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   462篇
  免费   22篇
  国内免费   3篇
林业   12篇
农学   6篇
基础科学   4篇
  54篇
综合类   65篇
农作物   14篇
水产渔业   33篇
畜牧兽医   268篇
园艺   10篇
植物保护   21篇
  2023年   2篇
  2022年   5篇
  2021年   6篇
  2020年   18篇
  2019年   10篇
  2018年   7篇
  2017年   5篇
  2016年   6篇
  2015年   8篇
  2014年   10篇
  2013年   20篇
  2012年   25篇
  2011年   44篇
  2010年   15篇
  2009年   11篇
  2008年   36篇
  2007年   25篇
  2006年   28篇
  2005年   28篇
  2004年   22篇
  2003年   22篇
  2002年   17篇
  2001年   10篇
  2000年   7篇
  1999年   3篇
  1997年   5篇
  1996年   7篇
  1995年   4篇
  1994年   3篇
  1992年   4篇
  1991年   8篇
  1990年   3篇
  1988年   2篇
  1987年   2篇
  1985年   5篇
  1984年   3篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   7篇
  1978年   4篇
  1977年   2篇
  1975年   5篇
  1972年   2篇
  1968年   2篇
  1966年   2篇
  1953年   1篇
  1937年   1篇
  1912年   1篇
排序方式: 共有487条查询结果,搜索用时 31 毫秒
361.
Abdominal ultrasonography is one of the most common diagnostic imaging modalities used for dogs with suspected insulinoma; however, pancreatic masses are clearly identified in fewer than half of affected dogs and benign pancreatic nodules can be difficult to differentiate from malignant ones. The purpose of this prospective study was to describe contrast‐enhanced ultrasonography (CEUS) characteristics of confirmed pancreatic insulinoma in a group of dogs. Inclusion criteria were as follows: (1) repeated hypoglycemia (blood glucose levels <60 mg/dl, twice or more); (2) elevated blood insulin levels with hypoglycemia; (3) pancreatic nodules detected with conventional ultrasonography; and (4) histological confirmation of pancreatic islet cell carcinoma. Immediately following conventional ultrasonography of the entire abdomen, CEUS of the pancreatic nodule and adjacent parenchyma was performed using contrast‐specific technology pulse inversion imaging and perflubutane microbubble contrast agent. Three dogs met inclusion criteria. Pancreatic nodules in all the three dogs became more clearly demarcated after injection of the contrast agent. Each nodule showed different enhancement patterns: markedly hyperechoic for 5 s, slightly hyperechoic for 1 s, and clearly hypoechoic for over 30 s. These results were not in complete agreement with previously reported CEUS findings in human patients with insulinoma. All nodules were surgically resected and histopathologically confirmed as malignant insulinomas. Findings from the current study indicated that contrast‐enhanced ultrasound may help to increase conspicuity of pancreatic insulinomas in dogs and that enhancement characteristics may be more variable in dogs than in humans.  相似文献   
362.
Objective – To evaluate various surrogate markers associated with the inflammatory and counter‐inflammatory responses with respect to mortality in dogs with systemic inflammatory response syndrome (SIRS). Design – Prospective observational study. Setting – Veterinary Teaching Hospital. Animals – Twenty‐eight dogs with naturally occurring diseases and SIRS from January 2007 to May 2009. Interventions – Upon admission to the veterinary hospital, history and baseline data from the physical examination, including parameters previously defined for meeting SIRS criteria, were documented. Heparinized blood samples were collected and plasma cytokines interleukin‐6 (IL‐6), IL‐10, and high‐mobility group box 1 (HMGB1) were measured by sandwich ELISA. Measurements and Main Results – In nonsurvivors, median plasma HMGB1 concentrations (0.718 μg/L, interquartile range [IQR]; 0.300–1.626 μg/L) and the ratio of HMGB1 to IL‐10 (2.236, IQR; 0.972–5.367) were significantly increased as compared with those found in survivors (0.300 μg/L, IQR; 0.300–0.312 μg/L for HMGB1; 1.017, IQR; 0.862–1.126 for the ratio of HMGB1 to IL‐10, P=0.007 and 0.024, respectively). Plasma IL‐6, IL‐10, and the ratio of IL‐6 to IL‐10 were not significantly different between groups. Among the parameters studied, HMGB1 and the ratio of HMGB1 to IL‐10 performed the best in discriminating outcome in dogs with SIRS according to receiver operator characteristic curve analysis. Conclusions – Increases in plasma HMGB1 concentration and the ratio of HMGB1 to IL‐10 may predict poorer outcomes in dogs with SIRS. The approach described may lead to reliable prognostic biomarkers and new therapeutic concepts in the study of SIRS in dogs.  相似文献   
363.
Little is known of the effect of selective plant defoliation at different intensities and frequencies in altering weed-forage dynamics in pasture. We conducted a field experiment to quantify Cirsium arvense responses to varying defoliation regimes of neighboring forage implemented for 2 years under high or low fertility conditions. Defoliation regimes were based on common grazing systems, and included: (1) high intensity–high frequency (HIHF) defoliation simulating continuous grazing, (2) high intensity–low frequency (HILF), (3) low intensity–high frequency (LIHF), and (4) deferred (DEF) defoliation to peak growth in late summer. All vegetation except C. arvense was defoliated during the growing season to examine weed responses to changes in neighboring forage abundance. Year-end C. arvense biomass at the end of the study was greatest in the HIHF treatment and lowest in the DEF, with the LIHF and HILF treatments intermediate in response. The HILF treatment also provided improved suppression of C. arvense biomass relative to the LIHF, although this response was inconsistent among sites. Trends in C. arvense shoot densities among defoliation treatments were similar to those for biomass. While weed abundance was lower in the absence of fertilization, rankings among defoliation treatments remained the same. Notably, trends in forage biomass among defoliation regimes followed a pattern opposite that of C. arvense, and are implicated in observed weed decreases. Our results indicate that defoliation regimes enhancing forage growth and biomass, particularly a DEF or HILF regime, reduce C. arvense the most. Grazing systems that employ these defoliation regimes are therefore likely to optimize the interspecific competitive suppression of C. arvense.  相似文献   
364.
365.
Using the reverse hemolytic plaque assay described in the present investigation, a secretagogue activity of bursal antisteroidogenic peptide (BASP) for growth hormone (GH) or prolactin (PRL) secretion was observed in chicken Day 20e pituitary cell monolayers. Partially purified BASP (ppBASP), at all concentrations evaluated (0.25 BEQ/ml, 0.75 BEQ/ml, or 1.5 BEQ/ml), induced PRL secretion by isolated lactotrophs above (P < 0.05) basal levels during the 2- and 6-hr incubation. At the 18-hr time point, neither ppBASP nor vasoactive intestinal polypeptide (VIP) was efficacious (P < 0.05) in causing an elevation in PRL-secreting cells above basal levels. ppBASP, at all concentrations evaluated (0.25 BEQ/ml, 0.75 BEQ/ml, or 1.5 BEQ/ml), caused an increase in the percentage of GH-secreting cells above (P < 0.05) basal levels during the 18-hr incubation. When evaluating the 2-hr time point alone, ppBASP, at 0.75 or 1.5 BEQ/ml, significantly (P < 0.05) elevated the percentage of GH-secreting cells to above basal levels. After the 6-hr incubation, ppBASP at 0.25 or 0.75 BEQ/ml, was efficacious in causing elevated (P < 0.05) GH secretion above basal levels. The present study indicates a secretagogue activity of BASP on PRL or GH secretion by chicken embryonic anterior pituitary cells in vitro.  相似文献   
366.
旱地马铃薯覆膜和膜侧种植处理比较试验   总被引:2,自引:0,他引:2  
通过旱地马铃薯覆膜和膜侧种植处理比较试验的研究,得出内蒙古中西部马铃薯覆膜和膜侧种植的差异性,探讨马铃薯膜侧种植在内蒙古中西部的应用价值和重要性。研究结果表明:膜侧种植出苗期比膜内种植可提前3 d,现蕾期提前3 d,开花期提前2 d,膜侧种植大薯个数、块茎重、商品薯率分别高于膜内种植36.4%、14.6%和22.9%。每667 m2膜侧种植收入为699.3元,膜内种植收入为678.4元,每667 m2收入膜侧种植比膜内种植多20.9元。说明膜侧种植可以在内蒙古中西部地区进行试验推广。  相似文献   
367.
Exploration of the biotype structure of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), would improve our knowledge regarding variation in virulence phenotypes and difference in genetic background. Microsatellites (simple sequence repeats) and single-nucleotide polymorphisms (SNPs) are highly variable genetic markers that are widely used in population genetic studies. This study developed and tested a panel of 18 microsatellite and 22 SNP markers to investigate the genetic structure of nine Hessian fly biotypes: B, C, D, E, GP, L, O, vH9, and vH13. The simple sequence repeats were more polymorphic than the SNP markers, and their neighbor-joining trees differed in consequence. Microsatellites suggested a simple geographic association of related biotypes that did not progressively gain virulence with increasing genetic distance from a founder type. Use of the k-means clustering algorithm in the STRUCTURE program shows that the nine biotypes comprise six to eight populations that are related to geography or history within laboratory cultures.  相似文献   
368.
Predation by feral cats (Felis catus) and red foxes (Vulpes vulpes) are key threatening processes for many endangered wildlife species. Toxin delivery through compulsive oral grooming is a potential mechanism to supplement existing control techniques for feral cats and red foxes, particularly when high prey densities reduce the uptake of toxic food baits by cats. We investigated the efficacy of different grooming traps by applying a gel containing toxic para-aminopropiophenone (PAPP) to the fur of feral cats and red foxes in experimental pens. Grooming behaviour and signs of poisoning in these animals were recorded by video. More cats interacted with “walk past” grooming traps triggered by sensor beams than with trap models that required the cat to enter a pipe or baited cage. After triggering a trap that had applied PAPP gel to their fur, 14 of 16 feral cats showed symptoms of anoxia, and 8 of these cats were dead by the following morning without exhibiting signs of distress. Seven of 12 foxes were observed to groom fur to which toxic gel had been applied and 3 of these ingested a lethal quantity of PAPP as a result. Our successful proof-of-concept trials support further development of grooming trap sensors and toxin delivery mechanisms to provide humane and targeted feral cat control, although this technique is unlikely to be as successful for fox control, given that foxes appear to not groom as fastidiously as cats.  相似文献   
369.
370.
Fucoxanthin is the primary carotenoid found in edible seaweeds, such as Eisenia bicyclis, Undaria pinnatifida, and others. The aim of this study was to determine the effectiveness of fucoxanthin against Parkinson’s disease (PD) by inhibiting monoamine oxidase (MAO) A and B because MAO inhibitors are used in early management of PD. A sensitive enzyme-based chemiluminescent assay and kinetics methods were used to investigate the enzyme inhibitory activities and mode of inhibition. A molecular docking simulation was performed to clarify the binding characteristics of fucoxanthin to hMAO-A (2z5x) and hMAO-B (2v5z). Our results suggest that fucoxanthin shows significant inhibitory activity against hMAO-A and hMAO-B with IC50 values of 197.41 ± 2.20 and 211.12 ± 1.17 μM, respectively. Selegiline was used as the positive control (IC50: 10.54 ± 1.25 and 0.128 ± 0.01 μM for hMAO-A and hMAO-B, respectively). The enzyme-based kinetics results demonstrated that fucoxanthin inhibited both hMAOs in a reversible competitive manner. The molecular docking simulation predicted that fucoxanthin exhibits higher binding affinity towards hMAO-A and hMAO-B through hydrogen bonding and hydrophobic interactions. These findings suggest that fucoxanthin is a reversible competitive hMAO inhibitor that could be used to manage PD.  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