全文获取类型
收费全文 | 19800篇 |
免费 | 2118篇 |
国内免费 | 1193篇 |
专业分类
电工技术 | 580篇 |
技术理论 | 1篇 |
综合类 | 1967篇 |
化学工业 | 2404篇 |
金属工艺 | 822篇 |
机械仪表 | 1325篇 |
建筑科学 | 4485篇 |
矿业工程 | 703篇 |
能源动力 | 470篇 |
轻工业 | 1251篇 |
水利工程 | 575篇 |
石油天然气 | 1615篇 |
武器工业 | 181篇 |
无线电 | 880篇 |
一般工业技术 | 3215篇 |
冶金工业 | 809篇 |
原子能技术 | 126篇 |
自动化技术 | 1702篇 |
出版年
2024年 | 164篇 |
2023年 | 415篇 |
2022年 | 644篇 |
2021年 | 715篇 |
2020年 | 767篇 |
2019年 | 668篇 |
2018年 | 598篇 |
2017年 | 676篇 |
2016年 | 677篇 |
2015年 | 734篇 |
2014年 | 1076篇 |
2013年 | 1309篇 |
2012年 | 1328篇 |
2011年 | 1348篇 |
2010年 | 1065篇 |
2009年 | 1109篇 |
2008年 | 1010篇 |
2007年 | 1270篇 |
2006年 | 1067篇 |
2005年 | 887篇 |
2004年 | 845篇 |
2003年 | 673篇 |
2002年 | 541篇 |
2001年 | 537篇 |
2000年 | 506篇 |
1999年 | 376篇 |
1998年 | 322篇 |
1997年 | 329篇 |
1996年 | 256篇 |
1995年 | 206篇 |
1994年 | 150篇 |
1993年 | 138篇 |
1992年 | 114篇 |
1991年 | 82篇 |
1990年 | 78篇 |
1989年 | 102篇 |
1988年 | 54篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 57篇 |
1984年 | 42篇 |
1983年 | 39篇 |
1982年 | 30篇 |
1981年 | 4篇 |
1980年 | 18篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A variety of test techniques have been developed to test the performance of adhesives bonded in situ within joints. Most of these techniques measure strength, fracture toughness, or adhesive modulus of the bonded joint. Techniques to measure actual stress or strain values within a bonded joint are quite few in number. The Krieger gage1 is able to measure the average shear displacement along a 12.5 mm. gage length of a thick adherend joint. It has been used primarily to measure in situ shear moduli of adhesives. Brinson and his colleagues2 proposed bonding strain gages within adhesive joints to measure strains within the adhesive. Unfortunately, these gages are only sensitive to the lateral strains and not shear or peel strains. Because the lateral strains are dominated by the behavior of the adherends rather than the adhesive, the information which can be gained is incomplete. 相似文献
952.
E. Sancaktar 《The Journal of Adhesion》2013,89(1-4):211-220
The correspondence principle based on the Maxwell model and a nonlinear viscoelastic solution involving an iterative scheme are used to describe the time dependent variation of the adhesive maximum shear stress in adhesively bonded double lap joints. The results indicate that if the correspondence principle is applied, the use of Maxwell chain is necessary to approximate the continuous change in the relaxation time and to coincide with the results calculated using the nonlinear viscoelastic theory. 相似文献
953.
A new approach based on the theory of elasticity is proposed to study relaxation properties of adhesive transition layers. It involves experimental evaluation of the rate dependence of the fracture energy of the bulk polymer and its adhesive joint. The investigation of the interaction of a polymer surface layer with electroplated copper by XPS using the effect of differential charging (the latter produced by potential shift of the sample by 10V), makes it possible to identify the functional groups of adhesive brought into contact with substrate surface. For ABS copolymers a bond of -O … Cu type was formed. The mechanism of adhesive contact formation and factors affecting the strength of adhesive joints could be understood better by determining the properties of surface and transition layers. 相似文献
954.
The glass transition temperature (Tg) of acrylated triglycerides was clearly a function of the level of acrylation of triglyceride‐based polymers and was modeled using simple empirical relationships. We began by calculating the distribution of unsaturation sites in plant oils. We assumed a binomial distribution of chemical functionality that was added to these unsaturation sites to calculate the distribution of epoxides, acrylates, and reacted acrylates to predict the crosslink density, thermal softening, and dynamic mechanical behavior. The glass transition temperatures of n‐acrylated triglycerides were used as the relaxation temperatures of acrylated oils with a broad distribution of functionality for prediction of the modulus as a function of temperature. Essentially, the percent drop in the elastic modulus is equal to the percentage of n‐acrylated triglycerides in the acrylated oil with Tg less than that of the ambient temperature. The tan (δ) was also accurately predicted based on the percentage change of n‐functional triglycerides as the temperature changes from one relaxation temperature to the next. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
955.
Drying of densified spent grain in superheated steam (SS) may cause breakage and disintegration of the product in the initial stage of SS drying. The present work investigated the effect of solubles (0, 10, 30, 50, and 70% solubles) on the percentage change in length, diameter, volume; hardness; and the asymptotic modulus (EA) of the cylindrical compacts during SS drying. An increase in dimensions along with a decrease in hardness and EA of the compact was observed immediately after exposing it to SS. We observed a 47% increase in length and 12% increase in diameter for compacts having 0% solubles during the first five seconds of SS drying; however, when the soluble content increased to 70%, the percentage increase in length and diameter became 12 and 2%, respectively. Also, with an increase in the amount of solubles in the compact, a considerable increase in the hardness and EA of the compact was observed. The study also aimed to find suitable explanatory variables for predicting the hardness and EA of the compact using a stepwise forward regression method. 相似文献
956.
Jane L. O’Dell Charles R. Frihart 《Journal of Adhesion Science and Technology》2013,27(18-19):2027-2042
We studied the high temperature performance of soy meal processed to different protein concentrations (flour, concentrate, and isolate), as well as formulated soy-based adhesives, and commercial nonsoy adhesives for comparison. No thermal transitions were seen in phenol-resorcinol-formaldehyde (PRF) or soy-phenol-formaldehyde (SoyPF) or in as-received soy flour adhesive during differential scanning calorimetry scans heating at 10?°C/min between 35 and 235?°C. Heat flow rates decreased in the order soy flour (as received)?>?SoyPF?>?PRF?>?emulsion polymer isocyanate (EPI). In thermogravimetric analysis (TGA) scans from 110 to 300?°C at 2?°C/min, total weight loss decreased in the order soy flour (as-received)>SoyPF?>?PRF?>?casein?>?maple?>?EPI. For bio-based materials, the total weight loss (TGA) decreased in the order soy flour (as-received) > concentrate, casein?>?isolate. Dynamic mechanical analysis from 35 to 235?°C at 5?°C/min of two veneers bonded by cured adhesive showed 30–40% decline in storage modulus for maple compared to 45–55% for the adhesive made from soy flour in water (Soy Flour) and 70–80% for a commercial poly(vinyl acetate) modified for heat resistance. DMA on glass fiber mats showed thermal softening temperatures increasing in the order Soy Flour?<?casein?<?isolate?<?concentrate. We suggest that the low molecular weight carbohydrates plasticize the flour product. When soy-based adhesives were tested in real bondlines in DMA and creep tests in shear, they showed less decrease in storage modulus than the glass fiber-supported specimens. This suggests that interaction with the wood substrate improved the heat resistance property of the adhesive. Average hot shear strengths (ASTM D7247) were 4.6 and 3.1?MPa for SoyPF and Soy Flour compared to 4.7 and 0.8?MPa for PRF and EPI and 4.7 for solid maple. As a whole, these data suggest that despite indications of heat sensitivity when tested neat, soy-based adhesives are likely to pass the heat resistance criterion required for structural adhesives. 相似文献
957.
Extraction of ground spruce sapwood with pressurized hot water in an accelerated solvent extractor (ASE) at 170°C during 20, 60, and 100 min resulted in isolation of galactoglucomannans and aromatic substances, including lignin. The isolated lignin preparations were characterized by spectrometric (UV, FT-IR, 1H NMR, liquid and solid-state 13C NMR), chromatographic (RP-HPLC, HP-SEC, GC-FID, and GC-MS), conventional pyrolysis, thermally assisted hydrolysis, and methylation techniques in tandem with GC-MS, and classical wet chemistry (methoxyl groups, total and phenolic hydroxyl groups, derivatization followed by reductive cleavage—DFRC). The content of β-O-4 bonds in isolated lignins was similar to that in MWL and their proportion decreased with extraction time. The oxidation of isolated lignins and content of total hydroxyl groups were significantly increased with extraction time. The lignin structure underwent condensation and demethylation reactions during hot-water extraction. The induction of new phenylcoumaran substructures was proposed in isolated lignins. 相似文献
958.
ABSTRACT The changes in density and porosity and the microstructural development of apple tissue throughout the equilibration in osmotic treatments were analyzed for different osmotic solution concentrations. The effect of vacuum impregnation of the sample with the osmotic solution, before the osmotic treatment was also studied. Two periods were differentiated in the process. For relatively short term treatments (24–48 h) cell walls shrunk or separated from plasmalemma because of the cell water loss while compositional pseudoequilibrium was achieved. Afterwards for long term treatments, a bulk flux of osmotic solution into the fruit tissue occurred in line with the relaxation of mechanical energy accumulated in the deformed cell wall matrix. So, the true equilibrium (chemical plus mechanical), achieved when no changes either in sample composition or weight occurred, implied cell wall sphericity and sample volume recovery. However, some degree of irreversibility was observed in cell wall recovery, especially for osmotic treatments at high concentration without previous vacuum impregnation of sample. 相似文献
959.
ABSTRACT A method and a device for determination of the effective diffusion coefficient of active solvents in composite polymeric materials (CPM) based on cellulose derivatives are proposed and examined. This method accounts for anomalous mass transfer phenomena, considerable shrinkage and changes of sorption capacity of the CPM specimen allowing selection of the rational technological regime. Results of experimental studies on diffusion of acetone and ethanol in cellulose nitrate with various degrees of substitution are given as examples. 相似文献
960.