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   225396篇
  免费   4053篇
  国内免费   660篇
电工技术   4292篇
综合类   146篇
化学工业   32585篇
金属工艺   8026篇
机械仪表   5972篇
建筑科学   4957篇
矿业工程   805篇
能源动力   5343篇
轻工业   19230篇
水利工程   2000篇
石油天然气   2951篇
武器工业   14篇
无线电   28647篇
一般工业技术   41839篇
冶金工业   50681篇
原子能技术   3699篇
自动化技术   18922篇
  2021年   2083篇
  2020年   1525篇
  2019年   1973篇
  2018年   3251篇
  2017年   3188篇
  2016年   3315篇
  2015年   2306篇
  2014年   3719篇
  2013年   9953篇
  2012年   6197篇
  2011年   7815篇
  2010年   6243篇
  2009年   7032篇
  2008年   7375篇
  2007年   7325篇
  2006年   6442篇
  2005年   6009篇
  2004年   5893篇
  2003年   5658篇
  2002年   5427篇
  2001年   5667篇
  2000年   5262篇
  1999年   5843篇
  1998年   17424篇
  1997年   11456篇
  1996年   8698篇
  1995年   6191篇
  1994年   5356篇
  1993年   5416篇
  1992年   3522篇
  1991年   3405篇
  1990年   3335篇
  1989年   3161篇
  1988年   2888篇
  1987年   2322篇
  1986年   2395篇
  1985年   2719篇
  1984年   2380篇
  1983年   2118篇
  1982年   1981篇
  1981年   2142篇
  1980年   1868篇
  1979年   1700篇
  1978年   1692篇
  1977年   2144篇
  1976年   2939篇
  1975年   1447篇
  1974年   1392篇
  1973年   1348篇
  1972年   1142篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
92.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
93.
Growing evidence is showing that acetylation plays an essential role in cancer, but studies on the impact of KDAC inhibition (KDACi) on the metabolic profile are still in their infancy. Here, we analyzed, by using an iTRAQ-based quantitative proteomics approach, the changes in the proteome of KRAS-mutated non-small cell lung cancer (NSCLC) A549 cells in response to trichostatin-A (TSA) and nicotinamide (NAM) under normoxia and hypoxia. Part of this response was further validated by molecular and biochemical analyses and correlated with the proliferation rates, apoptotic cell death, and activation of ROS scavenging mechanisms in opposition to the ROS production. Despite the differences among the KDAC inhibitors, up-regulation of glycolysis, TCA cycle, oxidative phosphorylation and fatty acid synthesis emerged as a common metabolic response underlying KDACi. We also observed that some of the KDACi effects at metabolic levels are enhanced under hypoxia. Furthermore, we used a drug repositioning machine learning approach to list candidate metabolic therapeutic agents for KRAS mutated NSCLC. Together, these results allow us to better understand the metabolic regulations underlying KDACi in NSCLC, taking into account the microenvironment of tumors related to hypoxia, and bring new insights for the future rational design of new therapies.  相似文献   
94.
Wireless Personal Communications - The majority of security systems for wireless sensor networks are based on symmetric encryption. The main open issue for these approaches concerns the...  相似文献   
95.
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions.  相似文献   
96.
97.
98.
99.
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films.  相似文献   
100.
The potential of time‐domain nuclear magnetic resonance (TD‐NMR) for the real‐time monitoring of solution radical polymerizations is demonstrated. A model system composed of a redox‐pair initiator system, acrylamide as monomer and water as solvent was investigated. A second‐generation continuous wave free precession technique was employed to measure the longitudinal relaxation time constant (T1) of the samples throughout the polymerization reactions. This parameter was shown to be sensitive to the reactant feed free‐radical enhancement of the water molecule relaxation time, making it a good probe to monitor monomer conversion in real time in an automated, non‐destructive fashion. It was found that the T1 value was better than the transverse relaxation time constant (T2) for describing the evolution of the polymerization reactions, due to its greater sensitivity to paramagnetic effects. The TD‐NMR signal variation observed was linked to the formation, propagation and termination steps of the radical polymerization kinetics scheme. These first results may contribute to the application of real‐time monitoring of radical polymerization reactions employing low‐cost and robust TD‐NMR spectrometers. © 2018 Society of Chemical Industry  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