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   62492篇
  免费   2869篇
  国内免费   42篇
林业   2515篇
农学   1645篇
基础科学   429篇
  6149篇
综合类   14756篇
农作物   2460篇
水产渔业   2344篇
畜牧兽医   31046篇
园艺   643篇
植物保护   3416篇
  2017年   553篇
  2016年   536篇
  2014年   540篇
  2013年   1862篇
  2012年   1202篇
  2011年   1436篇
  2010年   913篇
  2009年   877篇
  2008年   1427篇
  2007年   1389篇
  2006年   1371篇
  2005年   1386篇
  2004年   1318篇
  2003年   1391篇
  2002年   1354篇
  2001年   1493篇
  2000年   1473篇
  1999年   1206篇
  1998年   531篇
  1997年   538篇
  1995年   596篇
  1994年   573篇
  1993年   561篇
  1992年   1309篇
  1991年   1395篇
  1990年   1449篇
  1989年   1488篇
  1988年   1399篇
  1987年   1356篇
  1986年   1400篇
  1985年   1373篇
  1984年   1150篇
  1983年   1005篇
  1982年   718篇
  1981年   688篇
  1980年   644篇
  1979年   1127篇
  1978年   916篇
  1977年   819篇
  1976年   768篇
  1975年   860篇
  1974年   1126篇
  1973年   1063篇
  1972年   1128篇
  1971年   1080篇
  1970年   1022篇
  1969年   874篇
  1968年   710篇
  1967年   844篇
  1966年   693篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
831.
  1. The aim of this study, comprising two experiments, was (1) to determine in Experiment 1 the relationship of incremental dietary P (phosphorus) content on precaecal digestible P in male broilers and (2) to determine in Experiment 2 the precaecal P digestibility of various inorganic P sources at marginal levels of P supply.

  2. In Experiment 1, a total of 260 male Ross 308 broilers were divided into groups of 10 birds per pen resulting in 8 replicates for treatment 1 and 6 replicates for treatments 2–4. Experimental diets were formulated to contain 4 incremental concentrations of digestible P by means of increasing concentrations of monocalcium phosphate (MCP). In the second experiment, 480-d-old male Ross 308 broilers were divided in groups of 12 birds per pen resulting in 16 replicates for the basal diet and 6 replicates for each test diet. A total of 4 inorganic P sources, MCP, monodicalcium phosphate (MDCP), dicalcium phosphate (DCP) and defluorinated phosphate (DFP) were added to the basal diet to determine the precaecal P digestibility. Three of the 4 inorganic P sources (MCP, MDCP and DCP) represented a mix of batches from different producers. At the end of both experiments, the chyme of the posterior part of the small intestine was collected. Digestibility of P and Ca was determined using titanium dioxide as indigestible marker.

  3. In Experiment 1, a reduction in precaecal digestibility of P was observed above an estimated precaecal digestible dietary P concentration of 4.8 g/kg.

  4. The precaecal P digestibility of the tested inorganic P sources in Experiment 2 was 78.3% for MCP, 59.0% for DCP, 70.7% for MDCP and 31.5% for DFP.

  相似文献   
832.
833.
Four partially intact, female dogs with a median age of 6 · 5 years were presented to Angell Animal Medical Center for laparoscopic treatment of ovarian remnant syndrome. Dogs were positioned in dorsal recumbency and a three‐port laparoscopic technique was used to identify and remove en bloc any abnormal tissue in the area of the ovarian pedicles. None of the dogs required conversion to open coeliotomy and there were no major complications. Abnormal tissue, including granulosa thecal cell tumour (n = 1), was identified bilaterally in three dogs and unilaterally in one dog. Clinical signs associated with ovarian remnant syndrome resolved in all dogs following surgery.  相似文献   
834.
835.
836.
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   
837.
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   
838.
839.
840.
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