全文获取类型
收费全文 | 24008篇 |
免费 | 2691篇 |
国内免费 | 1088篇 |
专业分类
电工技术 | 733篇 |
综合类 | 1720篇 |
化学工业 | 7025篇 |
金属工艺 | 819篇 |
机械仪表 | 807篇 |
建筑科学 | 774篇 |
矿业工程 | 528篇 |
能源动力 | 820篇 |
轻工业 | 3941篇 |
水利工程 | 112篇 |
石油天然气 | 793篇 |
武器工业 | 136篇 |
无线电 | 3486篇 |
一般工业技术 | 3723篇 |
冶金工业 | 1278篇 |
原子能技术 | 372篇 |
自动化技术 | 720篇 |
出版年
2024年 | 71篇 |
2023年 | 469篇 |
2022年 | 589篇 |
2021年 | 740篇 |
2020年 | 814篇 |
2019年 | 709篇 |
2018年 | 694篇 |
2017年 | 849篇 |
2016年 | 889篇 |
2015年 | 938篇 |
2014年 | 1332篇 |
2013年 | 1524篇 |
2012年 | 1852篇 |
2011年 | 1886篇 |
2010年 | 1393篇 |
2009年 | 1452篇 |
2008年 | 1187篇 |
2007年 | 1618篇 |
2006年 | 1494篇 |
2005年 | 1121篇 |
2004年 | 995篇 |
2003年 | 920篇 |
2002年 | 731篇 |
2001年 | 605篇 |
2000年 | 506篇 |
1999年 | 440篇 |
1998年 | 343篇 |
1997年 | 292篇 |
1996年 | 233篇 |
1995年 | 185篇 |
1994年 | 179篇 |
1993年 | 137篇 |
1992年 | 135篇 |
1991年 | 118篇 |
1990年 | 66篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 38篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
121.
H. Perez-Blanco 《International Journal of Refrigeration》1993,16(6):429-433
The search for high-efficiency, gas-fired cooling cycles has led to the development of dual-loop absorption machines with cooling coefficients of performance (COPs) in the 1.2 to 1.7 range. This increased performance may call for high generator temperatures, new working fluids or new materials of construction. In most cases, two different sets of working fluids are required. The conceptual design presented here is aimed at obtaining high efficiencies with relatively low temperatures, employing only one set of fluids. The concept consists of two loops coupled in a configuration aimed at minimizing the loss of thermodynamic availability incurred when transferring refrigerant between the loops. The working fluid pair is a solution of lithium bromide-water. The calculated COPs are of the order of 1.8. The cycle relies on an elaborate evaporator-absorber combination. The paper presents the conceptual design, the critical assumptions, and the performance calculations for the concept. 相似文献
122.
本工作用XRD,EPMA,SEM等测试技术计算和示出了用不同活性粉料制备的Ba(Mg1/3Ta2/3)O3微波陶瓷晶格中B位离子有序度和元素的面分布情况,对它们在X面下的电行为作了探讨。实验结果表明,BMT陶瓷的微波损耗主要与其密度有序度和微观结构的均一度有关。 相似文献
123.
Keith S. Matlack Tomasz Labuda 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,62(1):91-93
A method for analyzing the fluorine content of glass using a microwave oven to digest the glass is presented. Analysis time and secondary waste generation are reduced using this method, without sacrificing accuracy. 相似文献
124.
Absorbability of Calcium From Common Beans 总被引:4,自引:0,他引:4
C.M. WEAVER R.P. HEANEY W.R. PROULX SM. HINDERS P.T. PACKARD 《Journal of food science》1993,58(6):1401-1403
Absorption of calcium from white, red, and pinto beans, labeled with 45Ca, was measured in 24 women in a three-way randomized design using a calcium load of 72 mg and milk as the referent. Fractional absorption for the three beans averaged 0.219 ± 0.047 and did not differ by type. Milk calcium absorption at the same load was more than two times higher, 0.451 ± 0.088 (P < 0.001). Oxalate content averaged 0.34%, and phytate averaged 1.7%, a stoichiometric excess relative to calcium. To evaluate the relation of phytate to reduced absorbability, labeled pinto beans were pre-treated with phytase and fed to 10 subjects. Fractional absorption rose, averaging 0.318 ± 0.071, (P <0.01 vs. untreated beans), but was significantly below that of milk. The difference was partly accounted for by phytate, with the remainder probably due to relatively high oxalate. 相似文献
125.
The influence of irreversibility of finite-rate heat transfer on the performance of an absorption refrigerator is investigated using an endoreversible cycle model with continuous flow. The cooling rate is adopted as an objective function for refrigerator optimization. The maximum cooling rate and the corresponding coefficient of performance are derived. The optimal performance with respect to heat transfer areas of the refrigerator is analysed. In addition, certain significant conclusions are reached. 相似文献
126.
沈阳太平洋广场空调冷热源方案比较 总被引:4,自引:1,他引:3
对一幢11.5万m^2的四星级综合建筑的空调冷热源不同的蓄冷和取冷比较了四种方案,论证了其中直燃型溴化锂吸收式冷热水机组供冷供暖、小型燃油锅炉供蒸汽的方案最为合理。 相似文献
127.
本文探讨了用X射线能谱仪(EDS)分析卤化银微晶的空间分辨率和吸收修正问题。对SEM-EDS和STEM-EDS两种不同分析模式的空间分辨率进行计算,表明STEM-EDS是研究单个卤化银微晶内碘的含量及分布的有效方法。并对定量分析数据和吸收修正参数进行了讨论,结果证明微晶不同区域厚度的差异,对碘含量的定量测定的影响可以忽略。 相似文献
128.
无源微波遥感用于地震预报的实验研究 总被引:4,自引:1,他引:3
对无源微波遥感用于地震预报在理论研究的基础上对不同岩性不同结构的岩石试件进行了加载实验,测量了岩石试件的微波辐射随载荷的变化.实验得出:岩石试件的微波辐射能量随岩石应力状态变化而显著变化;而且,不同的波段变化的幅度不同;同一波段不同极化方式的波随应力变化的变化量也不同;微波辐射能量的变化能够被卫星微波遥感探测器探测到.实验还发现,岩石试件临破裂前出现明显的微波辐射异常. 相似文献
129.
In recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C3D/EP composites are excellent. It was shown that a C3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002 相似文献
130.