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   1378篇
  免费   81篇
林业   95篇
农学   61篇
基础科学   1篇
  284篇
综合类   70篇
农作物   156篇
水产渔业   122篇
畜牧兽医   569篇
园艺   17篇
植物保护   84篇
  2024年   2篇
  2023年   19篇
  2022年   25篇
  2021年   38篇
  2020年   42篇
  2019年   45篇
  2018年   64篇
  2017年   60篇
  2016年   66篇
  2015年   49篇
  2014年   81篇
  2013年   79篇
  2012年   113篇
  2011年   123篇
  2010年   62篇
  2009年   40篇
  2008年   105篇
  2007年   81篇
  2006年   78篇
  2005年   67篇
  2004年   65篇
  2003年   47篇
  2002年   47篇
  2001年   16篇
  2000年   10篇
  1999年   6篇
  1998年   1篇
  1997年   5篇
  1996年   2篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   3篇
  1988年   3篇
  1985年   1篇
  1983年   1篇
  1977年   1篇
  1970年   1篇
排序方式: 共有1459条查询结果,搜索用时 15 毫秒
941.
Arbutus unedo, Prunus spinosa, Rosa micrantha and Rosa canina are good sources of phenolic compounds, including anthocyanins. These compounds have potent antioxidant properties, which have been related to anticancer activity. Herein, the in vitro antioxidant and antitumor properties of enriched phenolic extracts (non-anthocyanin phenolic compounds enriched extract- PE and anthocyanins enriched extract- AE) of the mentioned wild fruits were evaluated and compared. PE gave higher bioactive properties than the corresponding AE. It was observed a high capacity of A. unedo phenolic extract to inhibit lipid peroxidation in animal brain homogenates (EC50?=?7.21 μg/mL), as also a high antitumor potential against NCI-H460 human cell line (non-small lung cancer; GI50?=?37.68 μg/mL), which could be related to the presence of galloyl derivatives (exclusively found in this species). The bioactivity of the studied wild fruits proved to be more related to the phenolic compounds profile than to the amounts present in each extract, and could be considered in the design of new formulations of dietary supplements or functional foods.  相似文献   
942.
Canine parvovirus 2c infection in central Portugal   总被引:1,自引:0,他引:1  
Canine parvovirus (CPV) has been evolving, generating new genetic and antigenic variants throughout the world. This study was conducted to determine the types of CPV circulating in dogs in Figueira da Foz, Portugal. Thirty fecal samples, collected between 2006 and 2007 from dogs with clinical signs of CPV infection, were tested for CPV by a rapid, in-clinic, enzyme-linked immunosorbent assay (ELISA)/immunomigration test, by conventional real-time polymerase chain reaction (PCR), and by minor-groove binding TaqMan PCR. Of the 29 PCR-positive samples, 15 were identified as CPV-2b and 14 as CPV-2c. No CPV-2a was detected. The sensitivity of the ELISA test was 82.76% compared with the PCR assays. No significant associations were found between CPV type, clinical outcome, breed, vaccination status, or age.  相似文献   
943.
Lumichrome and lumiflavin were formed from riboflavin under light. pH had a significant influence on the formation of lumichrome and lumiflavin from riboflavin. Lumichrome was the only major product from riboflavin under neutral or acidic pH values. Lumiflavin was also formed from riboflavin in basic pH. The maximum concentration of lumiflavin from 100 microM riboflavin at pH 8.5 was 30.9 microM, and it was reached after 2 h of exposure at 1500 lux. The maximum concentration of lumichrome formed from 100 microM riboflavin at pH 4.5, 6.5, or 8.5 was 79.9, 58.7, and 73.1 microM, respectively, after 8, 6, or 2 h of light exposure. The formation of lumichrome and lumiflavin from riboflavin was due to the type I mechanism of the riboflavin photosensitized reaction. Singlet oxygen was also involved in the photosensitized degradation of lumiflavin and lumichrome. The reaction rates of riboflavin, lumiflavin, and lumichrome with singlet oxygen were 9.66 x 10(8), 8.58 x 10(8), and 8.21 x 10(8) M(-1) s(-1), respectively. The headspace oxygen depletion and headspace volatile formation were significant in soy milk containing lumichrome or lumiflavin under light (p < 0.05) and were insignificant (p > 0.05) in the dark. Ascorbic acid could inhibit the total volatile changes of soy milk under light. Soy milk should be protected from light to prevent the photodegradation of riboflavin and the oxidation of soy milk.  相似文献   
944.
Cereal seed storage proteins are encoded by complex multigene families and their subunit profiles are highly related to end-use qualities. Each fraction of albumin and hordein was extracted and its subunit profile was evaluated in related to malt and grain quality parameters. The purpose of this study was to provide selection criteria for high quality malting barley using grain and malt quality parameters and biochemical-genetic information. Grain and malt quality of 13 local adaptability test (LAT) lines were evaluated for malting process. A total of 16 germplasm accessions of high or low seed storage protein content were also evaluated for biochemicalgenetic analysis. The correlation coefficients among quality parameters were analyzed. Several important quality parameters in brewing process showed significant positive or negative correlations. Seed storage protein subunits of albumin and hordein of all tested lines and accessions were evaluated using 12% 1D SDS-PAGE. Scored data of protein subunit’s presence or absence was applied to Agglomerative Hierarchical Clustering (AHC) for statistical analysis and showed specific grouping patterns among tested lines. Clustered lines with subunit information were highly related with agricultural performance and grain and malt qualities. Based on the profiles of seed storage protein subunits, association of hordein subunit of 38, 43, and 65 kDa with high malt scored lines was found. The obtained results would provide improved selection criteria for high quality malting barley in the malting barley breeding program.  相似文献   
945.
To make informed planning decisions, community leaders, elected officials, scientists, and natural resource managers must be able to evaluate potential effects of policies on land use change. Many land use change models use remotely-sensed images to make predictions based on historical trends. One alternative is a survey-based approach in which landowners’ stated intentions are modeled. The objectives of our research were to: (1) develop a survey-based landowner decision model (SBM) to simulate future land use changes, (2) compare projections from the SBM with those from a trend-based model (TBM), and (3) demonstrate how two alternative policy scenarios can be incorporated into the SBM and compared. We modeled relationships between land management decisions, collected from a mail survey of private landowners, and the landscape, using remotely-sensed imagery and ownership parcel data. We found that SBM projections were within the range of TBM projections and that the SBM was less affected by errors in image classification. Our analysis of alternative policies demonstrates the importance of understanding potential effects of targeted land use policies. While policies oriented toward increasing enrollment in the Conservation Reserve Program (CRP) resulted in a large (11–13%) increase in CRP lands, policies targeting increased forest thinning on private non-industrial lands increased low-density forest projections by only 1%. The SBM approach is particularly appropriate for landscapes including many landowners, because it reflects the decision-making of the landowners whose individual actions will result in collective landscape change.  相似文献   
946.
This study aimed at assessing the potential of near-infrared reflectance spectroscopy (NIRS) for determining the distribution of soil organic matter (SOM) in particle size fractions, which has rarely been attempted. This was done on sandy soils from Burkina Faso (three sites) and Congo-Brazzaville (one site). Over the total sample set, NIRS accurately predicted carbon (C) and nitrogen (N) concentrations (g kg?1 fraction) in the fraction <20 μm. When considering Burkina Faso only, predictions were improved in general; those of C and N amounts (g kg?1 soil) became accurate for the fraction <20 μm but not for the coarser fractions, probably due to heterogeneous SOM repartition. However, most SOM being <20 μm in general, NIRS could be considered promising for determining SOM size distribution.  相似文献   
947.
Turmeric extracts were obtained from two lots of raw material (M and S) using various techniques: hydrodistillation, low pressure solvent extraction, Soxhlet, and supercritical extraction using carbon dioxide and cosolvents. The solvents and cosolvents tested were ethanol, isopropyl alcohol, and their mixture in equal proportions. The composition of the extracts was determined by gas chromatography-flame ionization detection (GC-FID) and UV. The largest yield (27%, weight) was obtained in the Soxhlet extraction (turmeric (S), ethanol = 1:100); the lowest yield was detected in the hydrodistillation process (2.1%). For the supercritical extraction, the best cosolvent was a mixture of ethanol and isopropyl alcohol. Sixty percent of the light fraction of the extracts consisted of ar-turmerone, (Z)-gamma-atlantone, and (E)-gamma-atlantone, except for the Soxhlet extracts (1:100, ethanol), for which only ar-turmeronol and (Z)-alpha-atlantone were detected. The maximum amount of curcuminoids (8.43%) was obtained using Soxhlet extraction (ethanol/isopropyl alcohol). The Soxhlet and low pressure extract exhibited the strongest antioxidant activities.  相似文献   
948.
Moderate consumption of red wine reduces the risk of heart disease and extends lifespan, but the relative contribution of wine polyphenols to these effects is unclear. In this work, the capacity of resveratrol and catechin to protect the eukaryotic microorganism Saccharomyces cerevisiae against oxidative stress caused by different agents, hydrogen peroxide, carbon tetrachloride, and cadmium, was evaluated. Under all stress conditions, both polyphenols increased tolerance, although their protection was more evident under peroxide exposure. By using mutant strains deficient in specific antioxidant defense systems (superoxide dismutases, catalase, or glutathione), it was observed that increased H2O2 tolerance produced by both polyphenols was associated with catalase, as well as the rise in survival rates caused by resveratrol under CCl4. The acquisition of tolerance was correlated with a reduction in lipid peroxidation, indicating that the antioxidant property of resveratrol and catechin involves protection against membrane oxidation.  相似文献   
949.
This study investigated the effects of early induction of autophagy on embryonic development in pigs. For this, oocytes or embryos were treated with an autophagy inducer, rapamycin (RP), during post‐activation (Pa), in vitro fertilization (IVF) and/or in vitro culture (IVC). When parthenogenesis (PA) embryos were untreated (control) or treated with various concentrations of RP for 4 hr during Pa, 100 nm RP showed a higher blastocyst formation (48.8 ± 2.7%) than the control (34.6 ± 3.0%). When PA embryos were treated during the first 24 hr of IVC, blastocyst formation was increased (< .05) by 1 and 10 nm RP (61.9 ± 3.0 and 59.6 ± 3.0%, respectively) compared to the control (43.2 ± 1.8%) and 100 nm RP (47.8 ± 3.2%), with a higher embryo cleavage in response to 10 nm RP (87.3 ± 2.4%) than the control (74.1 ± 3.2%). RP treatment during IVC and Pa + IVC showed increased blastocyst formation (44.7 ± 2.5 and 44.1 ± 2.0%, respectively) compared to the control (33.2 ± 2.0%). In addition, RP treatment during Pa and/or IVC increased glutathione content and inversely reduced reactive oxygen species. In IVF, RP treatment for 6 hr during IVF significantly increased embryonic development (34.0 ± 2.6%) compared to the control (24.8 ± 1.6%), but treatment during IVC for 24 hr with RP did not (23.0 ± 3.8%). Autophagy was significantly increased in PA oocytes by the RP treatment during Pa but not altered by the treatment during the first 24 hr of IVC. Overall, RP treatment positively regulated the pre‐implantation development of pig embryos, probably by regulating cellular redox state and stimulating autophagy.  相似文献   
950.
There are no accurate reference ranges for hematology parameters and lymphocyte subsets in Korean native beef cattle (Hanwoo). This study was performed to establish reliable reference ranges of hematology and lymphocyte subsets using a large number of Hanwoo cattle (n = 350) and to compare differences between Hanwoo and Holstein dairy cattle (n = 334). Additionally, age‐related changes in lymphocyte subsets were studied. Bovine leukocyte subpopulation analysis was performed using mono or dual color flow cytometry. The leukocyte subpopulations investigated in healthy cattle included: CD2+ cells, sIgM+ cells, MHC class II+ cells, CD3+CD4+ cells, CD3+CD8+ cells, and WC1+ cells. Although Hanwoo and Holstein cattle are the same species, results showed several differences in hematology and lymphocyte subsets between Hanwoo and Holstein cattle. This study is the first report to establish reference ranges of hematology and lymphocyte subsets in adult Hanwoo cattle.  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