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   2542篇
  免费   73篇
  国内免费   5篇
电工技术   32篇
综合类   4篇
化学工业   625篇
金属工艺   80篇
机械仪表   62篇
建筑科学   45篇
能源动力   103篇
轻工业   76篇
水利工程   19篇
石油天然气   2篇
无线电   501篇
一般工业技术   408篇
冶金工业   262篇
原子能技术   21篇
自动化技术   380篇
  2023年   8篇
  2022年   37篇
  2021年   48篇
  2020年   19篇
  2019年   27篇
  2018年   41篇
  2017年   34篇
  2016年   47篇
  2015年   42篇
  2014年   83篇
  2013年   206篇
  2012年   134篇
  2011年   149篇
  2010年   136篇
  2009年   153篇
  2008年   148篇
  2007年   112篇
  2006年   107篇
  2005年   91篇
  2004年   82篇
  2003年   70篇
  2002年   67篇
  2001年   50篇
  2000年   48篇
  1999年   51篇
  1998年   105篇
  1997年   67篇
  1996年   56篇
  1995年   38篇
  1994年   38篇
  1993年   29篇
  1992年   32篇
  1991年   21篇
  1990年   20篇
  1989年   26篇
  1988年   18篇
  1987年   17篇
  1985年   18篇
  1984年   17篇
  1983年   11篇
  1982年   9篇
  1981年   9篇
  1980年   9篇
  1979年   11篇
  1978年   5篇
  1977年   15篇
  1976年   12篇
  1975年   13篇
  1973年   8篇
  1967年   5篇
排序方式: 共有2620条查询结果,搜索用时 15 毫秒
11.
Previous studies on business simulation games (BSGs) have concluded that improved performance may not be the primary benefit of using BSGs, due to mixed results between student performance and perceptions. Two relevant and insightful issues attract our attention, namely, the impacts of the heterogeneous student population and the different complexity levels of BSG software. To address these issues, the present study aims to understand the relationship between student profile/characteristics and performance in the classroom with BSG-facilitated learning. An in-depth case study is conducted on a general college course designed to teach three different complexities of BSGs to students enrolled in different majors. Four student profile factors are individually tested for differences in performance scores as evaluated by the teacher. Additionally, the influences of 11 student characteristics are assessed with regard their self-reported perceived learning performances. Regression analysis and ANOVA are used to investigate the impacts of heterogeneous users and game complexity on student performance. Based on the regression analyses of the data collected from 43 respondents who participated in the general course, the study concludes that knowledge and skill may influence the heterogeneous student population; moreover, student participation and tacit learning preference improve performance, and students with an auditory learning preference or high learning motivation may not perform well in classroom BSG learning. However, the low value of adjusted R square implies that more dimensions or variables are needed to increase the explaining power of the performance scores in the regression analyses. In contrast, heterogeneous BSG software with different complexity levels present different results. The current research contributes practical and incremental knowledge on the complexity of heterogeneous BSG software on performance scores and the perceived learning performance of heterogeneous student populations. With the research limitations acknowledged, a series of suggestions for teachers pertaining to appropriate applications of BSGs in classes is offered as well as recommendations to BSG providers. Nevertheless, in-depth analyses are required, preferably with larger student population samples, to further explore the insignificant relationship between student perceptions and attitude under nonlinear extended complexity.  相似文献   
12.
Dihydroxyalcohols (DIOL route) and 2-methoxyethanol (MOE route) are two of the most commonly used solvents in preparing sol-gel lead zirconate titanate (PZT) films. The employment of the PT(MOE) film as a buffer layer for PZT(DIOL) films not only offers advantages of more precise film thickness and better adhesion to substrate, but also reduces the crystallization temperature, improves the surface smoothness, and increases the grain size of the PZT(DIOL)/PT(MOE) composite films. The PT (MOE) buffer layer also improves electrical properties, such as polarization-electric field behavior, fatigue endurance, and leakage behavior, of PZT films.  相似文献   
13.
14.
15.
对于可持续时尚的理解不仅反映了消费端的价值观,也引导着品牌发展的方向。2020年突如其来的疫情,让人们产生了更多思考。不再“报复式消费”,让可持续和经济繁荣共存,成为人们更加关注的焦点。  相似文献   
16.
Elevated levels of Mucin-16 (MUC16) in conjunction with a high expression of truncated O-glycans is implicated in playing crucial roles in the malignancy of pancreatic ductal adenocarcinoma (PDAC). However, the mechanisms by which such aberrant glycoforms present on MUC16 itself promote an increased disease burden in PDAC are yet to be elucidated. This study demonstrates that the CRISPR/Cas9-mediated genetic deletion of MUC16 in PDAC cells decreases tumor cell migration. We found that MUC16 enhances tumor malignancy by activating the integrin-linked kinase and focal adhesion kinase (ILK/FAK)-signaling axis. These findings are especially noteworthy in truncated O-glycan (Tn and STn antigen)-expressing PDAC cells. Activation of these oncogenic-signaling pathways resulted in part from interactions between MUC16 and integrin complexes (α4β1), which showed a stronger association with aberrant glycoforms of MUC16. Using a monoclonal antibody to functionally hinder MUC16 significantly reduced the migratory cascades in our model. Together, these findings suggest that truncated O-glycan containing MUC16 exacerbates malignancy in PDAC by activating FAK signaling through specific interactions with α4 and β1 integrin complexes on cancer cell membranes. Targeting these aberrant glycoforms of MUC16 can aid in the development of a novel platform to study and treat metastatic pancreatic cancer.  相似文献   
17.
A low-viscosity 60 SnO–40 P2O5 (mol%) glass was reheated at 280 °C (about 45 °C above the glass-transition temperature) for 20 min in various atmospheres (Ar, air, and O2), then the structure- and surface-related properties were examined. It was found that increase in textPtextO 2 {text{P}}_{{{text{O}}_{ 2} }} increases surface hardness, reduces optical transmittance, and improves chemical durability. The above phenomena are explained in terms of the increased oxidation tendency of Sn2+ to Sn4+ on the glass surface during reheating in increased textPtextO 2 {text{P}}_{{{text{O}}_{ 2} }} .  相似文献   
18.
In this investigation, we first propose and investigate a 40-Gb/s time-division-multiplexed passive optical network (TDM-PON) using four wavelength-multiplexed signals in both downstream and upstream traffic. Here, each downstream signal uses 10-Gb/s on–off keying (OOK) format encoded by a Mach–Zehnder modulator (MZM) in 1.5-$mu{hbox {m}}$ band. And each upstream channel utilizes the highly spectral efficient 10-Gb/s orthogonal frequency-division-multiplexing quadrature amplitude modulation (OFDM-QAM) generated by directly modulating a 1.3-$mu{hbox {m}}$ laser. Based on the proposed scheme, 40-Gb/s data traffic in a TDM-PON can be obtained easily by using four wavelength-multiplexed channels. In addition, the performance of the proposed PON architecture has also been discussed.   相似文献   
19.
Motivated by a variation of the channel assignment problem, a graph labeling analogous to the graph vertex coloring has been presented and is called an L(2,1)-labeling. More precisely, an L(2,1)-labeling of a graph G is a function f from the vertex set V(G) to the set of all nonnegative integers such that |f(x)-f(y)| /spl ges/ 2 if d(x,y)=1 and |f(x)-f(y)| /spl ges/ 1 if d(x,y) = 2. The L(2,1)-labeling number /spl lambda/(G) of G is the smallest number k such that G has an L(2,1)-labeling with max{f(v):v/spl isin/V(G)}=k. A conjecture states that /spl lambda/(G) /spl les/ /spl Delta//sup 2/ for any simple graph with the maximum degree /spl Delta//spl ges/2. This paper considers the graphs formed by the Cartesian product and the composition of two graphs. The new graph satisfies the conjecture above in both cases(with minor exceptions).  相似文献   
20.
In this paper, transient mechanical responses of the Cu/low-K structure during the impact stage of the wirebonding process were investigated. Parametric studies were carried out to examine the effect of elastic moduli of different constituent materials on the potential of structural defect on the copper via and the pad. The analysis applied the explicit time integration scheme, which is feasible in dealing with the nonlinear transient structural behavior.  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