全文获取类型
收费全文 | 1841篇 |
免费 | 24篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 10篇 |
综合类 | 26篇 |
化学工业 | 817篇 |
金属工艺 | 56篇 |
机械仪表 | 26篇 |
建筑科学 | 71篇 |
矿业工程 | 28篇 |
能源动力 | 129篇 |
轻工业 | 24篇 |
水利工程 | 6篇 |
石油天然气 | 17篇 |
武器工业 | 1篇 |
无线电 | 109篇 |
一般工业技术 | 509篇 |
冶金工业 | 27篇 |
原子能技术 | 16篇 |
自动化技术 | 18篇 |
出版年
2023年 | 16篇 |
2022年 | 36篇 |
2021年 | 37篇 |
2020年 | 44篇 |
2019年 | 41篇 |
2018年 | 36篇 |
2017年 | 40篇 |
2016年 | 33篇 |
2015年 | 34篇 |
2014年 | 91篇 |
2013年 | 107篇 |
2012年 | 78篇 |
2011年 | 112篇 |
2010年 | 92篇 |
2009年 | 123篇 |
2008年 | 121篇 |
2007年 | 145篇 |
2006年 | 112篇 |
2005年 | 113篇 |
2004年 | 83篇 |
2003年 | 76篇 |
2002年 | 70篇 |
2001年 | 64篇 |
2000年 | 55篇 |
1999年 | 27篇 |
1998年 | 30篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有1890条查询结果,搜索用时 78 毫秒
41.
Expanded polystyrene (EPS) concrete is a lightweight, low strength material with good energy-absorbing characteristics. However, due to the light weight of EPS beads and their hydrophobic surface, EPS concrete is prone to segregation during casting, which results in poor workability and lower strength. In this study, a premix method similar to the ‘sand-wrapping’ technique was utilized to make EPS concrete. Its mechanical properties were investigated as well. The research showed that EPS concrete with a density of 800-1800 kg/m3 and a compressive strength of 10-25 MPa can be made by partially replacing coarse and fine aggregate by EPS beads. Fine silica fume greatly improved the bond between the EPS beads and cement paste and increased the compressive strength of EPS concrete. In addition, adding steel fiber significantly improved the drying shrinkage. 相似文献
42.
Results of calorimeter tests on Portland cement-silica fume-fly ash mixtures are presented. Data indicate that silica fume accelerates cement hydration at high water/cementitious ratios and retards hydration at low water/cementitious ratios. On the other hand, fly ash retards cement hydration more significantly at high water/cementitious ratios. When silica fume and fly ash are added together with cement, the reactivity of the silica fume is hampered and the hydration of the cementitious system is significantly retarded. 相似文献
43.
介绍了一种用聚丙烯酸酯和硅溶胶改性聚乙烯醇缩甲醛的方法,用此法制得的白乳胶与传统的聚醋酸乙烯酯白乳胶相比较,具有抗冻性好、贮存稳定、成本低、性能好以及用途更广等特点。 相似文献
44.
45.
46.
《Current Opinion in Solid State & Materials Science》2017,21(1):43-53
Use of nanodiamonds (NDs) as nontoxic nanoparticles for biological imaging, sensing, and drug delivery is expanding rapidly. The interest in NDs is triggered by their unique combination of optical properties. ND can accommodate nitrogen-vacancy color centers which provide stable fluorescence without photobleaching or photoblinking and their electronic structure is very sensitive to magnetic and electric fields. The limited options to control ND properties during synthesis or by direct surface functionalization leave room to be improved upon by employing surface coatings engineered precisely for a particular application. The major disadvantages of unmodified NDs are their limited colloidal stability and tendency to non-specifically adsorb biomolecules. This review aims to summarize recent advances in coating NDs (namely with silica and polymer shells), which addresses these disadvantages and enables the use of NDs in biological applications such as targeting of specific cells, drug delivery, and biological imaging. 相似文献
47.
The present paper aims to clarify the pozzolanic behavior of sugar cane bagasse ash-SCBA by comparing it to amorphous and crystalline silica. It is shown that calcium silicate hydrate is formed in lime solution with SCBA but the reaction is slow and does not consume all the material. Comparing its results with the obtained in tests with silica fume and with crushed quartz show a better agreement with the latter. Characterization of cement pastes shows 20% of cement replacement by sugar cane bagasse ash leads to only a minor reduction in the amount of calcium hydroxide formed. This behavior is also closer to the observed in quartz than in silica fume. The results suggest SCBA should be used as a replacement for inert constituents in cement composites rather than pozzolanic addition. Analysis of the microstructure of the cement pastes revealed the presence of calcium hydroxide in samples prepared with partial replacement by silica fume, quartz and sugar cane bagasse ash. The presence of this phase in the sample prepared with silica fume was attributed to agglomeration of the particles that affected the reactivity of this material. 相似文献
48.
This work deals with the experimental tracking of a dispersion of very fine silica particles in PDMS using a new, easily implemented methodology. The dispersion experiments are carried out in an 8-l capacity mixer equipped with a torquemeter. Using a Couette analogy, the torque-rotational speed data can be converted into process viscosity-effective shear rate data. Simultaneously, the Particle Size Distribution (PSD) evolution is followed through Laser Light Scattering measurements on diluted samples. The PSD evolution allowed us to interpret the dispersion process in terms of different mechanisms, such as breaking-up and erosion of aggregates, as well as, in some cases, re-agglomeration (or flocculation) of particles. 相似文献
49.
K. Rózga-Wijas U. Mizerska W. Fortuniak J. Chojnowski R. Hałasa W. Werel 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(4):605-613
Three types of silica particles modified with vinyl groups were obtained: (i) xerogel formed by hydrolytic polycondensation
of the mixture of tetramethoxysilane (TMOS) and 1,1,1,7−tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyltetrasiloxane, (ii) mesoporous
silica obtained from the same precursors in the presence of the cetyltrimethylammonium bromide (CTAB), and (iii) commercial
Fluka silica gel 60A with a vinyltriethoxysilane-treated surface. Vinyl groups on these silica materials were transformed
into silyl chloride by hydrosilylation with HMe2SiCl. These groups were used to graft living polysiloxane that was synthesized by anionic ring-opening polymerization of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane
and initiated by BuLi. Chloropropyl groups on the grafted polymer were used to quaternize N,N-dimethyl-n-octylamine. Silica particles with grafted polysiloxane having quaternary ammonium salt (QAS) groups pendant to polymer chains
were obtained. Silica material with QAS groups directly attached to the surface were generated by the action of N,N-dimethyl-n-octylamine on particles obtained by the sol–gel process involving tetraethoxysilane (TEOS) with 3-chloropropyltriethoxysilane.
The bacteriocidal properties of all these materials were tested in water suspension against five representative strains for
Gram-positive and Gram-negative bacteria. Some of the silica–polysiloxane hybrid materials have good antibacterial properties
against Gram-positive strains, but not as good as the non-tethered QAS-substituted polysiloxane in water solution. The QAS
groups that are directly bonded to the silica material surface are inactive. 相似文献
50.
Synthesis and characterization of silica aerogels by a novel fast ambient pressure drying process 总被引:6,自引:0,他引:6
Using cheap waterglass as silica source, silica aerogels were synthesized via a novel fast ambient drying by using an ethanol/trimethylchlorosilane (TMCS)/Heptane solution for modification of the wet gel. One-step solvent exchange and surface modification were simultaneously progressed by immersing the hydrogel in EtOH/TMCS/Heptane solution, in which TMCS reacting with pore water and Si–OH group on the surface of the gel, with ethanol and heptane helping to decrease the rate of TMCS reacting with pore water and extrude water from gel pores. The synthesized silica aerogel was a light and crack-free solid, with the density of 0.128–0.136 g/cm3 and 93.8–94.2% porosity. The microstructure, morphology and properties of the aerogels were studied by FTIR, SEM, TEM and BET measurement. The results indicate that silica aerogels exhibit a sponge structure with uniform nano-particle and pores size distribution. The specific surface areas of silica aerogels are 559–618 m2/g. And there is an obvious Si–CH3 group on the surface of the silica aerogel. 相似文献