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   25942篇
  免费   2612篇
  国内免费   768篇
电工技术   1232篇
综合类   917篇
化学工业   6117篇
金属工艺   491篇
机械仪表   830篇
建筑科学   1443篇
矿业工程   68篇
能源动力   6757篇
轻工业   1499篇
水利工程   87篇
石油天然气   61篇
武器工业   21篇
无线电   4427篇
一般工业技术   4322篇
冶金工业   255篇
原子能技术   228篇
自动化技术   567篇
  2024年   82篇
  2023年   759篇
  2022年   1665篇
  2021年   1922篇
  2020年   1203篇
  2019年   1042篇
  2018年   923篇
  2017年   1176篇
  2016年   1233篇
  2015年   1206篇
  2014年   1743篇
  2013年   1727篇
  2012年   1795篇
  2011年   2416篇
  2010年   1553篇
  2009年   1425篇
  2008年   1197篇
  2007年   1192篇
  2006年   955篇
  2005年   664篇
  2004年   520篇
  2003年   440篇
  2002年   392篇
  2001年   343篇
  2000年   270篇
  1999年   179篇
  1998年   268篇
  1997年   164篇
  1996年   143篇
  1995年   85篇
  1994年   114篇
  1993年   84篇
  1992年   64篇
  1991年   52篇
  1990年   48篇
  1989年   39篇
  1988年   30篇
  1987年   36篇
  1986年   25篇
  1985年   33篇
  1984年   27篇
  1983年   15篇
  1982年   18篇
  1981年   7篇
  1980年   12篇
  1979年   7篇
  1978年   7篇
  1977年   6篇
  1975年   3篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
设计一种用ST7单片机构成的全数字化太阳能直流供电系统控制器。系统在ST7单片机的控制下,能将太阳能电池转换的直流电进行有效存储和合理使用。系统充分利用了ST7单片机的软件资源,最大程度地简化了硬件电路,使电源具有较高的性价比和可靠性。  相似文献   
72.
Interleukin-27 is constitutively secreted by microglia in the retina or brain, and upregulation of IL-27 during neuroinflammation suppresses encephalomyelitis and autoimmune uveitis. However, while IL-35 is structurally and functionally similar to IL-27, the intrinsic roles of IL-35 in CNS tissues are unknown. Thus, we generated IL-35/YFP-knock-in reporter mice (p35-KI) and demonstrated that photoreceptor neurons constitutively secrete IL-35, which might protect the retina from persistent low-grade inflammation that can impair photoreceptor functions. Furthermore, the p35-KI mouse, which is hemizygous at the il12a locus, develops more severe uveitis because of reduced IL-35 expression. Interestingly, onset and exacerbation of uveitis in p35-KI mice caused by extravasation of proinflammatory Th1/Th17 lymphocytes into the retina were preceded by a dramatic decrease of IL-35, attributable to massive death of photoreceptor cells. Thus, while inflammation-induced death of photoreceptors and loss of protective effects of IL-35 exacerbated uveitis, our data also suggest that constitutive production of IL-35 in the retina might have housekeeping functions that promote sterilization immunity in the neuroretina and maintain ocular immune privilege.  相似文献   
73.
杜俊  苏海智 《浙江电力》2011,30(11):15-17
光伏发电技术是可再生能源技术的一个重要组成部分。介绍了500 kV芝堰变电站光伏并网发电系统,采集了光伏并网发电的数据,分析、模拟计算太阳能光伏系统的效益,在此基础上总结光伏发电系统使用中的优点及存在的问题。  相似文献   
74.
介绍了国内外太阳能光伏发电的研究与应用现状,结合太阳能光伏发电的原理与主电路结构,详细分析了光伏并网中可能出现的电压偏差、电压波动、谐波与直流偏磁、不平衡和故障状态及保护配置等方面的问题。阐述了江西省太阳能资源的分布和近期的规划建设情况,以拟建设的新余10MW光伏并网电站为例,初步探讨了其并网可能产生的影响。针对江西电网光伏电源可能出现的规模化接入问题,从技术研究和管理手段两方面提出了相应建议。  相似文献   
75.
The potential energy of a nuclide is enhanced by about 10 MeV per nucleon from the repulsion between like nucleons, and diminished by about 20 MeV per nucleon from the attraction between unlike nucleons. Nuclear stability results mostly from the interplay of these opposing forces, plus Coulomb repulsion of positive charges. Whereas fusion may be the primary mechanism by which first generation stars produce energy, repulsion between like nucleons may cause neutron emission from the collapsed core (neutron star) produced in a terminal supernova explosion and initiate luminosity in second generation stars that accrete on such objects. As noted earlier [1], the scarcity of solar neutrinos, the enrichment of light isotopes in the solar wind, and the presence of abundant short-lived nuclides and interlinked chemical and isotopic heterogeneities in the early solar system might also be explained if the Sun formed in this manner.  相似文献   
76.
77.
伪装材料表面偏振散射的几何光学解   总被引:1,自引:1,他引:1  
散射光的偏振特征可以作为遥感信息来识别目标,给伪装技术带来了新的威胁.文中采用偏振相机在光学与红外波段测试了染料型和涂料型伪装材料的偏振散射光谱,研究了不同探测波段下粗糙材料表面的偏振散射机理.研究结果表明:染料型伪装材料的偏振度很小,当光源以不同的入射角照射其表面时,偏振度基本保持不变;涂料型伪装材料的偏振度较大,且随着入射角的增大,其散射光的偏振度也逐渐升高;材料散射光的偏振度与表面粗糙度成反比,染料型伪装材料具有较大的表面粗糙度,在与入射光的作用过程中多次散射占优,因此,其偏振度很小.利用几何光学理论分析了材料表面的偏振散射机理,分析结果与实验结论相吻合.在一定条件下,伪装材料的偏振散射特征与背景不同,偏振信息在伪装目标识别方面具有重要的军事应用价值.  相似文献   
78.
本研究以人肝癌细胞(HepG2)为对象,分为α-LA-OA处理组、牛-α乳白蛋白(α-LA)处理组和溶剂对照组,以细胞的糖酵解和线粒体有氧呼吸2个过程中胞外酸化率和细胞耗氧率的变化水平为衡量指标,评估α-LA-OA对肿瘤细胞能量代谢的影响.结果表明,α-LA-OA能够显著性降低人肝癌细胞的糖酵解能力以及线粒体有氧呼吸能...  相似文献   
79.
Neuropathy development is a major dose-limiting side effect of anticancer treatments that significantly reduces patient’s quality of life. The inadequate pharmacological approaches for neuropathic pain management warrant the identification of novel therapeutic targets. Mitochondrial dysfunctions that lead to reactive oxygen species (ROS) increase, cytosolic Ca2+ imbalance, and lactate acidosis are implicated in neuropathic pain pathogenesis. It has been observed that in these deregulations, a pivotal role is played by the mitochondrial carbonic anhydrases (CA) VA and VB isoforms. Hence, preclinical studies should be conducted to assess the efficacy of two novel selenides bearing benzenesulfonamide moieties, named 5b and 5d, and able to inhibit CA VA and VB against paclitaxel-induced neurotoxicity in mice. Acute treatment with 5b and 5d (30–100 mg/kg, per os – p.o.) determined a dose-dependent and long-lasting anti-hyperalgesic effect in the Cold plate test. Further, repeated daily treatment for 15 days with 100 mg/kg of both compounds (starting the first day of paclitaxel injection) significantly prevented neuropathic pain development without the onset of tolerance to the anti-hyperalgesic effect. In both experiments, acetazolamide (AAZ, 100 mg/kg, p.o.) used as the reference drug was partially active. Moreover, ex vivo analysis demonstrated the efficacy of 5b and 5d repeated treatments in reducing the maladaptive plasticity that occurs to glia cells in the lumbar portion of the spinal cord and in improving mitochondrial functions in the brain and spinal cord that were strongly impaired by paclitaxel-repeated treatment. In this regard, 5b and 5d ameliorated the metabolic activity, as observed by the increase in citrate synthase activity, and preserved an optimal mitochondrial membrane potential (ΔΨ) value, which appeared depolarized in brains from paclitaxel-treated animals. In conclusion, 5b and 5d have therapeutic and protective effects against paclitaxel-induced neuropathy without tolerance development. Moreover, 5b and 5d reduced glial cell activation and mitochondrial dysfunction in the central nervous system, being a promising candidate for the management of neuropathic pain and neurotoxicity evoked by chemotherapeutic drugs.  相似文献   
80.
Red blood cell-derived extracellular vesicles (RBCEVs) are vesicles naturally produced by red blood cells and play multiple roles such as acting as cell-to-cell communication messengers in both normal physiological and diseased states. RBCEVs are highly promising delivery vehicles for therapeutic agents such as biomolecules and nucleic acids as they are easy to source, safe, and versatile. RBCEVs autonomously target the liver and pass the blood–brain barrier into the brain, which is highly valuable for the treatment of liver and brain diseases. RBCEVs can be modified by various functional units, including various functional molecules and nanoparticles, to improve their active targeting capabilities for tumors or other sites. Moreover, the RBCEV level is significantly shifted in many diseased states; hence, they can also serve as important biomarkers for disease diagnoses. It is clear that RBCEVs have considerable potential in multiple medical applications. In this review, we briefly introduce the biological roles of RBCEVs, presented interesting advances in RBCEV applications, and discuss several challenges that need to be addressed for their clinical translation.  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