全文获取类型
收费全文 | 3861篇 |
免费 | 233篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 28篇 |
综合类 | 4篇 |
化学工业 | 1308篇 |
金属工艺 | 38篇 |
机械仪表 | 69篇 |
建筑科学 | 132篇 |
矿业工程 | 12篇 |
能源动力 | 80篇 |
轻工业 | 1083篇 |
水利工程 | 27篇 |
石油天然气 | 31篇 |
无线电 | 157篇 |
一般工业技术 | 499篇 |
冶金工业 | 204篇 |
原子能技术 | 4篇 |
自动化技术 | 419篇 |
出版年
2024年 | 12篇 |
2023年 | 31篇 |
2022年 | 181篇 |
2021年 | 217篇 |
2020年 | 111篇 |
2019年 | 109篇 |
2018年 | 142篇 |
2017年 | 140篇 |
2016年 | 154篇 |
2015年 | 136篇 |
2014年 | 156篇 |
2013年 | 294篇 |
2012年 | 259篇 |
2011年 | 306篇 |
2010年 | 212篇 |
2009年 | 252篇 |
2008年 | 196篇 |
2007年 | 186篇 |
2006年 | 152篇 |
2005年 | 106篇 |
2004年 | 90篇 |
2003年 | 78篇 |
2002年 | 76篇 |
2001年 | 45篇 |
2000年 | 37篇 |
1999年 | 42篇 |
1998年 | 63篇 |
1997年 | 59篇 |
1996年 | 39篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 24篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1970年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有4095条查询结果,搜索用时 15 毫秒
121.
María J. Martín de Vidales José Robles‐Molina Juan C. Domínguez‐Romero Pablo Cañizares Cristina Sáez Antonio Molina‐Díaz Manuel A. Rodrigo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(10):1441-1449
BACKGROUND: Sulfamethoxazole (SMX, used as a model bacteriostatic antibiotic) is persistent to conventional biological treatments of wastewaters. In this work, conductive‐diamond electrochemical oxidation (CDEO) was found to be an effective technology for its removal from the effluents of conventional wastewater treatment plants. RESULTS: The use of CDEO has been evaluated for the removal of the antibiotic SMX from water and wastewaters. The results show that CDEO can reduce the concentration of this organic pollutant to values below 0.1 µg dm?3. The variation of the SMX concentration during electrolysis shows a complex shape with a plateau zone that increases in size with the initial concentration of SMX. This complex trend is not observed in the changes of TOC, which seems to indicate that the CDEO of SMX solutions does not lead directly to the generation of carbon dioxide as a final product. A tentative reaction pathway has been proposed based on a thorough analysis of the reaction mixture, in which the main intermediate products were identified. The use of liquid chromatography time‐of‐flight mass spectrometry (LC‐TOFMS) allowed the identification of nine organic intermediates (with Mw 98, 108, 172, 173, 197, 203, 227, 269 and 287) during the electrolysis and the concentration of these compounds depends on the initial SMX concentration and on the current density applied. CONCLUSIONS: CDEO is able to reduce the concentration of the organic pollutant below 0.1 mg dm?3. SMX removal is faster than that of TOC. This fact indicates the formation of reaction intermediates. Analytical techniques show that nine reaction intermediates are generated in the system, and that their concentration depends on the initial SMX concentration and on the current density used. Copyright © 2012 Society of Chemical Industry 相似文献
122.
Carmen M González Henríquez Luis H Tagle Claudio A Terraza Andrés Barriga González Ulrich G Volkmann Alejandro L Cabrera Esteban Ramos‐Moore Maximiliano Pavez‐Moreno 《Polymer International》2012,61(2):197-204
Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl2 and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (1H, 13C, 29Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry 相似文献
123.
Volnei Tita Mauricio Francisco Caliri Júnior Ricardo Afonso Angélico Rodrigo Bresciani Canto 《Polymer Engineering and Science》2012,52(12):2654-2663
Assessing a full set of mechanical properties is a rather complicate task in the case of foams, especially if material models must be calibrated with these results. Many issues, for example anisotropy and heterogeneity, influence the mechanical behavior. This article shows through experimental analyses how the microstructure affects different experimental setups and it also quantifies the degree of anisotropy of a poly(vinyl chloride) foam. Monotonic and cyclic experimental tests were carried out using standard compression specimens and non‐standard tensile specimens. Results are complemented and compared with the aid of a digital image correlation technique and scanning electron microscopy analyses. Mechanical properties (e.g., elastic and plastic Poisson's ratios) are evaluated for compression and tensile tests, for two different material directions (normal and in‐plane). The material is found to be transversely isotropic. Differences in the results of the mechanical properties can be as high as 100%, or even more depending on the technique used and the loading direction. Also, the experimental analyses show how the material's microstructure behavior, like the evolution of the herein identified “yield fronts” and a “spring back” phenomenon, can influence the phenomenological response and the failure mechanisms as well as the hardening curves. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers 相似文献
124.
Carmen M González‐Henríquez Luis H Tagle Claudio A Terraza Ángel Leiva Andrés Barriga González Ulrich G Volkmann Alejandro L Cabrera Esteban Ramos‐Moore Maximiliano Pavez‐Moreno 《Polymer International》2012,61(5):810-817
Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (1H, 13C, 135‐DEPT and 29Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 105–2 × 105, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between ? 78 and ? 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm?1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry 相似文献
125.
Arturo Morales Susana Marmesat M. Carmen Dobarganes Gloria Márquez-Ruiz Joaquín Velasco 《Journal of the American Oil Chemists' Society》2012,89(4):675-684
The influence of temperature (40, 60 and 80 °C) and addition of α-tocopherol (0, 500 mg/kg) on the formation and distribution
of the main oxidation products of linoleic acid, i.e. hydroperoxy-, keto- and hydroxy-dienes, were studied in samples of fatty
acid methyl esters (FAME) derived from high-linoleic (HL) and high-oleic (HO) sunflower oils. In the range of temperatures
studied, the formation of hydroperoxydienes showed monomolecular and bimolecular rate constants that ranged from 0.01 to 1 mmol1/2kg−1/2h−1 and from 0.02 to 0.9 h−1, respectively. The overall activation energies involved were similar for both samples and for the monomolecular and bimolecular
periods (63–68 kJ/mol). The relative oxidation of methyl linoleate, which depended on the fatty acid composition of the FAME
sample, was unaffected by temperature. At the three temperatures assayed, hydroperoxydienes constituted approximately 90 and
50% of total hydroperoxides in the HL and HO samples, respectively. Formation of keto- and hydroxy-dienes was influenced by
temperature in a similar way to hydroperoxydienes and, consequently, changes in the distribution of compounds were not observed.
The addition of α-tocopherol not only decreased the overall oxidation rate, but also affected the distribution of compounds.
The content of hydroperoxydienes relative to that of total hydroperoxides was not affected by the presence of the antioxidant
in the HL sample, whereas a significant increase (75%) was found in the HO sample compared with the control (50%). The addition
of α-tocopherol in both samples also resulted in a slight increase of keto- and hydroxy-dienes in relation to hydroperoxydienes. 相似文献
126.
Mónica B. Betancor Ma. José Caballero Genciana Terova Samuela Corà Reda Saleh Tibiábin Benítez-Santana J. Gordon Bell Carmen María Hernández-Cruz Marisol Izquierdo 《Lipids》2012,47(12):1193-1207
Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, cellular and physiological functions in fish. However, high dietary levels of DHA increase free radical injury in sea bass (Dicentrarchus labrax) larvae muscle, even when vitamin E (α-tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with complementary antioxidant functions, such as vitamin C (ascorbic acid, vitC), could further contribute to prevent these lesions. The objective of the present study was to determine the effect of vitC inclusion (3,600?mg/kg) in high DHA (5?% DW) and α-TOH (3,000?mg/kg) microdiets (diets 5/3,000 and 5/3,000?+?vitC) in comparison to a control diet (1?% DHA DW and 1,500?mg/kg of α-TOH; diet 1/1,500) on sea bass larvae growth, survival, whole body biochemical composition and thiobarbituric acid reactive substances (TBARS) content, muscle morphology, skeletal deformities and antioxidant enzymes, insulin-like growth factors (IGFs) and myosin expression (MyHC). Larvae fed diet 1/1,500 showed the best performance in terms of total length, incidence of muscular lesions and ossification degree. IGFs gene expression was elevated in 5/3,000 diet larvae, suggesting an increased muscle mitogenesis that was confirmed by the increase in the mRNA copies of MyHC. vitC effectively controlled oxidative damages in muscle, increased α-TOH larval contents and reduced TBARS content and the occurrence of skull deformities. The results of the present study showed the antioxidant synergism between vitamins E and C when high contents of DHA are included in sea bass larvae diets. 相似文献
127.
Cristina Elena Ciomaga Mirela Airimioaei Valentin Nica Luminita M. Hrib Ovidiu F. Caltun Alexandra R. Iordan Carmen Galassi Liliana Mitoseriu Mircea N. Palamaru 《Journal of the European Ceramic Society》2012,32(12):3325-3337
Magnetoelectric composites of xNiFe2O4–(1 ? x)Pb(Zr,Ti)O3 with x = 2, 5, 10, 20, 30% were prepared by citrate–nitrate combustion using PZT-based template powders. In order to ensure a better connectivity of dissimilar phases, we have used chemical methods for preparation in situ composites, followed by adequate sintering procedure. The structural, microstructural and functional properties of di-phase magnetoelectric composites of NiFe2O4–PZT are reported. The XRD analysis is demonstrating the synthesis of pure ferrite phase directly on the ferroelectric templates. An excellent mixing was obtained in the composite powders, as proved by a detailed SEM analysis.The magnetic and dielectric behaviors of the ceramic composites vary with the ratio of the two phases. The dielectric behavior is greatly influenced by the magnetic phase. The magnetoelectric (ME) coefficient was measured as a function of applied DC magnetic field. The maximum ME coefficient (dE/dH) varies from 0.0011 mV/(cm Oe) to 0.5 mV/(cm Oe) with increasing of NF addition. 相似文献
128.
RM Domingues EL Oliveira CS Freire RM Couto PC Simões CP Neto AJ Silvestre CM Silva 《International journal of molecular sciences》2012,13(6):7648-7662
Eucalyptus bark contains significant amounts of triterpenoids with demonstrated bioactivity, namely triterpenic acids and their acetyl derivatives (ursolic, betulinic, oleanolic, betulonic, 3-acetylursolic, and 3-acetyloleanolic acids). In this work, the supercritical fluid extraction (SFE) of Eucalyptus globulus deciduous bark was carried out with pure and modified carbon dioxide to recover this fraction, and the results were compared with those obtained by Soxhlet extraction with dichloromethane. The effects of pressure (100-200 bar), co-solvent (ethanol) content (0, 5 and 8% wt), and multistep operation were studied in order to evaluate the applicability of SFE for their selective and efficient production. The individual extraction curves of the main families of compounds were measured, and the extracts analyzed by GC-MS. Results pointed out the influence of pressure and the important role played by the co-solvent. Ethanol can be used with advantage, since its effect is more important than increasing pressure by several tens of bar. At 160 bar and 40 °C, the introduction of 8% (wt) of ethanol greatly improves the yield of triterpenoids more than threefold. 相似文献
129.
Elton Joao Zierhut Rodrigo Battisti Ricardo Antonio Francisco Machado Cintia Marangoni 《化学工程与技术》2020,43(9):1884-1896
Intrinsic characteristics of distillation such as dead time and high nonlinearities do not allow the complete elimination of transient times when any external disturbance or set-point change occurs. Thus, aiming at the use of easy-tuning systems, a distributed-action control in trays of a diabatic distillation unit with Smith's predictor was implemented in the Simulink environment to further reduce transient times and out-of-specification product. The distributed-action strategy with Smith's predictor led to a reduction of 33.3 min (33 %) in the transient time of the top temperature control loop and 66 % in out-of-specification product, when compared with the conventional strategy, and thus is shown to be an efficient approach to increasing the productivity of distillation plants. 相似文献
130.
Frida S. Herrera-Vázquez Dr. Félix Matadamas-Martínez Dr. Rodrigo Aguayo-Ortiz Prof. Laura Dominguez Teresa Ramírez-Apan Prof. Lilián Yépez-Mulia Prof. Francisco Hernández-Luis 《ChemMedChem》2020,15(19):1802-1812
Microtubules are highly dynamic polymers composed of α- and β-tubulin proteins that have been shown to be potential therapeutic targets for the development of anticancer drugs. Currently, a wide variety of chemically diverse agents that bind to β-tubulin have been reported. Nocodazole (NZ) and colchicine (COL) are well-known tubulin-depolymerizing agents that have close binding sites in the β-tubulin. In this study, we designed and synthesized a set of nine 2,4-diaminoquinazoline derivatives that could occupy both NZ and COL binding sites. The synthesized compounds were evaluated for their antiproliferative activities against five cancer cell lines (PC-3, HCT-15, MCF-7, MDA-MB-231, and SK-LU-1), a noncancerous one (COS-7), and peripheral blood mononuclear cells (PBMC). The effect of compounds 4 e and 4 i on tubulin organization and polymerization was analyzed on the SK-LU-1 cell line by indirect immunofluorescence, western blotting, and tubulin polymerization assays. Our results demonstrated that both compounds exert their antiproliferative activity by inhibiting tubulin polymerization. Finally, a possible binding pose of 4 i in the NZ/COL binding site was determined by using molecular docking and molecular dynamics (MD) approaches. To our knowledge, this is the first report of non-N-substituted 2,4-diaminoquinazoline derivatives with the ability to inhibit tubulin polymerization. 相似文献