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61.
Real‐time monitoring by proton relaxometry of radical polymerization reactions of acrylamide in aqueous solution 下载免费PDF全文
Elton Jorge da Rocha Rodrigues Roberto Pinto Cucinelli Neto Pedro José Oliveira Sebastião Maria Inês Bruno Tavares 《Polymer International》2018,67(6):675-683
The potential of time‐domain nuclear magnetic resonance (TD‐NMR) for the real‐time monitoring of solution radical polymerizations is demonstrated. A model system composed of a redox‐pair initiator system, acrylamide as monomer and water as solvent was investigated. A second‐generation continuous wave free precession technique was employed to measure the longitudinal relaxation time constant (T1) of the samples throughout the polymerization reactions. This parameter was shown to be sensitive to the reactant feed free‐radical enhancement of the water molecule relaxation time, making it a good probe to monitor monomer conversion in real time in an automated, non‐destructive fashion. It was found that the T1 value was better than the transverse relaxation time constant (T2) for describing the evolution of the polymerization reactions, due to its greater sensitivity to paramagnetic effects. The TD‐NMR signal variation observed was linked to the formation, propagation and termination steps of the radical polymerization kinetics scheme. These first results may contribute to the application of real‐time monitoring of radical polymerization reactions employing low‐cost and robust TD‐NMR spectrometers. © 2018 Society of Chemical Industry 相似文献
62.
A polysaccharide‐immobilized chiral stationary phase (CSP) was prepared by the surface‐initiated atom transfer radical polymerization (SI‐ATRP), in pyridine, of cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate), having a polymerizable vinyl group, on the surface of SiO2 support. The successful preparation of the CSP was confirmed via Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, X‐ray photoelectron spectroscopy, elemental analysis and thermal analysis. The chiral recognition ability of the prepared CSP was evaluated with high‐performance liquid chromatography using 10 racemates with various mobile phases of hexane/alcohol, hexane/tetrahydrofuran and hexane/chloroform. As a result, this CSP prepared using SI‐ATRP can be used in tetrahydrofuran and chloroform solutions as eluents. Copyright © 2011 Society of Chemical Industry 相似文献
63.
Paula de Miranda Costa Maria Inês Bruno Tavares André L. B. S. Bathista Emerson O. da Silva José S. Nogueira 《应用聚合物科学杂志》2007,105(2):973-977
The nuclear magnetic resonance spectroscopy (NMR) studies of starches obtained by fruit seeds such as melon and watermelon were carried out as an analytical methodology to understand the molecular dynamic behavior. This study was also accompanied by the conventional X‐ray diffraction and thermal analysis. The NMR results give us a complete behavior of the samples at the molecular level. Thus, the information obtained from NMR will complement the data obtained from X‐ray and thermal analysis allowing us having responses on samples structure and dynamical behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
64.
65.
Juan Morote Anna Celma Jacques Planas José Placer Inés de Torres Mireia Olivan Juan Carles Jaume Reventós Andreas Doll 《International journal of molecular sciences》2014,15(8):13615-13623
The aim of this study was to analyze the relationship between statin use along with serum cholesterol levels and prostate cancer (PCa) detection and aggressiveness. Statin users of three years or more and serum cholesterol levels (SC) were assessed in 2408 men scheduled for prostate biopsy. SC was classified as normal (NSC: <200 mg/dL) or high (HSC: >200 mg/dL). High-grade PCa (HGPCa) was considered if the Gleason score was greater than 7. Statin users comprised 30.9% of those studied. The PCa detection rate was 31.2% of men on statins and 37% of non-statin users (p < 0.006). The PCa detection rate was 26.3% in men with NSC and 40.6% in those with HSC (p < 0.001). In the subset of NSC men, the PCa rate was 26.5% for statin users and 26.2% for non-users (p = 0.939), while in men with HSC, the PCa rate was 36.4% for statin users and 42.0% for non-statin users (p = 0.063). The HGPCa rate was 41.8% for statin users and 32.5% for non-users (p = 0.012). NSC men had a 53.8% rate of HGPCa, while the rate was only 27.6% in HSC men (p < 0.001). NSC men on statins had an HGPCa rate of 70.2%, while non-statin users had a rate of 41.2% (p < 0.001). The HGPCa rate for HSC men on statins was 18.8%, while the rate was 30.0% (p = 0.011) for non-users. Logistic regression analysis suggested that serum cholesterol levels could serve as an independent predictor of PCa risk, OR 1.87 (95% CI 1.56–2.24) and HGPCa risk, OR 0.31 (95% CI 0.23–0.44), while statin usage could not. Statin treatment may prevent PCa detection through serum cholesterol-mediated mechanisms. A disturbing increase in the HGPCa rate was observed in statin users who normalized their serum cholesterol. 相似文献
66.
Separation of guanine and cytosine base pairs in nucleotide is an interesting topic for investigation of DNA structure. Therefore, an understanding of nucleotide separation by chromatography is necessary to prepare DNA molecules. Guanine and cytosine separation in SMB was simulated by Aspen chromatography and it was experimented by assembled 3-zone simulated moving bed (SMB) with change of stream flow rates, sample concentration, and desorbent flow rate. The simulation of batch chromatography was also confirmed by HPLC experiments. Based on these, good operating conditions of SMB chromatography were determined. Three-zone SMB equipment was set up by connecting three C18-HPLC columns, four HPLC pumps, and six multiposition valves. Batch chromatography of cytosine and guanine was conducted to determine the isotherms of the two nucleotides. The outlet streams of SMB, raffinate and extract were sampled and analyzed by analytical HPLC system. The adsorption isotherms of cytosine and guanine were HC= 0.5 and H G =1.05. The highest experimental purity of cytosine and guanine in SMB was obtained as 94.9% and 89.8% with operating parameters of Q feed =0.2 mL/min, Q desorbent =0.6 mL/min, Q extract =0.2 mL/min, Q raffinate =0.6 mL/min, and switching time=7 min. 相似文献
67.
Physicochemical properties and bioactivity of brown seaweed fucoidan prepared by ultra high pressure-assisted enzyme treatment 总被引:1,自引:0,他引:1
Keunhyoung Park Eunhye Cho Man-Jin In Dong Chung Kim Hee Jeong Chae 《Korean Journal of Chemical Engineering》2012,29(2):221-227
The effects of ultra-high pressure (UHP, 100 MPa, 40, 24 h) processing and enzyme treatment on the physicochemical properties
and anticoagulant activity of fucoidan obtained from Undaria pinnatifida sporophyll (UPS) were investigated. Crude UPS fucoidan (F
UPS
) with an average MW of 877 kDa was slightly depolymerized by UHPassisted Tunicase treatment, yielding fucoidan with a lower
MW (600–800 kDa). UHP-enzyme treatment decreased the sulfate, fucose and galactose contents of F
UPS
but increased its glucose content. From FT-IR spectrum, UHP-enzyme treatment was found not to cause a structural change on
S=O and C-O-S. After UHP-enzyme treatment, the sulfate content and average MW of F
UPS
decreased with the increase of Tunicase concentration. It was found that among the UHP-enzyme-treated fucoidans, F
UPS
-T0.3-U (Tunicase 0.3% treatment+UHP treatment) possessed the highest anticoagulant activity. F
UPS
-T0.3-U appeared to inhibit blood coagulation via intrinsic pathway. With the increase of sulfate content in F
UPS
, activated partial thromboplastin time (APTT) and thrombin time (TT) showed a tendency of increase. APTT and TT had the highest
values in F
UPS
-T0.3-U in which the sulfate concentration was 24%, but on the contrary decreased at a sulfate concentration of above 24%.
This result indicates that there is an optimum sulfate concentration for the anticoagulant activity of fucoidan. Consequently,
UHP-assisted enzymatic treatment was found to be helpful for the improvement of anticoagulant activities of fucoidan. 相似文献
68.
Sunhwan Hwang Joongwon Lee Ung Gi Hong Ji Chul Jung Dong Jun Koh Hyojun Lim Changdae Byun In Kyu Song 《Journal of Industrial and Engineering Chemistry》2012,18(1):243-248
Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH4 decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H2 adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H2 adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH4 in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction. 相似文献
69.
Seung Bum Lee Hyung Jin Lee In Kwon Hong 《Journal of Industrial and Engineering Chemistry》2012,18(2):635-641
Epoxy resin is used as a material for electrical and electronics molding in various forms but its thermal conductivity must be controlled with various additives on account of its lower conductivity than metal or ceramics. Silicon dioxide (SiO2) and silica were selected as the reinforcement and diluent filler for epoxy resins, respectively. The optimum amount of reinforcement filler, SiO2, was 50 wt%. The thermal properties and thermal stability were observed according to silica ratio and particle size. An epoxy modified with a polyamide type hardener showed superior thermal conductivity to that modified with a cyclo-aliphatic amine type hardener. The thermal conductivity increased with increasing silica ratio and particle size. The thermal stability evaluation based on the particle size of silica was in the order of 14/18 mesh (1.00–1.16 mm) > 8/10 mesh (1.65–2.36 mm) > 28/35 mesh (0.42–0.59 mm). The optimum silica size of the diluent filler was 14/18 mesh (1.00–1.16 mm). An epoxy type resin transformer with excellent thermal properties and thermal stability could be designed when the mixing weight of epoxy resin was equal to that of the hardener. 相似文献
70.