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   2324篇
  免费   113篇
  国内免费   8篇
电工技术   23篇
综合类   3篇
化学工业   582篇
金属工艺   33篇
机械仪表   49篇
建筑科学   81篇
矿业工程   5篇
能源动力   95篇
轻工业   249篇
水利工程   37篇
石油天然气   10篇
无线电   176篇
一般工业技术   331篇
冶金工业   270篇
原子能技术   14篇
自动化技术   487篇
  2024年   5篇
  2023年   33篇
  2022年   92篇
  2021年   116篇
  2020年   78篇
  2019年   65篇
  2018年   69篇
  2017年   75篇
  2016年   79篇
  2015年   79篇
  2014年   66篇
  2013年   152篇
  2012年   155篇
  2011年   157篇
  2010年   105篇
  2009年   113篇
  2008年   99篇
  2007年   101篇
  2006年   92篇
  2005年   78篇
  2004年   65篇
  2003年   43篇
  2002年   53篇
  2001年   28篇
  2000年   16篇
  1999年   29篇
  1998年   60篇
  1997年   42篇
  1996年   30篇
  1995年   23篇
  1994年   20篇
  1993年   19篇
  1992年   12篇
  1991年   18篇
  1990年   9篇
  1989年   20篇
  1988年   12篇
  1987年   15篇
  1986年   13篇
  1985年   7篇
  1984年   11篇
  1983年   10篇
  1981年   10篇
  1980年   15篇
  1979年   4篇
  1977年   4篇
  1976年   11篇
  1975年   4篇
  1974年   7篇
  1972年   4篇
排序方式: 共有2445条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs is a major goal in repair medicine. Stem cells are classified by their potential to differentiate into functional cells. Compared with other sources, adipose-derived stem cells (ADSCs) have the advantage of being abundant and easy to obtain. ADSCs are considered to be tools for replacing, repairing, and regenerating dead or damaged cells. The capacity of ADSCs to maintain their properties depends on the balance of complex signals in their microenvironment. Their properties and the associated outcomes are in part regulated by reactive oxygen species, which mediate the oxidation-reduction state of cells as a secondary messenger. ADSC therapy has demonstrated beneficial effects, suggesting that secreted factors may provide protection. There is evidence that ADSCs secrete a number of cytokines, growth factors, and antioxidant factors into their microenvironment, thus regulating intracellular signaling pathways in neighboring cells. In this review, we introduce the roles of ADSCs in the protection of cells by modulating inflammation and immunity, and we develop their potential therapeutic properties.  相似文献   
5.
In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ r =3.80), crystal quartz (∈ r =4.53), silicon (∈ r =11.9) and GaAs (∈ r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies.  相似文献   
6.
7.
A micromechanics analysis is performed for the determination of the five independent elastic moduli of unidirectional fiber composites. By considering viscoelastic phases and by using the correspondence principle and the inversion of the Laplace transform, the five time-dependent functions which characterize the effective behavior of viscoelastic composites are established. The predicted time-dependent behavior is applied for the analysis of viscoelastic laminated plates. The resulting viscoelastic effects are shown, and comparison between the results obtained within the classical laminated plate theory and the first-order shear deformation theory is discussed.  相似文献   
8.
Gabriel Wainer 《Software》2002,32(13):1261-1306
The features of a toolkit for modeling and simulation based on the DEVS formalism are presented. The tool is built as a set of independent software pieces running on different platforms. Not only are the main characteristics of the environment presented, a focus on its use is also considered by inclusion of application examples for a variety of problems. Many models can be defined in an automated fashion, simplifying the construction of new models and easing their verification. The use of this formal approach has allowed the development of safe and cost‐effective simulations, significantly reducing development time. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
9.
10.
We present an algorithm for detecting periodicity in sequences produced by repeated application of a given function. Our algorithm uses logarithmic memory with high probability, runs in linear time, and is guaranteed to stop within the second loop through the cycle. We also present a partitioning technique that offers a time/memory tradeoff. Our algorithm is especially well suited for sequences where the cycle length is typically small compared to the length of the acyclic prefix.  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