全文获取类型
收费全文 | 1757159篇 |
免费 | 42475篇 |
国内免费 | 14381篇 |
专业分类
电工技术 | 45265篇 |
技术理论 | 14篇 |
综合类 | 17279篇 |
化学工业 | 305160篇 |
金属工艺 | 74727篇 |
机械仪表 | 56262篇 |
建筑科学 | 63309篇 |
矿业工程 | 16399篇 |
能源动力 | 55555篇 |
轻工业 | 132034篇 |
水利工程 | 19245篇 |
石油天然气 | 48033篇 |
武器工业 | 1477篇 |
无线电 | 219758篇 |
一般工业技术 | 317688篇 |
冶金工业 | 208380篇 |
原子能技术 | 36215篇 |
自动化技术 | 197215篇 |
出版年
2022年 | 14061篇 |
2021年 | 23065篇 |
2020年 | 17261篇 |
2019年 | 19268篇 |
2018年 | 22353篇 |
2017年 | 22647篇 |
2016年 | 27419篇 |
2015年 | 24395篇 |
2014年 | 37708篇 |
2013年 | 99094篇 |
2012年 | 49001篇 |
2011年 | 64192篇 |
2010年 | 55052篇 |
2009年 | 62715篇 |
2008年 | 57255篇 |
2007年 | 54487篇 |
2006年 | 56079篇 |
2005年 | 50135篇 |
2004年 | 48774篇 |
2003年 | 47938篇 |
2002年 | 45990篇 |
2001年 | 42991篇 |
2000年 | 41335篇 |
1999年 | 41919篇 |
1998年 | 62071篇 |
1997年 | 50193篇 |
1996年 | 43214篇 |
1995年 | 36190篇 |
1994年 | 33212篇 |
1993年 | 32548篇 |
1992年 | 27995篇 |
1991年 | 24912篇 |
1990年 | 24958篇 |
1989年 | 23848篇 |
1988年 | 22343篇 |
1987年 | 20321篇 |
1986年 | 19661篇 |
1985年 | 22899篇 |
1984年 | 22768篇 |
1983年 | 20694篇 |
1982年 | 19567篇 |
1981年 | 19701篇 |
1980年 | 18289篇 |
1979年 | 18724篇 |
1978年 | 17915篇 |
1977年 | 18057篇 |
1976年 | 19498篇 |
1975年 | 16141篇 |
1974年 | 15611篇 |
1973年 | 15750篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
The present study was aimed to utilize low‐cost alumina (Al2O3) nanoparticles for improving the heat transfer behavior in an intercooler of two‐stage air compressor. Experimental investigation was carried out with three different volume concentrations of 0.5%, 0.75%, and 1.0% Al2O3/water nanofluids to assess the performance of the intercooler, that is, counterflow heat exchanger at different loads. Thermal properties such as thermal conductivity and overall heat transfer coefficient of nanofluid increased substantially with increasing concentration of Al2O3 nanoparticles. Specific heat capacity of nanofluids were lower than base water. The intercooler performance parameters such as effectiveness and efficiency improved appreciably with the employment of nanofluid. The efficiency increased by about 6.1% with maximum concentration of nanofluid, that is, 1% at 3‐bar compressor load. It is concluded from the study that high concentration of Al2O3 nanoparticles dispersion in water would offer better heat transfer performance of the intercooler. 相似文献
993.
994.
Gorkunov E. S. Povolotskaya A. M. Zadvorkin S. M. 《Russian Journal of Nondestructive Testing》2018,54(12):861-870
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
995.
Konstantin V. Dergilev Evgeny K. Shevchenko Zoya I. Tsokolaeva Irina B. Beloglazova Ekaterina S. Zubkova Maria A. Boldyreva Mikhail Yu. Menshikov Elizaveta I. Ratner Dmitry Penkov Yelena V. Parfyonova 《International journal of molecular sciences》2020,21(24)
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
996.
Ana Rita Gomes Nasim Bahram Sangani Tiago G. Fernandes M. Margarida Diogo Leopold M. G. Curfs Chris P. Reutelingsperger 《International journal of molecular sciences》2020,21(24)
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
997.
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
998.
Tseluikin V. N. Yakovlev A. V. 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(2):374-378
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
999.
Brusov V. S. Korchagin P. O. Malyshev V. V. Piyavsky S. A. 《Journal of Computer and Systems Sciences International》2020,59(1):83-94
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
1000.
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