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   1910272篇
  免费   87024篇
  国内免费   49509篇
电工技术   80663篇
综合类   63778篇
化学工业   325103篇
金属工艺   98518篇
机械仪表   76034篇
建筑科学   83356篇
矿业工程   33869篇
能源动力   62740篇
轻工业   154452篇
水利工程   31987篇
石油天然气   54606篇
武器工业   8868篇
无线电   245868篇
一般工业技术   306924篇
冶金工业   137177篇
原子能技术   41955篇
自动化技术   240907篇
  2022年   28808篇
  2021年   40930篇
  2020年   29925篇
  2019年   26864篇
  2018年   27052篇
  2017年   28161篇
  2016年   33854篇
  2015年   39543篇
  2014年   57083篇
  2013年   120669篇
  2012年   75856篇
  2011年   88074篇
  2010年   83453篇
  2009年   90275篇
  2008年   83762篇
  2007年   79536篇
  2006年   77711篇
  2005年   65375篇
  2004年   59713篇
  2003年   52536篇
  2002年   51086篇
  2001年   46404篇
  2000年   42738篇
  1999年   35250篇
  1998年   31021篇
  1997年   30932篇
  1996年   30067篇
  1995年   27740篇
  1994年   26362篇
  1993年   26270篇
  1992年   25563篇
  1991年   22341篇
  1990年   22812篇
  1989年   21914篇
  1988年   20287篇
  1987年   18657篇
  1986年   17943篇
  1985年   21273篇
  1984年   21890篇
  1983年   19853篇
  1982年   18975篇
  1981年   19073篇
  1980年   17714篇
  1979年   18282篇
  1978年   17431篇
  1977年   16536篇
  1976年   16375篇
  1975年   15758篇
  1974年   15304篇
  1973年   15363篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
992.
993.
994.
The airborne dynamics of respiratory droplets, and the transmission routes of pathogens embedded within them, are governed primarily by the diameter of the particles. These particles are composed of the fluid which lines the respiratory tract, and is primarily mucins and salts, which will interact with the atmosphere and evaporate to reach an equilibrium diameter. Measuring organic volume fraction (OVF) of cough aerosol has proved challenging due to large variability and low material volume produced after coughing. Here, the diametric hygroscopic growth factors (GF) of the cough aerosol produced by healthy participants were measured in situ using a rotating aerosol suspension chamber and a humidification tandem differential mobility analyser. Using hygroscopicity models, it was estimated that the average OVF in the evaporated cough aerosol was 0.88 ± 0.07 and the average GF at 90% relative humidity (RH) was 1.31 ± 0.03. To reach equilibrium in dry air the droplets will reduce in diameter by a factor of approximately 2.8 with an evaporation factor of 0.36 ± 0.05. Hysteresis was observed in cough aerosol at RH = ∼35% and RH = ∼65% for efflorescence and deliquescence, respectively, and may depend on the OVF. The same behaviour and GF were observed in nebulized bovine bronchoalveolar lavage fluid.  相似文献   
995.
Bruton's tyrosine kinase (Btk) is an attractive target for the treatment of a wide array of B-cell malignancies and autoimmune diseases. Small-molecule covalent irreversible Btk inhibitors targeting Cys481 have been developed for the treatment of such diseases. In clinical trials, probe molecules are required in occupancy studies to measure the level of engagement of the protein by these covalent irreversible inhibitors. The result of this pharmacodynamic (PD) activity provides guidance for appropriate dosage selection to optimize inhibition of the drug target and correlation of target inhibition with disease treatment efficacy. This information is crucial for successful evaluation of drug candidates in clinical trials. Based on the pyridine carboxamide scaffold of a novel solvent-accessible pocket (SAP) series of covalent irreversible Btk inhibitors, we successfully developed a potent and selective affinity-based biotinylated probe 12 (2-[(4-{4-[5-(1-{5-[(3aS,4S,6aR)-2-oxo-hexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanamido}-3,6,9,12-tetraoxapentadecan-15-amido)pentanoyl]piperazine-1-carbonyl}phenyl)amino]-6-[1-(prop-2-enoyl)piperidin-4-yl]pyridine-3-carboxamide). Compound 12 has been used in Btk occupancy assays for preclinical studies to determine the therapeutic efficacy of Btk inhibition in two mouse lupus models driven by TLR7 activation and type I interferon.  相似文献   
996.
激光脉冲编码是激光制导武器的抗干扰措施之一。角度欺骗式干扰和高重频干扰是目前半主动激光制导武器的主要有源干扰来源。为研究不同激光脉冲编码方式对激光半主动制导武器抗这两种干扰性能的影响,本文针对敌方激光告警机的识别算法与我方导引头的解码过程,提出自相关函数与归一化互相关函数评价方法,并对目前主要编码方式进行仿真,仿真结果表明:激光脉冲编码的抗角度欺骗式干扰能力受编码序列周期性与脉冲间隔随机性的影响;抗高重频激光干扰能力受编码序列脉冲间隔随机性的影响;LFSR状态码的抗角度欺骗式干扰与抗高重频干扰效果均优于其他编码方式。  相似文献   
997.
998.
随着公路系统的新陈代谢,大量废弃物给城市的资源与环境协调发展带来了巨大压力,以沥青路面再生技术为路径的公路废弃物资源化符合循环经济的理念,是我国公路建设迈向生态文明的必然选择。通过 ANP-SWOT 对上海公路废弃物资源化发展战略进行实证分析,发现当前形势下其优势和机遇较为明显,确定以 SO 策略为核心的推广战略为最佳选择,并提出一系列配套发展策略,为推动上海公路废弃物资源化提供参考。  相似文献   
999.
Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards.  相似文献   
1000.
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