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   36310篇
  免费   2453篇
  国内免费   2057篇
电工技术   1244篇
综合类   1966篇
化学工业   12301篇
金属工艺   3590篇
机械仪表   961篇
建筑科学   2995篇
矿业工程   491篇
能源动力   1092篇
轻工业   1568篇
水利工程   96篇
石油天然气   1257篇
武器工业   293篇
无线电   3218篇
一般工业技术   5148篇
冶金工业   1440篇
原子能技术   664篇
自动化技术   2496篇
  2024年   111篇
  2023年   530篇
  2022年   1183篇
  2021年   1186篇
  2020年   985篇
  2019年   871篇
  2018年   747篇
  2017年   1056篇
  2016年   1279篇
  2015年   1241篇
  2014年   1679篇
  2013年   1881篇
  2012年   2084篇
  2011年   2734篇
  2010年   1992篇
  2009年   2461篇
  2008年   1915篇
  2007年   2377篇
  2006年   2205篇
  2005年   1763篇
  2004年   1471篇
  2003年   1479篇
  2002年   1203篇
  2001年   932篇
  2000年   849篇
  1999年   686篇
  1998年   527篇
  1997年   374篇
  1996年   340篇
  1995年   284篇
  1994年   258篇
  1993年   228篇
  1992年   204篇
  1991年   175篇
  1990年   150篇
  1989年   116篇
  1988年   92篇
  1987年   94篇
  1986年   107篇
  1985年   103篇
  1984年   90篇
  1983年   76篇
  1982年   76篇
  1981年   85篇
  1980年   77篇
  1978年   72篇
  1977年   73篇
  1976年   88篇
  1975年   86篇
  1974年   70篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Periodontitis is a multifactorial disease. The aim of this explorative study was to investigate the role of Interleukin-(IL)-1, IL-4, GATA-3 and Cyclooxygenase-(COX)-2 polymorphisms after non-surgical periodontal therapy with adjunctive systemic antibiotics (amoxicillin/metronidazole) and subsequent maintenance in a Caucasian population. Analyses were performed using blood samples from periodontitis patients of a multi-center trial (ClinicalTrials.gov NCT00707369=ABPARO-study). Polymorphisms were analyzed using quantitative real-time PCR. Clinical attachment levels (CAL), percentage of sites showing further attachment loss (PSAL) ≥1.3 mm, bleeding on probing (BOP) and plaque score were assessed. Exploratory statistical analysis was performed. A total of 209 samples were genotyped. Patients carrying heterozygous genotypes and single-nucleotide-polymorphisms (SNP) on the GATA-3-IVS4 +1468 gene locus showed less CAL loss than patients carrying wild type. Heterozygous genotypes and SNPs on the IL-1A-889, IL-1B +3954, IL-4-34, IL-4-590, GATA-3-IVS4 +1468 and COX-2-1195 gene loci did not influence CAL. In multivariate analysis, CAL was lower in patients carrying GATA-3 heterozygous genotypes and SNPs than those carrying wild-types. For the first time, effects of different genotypes were analyzed in periodontitis progression after periodontal therapy and during supportive treatment using systemic antibiotics demonstrating a slight association of GATA-3 gene locus with CAL. This result suggests that GATA-3 genotypes are a contributory but non-essential risk factor for periodontal disease progression.  相似文献   
102.
Recent evidence suggests that I2-imidazoline ligands have neuroprotective properties in animal models of neurodegeneration, such as Alzheimer’s disease (AD). We recently demonstrated that the I2-ligand BU224 reversed memory impairments in AD transgenic mice and this effect was not because of reductions in amyloid-β (Aβ) deposition. In this study, our aim was to determine the therapeutic potential of the powerful analgesic I2-imidazoline ligand CR4056 in the 5xFAD model of AD, since this ligand has been proven to be safely tolerated in humans. Sub-chronic oral administration of CR4056 (30 mg/kg for 10 days) led to an improvement in recognition memory in 6-month-old 5xFAD mice, but not in wild-type littermates, without affecting Aβ levels or deposition. Our results also revealed a change in the profile of microglia by CR4056, resulting in a suppression of pro-inflammatory activated microglia, but increased the density of astrocytes and the expression of ApoE, which is mainly produced by these glial cells. In addition, CR4056 restored fibrinogen extravasation, affecting the distribution of markers of astrocytic end feet in blood vessels. Therefore, these results suggest that CR4056 protects against Aβ-mediated neuroinflammation and vascular damage, and offers therapeutic potential at any stage of AD.  相似文献   
103.
食用油碟式分离机碟片的渗氮激光相变硬化复合处理研究   总被引:1,自引:1,他引:0  
吴健 《轻工机械》2006,24(3):77-80
介绍了食用油碟式分离机碟片的常规表面处理方法,提出了渗氮激光相变硬化复合处理技术,通过硬度实验、耐磨性实验、抗腐蚀性实验及残余应力分布曲线,对实验结果进行了较深入的分析,得出渗氮激光相变硬化复合处理技术可提高4C r13钢碟片抗腐蚀能力和抗疲劳性能的结论。  相似文献   
104.
随着储能设备和电力驱动产品的激增,特别是电动汽车的大规模推广应用,全固态电池被认为是最有可能解决电动设备日益严峻的安全问题和高能量密度需求的策略之一.本文报道了一种Al4B2O9纳米棒改性的聚环氧乙烷(PEO)基固体聚合物电解质(ASPE),其具有高离子电导率、宽电化学窗口、良好的机械性能和阻燃性能.具体来说,因为Al...  相似文献   
105.
采用石墨炉原子吸收光谱法(GFAAs)测定锂离子电池正极材料LiMn2O4中杂质Pb和Cd的含量.探讨了HNO2浓度、Pb和Cd的灰化温度和原子化温度、基体改进剂对测定结果的影响.该方法的操作简单,准确度高,Pb的回收率为91.22%~93.75%,Cd的回收率为96.5%~108.6%;精密度好,两种元素测定的相对标准偏差RSD(n=lO)<5%.  相似文献   
106.
107.
Patients with liver diseases not only experience the adverse effects of liver-metabolized drugs, but also the unexpected adverse effects of renally excreted drugs. Bile acids alter the expression of renal drug transporters, however, the direct effects of bile acids on drug transport remain unknown. Renal drug transporter organic anion-transporting polypeptide 4C1 (OATP4C1) was reported to be inhibited by chenodeoxycholic acid. Therefore, we predicted that the inhibition of OATP4C1-mediated transport by bile acids might be a potential mechanism for the altered pharmacokinetics of renally excreted drugs. We screened 45 types of bile acids and calculated the IC50, Ki values, and bile acid–drug interaction (BDI) indices of bile acids whose inhibitory effect on OATP4C1 was >50%. From the screening results, lithocholic acid (LCA), glycine-conjugated lithocholic acid (GLCA), and taurine-conjugated lithocholic acid (TLCA) were newly identified as inhibitors of OATP4C1. Since the BDI index of LCA was 0.278, LCA is likely to inhibit OATP4C1-mediated transport in clinical settings. Our findings suggest that dose adjustment of renally excreted drugs may be required in patients with renal failure as well as in patients with hepatic failure. We believe that our findings provide essential information for drug development and safe drug treatment in clinics.  相似文献   
108.
109.
设计了基于TMS320C6205DSP的MPEG-4数字视频监控系统,针对软硬件特性对优化方法做了详细阐述并完成了对该系统的仿真优化,最后给出了关键的测试结果。  相似文献   
110.
黄新强  朱珍民 《微计算机信息》2007,23(24):213-214,151
本文提出并实现了一种四步搜索块匹配的运动估计算法,并在运动估计算法的实现中给出了整象素搜索与半象素搜索相结合、单矢量估计与四矢量估计相结合的改进方法,该算法能够有效的提高编码效率。  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