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   321653篇
  免费   18378篇
  国内免费   9727篇
林业   31951篇
农学   25809篇
基础科学   9954篇
  53874篇
综合类   50852篇
农作物   21345篇
水产渔业   18712篇
畜牧兽医   99554篇
园艺   9492篇
植物保护   28215篇
  2022年   3363篇
  2021年   5604篇
  2020年   5599篇
  2019年   6366篇
  2018年   5597篇
  2017年   6921篇
  2016年   7199篇
  2015年   7981篇
  2014年   9196篇
  2013年   20411篇
  2012年   10904篇
  2011年   12888篇
  2010年   12709篇
  2009年   12849篇
  2008年   11386篇
  2007年   10568篇
  2006年   11110篇
  2005年   9825篇
  2004年   7518篇
  2003年   7219篇
  2002年   6414篇
  2001年   6599篇
  2000年   6370篇
  1999年   6471篇
  1998年   5680篇
  1997年   5556篇
  1996年   5191篇
  1995年   5569篇
  1994年   4817篇
  1993年   4572篇
  1992年   4843篇
  1991年   4846篇
  1990年   4503篇
  1989年   4418篇
  1988年   3866篇
  1987年   3743篇
  1986年   3529篇
  1985年   3854篇
  1984年   3592篇
  1983年   3402篇
  1982年   2890篇
  1981年   2832篇
  1980年   2763篇
  1979年   3148篇
  1978年   2826篇
  1977年   2639篇
  1976年   2495篇
  1974年   2598篇
  1973年   2496篇
  1972年   2364篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Coccidioidomycosis was diagnosed in 48 cats. Forty-one cases were identified within a period of 3 years. Coccidioides immitis was revealed by cytological or histopathological examinations, or culture in 70% of cats. The remaining 30% of cases were diagnosed by appropriate clinical signs, radiographic lesions, and serological test results. The average age of affected cats was 6.2 years with a median age of 5.0 years. Fifty-four percent (n = 26) were female and 46% (n = 22) were male. Domestic shorthaired and longhaired breeds comprised 89% (n = 41) of affected cats. Sixty-seven percent of cases were diagnosed during the 6-month period of December through May. Cats infected with C immitis were presented for evaluation of dermatologic (56%), respiratory (25%), musculoskeletal (19%), and neurological or ophthalmologic signs (19%). Fever, inappetence, and weight loss were present in 44% of the cats. Duration of clinical signs before diagnosis was less than 4 weeks in 85% (n = 42) of cats, with an average of 3.8 weeks and a median of 2 weeks. Agar gel immunodiffusion tests were positive in all 39 cats tested at sometime during the course of their disease. Hyperproteinemia (greater than 7.9 g/dL) was present in 52% (10/23) of cases. The majority of cats (n = 39) were negative for feline leukemia virus. Antibodies to feline immunodeficiency virus were absent in the 19 cats tested. Ketoconazole was the most common antifungal agent used to treat cats with Coccidioidomycosis. Duration of treatment ranged from less than 1 week to 43 months. Thirty-two cats are currently asymptomatic, with or without treatment. Eleven cats died or were euthanized. Five cats were lost to follow-up. Ketoconazole likely is more suppressive than curative because relapses were common after discontinuing therapy.  相似文献   
992.
993.
本文介绍一种新研制出的挖掘机特性测试仪。仪器应用微机技术、自动采集挖掘机特性的电压和电流数据、可在通用示波器上显示或X—y记录仪绘出挖掘机特性曲线。输入标准特性参数后,自动计算并打印出丰满系数,电流和电压测试数据。采样速度为2160点/秒,精度为±1%,量程满足目前使用的4~23m~3电铲.仪器工作可靠,操作维护方便,为挖掘机的调试提供了一个先进的工具。  相似文献   
994.
黑蚱蝉的鸣声和其发音器,具有基本的构造和特性,即种性.但也有一定的地理差异,鸣声有单音色,复合声,主峰频率高低等变化,这和形态的大小,发音器及其辅助发音器的变化相一致.黑蚱蝉的召唤声和求偶声是鸣声分类较理想的类型,而群鸣声不能用于种下分类.  相似文献   
995.
The bioavailability of three formulations of ivermectin was determined following oral administration to dogs. The average peak plasma level (C max) of ivermectin administered in the standard tablet formulation at 6 and 100 µg/kg of body weight was 2.97 and 44.31 ng/g, respectively. This suggest dose-dependent pharmacokinetics.C max and total ivermectin bioavailability, as assessed from the area under the plasma curve (AUC), were similar between two tablet formulations of ivermectin administered at 100 µg/kg. Furthermore,C max was similar following administration of radiolabelled ivermectin at 6 µg/kg in either a beef-based chewable formulation or in the standard tablet formulation.  相似文献   
996.
997.
998.
999.
The purpose of this study was to characterize the pharmacokinetics of a subcutaneously implanted tissue-chamber model. Thermoplastic tissue chambers were implanted in the paralumbar fossae of six steers. Starting 30 days after implantation, the distribution of intravenously administered antipyrine and phenylbutazone into the tissue chambers was studied. These pharmacokinetic experiments were repeated 10 days later to determine the effect of time after implantation on tissue-chamber distribution. Fifty days after implantation, tissue chambers were drained of transudate, refilled with sterile saline and the rate of influx of endogenous urea, creatinine and albumin was measured. Delayed diffusion of antipyrine and phenylbutazone into tissue chambers was well described using a compartmental model in which tissue-chamber fluid represented the third of three compartments arranged in series. The distribution of antipyrine into tissue chambers was greater than that of phenylbutazone; an observation which is well correlated with the high degree of protein binding of phenylbutazone. There was no effect of time on the penetration of the two agents. Rapid diffusion of urea and creatinine and extremely slow influx of albumin into chambers showed that these chambers formed true interstitial compartments.  相似文献   
1000.
As in the number of mammals, the most prominent feature of the ganglion-cell layer in the retina of the German shepherd dog is the sharp increase in the density of ganglion cells in the central area. There is an area of maximum density and also a ‘cat-like’ visual streak, located dorsal to the optic disc. The isodensity lines of ganglion-cell distribution is roughly concentric. Their values vary from 5300-13 000 cells/mm2 in the central area, with the cells densely packed, to 1000 cells/mm2 or less in the periphery, where the cells are sparsely distributed. There were some individual differences amongst the animals studied, although all of them were pure-bred dogs. This suggests that the configuration of the retina in the canine species is not only dependent on the breed itself but also on some other parameters such as phylogenetic heritage, environment, aptitude, lifestyle, or even training.  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