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   4949篇
  免费   181篇
  国内免费   24篇
电工技术   74篇
综合类   8篇
化学工业   953篇
金属工艺   156篇
机械仪表   116篇
建筑科学   50篇
矿业工程   16篇
能源动力   307篇
轻工业   225篇
水利工程   36篇
石油天然气   20篇
无线电   649篇
一般工业技术   1155篇
冶金工业   725篇
原子能技术   34篇
自动化技术   630篇
  2023年   72篇
  2022年   92篇
  2021年   172篇
  2020年   146篇
  2019年   124篇
  2018年   169篇
  2017年   157篇
  2016年   184篇
  2015年   108篇
  2014年   185篇
  2013年   412篇
  2012年   215篇
  2011年   230篇
  2010年   198篇
  2009年   267篇
  2008年   178篇
  2007年   129篇
  2006年   128篇
  2005年   111篇
  2004年   99篇
  2003年   101篇
  2002年   88篇
  2001年   69篇
  2000年   66篇
  1999年   71篇
  1998年   145篇
  1997年   108篇
  1996年   120篇
  1995年   83篇
  1994年   83篇
  1993年   80篇
  1992年   59篇
  1991年   69篇
  1990年   68篇
  1989年   47篇
  1988年   46篇
  1987年   45篇
  1986年   42篇
  1985年   47篇
  1984年   31篇
  1983年   25篇
  1982年   26篇
  1981年   35篇
  1980年   20篇
  1979年   30篇
  1978年   30篇
  1977年   27篇
  1976年   33篇
  1975年   15篇
  1973年   13篇
排序方式: 共有5154条查询结果,搜索用时 15 毫秒
181.
In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD3 which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo1−xNixD3, which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo1−xNix (x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content (x). The neutron diffraction study shows that deuterium occupies a new site 8e in addition to 4c2 and 8f1. Additionally, the Zr–D distance in 8e site is shorter than that in ZrD2. Therefore, increase in 8e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new 8e site decreases and its Zr–D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound.  相似文献   
182.
183.
This investigation was carried out to evaluate the antioxidant effect of turmeric (turmeric 1000 ppm, turmeric 5000 ppm), nitrite (nitrite 200 ppm) and ascorbic acid (ascorbic acid 500 ppm) on raw minced chicken stored at 4 ± 1 °C. Physicochemical properties [pH, water activity, cooking loss, thiobarbituric acid (TBA) value, peroxide value (PV), free fatty acid (FFA)] were evaluated on 0, 2, 4 and 6th day of storage. Highly significant differences (P < 0.01) in pH, TBA value, PV and FFA value were noticed between treatments and between storage periods. TBA values were observed to be lowest for nitrite 200 ppm and then turmeric 5000 ppm, and there was no significant difference between nitrite 200 ppm and turmeric 5000 ppm, and both were superior to ascorbic acid 500 ppm and turmeric 1000 ppm. Among different treatments, PV was found to be lowest in turmeric 5000 ppm and highest in nitrite 200 ppm. FFA value was found to be lowest in turmeric 5000 ppm and highest in ascorbic acid 500 ppm among all treated samples. It can be concluded that turmeric has potential to replace synthetic antioxidants presently used in meat processing with many added advantages.  相似文献   
184.
Background: The present study is to investigate the neuroprotective effect of ibuprofen by intranasal administration of mucoadhesive microemulsion (MMEI) against inflammation-mediated by dopaminergic neurodegeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson’s disease (PD).

Methods: Ibuprofen-loaded polycarbophil-based MMEI was developed by using response surface methodology (RSM). Ibuprofen with dose of 2.86 mg/kg/day was administered intranasally to male C57BL/6 mice for two consecutive weeks which were pre-treated with four intraperitoneal injections of MPTP (20?mg/kg of body weight) at 2?h intervals. Immunohistochemistry was performed.

Results: Optimal MMEI was stable and non-ciliotoxic with 66.29?±?4.15?nm as average globule size and??20.9?±?3.98?mV as zeta potential. PDI value and transmission electron microscopy result showed the narrow globule size distribution of MMEI. The result showed that all three independent variables had a significant effect (p?<?0.05) on the responses. Rota-rod and open-field test findings revealed the significant improvement in motor performance and gross behavioral activity of the mice. The results from in vivo study and immunohistochemistry showed that nasal administration of Ibuprofen significantly reduced the MPTP-mediated dopamine depletion. Furthermore TH neurons count in the substantia nigra and the density of striatal dopaminergic nerve terminals were found to be significant higher for ibuprofen treated groups.

Conclusion: Findings of the investigation revealed that Ibuprofen through developed MMEI was shown to protect neurons against MPTP-induced injury in the Substantia nigra pars compacta (SNpc) and striatum and hence, could be a promising approach for brain targeting of Ibuprofen through intranasal route to treat PD.  相似文献   
185.
BACKGROUND: Low energy and less expensive membrane based separation of acetic acid‐water mixtures would be a better alternative to conventional separation processes. However, suitable acid resistant membranes are still lacking. Thus, the objective of the present study was to develop mixed matrix membrane (MMM) which would allow high flux and water selectivity over a wide range of feed concentrations of acid in water. RESULTS: Three MMMs, namely PANBA0.5, PANBA1.5 and PANBA3 were made by emulsion copolymerization of acrylonitrile (AN) and butyl acrylate (BA) with 5.5:1 comonomer ratio and in situ incorporation of 0.5, 1.5 and 3 wt%, sodium montmorilonite (Na‐MMT) nanofillers, respectively. For a feed concentration of 99.5 wt% of acid in water the membranes show good permeation flux (2.61, 3.19, 3.97 kg m?2 h?1 µm?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and very high separation factors for water (1473, 1370, 1292 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at 30 °C. Similarly for a dilute acid–water solution, i.e. for 71.6 wt% acid the membrane showed a very high thickness normalize flux (8.67, 9.44, 11.56 kg m?2 h?1 µm?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and good water selectivity (101.7, 95.3, 79 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at the same feed temperature. The permeation ratio, permeability, diffusion coefficient and activation energy for permeation of the membranes were also estimated. CONCLUSION: Unlike most of the reported membranes, the present MMMs allowed high flux and selectivity over a wide range of feed concentrations. These membranes may also be effective for separating other similar organic‐water mixtures. Copyright © 2012 Society of Chemical Industry  相似文献   
186.
The study has focused on electricity generation from organic acid-rich bio-substrate like star fruit (Averrhoa carambola). The sap of star fruit was selected as an electrolyte due to the presence of significant amounts of organic acids such as citric acid and ascorbic acid. To preserve the sap, 2% phenol by volume was used to reduce the growth of microorganisms, and the addition of phenol did not affect the initial pH. It was observed that due to an increase in the electrode surface area, reaction rate and current generation had been amplified. Internal resistance also decreased rapidly because of the large electrode surface area. Furthermore, internal resistance was the significant barrier in electricity generation, which was also successfully controlled by the baffle flow agitation system. Moreover, the baffle flow agitation system reduces the formation of dead zones and increases the total dissolved solids inside the electrochemical cell compartments during operation.  相似文献   
187.
Ionic polythiophenes are important conjugated polymers because of their excellent optical properties and water solubility. They are classified as cationic, anionic and zwitterionic conjugated polyelectrolytes. This review article describes concisely their biological and analytical applications. The specific detection of different negatively charged biomolecules such as DNA and adenosine triphosphate, anions like halides and toxic pseudo‐halide (CN ?) and environmental pollutants, e.g. surfactants, is discussed. The conformational changes of cationic polythiophenes (CPTs ) induced by various analytes due to formation of ionic conjugates and the cooperative responses of all segments cause dominant signal amplification even in the presence of a small perturbation. In addition, reactive oxygen scavenging, antimicrobial photosensitizing and cell imaging applications of CPTs are documented. Use of anionic polythiophenes for sensing of protamine and cations like Cu2+ and Ca2+ is also discussed. Finally, sensing of DNA , peptides and surfactants by zwitterionic polythiophenes is included. The concluding part discusses future prospects. © 2016 Society of Chemical Industry  相似文献   
188.
Cu-SiC nanocomposite coatings have been deposited from an aqueous sulfate electrolyte using the technique of pulse reverse electrodeposition both in the absence and presence of three different types of surfactants, anionic, cationic, or nonionic. The effects of different electrodeposition parameters on some properties of the coatings have been studied. In all cases, it has been observed that the surface roughness, hardness, and resistivity increase with the increase in cathodic current density. However, they have been observed to decrease with the increase in anodic current density and the anodic current time. The variation in the amount of incorporated reinforcement with different deposition parameters has been observed to be dependent on the nature of the surfactant used. In the presence of cationic and nonionic surfactant, a noticeable increase in the amount of incorporated reinforcement and hardness has been observed. Samples prepared under higher anodic current density have been observed to possess lower stress, but intense texture. An increase in cathodic current density has been observed to decrease the extent of texturing.  相似文献   
189.
A new class of biodegradable crosslinked hydrogel, consisting of hydrophobic polylactic acid (PLA) and hydrophilic dextrin in presence of crosslinker N,N‐methylene bisacrylamide (MBA) has been synthesized by free‐radical polymerization technique using potassium persulfate (KPS) as initiator. By variation of crosslinker concentration, a series of hydrogels have been prepared and the optimized grade has been selected on the basis of higher crosslinking efficiency as well as lower equilibrium swelling characteristics, XRD analysis. The hydrogels have been characterized by FTIR spectra, 13C‐NMR spectra, CHN analysis, SEM analysis, swelling characteristics, and toxicity study. In vitro release study of model drugs (ciprofloxacin and ornidazole) from hydrogel matrix has been performed in various buffer solutions at 37°C. The drug release kinetics and mechanism have been studied using zero order, first‐order kinetic models, Korsemeyar–Peppas model, Higuchi model, Hixson–Crowell model, and nonlinear Kopcha model. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40039.  相似文献   
190.
The academic literature on manufacturing technology was reviewed to identify key contingency variables that can moderate the influence of advanced manufacturing technologies on manufacturing performance. Using this literature as a basis, this research proposes an ordering of relative importance of individual contingency variables among a set of contingency variables that influence the advanced manufacturing technologies–manufacturing performance relationship. Plant level data from a large multi-industry sample of firms are analysed, using regression and Chow tests, to confirm the hypothesized ordering among the contingency variables. The findings indicate that lean manufacturing and work organization practices are the primary contingency variables that affect the advanced manufacturing technologies–manufacturing performance relationship. The implications of the results are discussed in the light of past findings and their impact on practice.  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