全文获取类型
收费全文 | 6364篇 |
免费 | 234篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 88篇 |
综合类 | 16篇 |
化学工业 | 1546篇 |
金属工艺 | 132篇 |
机械仪表 | 89篇 |
建筑科学 | 294篇 |
矿业工程 | 25篇 |
能源动力 | 128篇 |
轻工业 | 592篇 |
水利工程 | 26篇 |
石油天然气 | 3篇 |
无线电 | 557篇 |
一般工业技术 | 1163篇 |
冶金工业 | 1158篇 |
原子能技术 | 81篇 |
自动化技术 | 703篇 |
出版年
2023年 | 61篇 |
2022年 | 30篇 |
2021年 | 108篇 |
2020年 | 69篇 |
2019年 | 97篇 |
2018年 | 90篇 |
2017年 | 90篇 |
2016年 | 138篇 |
2015年 | 144篇 |
2014年 | 153篇 |
2013年 | 278篇 |
2012年 | 253篇 |
2011年 | 343篇 |
2010年 | 234篇 |
2009年 | 269篇 |
2008年 | 291篇 |
2007年 | 234篇 |
2006年 | 223篇 |
2005年 | 193篇 |
2004年 | 165篇 |
2003年 | 147篇 |
2002年 | 150篇 |
2001年 | 129篇 |
2000年 | 125篇 |
1999年 | 148篇 |
1998年 | 349篇 |
1997年 | 245篇 |
1996年 | 161篇 |
1995年 | 149篇 |
1994年 | 135篇 |
1993年 | 116篇 |
1992年 | 82篇 |
1991年 | 117篇 |
1990年 | 69篇 |
1989年 | 73篇 |
1988年 | 76篇 |
1987年 | 70篇 |
1986年 | 48篇 |
1985年 | 69篇 |
1984年 | 69篇 |
1983年 | 47篇 |
1982年 | 31篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 33篇 |
1977年 | 43篇 |
1976年 | 81篇 |
1975年 | 35篇 |
1974年 | 28篇 |
排序方式: 共有6601条查询结果,搜索用时 250 毫秒
91.
92.
Pulp fibers can be spouted in water in a conical vessel. The entities which are spouted are fiber flocs rather than individual fibers. Synthetic fibers, which do not flocculate, cannot be spouted. For comparison, rigid spherical particles were spouted with water in the same conical vessel. Liquid spouting of rigid particles was similar to gaseous spouting. For pulp spouting, the minimum spouting velocity is proportional to the mass of fibers in the bed and inversely proportional to the diameter of the inlet. For rigid particles, the minimum spouting velocity is proportional to the height of the bed and inversely proportional to the square of the diameter of the inlet. A model for the minimum spouting velocity was developed for pulp spouting. 相似文献
93.
Summary Poly(1-methyl-1-phenyl-1-silapentane) (I) has been prepared by the chemical reduction of the carbon-carbon double bonds of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene (cis-II) with diimide, which was generatedin-situ by the thermal decomposition ofp-toluenesulfonhydrazide in refluxing toluene. At lower temperature (100°C),cis-II is isomerized byp-toluenesulfinic acid to lower molecular weight poly(1-methyl-1-phenyl-1-sila-cis andtrans-pent-3-ene) (cis/trans-II). Protodesilation of I with trifluoromethanesulfonic acid yields poly(1-methyl-1-trifluoromethanesulfonyl-1-silapentane) (III). The structures of I andcis/trans-II have been characterized by1H,13C and29Si NMR, GPC, TGA and elemental analysis. The structure of I has been characterized spectroscopically by1H,13C,19F and29Si NMR. 相似文献
94.
Attila Bereck Silke Dillbohner Burkhard Weber Dieter Riegel Jrg Mosel Johannes Michael Reper Axel Brakelmann 《Coloration Technology》1997,113(11):322-326
A simple method for the characterisation of fabric softness using a conventional tensile tester and a special measurement device has been developed. The method is demonstrated to be especially useful in detecting changes in softness of a given substrate due to different treatments. The results obtained, particularly hysteresis at 75% of the maximum extension, provide a good correlation with subjective ranking for samples that are subjectively distinguishable; they also differentiate well between samples which seem subjectively indistinguishable. Screening tests were carried out, mainly on wool fabrics, to find the effect of different treatments such as oxidative (alkaline and acidic) and reductive (Blankit IN) bleaching, dyeing with acid and a 1:2 metal complex, chrome and (mono and bi)reactive dyes, the effect of the antisetting agent Basolan AS (BASF) and of crosslinking with Irgasol HTW (CGY) on fabric softness. 相似文献
95.
The Spheron 6 surface acidity has been investigated by adsorption of ammonia at 70°C and microcalorimetry. The carbon samples are degassed at temperatures up to 950°C. The effects of degassing temperature on the adsorption isotherms of ammonia are shown in Fig. 2. Up to 350°C, the isotherms are characterized by a very slight decrease in the total amount adsorbed. On the contrary, these amounts considerably decrease for higher degassing temperatures. The differential heats of adsorption (Fig. 3), which are initially close to 100 kJ/mole, are shown to decrease with the amount of adsorbed ammonia: the higher the degassing temperature, the greater the decrease. By desorption, the adsorption of ammonia is found partly irreversible. By readsorption it is possible to measure the differential heat of the reversible adsorption and to deduce from it the differential heat of the irreversible adsorption (Fig. 4) as well as the amount irreversibly adsorbed, i.e. chemisorbed.The amounts of chemisorbed ammonia are found to be respectively 0.36 ± 0.01 × 10?6 mole m2 at 150°C and 0.29 ± 0.01 × 10?6 mole m?2 at 350°C. With the surface covering the differential heat of chemisorption of ammonia slightly decreases from 105 to 88 kJ. mole?1.These values suggest that carboxyl groups are responsible for irreversible adsorption of ammonia. This assumption has been checked by various experiments: the irreversible uptake of ammonia lies in the same range as the number of carboxyl surface groups determined by chemical analysis of functional groups (Table 1); the evolving of H2O during the decomposition of the ammonium salt formed by reacting with ammonia has been observed and is probably correlated with the irreversible uptake of ammonia (Fig. 8); moreover it must be pointed out that irreversible adsorption of ammonia disappears after methylation of sample by diazomethane (Figs. 5 and 6). Then, the amounts of carboxyl groups can be determined by measuring the irreversibly adsorbed ammonia.This method has been applied to the study of the thermal stability of functional groups. Carboxyl groups are shown to be quickly decomposed by heat treatment above 500–600°C (Fig. 8).It appears from our experiments that the oxidation at constant temperature followed by a cooling under nitrogen is unable to regenerate functional groups on the surface of carbon after their removal at 950°C. On the contrary, by an oxidation at decreasing temperature it is possible to regenerate functional groups because they are stabilized by the oxidising atmosphere.The groups thus created behave like those initially present on Spheron 6: particularly the graph of the thermal elimination of carbon dioxide presents two peaks (Table 2, Fig. 12). The amount of regenerated carboxyl groups is found to be 0.25 × 10?6 instead of 0.36 × 10?6mole m?2 on untreated Spheron 6. 相似文献
96.
Summary: This paper describes a step on the ambitious aim to “design” application properties of ldPE by first simulating the detailed molecular structure of a high‐pressure tubular reactor product. The reactor of a certain configuration produces under well‐defined operating conditions. The next step is to correlate the structure with the application properties. Finally, the sequence will be reversed in order to deduce the operating conditions, which lead to the desired product quality. Two‐dimensional distributions, in molecular weight and branching frequency, as well a two compartment models with a core and a shell stream were simulated and compared with experimental results. Therefore, CFD simulations were carried out to discretize the reaction medium. Samples were taken from both pilot and commercial plants. The TREF‐SEC analytical method was successfully applied in order to measure the microscopic structure of the material. The tremendous numerical problems were solved with the help of the software PREDICI .
97.
Roland Schmidt Ulrich Hammon Stefan Gottfried M. Bruce Welch Helmut G. Alt 《应用聚合物科学杂志》2003,88(2):476-482
The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by 1H‐ and 13C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003 相似文献
98.
The experiments reported are part of our effort to dissociate the tumor-enhancing effects of dietary fat and high caloric
intake. Rats either were fed ad libitum diets containing 4% corn oil or their calories were restricted by 40% and their diets
contained 13.1% corn oil. Incidence of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors was 80% in rats fed ad
libitum and 20% in those fed the calorie-restricted diets. Incidence of 1,2-dimethylhydrazine (DMH)-induced colon tumors was
100% in rats fed ad libitum and 53% in those whose caloric intake was restricted by 40%. The tumor yield (tumors per tumor-bearing
rat) was significantly lower in rats on caloric restriction. In another series, rats were fed diets containing 5, 15 or 20%
corn oil ad libitum or were fed calorie-restricted (by 25%) diets which provided 20 or 26.6% corn oil (therefore, the same
absolute amount of fat was consumed in each of the pair-fed groups). Tumor incidence and tumor yield in the two calorie-restricted
groups were similar to those seen in the rats fed 5% fat ad lititum; tumor burden (total g of tumor) was 45–65% lower in the
calorie-restricted rats. The data suggest that caloric intake is a more stringent determinant of tumor growth than fat intake. 相似文献
99.
Maria Casapu Jan-Dierk Grunwaldt Marek Maciejewski Meike Wittrock Ulrich Gbel Alfons Baiker 《Applied catalysis. B, Environmental》2006,63(3-4):232-242
The formation and stability of BaAl2O4 and BaCeO3 in Pt-Ba/Al2O3 and Pt-Ba/CeO2 based NOx storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO3. The formation of BaAl2O4 started above 850 °C, whereas the formation of BaCeO3 was already observed at 800 °C and was faster than that of BaAl2O4. The stability of BaAl2O4 and BaCeO3 in various liquid and gaseous atmospheres was different. BaAl2O4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO3)2 and γ-alumina in the presence of HNO3, whereas BaCeO3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO3 was transformed to Ba(NO3)2/CeO2 in the presence of NO2/H2O at 300–500 °C. Also, the presence of CO2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NOx-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts. 相似文献
100.
Nikolaus Weber 《Lipids》1988,23(1):42-47
[4-14C]Sitosteryl β-D-glucoside, intragastrically administered to rats, was not absorbed by the intestinal mucosa. At three hr
after the application, radioactivity was concentrated almost exclusively in the digesta of stomach, small intestine as well
as cecum and colon, whereas only low proportions of radioactively labeled compounds were found in the various tissues of the
gastrointestinal tract. Minor proportions of labeled metabolites of [4-14C]sitosteryl β-D-glucoside, such as sitosterol and sitosteryl esters, were formed in the small intestine in vivo and in slices
of small intestine in vitro. In the tissues of cecum and colon as well as the digesta derived from them, high proportions
of labeled coprositostanol, i.e. 24α-ethyl-5β-cholestan-3β-ol, that obviously had been formed by bacterial degradation of
the substrate were detected.
The feeding of sitosteryl β-D-glucoside (0.5 g/kg body weight×day) over a period of four weeks did not alter significantly
body weights or organ weights of rats. Analyses of steryl lipids of the various organs and tissues confirmed the findings
obtained with the radioactive substrate: neither sitosteryl β-D-glucoside nor sitosterol or sitosteryl esters derived therefrom
had been transported in appreciable amounts to organs and tissues outside the alimentary canal during the feeding period.
Minor proportions of unmetabolized sitosteryl β-D-glucoside were detected in the tissues of stomach and intestine, whereas
large proportions of the substrate were found in feces of rats that had received the sitosteryl β-D-glucoside-containing diet;
coprositostanol was found in feces of these animals in high proportions as well. Thus, the use of sitosteryl β-D-glucoside
as emulsifier or preservative in food and feed does not appear to involve any risk.
The systematic nomenclature of the sterols referred to by trivial names is, cholest-5-en-3β-ol (cholesterol); 5α-cholestan-3β-ol
(5α-cholestanol); 5β-cholestan-3β-ol (5β-cholestanol, coprostanol); 24α-methylcholest-5-en-3β-ol (campesterol); 24α-methyl-5α-cholestan-3β-ol
(5α-campestanol); 24α-methyl-5β-cholestan-3β-ol (5β-campestanol, coprocampestanol); 24α-methyl-cholesta-5,22-dien-3β-ol (brassicasterol);
24α-ethylcholest-5-en-3β-ol (sitosterol, β-sitosterol); 24α-ethyl-5α-cholestan-3β-ol (5α-sitostanol); 24α-ethyl-5β-cholestan-3β-cholestan-3β-ol
(5β-sitostanol, coprositostanol); 24α-ethylcholesta-5,22-dien-3β-ol (stigmasterol). 相似文献