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   432篇
  免费   35篇
  国内免费   1篇
林业   42篇
农学   9篇
基础科学   4篇
  89篇
综合类   32篇
农作物   23篇
水产渔业   25篇
畜牧兽医   191篇
园艺   10篇
植物保护   43篇
  2023年   6篇
  2022年   9篇
  2021年   19篇
  2020年   20篇
  2019年   17篇
  2018年   21篇
  2017年   21篇
  2016年   16篇
  2015年   21篇
  2014年   28篇
  2013年   26篇
  2012年   36篇
  2011年   50篇
  2010年   25篇
  2009年   17篇
  2008年   29篇
  2007年   22篇
  2006年   12篇
  2005年   21篇
  2004年   16篇
  2003年   10篇
  2002年   10篇
  2001年   2篇
  2000年   2篇
  1999年   3篇
  1998年   2篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1988年   1篇
  1984年   1篇
  1972年   1篇
  1969年   1篇
排序方式: 共有468条查询结果,搜索用时 15 毫秒
421.
‘Tonda di Giffoni’ is among the most highly appreciated Italian hazelnut (Corylus avellana L.) cultivars. Due to its round kernels and excellent processing quality, it was awarded a Protected Geographical Indication (PGI) from the European Union. To identify clones expressing improved nut and production qualities, a ‘Tonda di Giffoni’ clonal selection programme was conducted across hazelnut orchards in the Irno valley of Italy from 1995 to 2006. One hundred different clones were selected and propagated in a replicated trial under similar climate, soil, and cultural conditions. From this work, the 29 best clones were identified and from 2006 to 2008 their agronomic and pomological characteristics were observed. Microsatellite or simple sequence repeat (SSR) markers were used to successfully confirm true-to-type identity of the clones. Traits evaluated included flowering time (anthesis), bud break, suckering, trunk diameter, nut and kernel characteristics and productivity (yield). Best linear unbiased predictions for clone means and estimates of intraclass correlation coefficient were obtained using R environment, lme4 and ggplot2 packages. Five clones superior to that of the standard of ‘Tonda di Giffoni’ were identified in this study. Furthermore, yield and number of suckers produced showed sufficient variability to likely be exploited for breeding. The selected clones express features useful for both growers and the processing industry and will be propagated and planted in hazelnut orchards for further study and commercial production.  相似文献   
422.
423.
424.
Genetic analyses using sequences of partial cytochrome c oxidase subunit 1 (cox1) gene of mitochondrial DNA were conducted to determine the extent of genetic variation within and among Xiphinema diversicaudatum, X. pachtaicum, X. simile and X. vuittenezi populations. Pairwise distance among the four species was 22.5 to 31.2%. Four different sequence variants of cox1 were determined among six populations of X. diversicaudatum and three variants among three populations of X. simile. Nucleotide variation was detected at 18 of 414 bp (1.9 to 2.7%) in X. diversicaudatum and 4 of 435 bp (0.2 to 0.9%) in X. simile. All changes were at silent sites. No nucleotide variation was detected within three populations of X. pachtaicum and within three populations of X. vuittenezi.  相似文献   
425.
426.
This study was designed to evaluate the effects of two feeding methods on milk yield, composition and fatty acid (FA) profile obtained from dual‐purpose cattle. Twenty‐four Aosta Red Pied cows beyond peak of lactation were assigned to two groups and fed hay and concentrates in the proportions 0.69 and 0.31 on a dry matter basis for 10 weeks. Concentrates were offered separately from forages 6 times a day (separate ration, SR) or as a total mixed ration (TMR). The feeding method did not significantly influence dry matter intake (16.8 vs. 16.9 kg/head/day for SR‐ and TMR‐fed cows, respectively), milk yield (17.4 vs. 17.5 kg/head/day), milk fat, protein and lactose contents (36.4 vs. 35.2, 33.5 vs. 32.8, and 47.3 vs. 47.4 g/kg) and yields (607.9 vs. 613.4, 567.4 vs. 572.7 and 805.5 vs. 829.7 g/head/day). The overall milk FA profile was very similar between groups. Milk concentrations of FA used as indirect markers of rumen function (C18:2 t10c12, odd‐ and branched‐chain FA) and the extent of ruminal biohydrogenation were comparable (P > 0.05) between SR‐ and TMR‐fed cows, suggesting that ruminal pH did not vary considerably as a consequence of the feeding strategy applied.  相似文献   
427.
Silicon (Si) is a beneficial element for plants as it increases their resistance to several biotic and abiotic stresses. In the rhizosphere, root exudates, especially when released by nutritionally stressed plants, promote the mineral weathering and, consequently, influence Si biogeochemistry. This study aims at evaluating the mineralogical alterations in the rhizosphere of Fe‐deficient or Fe‐sufficient barley plants grown either in a natural or in an artificial calcareous soil, focusing on the dynamics of both Fe and Si. After 6 d of soil–plant contact, X‐ray diffraction (XRD) analysis of rhizosphere soil samples of Fe‐deficient plants revealed, for both natural and artificial soil, a decrease of amorphous phases and an increase of smectite compared to the unplanted soil. Root exudates released by Fe‐deficient plants were most likely the main responsible for the weathering of the amorphous phases by a ligand controlled dissolution mechanism. When the soil–plant contact was prolonged up to 12 d, plants overcame Fe nutritional stress and their effect on soil mineralogy completely changed, as proved by the considerable increase of amorphous and decrease of smectite. Smectite decrease might evidence the effort of plant to mobilize Si and micronutrients other than Fe from the soil through the exudation of organic ligands. When the artificial soil was treated with Fe‐sufficient barley plants, the mineral weathering trend appeared reversed compared to the experiments with Fe‐deficient plants. Plant nutritional status regulates the root exudation pattern and, consequently, drives mineral weathering processes in the rhizosphere. Barley has shown to be able to mobilize Si from smectite, yet depending on its Fe supply and proving the strict connection between Si and Fe dynamics in the rhizosphere.  相似文献   
428.
OBJECTIVE: To determine left ventricular free wall (LVFW) motions and assess their intra- and interday variability via tissue Doppler imaging (TDI) in healthy awake and anesthetized dogs. ANIMALS: 6 healthy adult Beagles. PROCEDURE: n the first part of the study, 72 TDI examinations (36 radial and 36 longitudinal) were performed by the same observer on 4 days during a 2-week period in all dogs. In the second part, 3 dogs were anesthetized with isoflurane and vecuronium. Two measurements of each TDI parameter were made on 2 consecutive cardiac cycles when ventilation was transiently stopped. The TDI parameters included maximal systolic, early, and late diastolic LVFW velocities. RESULTS: The LVFW velocities were significantly higher in the endocardial than in the epicardial layers and also significantly higher in the basal than in the mid-segments in systole, late diastole, and early diastole. The intraday coefficients of variation (CVs) for systole were 16.4% and 22%, and the interday CV values were 11.2% and 16.4% in the endocardial and epicardial layers, respectively. Isoflurane anesthesia significantly improved the intraday CV but induced a decrease in LVFW velocities, except late diastolic in endocardial layers and early diastolic in epicardial layers. CONCLUSIONS AND CLINICAL RELEVANCE: Left ventricular motion can be adequately quantified in dogs and can provide new noninvasive indices of myocardial function. General anesthesia improved repeatability of the procedure but cannot be recommended because it induces a decrease in myocardial velocities.  相似文献   
429.
430.
Bioretention cells, also known as raingardens, are increasingly being constructed as a means to collect, infiltrate, and treat stormwater runoff. There are concerns, however, about how stormwater management practices might function in terms of infiltration and pollutant removal as they age. Saturated hydraulic conductivity (K sat) values were obtained for eight cells in 2006 and again for three of those cells in 2010 using an infiltrometer. A strong positive correlation of mean K sat with service time was observed (slope = 10.2?±?2.4 cm/h per year, R 2 = 0.67). Results from metals analyses of bioretention media cores collected from six bioretention cells showed the expected trend of Cu and Zn enrichment at the surface while Cd was detected only in one out of 72 media samples analyzed. Sorption isotherms from batch testing of field media samples (T = 22.5 °C, pH = 7.2) were used to estimate metal sorption capacities based on representative stormwater Cd and Zn concentrations. Cu was not considered, as very little of the metal is dissolved under these conditions (22.8?±?7.1 %). The mean equilibrium sorption capacities for Cd (10.2?±?3.1 mg/kg) and Zn (294.9?±?14.9 mg/kg) far exceeded observed levels in the bioretention media such that the remaining sorption capacity was ≥83 % for Zn and ≥90 % for Cd for the cells. Overall, the results of this investigation suggest that bioretention cells can provide many years of effective infiltration (>6 years) and metals removal performance (>25 years).  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