and Pam®.  相似文献   
792.
Microorganisms (e.g., prokaryotes, fungi) are food sources for soil nematodes, but they can also be potential mutualists or pathogens. Understanding the linkages between microorganism and invertebrate diversity in soils requires the ability to distinguish between these microbial roles. We tested the potential of a taxon-specific fluorescent in situ hybridization (FISH) procedure for identifying and localizing microbial rRNA within the bodies of soil nematodes. Our objective was to determine whether the rate of digestion permitted detection and identification of food-source nucleic acids within the nematode digestive system (i.e., pharynges, intestines) before their breakdown. First, using laboratory cultures of Caenorhabditis elegans maintained on Escherichia coli, we were able to localize bacterial rRNA throughout the nematode pharynx with the universal bacterial-probe EUB338, although never in the intestines. Second, we applied the fungal rRNA probe FR1 to Aphelenchus avenae cultured on the fungus Rhizoctonia solani. We were unable to detect fungal rRNA within these nematodes, and it appears that this material may be digested rapidly. Next, we applied our technique to nematodes extracted directly from soils. We were able to localize bacterial rRNA within the pharynges of bacterial-feeding species of nematodes from desert soils. We also localized archaeal rRNA using the probe ARC344. Finally, application of EUB338 to desert soil nematodes revealed the presence of bacteria in the intestines of some nematodes and within the ovary of a single nematode. This technique has great potential for use in understanding the feeding behavior of bacterial-feeding soil nematodes and in studies of nematode:bacterial relationships.  相似文献   
793.
ABSTRACT

The consumer acceptability and proximate and fatty acid composition of crayfish (Procambarus clarkii) harvested from commercial systems and moist-soil wetlands were evaluated. Aroma and appearance acceptability scores for abdominal muscles from commercial crayfish were higher over samples from moist-soil wetlands. Aroma and texture acceptability scores for whole crayfish from commercial fields were also higher compared to moist-soil wetland samples. No differences existed between treatments for flavor and overall acceptability. Results indicate that although scores for aroma were slightly higher for commercial crayfish, crayfish from both populations were acceptable to consumers. Hierarchical cluster analyses of panelists’ scores for overall acceptability revealed that 25% of panelists rated moist-soil wetland and commercial crayfish abdominal samples equally high, and an additional 31% of panelists rated moist-soil wetland crayfish samples as more liked than commercial crayfish samples. Few differences existed in crayfish proximate composition and fatty acid content from the two harvest practices.  相似文献   
794.
Fifty-eight F2 individuals derived from an interspecific cross between cultivated eggplant, Solanum melongena, and its wild relative, S. linnaeanum, were phenotyped for 42 plant, leaf, flower, and fruit traits. Composite interval mapping analysis using genotypic data from 736 molecular markers revealed the positions of 71 statistically significant (P ≤ 0.05) quantitative trait loci (QTL) influencing 32 of the morphological traits. Although most QTL were location-specific, QTL governing three traits (leaf lobing, leaf prickles and prickle anthocyanin) were detected in both experimental locations. Analysis of three additional traits (stem prickles, fruit calyx prickles and fruit length) in both locations yielded QTL in similar but non-overlapping map positions. The majority (69 %) of the QTL corresponded closely with those detected in previous analyses of this data set. However the increased resolution of the linkage map combined with advances in QTL mapping permitted more precise localization, such that the average interval length of these QTL was reduced by 93 %. Thirty-one percent of the QTL were novel, suggesting that simple linear regression with a low density linkage map (the method used in previous studies of this population) missed a substantial portion of significant QTL. Hotspots of QTL affecting plant hairiness, prickliness, and pigmentation were identified on chromosomes 3, 6, and 10, respectively, and may reflect the pleiotropic activity of single structural or regulatory genes at these positions. Based on synteny between the eggplant, tomato, potato and pepper genomes, putative orthologs were identified for 35 % of the QTL suggesting strong conservation of gene function within the Solanaceae. These results should make it easier to target particular loci for map-based cloning and marker-assisted selection studies.  相似文献   
795.
The focus of biodiversity conservation is shifting to larger spatial scales in response to habitat fragmentation and the need to integrate multiple landscape objectives. Conservation strategies increasingly incorporate measures to combat fragmentation such as ecological networks. These are often based on assessment of landscape structure but such approaches fail to capitalise on the potential offered by more ecologically robust assessments of landscape function and connectivity. In this paper, we describe a modelling approach to identifying functional habitat networks and demonstrate its application to a fragmented landscape where policy initiatives seek to improve conditions for woodland biodiversity including increasing woodland cover. Functional habitat networks were defined by identifying suitable habitat and by modelling connectivity using least-cost approaches to account for matrix permeability. Generic focal species (GFS) profiles were developed, in consultation with stakeholders, to represent species with high and moderate sensitivity to fragmentation. We demonstrated how this form of analysis can be used to aid the spatial targeting of conservation actions. This ‘targeted’ action scenario was tested for effectiveness against comparable scenarios, which were based on random and clumped actions within the same landscape. We tested effectiveness using structural metrics, network-based metrics and a published functional connectivity indicator. Targeting actions within networks resulted in the highest mean woodland area and highest connectivity indicator value. Our approach provides an assessment of landscape function by recognising the importance of the landscape matrix. It provides a framework for the targeting and evaluation of alternative conservation options, offering a pragmatic, ecologically-robust solution to a current need in applied landscape ecology.  相似文献   
796.
797.
This study was undertaken to characterize otic fungal flora encountered in normal dogs, atopic dogs with no clinical or cytological evidence of otitis and dogs with otitis externa. Forty‐two normal dogs, 23 atopic dogs and 32 dogs with otitis were included in the study. Samples for otic fungal culture and cytology were obtained from all animals, for a total of 194 ears. Sixty‐seven ear samples (34%) were culture positive for saprophytic fungal organisms, as follows: 43 (64%) Penicillium species, 13 (19%) Aspergillus species and the remaining 17% comprised of various other saprophytic fungal organisms. Cytological evidence of saprophytic fungal colonization or infection was not found in any animal. There was no relationship between positive saprophytic fungal culture and any study group. Thirty‐three ear samples (17%) were positive for Malassezia pachydermatis. Cytological findings of Malassezia were significantly associated with positive culture for Malassezia (P = 0.006 left ear; P = 0.019 right ear). Furthermore, increased numbers of Malassezia led to a higher chance of positive culture (P = 0.003 left ear; P = 0.008 right ear; McNemar’s test). Malassezia pachydermatis was more likely to be cultured from ears with increased cerumen. Ear type (erect or pendulous) was not significantly associated with positive culture for Malassezia or saprophytic fungal organisms. There was no relationship between positive Malassezia culture and any study group; however, Malassezia was more likely to be cultured from individual dogs in the atopic or otitis groups that also had other dermatological signs consistent with allergic dermatitis and/or pyoderma (P = 0.031 left ear; P = 0.005 right ear).  相似文献   
798.
Advances in genomic technologies and the promise of "personalised medicine" have spurred the interest of researchers, healthcare systems, and the general public. However, the success of population-based genetic studies depends on the willingness of large numbers of individuals and diverse communities to grant researchers access to detailed medical and genetic information. Certain features of this kind of research - such as the establishment of biobanks and prospective data collection from participants' electronic medical records - make the potential risks and benefits to participants difficult to specify in advance. Therefore, community input into biobank processes is essential. In this report, we describe community engagement efforts undertaken by six United States biobanks, various outcomes from these engagements, and lessons learned. Our aim is to provide useful insights and potential strategies for the various disciplines that work with communities involved in biobank-based genomic research.  相似文献   
799.
800.
Immunoglobulin E (IgE) plays an important role in defense against parasitic infections as well as allergy. Knowledge of serum total IgE concentrations may have value in diagnosis and prognostication of various disorders; however, to date, no studies have reported feline serum total IgE concentrations. We hypothesize that serum total IgE concentrations will be greater in spontaneously parasitized and asthmatic cats compared to healthy pet cats. Healthy (n=10), parasitized (10) and asthmatic cats (eight) had measurement of serum total IgE by ELISA. Data were analyzed using a t-test with P<0.05 considered significant. Serum total IgE was higher in parasitized (mean±SEM, 328.4±123.8μg/ml; P<0.028) and asthmatic cats (85.5±19.5μg/ml; P<0.047) compared to healthy cats (45.9±19.6μg/ml). However, serum total IgE had poor discriminatory capability between diseased and healthy cats. In conclusion, this assay can detect small quantities of feline serum total IgE, which may be beneficial in future studies of parasitism or allergic disease.  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