全文获取类型
收费全文 | 299861篇 |
免费 | 7279篇 |
国内免费 | 1828篇 |
专业分类
电工技术 | 5715篇 |
技术理论 | 5篇 |
综合类 | 1166篇 |
化学工业 | 49684篇 |
金属工艺 | 11841篇 |
机械仪表 | 8680篇 |
建筑科学 | 7771篇 |
矿业工程 | 1740篇 |
能源动力 | 6404篇 |
轻工业 | 31936篇 |
水利工程 | 3270篇 |
石油天然气 | 6092篇 |
武器工业 | 250篇 |
无线电 | 29852篇 |
一般工业技术 | 56253篇 |
冶金工业 | 55960篇 |
原子能技术 | 5788篇 |
自动化技术 | 26561篇 |
出版年
2021年 | 3477篇 |
2020年 | 2549篇 |
2019年 | 3079篇 |
2018年 | 4996篇 |
2017年 | 4890篇 |
2016年 | 5354篇 |
2015年 | 4068篇 |
2014年 | 6200篇 |
2013年 | 14570篇 |
2012年 | 10081篇 |
2011年 | 12402篇 |
2010年 | 9943篇 |
2009年 | 10351篇 |
2008年 | 11110篇 |
2007年 | 11037篇 |
2006年 | 9501篇 |
2005年 | 8240篇 |
2004年 | 7500篇 |
2003年 | 6949篇 |
2002年 | 6867篇 |
2001年 | 6829篇 |
2000年 | 6427篇 |
1999年 | 6409篇 |
1998年 | 15479篇 |
1997年 | 11354篇 |
1996年 | 8453篇 |
1995年 | 6243篇 |
1994年 | 5644篇 |
1993年 | 5602篇 |
1992年 | 4204篇 |
1991年 | 3965篇 |
1990年 | 3987篇 |
1989年 | 3924篇 |
1988年 | 3674篇 |
1987年 | 3140篇 |
1986年 | 3173篇 |
1985年 | 3574篇 |
1984年 | 3438篇 |
1983年 | 3156篇 |
1982年 | 2843篇 |
1981年 | 3057篇 |
1980年 | 2822篇 |
1979年 | 2924篇 |
1978年 | 2818篇 |
1977年 | 3151篇 |
1976年 | 4326篇 |
1975年 | 2508篇 |
1974年 | 2345篇 |
1973年 | 2391篇 |
1972年 | 2011篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
151.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献
152.
Abraham G. Alvarado Rosaura Hernández-Montelongo Martin Rabelero Lourdes A. Pérez-Carrillo Jorge E. Puig Francisco López-Serrano 《Polymer Engineering and Science》2020,60(2):223-232
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers 相似文献
153.
154.
Correlation between instrumental texture and colour quality attributes with sensory analysis of selected cheeses as affected by fat contents 下载免费PDF全文
A. Półtorak J. Wyrwisz M. Moczkowska M. Marcinkowska‐Lesiak A. Stelmasiak U. Ulanicka M. Zalewska A. Wierzbicka Da‐Wen Sun 《International Journal of Food Science & Technology》2015,50(4):999-1008
This study evaluated several physical and sensory parameters of different types of cheese available in the Polish market. The measurements of textural properties were conducted in an Instron universal testing machine, while the colour properties of cheeses were measured using a Minolta chromameter. The chemical composition was determined by means of the near‐infrared spectroscopy (NIRs). Moreover, a trained sensory panel was invited to assess the cheese texture‐related properties. Generally, cheeses with reduced fat content were characterised by higher hardness, adhesiveness, cohesiveness and elasticity. Texture‐related parameters of cheese with canola oil were comparable to that of most of full‐fat cheeses. The correlation analysis between physical and sensory attributes related to cheese textural properties indicated the potential applications of TPA, shear and penetration tests (r = 0.766, r = 0.75 and r = 0.765, respectively) for the evaluation of sensory properties related to the hardness. Meanwhile, the elasticity of cheese obtained from sensory evaluation was strongly correlated with the elasticity determined from the shear test (r = 0.722) and moderately correlated with the elasticity from penetration test (r = 0.588), indicating a need to refine the method of penetration test. In addition, cheeses exhibited higher meltability during convection heating at 230 °C than microwave heating. The values of meltability for cheese with reduced fat content were lower than those of full‐fat cheese. 相似文献
155.
L. Bolzoni 《Metal Powder Report》2019,74(6):308-313
156.
Medel Manuel L. Zulueta Donala Janreddy Shang-Cheng Hung 《Israel journal of chemistry》2015,55(3-4):347-359
In recent years, there has been rapid expansion of glycan synthesis, fueled by the recognition that the structural complexity of sugars translates to a myriad of biological functions. Such chemical syntheses involve many challenges, mostly due to the regio- and stereochemical aspects of glycosidic bond formation. One-pot strategies were developed to assist in attaining faster and more economical access to the glycan constructs. In this front, achievements in protecting group manipulation, glycosylation, and combinations of these have been reported. Protecting group manipulations in one pot take advantage of the reaction compatibility of commonly used transformations, many of which occur in high regioselectivity. Sequential glycosylations, on the other hand, rely on leaving group orthogonalities and reactivity tuning, as well as the preactivation technique. Altogether, these approaches offer attractive means to the much needed glycan structures and, consequently, help usher in advances in glycoscience. 相似文献
157.
158.
159.
160.