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   21910篇
  免费   2225篇
  国内免费   1226篇
电工技术   763篇
综合类   1587篇
化学工业   5780篇
金属工艺   1544篇
机械仪表   1229篇
建筑科学   914篇
矿业工程   511篇
能源动力   1213篇
轻工业   2124篇
水利工程   196篇
石油天然气   1118篇
武器工业   603篇
无线电   1243篇
一般工业技术   2718篇
冶金工业   984篇
原子能技术   301篇
自动化技术   2533篇
  2024年   37篇
  2023年   411篇
  2022年   492篇
  2021年   688篇
  2020年   714篇
  2019年   724篇
  2018年   636篇
  2017年   774篇
  2016年   783篇
  2015年   749篇
  2014年   1130篇
  2013年   1282篇
  2012年   1311篇
  2011年   1463篇
  2010年   1134篇
  2009年   1163篇
  2008年   1055篇
  2007年   1364篇
  2006年   1366篇
  2005年   1258篇
  2004年   1120篇
  2003年   909篇
  2002年   855篇
  2001年   702篇
  2000年   601篇
  1999年   455篇
  1998年   345篇
  1997年   319篇
  1996年   238篇
  1995年   213篇
  1994年   225篇
  1993年   155篇
  1992年   151篇
  1991年   112篇
  1990年   79篇
  1989年   71篇
  1988年   48篇
  1987年   35篇
  1986年   28篇
  1985年   39篇
  1984年   32篇
  1983年   28篇
  1982年   24篇
  1981年   8篇
  1980年   10篇
  1979年   10篇
  1978年   3篇
  1976年   3篇
  1975年   2篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
11.
《Ceramics International》2022,48(1):157-163
NASICON-type structured compounds Li1+xMxTi2-x(PO4)3 (M = Al, Fe, Y, etc.) have captured much attention due to their air stability, wide electrochemical window and high lithium ion conductivity. Especially, Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a potential solid electrolyte due to its high ionic conductivity. However, its actual density usually has a certain gap with the theoretical density, leading the poor ionic conductivity of LATP. Herein, LATP solid electrolyte with series of SnO–P2O5–MgO (SPM, 0.4 wt%, 0.7 wt%, 1.0 wt%, 1.3 wt%) glass addition was successfully synthesized to improve the density and ionic conductivity. The SPM addition change Al/Ti–O bond and P–O bond distances, leading to gradual shrinkage of octahedral AlO6 and tetrahedral PO4. The bulk conductivity of the samples increases gradually with SPM glass addition from 0.4 wt% to 1.3 wt%. Both SPM and the second-phase LiTiPO5, caused by glass addition, are conducive to the improvement of compactness. The relative density of LATP samples increases first from 0 wt% to 0.7 wt%, and then decreases from 0.7 wt% to 1.3 wt% with SPM glass addition. The grain boundary conductivity also changes accordingly. Especially, the highest ionic conductivity of 2.45 × 10?4 S cm?1, and a relative density of 96.72% with a low activation energy of 0.34 eV is obtained in LATP with 0.7 wt% SPM. Increasing the density of LATP solid electrolyte is crucial to improve the ionic conductivity of electrolytes and SPM glass addition can promote the development of dense oxide ceramic electrolytes.  相似文献   
12.
13.
井间是剩余油的主要分布区域,为探测井间剩余油,提高采收率,提出了基于全空间几何因子的瞬变电磁井间勘探方法。在本井使用线圈发射、邻井使用线圈接收,根据瞬变电磁场理论,在阶跃信号的激励下发射线圈在地层中激发出沿圆周方向的闭合瞬变电场,该电场在导电地层中产生与地层电导率呈正比的涡流。由Doll地层环模型可知,地层中的涡流在空间任意点激发得到与地层电导率成正比的二次场响应信号(有用信号),并可表示为空间各点电导率的加权平均值,其权重即为井间瞬变电磁勘探的全空间几何因子;全空间几何因子集中分布在发射线圈和接收线圈附近,其它区域分布较少,在发射线圈和接收线圈两侧呈现不同的极性;对瞬变电磁响应与地层电导率、井间距和源距的变化规律研究可知,瞬变电磁井间勘探有用信号随着地层电导率的增大而增大,随着井间距的增加单调减小,在发射线圈和接收线圈处于同一深度时该响应信号幅度最大。  相似文献   
14.
The aim of the present study was to improve the dissolution and flow properties of lurasidone hydrochloride (LH) by solid dispersion adsorbate (SDA) technique. Solid dispersions (SDs) of LH were prepared by fusion method using Poloxamer P188. The melt dispersion was adsorbed onto the porous carrier Florite (calcium silicate). A 32 factorial design was employed to quantify the effect of two independent variables, namely ratio of carrier (Poloxamer 188) and LH in SD and ratio of adsorbent (Florite) to SD. SDA granules of LH were studied for flow properties and characterized using differential scanning calorimetry, scanning electron microscopy, and X-ray diffraction. Tablets of optimized composition of SDA granules (equivalent to 20?mg of drug) and plain tablets were prepared by direct compression method. The dissolution studies were carried out in Mcllvaine buffer (pH 3.8) as per USFDA guidelines and characterized for parameters such as percent dissolution efficiency, t50, and Q30. Tablets prepared from SDA granules showed almost four-fold increase in cumulative percentage drug release as compared to tablets prepared from plain LH. The value of dissolution efficiency was enhanced from 49.60% for plain tablets to 94.15% for SDA tablets. SDA granules did not show any change in drug release and X-ray diffraction pattern after storage at 40?°C/75% of RH for 3?months, which confirms that Florite prevented conversion of drug from amorphous form to crystalline form improving physical stability of the amorphous state of LH.  相似文献   
15.
Solid oxide fuel cell (SOFC) systems with anode off-gas recirculation (AGR) and diesel pre-reforming are advantageous because they can operate with the current fuel infrastructure. In the SchIBZ-project, the prototype of such a SOFC system for maritime applications has already been commissioned. In this first paper, we model the system devices to conduct an exergy analysis of this real SOFC plant and validate them with experimental values from experiments in laboratory scale. The results of our simulation agree well with the experimental values. The calculations with the validated results may be closer to the real thermodynamic behavior of such system components than previous literature.  相似文献   
16.
通过物理化学相分析研究了3种不同氮含量镀锡板中固溶氮、化合氮的含量,结合相关理论计算了镀锡板中氮的固溶强化和析出强化对强度的贡献。结果表明:随着总氮含量从0.0021%提高到0.0103%,钢中化合氮含量下降10.1%,但是AlN析出相中的氮的含量上升10.7%。氮在提高镀锡板强度方面发挥重要作用,钢中总氮含量提高0.0082%,其对屈服强度的贡献值提升约30 MPa。  相似文献   
17.
综述了有色金属工业砷污染物的来源及其无害化处理的方法,分析了包封固砷(水泥固化和玻璃固化)和矿物固砷(钙盐、铝盐、镁盐、硫化沉淀法)的优缺点和局限性,重点对将砷以臭葱石形式进行安全处理的合成方法和浸出稳定性的研究现状进行阐述。分析表明,晶态臭葱石合成是将砷以臭葱石形式进行安全处置的基础,稳定性是关键,进一步降低溶液过饱和度以实现大尺寸、高稳定性臭葱石的合成是发展方向。  相似文献   
18.
针对未考虑正偏心正交车铣切削层几何形状而导致难以全面反映正交车铣切削层几何形状变化规律的问题,基于正交车铣运动规律,在不考虑动力学影响的情况下,对切削层的形成过程进行了静态分析。建立的正偏心正交车铣切削层几何形状的解析模型涉及铣刀侧刃和底刃的切入/切出角度、切削厚度和切削深度。通过试验验证了该解析模型的正确性,并分析了切削参数对铣刀切削层的影响。研究结果为正偏心正交车铣切削层几何形状的变化提供了定量的分析依据,为切削力和颤振的研究提供了理论指导。  相似文献   
19.
Solid solution-strengthened ductile iron (DI) exhibits outstanding mechanical properties due to the high silicon content. The strengthening by silicon addition is limited since additions above 4.3?wt-% lead to embrittlement. For a further improvement of mechanical properties, other alloying elements need to be considered. In the present work, the effect of various copper additions on the microstructure and the mechanical properties of solid solution-strengthened DI were investigated. The results show that no appreciable strengthening can be achieved by copper addition without the formation of pearlite in the matrix. The pearlite content increases considerably for Cu-additions above 0.23?wt-% and is independent of the cooling rate for the cooling conditions analysed.  相似文献   
20.
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