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   591887篇
  免费   8464篇
  国内免费   1103篇
电工技术   10788篇
综合类   701篇
化学工业   95071篇
金属工艺   23857篇
机械仪表   19080篇
建筑科学   13544篇
矿业工程   4404篇
能源动力   15270篇
轻工业   49779篇
水利工程   7184篇
石油天然气   15111篇
武器工业   49篇
无线电   62046篇
一般工业技术   119682篇
冶金工业   100904篇
原子能技术   14841篇
自动化技术   49143篇
  2021年   6515篇
  2020年   4642篇
  2019年   5938篇
  2018年   9976篇
  2017年   10232篇
  2016年   10620篇
  2015年   6699篇
  2014年   11185篇
  2013年   27607篇
  2012年   17066篇
  2011年   22667篇
  2010年   18103篇
  2009年   19984篇
  2008年   20161篇
  2007年   19716篇
  2006年   17018篇
  2005年   15495篇
  2004年   14827篇
  2003年   14439篇
  2002年   13956篇
  2001年   13457篇
  2000年   12745篇
  1999年   12401篇
  1998年   29147篇
  1997年   21025篇
  1996年   16335篇
  1995年   12483篇
  1994年   11235篇
  1993年   11035篇
  1992年   8505篇
  1991年   8310篇
  1990年   8169篇
  1989年   7911篇
  1988年   7664篇
  1987年   6888篇
  1986年   6678篇
  1985年   7535篇
  1984年   6800篇
  1983年   6519篇
  1982年   5881篇
  1981年   5997篇
  1980年   5738篇
  1979年   5805篇
  1978年   5729篇
  1977年   6290篇
  1976年   7870篇
  1975年   5171篇
  1974年   4931篇
  1973年   5019篇
  1972年   4305篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations.  相似文献   
12.
Water Resources Management - The water evaluation and planning (WEAP) approach and the invasive weed optimization algorithm (IWOA) are herein employed to determine the optimal operating policies in...  相似文献   
13.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  相似文献   
14.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
15.
Glass and Ceramics - Ceramic bricks based on low-melting clay and ferro-dust from self-disintegrating, low-carbon, ferrochrome slags, graded from M100 to M175, respectively, were obtained in the...  相似文献   
16.
This work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X-ray fluorescence, loss on ignition (LOI), X-ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre-sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X-ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.  相似文献   
17.
Automation and Remote Control - A linear-quadratic positional differential game of three persons is considered. Coefficient criteria are established under which there is no Nash equilibrium...  相似文献   
18.
19.
Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC.  相似文献   
20.
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa.  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