全文获取类型
收费全文 | 75154篇 |
免费 | 718篇 |
国内免费 | 690篇 |
专业分类
电工技术 | 1493篇 |
综合类 | 47篇 |
化学工业 | 11221篇 |
金属工艺 | 3452篇 |
机械仪表 | 2638篇 |
建筑科学 | 1642篇 |
矿业工程 | 503篇 |
能源动力 | 1871篇 |
轻工业 | 6391篇 |
水利工程 | 850篇 |
石油天然气 | 2303篇 |
武器工业 | 41篇 |
无线电 | 7253篇 |
一般工业技术 | 16522篇 |
冶金工业 | 12483篇 |
原子能技术 | 2636篇 |
自动化技术 | 5216篇 |
出版年
2022年 | 574篇 |
2021年 | 908篇 |
2020年 | 695篇 |
2019年 | 778篇 |
2018年 | 1554篇 |
2017年 | 1565篇 |
2016年 | 1764篇 |
2015年 | 949篇 |
2014年 | 1567篇 |
2013年 | 3578篇 |
2012年 | 2364篇 |
2011年 | 2827篇 |
2010年 | 2379篇 |
2009年 | 2648篇 |
2008年 | 2625篇 |
2007年 | 2570篇 |
2006年 | 2197篇 |
2005年 | 1921篇 |
2004年 | 1846篇 |
2003年 | 1798篇 |
2002年 | 1714篇 |
2001年 | 1682篇 |
2000年 | 1682篇 |
1999年 | 1574篇 |
1998年 | 3705篇 |
1997年 | 2617篇 |
1996年 | 1946篇 |
1995年 | 1532篇 |
1994年 | 1333篇 |
1993年 | 1356篇 |
1992年 | 1004篇 |
1991年 | 1054篇 |
1990年 | 1076篇 |
1989年 | 1058篇 |
1988年 | 943篇 |
1987年 | 889篇 |
1986年 | 881篇 |
1985年 | 939篇 |
1984年 | 783篇 |
1983年 | 774篇 |
1982年 | 684篇 |
1981年 | 698篇 |
1980年 | 663篇 |
1979年 | 653篇 |
1978年 | 621篇 |
1977年 | 777篇 |
1976年 | 932篇 |
1975年 | 581篇 |
1974年 | 555篇 |
1973年 | 544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
T. J. WEiss Mona Brown H. J. Zeringue Jr. R. O. Feuge 《Journal of the American Oil Chemists' Society》1971,48(4):145-148
Thin layer chromatography was adapted for direct quantitative estimation of sucrose esters of palmitic acid. Urea-phosphoric
acid spray was used to detect the sucrose moiety of the various esters. The photometrically metermined density density of
each spot on the thin layer plate was found to be proportional to its sucrose content. Ester content was then obtained by
multiplying sucrose found by the factor, mol. wt. ester/mol. wt. sucrose. Ester mixtures were prepared by interesterifying
sucrose with various proportions of methyl palmitate in dimethylformamide solution. Positional isomers were observed at each
level of substitution but could not be adequately separated from each other for quantitative evaluation.
Presented at the AOCS Meeting, Minneapolis, October 1969.
So. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
992.
Kinetics of chemisorption of sulfur dioxide by a limestone suspension is theoretically analyzed and a chemisorption mathematical model, which is used to determine the treatment efficiency of the gas, is developed. It is shown that the gas treatment efficiency considerably increases for the chemical absorption by a suspension containing solid absorbent particles as compared with physical absorption. The gas treatment efficiency rises with increasing solid absorbent mass in the solution and decreasing size of the particles. 相似文献
993.
Megh Singh J. R. Orsenigo D. O. Shah 《Journal of the American Oil Chemists' Society》1984,61(3):596-600
Contact angle and surface tension were measured for distilled and hard water solutions of adjuvants, Ortho X-77, Span-20,
Sterox-NJ. Surfactant-WK, Triton B-1956, Triton X-114, Tween-20, and Sun Oil 11E. The same parameters were measured for suspensions
of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] with and without each adjuvant. All adjuvants reduced surface tension and contact angle of distilled water; Surfactant-WK
was most effective and Tween-20 was least effective. Increasing concentration of surfactants from 0 to 0.1% (v/v) gave progressive
reduction in surface tension and contact angle while higher concentrations, 0.1 to 2.0% (v/v), had no further effect. Surfactant-WK
at 0.1% (v/v) in distilled water reduced the surfact tension from 72.8 dynes/cm to 27 dynes/cm and contact angle from 110°
to 41°. An additional increase in Surfactant-WK concentration from 0.1% (v/v) to 2% (v/v) did not further reduce surface tension
and contact angle. Sun Oil 11E was identical in behavior except that it was less effective than the surfactants. Water hardness
up to 1,000 ppm as Ca ions did not affect surface tension and contact angle in surfactant solutions. An aqueous solution of
atrazine had a higher surface tension and contact angle than ametryne in the absence of surfactants. However, these differences
were not observed when surfactants were added to either herbicide. 相似文献
994.
995.
996.
997.
998.
Polyesters were synthesized with monoglycerides prepared from rubber seed oil, a renewable resource. Monoglycerides were obtained by an alcoholysis method from the oil, which was neat or modified by treatments with different amounts of maleic anhydride at 230°C. The polyester resins were subsequently prepared by the condensation polymerization of the monoglycerides with phthalic anhydride. The monoglycerides and resins were characterized by spectroscopic analysis and measurements of the physicochemical properties. The chemical resistance of the polyesters was also studied. The results revealed that the polyesters prepared from the modified monoglycerides possessed better properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3748–3755, 2006 相似文献
999.
Soluble polypyrrole (PPy) samples advanced in electrical conductivity σ were chemically synthesized with dodecylbenzenesulfonate (DBS) sodium salt as a dopant, with poly(ethylene glycol) (PEG) as an additive, and with ammonium persulfate as an oxidant. The PPy–DBS–PEG samples were soluble in organic solvents (N‐methylpyrrolinone and m‐cresol). The greater the molar percentage ratio was of DBS, the greater the solubility was of synthesized PPy composites (PPy–DBS–PEG). The maximum electrical conductivity at room temperature for PPy–DBS–PEG was 1.02 S/cm, which was in fact the true conductivity of 100/10 (mol %) PPy/DBS. The chemical composition and doping level of PPy–DBS–PEG were determined by elemental analysis. The results of Fourier transform infrared spectroscopy were used for the structural characterization of PPy–DBS–PEG. The scanning electron microscopy results showed that the electrical conductivity was related to the morphology of PPy–DBS–PEG. According to thermogravimetric analysis, PPy–DBS–PEG was more thermostable than PPy–DBS. Electron spin resonance measurements showed that the polaron and bipolaron acted as charge carriers of PPy–DBS–PEG. According to the temperature dependence of the electrical conductivity, PPy–DBS–PEG was a semiconductor and followed the three‐dimensional variable‐range hopping model. The improved electrical conductivity apparently resulted from the reduction of the crosslinking and structural defects of the PPy chains. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1170–1175, 2005 相似文献
1000.
O. Zahiri 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2014,18(3):419-426
The aim of this paper is to solve the open problem appeared in Motamed and Moghaderi (Soft Comput 2012), about the relation between Noetherian (Artinian) $\textit{BL}$ -algebras in short exact sequences. Also, a better theorem to improve its results is suggested. The relation between Noetherian and Artinian $\textit{BL}$ -algebras is found, the concept of length for a filter in $\textit{BL}$ -algebras is introduced and properties of finite length $\textit{BL}$ -algebras are developed. Finally, it is proved that any $\textit{BL}$ -algebra has finite length if and only if be Noetherian and Artinian. 相似文献