全文获取类型
收费全文 | 86509篇 |
免费 | 6273篇 |
国内免费 | 2928篇 |
专业分类
电工技术 | 4353篇 |
技术理论 | 9篇 |
综合类 | 4650篇 |
化学工业 | 15511篇 |
金属工艺 | 4454篇 |
机械仪表 | 5233篇 |
建筑科学 | 7028篇 |
矿业工程 | 1985篇 |
能源动力 | 2480篇 |
轻工业 | 4902篇 |
水利工程 | 1447篇 |
石油天然气 | 4539篇 |
武器工业 | 488篇 |
无线电 | 10443篇 |
一般工业技术 | 11301篇 |
冶金工业 | 4687篇 |
原子能技术 | 831篇 |
自动化技术 | 11369篇 |
出版年
2024年 | 324篇 |
2023年 | 1314篇 |
2022年 | 2280篇 |
2021年 | 3113篇 |
2020年 | 2337篇 |
2019年 | 2029篇 |
2018年 | 2256篇 |
2017年 | 2518篇 |
2016年 | 2359篇 |
2015年 | 2943篇 |
2014年 | 4018篇 |
2013年 | 5070篇 |
2012年 | 5245篇 |
2011年 | 5519篇 |
2010年 | 4901篇 |
2009年 | 4716篇 |
2008年 | 4466篇 |
2007年 | 4402篇 |
2006年 | 4647篇 |
2005年 | 4133篇 |
2004年 | 2784篇 |
2003年 | 2497篇 |
2002年 | 2192篇 |
2001年 | 2019篇 |
2000年 | 2281篇 |
1999年 | 2560篇 |
1998年 | 2386篇 |
1997年 | 1886篇 |
1996年 | 1743篇 |
1995年 | 1447篇 |
1994年 | 1216篇 |
1993年 | 880篇 |
1992年 | 655篇 |
1991年 | 543篇 |
1990年 | 409篇 |
1989年 | 367篇 |
1988年 | 318篇 |
1987年 | 175篇 |
1986年 | 165篇 |
1985年 | 112篇 |
1984年 | 98篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 38篇 |
1979年 | 32篇 |
1978年 | 13篇 |
1977年 | 33篇 |
1976年 | 16篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
811.
Rejection of nasturtium,Tropaeolum majus, by cabbage-reared larvae ofPieris rapae has been explained by the presence of feeding deterrents in the nastrutium foliage. Sensitivity to the deterrents develops as neonate larvae feed on cabbage. The most prominent deterrent compound, which is present in nasturtium at a concentration of 40 mg/100 g fresh leaves, was identified as chlorogenic acid. When neonate larvae were fed on a cabbage leaf treated with high concentrations of deterrent-containing extracts of nasturtium foliage, they remained insensitive to the deterrents, so they accepted nasturtium when transferred as second instars. When neonate larvae were reared on a cabbage leaf treated with 0.1 mg chlorogenic acid, ca. 35% of the second instars accepted nasturtium. Similar dietary exposure of neonates to the subunits of chlorogenic acid, caffeic acid and quinic, acid resulted in much less or no effect on the rejection behavior of second instars. The results suggest that the combined effects of specific chemical constituents of nasturtium can explain the rejection of this plant by larvae ofP. rapae, but if larvae are continuously exposed to these compounds immediately after hatching, they apparently become habituated to the feeding deterrents. The lack of activity of the subunits of chlorogenic acid suggests that specific structural features are necessary for a dietary constituent to cause such habituation or suppression of sensitivity development. 相似文献
812.
Butan‐1‐ol modified toluene diisocyanate tri mer (TDI‐trimer) was synthesized and characterized with Fourier transform infrared spectroscopy, gel permeation chromatography, and thermal gravimetry analysis techniques. The modified TDI‐trimer showed good dissolvable ability with hydroxy resin and can be used to produce paints with acrylic polyol resin. The thermal stability of the modified TDI‐trimer was improved by simply increasing both the amount of catalyst and the ratio of ? NCO/? OH, less depended on the kind of catalyst. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4958–4962, 2006 相似文献
813.
An experimental study was carried out on the AIBN-initiated polymerization of styrene at 60°C. The kinetic rate constants were determined by the method of moments and the MWD method, which was proposed in a previous paper. The results compared favorably with the data in the literature and the MWD method was noted to yield more consistent results than the method of moments, which indicates the importance of considering the whole molecular weight distribution. The theoretical MWD was found to approximate the experimental MWD well. The chain-transfer constant to AIBN was found to be between 0.09 and 0.14. 相似文献
814.
For mitigating the emission of greenhouse gas CO2 from general air combustion systems, a clean combustion technology O2/RFG is in development. The O2/RFG combustion technology can significantly enhance the CO2 concentration in the flue gas; however, using almost pure oxygen or pure CO2 as feed gas is uneconomic and impractical. As a result, this study proposes a modified O2/RFG combustion technology in which the minimum pure oxygen is mixed with the recycled flue gas and air to serve as the feed gas. The effects of different feed gas compositions and ratios of recycled flue gas on the emission characteristics of CO2, CO and NOx during the plastics incineration are investigated by theoretical and experimental approaches.Theoretical calculations were carried out by a thermodynamic equilibrium program and the results indicated that the emissions of CO2 were increased with the O2 concentrations in the feed gas and the ratios of recycled flue gas increased. Experimental results did not have the same trends with theoretical calculations. The best feed gas composition of the modified O2/RFG combustion was 40% O2 + 60% N2 and the best ratio of recycled flue gas was 15%. As the O2 concentration in feed gas and the ratio of recycled flue gas increased, the total flow rates and pressures of feed gas reduced. The mixing of solid waste and feed gas was incomplete and the formation of CO2 decreased. Moreover, the emission of CO was decreased as the O2 concentration in feed gas and the ratio of recycled flue gas increased. The emission of NOx gradually increased with rising the ratio of recycled flue gas at lower O2 concentration (<40%) but decreased at higher O2 concentration (>60%). 相似文献
815.
816.
Summary A new route for the preparation of soluble fullerenated polymer through the reaction of carbanion intermediates of polymers with fullerenes, particularly C60, is demonstrated. Confirmation of the covalent attachment of C60 to the polystyrene backbone is by a variety of techniques such as UV-Vis, FT-IR, TGA, SEM and 13C NMR etc. The product, which has a visibly brownish yellow cast when compared with the unreacted polymer, is soluble in some common organic solvents. The thermal stability of pure polystyrene is enhanced by C60-chemical modification, and no bonds within the carbon sphere are broken. 相似文献
817.
The promoting effect of ultrasonic wave on the hydrodynamics and mass transfer characteristics of the loop airlift reactor was studied. The gas holdup, liquid circulation velocity, mixing time and overall volumetric mass transfer coefficient were examined and compared, with and without ultrasonic wave in the reactor. The experimental results show that ultrasound has almost no notable effect on the gas holdup, but has a tendency to decrease gradually the liquid circulation velocity and increase the overall volumetric mass transfer coefficient; and the effect on the mixing time is relatively complex. At low superficial gas velocity, the low powered ultrasound promotes the radial mixing of fluid; with the ultrasonic power increasing, ultrasonic vibration obstructs the axial mixing of fluid. Moreover, the effect of ultrasonic wave on the mixing time gradually decreases with the increase in the superficial gas velocity. Therefore there exists an optimal ultrasonic power for hydrodynamics and mass transfer. Correlations were also proposed for the hydrodynamics and mass transfer characteristics of the reactor. 相似文献
818.
以扫描仪面框薄壁件注塑成型为例,应用Moldflow软件分析了模具温度、熔体温度、浇口位置和保压参数对翘曲变形的影响规律,提出了减小翘曲变形的工艺措施,分析结果与生产实际吻合。 相似文献
819.
A real‐time cell electronic sensing (RT‐CES) system has been used for label‐free dynamic measurements of cell responses to toxicant. Cells are grown onto the surfaces of the microelectronic sensors. Changes in cell number expressed as cell index (CI) have been recorded on‐line as time series. The CI data are used for dynamic modelling or parameter estimation for cell cytotoxicity process. We consider two dynamic modelling approaches, namely data‐based system identification and first principle modelling. It is shown that data‐based system identification can provide a quick solution for the cytotoxicity dynamic models and is effective for short‐term predictions. It, however, can be poor for long‐term predictions, particularly if there is no output correction, i.e., when the model is used for simulation. In view of this, the first principle modelling approach by considering fundamental physical principles such as toxicant transport is explored. For long‐term prediction or simulation, the prediction performance for some of cytotoxicity process is dramatically improved using the models obtained from the latter approach. This happens only if the underlying mechanism is truly understood. Through several cytotoxicity modelling and validation studies, it is shown that the black box modelling and first principle modelling both should be considered in challenging modelling problems such as the cytotoxicity. Pros and cons of the two modelling approaches are discussed. 相似文献
820.
Fengyang Wang Xueying Huang Li Du Weiguo Li Hongxuan He Chao Qi 《International journal of molecular sciences》2007,8(5):445-454
The small molecule, meso-tetra(α,α,α,α-o-phenylacetamidophenyl) porphyrin (Mr1147.0) was used as complete antigen to elicit MAb through the immunization and cell fusion techniques. The MAb 1F2 obtained was demonstrated to be very pure by MALDI/TOFMS. The subtype of MAb 1F2 is IgG2a, which has a relative molecular weight of 156,678.8 Da.No significant change in the intensity of absorption peaks in UV and CD spectra was observed over a pH range between 6 and 12. The high stability of the abzyme and the tight binding between Fe porphyrin and antibody were also demonstrated. Vmax, Km, κcat, κcat/Km for abzyme are 5.18 × 10−8 Ms−1, 1.50 × 10−8 M, 0.518 s−1, 3.45 × 107 M−1s−1, respectively. The data obtained indicate that catalytic antibody has high catalytic activity. The chloroperoxidase activity of MAb 1F2-Fe porphyrin complex is stable from 10 °C to 60 °C. 相似文献