全文获取类型
收费全文 | 82854篇 |
免费 | 8564篇 |
国内免费 | 5151篇 |
专业分类
电工技术 | 3265篇 |
综合类 | 6110篇 |
化学工业 | 13883篇 |
金属工艺 | 3367篇 |
机械仪表 | 5689篇 |
建筑科学 | 5925篇 |
矿业工程 | 5758篇 |
能源动力 | 3291篇 |
轻工业 | 14490篇 |
水利工程 | 2478篇 |
石油天然气 | 7981篇 |
武器工业 | 769篇 |
无线电 | 3780篇 |
一般工业技术 | 5625篇 |
冶金工业 | 3464篇 |
原子能技术 | 1289篇 |
自动化技术 | 9405篇 |
出版年
2024年 | 426篇 |
2023年 | 1202篇 |
2022年 | 2257篇 |
2021年 | 2818篇 |
2020年 | 3089篇 |
2019年 | 2500篇 |
2018年 | 2421篇 |
2017年 | 2889篇 |
2016年 | 3136篇 |
2015年 | 3333篇 |
2014年 | 5142篇 |
2013年 | 5632篇 |
2012年 | 7149篇 |
2011年 | 6999篇 |
2010年 | 4845篇 |
2009年 | 4637篇 |
2008年 | 4145篇 |
2007年 | 5239篇 |
2006年 | 4861篇 |
2005年 | 3944篇 |
2004年 | 3391篇 |
2003年 | 2821篇 |
2002年 | 2339篇 |
2001年 | 1982篇 |
2000年 | 1699篇 |
1999年 | 1381篇 |
1998年 | 1154篇 |
1997年 | 1018篇 |
1996年 | 786篇 |
1995年 | 696篇 |
1994年 | 581篇 |
1993年 | 357篇 |
1992年 | 343篇 |
1991年 | 273篇 |
1990年 | 223篇 |
1989年 | 178篇 |
1988年 | 120篇 |
1987年 | 108篇 |
1986年 | 79篇 |
1985年 | 83篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 34篇 |
1981年 | 30篇 |
1980年 | 34篇 |
1979年 | 28篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1959年 | 19篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In accord with the increasing concern about the global environmental issues, the absorption refrigeration heat-pump systems are currently being considered very promising and attractive. For the purpose of supporting the advanced R&D technology in this area, we have developed a novel correlation to represent the bubble-point pressures of LiBr H2O solutions. The developed correlation covers the most extensive range of validity ever proposed: 273–483 K for temperatures, 0.05 kPa to 1.0 MPa for pressures. and 29 76 wt% LiBr for concentrations.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994. Boulder, Colorado, U.S.A. 相似文献
62.
Uniformity of bulk density distribution during the die filling process is required to minimize quality problems, such as distortion and cracking, for powder compacts. Understanding the die filling process is necessary in ensuring a uniform powder deposition. The second-generation pressure deposition tester (PDT-II) was used to investigate the deposition process and final pressure distribution of powder filling in toroidal, cylindrical, and E-shaped dies. All tests were conducted using a spray-dried free-flowing granular powder. The results indicated that for toroidal dies: (1) the area around 0° orientation (the leeward end) had the highest pressure values (1186.7 to 2498.0 Pa), with the average pressure values of the remaining area 353.7-648.0 Pa; (2) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; (3) the highest feed shoe speed (500 mm/s) led to the most nonuniform pressure distribution among the three speeds; (4) higher feed shoe speed did not always result in higher final pressure values; and (5) the right die tended to have higher final pressure values (215.0 to 2498.0 Pa) than the center die (95.4 to 2052.5 Pa). For E-shaped dies: (1) the final pressure values of the middle leg (308.9 to 760.7 Pa) were higher than those of the left and the right legs (148.9 to 530.3 Pa); (2) the area along the backside had the highest final pressure value (1054.6 to 1303.8 Pa); (3) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; and (4) neither the center die nor the right die always had higher pressure values than the other one at all locations. Comparison between cylindrical and toroidal dies indicated that: (1) neither of the two die shapes (cylinder and toroid) led to consistently higher or lower final pressure values at all locations and (2) for all three feed shoe speeds, the toroidal die had higher average final pressure values in the 0° orientation. 相似文献
63.
本文分析日产车用PDG型柴油机的结构特点及其缸套穴蚀的形成原因、危害和检查与判断方法,并提出在使用中应采取的预防措施。 相似文献
64.
Jaroslav Mackerle 《International Journal of Pressure Vessels and Piping》1996,69(3):279-339
The paper gives a bibliographical review of the finite element methods (FEMs) applied for the analysis of pressure vessel structures/components and piping from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore the aim of this review is to give the reader an encyclopaedic view of the differnt possibilities that exist today for the finite element analysis in the fields of pressure vessels and piping. The bibliography at the end of the paper contains approximately 1900 references to papers, conference proceedings and theses/dissertations on the subject that were published in 1976–1996. These are classified in the following categories: linear and non-linear, static and dynamic, stress and deflection analysis; stability problems; thermal problems; fracture mechanics problems; contact problems; fluid-structure interaction problems; manufacturing of pipes and tubes; welded pipes and pressure vessel components; development of special finite elements for pressure vessels and pipes; finite element software; and other topics. Also finite element software, general purpose and special purpose codes, used for the analysis of pressure vessels and pipes are briefly discussed and presented. 相似文献
65.
66.
67.
Zhang Sheng-ming Yangtze River Scientific Research Institute Wuhan Hubei P. R. China 《水动力学研究与进展(B辑)》1992,(2)
Through a series of model tests of five scales for 2-D free hydraulic jump, the da-ta of fluctuating pressure acting on the floor level within the hydraulic jump were obtained. Dur-ing the experiments, Froude number varied from 2.94 to 8.61, and Reynolds number rangedfrom 2×10~4 to 6×10~5. Experiment results indicate that the amplitude scale of fluctuating pres-sure is the length scale of model, i. e. P'=L, which agrees with gravity similarity law: Thefrequency scale of the fluctuating pressure is a unity i. e., f=1, which does not satisfy thegravity similarity law. 相似文献
68.
Ti-0.2Pd合金SF-1000双级风机叶轮是大型盐酸再生设备的主要部件,采用整体铸造方法制造,无论在技术上还是经济上都是十分有利的。本文主要介绍采用加工石墨,铸铁组合型,真空电弧凝壳熔炼铸造工艺,成功地研制出整体铸造风机叶轮。 相似文献
69.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献
70.
介绍了VLSI版图验证中电阻提取的基本原理和主要方法,给出了一种新颖的基于边界元法的电阻提取算法。该算法采用变节点单元,较好地解决了实际问题中经常出现的角点问题。通过应用该算法对几个实例进行提取,证明使用本文的算法不仅在精度上而且在占用CPU时间上都取得了令人满意的效果 相似文献