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   33574篇
  免费   2483篇
  国内免费   1260篇
电工技术   1668篇
综合类   990篇
化学工业   10146篇
金属工艺   1142篇
机械仪表   1369篇
建筑科学   454篇
矿业工程   217篇
能源动力   7988篇
轻工业   3295篇
水利工程   54篇
石油天然气   122篇
武器工业   53篇
无线电   3275篇
一般工业技术   3577篇
冶金工业   958篇
原子能技术   463篇
自动化技术   1546篇
  2024年   108篇
  2023年   864篇
  2022年   2822篇
  2021年   3015篇
  2020年   1530篇
  2019年   1403篇
  2018年   1072篇
  2017年   1258篇
  2016年   1206篇
  2015年   1123篇
  2014年   1839篇
  2013年   2072篇
  2012年   1959篇
  2011年   2759篇
  2010年   2019篇
  2009年   1715篇
  2008年   1737篇
  2007年   1607篇
  2006年   1305篇
  2005年   1068篇
  2004年   844篇
  2003年   638篇
  2002年   621篇
  2001年   491篇
  2000年   380篇
  1999年   300篇
  1998年   280篇
  1997年   223篇
  1996年   185篇
  1995年   163篇
  1994年   138篇
  1993年   112篇
  1992年   86篇
  1991年   64篇
  1990年   52篇
  1989年   49篇
  1988年   37篇
  1987年   25篇
  1986年   26篇
  1985年   30篇
  1984年   18篇
  1983年   13篇
  1982年   13篇
  1981年   10篇
  1980年   15篇
  1979年   7篇
  1978年   3篇
  1976年   2篇
  1975年   2篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
铝电解槽磁流体稳定性有限元分析   总被引:2,自引:0,他引:2  
本文采用有限元法求解分层磁流体小扰动方程系统特征值,研究铝电解槽稳定性。研究结果表明,在没有电磁力时,铝液表面波动(内波)是稳定的。存在电磁力时,它会激发铝液表面波动的某些低频长波分量不稳定性,高频短波不受影响。被激发的不稳定波动频率和扰动增长率与电流密度,磁感应强度垂直分量,铝电解槽长宽比,电解质和铝液的密度差,厚度等因素密切相关。减少电流密度,磁感应强度,增加电极距离和铝液厚度可以提高铝电解槽的稳定性。这对铝电解槽优化设计和在线控制有重要意义。  相似文献   
22.
Cation-doped CeO2 electrolyte has been evaluated in single-cell and short-stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ∼0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm2. Multicell stacks have demonstrated a peak performance of >100 mW/cm2 at 700°C using metallic separators.  相似文献   
23.
This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material.  相似文献   
24.
The newly developed ingot growing techniques, as the three-grain and the columnar multigrain ingot processes, are now offering the possibility of slicing thinner wafers (≤ 100 μm). In this paper we present the results obtained on p type large area (≥ 100 cm2) and 100 μm thick wafers by using both conventional and reverse cell manufacturing technologies.The conventional cells are provided with aluminium or boron BSF plus screen-printed silver mirror or a silver-aluminium net; the reverse cells have a FSF and the deep back junction completely covered by a screen-printed or CVD silver layer.The constructing parameters have been chosen on the base of one and two dimensions modeling and both raw material and devices have been completely characterized.This work shows that very thin wafers do not introduce serious problems for the conventional manufacturing of solar cells. The efficiencies of the normal and of the reverse cells are found to be comparable and are of the same order than those of thicker cells, however at a significant lower cost. The main obtained result has to be related to the demonstration of a cell manufacturing feasibility starting from very thin wafers.  相似文献   
25.
本文从无线电通信基本要素出发 ,阐述上行信号和下行信号的无线传播 ,得出上下行信号平衡链路方程 ,并以我国普遍使用的TACS系统和GSM系统为例 ,着重讨论了信号平衡与蜂窝小区设计之间的关系。  相似文献   
26.
乳腺癌中着丝粒蛋白CenpG的差异表达   总被引:4,自引:0,他引:4  
用间接免疫荧光(IIF)验证了着丝粒蛋白CenpG的一种抗血清;通过对31例乳腺癌组织块及每一例病人的癌旁正常(非癌性)组织块蛋白提取物进行免疫印迹(Western blot)分析,发现多数情况下(71%)癌组织中着丝粒蛋白CenpG(95kD)过表达;在两例乳腺癌组织中还发现了一种能被CenpG抗血清识别的43kD蛋白质成分。结果表明,新近发现和命名的CenpG(或者还有其他相关成分)的差异表达可能与细胞恶性增殖有关。  相似文献   
27.
简要地叙述了国内外乙醇电催化氧化的研究进展,着重介绍不同电极材料对乙醇电氧化的影响及目前所提山的机理,并对其可能的研究方向提出了建议。  相似文献   
28.
To study cell-cycle-related variations in wall permeability of Saccharomyces cerevisiae, two approaches were used. First, an asynchronous culture was fractionated by centrifugal elutriation into subpopulations containing cells of increasing size. The subpopulations represented different stages of the cell cycle as judged by light microscopy. Cell wall porosity increased when these subpopulations became enriched with budded cells. Secondly, synchronous cultures were obtained by releasing MATa cells from alpha-factor induced G1-arrest. These cultures grew synchronously for at least two generations. The cell wall porosity increased sharply in these cultures, shortly before buds became visible and was maximal during the initial stages of bud growth. It decreased in cells which had completed nuclear migration and before abscission of the bud had occurred. The porosity reached its lowest value during abscission and in unbudded cells. We examined the incorporation of mannoproteins into the wall during the cell cycle. SDS-extractable mannoproteins were incorporated continuously. However, the incorporation of glucanase-extractable mannoproteins, which are known to affect cell wall porosity, showed cyclic oscillations and reached its maximum after nuclear migration. This coincided with a rapid decrease in cell wall porosity, indicating that glucanase-extractable mannoproteins might contribute to this decrease.  相似文献   
29.
Vero细胞在微载体上迁移和多层生长现象   总被引:1,自引:1,他引:0  
本文通过对电子显微镜观察了Vero细胞有微载体增减过程中的迁移民政部发现在不同增减阶段,Vro细胞迁移方式不同;在分泌形成的细胞外基质,上,Vero细胞迁移是通过 层粘连蛋白介导进行的,被层粘连蛋白抗体抑制;这种迁移导致Vero细胞在微载体上形成多层生长现象。  相似文献   
30.
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