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   371篇
  免费   27篇
化学工业   212篇
金属工艺   8篇
机械仪表   3篇
建筑科学   9篇
矿业工程   1篇
能源动力   14篇
轻工业   70篇
水利工程   3篇
石油天然气   1篇
无线电   3篇
一般工业技术   48篇
冶金工业   9篇
自动化技术   17篇
  2024年   1篇
  2023年   5篇
  2022年   48篇
  2021年   60篇
  2020年   9篇
  2019年   8篇
  2018年   12篇
  2017年   19篇
  2016年   12篇
  2015年   17篇
  2014年   15篇
  2013年   15篇
  2012年   19篇
  2011年   24篇
  2010年   12篇
  2009年   14篇
  2008年   23篇
  2007年   14篇
  2006年   19篇
  2005年   8篇
  2004年   6篇
  2003年   6篇
  2002年   4篇
  2001年   2篇
  2000年   5篇
  1999年   4篇
  1998年   5篇
  1997年   1篇
  1996年   1篇
  1995年   2篇
  1994年   1篇
  1992年   3篇
  1991年   1篇
  1985年   1篇
  1984年   1篇
  1980年   1篇
排序方式: 共有398条查询结果,搜索用时 15 毫秒
341.
342.
Herein, nine phthalimide-based thiazoles (4a–4i) were synthesized and investigated as new human neutrophil elastase (HNE) inhibitors using spectrofluorimetric and computational methods. The most active compounds containing 4-trifluoromethyl (4c), 4-naphthyl (4e) and 2,4,6-trichloro (4h) substituents in the phenyl ring exhibited high HNE inhibitory activity with IC50 values of 12.98–16.62 µM. Additionally, compound 4c exhibited mixed mechanism of action. Computational investigation provided a consistent picture of the ligand-receptor pattern of inter-actions, common for the whole considered group of compounds. Moreover, compounds 4b, 4c, 4d and 4f showed high antiproliferative activity against human cancer cells lines MV4-11, and A549 with IC50 values of 8.21 to 25.57 µM. Additionally, compound 4g showed high activity against MDA-MB-231 and UMUC-3 with IC50 values of 9.66 and 19.81 µM, respectively. Spectrophotometric analysis showed that the most active compound 4c demonstrated high stability under physiological conditions.  相似文献   
343.
Oxaliplatin, similar to Cisplatin, exhibits anticancer activity by interacting with DNA and inducing programmed cell death. It is biotransformed through a number of spontaneous and non-enzymatic processes. In this way, several transient reactive species are formed, including dichloro-, monochloro-, and diaqua-DACH platin, which can complex with DNA and other macromolecules. The molecular level suggests that such interactions can also take place with vitamins containing aromatic rings with lone pair orbitals. Theoretical and experimental studies were performed to investigate interactions of vitamins from the B group with Oxaliplatin, and the results were compared with values characterizing native purines. Quantum-chemical simulations were carried out at the B3LYP/6-31G(d,p) level, with the LANL2DZ basis set representing atomic orbitals of platinum atom, and at the MN15/def2-TZVP levels of theory with the use of Polarizable Continuum Model (IEF-PCM formulation) and water as a solvent. Additionally, time-dependent density functional theory (TD-DFT) was employed to study molecular properties in the electronic excited state. Interactions of vitamins and Oxaliplatin were investigated using UV-Vis spectroscopy. Values of the free energy (ΔGr) indicate spontaneous reactions with monoaqua [PtH2OClDACH]+ and diaqua [Pt(H2O)2DACH]2+ derivatives of Oxaliplatin. However, diaqua derivatives were found to be preferable. The free energy (ΔGr) values obtained for vitamins from the B group indicate lower affinity of Oxaliplatin compared with values characterizing complexes formed by guanine, adenine, and cytosine. The exception is the monoaqua form of vitamin B1 (thiamine) at the MN15/def2-TZVP levels of calculations. An application of atoms in molecules (AIM) theory revealed non-covalent interactions present in the complexes studied. The comparison of computed and experimental spectroscopic properties showed a good agreement.  相似文献   
344.
Vitamin D takes part in the functioning of many processes that ensure the homeostasis of the body. In orthopedics, it is indicated as an inseparable element ensuring proper bone growth and functioning, and its deficiencies are indicated in various diseases, mainly in the proper structure and function of the skeleton. In this review, we focus on the most important components of the vitamin D metabolic pathway, in correlation with selected orthopedic conditions. Records were obtained from the PubMed database in a timeline of 2010–2022. The keywords were as follows: vitamin D/cholesterol/vitamin D binding protein/ VDBP/Cytochrome/CYP24A1/CYP 27B1/Vitamin D receptor/VDR/ + diseases (ACL reconstruction, rotator cuff, arthroplasty knee/hip/shoulder). The recent original studies were analyzed, discussed, and the most important data were shown. The vast majority of articles concern the metabolite of vitamin D (25(OH)D), which is measured as a standard in diagnostic laboratories. Even though there is a lot of valuable information in the literature, we believe that the other elements of the vitamin D pathway also deserve attention and suggest their research in correlation with orthopedic disorders to supplement the missing knowledge on this topic.  相似文献   
345.
Summary Borate hemicyanine salts, namely sec-butyltriphenyl styrylbenzoxazole borates are shown to be effective photoinitiators for the polymerization of vinyl monomers. Mechanism of the photoinitiation involves sec-butyl radicals formed from the heterolytic cleavage of carbon-boron bond that follows the electron transfer process. The capability of the salts to act as initiators for the polymerization of multifunctional monomer is documented.  相似文献   
346.
Two series of samples were prepared from titanium tetraisopropoxide (TTIP) through hydrolysis with different aging times, 10 min and 24 h, at room temperature and then annealed at different temperatures. Photocatalytic activities of these samples for methylene blue (MB) in water and for diluted NO gas were examined. For MB decomposition, rate constant k was determined from linear relation between logarithm of relative concentration of MB remained in water and UV irradiation time. For NO, its decomposition fraction after 10 h irradiation was determined. Difference in aging time gave different crystalline state of the precipitates, anatase phase with poor crystallinity after 10 min aging, but amorphous state after 24 h aging. These two precipitates showed different changes in crystallinity and in photoactivity for MB and NO with annealing temperature. Maximum rate constant k for MB decomposition was obtained at around 0.6° of full width at half maximum intensity (FWHM) of 101 diffraction line. For NO gas, a maximum decomposition fraction was obtained at FWHM of around 1.6°. Different crystallinity of anatase was shown to be required for the decomposition of MB in water and NO gas, high crystallinity of anatase phase for the former but poor crystallinity for the latter.  相似文献   
347.
Functional lignin-SiO2 hybrid fillers were synthesized and characterized with a view to their potential application in binders for phenolic resins. The properties of these fillers and of composites obtained from them with phenolic resin were compared with those of systems with lignin or silica alone. The chemical structure of the materials was investigated by Fourier transform infrared spectroscopy. Surface properties of lignin-SiO2 fillers were tested using inverse gas chromatography (IGC). IGC was used for determination of surface energy and surface heterogeneity of the studied fillers. IGC made it possible to assess the adhesion between the tested fillers and phenolic resins. Interactions of functional fillers with phenolic resins were also evaluated by IGC. The results indicated that lignin-SiO2 interacted strongly with the phenolic resin, more strongly than pure lignin. This was proved by SEM observations: thanks to the stronger interactions of lignin-SiO2 hybrid with phenolic resins, a more homogeneous composite was obtained. Thermo-mechanical properties of lignin–silica and resin systems were investigated by DMTA. DMTA results showed that phenolic binders with lignin-SiO2 fillers have better thermo-mechanical properties than systems with lignin or silica alone: higher glass transition temperature and a smaller decrease in storage modulus. Lignin fillers can thus provide new, promising properties for a phenolic binder combining the good properties of lignin as a plasticizer and of silica as a filler improving mechanical properties.  相似文献   
348.
In northwestern Germany slurry injection below maize (Zea mays L.) seeds is gaining increasing interest of farmers, because of the expected enhanced nitrogen (N) and phosphorus (P) use efficiencies compared to the usual fertilizing practice. The present study aims to compare the spatial and temporal soil mineral nitrogen (SMN) dynamics for these fertilizing strategies. Field trials with four treatments (unfertilized control, broadcast application + N P mineral starter fertilizer (+MSF), injection and injection + nitrification inhibitor (NI)) were conducted using pig slurry on sandy soil in 2014 and 2015. Soil samples were taken from three soil layers at 30 cm intervals down to 90 cm, and at three positions (below the maize row, 15 and 30 cm distance to the row) at several dates over the growing season. Soil monoliths (15 × 15 × 10 cm) were sampled around the injection zone, and for all other soil zones an auger was used. In 2014 due to heavy rainfall all fertilized N was displaced from the top soil layer of the broadcast treatment until 6-leaf stage, while N displacement was significantly smaller after slurry injection (about 20 kg SMN ha?1 more in top layer). The lateral movement of injected slurry N was negligible. In 2015 almost no displacement of fertilized N out of the top soil layer occurred independently of treatments, because of lower rainfall. The release of slurry N was delayed following broadcast application and large SMN concentrations were detected in the injection zones until 10-leaf stage. The addition of a NI resulted in significantly increased ammonium N concentrations in the injection zone throughout the early growth stages [+46 % (2014) and +12 % (2015) at 6-leaf stage]. Thus, N displacement was delayed in 2014 and in 2015 at 6-leaf stage increased SMN concentrations (+1/3 with NI) were found around the slurry band. Due to slurry injection, especially when combined with a nitrification inhibitor, the applied nitrogen is located in a soil zone with better spatial availability for plant roots compared to broadcast application and the risk of nitrate leaching is significantly reduced.  相似文献   
349.
The water sorption and desorption behaviour of three commercial glass-ionomer cements used in clinical dentistry have been studied in detail. Cured specimens of each material were found to show slight but variable water uptake in high humidity conditions, but steady loss in desiccating ones. This water loss was found to follow Fick’s law for the first 4–5 h. Diffusion coefficients at 22 °C were: Chemflex 1.34 × 10−6 cm2 s−1, Fuji IX 5.87 × 10−7 cm2 s−1, Aquacem 3.08 × 10−6 cm2 s−1. At 7 °C they were: Chemflex 8.90 × 10−7 cm2 s−1, Fuji IX 5.04 × 10−7 cm2 s−1, Aquacem 2.88 × 10−6 cm2 s−1. Activation energies for water loss were determined from the Arrhenius equation and were found to be Chemflex 161.8 J mol−1, Fuji IX 101.3 J mol−1, Aquacem 47.1 J mol−1. Such low values show that water transport requires less energy in these cements than in resin-modified glass-ionomers. Fick’s law plots were found not to pass through the origin. This implies that, in each case, there is a small water loss that does not involve diffusion. This was concluded to be water at the surface of the specimens, and was termed “superficial water”. As such, it represents a fraction of the previously identified unbound (loose) water. Superficial water levels were: Chemflex 0.56%, Fuji IX 0.23%, Aquacem 0.87%. Equilibrium mass loss values were shown to be unaffected by temperature, and allowed ratios of bound:unbound water to be determined for all three cements. These showed wide variation, ranging from 1:5.26 for Chemflex to 1:1.25 for Fuji IX.  相似文献   
350.
This paper describes the mechanism of formation of bubbles of nitrogen in water containing Tween 20 as a surfactant, and of droplets of water in hexadecane containing Span 80 as a surfactant. The study of these microfluidic systems compares two or four flow-focusing generators coupled through shared inlets, supplying the continuous phase, and through a common outlet channel. The processes that form bubbles in neighboring generators interact for a wide range of flow parameters; the formation of bubbles alternates in time and space, and the bubbles assemble into complex patterns in the outlet channel. The dynamics of formation of bubbles in these systems are stable for long time (at least 10 min). For a certain range of flow parameters, the coupled flow-focusing generators exhibit two stable modes of operation for a single set of flow parameters. The dynamics of formation of droplets of water in hexadecane by the coupled flow-focusing generators are simpler--the adjacent generators produce only monodisperse droplets over the entire range of flow parameters that are explored. These observations suggest that the mechanism of interaction between coupled flow-focusing generators relies on the compressibility of the dispersed phase (e.g., the gas or liquid), and on variations in pressure at the flow-focusing orifices induced by the breakup of bubbles or droplets.  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