全文获取类型
收费全文 | 52253篇 |
免费 | 4829篇 |
国内免费 | 3045篇 |
专业分类
电工技术 | 2553篇 |
综合类 | 4062篇 |
化学工业 | 7528篇 |
金属工艺 | 2837篇 |
机械仪表 | 4416篇 |
建筑科学 | 5685篇 |
矿业工程 | 4703篇 |
能源动力 | 3022篇 |
轻工业 | 3691篇 |
水利工程 | 2103篇 |
石油天然气 | 7207篇 |
武器工业 | 621篇 |
无线电 | 1688篇 |
一般工业技术 | 4787篇 |
冶金工业 | 2300篇 |
原子能技术 | 866篇 |
自动化技术 | 2058篇 |
出版年
2024年 | 187篇 |
2023年 | 592篇 |
2022年 | 1272篇 |
2021年 | 1620篇 |
2020年 | 1757篇 |
2019年 | 1416篇 |
2018年 | 1309篇 |
2017年 | 1641篇 |
2016年 | 1801篇 |
2015年 | 1830篇 |
2014年 | 3227篇 |
2013年 | 3335篇 |
2012年 | 4034篇 |
2011年 | 4241篇 |
2010年 | 2969篇 |
2009年 | 2839篇 |
2008年 | 2534篇 |
2007年 | 3241篇 |
2006年 | 3159篇 |
2005年 | 2686篇 |
2004年 | 2388篇 |
2003年 | 1951篇 |
2002年 | 1697篇 |
2001年 | 1485篇 |
2000年 | 1276篇 |
1999年 | 1031篇 |
1998年 | 865篇 |
1997年 | 730篇 |
1996年 | 571篇 |
1995年 | 537篇 |
1994年 | 461篇 |
1993年 | 263篇 |
1992年 | 232篇 |
1991年 | 204篇 |
1990年 | 155篇 |
1989年 | 131篇 |
1988年 | 90篇 |
1987年 | 67篇 |
1986年 | 57篇 |
1985年 | 61篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1960年 | 5篇 |
1959年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
91.
92.
93.
建(构)筑物机械拆除方法综述 总被引:1,自引:0,他引:1
介绍了几种常用的建(构)筑物机械拆除方法,对其工作原理、特点、应用条件及局限性加以分析和说明。 相似文献
94.
95.
FLOW OF NEWTONIAN FLUIDS THROUGH SINUSOID ALLY CONSTRICTED TUBES. NUMERICAL AND EXPERIMENTAL RESULTS
J. A. Deiber Mb. Peirotti R. A. Bortolozzi R. J. Durelli 《Chemical Engineering Communications》1992,117(1):241-262
Numerical and experimental predictions of pressure drops in the flow of Newtonian fluids through sinusoidally constricted tubes (SCT) are carried out. The numerical evaluations analyzed in this work are obtained from the following methods: Geometric Iteration (GJM), Geometric Iteration with First and Second Upwinds (GIM1, GIM2), Successive Over Relaxation by Line (SORBLM), Global Galerkin Spectral Method (GGSM), Collocation (CM) and Dufort-Frankel (DFM). The GIM1, GIM2 and SORBLM are applied to SCT and explained in this work. The other methods have been previously reported in the literature with the same purpose. Experiments are accomplished for constrictions of approximately 40,60 and 80% of the average tube diameter and results compare well with numerical predictions of the steady flow. It is concluded that special attention should be given to evaluations of the friction factor ƒ for Reynolds numbers Re between the onsets of flow separation and turbulence due to flow instability. Finally, the SCT as a model for porous media (PM) is discussed. 相似文献
96.
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
97.
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
98.
99.
Bubble-point pressures and saturated-liquid densities of the binary R-135 (pentafuoroethane) + R- 143a ( 1, 1, 1-trifluoroethane) system have been measured for several compositions at temperatures from 280 to 330 K by means of a magnetic densimeter coupled with a variable-volume cell mounted with a metallic bellows. The experimental uncertainties of the temperature, pressure. and density measurements and the composition determination were estimated to be within ±15 mK, ±13 k Pa, ±0.2%, and ±0.1 wt%, respectively. The purities of the samples used throughout the measurements are 99.98 wt% for R-125 and 99.0 mol % for R- 143a. Based on the present data, the thermodynamic behavior of the vapor-liquid equilibria of this binary refrigerant mixture has been evaluated by using the Peng-Robinson equation for the bubble-point pressures, and the modified Hankinson-Brobst-Thomson equation for the saturated-liquid densities. This was done to identify the optimized binary interaction parameters.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A. 相似文献
100.
柴油机针阀体的乙炔低压渗碳 总被引:2,自引:0,他引:2
乙炔低压渗碳可以有效地避免在真空渗碳过程中产生炭黑和焦油,同时由于乙炔具有较高的供碳能力,使这一技术尤其适用于针阀体这样的小直径深盲孔零件。 相似文献