全文获取类型
收费全文 | 138074篇 |
免费 | 8738篇 |
国内免费 | 4333篇 |
专业分类
电工技术 | 6489篇 |
技术理论 | 8篇 |
综合类 | 12384篇 |
化学工业 | 10441篇 |
金属工艺 | 5774篇 |
机械仪表 | 14986篇 |
建筑科学 | 31609篇 |
矿业工程 | 4439篇 |
能源动力 | 3246篇 |
轻工业 | 5768篇 |
水利工程 | 4042篇 |
石油天然气 | 5361篇 |
武器工业 | 1557篇 |
无线电 | 8049篇 |
一般工业技术 | 15094篇 |
冶金工业 | 3514篇 |
原子能技术 | 741篇 |
自动化技术 | 17643篇 |
出版年
2024年 | 481篇 |
2023年 | 1463篇 |
2022年 | 2461篇 |
2021年 | 3134篇 |
2020年 | 3365篇 |
2019年 | 2607篇 |
2018年 | 2533篇 |
2017年 | 3150篇 |
2016年 | 3576篇 |
2015年 | 3900篇 |
2014年 | 9701篇 |
2013年 | 7883篇 |
2012年 | 9762篇 |
2011年 | 10413篇 |
2010年 | 8837篇 |
2009年 | 9098篇 |
2008年 | 8164篇 |
2007年 | 9816篇 |
2006年 | 8244篇 |
2005年 | 7228篇 |
2004年 | 5924篇 |
2003年 | 5508篇 |
2002年 | 4342篇 |
2001年 | 3731篇 |
2000年 | 3077篇 |
1999年 | 2393篇 |
1998年 | 1964篇 |
1997年 | 1678篇 |
1996年 | 1418篇 |
1995年 | 1117篇 |
1994年 | 885篇 |
1993年 | 645篇 |
1992年 | 511篇 |
1991年 | 419篇 |
1990年 | 287篇 |
1989年 | 296篇 |
1988年 | 207篇 |
1987年 | 162篇 |
1986年 | 94篇 |
1985年 | 118篇 |
1984年 | 139篇 |
1983年 | 95篇 |
1982年 | 101篇 |
1981年 | 35篇 |
1980年 | 51篇 |
1979年 | 29篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1975年 | 9篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
61.
Kinetic,thermodynamic parameters and in vitro digestion of tannase from Aspergillus tamarii URM 7115
Amanda Reges de Sena Tonny Cley Campos Leite Talita Camila Evaristo da Silva Nascimento Anna Carolina da Silva Catiane S. Souza Antônio Fernando de Mello Vaz 《Chemical Engineering Communications》2018,205(10):1415-1431
Tannase is an enzyme used in various industries and produced by a large number of microorganisms. The aim of this study was to evaluate tannase production to determine the biochemical, kinetic, and thermodynamic properties and to simulate tannase in vitro digestion. The tannase-producing fungal strain was isolated from “jamun” leaves and identified as Aspergillus tamarii. Temperature at 26°C for 67?h was the best combination for maximum tannase activity (6.35-fold; initial activity in Plackett–Burman design—15.53?U/mL and average final activity in Doehlert design—98.68?U/mL). The crude extract of tannase was optimally active at 40°C, pH 5.5 and 6.5. Moreover, tannase was stimulated by Na+, Ca2+, Mg2+, and Mn2+. The half-life at 40°C lasted 247.55?min. The free energy of Gibbs, enthalpy, and entropy, at 40°C, was 81.47, 16.85, and ?0.21?kJ/mol?·?K, respectively. After total digestion, 123.95% of the original activity was retained. Results suggested that tannase from A. tamarii URM 7115 is an enzyme of interest for industrial applications, such as gallic acid production, additive for feed industry, and for beverage manufacturing, due to its catalytic and thermodynamic properties. 相似文献
62.
63.
张峰水库溢洪道体型优化设计 总被引:1,自引:0,他引:1
本文对已设计的张峰水库溢洪道进行了模型试验,根据对试验结果分析,认为原方案设计存在一些问题,并针对问题进行了优化设计。通过对修改方案模型试验结果分析,得出修改方案改进了原方案中存在的不足,优化合理,是可以采用的。 相似文献
64.
Defects are often present in rolled products, such as wire rod. The market demand for wire rod without any defects has increased. In the final wire rod products, defects originating from steel making, casting, pre‐rolling of billets and during wire rod rolling can appear. In this work, artificial V‐shaped longitudinal surface cracks have been analysed experimentally and by means of FEM. The results indicate that the experiments and FEM calculations show the same tendency except in two cases, where instability due to fairly “round” false round bars disturbed the experiment. FE studies in combination with practical experiments are necessary in order to understand the behaviour of the material flows in the groove and to explain whether the crack will open up as a V‐shape or if it will be closed as an I‐shape. 相似文献
65.
The NW‐SE trending Cantarell structure in the Gulf of Campeche hosts the largest oilfield in Mexico. The oil occurs predominantly in latest Cretaceous – earliest Tertiary breccias with subsidiary reserves in Upper Jurassic (Oxfordian and Kimmeridgian) and Lower Cretaceous oolitic and partially dolomitized limestones, dolomites and shaly limestones. Cantarell has been interpreted both as a fold‐and‐thrust zone and as a dextral transpressional structure. Analysis of structure contours at 100m intervals, on the tops of the Tertiary breccia and the Kimmeridgian (Upper Jurassic) dolomite, indicates that the structure is an upright cylindrical fold with gently plunging conical terminations; there is also a conical portion in the central part of the structure. The axes of the central, NW and SE cones are subvertical. This geometry indicates that the two fold terminations and the central cone are aprons rather than points, with the NW and central cone axes intersecting the cylindrical fold axis at the point where the geometry switches from conical to cylindrical. The apical angle (i.e. the angle between the fold and cone axes) varies as follows: (i) in the NW cone, it is ~70° in the breccia and ~76° in the Kimmeridgian dolomite; (ii) in the central cone, it is ~77° in the breccia and ~73° in the Kimmeridgian dolomite; and (iii) in the SE cone, it is ~64° in the breccia and ~57° in the Kimmeridgian dolomite. This indicates that whereas the fold opens with depth in the NW cone, it tightens with depth in the central and SE cones. Assuming a parallel fold geometry, these apical angles indicate an increase in volume in the NW cone (i.e. larger hydrocarbon reservoirs), compared to the central and SE cones. Theoretical considerations indicate that the curvature increases dramatically towards the point of the cone. In the case of the Cantarell structure, the apices of the cones are located at the conical‐cylindrical fold junctions, where the highest curvature may have resulted in a higher degree of fracturing. The coincidence of maximum curvature and the intersection of the conical and cylindrical fold axes in the fold culminations with porous and permeable reservoir rocks may have made these locations favourable for the accumulation of hydrocarbons. 相似文献
66.
PDC钻头水力结构优化设计研究 总被引:9,自引:0,他引:9
在PDC钻头工作过程中,钻井液对钻头体表面的冲洗、冷却和润滑是保证钻头正常工作的一个非常重要的条件。对PDC钻头而言,水力结构(主要是中心水眼和冠部水道)设计的重要性尤其突出。以前,对钻头水力系统研究只能通过实验的方法进行,研究周期长、成本高、结构调整不方便,而数值模拟的方法在几年前还不成熟,甚至静态的复杂结构流场问题基本无法解决。为此,在提出PDC钻头水力结构优化设计原则的基础上,对PDC钻头的三维流场进行了数值模拟。模拟中考虑了钻头的喷嘴布置位置、直径、数量以及切削齿对流场的影响。计算结果表明,原设计在喷嘴布置位置和喷射角度上存在不足,以此为基础进行了水力结构的优化设计。文中的研究成果成功地应用在新型钻头水力结构的设计中,研究方法为PDC钻头水力结构优化分析奠定了理论基础。 相似文献
67.
68.
继电器微机检测装置的软件设计 总被引:2,自引:0,他引:2
继电器作为主要电气元件之一,广泛应用于各个领域。对继电器的检测主要包括机械参数和电气参数的检测。电气参数由于其项目多,实现微机测试比较困难,据此,开发了电磁继电器电参数的自动测试装置,本文仅介绍其软件设计。 相似文献
69.
70.