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   77408篇
  免费   3671篇
  国内免费   56篇
林业   3286篇
农学   2139篇
基础科学   534篇
  8456篇
综合类   17000篇
农作物   3232篇
水产渔业   3204篇
畜牧兽医   38217篇
园艺   831篇
植物保护   4236篇
  2018年   808篇
  2017年   897篇
  2016年   783篇
  2014年   824篇
  2013年   2465篇
  2012年   1653篇
  2011年   2003篇
  2010年   1307篇
  2009年   1263篇
  2008年   1973篇
  2007年   1889篇
  2006年   1838篇
  2005年   1785篇
  2004年   1691篇
  2003年   1782篇
  2002年   1670篇
  2001年   1924篇
  2000年   1872篇
  1999年   1534篇
  1997年   719篇
  1995年   771篇
  1994年   710篇
  1993年   705篇
  1992年   1529篇
  1991年   1664篇
  1990年   1718篇
  1989年   1770篇
  1988年   1657篇
  1987年   1570篇
  1986年   1657篇
  1985年   1583篇
  1984年   1325篇
  1983年   1187篇
  1982年   840篇
  1981年   812篇
  1980年   762篇
  1979年   1340篇
  1978年   1056篇
  1977年   945篇
  1976年   883篇
  1975年   1006篇
  1974年   1325篇
  1973年   1244篇
  1972年   1329篇
  1971年   1270篇
  1970年   1185篇
  1969年   1030篇
  1968年   842篇
  1967年   971篇
  1966年   832篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
992.
993.
In the ovary, the development of new capillaries from pre‐existing ones (angiogenesis) is a complex event regulated by numerous local factors. The dominant regulators of angiogenesis in ovarian follicles and corpora lutea are the vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), insulin‐like growth factor (IGF), angiopoietin (ANPT) and hypoxia‐inducible factor (HIF) family members. Antral follicles in our study were classified according to the oestradiol‐17‐beta (E2) content in follicular fluid (FF) and were divided into five classes (E2 < 0.5, 0.5–5, 5–20, 20–180 and >180 ng/ml FF). The corresponding sizes of follicles were 5–7, 8–10, 10–13, 12–14 and >14 mm, respectively. Follicle tissue was separated in theca interna (TI) and granulosa cells (GC). The corpora lutea (CL) in our study were assigned to the following stages: days 1–2, 3–4, 5–7, 8–12 13–16 and >18 of the oestrous cycle and months 1–2, 3–4, 6–7 and >8 of pregnancy. The dominant regulators were measured at mRNA and protein expression levels; mRNA was quantified by RT‐qPCR, hormone concentrations by RIA or EIA and their localization by immunohistochemistry. The highest expression for VEGF‐A, FGF‐2, IGF‐1 and IGF‐2, ANPT‐2/ANPT‐1 and HIF‐1‐alpha was found during final follicle maturation and in CL during the early luteal phase (days 1–4) followed by a lower plateau afterwards. The results suggest the importance of these factors for angiogenesis and maintenance of capillary structures for final follicle maturation, CL development and function.  相似文献   
994.
The objective of this study was to provide a detailed multiplanar computed tomographic (CT) anatomic reference for the bovine tarsus. The tarsal regions from twelve healthy adult cow cadavers were scanned in both soft and bone windows via a 16‐slice multidetector CT scanner. Tarsi were frozen at ?20o C and sectioned to 10‐mm‐thick slices in transverse, dorsal and sagittal planes respecting the imaging protocol. The frozen sections were cleaned and then photographed. Anatomic structures were identified, labelled and compared with the corresponding CT images. The sagittal plane was indispensable for evaluation of bone contours, the dorsal plane was valuable in examination of the collateral ligaments, and both were beneficial for assessment of the tarsal joint articulations. CT images allowed excellent delineation between the cortex and medulla of bones, and the trabecular structure was clearly depicted. The tarsal soft tissues showed variable shades of grey, and the synovial fluid was the lowest attenuated structure. This study provided full assessment of the clinically relevant anatomic structures of the bovine tarsal joint. This technique may be of value when results from other diagnostic imaging techniques are indecisive. Images presented in this study should serve as a basic CT reference and assist in the interpretation of various bovine tarsal pathology.  相似文献   
995.
996.
997.
998.
999.
This report represents a scientific and working clinical consensus statement on seizure management in dogs based on current literature and clinical expertise. The goal was to establish guidelines for a predetermined, concise, and logical sequential approach to chronic seizure management starting with seizure identification and diagnosis (not included in this report), reviewing decision‐making, treatment strategies, focusing on issues related to chronic antiepileptic drug treatment response and monitoring, and guidelines to enhance patient response and quality of life. Ultimately, we hope to provide a foundation for ongoing and future clinical epilepsy research in veterinary medicine.  相似文献   
1000.
Development of effective and safe treatments for companion animals with cancer requires the collaboration of numerous animal health professionals and the full engagement of animal owners. Establishing ‘Best Practice Recommendations’ for clinical trials in veterinary oncology represents an important step toward meeting the goal of rigorous clinical trial design and conduct that is required to establish valid evidence. Likewise, optimizing patient welfare and owner education and advocacy is crucial to meet the unique ethical obligations to both owners and animals enrolled in these clinical trials and to ensure trust in the team conducting the research. To date, ‘Best Practice Recommendations’ for clinical trial conduct have not been reported for veterinary oncology. This document summarizes the consensus of a workshop held in November, 2014 to identify relevant ethical principles and to ensure responsible conduct of clinical research in companion animals with cancer. It is intended as a working document that will be updated as advances in science and ethical considerations require. To the extent possible, existing guidelines for the conduct and oversight of clinical trials in humans have been adapted for veterinary trials to avoid duplicative effort and to facilitate integration of clinical trials such that translational research with benefits for both companion animals and humans are encouraged.  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