全文获取类型
收费全文 | 391013篇 |
免费 | 5636篇 |
国内免费 | 2204篇 |
专业分类
电工技术 | 7466篇 |
技术理论 | 5篇 |
综合类 | 3448篇 |
化学工业 | 58183篇 |
金属工艺 | 20369篇 |
机械仪表 | 15580篇 |
建筑科学 | 9457篇 |
矿业工程 | 2813篇 |
能源动力 | 7192篇 |
轻工业 | 29398篇 |
水利工程 | 4736篇 |
石油天然气 | 7479篇 |
武器工业 | 243篇 |
无线电 | 41343篇 |
一般工业技术 | 78531篇 |
冶金工业 | 53935篇 |
原子能技术 | 6784篇 |
自动化技术 | 51891篇 |
出版年
2021年 | 2483篇 |
2019年 | 2107篇 |
2018年 | 22714篇 |
2017年 | 22240篇 |
2016年 | 15980篇 |
2015年 | 3767篇 |
2014年 | 4843篇 |
2013年 | 11588篇 |
2012年 | 12394篇 |
2011年 | 24844篇 |
2010年 | 21506篇 |
2009年 | 19043篇 |
2008年 | 20432篇 |
2007年 | 22996篇 |
2006年 | 8611篇 |
2005年 | 11533篇 |
2004年 | 9235篇 |
2003年 | 8582篇 |
2002年 | 7217篇 |
2001年 | 6472篇 |
2000年 | 6166篇 |
1999年 | 5948篇 |
1998年 | 12917篇 |
1997年 | 9567篇 |
1996年 | 7327篇 |
1995年 | 5552篇 |
1994年 | 5119篇 |
1993年 | 4984篇 |
1992年 | 3970篇 |
1991年 | 3803篇 |
1990年 | 3823篇 |
1989年 | 3770篇 |
1988年 | 3537篇 |
1987年 | 3019篇 |
1986年 | 3050篇 |
1985年 | 3408篇 |
1984年 | 3321篇 |
1983年 | 3074篇 |
1982年 | 2703篇 |
1981年 | 2905篇 |
1980年 | 2642篇 |
1979年 | 2839篇 |
1978年 | 2736篇 |
1977年 | 2843篇 |
1976年 | 3696篇 |
1975年 | 2457篇 |
1974年 | 2291篇 |
1973年 | 2321篇 |
1972年 | 1981篇 |
1971年 | 1787篇 |
排序方式: 共有10000条查询结果,搜索用时 370 毫秒
951.
952.
953.
954.
Seven ferrocene-bound polyester resins were prepared from fumaric acid and diethylene glycol in the presence of different ferrocene derivatives. To accomplish the incorporation of the organometallic moiety into the polyester resin chain, the cyclopentadienyl rings of ferrocene were substituted in the 1,1′ positions with reactive functional groups. The ferrocene derivatives used were: 1,1′-bis(1-hydroxyethyl) ferrocene 1 , 1,1′-ferrocene dicarboxylic acid 2 , and 1,1′-ferrocene diacetic acid 3 . The incorporation of an organometallic complex significantly increased the rate of the polyesterification process. In order of increasing rate enhancement, the effect was 2 < 3 < 1 . The effectiveness of ferrocene derivatives chemically incorporated into the polyester backbone during copolymerization with styrene was studied by monitoring the gel time, cure rate, and the resin properties. The efficiency of the copolymerization reaction of ferrocene-bound polymers with styrene decreased in the order 1 ≥ 3 > 2 . Mechanisms to account for these results are presented. Some of the strength related properties were also studied. 相似文献
955.
V. V. Shilov Yu. P. Gomza V. N. Bliznyuk Yu. S. Lipatov D. B. Boguslavsky V. L. Pikalov Z. F. Suvorova 《应用聚合物科学杂志》1985,30(5):1927-1934
The structural peculiarities of cis-1,4-isoprene rubber, oligodiene diisocyanate, and derivative of phenol–formaldehyde resin blends have been studied by WAXS and SAXS methods and electron microscopy. It has been demonstrated that the addition of modifiers and further thermal treatment under conventional curing conditions change considerably the microheterogeneous structure and morphology and contribute to the improvement of the short-range order in the rubber matrix. 相似文献
956.
957.
The electronic band structure of ZrO2 is calculated for the fluorite structure using the self-consistent augmented-plane-wave method in the muffin-tin approximation. The crystal charge density is then site decomposed by fitting Slater orbitals to the wave functions in the muffin tins. The resultant charge densities for Zr4+ and O2− are then used in the Gordon-Kim method to derive pair potentials, from which a number of structural, elastic, and thermodynamic properties are calculated and compared with experimental results and similar calculations for MgO. 相似文献
958.
W. L. Siew F. C. H. Oh A. S. H. Ong 《Journal of the American Oil Chemists' Society》1985,62(6):1036-1039
Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories. 相似文献
959.
L. M. Du Plessis J. B. M. De Villiers W. H. Van Der Walt 《Journal of the American Oil Chemists' Society》1985,62(4):748-752
Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics. Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves. Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels. A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test. The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability. 相似文献
960.
D L Ranum 《Computer methods and programs in biomedicine》1989,30(2-3):209-215
A data acquisition tool which will extract pertinent diagnostic information from radiology reports has been designed and implemented. Pertinent diagnostic information is defined as that clinical data which is used by the HELP medical expert system. The program uses a memory-based semantic parsing technique to 'understand' the text. Moreover, the memory structures and lexicon necessary to perform this action are automatically generated from the diagnostic knowledge base by using a special purpose compiler. The result is a system where data extraction from free text is directed by an expert system whose goal is diagnosis. 相似文献