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   563篇
  免费   32篇
  国内免费   1篇
林业   29篇
农学   8篇
基础科学   2篇
  112篇
综合类   65篇
农作物   25篇
水产渔业   26篇
畜牧兽医   279篇
园艺   20篇
植物保护   30篇
  2024年   4篇
  2023年   7篇
  2022年   18篇
  2021年   22篇
  2020年   20篇
  2019年   20篇
  2018年   16篇
  2017年   12篇
  2016年   15篇
  2015年   18篇
  2014年   21篇
  2013年   26篇
  2012年   49篇
  2011年   58篇
  2010年   32篇
  2009年   18篇
  2008年   26篇
  2007年   30篇
  2006年   28篇
  2005年   32篇
  2004年   14篇
  2003年   19篇
  2002年   12篇
  2001年   6篇
  2000年   4篇
  1999年   2篇
  1998年   2篇
  1997年   5篇
  1996年   7篇
  1994年   4篇
  1993年   2篇
  1992年   3篇
  1990年   3篇
  1984年   2篇
  1982年   3篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1978年   4篇
  1977年   2篇
  1976年   1篇
  1974年   2篇
  1973年   4篇
  1972年   4篇
  1971年   1篇
  1969年   1篇
  1968年   1篇
  1965年   1篇
  1964年   1篇
  1925年   2篇
排序方式: 共有596条查询结果,搜索用时 15 毫秒
101.
Cytochemistry was used to differentiate chicken heterophils and eosinophils in blood smears and cytospin preparations of isolated leukocytes. Cytochemical staining also was performed to evaluate any alteration of cell staining characteristics after heterophils had been isolated using discontinuous Ficoll-Hypaque gradients. Cytochemical staining reactions of heterophils and eosinophils were the same before and after discontinuous gradient cell separation. Characteristic positive reactions did not occur when chicken heterophils were stained with alkaline phosphatase, peroxidase, Sudan black B, acid phosphatase, alpha-naphthyl acetate esterase, naphthol AS-D chloroacetate esterase, periodic acid-Schiff, or Luna's eosinophil granule techniques. Chicken eosinophils stained positively when peroxidase, Sudan black B, acid phosphatase, and Luna methods were performed. In highly cellular cytospin preparations, peroxidase reactions readily distinguished the few contaminating eosinophils (< 1%) from the heterophils.  相似文献   
102.

Context

Agroecosystems produce food and many other services that are crucial for human well-being. Given the scales at which the processes underlying these services take place, agricultural landscapes appear as appropriate spatial units for their evaluation and management. The design of sustainable agricultural landscapes that value these services has thus become a pressing issue but faces major challenges stemming from the diversity of processes, their interactions and the number of scales at stake. Agricultural landscape modelling can provide a key contribution to this design but must still overcome several difficulties to offer reliable tools for decision makers.

Objectives

Our study aimed at shedding light on the main scientific and technical difficulties that make the building of landscape models that may efficiently inform decision-makers a complex task, as well as translating them in terms of challenges that can be further investigated and discussed.

Methods

We examine current issues and challenges and indicate future research needs to overcome the scientific and technical obstacles in the development of useful agricultural landscape models.

Results

We highlight research perspectives to better couple landscape patterns and process models and account for feedbacks, integrate the decisions of multiple stakeholders, consider the spatial and temporal heterogeneity of data and processes, explore alternative landscape organisations and assess multiobjective performance.

Conclusion

Coping with the issues and challenges discussed in this paper should improve our understanding of agroecosystems and give rise to new hypotheses, thereby informing future research.
  相似文献   
103.
Cyclosporine is a powerful T‐cell inhibitor used in the treatment of immune‐mediated and inflammatory diseases in the dog. There is limited information on how to best monitor patients on cyclosporine therapy. Currently, pharmacokinetic and pharmacodynamic assays are available. Pharmacokinetic assays that measure the concentration of cyclosporine in the blood are used to assess if an appropriate drug concentration has been achieved; however, target blood drug concentrations have not been shown to reliably correlate with suppression of T‐cell function in the dog. In human transplant recipients, therapeutic drug monitoring has shifted to include pharmacodynamic‐based monitoring. Our laboratory has validated a RT‐qPCR assay to measure the pharmacodynamic effects of cyclosporine in the dog. In this study, activated T‐cell expression of IL‐2 and IFN‐γ was measured using RT‐qPCR daily for 7 consecutive days in 8 healthy Walker hounds receiving oral cyclosporine at a dosage of 10 mg/kg every 12 hr. Cytokine production was found to be markedly decreased within 24 hr after the initiation of cyclosporine and remained significantly decreased for the duration of the project. Based on these results, cyclosporine causes a rapid drop in T‐cell cytokine production that is sustained with continued dosing in healthy dogs. Although performed in healthy dogs, this study demonstrated a marked decrease in cytokine suppression within 24 hr of drug administration, suggesting that pharmacodynamic monitoring of cyclosporine's effects on T cells could be considered within several days of commencing therapy in dogs suffering from life‐threatening immune‐mediated disorders.  相似文献   
104.
Fifty-one specific pathogen-free (SPF) cats 10 weeks to 13 years of age were infected with a cat-to-cat fecal-oral passed strain of feline enteric coronavirus (FECV). Clinical signs ranged from unapparent to a mild and self-limiting diarrhea. Twenty-nine of these cats were FECV na?ve before infection and followed sequentially for fecal virus shedding and antibody responses over a period of 8-48 months. Fecal shedding, as determined by real-time polymerase chain reaction (RT-PCR) from rectal swabs, appeared within a week and was significantly higher in kittens than older cats. FECV shedding remained at high levels for 2-10 months before eventually evolving into one of three excretion patterns. Eleven cats shed the virus persistently at varying levels over an observation period of 9-24 months. Eleven cats appeared to have periods of virus shedding interlaced with periods of non-shedding (intermittent or recurrent shedders), and seven cats ceased shedding after 5-19 months (average 12 months). There was no change in the patterns of virus shedding among cats that were excreting FECV at the time of a secondary challenge exposure. Four cats, which had ceased shedding, re-manifested a primary type infection when secondarily infected. Cats with higher feline coronavirus (FCoV) antibody titers were significantly more likely to shed virus, while cats with lower titers were significantly less likely to be shedding. Twenty-two kittens born to experimentally infected project queens began shedding virus spontaneously, but never before 9-10 weeks of age. Natural kittenhood infections appeared to be low grade and abortive. However, a characteristic primary type infection occurred following experimental infection with FECV at 12-15 weeks of age. Pregnancy, parturition and lactation had no influence on fecal shedding by queens. Methylprednisolone acetate treatment did not induce non-shedders to shed and shedders to increase shedding.  相似文献   
105.
106.
107.
108.
109.
The seedling growth trait, cyclic growth, is well-correlated with older-tree heights measured in Pinus taeda L. field trials. These results have been repeatable across locations and seed sources if a standard greenhouse procedure is followed. This work is been limited to cyclic growth measured on P. taeda families and seed sources. The use of a standard greenhouse procedure will facilitate comparison with other early genetic evaulation methods for P. taeda and with similar studies on other Pinus species.  相似文献   
110.
The homogeneity of analytical samples and the stability of pesticides during the sample processing of oranges and tomatoes were evaluated. The mean concentrations of 14C-labeled chlorpyrifos in analytical portions (subsamples) after processing show that homogeneity is dependent on sample type as well as the processing procedure. The homogeneity of analytical samples of tomatoes processed cryogenically was much better than those processed at ambient temperature. For tomatoes, the minimum analytical portion masses required for between-analytical portion variation of < 0.3 Ho were 110 and 5 g for processing at ambient and cryogenic temperatures, respectively. Results for orange showed that analytical portion sizes of 5 g provided sufficient homogeneity from both sample processing procedures. Assessments of pesticide stability demonstrated that most were relatively stable during processing at either ambient or cryogenic temperatures. However, some pesticides, including dichlofluanid, chlorothalonil, tolylfluanid, and dicloran, appeared to suffer much greater losses (>20%) during processing at ambient temperature. For these analytes, loss is interpreted as chemical degradation.  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