全文获取类型
收费全文 | 3784篇 |
免费 | 104篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 48篇 |
综合类 | 6篇 |
化学工业 | 706篇 |
金属工艺 | 117篇 |
机械仪表 | 60篇 |
建筑科学 | 141篇 |
矿业工程 | 27篇 |
能源动力 | 73篇 |
轻工业 | 364篇 |
水利工程 | 24篇 |
石油天然气 | 3篇 |
无线电 | 338篇 |
一般工业技术 | 687篇 |
冶金工业 | 900篇 |
原子能技术 | 55篇 |
自动化技术 | 344篇 |
出版年
2023年 | 19篇 |
2022年 | 25篇 |
2021年 | 71篇 |
2020年 | 41篇 |
2019年 | 59篇 |
2018年 | 67篇 |
2017年 | 61篇 |
2016年 | 61篇 |
2015年 | 47篇 |
2014年 | 75篇 |
2013年 | 182篇 |
2012年 | 126篇 |
2011年 | 178篇 |
2010年 | 130篇 |
2009年 | 122篇 |
2008年 | 128篇 |
2007年 | 123篇 |
2006年 | 118篇 |
2005年 | 91篇 |
2004年 | 81篇 |
2003年 | 91篇 |
2002年 | 91篇 |
2001年 | 77篇 |
2000年 | 73篇 |
1999年 | 90篇 |
1998年 | 274篇 |
1997年 | 185篇 |
1996年 | 143篇 |
1995年 | 89篇 |
1994年 | 93篇 |
1993年 | 87篇 |
1992年 | 46篇 |
1991年 | 38篇 |
1990年 | 39篇 |
1989年 | 57篇 |
1988年 | 37篇 |
1987年 | 31篇 |
1986年 | 35篇 |
1985年 | 28篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 19篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 22篇 |
1978年 | 29篇 |
1977年 | 32篇 |
1976年 | 67篇 |
1975年 | 27篇 |
1974年 | 19篇 |
排序方式: 共有3893条查询结果,搜索用时 31 毫秒
131.
In a Rheotens experiment, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. For thermo-rheologically simple polymer melts, the existence of Rheotens-mastercurves is proven. Rheotens-mastercurves are invariant with respect to changes in melt temperature. Also, for polymer melts with different average molar masses, but similar molar mass distribution and branching structure, Rheotens-mastercurves are invariant to changes in the average molar mass. It is shown, by testing several polyethylenes with different molar mass distribution and different long-chain branching, that Rheotens-mastercurves allow a direct and quantitative assessment of the drawability of polymer melts under actual processing conditions, i.e. under the action of a constant tensile force and including the effects of the rheological prehistory in the extrusion die. 相似文献
132.
G. Glas Rudolf Gompper M. Junius R. Mertz H.-U. Wagner Heinrich Nth M. Staudigl 《Advanced Synthesis \u0026amp; Catalysis》1990,332(6):949-967
Donor Substituted 2,4-Diazacyclopentadienones and Indigoid 1,3,5,7-Tetraazafulvalenes Hydrolysis of tris(diethylamino)imidazolylium chloride gives rise to 2,5-bis-diethyl-amino-4H-imidazolin-4-one; thiolysis leads, depending on conditions, to 2,5-bis-diethylamino-4H-imidazolin-4-thione or potassium 2,6-bis-diethylamino-1,3,5,7-tetraazafulvalene-4,8-dithiolate. The latter can be protonated to form green 2,6-bis(dimethylamino)-3,4,7,8-tetrahydro-1,3,5,7-tetraaza-fulvalen-4,8-dithione, a new indigoid compound, and alkylated to give blue 2,6-bis-diethylamino-4,8-bis-alkylthio-1,3,5,7-tetraazafulvalenes. Treatment of 2,5-bis-diethylamino-4H-imidazolin-4-thione with copper furnishes 2,6,4,8-tetrakis-diethylamino-1,3,5,7-tetraazafulvalene. – Oxidation of 2,6-bis-dimethylamino-3,4,7,8-tetrahydro-1,3,5,7-tetraazafulvalen-4,8-dithione gives rise to (2,2′-bis-diethylamino-4,4′-bi(4H-imidazol)-5,5′-dithione, corresponding to dehydroindigo, and reduction leads to a colorless compound, corresponding to leucoindigo. 相似文献
133.
Luz Bertoia Jorge R. Wagner Andrés L. Márquez 《Journal of the American Oil Chemists' Society》2020,97(10):1071-1081
The objective was to study the microstructure and freeze–thaw stability of margarine-like emulsions formulated with vegetable fats using differential scanning calorimetry. Emulsions were prepared with 20% w/w dispersed aqueous phase and a continuous lipid phase composed by coconut oil (CO) and/or palm oil (PO) plus polyglycerol polyricinoleate (PGPR) as emulsifier. Mean temperature (TM) and crystallization enthalpy (ΔHc) were obtained from the exothermic peaks corresponding to freezing of aqueous phase. Successive cooling–heating–cooling cycles were applied to analyze changes in the exothermic peak. The emulsion prepared with CO (without PO) and 1% w/w PGPR in lipid phase showed higher water droplets size (TM = −44.8 ± 0.1 °C) and lower quantity of stabilized aqueous phase (ΔHc = 28.9 ± 1.2 J g−1) prior to application of temperature cycles, while coalescence and (presumably) water transfer processes occurred during the treatment. The use of 2% w/w PGPR was sufficient to accomplish full stabilization of aqueous phase (TM = −45.9 ± 0.1 °C; ΔHc = 42.6 ± 0.3 J g−1) before and after the freeze–thaw treatment. The total or partial (50%) substitution of CO by PO in emulsions with 1% w/w PGPR also improved the stability of the system, exhibiting slight microstructural changes. This enhanced stability would be linked to reduced water droplets size because of more rapid crystallization of lipid phase and immobilization of aqueous phase after emulsion preparation. In conclusion, it is possible to obtain margarine-like emulsions prepared with CO and/or PO using relatively low emulsifier concentration and maintaining a desired microstructure after freeze-thawing if the percentage ratio of both fats is controlled. 相似文献
134.
135.
Long‐term testing of a high temperature polymer electrolyte membrane fuel cell: The effect of reactant gases
下载免费PDF全文
![点击此处可从《American Institute of Chemical Engineers》网站下载免费的PDF全文](/ch/ext_images/free.gif)
F. Javier Pinar Nadine Pilinski Peter Wagner 《American Institute of Chemical Engineers》2016,62(1):217-227
The investigations have been conducted with different oxidants and fuels with the aim of determining the state‐of‐the‐art of commercially available high temperature polymer electrolyte fuel cells based on polybenzimidazole for its application in combined heat and power generation systems. The fuel cell test performed with synthetic reformate (?63 μV/h) showed an increase of anode charge and mass transfer resistances. This behavior has suggested that CO may be generated from the CO2 included in the synthetic reformate via reverse water gas shift reaction. The fuel cell test performed with pure O2 developed the highest degradation rates (?70 μV/h) due to fast oxidative degradation of membrane electrode assembly materials such as cathode catalyst and membrane. Fuel cell operation with H2/air exhibited the lowest degradation rates (?57 μV/h) and it requires longer investigating times to identify the different degradation mechanisms. Moreover, fuel cell tests performed with air suggested longer break‐in procedures to complete catalyst activation and redistribution of electrolyte. © 2015 American Institute of Chemical Engineers AIChE J, 62: 217–227, 2016 相似文献
136.
J. Porstendörfer H. G. Scheibel F. G. Pohl O. Preining G. Reischl P. E. Wagner 《Aerosol science and technology》2013,47(2):207-209
Please click here to find the Letter to the Editor to which this Response refers: http://dx.doi.org/10.1080/02786828608959113 相似文献
137.
Zero‐Modified Geometric INAR(1) Process for Modelling Count Time Series with Deflation or Inflation of Zeros
下载免费PDF全文
![点击此处可从《时间序列分析杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wagner Barreto‐Souza 《时间序列分析杂志》2015,36(6):839-852
In this article, we propose a first‐order integer‐valued autoregressive [INAR(1)] process for dealing with count time series with deflation or inflation of zeros. The proposed process has zero‐modified geometric marginals and contains the geometric INAR(1) process as a particular case. The proposed model is also capable of capturing underdispersion and overdispersion, which sometimes are caused by deflation or inflation of zeros. We explore several statistical and mathematical properties of the process, discuss point estimation of the parameters and find the asymptotic distribution of the proposed estimators. We also propose a test based on our model for checking if the count time series considered is deflated or inflated of zeros. Two empirical illustrations are presented in order to show the potential for practice of our zero‐modified geometric INAR(1) process. This article contains a Supporting Information. 相似文献
138.
We propose a consistent monitoring procedure for structural change in a cointegrating relationship. The procedure is inspired by Chu et al. (1996) by being based on parameter estimation on a prebreak ‘calibration’ period. We use three modified least squares estimators to obtain nuisance parameter‐free limiting distributions. We study the asymptotic and finite sample properties of the procedures and finally apply the approach to monitor two‐fundamentals‐driven US housing prices cointegrating relationships over the period 1976:Q1–2010:Q4 using the data of Anundsen (2015). Depending on the relationship considered and the estimation method used, a break point is detected as early as 2003:Q2, that is, well before US housing prices started to fall in 2007. 相似文献
139.
Application of β-Sitosterol + γ-Oryzanol-Structured Organogel as Migration Barrier in Filled Chocolate Products
下载免费PDF全文
![点击此处可从《Journal of the American Oil Chemists](/ch/ext_images/free.gif)
Alexandra Wendt Karin Abraham Christin Wernecke Julia Pfeiffer Eckhard Flöter 《Journal of the American Oil Chemists' Society》2017,94(9):1131-1140
Oil migration in filled pralines is a phenomenon that is highly correlated with the occurrence of chocolate bloom. In this study the potential to suppress or prevent oil migration by incorporation of sterol/sterolster-structured organogels was evaluated. Different quantities, 2.5 or 14% (w/w), of gel with structurant levels of either 10 or 25% (w/w) were studied in a layered model system. The gel was either a part of the nougat or of the chocolate phase, or as a separate layer. Samples were monitored regularly for a period of 24 weeks at storage temperatures of 10, 18 and 28 °C. The amount of migrated oil was determined via DSC analysis of a surface sample. The results indicate that, despite the additional oil brought into the system via the oleogel, the level of oil found in the chocolate layer is reduced through the presence of the gel. In particular, the three-layer system and gelled chocolate appear to be promising routes to either suppress oil migration or improve nutritional profiles by incorporation of liquid oils. 相似文献
140.
Characterization of activated sludge flocs by confocal laser scanning microscopy and image analysis 总被引:7,自引:0,他引:7
Schmid M Thill A Purkhold U Walcher M Bottero JY Ginestet P Nielsen PH Wuertz S Wagner M 《Water research》2003,37(9):2043-2052
In this study we present a new approach to determine volumes, heterogeneity factors, and compositions of the bacterial population of activated sludge flocs by 3D confocal imaging. After staining the fresh flocs with fluorescein-isothiocyanate, 75 stacks of images (containing approx. 3000 flocs) were acquired with a confocal laser scanning microscope. The self-developed macro 3D volume and surface determination for the KS 400 software package combined the images of one stack to a 3D image and calculated the real floc volume and surface. We determined heterogeneity factors like the ratio of real floc surface to the surface of a sphere with the respective volume and the fractal dimension (D(f)). According to their significant influence on floc integrity and quality, we also investigated the chemical composition of flocs and quantified their bacterial population structure by using group-specific rRNA-targeted probes for fluorescence in situ hybridization. By a settling experiment we enriched flocs with poor settling properties and determined the above-mentioned parameters. This approach revealed shifts in floc volume, heterogeneity, and bacterial and chemical composition according to the settling quality of the flocs. 相似文献