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   1559765篇
  免费   27762篇
  国内免费   6971篇
电工技术   34583篇
综合类   6452篇
化学工业   272445篇
金属工艺   64966篇
机械仪表   44180篇
建筑科学   47339篇
矿业工程   11552篇
能源动力   50388篇
轻工业   119850篇
水利工程   15695篇
石油天然气   37834篇
武器工业   150篇
无线电   197942篇
一般工业技术   292112篇
冶金工业   193379篇
原子能技术   34234篇
自动化技术   171397篇
  2021年   15534篇
  2020年   11950篇
  2019年   14690篇
  2018年   17157篇
  2017年   16484篇
  2016年   22055篇
  2015年   17544篇
  2014年   28788篇
  2013年   88084篇
  2012年   37059篇
  2011年   50643篇
  2010年   43930篇
  2009年   51842篇
  2008年   46918篇
  2007年   44294篇
  2006年   45875篇
  2005年   40874篇
  2004年   42778篇
  2003年   42525篇
  2002年   41360篇
  2001年   38518篇
  2000年   36727篇
  1999年   36376篇
  1998年   54833篇
  1997年   45154篇
  1996年   39056篇
  1995年   32875篇
  1994年   30511篇
  1993年   30462篇
  1992年   26680篇
  1991年   23775篇
  1990年   24072篇
  1989年   23157篇
  1988年   21650篇
  1987年   19918篇
  1986年   19232篇
  1985年   22544篇
  1984年   22508篇
  1983年   20452篇
  1982年   19442篇
  1981年   19611篇
  1980年   18201篇
  1979年   18621篇
  1978年   17908篇
  1977年   18074篇
  1976年   19711篇
  1975年   16070篇
  1974年   15543篇
  1973年   15659篇
  1972年   13122篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
811.
In this study, we have proposed an automated classification approach to identify meaningful patterns in wind field data. Utilizing an extensive simulated wind database, we have demonstrated that the proposed approach can identify low‐level jets, near‐uniform profiles, and other patterns in a reliable manner. We have studied the dependence of these wind profile patterns on locations (eg, offshore vs onshore), seasons, and diurnal cycles. Furthermore, we have found that the probability distributions of some of the patterns depend on the underlying planetary boundary layer schemes in a significant way. The future potential of the proposed approach in wind resource assessment and, more generally, in mesoscale model parameterization improvement is touched upon in this paper.  相似文献   
812.
813.
A methodology for estimation of the limit energy characteristics of volumetric pneumatic motors based on the Parameter Space Investigation method and a generalized mathematical model in dimensionless (normalized) form taking into account the dynamics of working processes is proposed. A calculated example is presented. The methodology is applicable for determination of the limit energy characteristics of newly created design solutions, of prospects to improve the known designs of pneumatic motors, of evaluation of energy capacity of several pneumatic motors supplied from a single source of compressed air, and of the initial data preparation for parametric synthesis of rotational pneumatic drives for two or more robots taking into account their interaction.  相似文献   
814.
Russian Journal of Nondestructive Testing - Comparative analysis of the distribution of magnetic-induction vector components over the volume of a bulk homogeneous sample of 40Kh steel has been...  相似文献   
815.
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function.  相似文献   
816.
The central nervous system (CNS) is the most complex structure in the body, consisting of multiple cell types with distinct morphology and function. Development of the neuronal circuit and its function rely on a continuous crosstalk between neurons and non-neural cells. It has been widely accepted that extracellular vesicles (EVs), mainly exosomes, are effective entities responsible for intercellular CNS communication. They contain membrane and cytoplasmic proteins, lipids, non-coding RNAs, microRNAs and mRNAs. Their cargo modulates gene and protein expression in recipient cells. Several lines of evidence indicate that EVs play a role in modifying signal transduction with subsequent physiological changes in neurogenesis, gliogenesis, synaptogenesis and network circuit formation and activity, as well as synaptic pruning and myelination. Several studies demonstrate that neural and non-neural EVs play an important role in physiological and pathological neurodevelopment. The present review discusses the role of EVs in various neurodevelopmental disorders and the prospects of using EVs as disease biomarkers and therapeutics.  相似文献   
817.
Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano‐biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles—from self‐assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models.  相似文献   
818.
Protection of Metals and Physical Chemistry of Surfaces - Nickel-based composite electrochemical coatings (CECs) modified with graphite nitrate have been obtained. Their microstructure and...  相似文献   
819.
Journal of Computer and Systems Sciences International - The article considers the problem of making multicriteria decisions in which the decision maker (DM) has the opportunity to indicate the...  相似文献   
820.
Wan  Huan  Wang  Hui  Scotney  Bryan  Liu  Jun  Ng  Wing W. Y. 《Multimedia Tools and Applications》2020,79(39-40):29327-29352
Multimedia Tools and Applications - In many real-world classification problems there exist multiple subclasses (or clusters) within a class; in other words, the underlying data distribution is...  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