全文获取类型
收费全文 | 47486篇 |
免费 | 4264篇 |
国内免费 | 2748篇 |
专业分类
电工技术 | 2308篇 |
综合类 | 3705篇 |
化学工业 | 6546篇 |
金属工艺 | 2626篇 |
机械仪表 | 4252篇 |
建筑科学 | 5432篇 |
矿业工程 | 4420篇 |
能源动力 | 2750篇 |
轻工业 | 3075篇 |
水利工程 | 1997篇 |
石油天然气 | 7002篇 |
武器工业 | 564篇 |
无线电 | 1286篇 |
一般工业技术 | 3971篇 |
冶金工业 | 2013篇 |
原子能技术 | 785篇 |
自动化技术 | 1766篇 |
出版年
2024年 | 145篇 |
2023年 | 503篇 |
2022年 | 1133篇 |
2021年 | 1443篇 |
2020年 | 1515篇 |
2019年 | 1215篇 |
2018年 | 1107篇 |
2017年 | 1425篇 |
2016年 | 1577篇 |
2015年 | 1636篇 |
2014年 | 2966篇 |
2013年 | 2987篇 |
2012年 | 3757篇 |
2011年 | 3953篇 |
2010年 | 2750篇 |
2009年 | 2637篇 |
2008年 | 2295篇 |
2007年 | 2972篇 |
2006年 | 2911篇 |
2005年 | 2442篇 |
2004年 | 2205篇 |
2003年 | 1806篇 |
2002年 | 1569篇 |
2001年 | 1367篇 |
2000年 | 1156篇 |
1999年 | 931篇 |
1998年 | 785篇 |
1997年 | 672篇 |
1996年 | 532篇 |
1995年 | 478篇 |
1994年 | 421篇 |
1993年 | 219篇 |
1992年 | 195篇 |
1991年 | 171篇 |
1990年 | 128篇 |
1989年 | 115篇 |
1988年 | 73篇 |
1987年 | 63篇 |
1986年 | 45篇 |
1985年 | 50篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 20篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1964年 | 4篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
151.
152.
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
153.
For the investigations of the gas-liquid phase equilibria, a new apparatus has been developed capable of simultaneously determining the pressure and the liquid and vapor densities using Archimedes' principle. The relative measurement uncertainties of the liquid and vapor densities of R134a (purity, 99.999%) at 313 K are 2×10–4 and 7×10–4, respectively (95% confidence level). For the measurements in the liquid region along nine quasi-isochores at pressures up to 5 MPa, an isochoric apparatus was used. The relative measurement uncertainty ofpv/(RT) is less than 1×10–3. In addition to the investigation of the (p, v, T) properties, the temperature and pressure at the triple point and the vapor pressure between the triple point and 265 K were measured. On the basis of these data, a vapor pressure correlation has been developed that reproduces the measured vapor pressures within the uncertainty of measurement. The results of our measurements are compared with a fundamental equation for R134a, which is based on the measurements of other research groups.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A. 相似文献
154.
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
155.
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
156.
本文用逐步选择因素组合法,对锥形件拉深临界压边力试验数据进行了处理,所得数学模型比一般逐步回归法具有更高的精度和可靠性,模型更为完善。 相似文献
157.
158.
挡土墙填土曲线破裂面的地震主动土压力分析 总被引:2,自引:0,他引:2
在地震作用影响下,墙后填土处于极限平衡状态时,假定破裂面为一条通过墙趾的旋轮线。从墙后土楔中取出一微薄水平层,研究其在水平惯性力下的平衡,得到的地震土压力分布和土压力合力作用点位置均与实验结果相吻合。 相似文献
159.
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
160.
����ѹ���ָ����ߵ���ͼ�漰�������������е�Ӧ�� 总被引:4,自引:3,他引:1
本文提出了凹型压力恢复曲线的一阶导数图版和二阶导数图版。综合使用这两种导数图版,提高了匹配的精度,使匹配结果准确。无量纲起始压力梯度D很难确定。本文提出的两种导数图版综合匹配法能准确确定D值,是致密储层动态评价的有效工具。 相似文献