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   4605篇
  免费   475篇
  国内免费   446篇
  5526篇
  2024年   10篇
  2023年   53篇
  2022年   125篇
  2021年   192篇
  2020年   156篇
  2019年   229篇
  2018年   184篇
  2017年   172篇
  2016年   191篇
  2015年   284篇
  2014年   299篇
  2013年   336篇
  2012年   369篇
  2011年   335篇
  2010年   237篇
  2009年   205篇
  2008年   227篇
  2007年   209篇
  2006年   178篇
  2005年   159篇
  2004年   172篇
  2003年   199篇
  2002年   227篇
  2001年   142篇
  2000年   116篇
  1999年   93篇
  1998年   84篇
  1997年   59篇
  1996年   39篇
  1995年   32篇
  1994年   22篇
  1993年   16篇
  1992年   14篇
  1991年   26篇
  1990年   20篇
  1989年   23篇
  1988年   9篇
  1987年   11篇
  1986年   12篇
  1985年   9篇
  1984年   9篇
  1983年   7篇
  1982年   5篇
  1981年   3篇
  1979年   6篇
  1973年   4篇
  1966年   2篇
  1959年   1篇
  1948年   1篇
  1947年   1篇
排序方式: 共有5526条查询结果,搜索用时 15 毫秒
31.

Background

The Supreme? laryngeal mask airway (SLMA) is a single-use LMA with double lumen design that allows separation of the respiratory and the alimentary tract, hence potentially reducing the gastric volume and risk of aspiration. The purpose of this prospective cohort study is to evaluate the the role of the SLMA as an airway technique for women undergoing category 2 and 3 Cesarean delivery under general anesthesia.

Methods

We recruited 584 parturients who underwent category 2 or 3 Cesarean delivery under general anesthesia, in which 193 parturients underwent category 2 and 391 parturients underwent category 3 Cesarean delivery. The primary outcome was insertion success rate at 1st attempt in SLMA insertion. The secondary outcomes included anaesthetic, obstetric outcomes and maternal side effects associated with airway device.

Results

The 1st attempt insertion success rate was 98.3%, while the overall insertion success rate was 100%. The mean (Standard deviation) time to effective ventilation was 15.6 (4.4) seconds. Orogastric tube insertion was successful at the 1st attempt in all parturients. There was no clinical evidence of aspiration or regurgitation. No episodes of hypoxemia, laryngospasm or bronchospasm were observed intra-operatively. The incidence of complications was low and with good maternal satisfaction reported.

Conclusions

The SLMA could be an alternative effective airway in category 2 and 3 parturients emergency Cesarean Delivery under general anesthesia in a carefully-selected obstetric population.

Trial registration

Clinical Trials Registration: Clinicaltrials.gov Registration NCT02026882. Registered on December 31, 2013.
  相似文献   
32.
33.
蛋白酪氨酸磷酸酶SHP-2在乳腺癌细胞移动及粘附中的作用   总被引:2,自引:0,他引:2  
探讨蛋白酪氨酸磷酸酶SHP 2在乳腺癌细胞MCF 7的移动及粘附中的作用 .利用基因重组技术分别将野生型SHP 2与突变型SHP 2与绿色荧光蛋白GFP的基因片段构成重组质粒 (SHP 2 GFP、SHP 2C >S GFP) .脂质体转染法分别转入MCF 7中 ,表达成功后筛选并建立SHP 2 GFP和SHP 2C >S GFP细胞株 .荧光显微镜观察细胞移动情况 ,免疫印迹法检测粘附分子E 钙粘蛋白和金属蛋白酶MMP 1及MMP 9的表达 .实验后建立SHP 2 GFP及SHP 2C >S GFP细胞株 ,同时观察到SHP 2C >S GFP细胞的形态发生明显改变 :从梭形状态变成圆形状态 .荧光显微镜发现 ,MCF 7细胞和SHP 2 GFP、SHP 2C >S GFP转染的细胞在 3h、6h、9h的移动情况分别是MCF 7为 10 %、2 3%、5 4% ,SHP 2 GFP为 15 %、4 9%、98% ,SHP 2C >S GFP为 4 %、11%、30 % .免疫印迹结果表明 ,SHP 2C >S GFP细胞的E 钙粘蛋白表达比SHP 2 GFP细胞明显升高 (P <0 0 5 ) .MMP 1及MMP 9的表达量在SHP 2 GFP细胞中有所增强 (P <0 0 5 ) .实验表明 ,SHP 2可能通过调节粘附分子和基质金属磷酸酶而在细胞移动、粘附中发挥重要作用  相似文献   
34.
Hybrid cells generated by fusing dendritic cells with tumor cells (DC-TC) are currently being evaluated as cancer vaccines in preclinical models and human immunization trials. In this study, we evaluated the production of human DC-TC hybrids using an electrofusion protocol previously defined for murine cells. Human DCs were electrically fused with allogeneic melanoma cells (888mel) and were subsequently analyzed for coexpression of unique DC and TC markers using FACS and fluorescence microscopy. Dually fluorescent cells were clearly observed using both techniques after staining with Abs against distinct surface molecules suggesting that true cell fusion had occurred. We also evaluated the ability of human DC-TC hybrids to present tumor-associated epitopes in the context of both MHC class I and class II molecules. Allogeneic DCs expressing HLA-A*0201, HLA-DR beta 1*0401, and HLA-DR beta 1*0701 were fused with 888mel cells that do not express any of these MHC molecules, but do express multiple melanoma-associated Ags. DC-888mel hybrids efficiently presented HLA-A*0201-restricted epitopes from the melanoma Ags MART-1, gp100, tyrosinase, and tyrosinase-related protein 2 as evaluated by specific cytokine secretion from six distinct CTL lines. In contrast, DCs could not cross-present MHC class I-restricted epitopes after exogenously loading with gp100 protein. DC-888mel hybrids also presented HLA-DR beta 1*0401- and HLA-DR beta 1*0701-restricted peptides from gp100 to CD4(+) T cell populations. Therefore, fusions of DCs and tumor cells express both MHC class I- and class II-restricted tumor-associated epitopes and may be useful for the induction of tumor-reactive CD8(+) and CD4(+) T cells in vitro and in human vaccination trials.  相似文献   
35.
植物种质资源的超低温保存研究进展(综述)   总被引:18,自引:0,他引:18  
植物种质资源的超低温保存研究进展(综述)殷晓辉,舒理慧(武汉大学生命科学学院,武汉430072)ADVANCESINCRYOPRESERVATIONRESEARCHONPLANTGERMPLASM¥YingXiaohui;ShuLihui(Schoo...  相似文献   
36.
戚秋慧  盛修武  姜恕 《植物研究》1990,10(3):99-105
对天然羊草群落进行灌水和施肥后,测定了它们(灌水、灌水加施肥和对照)的群落光合速率。结果如下:1.在灌水、施肥加灌水处理后23天测定,处理群落的叶层高度分别比对照高8%和9%;群落LAI分别比对照高68.97%和99.93%;群落生物量分别比对照高41%和65.69%;群落日净光合量分别是对照的2.48倍和3.76倍;最大光合量分别是对照的2.82倍和3.12倍。2.灌水施肥处理后,羊草群落光合速率日变化的类型与对照基本一致,属于双峰型。唯独灌水加施肥群落(处理后3天)是单峰型,没有中午降低现象。看出较好的水肥条件能改变群落的日变化类型。3.在温湿度条件较差时或随着处理时间的推移,处理的效果越显著。第一阶段测定时,灌水、灌水加施肥处理的群落日净光合量分别是对照的1.26和1.17倍。第二阶段测定时,分别是对照的1.40和1.84倍。第三阶段测定时,分别是对照的2.48和3.76倍。  相似文献   
37.
磷酸酪氨酸蛋白专一抗体的制备和纯化   总被引:1,自引:0,他引:1  
以偶联磷酸化酪氨酸的牛血清白蛋白(BSA)作为免疫原免疫兔获得抗血清.自抗血清中分离获得抗体.自酪胺合成磷酸酪胺,并偶联到溴化氰活化的Sepharose4B上.抗体经磷酸酪胺-Sepharose4B亲和柱纯化,所得抗体专一性强,Dotblot显示:抗体仅对酪氨酸磷酸化的蛋白质包括酪氨酸磷酸化的血清白蛋白,溶菌酶,卵清蛋白起抗原抗体反应,而不识别非酪氨酸磷酸化的溶菌酶,卵清蛋白,也不识别作为免疫原的骨架成分BSA,也不识别丝氨酸磷酸化的卵清蛋白和苏氨酸磷酸化的卵清蛋白.  相似文献   
38.
FoF1-ATPase activity is regulated by external links on β subunits with different molecular weight. It is inhibited when anti-β subunit antibody, streptavidin and H9 antibody link on the β subunits successively, but is activated when virus was binded. Western blotting indicated that the employed anti-β antibody target was on the non-catalytic site of the β subunit. Furthermore, an ESR study of spin-labeled ATP (SL-ATP) showed that the affinity of ATP to the holoenzyme increases with increasing external links on the β subunits. This simple regulation method may have great potential in the design of rapid, free labeled, sensitive and selective biosensors.  相似文献   
39.
Development of the retinal vascular network is strictly confined within the neuronal retina, allowing the intraocular media to be optically transparent. However, in retinal ischemia, pro-angiogenic factors (including vascular endothelial growth factor-A, VEGF-A) induce aberrant guidance of retinal vessels into the vitreous. Here, we show that the soluble heparan sulfate level in murine intraocular fluid is high particularly during ocular development. When the eyes of young mice with retinal ischemia were treated with heparan sulfate-degrading enzyme, the subsequent aberrant angiogenesis was greatly enhanced compared to PBS-injected contralateral eyes; however, increased angiogenesis was completely antagonized by simultaneous injection of heparin. Intraocular injection of heparan sulfate or heparin alone in these eyes resulted in reduced neovascularization. In cell cultures, the porcine ocular fluid suppressed the dose-dependent proliferation of human umbilical vein endothelial cells (HUVECs) mediated by VEGF-A. Ocular fluid and heparin also inhibited the migration and tube formation by these cells. The binding of VEGF-A and HUVECs was reduced under a high concentration of heparin or ocular fluid compared to lower concentrations of heparin. In vitro assays demonstrated that the ocular fluid or soluble heparan sulfate or heparin inhibited the binding of VEGF-A and immobilized heparin or VEGF receptor 2 but not VEGF receptor 1. The recognition that the high concentration of soluble heparan sulfate in the ocular fluid allows it to serve as an endogenous inhibitor of aberrant retinal vascular growth provides a platform for modulating heparan sulfate/heparin levels to regulate angiogenesis.  相似文献   
40.
C. kiangsu adults were observed visiting human urine, especially on hot summer days. The main chemicals in fresh human urine include inorganic salts and CO(NH2)2. When human urine was incubated, NH4HCO3 became the richest nitrogenous compound. The phagostimulants, repellents and attractants in urine were identified here. On the filter papers treated with fresh or incubated urine samples, the 5th instar nymphs and the adults started and continued gnawing around the edges, in contrast to the 3rd and the 4th instar nymphs. The consumed areas were dramatically greater on the filters treated with the urine samples incubated for 3-6 days. The feedings of both male and female adults were also stimulated by several urine-borne components such as NaCl, NaH2PO4, Na2SO4, KCl, NH4Cl and NH4HCO3 but not by CO(NH2)2. Among them NaCl was the most powerful phagostimulant. The repelling, or attractive/arresting effects of CO(NH2)2 and NH4HCO3 were also evaluated by a two-choice test. When exposed to water- and CO(NH2)2 solution-immersed filters simultaneously, the adults prefer to stay on water-immersed filter. In contrast, when provided water- and NH4HCO3 solution-treated filters, the adults prefer to stay on NH4HCO3 solution-treated filter. This demonstrated that CO(NH2)2 acted as a repellent and NH4HCO3 as an attractant/arrestant. In the bamboo forest, similar feeding behavior was also elicited by NaCl, NH4HCO3 but not by CO(NH2)2. Comparing to NaCl solution, a mixed solution of NaCl and CO(NH2)2 (1:1) significantly decreased the consumed area of the treated filters whereas a mixed solution of NaCl and NH4HCO3 (1:1) dramatically increased the consumed area. These results demonstrated that the phagostimulatory effect by NaCl was reduced by CO(NH2)2 in fresh urine and was enhanced by NH4HCO3 in incubated urine.  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