全文获取类型
收费全文 | 73908篇 |
免费 | 17042篇 |
国内免费 | 1341篇 |
专业分类
电工技术 | 2403篇 |
技术理论 | 3篇 |
综合类 | 2123篇 |
化学工业 | 22674篇 |
金属工艺 | 1997篇 |
机械仪表 | 2657篇 |
建筑科学 | 3726篇 |
矿业工程 | 848篇 |
能源动力 | 1877篇 |
轻工业 | 9906篇 |
水利工程 | 906篇 |
石油天然气 | 1355篇 |
武器工业 | 247篇 |
无线电 | 10838篇 |
一般工业技术 | 15826篇 |
冶金工业 | 5138篇 |
原子能技术 | 370篇 |
自动化技术 | 9397篇 |
出版年
2024年 | 95篇 |
2023年 | 314篇 |
2022年 | 836篇 |
2021年 | 1350篇 |
2020年 | 2141篇 |
2019年 | 3861篇 |
2018年 | 3883篇 |
2017年 | 4252篇 |
2016年 | 4681篇 |
2015年 | 4874篇 |
2014年 | 5155篇 |
2013年 | 6750篇 |
2012年 | 4499篇 |
2011年 | 4424篇 |
2010年 | 4362篇 |
2009年 | 4273篇 |
2008年 | 3753篇 |
2007年 | 3606篇 |
2006年 | 3258篇 |
2005年 | 2729篇 |
2004年 | 2714篇 |
2003年 | 2979篇 |
2002年 | 3470篇 |
2001年 | 3005篇 |
2000年 | 2154篇 |
1999年 | 1368篇 |
1998年 | 1563篇 |
1997年 | 1058篇 |
1996年 | 815篇 |
1995年 | 563篇 |
1994年 | 434篇 |
1993年 | 434篇 |
1992年 | 264篇 |
1991年 | 229篇 |
1990年 | 188篇 |
1989年 | 171篇 |
1988年 | 156篇 |
1987年 | 132篇 |
1986年 | 129篇 |
1985年 | 154篇 |
1984年 | 96篇 |
1983年 | 96篇 |
1982年 | 87篇 |
1981年 | 106篇 |
1980年 | 105篇 |
1979年 | 62篇 |
1977年 | 101篇 |
1976年 | 192篇 |
1975年 | 52篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
N. De Belie J. Monteny A. Beeldens E. Vincke D. Van Gemert W. Verstraete 《Cement and Concrete Research》2004,34(12):2223-2236
New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity). 相似文献
994.
In some industrial fluidized bed processes, notably coal combustion, the bed contains a very wide size range (50 – 5000 μm) of equal density particles. In others the particles change their density as the reaction proceeds, giving a bed of particles having similar sizes but densities varying by a factor of up to 2.
Experiments have been done in a bed 0.29 m diam. at velocities up to 5 m/s, using coarse particles up to 6 mm. They show that segregation by density difference can be reduced to negligible proportions by using high velocities, but that segregation by size appears to be an intrinsic feature of coarse particle systems at all velocities when a very wide size range is present. A tentative form of equation is proposed for segregation by size; the equations of Rowe are useful predictors for segregation by density difference. 相似文献
995.
The tensile behavior of polycarbonate was studied at large strains below the glass‐transition temperature. Experiments were carried out at a series of constant temperatures and also under conditions of falling temperatures. The specimens necked with a natural draw ratio of approximately 2, and the study was mainly focused on the necked material. Isothermal experiments revealed an elastic mechanism that initiated beyond the natural draw ratio. A model consisting of an Eyring process and two Gaussian elastic mechanisms was found to be applicable to both the isothermal and anisothermal stress‐relaxation and stress–strain results. The same model also produced reasonable estimates of the stresses generated during the necking process. In addition, a simple relationship between the isothermal and anisothermal stress relaxation was demonstrated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2105–2116, 2005 相似文献
996.
沙德宏 《硫磷设计与粉体工程》2003,(1):25-27
针对目前磷酸铵生产排出的高温冷凝水的热能未得到充分利用及由此产生的热污染,介绍了一种把排出的高温冷凝水密闭循环回收利用技术,可使蒸汽热力系统的运行效率提高10%以上。分析了该技术的特点和运行状况,认为采用该技术对蒸汽能力系统进行改造,投资少、见效快,投资回收期短、经济效益好,又消除了热污染现象,在磷酸铵生产中有推广价值。 相似文献
997.
The influence of ultrafine coal filler (UFC) content on tensile properties, water absorption, and biodegradability of soy protein plastics were investigated. The addition of UFC in the soy protein plastics, with different content of glycerol as a plasticizer, was at different ratio varying from 10:0 to 6:4. Blend sheets of the soy protein composites were prepared by the compression molding processing. The results show that, with 23.08 wt % glycerol, the tensile strength and elongation at break for the soy protein sheet with coal filler (range from 5 to 30 parts) can be enhanced as compared with nonfilled soy protein plastics. Water resistance of the soy protein plastics improves with the increase in UFC content. The derivative thermogravimetry (DTG) curves indicate a double‐stage degradation process for defatted soy flour (SPF), while three‐stage degradation process for soy plastics and the soy protein composites. FT‐IR, XPS, and SEM were applied to study the interfacial interaction between coal macromolecules and soy protein molecules in UFC filled soy protein plastics. The results demonstrated that there is strong interfacial interaction in the soy protein plastics caused by the compression molding processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3134–3143, 2006 相似文献
998.
999.
Gelatin is a natural macromolecular protein. It contains a wide variety of amino acids in its polymer structure, and it is colorless to yellowish, water‐soluble, and tasteless. It is used as a dispersing agent, sizing medium, and coating for photographic films and in pharmaceutical formulations. In this study, biodegradable mulching, based on waste gelatin from pharmaceutical gelatin scraps (derived from pharmaceutical soft gelatin capsule production), was formulated via the casting of water solutions or suspensions into flexible and consistent films. Gelatin was blended with synthetic materials such as poly(vinyl alcohol) and other natural wastes such as sugar cane bagasse and sawdust. To all formulations, 2,4‐dichlorophenoxy acetic acid (2,4‐D) was added as a herbicide. The morphology and mechanical properties of the samples were investigated with scanning electron microscopy and tensile testing, respectively. The results showed that the produced films had controlled‐release properties. The effects of various additives and crosslinking on the films and the release of the herbicide 2,4‐D from the films were also investigated. The introduction of synthetic and natural additives reduced the release rate of 2,4‐D. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2313–2319, 2004 相似文献
1000.
Ghada Al‐Bandak Vassiliki Oreopoulou 《European Journal of Lipid Science and Technology》2007,109(3):247-255
Majorana syriaca is an important food‐flavouring ingredient in the Middle Eastern culture known commonly as Za'atar. The components of the plant were extracted in a Soxhlet apparatus sequentially with solvents of increasing polarity, specifically with petroleum ether (P), diethyl ether (D), ethyl acetate (EAc), and ethanol (E). The activity of the extracts to scavenge the 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH?) followed the order D > E > EAc > P. Moreover, the antioxidant activity in corn oil at concentrations of 200, 500 and 1000 ppm was monitored through peroxide value and conjugated hydroperoxide measurements and revealed that D and E extracts resulted in the highest protection followed by EAc and P extracts. Increasing the concentration from 200 to 500 ppm depressed peroxide formation, while a further increase had no effect. The main components of the P extract according to GS‐MS analysis were thymol (42.89%) and carvacrol (42.75%). The remaining extracts comprise flavonoids and phenolic acids that provide the antiradical and antioxidant activity. 相似文献