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   356738篇
  免费   8984篇
  国内免费   3497篇
电工技术   8832篇
技术理论   6篇
综合类   4566篇
化学工业   56595篇
金属工艺   15708篇
机械仪表   13357篇
建筑科学   11868篇
矿业工程   4206篇
能源动力   8923篇
轻工业   30150篇
水利工程   4158篇
石油天然气   12268篇
武器工业   476篇
无线电   38846篇
一般工业技术   65904篇
冶金工业   55017篇
原子能技术   8259篇
自动化技术   30080篇
  2021年   4842篇
  2020年   3728篇
  2019年   3831篇
  2018年   5888篇
  2017年   6069篇
  2016年   5937篇
  2015年   5128篇
  2014年   7626篇
  2013年   16149篇
  2012年   11118篇
  2011年   13994篇
  2010年   11693篇
  2009年   12542篇
  2008年   12721篇
  2007年   12474篇
  2006年   11576篇
  2005年   10698篇
  2004年   9031篇
  2003年   8608篇
  2002年   8473篇
  2001年   8104篇
  2000年   7957篇
  1999年   8243篇
  1998年   16458篇
  1997年   12392篇
  1996年   9937篇
  1995年   7681篇
  1994年   6845篇
  1993年   6478篇
  1992年   5007篇
  1991年   4850篇
  1990年   4545篇
  1989年   4455篇
  1988年   4388篇
  1987年   3666篇
  1986年   3651篇
  1985年   4173篇
  1984年   3958篇
  1983年   3588篇
  1982年   3407篇
  1981年   3522篇
  1980年   3396篇
  1979年   3319篇
  1978年   3409篇
  1977年   3874篇
  1976年   4996篇
  1975年   3119篇
  1974年   2969篇
  1973年   2988篇
  1972年   2623篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
2.
3.
The effects of cellulose microfibres (CMFs, Average size: 100 ± 5 μm) and cellulose nanofibres (CNFs, Average size: 60 ± 3 nm) on the properties of myofibrillar protein (MP) gels from duck breast meat were studied. The results demonstrated that CMFs and CNFs were mostly connected to MP by non-covalent bonds, the diffusion and cross-linking of MP molecules was promoted, and a denser and more complete gel network was formed. With the increases of CMFs and CNFs concentration (0–10%), the hardness was increased by 13.15% and 19.78% for CMFs10% and CNFs10% gels, respectively, and the elasticity was increased by 40% and 80%, respectively. At the same concentration (0–10%), the increase in gel hardness, viscoelasticity and immobilised water content was greater in the CNFs-MP group than in the CMFs-MP group. The CNFs-MP group had a tighter gel network, and CNFs had a better potential to improve the gelation performance of MP.  相似文献   
4.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  相似文献   
5.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
6.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
7.
A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices.  相似文献   
8.
9.
Sun  Junli  Wang  Huaibin  Li  Yang  Zhao  Min 《Journal of Porous Materials》2021,28(3):889-894
Journal of Porous Materials - Co3O4 has been widely investigated as a promising candidate anode material for lithium-ion batteries. We report on the porous Co3O4 column synthesized via a simple...  相似文献   
10.
Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO3-xBi(Ni2/3Nb1/3)O3(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni0·5Nb0.5)O3 boosts the insulation ability, thus obtaining a high breakdown strength (Eb) of 440 kV/cm in xBNN ceramics. A high energy storage density (Wtotal) of 4.09 J/cm3, recoverable energy storage density (Wrec) of 3.31 J/cm3, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of Wrec ≤ 0.4% over 5–100 Hz and Wrec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm3) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.  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