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   14612篇
  免费   840篇
  国内免费   66篇
电工技术   239篇
综合类   58篇
化学工业   3598篇
金属工艺   347篇
机械仪表   501篇
建筑科学   598篇
矿业工程   45篇
能源动力   558篇
轻工业   2377篇
水利工程   177篇
石油天然气   118篇
武器工业   14篇
无线电   872篇
一般工业技术   2267篇
冶金工业   1532篇
原子能技术   125篇
自动化技术   2092篇
  2024年   42篇
  2023年   151篇
  2022年   456篇
  2021年   612篇
  2020年   417篇
  2019年   446篇
  2018年   550篇
  2017年   577篇
  2016年   580篇
  2015年   458篇
  2014年   614篇
  2013年   1057篇
  2012年   885篇
  2011年   1109篇
  2010年   761篇
  2009年   760篇
  2008年   715篇
  2007年   601篇
  2006年   483篇
  2005年   361篇
  2004年   334篇
  2003年   343篇
  2002年   349篇
  2001年   233篇
  2000年   216篇
  1999年   197篇
  1998年   486篇
  1997年   361篇
  1996年   224篇
  1995年   152篇
  1994年   136篇
  1993年   111篇
  1992年   65篇
  1991年   53篇
  1990年   50篇
  1989年   55篇
  1988年   44篇
  1987年   28篇
  1986年   28篇
  1985年   45篇
  1984年   41篇
  1983年   41篇
  1982年   34篇
  1981年   29篇
  1980年   30篇
  1979年   18篇
  1977年   35篇
  1976年   48篇
  1975年   16篇
  1974年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
研制了具有消毒杀菌、洗涤去污双重功效的液体消毒洗涤剂 ,测定了其对金黄色葡萄球菌的杀灭效果。结果表明 ,消毒洗涤剂的杀菌效果随其浓度的增加 ,作用时间的延长而提高 ;戊二醛浓度为 2 0 0× 10 -6时 ,与金黄色葡萄球菌作用 5min ,杀灭率可达 99.99%。将消毒洗涤剂在室温下放置半年 ,戊二醛分解率为 17.3 1%  相似文献   
82.
Transient receptor potential ankyrin member 1 (TRPA1) belongs to the family of thermo TRP cation channels that detect harmful temperatures, acids and numerous chemical pollutants. TRPA1 is expressed in nervous tissue, where it participates in the genesis of nociceptive signals in response to noxious stimuli and mediates mechanical hyperalgesia and allodynia associated with different neuropathies. The glutamate N-methyl-d-aspartate receptor (NMDAR), which plays a relevant role in allodynia to mechanical stimuli, is connected via histidine triad nucleotide-binding protein 1 (HINT1) and type 1 sigma receptor (σ1R) to mu-opioid receptors (MORs), which mediate the most potent pain relief. Notably, neuropathic pain causes a reduction in MOR antinociceptive efficacy, which can be reversed by blocking spinal NMDARs and TRPA1 channels. Thus, we studied whether TRPA1 channels form complexes with MORs and NMDARs that may be implicated in the aforementioned nociceptive signals. Our data suggest that TRPA1 channels functionally associate with MORs, delta opioid receptors and NMDARs in the dorsal root ganglia, the spinal cord and brain areas. These associations were altered in response to pharmacological interventions and the induction of inflammatory and also neuropathic pain. The MOR-TRPA1 and NMDAR-TRPA1 associations do not require HINT1 or σ1R but appear to be mediated by calcium-activated calmodulin. Thus, TRPA1 channels may associate with NMDARs to promote ascending acute and chronic pain signals and to control MOR antinociception.  相似文献   
83.
A new type of polyimide/silica (PI/SiO2) hybrid composite films was prepared by blending polymer‐modified colloidal silica with the semiflexible polyimide. Polyimide was solution‐imidized at higher temperature than the glass transition temperature (Tg) using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organic–inorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both Tg and thermal stability of the resulting films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2053–2061, 2006  相似文献   
84.
A bubbling fluidized bed reactor was used to study CO2 capture from flue gas by using a potassium-based solid sorbent, sorbKX35 which was manufactured by the Korea Electric Power Research Institute. A dry sorbent, sorbKX35, consists of K2CO3 for absorption and supporters for mechanical strength. To increase initial CO2 removal, some amount of H2O was absorbed in the sorbent before injecting simulated flue gas. It was possible to achieve 100% CO2 removal for more than 10 minutes at 60°C and a residence time of 2 s with H2O pretreatment. When H2O pretreatment time was long enough to convert K2CO3 of sorbKX35 into K2CO3 · 1.5H2O, CO2 removal was excellent. The results obtained in this study can be used as basic data for designing and operating a large scale CO2 capture process with two fluidized bed reactors. This work was presented at the 6 th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.  相似文献   
85.
The adsorption of cobalt phthalocyanine dye onto activated carbon in a continuous stirred tank adsorber was studied. The variables investigated were: adsorbent mass, adsorbent particle size and fluid flowrate. Several models based on film, pore and surface diffusion were constructed and fitted to the experimental data. Experimental results showed: (i) the increasing importance of the film mass transfer resistance for increasing adsorbent loads; (ii) the increasing importance of the surface diffusion mechanism for increasing adsorbent loads; and (iii) the better discrimination among different models for higher adsorbent loads and lower flowrate.  相似文献   
86.
Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and, vice versa, HMW homopolymer to LMW copolymer. The physical properties of the blends were found to be consistent with the nature of the individual components. For the tensile properties, the stiffness decreases with increasing the fraction of the copolymer, regardless of the molecular weight of the homopolymer fraction. For these blends with bimodal microstructures, it was confirmed that the degree of crystallinity governs the stiffness of the polymer. However, the energy dampening properties of the polymers benefit from the presence of the copolymer. A balance of stiffness and toughness can be obtained by altering the composition of the blends. For some blends, the presence of HMW homopolymer can dominate the tensile properties, showing little variation in the stiffness with increased addition of copolymer. It was also demonstrated that the testing conditions and thermal treatment of the polymer greatly influence the resulting elastic and energy dampening properties. Depending on the desired application, annealing these polymers (especially very low density copolymers) not only increases the crystallinity and stiffness, but also changes the frequency response of the dynamic mechanical properties.  相似文献   
87.
Impurity poisoning of a catalyst particle having a non-uniform activity distribution is analyzed. Equations that relate the position of the poison-front with time for different activity profiles are derived. It is shown that the effect of the activity distribution on the poisoning rate is apparent in the case of intraparticle-diffusion control. The performance of a non-uniform bifunctional catalyst in such conditions is also studied.  相似文献   
88.
A business process is a set of activities performed in a coordinated manner within an organizational and technical environment that is aimed toward a business goal. The flexibility of a process is related to an understanding of the unexpected events that occur when people, systems and resources interact and require adjustments. Thus, business processes must be designed to respond to information about different events and their specificity. This information defines what the literature calls “context”. To broaden the perception of context in the case of a business process, this work proposes an approach to characterize the context of a business process activity in a given domain through conceptual models structured in layers. A case study was conducted to evaluate the proposal, which provided evidence of the applicability of the model.  相似文献   
89.
Nitrogen transformations occurring in ten soils fertilized with urea were determined during incubation in the laboratory for four weeks. Urea was applied at one rate, but with different placement methods. Urea was applied in solution, as prills with a 1 cm grid spacing and as prills with no spacing. Unfertilized soils and soils amended with KNO3 solution were included as controls.Nitrite accumulated in the majority of soils treated with urea, and the maximum nitrite concentration measured was directly related to initial soil pH. Cumulative gaseous N losses as percentages of applied N were: NH3, 0-59.6; N2, 0-4.9; N2O, 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. No gaseous N evolution was detected in control treatments. Gaseous N losses were correlated with soil pH (NH3) maximum NO 2 - concentration (N2, N2O, KMnO4-N) and organic C content (N2, N2O). Fertilizer placement effects were generally not significant and were small in comparison with differences between soils.
Resumo Foram determinadas, durante incubação em laboratório por quatro semanas, as transformações do nitrogênio ocorridas em dez solos fertilizados com uréia. A uréia foi aplicada a um só nivel, mas com diferentes métodos de aplicação: em solução e em grânulos com 1 cm de espaçamento de grade e em grânulos sem espaçamento. Solos não fertilizados e solos corrigidos com solução de KNO3 foram incluidos como controles.O nitrito acumulado na maioria dos solos tratados com uréia e a concentração máxima de nitrito medido foram diretamente relacionados ao pH inicial do solo. As perdas cumulativas de N gasoso tomadas em percentagens de N aplicado foram: NH3, 0-59.6; N2, 0-4.9; N2O; 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. Não foi detectada liberação de N gasoso nos tratamentos de controle. As perdas de N gasoso foram relacionadas com o pH do solo (NH3), concentração máxima de NO 2 - (N2, N2O, KMnO4-N) e teor de C orgânico (N2, N2O). Efeitos da aplicação de fertilizante não foram de um modo geral significativos e foram pequenos em comparação com as diferenças entre os solos.
  相似文献   
90.
药用中间体苯丙酮含量的气相色谱/质谱分析   总被引:1,自引:0,他引:1  
苯丙酮是合成利胆药苯丙醇的重要中间体。本文建立了用气相色谱 /质谱法 (GC/MS)测定苯丙酮含量的方法。组分的定性依靠GC/MS联用技术和NIST谱库标准质谱图对照分析。以苯乙酮为内标 ,苯丙酮含量在 1.0× 10 -5~ 2 .0× 10 -4g/mL范围内呈线性 ,线性相关系数r =0 .994 9,苯丙酮最低检测浓度为 1.0× 10 -8g/mL。该法操作简便、快速 ,结果准确可靠 ,且具有很好的实用价值  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