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   1450519篇
  免费   26964篇
  国内免费   6906篇
电工技术   34043篇
综合类   6332篇
化学工业   266554篇
金属工艺   63490篇
机械仪表   40601篇
建筑科学   44945篇
矿业工程   11306篇
能源动力   50141篇
轻工业   105577篇
水利工程   14463篇
石油天然气   37378篇
武器工业   128篇
无线电   194386篇
一般工业技术   274495篇
冶金工业   140372篇
原子能技术   33844篇
自动化技术   166334篇
  2021年   15387篇
  2020年   11720篇
  2019年   14480篇
  2018年   14509篇
  2017年   13731篇
  2016年   20622篇
  2015年   17146篇
  2014年   28507篇
  2013年   87476篇
  2012年   33818篇
  2011年   45296篇
  2010年   41145篇
  2009年   49952篇
  2008年   42663篇
  2007年   39590篇
  2006年   43339篇
  2005年   37859篇
  2004年   40303篇
  2003年   40240篇
  2002年   39545篇
  2001年   35989篇
  2000年   34717篇
  1999年   33362篇
  1998年   37579篇
  1997年   34757篇
  1996年   32475篇
  1995年   29045篇
  1994年   27438篇
  1993年   27321篇
  1992年   25658篇
  1991年   22697篇
  1990年   23101篇
  1989年   22164篇
  1988年   20643篇
  1987年   19030篇
  1986年   18293篇
  1985年   21666篇
  1984年   22053篇
  1983年   20021篇
  1982年   19066篇
  1981年   19177篇
  1980年   17780篇
  1979年   18363篇
  1978年   17610篇
  1977年   17102篇
  1976年   17513篇
  1975年   15903篇
  1974年   15426篇
  1973年   15517篇
  1972年   12994篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
903.
904.
905.
Itaconate (ITA) is an emerging powerhouse of innate immunity with therapeutic potential that is limited in its ability to be administered in a soluble form. A library of polyester materials that incorporate ITA into polymer backbones resulting in materials with inherent immunoregulatory behavior is developed. Harnessing hydrolytic degradation release from polyester backbones, ITA polymers result in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released ITA inhibits bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrate a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of ITA.  相似文献   
906.
Fluorescent nanodiamonds (fNDs) containing nitrogen vacancy (NV) centers are promising candidates for quantum sensing in biological environments. This work describes the fabrication and implementation of electrospun poly lactic‐co‐glycolic acid (PLGA) nanofibers embedded with fNDs for optical quantum sensing in an environment, which recapitulates the nanoscale architecture and topography of the cell niche. A protocol that produces uniformly dispersed fNDs within electrospun nanofibers is demonstrated and the resulting fibers are characterized using fluorescent microscopy and scanning electron microscopy (SEM). Optically detected magnetic resonance (ODMR) and longitudinal spin relaxometry results for fNDs and embedded fNDs are compared. A new approach for fast detection of time varying magnetic fields external to the fND embedded nanofibers is demonstrated. ODMR spectra are successfully acquired from a culture of live differentiated neural stem cells functioning as a connected neural network grown on fND embedded nanofibers. This work advances the current state of the art in quantum sensing by providing a versatile sensing platform that can be tailored to produce physiological‐like cell niches to replicate biologically relevant growth environments and fast measurement protocols for the detection of co‐ordinated endogenous signals from clinically relevant populations of electrically active neuronal circuits.  相似文献   
907.
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices.  相似文献   
908.
Beardless barb is a common fish species used in fermentation of fish paste Ka-pi-plaa. Autolytic profile of beardless barb muscle showed the maximum autolysis was at 50 °C, at both acidic and alkaline pH values. With augmentation concentration of NaCl, autolytic activity slightly decreased. Endogenous proteinases isolated from fish muscle in crude extract forms were also characterised. The acidic proteinases had optimum activity at pH 3.0 and 50°C, and they showed higher proteolytic activity than the alkaline proteinases which were optimally active at pH 9.0 and 50 °C. Proteinases in peak at pH 3.0 were inhibited by pepstatin A, but those in peak at pH 9.0 were highly inhibited by PMSF, TLCK and soybean trypsin inhibitor, suggesting that both aspartic and serine proteinases were existed in beardless barb muscle. The proteinases were stable in pH range of 2.0-5.0 but unstable at the temperatures higher than 40 °C. NaCl suppressed the proteolytic activity, ATP activated the proteinase activity, while CaCl2, MgCl2 and CoCl2 exhibited no influence on the activity. The results implied that cathepsin D is the predominant proteinase responsible for autolysis in beardless barb. The findings were useful to improve the processing and qualities of Ka-pi-plaa product using beardless barb as raw material.  相似文献   
909.
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations.  相似文献   
910.
Bulletin of Engineering Geology and the Environment - Local soil characteristics play a key role in determining soil-structure interaction and reliability of the superstructure behavior under...  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