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   1756篇
  免费   154篇
  1910篇
  2024年   2篇
  2023年   6篇
  2022年   14篇
  2021年   26篇
  2020年   18篇
  2019年   19篇
  2018年   29篇
  2017年   28篇
  2016年   34篇
  2015年   84篇
  2014年   89篇
  2013年   89篇
  2012年   106篇
  2011年   96篇
  2010年   73篇
  2009年   72篇
  2008年   106篇
  2007年   104篇
  2006年   111篇
  2005年   110篇
  2004年   95篇
  2003年   94篇
  2002年   90篇
  2001年   80篇
  2000年   71篇
  1999年   60篇
  1998年   18篇
  1997年   15篇
  1996年   14篇
  1995年   13篇
  1994年   13篇
  1993年   9篇
  1992年   21篇
  1991年   13篇
  1990年   15篇
  1989年   11篇
  1988年   7篇
  1987年   7篇
  1986年   9篇
  1984年   5篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1979年   2篇
  1978年   2篇
  1977年   4篇
  1975年   3篇
  1972年   4篇
  1969年   4篇
  1963年   1篇
排序方式: 共有1910条查询结果,搜索用时 15 毫秒
101.
Stereopsis or depth perception is an awareness of the distances of objects from the observer, and binocular disparity is a necessary component of recognizing objects through stereopsis. In the past studies, patients with neurodegenerative disease (Alzheimer dementia, AD; Parkinson’s disease IPD) have problems of stereopsis but they did not have actual stimulation of stereopsis. Therefore in this study, we used a 3-dimensional (3D) movie on 3D television (TV) for actual stereopsis stimulation. We propose research through analyzing differences between the three groups (AD, IPD, and Controls), and identified relations between the results from the Titmus Stereo Fly Test, and the 3D TV test. The study also looked into factors that affect the 3D TV test. Before allowing the patients to watch TV, we examined Titmus stereo Fly Test and cognitive test. We used the 3D version of a movie, of 17 minutes 1 second duration, and carried out a questionnaire about stereopsis. The scores of the stereopsis questionnaire were decreased in AD patients, compared with in IPD and controls, although they did not have any difference of Titmus Stereo Fly Test scores. In IPD patients, cognitive function (Montreal cognitive assessment, MoCA) scores were correlated with the scores of the stereopsis questionnaire. We could conclude that Titmus fly test could not distinguish between the three groups and cognitive dysfunction contributes to actual stereopsis perception in IPD patients. Therefore the 3D TV test of AD and IPD patients was more effective than Titmus fly test.  相似文献   
102.
Hydroxy fatty acids (HFAs), originally obtained in small amounts from plant systems, are good examples of structurally modified lipids, and they render special properties such as higher viscosity and reactivity compared to normal fatty acids. Based on these properties, HFAs possess high industrial potential in a wide range of applications. Recently, various microbial strains were tested for the production of HFAs from different unsaturated fatty acids since HFA production is limited to plant systems. Among the microbial strains tested, Pseudomonas aeruginosa PR3 has been well studied for the production of 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) from oleic acid. Previously, we reported that strain PR3 could utilize triolein instead of oleic acid as a substrate for the production of DOD (Appl. Microbiol. Biotechnol. 2007, 74: 301–306). In this study, we focused on utilization of vegetable oil as a substrate for DOD production by PR3. Consequently, strain PR3 efficiently utilized high oleic safflower oil as a substrate for DOD production. Optimal initial medium pH and incubation time were pH 8.0 and 72 h, respectively. Optimal carbon and nitrogen sources were fructose and glutamine, respectively. Results from this study demonstrate that normal vegetable oils could be used as efficient substrates for the production of value-added HFAs by microbial bioconversion.  相似文献   
103.
Based on the observed anticancer activity of chalcones and retinoids, a novel class of retinoid-chalcone hybrids was designed and synthesized. As part of our ongoing studies to discover natural product based anticancer compounds, the retinoid-chalcone hybrids were tested against the colon cancer cell line HT-29. Retinoid like moiety was introduced through Friedel-Crafts alkylation of toluene. Among the synthesized compounds, the cyano derivative (E)-3-(3-oxo-3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)prop-1-enyl)benzonitrile 8 showed submicromolar inhibitory activity with an IC(50) of 0.66 μM.  相似文献   
104.
A series of 3-substituted-benzofuran-2-carboxylic esters was synthesized and evaluated for biological activity as ischemic cell death inhibitors in H9c2 cells and rat primary cardiac myocytes under conditions of oxygen and glucose deprivation. The introduction of a sulfur atom at the three-position substituent of the benzofuran ring markedly improved ischemic cell death inhibitory potency. In particular, 3-[2-(4-nitro-phenylsulfanyl)-acetylamino]-benzofuran-2-carboxylic acid ester (10) (EC(50)=0.532 μM, cell death=6.18%) and 4-chloro-3-[3-(pyridin-2-ylsulfanyl)-propionylamino]-benzofuran-2-carboxylic ester (18) (EC(50)=0.557 μM, cell death=7.02%) were shown to be the most potent in this series of benzofuran analogs.  相似文献   
105.
In searching for new agents with a depigmenting effect, we synthesized a derivative of resveratrol, 5-(6-hydroxy-2-naphthyl)-1,2,3-benzenetriol (5HNB) with a potent tyrosinase inhibitory activity. 5HNB inhibited mushroom tyrosinase with an IC50 value of 2.95 μM, which is more potent than the well-known anti-tyrosinase activity of kojic acid (IC50 = 38.24). The results of the enzymatic inhibition kinetics by Lineweaver–Burk analysis indicated 5HNB inhibits tyrosinase non-competitively when l-tyrosine was used as the substrate. Based on the strong inhibitory action of 5HNB, it is expected that 5HNB can suppress melanin production in which tyrosinase plays the essential role. Our expectation was confirmed by the experimentations with B16 melanoma cells in which 5HNB inhibited melanin production. We propose that 5HNB might have skin-whitening effects as well as therapeutic potential for treating skin pigmentation disorders.  相似文献   
106.
107.
Adipogenesis is a complex process that is accompanied by a number of molecular events. In this study, a proteomic approach was adopted to identify secretory factors associated with adipogenesis. A label‐free shotgun proteomic strategy was implemented to analyze proteins secreted by human adipose stromal vascular fraction cells and differentiated adipocytes. A total of 474 proteins were finally identified and classified according to quantitative changes and statistical significances. Briefly, 177 proteins were significantly upregulated during adipogenesis (Class I), whereas 60 proteins were significantly downregulated (Class II). Changes in the expressions of several proteins were confirmed by quantitative RT‐PCR and immunoblotting. One obvious finding based on proteomic data was that the amounts of several extracellular modulators of Wnt and transforming growth factor‐β (TGF‐β) signaling changed during adipogenesis. The expressions of secreted frizzled‐related proteins, dickkopf‐related proteins, and latent TGF‐β‐binding proteins were found to be altered during adipogenesis, which suggests that they participate in the fine regulation of Wnt and TGF‐β signaling. This study provides useful tools and important clues regarding the roles of secretory factors during adipogenic differentiation, and provides information related to obesity and obesity‐related metabolic diseases.  相似文献   
108.
A family of calcium-dependent protein kinases (CDPKs) is a unique enzyme which plays crucial roles in intracellular calcium signaling in plants, algae, and protozoa. CDPKs of malaria parasites are known to be key regulators for stage-specific cellular responses to calcium, a widespread secondary messenger that controls the progression of the parasite. In our study, we identified a gene encoding Plasmodium vivax CDPK4 (PvCDPK4) and characterized its molecular property and cellular localization. PvCDPK4 was a typical CDPK which had well-conserved N-terminal kinase domain and C-terminal calmodulin-like structure with 4 EF hand motifs for calcium-binding. The recombinant protein of EF hand domain of PvCDPK4 was expressed in E. coli and a 34 kDa product was obtained. Immunofluorescence assay by confocal laser microscopy revealed that the protein was expressed at the mature schizont of P. vivax. The expression of PvCDPK4-EF in schizont suggests that it may participate in the proliferation or egress process in the life cycle of this parasite.  相似文献   
109.
AimsThis study examined the effects of oxidized low-density lipoprotein (LDL) and its major lipid constituent lysophosphatidylcholine (LPC) on nonselective cation (NSC) current and its inhibitory contribution to LPC-induced cytotoxicity in cultured human umbilical endothelial cells (HUVECs).Main methodsPatch-clamp technique and the resazurin-based cell viability assay were used.Key findingsIn voltage-clamped cells, oxidized LDL or LPC slowly activated NSC current. NSC current was also activated by loading cells with Ca2+ solution buffered at various concentrations using a patch pipette or by applying the sarcoplasmic reticulum Ca2+ pump blocker 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), the metabolic inhibitor CN? or the hydroperoxide donor tert-butyl hydroperoxide (TBHP). On the contrary, when intracellular Ca2+ was strongly buffered with 12 mM BAPTA or cells were loaded with superoxide dismutase using a patch pipette, LPC or BHQ did not activate NSC current. Furthermore, NSC current activated by LPC, TBHP or CN? was inhibited by the antioxidant tempol or extracellular Ca2+ depletion and NSC current activated by intracellular Ca2+ was further augmented by oxidized LDL or LPC. LPC or oxidized LDL released Ca2+ from intracellular stores and further enhanced store-operated Ca2+ entry. LPC-induced cytotoxicity was augmented by inhibiting Ca2+ influx and NO synthesis.SignificanceOxidized LDL or its main component LPC activated Ca2+-permeable NSC current via releasing Ca2+ from intracellular stores and producing ROS and thereby increased Ca2+ influx. Ca2+ influx through NSC channel might protect endothelial cells by producing NO.  相似文献   
110.
Activities of phospholipase D (PLD) in diverse subcellular organelles have been identified but the details of regulatory mechanisms in such locations are unknown. Protein kinase C (PKC) is a major regulator of PLD. Serine 2, threonine 147, and serine 561 residues of phospholipase D1 (PLD1) were determined as sites of phosphorylation by PKC (Kim, Y., Han, J. M., Park, J. B., Lee, S. D., Oh, Y. S., Chung, C., Lee, T. G., Kim, J. H., Park, S. K., Yoo, J. S., Suh, P. G., Ryu, S. H. (1999) Biochemistry 38, 10344-10351). In our present study, a triple mutation of these phosphorylation sites diminished markedly phorbol 12-myristate 13-acetate (PMA)-induced PLD1 activity in COS-7 cells. We looked at the location of the PLD1 phosphorylation by PKC by observing PMA induced band shifts and by use of anti-phospho-PLD1 monoclonal antibody. The shifted PMA-induced proteins and the immunoreactivity of the anti-phospho-PLD1 antibody were mainly found in the caveolin-enriched membrane (CEM) fraction. Depletion of cellular cholesterol led to a loss of this compartmentalization of phosphorylated PLD1 in the CEM. Replacement of the cellular cholesterol led to the restoration of phosphorylated PLD1 in the CEM. Immunocytochemical studies of COS-7 cells revealed that PLD1 was localized in the plasma membrane as well as in the vesicular structures in the cytoplasm, but the phosphorylation of PLD1 occurred only in the plasma membrane. Our results, therefore, show that phosphorylation, and thereby activation, of PLD1 by PKC occurs in the caveolin and cholesterol-enriched low density domain of the plasma membrane in COS-7 cells.  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