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   5147篇
  免费   247篇
  国内免费   477篇
林业   135篇
农学   124篇
基础科学   16篇
  296篇
综合类   1328篇
农作物   161篇
水产渔业   260篇
畜牧兽医   2097篇
园艺   1402篇
植物保护   52篇
  2024年   17篇
  2023年   62篇
  2022年   185篇
  2021年   212篇
  2020年   206篇
  2019年   271篇
  2018年   155篇
  2017年   228篇
  2016年   255篇
  2015年   268篇
  2014年   317篇
  2013年   340篇
  2012年   398篇
  2011年   411篇
  2010年   244篇
  2009年   255篇
  2008年   274篇
  2007年   365篇
  2006年   215篇
  2005年   167篇
  2004年   190篇
  2003年   141篇
  2002年   108篇
  2001年   86篇
  2000年   93篇
  1999年   51篇
  1998年   50篇
  1997年   28篇
  1996年   29篇
  1995年   23篇
  1994年   36篇
  1993年   39篇
  1992年   28篇
  1991年   10篇
  1990年   13篇
  1989年   18篇
  1988年   16篇
  1987年   14篇
  1986年   5篇
  1985年   5篇
  1984年   4篇
  1983年   3篇
  1982年   2篇
  1981年   6篇
  1980年   7篇
  1979年   3篇
  1978年   2篇
  1974年   1篇
  1973年   1篇
  1956年   12篇
排序方式: 共有5871条查询结果,搜索用时 15 毫秒
941.
Objective – To determine the safety and efficacy of high‐dose fomepizole compared with ethanol (EtOH) in cats with ethylene glycol (EG) toxicosis. Design – Prospective study. Setting – University veterinary research laboratory. Animals – Thirteen cats. Interventions – Two cats received injections of high‐dose fomepizole (Study 1). Three cats received lethal doses of EG and fomepizole treatment was initiated 1, 2, or 3 hours later (Study 2). Eight cats received a lethal dose of EG and were treated with fomepizole or EtOH (Study 3). Cats treated with fomepizole received 125 mg/kg IV initially, then 31.25 mg/kg at 12, 24, and 36 hours. Cats treated with EtOH received 5 mL of 20% EtOH/kg IV initially, then every 6 hours for 5 treatments, then every 8 hours for 4 treatments. Cats also received fluids and supportive therapy as needed. Measurements and Main Results – Clinical signs were monitored and serial blood analyses performed. Cats receiving fomepizole experienced mild sedation but no biochemical evidence of toxicity. Cats receiving fomepizole for EG intoxication survived if therapy was initiated within 3 hours of EG ingestion. One of the 6 developed acute renal failure (ARF) but survived. Only 1 of the 3 cats treated with EtOH 3 hours following EG ingestion survived; 2 developed ARF and were euthanized. Cats treated 4 hours following EG ingestion developed ARF, whether treated with EtOH or fomepizole. Conclusions – Fomepizole is safe when administered to cats in high doses, prevents EG‐induced fatal ARF when therapy is instituted within 3 hours of EG ingestion, and is more effective than treatment with EtOH.  相似文献   
942.
Objective – To describe a case of presumptive secondary pseudohypoaldosteronism (PHA) in a cat with urinary tract infection and chronic urethral obstruction. The obstruction was believed to have resulted from sloughed urinary bladder mucosa secondary to pressure necrosis. Case Summary – A 5‐year‐old, 4 kg, castrated male Siamese cat presented for vomiting and stranguria. Medical history included a perineal urethrostomy for urethral obstruction. Physical examination revealed a large, painful, nonexpressible urinary bladder. Point‐of‐care testing demonstrated electrolyte derangements consistent with a postrenal azotemia and metabolic acidosis. Results of urine culture was positive for bacterial growth. Diagnostic imaging revealed presence of retroperitoneal fluid, marked urinary bladder wall thickening, bilateral hydroureter, mild bilateral pyelectasia, and small nephroliths. The patient was treated for a urinary tract obstruction and infection. In the 3 weeks following initial discharge, the patient was evaluated on multiple occasions for lethargy, intermittent vomiting, inappropriate urination, and progressive polyuria and polydipsia. Although the urinary bladder was easily expressed during repeat examinations, it was persistently distended and subjectively thickened upon palpation. Repeat ultrasound of the urinary tract showed evidence of sloughed tissue in the bladder lumen, likely secondary to chronic urethral obstruction and pressure necrosis. A cystotomy was performed to remove the necrotic tissue, and a revised perineal urethrostomy was done due to a partial urethral stricture. Bladder biopsies were obtained at this time. Postoperatively, the cat was reported by the owners to be urinating normally but continued to be polyuric and polydipsic in the week following discharge. One week after surgery, the cat presented in hypovolemic shock with laboratory findings consistent with a presumptive diagnosis of secondary PHA. New or Unique Information Provided – PHA has not been reported previously in a cat. This case report suggests that aldosterone resistance should be considered in cats with consistent laboratory findings and a history of documented obstructive uropathy and urinary tract infection.  相似文献   
943.
生长分化因子9(growth differentiation factor 9,GDF-9)属于TGF-β超家族,其在卵泡的发育过程中发挥着重要的作用。作者将对GDF-9基因的结构和功能,GDF-9的表达与调控及其对卵泡发育和颗粒细胞增殖的影响等方面进行详细的阐述,进而分析GDF-9基因与哺乳动物繁殖性能的关系。  相似文献   
944.
不同培养液对体外培养的小鼠胸腺上皮细胞增殖的影响   总被引:1,自引:1,他引:0  
分离纯化小鼠胸腺上皮细胞(mTEC),以DMEM、DMEM/F12、RPMI 1640 3种基础培养液加10%胎牛血清完全培养液进行培养, MTT法和流式细胞术分别检测mTEC的增殖及细胞周期,筛选出最适合mTEC生长的培养液。结果表明,DMEM培养的mTEC增殖快,细胞增殖指数明显高于DMEM/F12、RPMI 1640培养液,表明DMEM是mTEC体外培养的最佳培养液。  相似文献   
945.
诱导多能干( induced pluripotent stem,iPS)细胞在维持多能的同时能够持续自我更新。由于诱导多能干细胞能够创造病人特异或者疾病特异的多能干细胞,这些细胞对于研究疾病的机理和药物的发现非常有用。作者主要从iPS细胞建立的优化、被重编程的细胞类型、iPS细胞的发育潜能、iPS细胞产生的2种模型及iPS细胞的应用等5个方面进行了综述。  相似文献   
946.
毛囊干细胞的分离方法及其应用   总被引:1,自引:1,他引:0  
毛囊干细胞是皮肤组织工程理想的种子细胞,分离纯化是其研究的基础手段。毛囊干细胞能分化成毛囊、皮脂腺、表皮,在组织维持与更新及某些临床疾病的治疗中均起到重要的作用。作者介绍了近年来毛囊干细胞几种常用的分离纯化方法,包括组织块法和酶消化法等,为进一步研究毛囊干细胞的特性和应用提供参考。  相似文献   
947.
人居环境已成为推动城市可持续发展和提升城市核心竞争力的重要因素。具有环境优美、气候宜人的人居环境是人们的共同愿望,实现城市人居环境的和谐发展是社会发展的迫切需要。以国内外人居环境的研究为背景,论述了我国城市人居环境现状及特点,提出了我国建设城市理想人居环境的方法和对策。  相似文献   
948.
Repeated biomass harvesting for human livelihood needs can cause significant changes in forest structure, composition and diversity. Such impacts have often been associated with the distance to villages and their size, but the effects of individual villages in relation to their characteristics have been little studied. Focussing on the issues around communities’ impacts on the forest, this research aimed to understand how resource extraction by two Buffer Zone villages in Nepal's Bardia National Park affects forest structure and diversity. Tree density, basal area, diameter at breast height (DBH), species richness, two diversity indices and disturbance indices were recorded in 108 plots in 12 transects, from March till May 2005, within the park along the village boundaries, where resource extraction occurs, and in the core park area which is isolated from human disturbance. Forest subject to resource extraction had a lower density of trees, smaller DBH and lower species richness and diversity. Forest disturbance declined with distance from the villages but the two villages differed widely in their impact on the forest. Resource use was more intensive in Shivapur village and percentage of trees lopped, average lopping intensity and numbers of dung piles were statistically significant. This was mainly due to the lack of access to Buffer Zone community Forest for Shivapur households. Interviews with villagers suggested that there have been changes in species availability compared to 5 years ago. Households also underestimated the impact of their resource extraction, which may prevent them from changing their behaviour to benefit conservation. It is clear that understanding rural communities’ needs, their framing of resource extraction and utilisation, and dependence on forest resources will be very helpful for long term conservation measures.  相似文献   
949.
长期冻存对昆虫细胞系SL2和NIH-SaPe-4活性的影响   总被引:1,自引:1,他引:0       下载免费PDF全文
对2种双翅目昆虫细胞系(黑腹果蝇胚细胞系SL2以及麻蝇胚细胞系NIH-SaPe-4)38个月长期液氮深低温保存效果进行了研究,通过对冻存时间和保护剂对2种细胞系冻后活力、圆度以及恢复时间影响的测定,比较了3种不同配方冻存保护液的效果。结果表明:2种昆虫细胞系冻后活性均随着冻存时间的增长而逐渐降低。长期冻存期中,使用90%胎牛血清(FBS)+10%二甲基亚砜(DMSO)冻存SL2效果较好,NIH-SaPe-4使用10%DMSO即可满足冻存的需要,而无需额外添加高浓度FBS。甘油不适用于这2种昆虫细胞系的长期保存。  相似文献   
950.
AIM: To investigate the implantation of matrigel carrying human adipose-derived mesenchymal stem cells to enhance the cell survival and the improvement of the ventricular functions in infarct heart.METHODS: Human adipose-derived mesenchymal stem cells (ADMSCs) were isolated and cultured from adult adipose tissue. SD rats with one-week-old myocardial infarction were randomly received the following 4 treatments: injection of PBS, matrigel, PBS+ADMSCs or matrigel+ADMSCs, respectively. Labeled ADMSCs either in matrigel or in saline were injected into the border area of ischemia. The controls received the injection of matrigel or saline only. Four weeks after injection, the heart functions were determined by echocardiography. The densities of the micro-vessels within the infarct area were also measured.RESULTS: Four weeks after implantation of ADMSCs, the cell graft size, the heart functions and the micro-vessel densities within the infarct area improved in matrigel+ADMSCs group as compared to other groups.CONCLUSION: The co-injection of ADMSCs with matrigel enhances the graft survival, increases the density of the micro-vessels in the myocardium and improves the cardiac functions.  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