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   6701篇
  免费   657篇
  国内免费   1424篇
  8782篇
  2024年   27篇
  2023年   117篇
  2022年   294篇
  2021年   365篇
  2020年   269篇
  2019年   317篇
  2018年   248篇
  2017年   210篇
  2016年   254篇
  2015年   398篇
  2014年   510篇
  2013年   542篇
  2012年   644篇
  2011年   585篇
  2010年   409篇
  2009年   426篇
  2008年   448篇
  2007年   401篇
  2006年   345篇
  2005年   333篇
  2004年   295篇
  2003年   277篇
  2002年   221篇
  2001年   160篇
  2000年   155篇
  1999年   119篇
  1998年   114篇
  1997年   62篇
  1996年   37篇
  1995年   33篇
  1994年   31篇
  1993年   22篇
  1992年   22篇
  1991年   18篇
  1990年   8篇
  1989年   5篇
  1988年   9篇
  1987年   3篇
  1986年   11篇
  1985年   12篇
  1984年   9篇
  1983年   4篇
  1982年   6篇
  1981年   5篇
  1973年   1篇
  1967年   1篇
排序方式: 共有8782条查询结果,搜索用时 15 毫秒
111.
The human absent in melanoma 2 (AIM2) is considered as a DNA recognizer. AIM2 has been described as a tumor suppressor gene in the early years. But recent studies suggested that it functions as an oncogene in several cancers. However, its roles in non-small-cell lung cancer (NSCLC) remain unclear. Here we reported that AIM2 highly expressed in NSCLC cells and exhibited a tumor-promoting property both in vitro and in vivo. Besides, AIM2 short hairpin RNA (shRNA)-mediated suppression of cell proliferation was triggered by the accumulation of cells at the G2/M phase. Knockdown of AIM2 reduced the inflammasome formation, while overexpression of AIM2 or stimulation by poly(dA:dT) induced the inflammasome formation. Interestingly, blockade of the inflammasome by caspase-1 inhibitor VX-765 or ASC small interfering RNA (siRNA) abolished the effects brought by AIM2 shRNA and AIM2 plasmid. In summary, our results revealed that AIM2 functioned as an oncogene in NSCLC in an inflammasome-dependent way.  相似文献   
112.

Background

Brucellosis presents a significant economic burden for China because it causes reproductive failure in host species and chronic health problems in humans. These problems can involve multiple organs. Brucellosis is highly endemic in Shanxi Province China. Molecular typing would be very useful to epidemiological surveillance. The purpose of this study was to assess the diversity of Brucella melitensis strains for epidemiological surveillance. Historical monitoring data suggest that Brucella melitensis biovar 3 is the predominant strain associated with the epidemic of brucellosis in Shanxi Province.

Methods/Principal Findings

Multiple-locus variable-number repeat analysis (MLVA-16) and hypervariable octameric oligonucleotide fingerprinting (HOOF-print) were used to type a human-hosted Brucella melitensis population (81 strains). Sixty-two MLVA genotypes (discriminatory index: 0.99) were detected, and they had a genetic similarity coefficient ranging from 84.9% to 100%. Eighty strains of the population belonged to the eastern Mediterranean group with panel 1 genotypes 42 (79 strains) and 43 (1 strain). A new panel 1 genotype was found in this study. It was named 114 MLVAorsay genotype and it showed similarity to the two isolates from Guangdong in a previous study. Brucella melitensis is distributed throughout Shanxi Province, and like samples from Inner Mongolia, the eastern Mediterranean genotype 42 was the main epidemic strain (97%). The HOOF-printing showed a higher diversity than MLVA-16 with a genetic similarity coefficient ranging from 56.8% to 100%.

Conclusions

According to the MLVA-16 and HOOF-printing results, both methods could be used for the epidemiological surveillance of brucellosis. A new genotype was found in both Shanxi and Guangdong Provinces. In areas with brucellosis, the MLVA-16 scheme is very important for tracing cases back to their origins during outbreak investigations. It may facilitate the expansion and eradication of the disease.  相似文献   
113.
Mounting evidence suggests that an excess of matrix metalloproteinase-13 (MMP-13) plays an important role in the breakdown of extracellular matrix in osteoarthritis (OA). Here, the effects of ginsenoside Rb1 (GRb1) on the expression of MMP-13 in IL-1β-induced SW 1353 chondrosarcoma cells and an experimental rat model of OA induced by anterior cruciate ligament transection (ACLT) were investigated. SW1353 chondrosarcoma cells were pretreated with or without GRb1 and Notch signaling pathway inhibitor, DAPT, then were stimulated with IL-1β. In rats, experimental OA was induced by ACLT. These rats then received intra-articular injections of vehicle, an inhibitor of γ-secretase, DAPT, and/or GRb1. Expression of MMP-13, collagen type II (CII), Notch1, and jagged 1 (JAG1) were verified by western blotting and immunohistochemistry. In addition, levels of MMP-13 mRNA were detected using quantitative real-time PCR. In histological analyses, treatment with DAPT reduced the number of cartilage lesions present and the expressions of MMP-13, CII, Notch1, and JAG1. In addition, treatment with GRb1 was associated with lower levels of Notch1 and JAG1 in both IL-1β-induced SW1353 chondrosarcoma cells and in the rat OA model. Furthermore, the suppressive effect of GRb1 on MMP-13 was greater than that exhibited by the signaling pathway inhibitor. In conclusion, GRb1 inhibits MMP-13 through down-regulating Notch signaling pathway in OA.  相似文献   
114.
Hua S  Zhang Y  Li XC  Ma LB  Cao JW  Dai JP  Li R 《Cloning and stem cells》2007,9(2):237-246
The objective of this study was to determine the effect of exogenous mitochondria obtained from granulosa cells on the development of bovine embryos in vitro. We classified cumulus oocyte complexes (COCs) as good (G)- and poor (P)-quality oocytes based on cytoplasmic appearance and cumulus characteristics, and assessed mtDNA copy numbers in the G and P oocytes with real-time polymerase chain reaction (PCR). The mitochondria were isolated by fractionation and suspended in mitochondria injection buffer (MIB). Part one of the experiment consisted of the following treatments: (1) G-oocytes + sperm, (2) P-oocytes + mitochondria + MIB + sperm, (3) P-oocytes + MIB + sperm, and (4) P-oocytes + sperm. In part 2, oocytes were parthenogenetically activated. The treatments were: (1) G-oocytes, (2) P-oocytes + mitochondria + MIB, (3) P-oocytes + MIB, and (4) P-oocytes alone. The results indicated a significant difference in mtDNA copy number between G (361 113 +/- 147 114) and P (198 293 +/- 174 178) oocytes (p < 0.01). The rates of morula, blastocyst, and hatched blastocysts derived from P-oocytes + mitochondria were similar to those of G-oocytes, but significantly higher than P-oocytes without exogenous mitochondria in both the ICSI and parthenogenetic activation experiments. We found no difference in blastomere numbers between G-oocytes and P-oocytes + mitochondria in either experiment, but blastomere numbers in these two groups were significantly higher than in P-oocyte groups without exogenous mitochondria. These data suggest that mtDNA content is very important for early embryo development. Furthermore, the transfer of mitochondria from the same breed may improve embryo quality during preimplantation development.  相似文献   
115.
新疆蓝刺头化学成分研究   总被引:1,自引:0,他引:1  
以新疆蓝刺头(Echinops ritro L.)全草为研究材料,通过硅胶柱色谱,Sephadex LH-20柱色谱,重结晶等技术对新疆蓝刺头化学成分进行分离纯化,通过理化性质分析及1H-NMR,13C-NMR等技术对化合物结构进行鉴定.结果表明,共分离出5个化合物,分别是三萜类化合物蒲公英甾醇乙酰酯(化合物1)、蒲公英甾醇(化合物2)、黄酮苷类化合物金丝桃苷(化合物3)、胡萝卜苷(化合物4)与β-豆甾醇葡萄糖苷(化合物5).其中化合物1,2,5首次从该种植物中分离,化合物3为首次从该属植物中分离.  相似文献   
116.
117.
In this paper, a new effective model is proposed to forecast how long the postoperative patients suffered from non-small cell lung cancer will survive. The new effective model which is based on the extreme learning machine (ELM) and principal component analysis (PCA) can forecast successfully the postoperative patients' survival time. The new model obtains better prediction accuracy and faster convergence rate which the model using backpropagation (BP) algorithm and the Levenberg-Marquardt (LM) algorithm to forecast the postoperative patients' survival time can not achieve. Finally, simulation results are given to verify the efficiency and effectiveness of our proposed new model.  相似文献   
118.
论昆虫空间生态学研究   总被引:15,自引:1,他引:15  
空间特征是昆虫生态学研究的热点之一 ,具有重要的理论与应用意义。该文从理论、尺度、时空动态模型、技术手段及研究热点几个方面概述近期昆虫空间生态学研究进展。主要理论包括概率及统计模型、地学统计学、景观生态学、集合种群生态学 ;研究技术涉及地理信息系统、遥感、计算机辅助分析等。简要论述研究的空间尺度问题 ,介绍空间分子生态、进化生态等新研究热点在昆虫空间生态领域的发展 ,并分析昆虫空间生态学存在的问题和发展趋势。  相似文献   
119.
Objectives: The relationship of plasma adiponectin levels with various anthropometric and metabolic factors has been surveyed extensively in adults. However, how plasma adiponectin levels are related to various anthropometric indices and cardiovascular risk factors in adolescents is not as vigorously studied. In this study, we investigated this among healthy nondiabetic adolescents. Research Methods and Procedures: Two hundred thirty nondiabetic subjects (125 boys and 105 girls, ~10 to 19 years old) were included. The plasma adiponectin, fasting plasma glucose, insulin, lipids and anthropometric indices including body height, weight, waist circumference, and hip circumference were examined. Body fat mass (FM) and percentage were obtained from DXA scan. The homeostasis model assessment was applied to estimate the degree of insulin resistance. Results: The plasma adiponectin levels were significantly higher in girls (30.79 ± 14.48 μg/mL) than boys (22.87 ± 11.41 μg/mL). The plasma adiponectin levels were negatively related to BMI, FM, FM percentage, waist circumference, waist‐to‐hip ratio, insulin resistance, plasma insulin, triglycerides, and uric acid levels, but positively with high‐density lipoprotein cholesterol (HDL‐C) with the adjustment for age and gender. Using different multivariate linear regression models, only age and HDL‐C were consistently related to the plasma adiponectin levels after adjustment for the other variables. Discussion: The relationship between plasma adiponectin and various anthropometric indices and metabolic factors, especially HDL‐C, previously reported in adults was present in the healthy nondiabetic adolescents. Whether variation of plasma adiponectin levels in healthy nondiabetic adolescents may influence their future coronary artery disease risk warrants further investigation.  相似文献   
120.
Biological treatment is an emerging and prevalent technology for treating off-gases from wastewater treatment plants. The most commonly reported odorous compound in off-gases is hydrogen sulfide (H2S), which has a very low odor threshold. A self-designed, bench-scale, cross-flow horizontal biotrickling filter (HBF) operated with bacteria immobilized activated carbon (termed biological activated carbon—BAC), was applied for the treatment of H2S. A mixed culture of sulfide-oxidizing bacteria dominated by Acidithiobacillus thiooxidans acclimated from activated sludge was used as bacterial seed and the biofilm was developed by culturing the bacteria in the presence of carbon pellets in mineral medium. HBF performance was evaluated systematically over 120 days, depending on a series of changing factors including inlet H2S concentration, gas retention time (GRT), pH of recirculation solution, upset and recovery, sulfate accumulation, pressure drop, gas-liquid ratio, and shock loading. The biotrickling filter system can operate at high efficiency from the first day of operation. At a volumetric loading of 900 m3 m–3 h–1 (at 92 ppmv H2S inlet concentration), the BAC exhibited maximum elimination capacity (113 g H2S/m–3 h–1) and a removal efficiency of 96% was observed. If the inlet concentration was kept at around 20 ppmv, high H2S removal (over 98%) was achieved at a GRT of 4 s, a value comparable with those currently reported for biotrickling filters. The bacterial population in the acidic biofilter demonstrated capacity for removal of H2S over a broad pH range (pH 1–7). A preliminary investigation into the different effects of bacterial biodegradation and carbon adsorption on system performance was also conducted. This study shows the HBF to be a feasible and economic alternative to physical and chemical treatments for the removal of H2S.  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