全文获取类型
收费全文 | 33467篇 |
免费 | 4760篇 |
国内免费 | 3456篇 |
专业分类
电工技术 | 2024篇 |
综合类 | 2992篇 |
化学工业 | 5879篇 |
金属工艺 | 3836篇 |
机械仪表 | 2071篇 |
建筑科学 | 2095篇 |
矿业工程 | 1666篇 |
能源动力 | 1019篇 |
轻工业 | 1045篇 |
水利工程 | 951篇 |
石油天然气 | 3324篇 |
武器工业 | 534篇 |
无线电 | 1626篇 |
一般工业技术 | 6483篇 |
冶金工业 | 1463篇 |
原子能技术 | 543篇 |
自动化技术 | 4132篇 |
出版年
2024年 | 139篇 |
2023年 | 517篇 |
2022年 | 1066篇 |
2021年 | 1255篇 |
2020年 | 1409篇 |
2019年 | 1267篇 |
2018年 | 1232篇 |
2017年 | 1502篇 |
2016年 | 1538篇 |
2015年 | 1665篇 |
2014年 | 2007篇 |
2013年 | 2373篇 |
2012年 | 2582篇 |
2011年 | 2707篇 |
2010年 | 2027篇 |
2009年 | 2084篇 |
2008年 | 1872篇 |
2007年 | 2065篇 |
2006年 | 1860篇 |
2005年 | 1585篇 |
2004年 | 1267篇 |
2003年 | 1085篇 |
2002年 | 979篇 |
2001年 | 860篇 |
2000年 | 732篇 |
1999年 | 690篇 |
1998年 | 566篇 |
1997年 | 508篇 |
1996年 | 404篇 |
1995年 | 351篇 |
1994年 | 273篇 |
1993年 | 231篇 |
1992年 | 200篇 |
1991年 | 151篇 |
1990年 | 193篇 |
1989年 | 137篇 |
1988年 | 67篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 30篇 |
1984年 | 23篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 4篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1959年 | 10篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
A probabilistic model for cleavage fracture with a length scale--parameter estimation and predictions of stationary crack experiments 总被引:1,自引:0,他引:1
This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 °C. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures. 相似文献
52.
In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three‐dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
53.
The deformation behavior of dispersion strengthened copper alloy Cu-Al2O3 was studied by TEM. The results show that nano-scaled dispersed second phase not only increases dislocation density in matrix, but also has an important influence on the dislocation substructure. The presence of fine dispersed Al2 O3 particles results in a uniform and random dislocation distribution in matrix copper and causes the difficulty in formation of dislocation cell structure and the decrease in the amount of cell structure during deformation. Deformation gives rise to much more dislocations and dislocation cells form more difficultly and the decrease in the cell size with the increase of dispersion degree. 相似文献
54.
Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献
55.
Preparation of Plate Fe_(60)Co_8Zr_(10)Mo_5W_2B_(15) Bulk Amorphous Alloy and Its Fracture Toughness
肖华星 《武汉理工大学学报(材料科学英文版)》2005,20(2)
1Introduction Duwez[1]synthesizedthefoilAu Siamorphousalloyforthefirsttimewithrapidsolidification,whichinitiatedthepreparationofamorphousalloysintheprocessofalloysolidification,andthereaftertheresearchonamorphousal loysdevelopedrapidly.Since1980s,withthec… 相似文献
56.
通过对机前推床同步拉杆的受力分析及强度计算,查找出了造成拉杆断裂的原因,并提出了解决拉杆断裂的具体措施。 相似文献
57.
R. Adam Rebeles A. Hermanne S. Takcs F. Trknyi S.F. Kovalev A. Ignatyuk 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,260(2):672-684
In the frame of a systematic study of light ion induced threshold reactions on natural tin (Sn) excitation functions for alpha particles induced reactions are presented in a 12–38 MeV energy domain. Using a stacked foil activation method the following radioisotopes were identified: 116Te, 117Te, 118Te, 119Te, 121Te, 123Te, 117Sb, 118Sb, 120Sb, 122Sb, 124Sb, 126Sb, 117Sn, 111In. The experimental cross sections for these isotopes are presented for the first time in this energy range and a direct comparison with values calculated with the ALICE-IPPE code is discussed. Possible use of these data for production of some isotopes relevant in nuclear medicine is suggested. 相似文献
58.
A model is presented for drying of a single porous particle with superheated steam and humid air. Experimental data for spherical porous ceramic particle reported in the literature were used for the validation of the model. An inversion temperature at which the evaporation rates within superheated steam and humid air are equal was predicted. The effect of thermophysical properties of the particle (permeability 10-14 - 10-17 m2, diameter 3 × 10-3 - 10 × 10-3 m) and operating variables (gas mass flux 0.26 - 0.78 kg m-2 s-1, drying agent temperature 120-200°C) is tested. The inversion temperature is shown to be affected by the thermophysical properties of the porous particle and of the drying agent. 相似文献
59.
高压水射流射孔井眼应力数值模拟研究 总被引:3,自引:0,他引:3
水力射孔技术是一种新型完井方式,利用深穿透水力射孔技术辅助定向压裂,可实现油层改造和油井增产。考虑套管水泥环的影响,采用有限元理论结合ANSYS软件计算了高压水射流水力射孔井眼周围的应力,重点分析了水力射孔参数对井周应力的影响规律,初步研究了直井水力压裂时水力射孔对裂缝起裂的影响。计算结果表明,沿最大水平地应力方向布孔时,孔眼根部的周向拉应力最大,裂缝将会在孔眼根部起裂;选择合理水力射孔参数可有效降低地层破裂压力。研究结果可为高压水射流水力射孔辅助定向压裂提供参数优选的依据。 相似文献
60.