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   9344篇
  免费   706篇
  国内免费   799篇
  10849篇
  2024年   18篇
  2023年   130篇
  2022年   302篇
  2021年   512篇
  2020年   314篇
  2019年   447篇
  2018年   408篇
  2017年   258篇
  2016年   434篇
  2015年   609篇
  2014年   711篇
  2013年   806篇
  2012年   900篇
  2011年   780篇
  2010年   445篇
  2009年   441篇
  2008年   465篇
  2007年   410篇
  2006年   367篇
  2005年   266篇
  2004年   253篇
  2003年   204篇
  2002年   154篇
  2001年   137篇
  2000年   123篇
  1999年   105篇
  1998年   100篇
  1997年   93篇
  1996年   84篇
  1995年   73篇
  1994年   66篇
  1993年   47篇
  1992年   80篇
  1991年   47篇
  1990年   35篇
  1989年   37篇
  1988年   22篇
  1987年   25篇
  1986年   25篇
  1985年   24篇
  1984年   11篇
  1983年   9篇
  1982年   10篇
  1981年   6篇
  1980年   5篇
  1979年   9篇
  1976年   4篇
  1973年   5篇
  1971年   4篇
  1968年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Yin W  Jiang Y  Shen Z  Shao Z  Lu J 《PloS one》2011,6(6):e21030

Background

Adjuvant trastuzumab therapy has yielded conflicting results for overall survival, concerns about central nervous system (CNS) metastasis, and questions about optimal schedule. Therefore, we carried out a meta-analysis to assess the benefits of concurrent or sequential trastuzumab with adjuvant chemotherapy for early breast cancer patients with HER2-positive tumors.

Methods

Computerized and manual searches were performed to identify randomized clinical trials comparing adjuvant chemotherapy with or without trastuzumab in HER2-positive early breast cancer patients. Odds ratios were used to estimate the association between the addition of trastuzumab to adjuvant chemotherapy and various survival outcomes. The fixed-effects or random-effects model was used to combine data.

Findings

With six eligible studies identified, this analysis demonstrated that patients with HER2-positive breast cancer derived benefit in disease-free survival, overall survival, locoregional recurrence and distant recurrence (all P<0.001) from the addition of trastuzumab to adjuvant chemotherapy, whereas trastuzumab did worse in CNS recurrence as compared to the control group (P = 0.018). Furthermore, concomitant use of trastuzumab significantly lowered the hazard of death (P<0.001) but bore a higher incidence of CNS recurrence (P = 0.010), while statistical significance failed to be discerned for either overall survival (P = 0.069) or CNS metastasis (P = 0.374) between the sequential and observation arms.

Conclusion

This analysis verifies the efficacy of trastuzumab in the adjuvant setting. Additionally, our findings indirectly corroborate the superiority of concurrent trastuzumab to sequential use and also illuminate that prolonged survival is the possible reason for the higher incidence of CNS with trastuzumab versus observation.  相似文献   
992.
The cell wall of the human pathogen Candida glabrata governs initial host-pathogen interactions that underlie the establishment of fungal infections. With the aim of identifying species-specific features that may directly relate to its virulence, we have investigated the cell wall of C. glabrata using a multidisciplinary approach that combines microscopy imaging, biochemical studies, bioinformatics, and tandem mass spectrometry. Electron microscopy revealed a bilayered wall structure in which the outer layer is packed with mannoproteins. Biochemical studies showed that C. glabrata walls incorporate 50% more protein than Saccharomyces cerevisiae walls and, consistent with this, have a higher mannose/glucose ratio. Evidence is presented that C. glabrata walls contain glycosylphosphatidylinositol (GPI) proteins, covalently bound to the wall 1,6-β-glucan, as well as proteins linked through a mild-alkali-sensitive linkage to 1,3-β-glucan. A comprehensive genome-wide in silico inspection showed that in comparison to other fungi, C. glabrata contains an exceptionally large number, 67, of genes encoding adhesin-like GPI proteins. Phylogenetically these adhesin-like proteins form different clusters, one of which is the lectin-like EPA family. Mass spectrometric analysis identified 23 cell wall proteins, including 4 novel adhesin-like proteins, Awp1/2/3/4, and Epa6, which is involved in adherence to human epithelia and biofilm formation. Importantly, the presence of adhesin-like proteins in the wall depended on the growth stage and on the genetic background used, and this was reflected in alterations in adhesion capacity and cell surface hydrophobicity. We propose that the large repertoire of adhesin(-like) genes of C. glabrata contributes to its adaptability and virulence.  相似文献   
993.
低棉酚棉籽为高蛋白含油的植物资源,适宜于水溶法制备油及蛋白粉,出油率一般可达95%。  相似文献   
994.
悬钩子属种质的评价   总被引:30,自引:0,他引:30  
在进行了7省悬钩子资源调查的基础上,在南京建立了悬钩子属田间基因库。3年来对田间基因库内保存并开花结果的30个种进行了开花结果性状的记栽和评价。内容包括果实特征,糖、酸、维生素类、氨基酸、矿质元素含量分析,染色体计数等。分析了种间和种内多样性物存在及在良种选育中利用的可能性。  相似文献   
995.
996.
997.

Introduction

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is characterised by the autoinflammation and necrosis of blood vessel walls. The renal involvement is commonly characterised by a pauci-immune crescentic glomerulonephritis (PiCGN) with a very rapid decline in renal function. Cathelicidin LL37, an endogenous antimicrobial peptide, has recently been implicated in the pathogenesis of autoimmune diseases. To assess whether serum LL37 reflects renal crescentic formation, we measured the serum levels of LL37 in AAV patients with and without crescentic glomerulonephritis (crescentic GN) as compared to healthy controls (HCs). We also analysed the correlation of the serum levels of LL37 and interferon-α (IFN-α) with the clinical characteristics of the patients.

Methods

The study population consisted of 85 AAV patients and 51 HCs. In 40 ANCA-positive patients, a parallel analysis was performed, including the assessment of LL37 and IFN-α levels in the serum and renal biopsies. Of those studied, 15 AAV patients had biopsy-proven crescentic GN, and 25 AAV patients lacked crescent formation. The serum levels of cathelicidin LL37 and IFN-α were both measured by ELISA, and the clinical and serological parameters were assessed according to routine procedures. Immunofluorescence staining was performed on frozen sections of kidney needle biopsies from AAV patients with crescentic GN.

Results

The serum levels of LL37 and IFN-α were significantly increased in AAV patients with crescentic GN compared to AAV patients without crescentic formation and HCs, and patients with high LL37 and IFN-α levels were more likely to be in the crescentic GN group. The LL37 levels were positively correlated with the IFN-α levels, and both LL37 and IFN-α levels showed a positive correlation with serum creatinine and no correlation with complement C3. The renal tissue of crescentic GN patients showed expression of LL37 and IFN-α at the Bowman’s capsule and extracellular sites, suggesting the active release of LL37 and IFN-α.

Conclusions

Significantly higher levels of LL-37 and IFN-α were observed in AAV patients, particularly those with crescentic formation, and LL37 and IFN-α were expressed in the renal tissue of patients with crescentic GN. These data suggest that serum levels of LL37 and IFN-α may reflect both local renal inflammation and systemic inflammation.  相似文献   
998.
This report investigated mechanisms responsible for failed Schwann cell myelination in mice that overexpress P(0) (P(0)(tg)), the major structural protein of PNS myelin. Quantitative ultrastructural immunocytochemistry established that P(0) protein was mistargeted to abaxonal, periaxonal, and mesaxon membranes in P(0)(tg) Schwann cells with arrested myelination. The extracellular leaflets of P(0)-containing mesaxon membranes were closely apposed with periodicities of compact myelin. The myelin-associated glycoprotein was appropriately sorted in the Golgi apparatus and targeted to periaxonal membranes. In adult mice, occasional Schwann cells myelinated axons possibly with the aid of endocytic removal of mistargeted P(0). These results indicate that P(0) gene multiplication causes P(0) mistargeting to mesaxon membranes, and through obligate P(0) homophilic adhesion, renders these dynamic membranes inert and halts myelination.  相似文献   
999.
为了探讨雌激素作用于神经系统的机理,采用硫酸镍铵增强显色的免疫组化SP法研究了新的雌激素受体(ER-β)在成年雌雄大鼠脑内的分布。研究证实ER-β免疫阳性物质主要位于神经元的细胞核内,但在个别脑区也可在胞浆甚至突起内检测到。最强的ER-β免疫阳性信号见于前嗅核、大脑皮质、小脑浦肯野细胞、斜角带垂直部、蓝斑和三叉神经运动核等部位;中等强度的染色见于隔内侧核、杏仁外侧核、黑质、中央灰质等部位;较弱的阳性反应见于下丘脑与杏仁复合体的部分核团。在一些部位还存在表达水平甚至细胞内定位模式的性别差异,如前庭上核内的表达只见于雌性;雄性大鼠三叉神经运动核内ER-β蛋白主要表达于胞浆内,细胞核为阴性;而在雌性大鼠该部位ER-β蛋白主要位于细胞核等。以上结果表明ER-β蛋白在大鼠脑内分布广泛并具有一定的性别差异,在与学习记忆有关的脑区如大脑皮质和基底前脑内有很高的表达,提示在脑组织内雌激素可能通过ER-β这一新的信号途径发挥多种重要的调控作用,如学习记忆等。  相似文献   
1000.
保护性耕作(conservationtillage)能够减少水土流失、提高耕地产量,是一类具有生态保护意义的持续性农业耕作形式。2002年至2004年在定西旱地农业地区进行了保护性耕作条件下旱地农田春小麦豌豆双序列轮作土壤水分动态及产量效应的试验研究,结果表明:保护性耕作能够显著改善0~200cm土层土壤贮水量及含水量,随着降水量的增多土壤对降水的保蓄能力增强。在降水较少年份免耕秸秆覆盖的这种作用表现突出,而在降水充沛的年份免耕地膜覆盖则更具优势。耕层土壤水分因受降水等因素的影响而变化剧烈,耕层以下土壤水分变幅相对较小。播种期、五叶期及收获期土壤具有较高含水量,而开花期土壤含水量则较低。在两种轮作体系中,播种期春小麦和豌豆免耕秸秆覆盖处理0~50cm土层含水量分别较常规耕作增加28%、26%和11%、23%,降水生产效率较常规耕作提高了17.79%~26.81%。在春小麦豌豆轮作体系中免耕秸秆覆盖处理的作物产量(春小麦 豌豆)及水分利用效率分别为3420kghm2和8.11kg(hm2·mm),较常规耕作分别提高26.81%和25.39%。  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