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   1090篇
  免费   67篇
  国内免费   5篇
电工技术   16篇
综合类   1篇
化学工业   319篇
金属工艺   10篇
机械仪表   8篇
建筑科学   62篇
能源动力   34篇
轻工业   85篇
水利工程   6篇
无线电   103篇
一般工业技术   214篇
冶金工业   32篇
原子能技术   5篇
自动化技术   267篇
  2024年   3篇
  2023年   23篇
  2022年   106篇
  2021年   100篇
  2020年   52篇
  2019年   45篇
  2018年   39篇
  2017年   43篇
  2016年   54篇
  2015年   45篇
  2014年   59篇
  2013年   90篇
  2012年   67篇
  2011年   90篇
  2010年   48篇
  2009年   55篇
  2008年   52篇
  2007年   36篇
  2006年   27篇
  2005年   30篇
  2004年   15篇
  2003年   20篇
  2002年   7篇
  2001年   4篇
  2000年   7篇
  1999年   5篇
  1998年   8篇
  1997年   6篇
  1996年   7篇
  1995年   3篇
  1994年   6篇
  1993年   1篇
  1992年   2篇
  1990年   2篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
  1976年   1篇
  1973年   1篇
排序方式: 共有1162条查询结果,搜索用时 15 毫秒
91.
The paper aims to show how regional policy‐makers can stimulate firms' co‐operation with research organizations by granting an R&D subsidy. Using an original dataset for the Italian region of Emilia‐Romagna, propensity score matching is first applied to identify the impact of the subsidy received. A generalized propensity score technique is then employed to investigate the effect of an increasing amount of support. The firm's co‐operation is policy sensitive. The award of a subsidy to regional firms affects their intra‐regional more than their extra‐regional co‐operation. The propensity toward the latter appears subject to a monetary effect and is influenced by the amount of public funding received providing the subsidy overcomes a minimum threshold.  相似文献   
92.
A convenient photochemical flow protocol for the formation of aryl‐carbon bonds via photogenerated phenyl cations has been developed. A wide range of phenylated products, including biaryls, allylarenes, 2‐arylacetals and benzyl γ‐lactones, was smoothly synthesized in satisfactory yields under metal‐free conditions. The adoption of a flow reactor often allowed us to adopt higher concentrations of substrates and shorter irradiation times compared to those usually employed in batch systems.

  相似文献   

93.
This paper investigates the removal of formic acid by unacclimated biomass from a municipal activated sludge wastewater treatment plant. The biomass was initially able to remove formic acid, but its removal rate and Oxygen Uptake Rate (OUR) decreased with time, until formic acid removal stopped before the formic acid had been exhausted. Formaldehyde was removed in a similar way, whereas the same biomass was simultaneously able to grow and store PHAs when acetic acid was used as substrate.Batch tests with glycine and 13C NMR analysis were performed, showing that unacclimated biomass was not able to synthesize all the metabolic intermediates from formic acid alone. At least glycine needed to be externally supplemented, in order to activate the serine synthesis pathway. A small amount of formic acid removal in the absence of growth was also possible through formaldehyde formation and its further conversion to formalin (1,2-formaldehyde dimer), whereas no PHAs were formed.  相似文献   
94.
Spherical silica nanoparticles containing fluorescent trimethine indocyanine dyes (λabs = 547 nm, λem = 570 nm) were prepared using a water-in-oil microemulsion method. The nanoparticles were of 50 nm diameter and were almost monodispersed in aqueous solution at pH 5.5. Entrapment of dye molecules in the silica matrix stabilised photoemission over several hours of continuous irradiation. The photoemission intensity of the indocyanine was increased 13-fold over that recorded in solution. As each nanoparticle contained 110 dye molecules, the photoemission brightness of each particle was enhanced by three orders of magnitude. The fluorescent nanoparticles have been tested as imaging tools in in vitro tests. As an example of non-macrophagic cells, a highly differentiated neuronal cell line (GT1-7) was used and the results showed that the prepared nanoparticles can be incorporated into these cells with no apparent toxicity for up to three days.  相似文献   
95.
HPLC is applied and assessed as an effective tool to investigate both the production of PLA by polycondensation and its corresponding degradation. A new HPLC calibration procedure, through which it is possible to fully characterize LMW PLA samples by determining the concentration of each individual oligomer, is developed. A comparison between HPLC, 1H NMR spectroscopy and non‐aqueous solution titration is also reported in order to confirm the reliability of the proposed method. Finally, the proposed analytical technique is applied to monitor the development of a polycondensation reaction performed at 150 °C and 133.3 mbar for 12 h.

  相似文献   

96.
97.
98.
A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5 m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients (OH, 3CDOM* and CO3-•) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals OH and CO3−•. Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical OH source) and the summer maxima of DOC (OH sink and 3CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving OH and CO3−• would be most important in spring, while the reactions involving 3CDOM* would be most important in summer.  相似文献   
99.
This paper reports the results of a comparison between two TiO2 photocatalysts that differ for particle size and absorption/scattering optical properties. The catalyst with larger particles and lower surface area performed better in the degradation of phenol than the specimen with smaller particles and larger surface area. Following carefully designed experiments, it is possible to assess the relative role of light absorption/scattering properties and catalyst-related efficiency by means of a basic kinetic model for the rate of photocatalytic reactions. Explicit relationships are derived in the framework of the steady-state approximation for the quantum yield as a function of one a-dimensional number collecting surface kinetic constants for charge carrier reactions at the interface, absorbed light and surface substrate concentrations. The dimensionality change to volume-defined quantities allows derivation of the explicit dependence of the quantum yield on substrate concentration and partition constants, catalyst concentration, and the rate of volumetric light absorption. Following this approach, the rate expression for slurry systems, valid in the absence of back reactions, is directly derived. Some further simplification of the rate equation for the case of low quantum yield regime leads to analytical relationships able to account for the dependence of the rate on catalyst concentration and absorbed light in the case of stirred and unstirred conditions. The reported properly designed experiments allow the estimation of catalyst-specific micro-kinetic constants.  相似文献   
100.
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