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311.
Binary blend films from lactide-rich poly(D -lactide-co-glycolide) (PDLG) and poly(L -lactide-co-glycolide) (PLLG) were obtained by casting methylene chloride solutions of the two mixed copolymers with different D- and L-lactide contents (XDI and XLI ), and their crystallization was studied by differential scanning calorimetry (DSC). Four combinations were selected from the binary (A-B) blends: mixing of the same polymer [XDI (A) = XDI (B) or XLI (A) = XLI(B)], blending under XDI (B) = XLI (A), blending of a D -lactide homopolymer [XDI(B) = 1] with other PDLGs, and blending of a D -lactide homopolymer [XDI(B) = 1] with other PLLGs. Racemic crystallites were exclusively formed between PDLG and PLLG when they had high lactide unit contents. The melting point and enthalpy of fusion of the racemic crystallites decreased with a decrease in XDI of PDLG or XLI of PLLG, suggesting that glycolide units in the polymer disturbed the growth of the racemic crystallites. A similar behavior was also observed for the homocrystallization in nonblended copolymer films. Homocrystallites composed entirely either of D -lactide unit or L-lactide unit sequences were formed when one component was crystallizable and the other component had the same sign of optical rotation or very different lactide content. An interesting finding was that even nonhomocrystallizable lactide-poor PDLG and PLLG could form racemic crystallites when both were blended. © 1994 John Wiley & Sons, Inc. 相似文献
312.
This research addresses some factors that control the stability of dilute suspensions in sedimentation processes under a dynamic environment. Experimental and numerical studies were conducted about the sedimentation velocity control of dilute suspensions by horizontal movement for particle concentrations up to 8 wt.%. Nearly monodispersed particles were used as test particles. The effects of horizontal movement speed and amplitude on particle sedimentation process were investigated. Under stationary conditions, particles settle in only one vertical direction because of gravitational force. However, complicated particle motions arise under moving conditions due to circulation flow in horizontal moving conditions. The results show that horizontal movement can reduce the particle settling velocity or maintain the stability of the suspension. 相似文献
313.
T Inokuma N Tamaki T Torizuka Y Magata M Fujii Y Yonekura T Kajiyama G Ohshio M Imamura J Konishi 《Canadian Metallurgical Quarterly》1995,195(2):345-352
PURPOSE: To assess the clinical value of positron emission tomography (PET) with fluorine-18-labeled fluorodeoxyglucose (FDG) for identification of pancreatic carcinoma. MATERIALS AND METHODS: Forty-six patients suspected of having a pancreatic neoplasm and who were to undergo surgery prospectively underwent FDG PET, computed tomography (CT), and transabdominal ultrasound (US). Endoscopic US was performed in 40 patients. Images were independently interpreted and compared with the histopathologic findings at surgery (41 patients) or with clinical follow-up findings (five patients). RESULTS: In 33 of 35 patients, foci of pancreatic carcinomas (10-100 mm in diameter) were identified as an increase in FDG uptake, whereas CT, transabdominal US, and endoscopic US depicted the foci in 31, 31, and 28, cases, respectively. Among 11 benign lesions, nine showed no increased FDG uptake (specificity = 82%). Specificities of the other modalities were lower. False-positive findings were obtained in a case of chronic active pancreatitis and in a serous cystadenoma. CONCLUSION: FDG PET, which provides "biochemical" information, is accurate in identifying pancreatic carcinoma and may be a method of choice when imaging equivocal masses detected with other "anatomic" imaging studies. 相似文献
314.
Voice signal processing requires real-time processing. For this reason, a new method which updates the spectrum by using input
data is proposed. In this method, analysis in the time-frequency domain is executed as well as wavelet transform. Vowels /i/
and /e/ consist of fundamental, harmonic, and high frequency waves. These high frequency waves determine the sounds of /i/
and /e/. These high frequency waves may also exist in /a/ and /o/. In this article, we analyze these high frequency waves
by using a new analyzing method, and we show the constitution of high frequency waves. Since the waveform of a consonant does
not repeat, the analysis cannot be performed like the analysis of the high frequency wave of a vowel. In a consonant, we show
the fluctuation of the spectrum with time. 相似文献
315.
Youhei Sugimoto Hideto Adachi Keisuke Yamamoto Dong Wang Hideharu Nakashima Hiroshi Nakashima 《Materials Science in Semiconductor Processing》2006,9(6):1031
High permittivity (high-k) gate dielectrics were fabricated using the plasma oxidation of Hf metal/SiO2/Si followed by the post-deposition annealing (PDA), which induced a solid-phase reaction between HfOx and SiO2. The oxidation time and PDA temperature affected the equivalent oxide thickness (EOT) and the leakage current density of the high-k dielectric films. The interfacial structure of the high-k dielectric film/Si was transformed from HfOx/SiO2/Si to HfSixOy/Si after the PDA, which led to a reduction in EOT to 1.15 nm due to a decrease in the thickness of SiO2. These high-k dielectric film structures were investigated by X-ray photoelectron spectroscopy. The leakage current density of high-k dielectric film was approximately four orders of magnitude lower than that of SiO2. 相似文献
316.
Kiyoshi Matsuyama Kenji Mishima Ken‐Ichiro Hayashi Hideharu Ishikawa Hideto Matsuyama Toru Harada 《应用聚合物科学杂志》2003,89(3):742-752
The rapid expansion from a supercritical solution with a nonsolvent (RESS‐N) was applied to the formation of polymeric microcapsules containing medicines such as p‐acetamidophenol, acetylsalicylic acid, 1,3‐dimethylxanthine, flavone, and 3‐hydroxyflavone. A suspension of medicine in carbon dioxide (CO2) containing a cosolvent and dissolved polymer was sprayed through a nozzle to atmospheric pressure. The pre‐expansion pressure was 10–25 MPa, and the temperature was 308–333 K. The polymers were poly(L ‐lactic acid) (molecular weight = 5000), poly(ethylene glycol) (PEG; PEG4000, molecular weight = 3000; PEG6000, molecular weight = 7500; and PEG20000, molecular weight = 20,000), poly(methyl methacrylate) (molecular weight = 15,000), ethyl cellulose (molecular weight = 5000), and PEG–poly(propylene glycol)–PEG triblock copolymer (molecular weight = 13,000). The solubilities of the polymers as coating materials and these medicines as core substance were very low in CO2. However, the solubilities of these polymers in CO2 significantly increased with the addition of low molecular weight alcohols as cosolvents. After RESS‐N, polymeric microcapsules were formed according to the precipitation of the polymer caused by a decrease in the solvent power of CO2. This method offered three advantages: (1) enough of the coating polymers, which were insoluble in pure CO2, dissolved; (2) the microparticles of the medicine were encapsulated without adhesion between the particles because a nonsolvent was used as a cosolvent and the cosolvent remaining in the mixture was removed by the gasification of CO2; and (3) the polymer‐coating thickness was controlled with changes in the feed composition of the polymer for drug delivery. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 742–752, 2003 相似文献
317.
Koichiro Fukuda Shinji Inoue Hideto Yoshida 《Journal of the American Ceramic Society》2003,86(1):112-114
Four types of tricalcium aluminate solid solutions with different concentrations of Na2 O and SiO2 were prepared and examined using an electron probe microanalyzer. The atomic ratios, including those determined in a previous study, were derived from the oxide compositions and provided excellent correlations between Ca and Na + Si (i.e., Ca = 3.003 − 0.48[Na + Si]), and Al and Si (Al = 1.997 − 1.02Si). Because the replacement reactions, Ca2+ ↔ 2Na+ and Ca2+ + 2Al3+ ↔ 2Si4+ , independently occur within the same crystal, these reactions have been simply combined together to generate a new formula, Na2 x Ca3− x − y (Al1− y Si y )2 O6 , where x is the amount of Ca substituted by Na, and y is the amount of Al substituted by Si. This formula leads to the equations Ca = 3 − 0.5[Na + Si] and Al = 2 − Si, which nicely account for the constrained chemical variation of the actual solid solutions with 0 ≤ x < 0.049 and 0 ≤ y < 0.073. 相似文献
318.
The thermal properties of n‐hexadecane (HD) encapsulated in crosslinked capsule particles containing a water and/or air domain were studied from the viewpoint of heat‐storage applications. The capsule particles were prepared by the microsuspension polymerization of divinylbenzene at 70°C with the self‐assembling of phase‐separated polymer method that we developed. In the differential scanning calorimetric thermograms, pure HD had a single solidification temperature (Ts) peak at 15°C, whereas the encapsulated HD containing a water domain had two peaks at 6 and 1°C. That is, the encapsulated HD containing the water domain required a longer time and lower temperature to complete the solidification than pure HD, which was negative for heat‐storage applications. However, once the particles were dried and the water domain was replaced with air, the problem with the partially lowered Ts improved. The air domain was also found in the encapsulated HD core after solidification because of the shrinkage of HD. The presence of the air domain did not affect the thermal stability of the encapsulated HD. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
319.
320.
For a comprehensive understanding of material selection and utilization at the beginning of human history, the mechanical properties, surface morphologies, surface roughness, and internal microstructures of lithic raw materials used in the Upper Paleolithic age are analyzed. A case study reveals that certain materials with hardness greater than approximately 6.0 GPa with even surfaces, which were composed of extremely fine crystal grains with diameters from approximately 0.1 to 0.5 µm, were elaborately selected for fabricating sharp-edged blades. Additionally, material influence on the progress of the manufacture of tools was observed: materials with high hardness and strength tended to halt the manufacture process in the initial stages, whereas materials with low hardness and strength tended to facilitate the fabrication process to the final stages. These results demonstrate that detailed analyses of the intrinsic properties of actual prehistoric materials could provide useful and significant information for understanding material-related activities in prehistoric ages. 相似文献