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   5264篇
  免费   276篇
  国内免费   57篇
耳鼻咽喉   62篇
儿科学   137篇
妇产科学   124篇
基础医学   703篇
口腔科学   581篇
临床医学   449篇
内科学   1142篇
皮肤病学   141篇
神经病学   319篇
特种医学   280篇
外科学   500篇
综合类   34篇
一般理论   1篇
预防医学   544篇
眼科学   96篇
药学   298篇
中国医学   38篇
肿瘤学   148篇
  2023年   52篇
  2022年   120篇
  2021年   181篇
  2020年   137篇
  2019年   136篇
  2018年   199篇
  2017年   126篇
  2016年   143篇
  2015年   176篇
  2014年   242篇
  2013年   281篇
  2012年   420篇
  2011年   425篇
  2010年   198篇
  2009年   212篇
  2008年   301篇
  2007年   313篇
  2006年   255篇
  2005年   234篇
  2004年   160篇
  2003年   139篇
  2002年   143篇
  2001年   107篇
  2000年   84篇
  1999年   68篇
  1998年   73篇
  1997年   58篇
  1996年   45篇
  1995年   45篇
  1994年   29篇
  1993年   39篇
  1992年   18篇
  1991年   35篇
  1990年   27篇
  1989年   40篇
  1988年   23篇
  1987年   30篇
  1986年   26篇
  1985年   25篇
  1984年   20篇
  1983年   21篇
  1982年   16篇
  1981年   19篇
  1980年   21篇
  1978年   11篇
  1977年   13篇
  1976年   11篇
  1973年   11篇
  1970年   16篇
  1969年   12篇
排序方式: 共有5597条查询结果,搜索用时 15 毫秒
31.
Blend films based on sodium alginate (SA) and citrus pectin (P) reinforced with different concentrations of SiO2 (0–10% w/w) were developed in this study. From the morphological (SEM) and structural (FT-IR) evaluation, it was verified that the incorporation of the reinforcing agent did not drastically modify the microstructure of the films, nor did new chemical bonds form. However, the XRD results suggested a slight reduction in the crystallinities of the blends by the incorporation of SiO2. Among the formulations prepared, the addition of a 5% reinforcing agent was responsible for the simultaneous improvement of mechanical and barrier properties. Comparing the control sample (SA/P) with the SA/P/5.0%SiO2 film, the tensile strength increased from 27.7 ± 3.7 to 40.6 ± 4.5 MPa, and the water-vapor transmission rate decreased from 319.8 ± 38.7 to 288.9 ± 23.5 g m−2 day−1. Therefore, SiO2, as a reinforcing agent in SA/P blends, represents a simple and effective strategy for improving the properties of biopolymer-based films in applications, such as packaging.  相似文献   
32.
This study sought to determine the frequency of possible cases of avoidant/restrictive food intake disorder (ARFID) in a Portuguese sample of school-aged children and to assess the associations with child’s internalizing problems, BMI z-score and body dissatisfaction, and parents’ eating habits, attitudes and practices. We assessed 330 children through child’s and parents’measures. Fifty-one (15.5%) children were possible cases of ARFID based on their symptom’s presentation. There were no association between sex and possible cases of ARFID, and no significant differences between possible cases of ARFID and nonpossible cases of ARFID regarding age. Lower BMI z-score and anxiety/depression were associated with possible cases of ARFID.  相似文献   
33.
This review summarizes the history and current state of the known genetic basis for soybean resistance to Soybean mosaic virus (SMV), and examines how the integration of molecular markers has been utilized in breeding for crop improvement. SVM causes yield loss and seed quality reduction in soybean based on the SMV strain and the host genotype. Understanding the molecular underpinnings of SMV–soybean interactions and the genes conferring resistance to SMV has been a focus of intense research interest for decades. Soybean reactions are classified into three main responses: resistant, necrotic, or susceptible. Significant progress has been achieved that has greatly increased the understanding of soybean germplasm diversity, differential reactions to SMV strains, genotype–strain interactions, genes/alleles conferring specific reactions, and interactions among resistance genes and alleles. Many studies that aimed to uncover the physical position of resistance genes have been published in recent decades, collectively proposing different candidate genes. The studies on SMV resistance loci revealed that the resistance genes are mainly distributed on three chromosomes. Resistance has been pyramided in various combinations for durable resistance to SMV strains. The causative genes are still elusive despite early successes in identifying resistance alleles in soybean; however, a gene at the Rsv4 locus has been well validated.  相似文献   
34.
Embossing is a converting process in which the surface of a tissue paper sheet is changed under high pressure, allowing different functions. In this work, the authors intend to study how the embossing pressure affects the main properties of tissue paper, using a laboratory embossing system. An optimum pressure was achieved at 2.8 bar to this embossing laboratory set-up. The effect of pressure when densifying the paper sheet gives it a gain in mechanical strength but no differences in terms of liquid absorbency. The two embossing patterns present different behaviors but both evidence losses in mechanical and softness properties. On the other hand, the finite element method (FEM) does not show clear evidence of how the pressure affects the paper strength. For the deco die, it is possible to observe that the amount of yielding is slightly higher for lower pressure (2.4 bar), but this plasticity state parameter is very similar for 2.8 bar and 3.2 bar. For the micro die, FEM simulations of the manufacturing pressure do not show a considerable impact on the amount of plasticity state of the material; only for 3.2 bar, it shows a change in the pattern of the plasticity state of the paper during the embossing processes. In the end, to achieve a final product with excellent quality, it is important to make a compromise between the various properties.  相似文献   
35.
The amino acid L-arginine is crucial for nitric oxide (NO) synthesis, an important molecule regulating vascular tone. Considering that vascular dysfunction precedes cardiovascular disease, supplementation with precursors of NO synthesis (e.g., L-arginine) is warranted. However, supplementation of L-citrulline is recommended instead of L-arginine since most L-arginine is catabolized during its course to the endothelium. Given that L-citrulline, found mainly in watermelon, can be converted to L-arginine, watermelon supplementation seems to be effective in increasing plasma L-arginine and improving vascular function. Nonetheless, there are divergent findings when investigating the effect of watermelon supplementation on vascular function, which may be explained by the L-citrulline dose in watermelon products. In some instances, offering a sufficient amount of L-citrulline can be impaired by the greater volume (>700 mL) of watermelon needed to reach a proper dose of L-citrulline. Thus, food technology can be applied to reduce the watermelon volume and make supplementation more convenient. Therefore, this narrative review aims to discuss the current evidence showing the effects of watermelon ingestion on vascular health parameters, exploring the critical relevance of food technology for acceptable L-citrulline content in these products. Watermelon-derived L-citrulline appears as a supplementation that can improve vascular function, including arterial stiffness and blood pressure. Applying food technologies to concentrate bioactive compounds in a reduced volume is warranted so that its ingestion can be more convenient, improving the adherence of those who want to ingest watermelon products daily.  相似文献   
36.
37.
38.
It is well known the involvement of the gastrointestinal tract in Epidermolysis Bulhosa (EB) and its consequences on both nutrition and growth. We present a case of a young girl with EB diagnosed soon after birth, admitted to our emergency room with food impactation. The endoscopy revealed a double barrel esophagus. No medical or surgical therapy was started and after 2 months of enteric feeding, spontaneous resolution was observed at endoscopy. Skin biopsy was compatible with EB Simplex. According to the literature EB Simplex is the subtype the least associated with GI tract involvement, presenting with dysphagia in only 2% of the patients, and with the lowest cumulative risk of esophageal stricturing.  相似文献   
39.
40.
Surfactants have long been known to have microbicidal action and have been extensively used as antiseptics and disinfectants for a variety of general hygiene and clinical purposes. Among surfactants, quaternary ammonium compounds (QAC) are known to be the most useful antiseptics and disinfectants. However, our previous toxicological studies showed that QAC are also the most toxic surfactants for mammalian cells. An understanding of the mechanisms that underlie QAC toxicity is a crucial first step in their rational use and in the design and development of more effective and safer molecules. We show that QAC-induced toxicity is mediated primarily through mitochondrial dysfunction in mammalian columnar epithelial cell cultures in vitro. Toxic effects begin at sublethal concentrations and are characterized by mitochondrial fragmentation accompanied by decreased cellular energy charge. At very low concentrations, several QAC act on mitochondrial bioenergetics through a common mechanism of action, primarily by inhibiting mitochondrial respiration initiated at complex I and, to a lesser extent, by slowing down coupled ADP phosphorylation. The result is a reduction of cellular energy charge which, when reduced below 50% of its original value, induces apoptosis. The lethal effects are shown to be primarily a result of this process. At higher doses (closer to the critical micellar concentration), QAC induce the complete breakdown of cellular energy charge and necrotic cell death.  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