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   697篇
  免费   28篇
林业   217篇
农学   8篇
基础科学   5篇
  56篇
综合类   89篇
农作物   10篇
水产渔业   32篇
畜牧兽医   297篇
园艺   2篇
植物保护   9篇
  2021年   6篇
  2020年   8篇
  2019年   13篇
  2018年   9篇
  2017年   6篇
  2015年   10篇
  2014年   6篇
  2013年   22篇
  2012年   24篇
  2011年   15篇
  2010年   10篇
  2009年   10篇
  2008年   25篇
  2007年   19篇
  2006年   27篇
  2005年   14篇
  2004年   24篇
  2003年   18篇
  2002年   16篇
  2001年   15篇
  2000年   9篇
  1999年   6篇
  1993年   9篇
  1992年   17篇
  1991年   14篇
  1990年   13篇
  1989年   10篇
  1988年   12篇
  1987年   11篇
  1986年   13篇
  1985年   7篇
  1984年   11篇
  1983年   7篇
  1982年   6篇
  1976年   6篇
  1973年   6篇
  1972年   7篇
  1938年   6篇
  1926年   7篇
  1925年   9篇
  1916年   5篇
  1912年   6篇
  1911年   11篇
  1910年   6篇
  1900年   7篇
  1869年   6篇
  1868年   7篇
  1867年   9篇
  1866年   5篇
  1863年   8篇
排序方式: 共有725条查询结果,搜索用时 15 毫秒
261.
Bilaterally symmetric opacities were detected in the corneal stroma of 78 (14%) of 560 Siberian Huskies, aged 7 months to 12 years, examined in ophthalmology screening clinics. The opacities were round or horizontally oval and consisted of a diffuse gray homogeneous haze in the anterior stroma or an array of fine polychromatic crystals in the posterior stroma, or both. The corneas were not inflamed. The frequency of occurrence and density of the opacities increased with age. Several affected dogs were closely related, but a specific inheritance pattern could not be established. Light and electron microscopy disclosed clusters of extracellular, thin, needle-shaped, crystalline clefts. Histochemical stains on frozen sections identified neutral fats, phospholipids, and cholesterol as components of the crystals.  相似文献   
262.
263.
264.
265.
Yearling steers were treated with ACTH to determine the effect of increased plasma cortisol concentration on bovine lymphocyte and polymorphonuclear leukocyte (PMN) function. The administration of ACTH caused a significant (P less than 0.01) increase in serum cortisol concentration and depression of lymphocyte blastogenesis in response to phytohemagglutinin and concanavalin A. The response to pokeweed mitogen was also depressed, but not significantly. Random migration by PMN was significantly enhanced by ACTH treatment, but there was no effect on ingestion of Staphylococcus aureus, nitroblue tetrazolium reduction, or antibody-dependent cell-mediated cytotoxicity by PMN. The iodination reaction, which evaluates the activity of the myeloperoxidase-hydrogen peroxide-halide antibacterial system of the PMN, was significantly impaired after ACTH treatment. These data indicate that specific parameters of lymphocyte and neutrophil function were impaired directly or indirectly by elevated in vivo concentrations of plasma cortisol.  相似文献   
266.
Polymorphonuclear leukocyte (PMN) function and serum concentrations of estradiol, progesterone, and cortisol (hydrocortisone) were monitored concurrently in clinically normal cows during the estrous cycle. Five parameters were used to evaluate PMN function: (i) random migration under agarose, (ii) ingestion of 125I-labeled Staphylococcus aureus, (iii) nitroblue tetrazolium (NBT) reduction, (iv) iodination, and (v) antibody-dependent cell-mediated cytotoxicity. Increased serum estradiol concentrations were associated with enhanced random migration, but had no apparent effect on NBT reduction, iodination, or ingestion of S aureus by bovine PMN. Increased serum estradiol was also associated with increased serum cortisol. Increased serum progesterone values were associated with a depression of NBT reduction and iodination by PMN, but with enhanced random migration and antibody-dependent cell-mediated cytotoxicity. These results indicate that physiologic changes in steroid hormone values during the normal estrous cycle of the cow are associated with alterations in PMN function.  相似文献   
267.
268.
269.
Neutrophils isolated from the peripheral blood of pigs free of infection withMycoplasma hyopneumoniae were loaded with a fluorescent indicator (Fura-2) for detection of cytosolic free calcium concentration. The kinetics of the intracellular calcium flux were examined after incubation with or without a pathogenic or a non-pathogenic strain ofM. hyopneumoniae. The basal intracellular calcium concentration was not altered by incubation withM. hyopneumoniae. However, the relative increase in cytoplasmic calcium concentration caused by the addition of opsonized zymosan was significantly (p<0.05) higher in neutrophils incubated withM. hyopneumoniae as compared to neutrophils not incubated withM. hyopneumoniae. Additionally, after zymosan stimulation, the intracellular calcium concentration was greater in neutrophils incubated with a pathogenic strain ofM. hyopneumoniae than in those incubated with a non-pathogenic strain. This suggests thatM. hyopneumoniae alters the signal transduction mechanisms in neutrophils and that this alteration may be related to virulence.Abbreviations [Ca]i intracellular concentration of calcium - CCU colour changing units/ml - Fura-2/AM pentaacetoxymethyl ester - PBS phosphate-buffered saline, pH 7.2 - TNF tumour necrosis factor  相似文献   
270.
Genetic Resources and Crop Evolution - Most orphan crops have not been fully sequenced, hence we rely on genome sequences of related species to align markers to different chromosomes. This hinders...  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