全文获取类型
收费全文 | 48228篇 |
免费 | 3696篇 |
国内免费 | 3443篇 |
出版年
2024年 | 120篇 |
2023年 | 577篇 |
2022年 | 1375篇 |
2021年 | 2226篇 |
2020年 | 1519篇 |
2019年 | 1923篇 |
2018年 | 2051篇 |
2017年 | 1679篇 |
2016年 | 2175篇 |
2015年 | 2515篇 |
2014年 | 3222篇 |
2013年 | 3484篇 |
2012年 | 3971篇 |
2011年 | 3712篇 |
2010年 | 2625篇 |
2009年 | 2301篇 |
2008年 | 2634篇 |
2007年 | 2365篇 |
2006年 | 2066篇 |
2005年 | 1697篇 |
2004年 | 1595篇 |
2003年 | 1503篇 |
2002年 | 1225篇 |
2001年 | 1000篇 |
2000年 | 839篇 |
1999年 | 614篇 |
1998年 | 384篇 |
1997年 | 318篇 |
1996年 | 307篇 |
1995年 | 318篇 |
1994年 | 291篇 |
1993年 | 225篇 |
1992年 | 291篇 |
1991年 | 259篇 |
1990年 | 208篇 |
1989年 | 192篇 |
1988年 | 129篇 |
1987年 | 175篇 |
1986年 | 145篇 |
1985年 | 128篇 |
1984年 | 101篇 |
1983年 | 95篇 |
1982年 | 82篇 |
1981年 | 78篇 |
1980年 | 52篇 |
1979年 | 62篇 |
1978年 | 66篇 |
1976年 | 51篇 |
1973年 | 63篇 |
1972年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
目的 探讨血管生成拟态( vasculogenic mimicry,VM)与E-钙粘蛋白(E-cadherin,E-cad))在食管鳞癌(esophageal squamous cell carcinoma)组织中的表达及意义.方法 收集食管鳞状细胞癌术后标本100例和30例癌旁正常食管黏膜,应用免疫组化法和组织化学法检测食管鳞状细胞癌和正常食管黏膜组织中VM和E-cad的表达情况.结果 在食管鳞状细胞癌组织和正常食管黏膜组织中,VM和E-cad的阳性表达率分别为47.0%、48.0%和0%、70.0%,差异有统计学意义(P<0.05);VM及E-cad的表达与食管鳞癌的组织学分级、临床分期及淋巴结转移(P<0.05);VM与E-cad在食管鳞癌中的表达呈负相关(r=-0.865,P=0.000).多因素分析:PTNM分期、淋巴结转移、VM和E-cad的表达是影响食管鳞癌根治术后患者预后的独立因素(P<0.05);VM阳性组与阴性组的5年生存率分别为4.3%和64.2%,,差异有统计学意义(P=0.000);E-cad阳性组与阴性组5年生存率分别为60.4%和15.4%,差异有统计学意义(P=0.000).结论 具有VM结构的食管鳞状细胞癌的分化程度低,恶性度高,预后差,VM和E-cad表达的程度与食管鳞状细胞癌的进展和预后密切相关. 相似文献
922.
Bilian Chen Wenlang You Jian Huang Ying Yu Weiping Chen 《World journal of microbiology & biotechnology》2010,26(5):833-840
The extracellular polysaccharide from Rhodella reticulata was separated from the culture medium followed by concentration and ethanol precipitation, and purified by anion exchange
chromatography on DEAE-Sepharose Fast Flow. This study compared the free radical-scavenging property and antioxidant activity
with various treatments of crude extracellular polysaccharides of R. reticulata. The results showed that both the crude extracellular polysaccharide and deproteinized crude extracellular polysaccharide
gave evidence of the free radical scavenging and antioxidant activity in a dose-dependent manner. The crude extracellular
polysaccharide exhibited higher free radical scavenging capacity and better antioxidant activity than the various treatments
of crude extracellular polysaccharide samples. The superoxide anion radical scavenging ability of various samples was significantly
higher compared to standard antioxidant (α-tocopherol). These results indicate that the extracellular polysaccharide of R. reticulata is a potent natural antioxidant. 相似文献
923.
不同培养料和发酵次数栽培巴氏菇比较 总被引:1,自引:0,他引:1
分别以玉米秸秆和稻草为培养料栽培巴氏菇,对菌丝生长性状进行对比;同时,在我国传统发酵栽培方法的基础上,将三次发酵法与二次发酵法进行了对比。试验结果表明:利用玉米秸秆栽培的巴氏菇在发菌速度及子实体质量和产量上均优于稻草;培养料经过3次发酵更适宜巴氏菇生长。经过3次发酵的玉米秸秆培养料栽培的巴氏菇产量和生物学效率分别为7.7 kg/m2和27.5%,子实体粗蛋白含量44.89%,可溶性糖含量44.01%,18种氨基酸总量31.70%,明显高于2次发酵的玉米秸秆培养料及2次、3次发酵的稻草培养料。 相似文献
924.
925.
Juan Li Lijuan Wang Margaret Ip Mingjiao Sun Jing Sun Guoying Huang Chuanqing Wang Li Deng Yuejie Zheng Zhou Fu Changcong Li Yunxiao Shang Changan Zhao Sangjie Yu Kaihu Yao Yonghong Yang Xuzhuang Shen 《PloS one》2013,8(8)
Detailed molecular analyses of Clonal Complex 59 (CC59) methicillin-resistant Staphylococcus aureus (MRSA) isolates from children in seven major cities across Mainland China were examined. A total of 110 CC59 isolates from invasive and non-invasive diseases were analyzed by multilocus sequence typing (MLST), Staphylococcus cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing and pulsed-field gel electrophoresis (PFGE). Antibiotics susceptibilities, carriage of plasmids and 42 virulence genes and the expression of virulence factors were examined. ST59 (101/110, 91.8%) was the predominant sequence type (ST), while single locus variants (SLVs) belonging to ST338 (8/110, 7.3%) and ST375 (1/110, 0.9%) were obtained. Three SCCmec types were found, namely type III (2.7%), type IV (74.5%) and type V (22.7%). Seven spa types including t437, which accounted for 87.3%, were determined. Thirteen PFGE types were obtained. PFGE types A and B were the major types totally accounting for 81.8%. The dominant clone was ST59-t437-IVa (65.5%), followed by ST59-t437-V (14.5%). The positive rate of luks-PV and lukF-PV PVL encoding (pvl) gene was 55.5%. Plasmids were detected in 83.6% (92/110) of the strains. The plasmid size ranging from 23.4 kb to 50 kb was most prevalent which accounted for 83.7% (77/92). A significantly lower expression of hla was found in ST59-t437-IVa compared with ST59-t437-V. Among the 110 cases, 61.8% of the patients were less than 1 year old. A total of 90 cases (81.8%) were community-associated (CA) infections whereas 20 cases (18.2%) were hospital-associated (HA) infections. Out of the 110 patients, 36.4% (40/110) were diagnosed with invasive infectious diseases in which ST59-t437-IVa accounted for 67.5% (27/40). In brief, ST59-t437-IVa was proved as the dominant clone in CC59 MRSA strains. The carriage rate of pvl gene was high. CC59 MRSA could result in CA and HA infections. The majortiy of MRSA infection children were in young age. 相似文献
926.
在NCBI数据库中搜索已知多黏类芽孢杆菌基因组中分别编码Fusaricidin合成酶3个NRPS功能区段的核苷酸保守序列,利用Primer5.0软件设计3对引物,对供试的95个细菌菌株进行PCR检测,筛选到1株阳性菌株T99,其3对引物扩增产物的测序结果表明,所得3个功能片段核苷酸序列与多黏类芽孢杆菌SC2和M1的Fusaricidin合成酶基因序列的一致性分别为99%、97%和99%,说明菌株T99基因组中具有Fusaricidin合成相关功能基因.结合形态特征及培养性状、生理生化特性和16SrDNA序列同源性分析的结果,将菌株T99鉴定为多黏类芽孢杆菌. 相似文献
927.
Yu PJ Ferrari G Pirelli L Gulkarov I Galloway AC Mignatti P Pintucci G 《Cellular signalling》2007,19(7):1359-1371
Cardiovascular interventions that restore blood circulation to ischemic areas are accompanied by significant tissue damage, which triggers a vascular remodeling response that may result in restenosis of blood conduits. Early endothelial dysfunction and/or impairment is the early event of a cascade that leads, through an inflammatory response and dedifferentiation of medial smooth muscle cells with abundant deposition of extracellular matrix, to intimal hyperplasia. Here we present the molecular and cellular mechanisms of intimal hyperplasia secondary to vascular injury and discuss the potential role of therapeutic modulation of the intracellular signaling pathways that differentially effect vascular endothelial and smooth muscle cells. The role of mitogen-activated protein kinases (MAPKs) and the outcome of their modulation in these processes are highlighted here as they provide a promising therapeutic target for prevention of restenosis. 相似文献
928.
Human chorionic gonadotropin (hCG) has been used as an anti-fertility vaccine and as a target for cancer immunotherapy. We have explored the use of three copies of C3d in DNA vaccine as molecular adjuvant to improve the immunogenicity of this hormone in previous work and found that the immune response induced by pcDNA3-hCGbeta-C3d3 has been enhanced 243-fold compared with pcDNA3-hCGbeta following DNA immunization in BALB/c mice. In the present study, a new functionally active DNA vaccine of hCGbeta-C3d3 chimera based on pCMV4 vector has been described. We compared the expression efficiency of pCMV4 and pcDNA3 eukaryotic vectors for hCGbeta and hCGbeta-C3d3 fusion protein and the immune response of mice immunized with pcDNA3-hCGbeta, pCMV4-hCGbeta, pcDNA3-hCGbeta-C3d3 and pCMV4-hCGbeta-C3d3, respectively, at 25, 50 and 100 pmol dose, and further analyzed the levels of Th1 and Th2 cytokines produced by spleen lymphocytes of the immunized mice upon hCG restimulation in vitro. It was found that pCMV4 vector achieved 1.3-1.5-fold higher protein expression and raised 1.1-1.2 (primary) and 1.2-1.3 (booster) logs higher titer of anti-hCGbeta IgG than pcDNA3. Mice vaccinated with 50 pmol of hCGbeta-C3d3-DNAs elicited the highest titer of hCGbeta-specific antibody among the serial doses and the immune response induced by pCMV4-hCGbeta-C3d3 were, respectively, 1.3, 1.3 and 1.2 logs higher than that of pcDNA3-hCGbeta-C3d3 and 2.2, 2.9 and 2.4 logs higher than that of pCMV4-hCGbeta at week 2 following the booster immunization. Moreover, we observed that the production of IL-4 and IL-10 increased in mice vaccinated with hCGbeta-C3d3-DNAs and the ratio of IL-4/IFN-(gamma) showed a Th2 bias of immune response in the mice immunized with hCGbeta-C3d3-DNAs. These findings indicated that gene fusion of C3d3 to hCGbeta, as a means of harnessing the adjuvant potential of the innate immune system, may improve the antigen-specific Th2 humoral immune response of the hCGbeta DNA vaccine and the pCMV4 vector is a more ideal eukaryotic vector for DNA vaccine than pcDNA3. 相似文献
929.
通过逆转录-聚合酶链反应从我国河南省2例重叠感染HCV或HBV/HDV的献血啼中,分离到HBVNS5区的部分cDNA,对其进行序列分析比较,结果表明,河南株HGVNS5工核苷酸与两中国HGV主同源性高于国外代表株(88.5-90.6%),但由核苷酸推导的氨基酸的同源性都无明显的地区性区别。HGVNS5区氨基酸序列较保守,缺乏明显高变区,中国4株HGV在7384位发生了由C→T的变异,从而导致一个人 相似文献
930.
中国西北地区降水量及极端干旱气候变化特征 总被引:12,自引:0,他引:12
采用1960—2011年西北地区111个观测站逐日气象资料,利用FAO Penman-Monteith模型,计算出各气象站的潜在蒸散量,由此计算出各站的湿润指数,并对其进行标准化,统计极端干旱发生频率。对西北全区和不同自然区的降水量及极端干旱发生频率的时空变化特征进行了探讨分析。结果表明:近52年来西北全区年降水量变化倾向率表现出微弱的上升趋势,平均每年上升0.17 mm。由该区年降水量变化的空间差异,可将研究区划分为3个部分:明显增加区、轻度增加区、减少区。西北全区极端干旱发生频率的平均值为3.8月/a,气候变化倾向率总体上表现出明显的下降趋势,平均每年下降0.011月。根据西北地区极端干旱发生频率变化的空间差异,也可将研究区划分为3个部分:明显减少区、轻度减少区、增加区。极端干旱发生频率与降水量和平均气温表现为显著的负相关性,与无雨总日数呈现出显著的正相关性。 相似文献