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   1152篇
  免费   60篇
  2023年   3篇
  2022年   8篇
  2021年   28篇
  2020年   18篇
  2019年   10篇
  2018年   16篇
  2017年   18篇
  2016年   30篇
  2015年   61篇
  2014年   65篇
  2013年   80篇
  2012年   87篇
  2011年   84篇
  2010年   48篇
  2009年   55篇
  2008年   51篇
  2007年   64篇
  2006年   46篇
  2005年   50篇
  2004年   41篇
  2003年   53篇
  2002年   40篇
  2001年   37篇
  2000年   31篇
  1999年   36篇
  1998年   11篇
  1997年   2篇
  1996年   7篇
  1995年   4篇
  1994年   7篇
  1993年   6篇
  1992年   8篇
  1991年   9篇
  1990年   9篇
  1989年   15篇
  1988年   2篇
  1987年   6篇
  1986年   5篇
  1985年   2篇
  1984年   2篇
  1982年   2篇
  1981年   7篇
  1980年   2篇
  1979年   13篇
  1978年   11篇
  1977年   6篇
  1975年   3篇
  1974年   6篇
  1914年   1篇
  1891年   1篇
排序方式: 共有1212条查询结果,搜索用时 625 毫秒
31.
EGFR and cMET cross-talk is involved in breast cancer (BC) progression and resistance to different targeted therapies, however little is known about the co-expression patterns of EGFR and cMET or its prognostic significance in BC. Protein levels of EGFR, cMET and their phosphorylated proteins were measured in 825 BC samples using reverse phase protein array (RPPA). Given unimodal distribution of proteins, the median was selected as a cut-off after sensitivity analyses. Kaplan-Meier survival curves were used to estimate relapse-free (RFS) and overall survival (OS). Cox-proportional hazards models were utilized to determine associations between EGFR and cMET with outcomes. Mean age was 58 years with 457 (55%) hormone receptor (HR) positive, 211 (26%) triple-negative (TN) and 148 (18%) HER2 positive tumors (HER2+). HER2+ was associated with higher EGFR expression and phosphorylation, compared to HR and TN (p<0.05). High EGFR expression was associated with higher phosphorylated-cMET (p-cMET) but not cMET (ANOVA p-cMET p < 0.001; cMET p = 0.34). The same association was found with high phosphorylated-EGFR (p-EGFR) group at Tyr992 and Tyr1068 (both p < 0.001). High expressions in either of two p-EGFRs were linked with higher cMET as well (all p<0.001). For the TN subtype, high expression in EGFR and p-EGFR at Tyr992 but not at Tyr1068 was associated with higher p-cMET (p<0.00, p = 0.012, p = 0.4 respectively). Only high expression in p-EGFR at Tyr992 was linked with higher expression of cMET (p = 0.02). In contrast, among HER2 subtype, high expression in p-EGFR at Tyr1068 but not at Tyr992 was associated with higher cMET and p-cMET (cMET p = 0.023;p-cMET p<0.001). Four subgroups of patients defined by dichotomized EGFR/p-EGFR and cMET/p-cMET level demonstrated no significant differences in survival. In multivariate analyses, neither cMET nor EGFR expression/activation was found to be an independent prognostic factor in survival outcome.  相似文献   
32.
Aluminium oxide (Al2O3) has widely been used for catalysts, insulators, and composite materials for diverse applications. Herein, we demonstrated if γ‐Al2O3 was useful as a luminescence support material for europium (Eu) (III) activator ion. The hydrothermal method and post‐thermal treatment at 800°C were employed to synthesize Eu(III)‐doped γ‐Al2O3 nanofibre structures. Luminescence characteristics of Eu(III) ions in Al2O3 matrix were fully understood by taking 2D and 3D‐photoluminescence imaging profiles. Various sharp emissions between 580 to 720 nm were assigned to the 5D07FJ (J = 0, 1, 2, 3, 4) transitions of Eu(III) activators. On the basis of X‐ray diffraction crystallography, Auger elemental mapping and the asymmetry ratio, Eu(III) ions were found to be well doped into the γ‐Al2O3 matrix at a low (1 mol%) doping level. A broad emission at 460 nm was substantially increased upon higher (2 mol%) Eu(III) doping due to defect creation. The first 3D photoluminescence imaging profiles highlight detailed understanding of emission characteristics of Eu(III) ions in Al oxide‐based phosphor materials and their potential applications.  相似文献   
33.
This study aims at examining the reduction of indoor air contaminants by plants placed in an indoor space. Field measurements were performed using Aglaonema brevispathum, Pachira aquatica, and Ficus benjamiana, which were verified as air-purifying plants by NASA. Three conditions for the amount of plants and positions were used in two separate rooms whose dimensions are identical. The concentration of Volatile Organic Compounds (VOCs) was monitored three hours after the plants were placed and three days after the plants were placed. The variations of concentration of Benzene, Toluene, Etylbenzene, and Xylene (BTEX), as well as Formaldehyde, which are all known as the major elements of Volatile Organic Compounds were monitored. The amount of reduction in concentration of Toluene and Formaldehyde was monitored 3 hours and 3 days after the plants were placed in the space. The reduction in the concentration of Benzene, Toluene, Etylbenzene, Xylene, and Formaldehyde was significantly greater when plants were present. When plants were placed near a window, the reduction of concentration was greater. The more plants were used, the more a reduction of indoor air contaminants occurred. The effect of reducing the concentration of air contaminants increased when the amount of plants increased, and when the plants were placed in sunny area. The concentration of Toluene was reduced by 45.6 microg/m(3) when 10% of the model space was occupied by Aglaonema brevispathum.  相似文献   
34.
35.
Sohn JH  Kim LS  Chae SW  Shin HS 《Acta cytologica》2001,45(5):723-729
OBJECTIVE: To report the cytologic findings of mucocelelike tumor and mucinous carcinoma. STUDY DESIGN: All mucinous neoplasms diagnosed by fine needle aspiration and confirmed by histologic examination were reviewed to detect the cytologic findings helpful for the differentiation. The cytologic findings were correlated with the histologic findings. RESULTS: Cytologically, mucinous carcinomas were highly cellular and showed many single epithelial cells and variably formed epithelial cell clusters in abundant extracellular mucin. Malignant cells exhibited round, atypical nuclei; granular chromatin; and small nucleoli. Mucocele like tumor showed low cellularity with scanty, monolayered, small sheets of epithelial cells and abundant, extracellular mucin. Myoepithelial cells were present within the epithelial cell sheets. Tumor cells were usually small, with uniform, round nuclei; fine chromatin; and absence of nucleoli. CONCLUSION: Cytologic findings of mucocelelike tumor and mucinous carcinoma were different in cellularity, shape of cell clusters and nuclear features, although mucocelelike tumors having a carcinoma component were similar to mucinous carcinoma. Awareness of the cytologic findings of breast mucinous neoplasms is important to make a specific diagnosis.  相似文献   
36.
Members of the transforming growth factor-beta (TGF-beta) superfamily signal through heteromeric type I and type II serine/threonine kinase receptors. Transgenic mice that overexpress a dominant-negative mutation of the TGF-beta type II receptor (DNIIR) under the control of a metallothionein-derived promoter (MT-DNIIR) were used to determine the role of endogenous TGF-betas in the developing mammary gland. The expression of the dominant-negative receptor was induced with zinc and was primarily localized to the stroma underlying the ductal epithelium in the mammary glands of virgin transgenic mice from two separate mouse lines. In MT-DNIIR virgin females treated with zinc, there was an increase in lateral branching of the ductal epithelium. We tested the hypothesis that expression of the dominant-negative receptor may alter expression of genes that are expressed in the stroma and regulated by TGF-betas, potentially resulting in the increased lateral branching seen in the MT-DNIIR mammary glands. The expression of hepatocyte growth factor mRNA was increased in mammary glands from transgenic animals relative to the wild-type controls, suggesting that this factor may play a role in TGF-beta-mediated regulation of lateral branching. Loss of responsiveness to TGF-betas in the mammary stroma resulted in increased branching in mammary epithelium, suggesting that TGF-betas play an important role in the stromal-epithelial interactions required for branching morphogenesis.  相似文献   
37.
A suitable and economical animal model of ovarian hormone deficiency can greatly enhance the understanding of postmenopausal-elevated risk of coronary heart disease. The male Golden Syrian hamster is a well-established small animal model of hypercholesterolemia, but the effect of ovariectomy on lipid profile in the female hamster is unclear. The objective of this study was to determine whether ovariectomized hamsters develop hypercholesterolemia and experience changes in body fat distribution consistent with changes observed in postmenopausal women. Twenty-two 90-day-old female Golden Syrian hamsters were divided into two groups and were either ovariectomized or sham-operated and given free access to a standard cholesterol-free laboratory diet for 65 days. Ovariectomized hamsters had significantly (P < 0.05) elevated serum total cholesterol concentrations (16.6%) as well as abdominal fat mass (56%; P< 0.01) despite equal food intake compared with the sham-operated group. In contrast, the mean intestinal weight and in vivo rate of sterol biosynthesis were significantly (P < 0.002 and P = 0.01, respectively) lower in the ovariectomized compared with the sham-operated group. In vivo rates of hepatic sterol biosynthesis were directionally lower (P = 0.1) in the ovariectomized group. No significant differences were observed in final body weight, serum triglycerides, or liver total cholesterol and lipids between the two groups. In conclusion, ovariectomized hamsters undergo changes in serum cholesterol and fat distribution similar to those experienced by postmenopausal women, and thus may serve as an appropriate model for postmenopausal hypercholesterolemia.  相似文献   
38.
Song HK  Sohn SH  Suh SW 《The EMBO journal》1999,18(5):1104-1113
Bacteriophage T4 deoxycytidylate hydroxymethylase (EC 2.1.2.8), a homodimer of 246-residue subunits, catalyzes hydroxymethylation of the cytosine base in deoxycytidylate (dCMP) to produce 5-hydroxymethyl-dCMP. It forms part of a phage DNA protection system and appears to function in vivo as a component of a multienzyme complex called deoxyribonucleoside triphosphate (dNTP) synthetase. We have determined its crystal structure in the presence of the substrate dCMP at 1.6 A resolution. The structure reveals a subunit fold and a dimerization pattern in common with thymidylate synthases, despite low (approximately 20%) sequence identity. Among the residues that form the dCMP binding site, those interacting with the sugar and phosphate are arranged in a configuration similar to the deoxyuridylate binding site of thymidylate synthases. However, the residues interacting directly or indirectly with the cytosine base show a more divergent structure and the presumed folate cofactor binding site is more open. Our structure reveals a water molecule properly positioned near C-6 of cytosine to add to the C-7 methylene intermediate during the last step of hydroxymethylation. On the basis of sequence comparison and crystal packing analysis, a hypothetical model for the interaction between T4 deoxycytidylate hydroxymethylase and T4 thymidylate synthase in the dNTP-synthesizing complex has been built.  相似文献   
39.
Bacillus thuringiensis 656-3, isolated from a soil sample collected at mushroom houses, showed high toxicity to mushroom flies, Lycoriella mali and Coboldia fuscipes. B. thuringiensis 656-3 produced bipyramidal inclusions and reacted with the H antiserum of B. thuringiensis subsp. morrisoni (H8a8b). The plasmid and protein profiles of B. thuringiensis 656-3 were similar to those of its reference strain, subsp. morrisoni PG-14. However, PCR analysis using cry gene primers showed that B. thuringiensis 656-3, unlike its reference strain, had cry4A, cry4B, cry10A, cry11A, and cry1Ac genes, suggesting that B. thuringiensis 656-3 was a unique strain with respect to gene type. In addition, B. thuringiensis 656-3 showed a high level of toxicity against mushroom flies, L. mali and C. fuscipes.  相似文献   
40.
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