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   5813篇
  免费   550篇
  国内免费   153篇
  6516篇
  2023年   67篇
  2022年   109篇
  2021年   212篇
  2020年   117篇
  2019年   178篇
  2018年   140篇
  2017年   142篇
  2016年   175篇
  2015年   317篇
  2014年   299篇
  2013年   379篇
  2012年   432篇
  2011年   385篇
  2010年   267篇
  2009年   247篇
  2008年   293篇
  2007年   295篇
  2006年   267篇
  2005年   238篇
  2004年   199篇
  2003年   213篇
  2002年   204篇
  2001年   72篇
  2000年   62篇
  1999年   75篇
  1998年   48篇
  1997年   38篇
  1996年   39篇
  1995年   25篇
  1994年   37篇
  1993年   36篇
  1992年   42篇
  1991年   45篇
  1990年   37篇
  1989年   37篇
  1988年   37篇
  1987年   43篇
  1986年   31篇
  1985年   25篇
  1984年   45篇
  1982年   34篇
  1980年   25篇
  1979年   42篇
  1978年   31篇
  1977年   36篇
  1976年   38篇
  1975年   45篇
  1974年   27篇
  1972年   29篇
  1968年   25篇
排序方式: 共有6516条查询结果,搜索用时 15 毫秒
991.
Hypoxia has been shown to cause lung edema and impair lung edema clearance. In the present study, we exposed isolated rat lungs to pO(2) = 40 mm Hg for 60 min or rats to 8% O(2) for up to 24 h and then measured changes in alveolar fluid reabsorption (AFR) and Na,K-ATPase function. Low levels of oxygen severely impaired AFR in both ex vivo and in vivo models. The decrease in AFR was associated with a decrease in Na,K-ATPase activity and protein abundance in the basolateral membranes from peripheral lung tissue of hypoxic rats. Beta-adrenergic agonists restored AFR in rats exposed to 8% O(2) (from 0.02 +/- 0.07 ml/h to 0.59 +/- 0.03 ml/h), which was associated with parallel increases in Na,K-ATPase protein abundance in the basolateral membrane. Hypoxia is associated with increased production of reactive oxygen species. Therefore, we examined whether overexpression of SOD2, manganese superoxide dismutase, would prevent the hypoxia-mediated decrease in AFR. Spontaneously breathing rats were infected with a replication-deficient human type 5 adenovirus containing cDNA for SOD2. An otherwise identical virus that contained no cDNA was used as a control (Adnull). Hypoxic Adnull rats had decreased rates of AFR (0.12 +/- 0.1 ml/h) as compared with hypoxic AdSOD2 and normoxic control rats (0.47 +/- 0.04 ml/h and 0.49 +/- 0.02 ml/h, respectively), with parallel changes in Na,K-ATPase.  相似文献   
992.
993.
A novel cation-exchange resin, Eshmuno™ S, was compared to Fractogel® SO3 (M) and Toyopearl GigaCap S-650M. The stationary phases have different base matrices and carry specific types of polymeric surface modifications. Three monoclonal antibodies (mAbs) were used as model proteins to characterize these chromatographic resins. Results from gradient elutions, stirred batch adsorptions and confocal laser scanning microscopic investigations were used to elucidate binding behavior of mAbs onto Eshmuno™ S and Fractogel® SO3 and the corresponding transport mechanisms on these two resins. The number of charges involved in mAb binding for Eshmuno™ S is lower than for Fractogel® SO3, indicating a slightly weaker electrostatic interaction. Kinetics from batch uptake experiments are compared to kinetic data obtained from confocal laser scanning microscopy images. Both experimental approaches show an accelerated protein adsorption for the novel stationary phase. The influence of pH, salt concentrations and residence times on dynamic binding capacities was determined. A higher dynamic binding capacity for Eshmuno™ S over a wider range of pH values and residence times was found compared to Fractogel® SO3 and Toyopearl GigaCap S-650M. The capture of antibodies from cell culture supernatant, as well as post-protein A eluates, were analyzed with respect to their host cell protein (hcp) removal capabilities. Comparable or even better hcp clearance was observed at much higher protein loading for Eshmuno™ S than Fractogel® SO3 or Toyopearl GigaCap S-650M.Key words: ion-exchange chromatography, dynamic binding capacity, tentacle surface modification, linear gradient elution, hcp removal  相似文献   
994.
995.
Phytochemical investigation of the leaf surface exudate of Dodonaea angustifolia L.f. yielded two new neo-clerodane diterpenes, neo-clerodan-3,13-dien-16,15:18,19-diolide (mkapwanin) and 15-methoxy-neo-clerodan-3,13-dien-16,15:18,19-diolide (15-methoxymkapwanin). In addition, ten known compounds were identified. The structures were determined on the basis of spectroscopic evidence. This additional chemical information could contribute towards solving the taxonomical controversy that exists between Dodonaea angustifolia and Dodonaea viscosa Jacq., which are morphologically similar.  相似文献   
996.
Incubation with protein kinase NII did not result in phosphorylation or inactivation of mouse kidney ornithine decarboxylase. Partially purified ornithine decarboxylase preparations contained a protein kinase activity and stimulated the activity of RNA polymerase I. However, these properties were due to contaminating protein(s) since further purification reduced the kinase activity and removal of the ornithine decarboxylase with a specific antiserum did not abolish the ability to stimulate RNA polymerase I. Antibodies to RNA polymerase I did not interact with ornithine decarboxylase and antibodies to ornithine decarboxylase did not interact with RNA polymerase I. These results indicate that: a) mammalian ornithine decarboxylase activity is not regulated by phosphorylation by protein kinase NII or the contaminating kinase, and b) the ability of impure preparations of ornithine decarboxylase to stimulate RNA polymerase I is due to a contaminating unrelated protein.  相似文献   
997.
Bariatric surgery is currently the most effective treatment of obesity, which has spurred an interest in developing pharmaceutical mimetics. It is thought that the marked body weight‐lowering effects of bariatric surgery involve stimulated secretion of appetite‐regulating gut hormones, including glucagon‐like peptide 1. We here report that intestinal expression of secretin is markedly upregulated in a rat model of Roux‐en‐Y gastric bypass, suggesting an additional role of secretin in the beneficial metabolic effects of Roux‐en‐Y gastric bypass. We therefore developed novel secretin‐based peptide co‐agonists and identified a lead compound, GUB06‐046, that exhibited potent agonism of both the secretin receptor and glucagon‐like peptide 1 receptor. Semi‐acute administration of GUB06‐046 to lean mice significantly decreased cumulative food intake and improved glucose tolerance. Chronic administration of GUB06‐046 to diabetic db/db mice for 8 weeks improved glycemic control, as indicated by a 39% decrease in fasting blood glucose and 1.6% reduction of plasma HbA1c levels. Stereological analysis of db/db mice pancreata revealed a 78% increase in beta‐cell mass after GUB06‐046 treatment, with no impact on exocrine pancreas mass or pancreatic duct epithelial mass. The data demonstrate beneficial effects of GUB06‐046 on appetite regulation, glucose homeostasis, and beta‐cell mass in db/db mice, without proliferative effects on the exocrine pancreas and the pancreatic duct epithelium. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.  相似文献   
998.
999.
对个体而言,不经父母遗传而后天获得的突变称为新生突变,绝大多数癌症都起自新生突变。构建快速精确的变异识别算法将有助于对癌症的研究。然而,针对前期新生突变识别算法准确率不高,且耗时多等问题,本文引入了基于变异位点的先验概率分布模型,运用基于混合泊松分布的期望最大化(EM)算法对新生突变识别算法进行改进与优化,研究了有亲缘关系的新生突变的识别,并在识别精度与运算速度方面与已有算法进行对比。结果表明,基于混合泊松分布的 期望最大化算法在提高运算速度的同时降低了假阳性比率,具有良好的识别效果。  相似文献   
1000.
ABSTRACT

Olivia Gude has a long and distinguished career as both a public artist and an art educator. She is currently the Angela Gregory Paterakis Professor and Chair of Art Education at the School of the Art Institute of Chicago (SAIC), where she works with graduate and undergraduate students to prepare for working as artist educators in school and community settings. Her scholarly work includes a number of articles and book chapters about art education and community art. Prof. Gude has worked as a community public artist for many years and has created over 30 large-scale mural and mosaic projects, working with intergenerational groups, teens, elders, and children. I interviewed Prof. Gude at the SAIC building in downtown Chicago to discuss how her school, university, and community art engagement as well as her work with the National Coalition for Core Arts Standards, might offer suggestions for transforming arts education for the twenty-first century and provide authentic connections between school and community. Prof. Gude discusses important enduring understandings and big ideas from the new Visual Arts National Core Arts Standards, the Spiral Workshop youth art and research project she created while at University of Illinois at Chicago, and how her experience as a community artist informs her work with students in classroom settings.  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