全文获取类型
收费全文 | 47735篇 |
免费 | 1021篇 |
国内免费 | 180篇 |
专业分类
电工技术 | 592篇 |
综合类 | 643篇 |
化学工业 | 5148篇 |
金属工艺 | 642篇 |
机械仪表 | 921篇 |
建筑科学 | 1204篇 |
矿业工程 | 392篇 |
能源动力 | 499篇 |
轻工业 | 2601篇 |
水利工程 | 618篇 |
石油天然气 | 51篇 |
武器工业 | 4篇 |
无线电 | 2052篇 |
一般工业技术 | 3873篇 |
冶金工业 | 23513篇 |
原子能技术 | 241篇 |
自动化技术 | 5942篇 |
出版年
2023年 | 208篇 |
2022年 | 144篇 |
2021年 | 167篇 |
2019年 | 91篇 |
2018年 | 515篇 |
2017年 | 722篇 |
2016年 | 1114篇 |
2015年 | 828篇 |
2014年 | 483篇 |
2013年 | 493篇 |
2012年 | 2247篇 |
2011年 | 2610篇 |
2010年 | 792篇 |
2009年 | 873篇 |
2008年 | 729篇 |
2007年 | 902篇 |
2006年 | 658篇 |
2005年 | 3436篇 |
2004年 | 2636篇 |
2003年 | 2133篇 |
2002年 | 928篇 |
2001年 | 803篇 |
2000年 | 349篇 |
1999年 | 749篇 |
1998年 | 6841篇 |
1997年 | 4189篇 |
1996年 | 2753篇 |
1995年 | 1635篇 |
1994年 | 1198篇 |
1993年 | 1248篇 |
1992年 | 301篇 |
1991年 | 369篇 |
1990年 | 355篇 |
1989年 | 337篇 |
1988年 | 327篇 |
1987年 | 266篇 |
1986年 | 231篇 |
1985年 | 210篇 |
1984年 | 95篇 |
1983年 | 103篇 |
1982年 | 150篇 |
1981年 | 220篇 |
1980年 | 222篇 |
1979年 | 98篇 |
1978年 | 118篇 |
1977年 | 663篇 |
1976年 | 1422篇 |
1975年 | 116篇 |
1974年 | 62篇 |
1973年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Jan Tobi? 《Chemical engineering science》2006,61(8):2447-2456
The pressure drop and the fluid velocity profiles were investigated experimentally and numerically in the model packings of complex geometry. The numerical estimations were performed by means of the hybrid method involving the use of structural macro-correlations. In this paper it has been demonstrated on several examples that the structural macro-correlations allow to predict the macro-scale flow behaviour in non-homogeneous packings. Finally, the recent mechanistic approaches to flow modelling in packed tubes of low tube-to-particle diameter ratio have been discussed. 相似文献
992.
Guan-Chiun?Lee Dong-Lin?Wang Yi-Fang?Ho Jei-Fu?ShawEmail author 《Journal of the American Oil Chemists' Society》2004,81(6):533-536
Lipase from Pseudomonas fluorescens efficiently catalyzed the alcoholysis of various TG in dry alcohols. For TG with short-chain FA, more MG were accumulated.
The yields of MG were affected by the alcohols used. The maximum yields of MG were as follows: 85% for monoacetin in n-butanol, 96% for monobutyrin in ethanol or n-butanol, 50% for monocaprylin in n-butanol, 48% for monolaurin in isopropanol, and 45% for monopalmitin in isopropanol. The MG produced were judged to be 2-MG
by TLC analysis. The presence of organic cosolvent affected the reaction rate of the lipase-catalyzed alcoholysis of TG. For
the alcoholysis of various TG in ethanol and cosolvent (1∶1, vol/vol), the rates had the following orders: (i) for tributyrin,
hexane > toluene > acetone > ethyl acetate > chloroform > acetonitrile > pyridine; (ii) for tricaprylin, hexane > acetone
> toluene > acetonitrile > ethyl acetate > pyridine > chloroform; and (iii) for trialurin, hexane > acetonitrile=acetone >
ethyl acetate > pyridine=chloroform > toluene. 相似文献
993.
Liane Gabor Stefan Leijnen Tiha von Ghyczy 《International Journal of Software and Informatics》2013,7(4):615-627
There are both benefits and drawbacks to cultural diversity. It can lead to friction and exacerbate differences. However, as with biological diversity, cultural diversity is valuable in times of upheaval; if a previously effective solution no longer works, it is good to have alternatives available. What factors give rise to cultural diversity? This paper describes a preliminary investigation of this question using a computational model of cultural evolution. The model is composed of neural network based agents that evolve fitter ideas for actions by (1) inventing new ideas through modification of existing ones, and (2) imitating neighbors'' ideas. Numerical simulations indicate that the diversity of ideas in a population is positively correlated with both the proportion of creators to imitators in the population, and the rate at which creators create. This is the case for both minimum and peak diversity of actions over the duration of a run. 相似文献
994.
995.
Yue?Hung K.?M.?EL-KhatibEmail author Hazem?Tawfik 《Journal of Applied Electrochemistry》2005,35(5):445-447
Corrosion resistant treated metal bipolar plates with higher rigidity and electrical conductivity than graphite were developed and tested for PEM fuel cell applications. Six replicas of single cells were used three of which were made of graphite composites bipolar plates and the other three of the treated metallic plates. A Membrane Electrode Assembly (MEA) with 5.55 cm2 active electrode areas, 0.3 mg cm–2 Pt loading and Nafion membrane 115 was fitted to each cell and operated under identical conditions. The experimental testing was conducted at room temperature (20 °C). The average value of the data obtained for the three graphite cells was plotted. Similarly, the average value of the data obtained for the three treated metal cells was plotted on the same graph for comparison. Generally, the treated metal bipolar plate provided at least 12% saving in hydrogen consumption in comparison to graphite. This is attributed to the lower bulk and surface contact resistance of the metal used in this study in relation to graphite. The results of lifetime testing, conducted at room temperature under variable loading showed no indication of power degradation due to metal corrosion for at least 1500 hours. 相似文献
996.
The present study was designed to examine the effects of EFA deficiency (EFAD) on biochemical, functional, and structural
aspects of the kidney in growing and adult rats fed a normal or EFAD diet for 9 wk after weaning. Food and fluid intake (FI),
urine volume, and Na+ and K+ excretions were measured weekly from weeks 4 to 8 by placing the rats in individual metabolic cages for 24 h. At week 9,
Li+ and a 5% water load, respectively, were administered at 14 and 1.5 h prior to glomerular and proximal tubular function studies,
as assessed by 3-h creatinine (CCr) and Li+ (CLi+) clearances. Hematocrit and urine volume; serum and urine [Cr], [Li+], [Na+], and [K+]; and renal FA distribution were also measured. Data [corrected to 100 g/body weight (bw) and presented as means ±SEM] were
significant, at P<-0.05. Despite a similar ingestion of solids from weeks 4 to 7 (weeks 7 to 10 of life), the rats on the EFAD diet showed
a decreased body weight from week 5. From weeks 4 to 8, Fl and urine volume were similar for both groups, but the Fl increased
at week 6 in the EFAD group; 24-h Na+ and K+ excretions were similar at all weeks, except for an increase in the EFAD group for both ions at week 7. In the EFAD group,
CCr and CLi+ decreased by 27 and 56.3%, respectively (385.7±33.4 vs. 280±21.1, and 21.0±2.1 vs. 9.2±1.1 μL/min/100 g; n=9 vs. 10), the latter result suggesting increased proximal reabsorption. The 3-h Na+ and K+ excretions were similar, but the Li+ decreased (0.78±0.06×10−2 vs. 0.32±0.03×10−2 μeq/min/100 g) in the EFAD group, giving additional support to the suggestion. Renal structure was normal and similar for
both groups, but the EFAD group showed a more prominent proximal tubule brush border, together with heavier periodic acid-Schiff
staining in all specimens from weeks 5 to 9. In the EFAD group, FA of the n−9 and n−7 series were higher, but most of the
n−6 series were lower as a percentage of total lipids in the medulla and cortex. Medullary levels of 20∶4n−6 were maintained,
22∶4n−6 declined twice, arachidonic acid was maintained, and 20∶5n−3 was lower. The EFAD diet affected glomerular function,
proximal tubular structure and function, and FA distribution in the rat kidney. 相似文献
997.
Silvana?Martini Constantin?Bertoli Maria?Lidia?Herrera Ian?Neeson Alejandro?MarangoniEmail author 《Journal of the American Oil Chemists' Society》2005,82(5):305-312
An ultrasonic technique was developed to study the crystallization process of edible fats on-line. A chirp wave was used instead
of the conventional pulser signal, thus achieving a higher signal-to-noise ratio. This enabled measurements to be made in
concentrated systems [≈20% solid fat content (SFC)] through a 8.11-cm thick sample without significant signal loss. Fat samples
were crystallized at 20, 25, and 30°C at a constant agitation rate of 400 rpm for 90 min. The crystallization process was
followed by ultrasonic spectroscopy and a low-resolution pulsed nuclear magnetic resonance spectrometer. Specific relationships
were found between ultrasonic parameters [integrated response, time of flight (TF), and full width half maximum] and SFC.
TF, which is an indirect measurement of the ultrasonic velocity (v), was highly correlated to SFC (r
2>0.9) in a linear fashion (v=2.601 SFC+1433.0). 相似文献
998.
999.
?akir Erdo?du 《Cement and Concrete Research》2005,35(5):907-912
To have concrete possesses the specified engineering properties, its slump loss has to be compensated somehow at construction site so that concrete could be placed and compacted properly. Several attempts have been tried so far to render concrete workable at construction site including starting with a high initial slump at the stationary plant, or retempering with water and/or with chemical admixtures at construction site. In this investigation, ASTM C 494 Type F superplasticizer was used for retempering concrete to restore its initial slump. Concrete mixes having an initial slump of about 19 cm were prepared and subjected to prolonged mixing with different mixing duration such as 30, 60, 90, 120, and 150 min following an initial mixing of 5 min to ensure homogeneity. At the end of each mixing period, cube specimens of 15 cm were cast from concrete retempered to its initial slump level and tested at the age of 28 days for compressive strength. Results revealed that compared to the concrete retempered with water, those retempered with a superplasticizer admixture have yielded significantly higher strength regardless of the mixing duration. 相似文献
1000.
We undertook numerical and experimental studies to develop a better incineration method for the destruction of CC14. A phenomenological model for the turbulent reaction of CC14, including a flame inhibition feature, has been successfully incorporated into a commercial code, simulating the incineration
processes of this compound. The gaseous flow solution was obtained using SIMPLEST, a derivative of Patankar’s SIMPLE algorithm,
with a k-ε turbulence model. A modified fast chemistry turbulent reaction model was developed to describe the flame inhibition
due to the presence of CC14, considering the corresponding burning velocity data of these mixtures. An experiment was carried out on a 5.2 kW laboratory
scale, transportable, cavity-type incinerator, which warrants a sufficient residence time and effective turbulent mixing by
the formation of a strong recirculation region in a combustor. To this end, the specific configuration of the incinerator
was manufactured to consist of two opposing jets and a rearward facing step. The calculated data were in close agreement with
the experimental data for the concentrations of major species, such as CCI4 and HCl, together with the temperature profiles. The experimental test gave the desired DRE of above 99.99%. 相似文献