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   3121篇
  免费   269篇
  2023年   10篇
  2022年   10篇
  2021年   54篇
  2020年   27篇
  2019年   47篇
  2018年   66篇
  2017年   54篇
  2016年   99篇
  2015年   161篇
  2014年   177篇
  2013年   196篇
  2012年   265篇
  2011年   254篇
  2010年   149篇
  2009年   135篇
  2008年   195篇
  2007年   190篇
  2006年   187篇
  2005年   161篇
  2004年   180篇
  2003年   128篇
  2002年   146篇
  2001年   28篇
  2000年   13篇
  1999年   29篇
  1998年   46篇
  1997年   33篇
  1996年   26篇
  1995年   27篇
  1994年   16篇
  1993年   17篇
  1992年   19篇
  1991年   21篇
  1990年   19篇
  1989年   10篇
  1988年   15篇
  1987年   16篇
  1986年   9篇
  1985年   20篇
  1984年   9篇
  1983年   9篇
  1982年   9篇
  1981年   18篇
  1980年   15篇
  1979年   21篇
  1978年   13篇
  1976年   6篇
  1974年   6篇
  1973年   8篇
  1967年   4篇
排序方式: 共有3390条查询结果,搜索用时 15 毫秒
81.
Angelman syndrome is a neurodevelopmental disorder characterized by mental retardation, severe speech disorder, facial dysmorphism, secondary microcephaly, ataxia, seizures, and abnormal behaviors such as easily provoked laughter. It is most frequently caused by a de novo maternal deletion of chromosome 15q11–q13 (about 70–90%), but can also be caused by paternal uniparental disomy of chromosome 15q11–q13 (3–7%), an imprinting defect (2–4%) or in mutations in the ubiquitin protein ligase E3A gene UBE3A mostly leading to frame shift mutation. In addition, for patients with overlapping clinical features (Angelman-like syndrome), mutations in methyl-CpG binding protein 2 gene MECP2 and cyclin-dependent kinase-like 5 gene CDKL5 as well as a microdeletion of 2q23.1 including the methyl-CpG binding domain protein 5 gene MBD5 have been described. Here, we describe a patient who carries a de novo 5 Mb-deletion of chromosome 15q11.2–q13.1 known to be associated with Angelman syndrome and a further, maternally inherited deletion 2q21.3 (~ 364 kb) of unknown significance. In addition to classic features of Angelman syndrome, she presented with severe infections in the first year of life, a symptom that has not been described in patients with Angelman syndrome. The 15q11.2–q13.1 deletion contains genes critical for Prader–Willi syndrome, the Angelman syndrome causing genes UBE3A and ATP10A/C, and several non-imprinted genes: GABRB3 and GABRA5 (both encoding subunits of GABA A receptor), GOLGA6L2, HERC2 and OCA2 (associated with oculocutaneous albinism II). The deletion 2q21.3 includes exons of the genes RAB3GAP1 (associated with Warburg Micro syndrome) and ZRANB3 (not disease-associated). Despite the normal phenotype of the mother, the relevance of the 2q21.3 microdeletion for the phenotype of the patient cannot be excluded, and further case reports will need to address this point.  相似文献   
82.
The IQ-motif is an amphipathic, often positively charged, α-helical, calmodulin binding sequence found in a number of eukaryote signalling, transport and cytoskeletal proteins. They share common biophysical characteristics with established, cationic α-helical antimicrobial peptides, such as the human cathelicidin LL-37. Therefore, we tested eight peptides encoding the sequences of IQ-motifs derived from the human cytoskeletal scaffolding proteins IQGAP2 and IQGAP3. Some of these peptides were able to inhibit the growth of Escherichia coli and Staphylococcus aureus with minimal inhibitory concentrations (MIC) comparable to LL-37. In addition some IQ-motifs had activity against the fungus Candida albicans. This antimicrobial activity is combined with low haemolytic activity (comparable to, or lower than, that of LL-37). Those IQ-motifs with anti-microbial activity tended to be able to bind to lipopolysaccharide. Some of these were also able to permeabilise the cell membranes of both Gram positive and Gram negative bacteria. These results demonstrate that IQ-motifs are viable lead sequences for the identification and optimisation of novel anti-microbial peptides. Thus, further investigation of the anti-microbial properties of this diverse group of sequences is merited.  相似文献   
83.
The nuclear factor E2-related factor 2 (Nrf2) plays an important role in cellular protection against cancer, renal, pulmonary, cardiovascular and neurodegenerative diseases where oxidative stress and inflammation are common conditions. The Nrf2 regulates the expression of detoxifying enzymes by recognizing the human Antioxidant Response Element (ARE) binding site and it can regulate antioxidant and anti-inflammatory cellular responses, playing an important protective role on the development of the diseases. Studies designed to investigate how effective Nrf2 activators or modulators are need to be initiated. Several recent studies have shown that nutritional compounds can modulate the activation of Nrf2–Keap1 system. This review aims to discuss some of the key nutritional compounds that promote the activation of Nrf2, which may have impact on the human health.  相似文献   
84.
Chromoblastomycosis is a chronic cutaneous and subcutaneous mycosis. The management of this infection continues to be challenging because there is no consensus on the therapeutic regimen. We report here a case of a 69-year-old male patient with cauliflower-like lesions on his left leg and foot. He had already been treated with itraconazole at a dose of 200 mg/day for 5 months, with mycological cure for all the affected areas. However, the lesions relapsed at both sites, and treatment with itraconazole was resumed at the dose previously used. Initially, direct mycological examination, cultural, and microculture slide observation were performed. Afterward, sequencing of the ITS1-5.8S rDNA-ITS2 region of the fungal DNA and evaluation of its susceptibility to antifungal agents alone and in combination were performed. In direct mycological examination, the presence of sclerotic cells was verified, and the fungus was identified as Fonsecaea based on cultural and microscopic examinations. Identification as Fonsecaea monophora was confirmed after sequencing of the ITS region and phylogenetic analysis. The isolate was susceptible to itraconazole and terbinafine. The combinations of amphotericin B and terbinafine and terbinafine and voriconazole were synergistic. The use of drugs for which the causative agent is susceptible to singly or in combination may be an alternative for the treatment of mycosis. Furthermore, the identification of the agent by molecular techniques is important for epidemiological purposes. To the best of our knowledge, this is the first case of relapsed chromoblastomycosis caused by F. monophora in Brazil.  相似文献   
85.
An important mechanism contributing to cell cholesterol efflux is aqueous transfer in which cholesterol diffuses from cells into the aqueous phase and becomes incorporated into an acceptor particle. Some compounds can enhance diffusion by acting as shuttles transferring cholesterol to cholesterol acceptors, which act as cholesterol sinks. We have examined whether particles in serum can enhance cholesterol efflux by acting as shuttles. This task was accomplished by incubating radiolabeled J774 cells with increasing concentrations of lipoprotein-depleted sera (LPDS) or components present in serum as shuttles and a constant amount of LDL, small unilamellar vesicles, or red blood cells (RBC) as sinks. Synergistic efflux was measured as the difference in fractional efflux in excess of that predicted by the addition of the individual efflux values of sink and shuttle alone. Synergistic efflux was obtained when LPDS was incubated with cells and LDL. When different components of LPDS were used as shuttles, albumin produced synergistic efflux, while apoA-I did not. A synergistic effect was also obtained when RBC was used as the sink and albumin as shuttle. The previously observed negative association of albumin with coronary artery disease might be linked to reduced cholesterol shuttling that would occur when serum albumin levels are low.  相似文献   
86.
87.
88.
Several mite species commonly attack cultivated citrus around the world. Up to 104 phytophagous species have been reported causing damage to leaves, buds and fruits, but only a dozen can be considered major pests requiring control measures. In recent years, several species have expanded their geographical range primarily due to the great increase in trade and travel worldwide, representing a threat to agriculture in many countries. Three spider mite species (Acari: Tetranychidae) have recently invaded the citrus-growing areas in the Mediterranean region and Latin America. The Oriental red mite, Eutetranychus orientalis (Klein), presumably from the Near East, was detected in southern Spain in 2001. The Texas citrus mite, Eutetranychus banksi (McGregor), is widely distributed in North, Central and South America. It was first reported in Europe in 1999 on citrus in Portugal; afterwards the mite invaded the citrus orchards in southern Spain. In Latin America, the Hindustan citrus mite, Schizotetranychus hindustanicus (Hirst), previously known only from citrus and other host plants in India, was reported causing significant damage to citrus leaves and fruits in Zulia, northwest Venezuela, in the late 1990s. Later, this mite species spread to the southeast being detected on lemon trees in the state of Roraima in northern Brazil in 2008. Whereas damage levels, population dynamics and control measures are relatively well know in the case of Oriental red mite and Texas citrus mite, our knowledge of S. hindustanicus is noticeably scant. In the present paper, information on pest status, seasonal trends and natural enemies in invaded areas is provided for these species, together with morphological data useful for identification. Because invasive species may evolve during the invasion process, comparison of behavior, damage and management options between native and invaded areas for these species will be useful for understanding the invader’s success and their ability to colonize new regions.  相似文献   
89.
90.
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