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   2881篇
  免费   210篇
  国内免费   1篇
  2023年   29篇
  2022年   24篇
  2021年   81篇
  2020年   72篇
  2019年   67篇
  2018年   129篇
  2017年   126篇
  2016年   141篇
  2015年   196篇
  2014年   198篇
  2013年   249篇
  2012年   286篇
  2011年   256篇
  2010年   128篇
  2009年   107篇
  2008年   186篇
  2007年   131篇
  2006年   134篇
  2005年   111篇
  2004年   90篇
  2003年   79篇
  2002年   67篇
  2001年   25篇
  2000年   28篇
  1999年   23篇
  1998年   7篇
  1997年   7篇
  1996年   10篇
  1995年   9篇
  1994年   5篇
  1993年   3篇
  1992年   6篇
  1991年   9篇
  1990年   5篇
  1989年   6篇
  1988年   3篇
  1987年   7篇
  1986年   4篇
  1985年   3篇
  1984年   7篇
  1981年   5篇
  1977年   4篇
  1975年   5篇
  1974年   3篇
  1973年   3篇
  1969年   2篇
  1968年   2篇
  1967年   3篇
  1965年   2篇
  1957年   1篇
排序方式: 共有3092条查询结果,搜索用时 31 毫秒
911.
The present study aimed to develop a protocol for somatic embryogenesis and encapsulation of coffee embryos (Coffea arabica L.), for the conservation of genotypes with characteristics of commercial interest. Somatic embryos were induced from leaf explants in Murashige and Skoog medium (MS) supplemented with 1 mg · L−1 of 2,4-dichlorophenoxiacetic acid (2,4-D) combined with 2 mg · L−1 of benzyladenine (BA). Somatic embryos (SE) at the globular stage were encapsulated in a sodium alginate matrix; two treatments were tested: MS + 5 mg · L−1 BA + 1 mg · L−1 NAA + 3% (w/v) alginate, and MS + 7 mg · L−1 BA + 5.7 mg · L−1 indoleacetic acid (IAA) + 3% (w/v) alginate. Alginate was complexed with 100 mM calcium chloride (CaCl2). Viability of the encapsulated SE was determined by staining with 0.01% fluorescein diacetate (FDA) after 0, 15, 30, and 45 days of storage at 4°C. Embryo viability was 100% in both treatments.  相似文献   
912.
BackgroundParacoccidioidomycosis (PCM) is an endemic disease in Latin America. In immunocompetent hosts, PCM occurs in two main clinical forms: acute and chronic. However, in HIV-infected patients PCM may show up simultaneous manifestations of acute and chronic forms.Case reportWe present the case of a patient diagnosed with HIV who had disseminated skin lesions and generalized lymphadenopathy, as well as respiratory and central nervous system involvement. The PCM diagnosis was confirmed by direct KOH examination, double immunodiffusion and the isolation of the fungus in samples of an abscess in the subcostal region. The isolate was identified as Paracoccidioides brasiliensis S1 by species-specific PCR using primers for protein-coding gene GP43 (exon 2) followed by PCR-RFLP of the alpha-tubulin gene.ConclusionsThere are few data in literature reporting species-specific molecular identification of Paracoccidioides in HIV/PCM patients. Therefore, this case report may contribute to improve the knowledge about this severe disease, its causative cryptic species, and its consequences to patients.  相似文献   
913.
Aquatic Ecology - Intermittent streams, dominant in arid and semi-arid regions, are considered to be more representative of global river networks than perennial rivers. The impacts of constant...  相似文献   
914.
This work aims to evaluate the fermentability of cellulosic hydrolysates obtained by enzymatic saccharification of sugarcane bagasse pretreated by hydrothermal processing using Candida guilliermondii FTI 20037 yeast. The inoculum was obtained from yeast culture in a medium containing glucose as a carbon source supplemented with rice bran extract, CaCl2·2H2O and (NH4)2SO4 in 50 mL Erlenmeyer flasks, containing 20 mL of medium, initial 5.5 pH under agitation of an orbital shaker (200 rpm) at 30°C for 24 h. The cellulosic hydrolysates, prior to being used as a fermentation medium, were autoclaved for 15 min at 0.5 atm and supplemented with the same nutrients employed for the inoculum, except the glucose, using the same conditions for the inoculum, but with a period of 48 h. Preliminary results showed the highest consumption of glucose (97%) for all the hydrolysates, at 28 h of fermentation. The highest concentration of ethanol (20.5 g/L) was found in the procedure of sugarcane bagasse pretreated by hydrothermal processing (195°C/10 min in 20 L reactor) and delignificated with NaOH 1.0% (w/v), 100°C, 1 h in 500 mL stainless steel ampoules immersed in an oil bath.  相似文献   
915.
916.
There is strong evidence implicating nitric oxide (NO) in the pathophysiology of migraine and aura. Therefore, genetic polymorphisms in the endothelial NO synthase (eNOS) gene have been studied as candidate markers for migraine susceptibility. We compared for the first time the distribution of eNOS haplotypes including the three clinically relevant eNOS polymorphisms (T(-786)C in the promoter, rs2070744; Glu298Asp in exon 7, rs1799983; and a 27?bp variable number of tandem repeats in intron 4) and two additional tagging single-nucleotide polymorphisms (rs3918226 and rs743506) in 178 women with migraine (134 without aura and 44 with aura) and 117 healthy controls (control group). Genotypes were determined by TaqMan allele discrimination assay, real-time polymerase chain reaction, and polymerase chain reaction followed by fragment separation by electrophoresis. The GA (rs743506) genotype was more common in the control group than in women with migraine (odds ratio?=?0.47, 95% confidence interval [CI]?=?0.29-0.78, p?相似文献   
917.
918.
919.
920.
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