全文获取类型
收费全文 | 11618篇 |
免费 | 1083篇 |
国内免费 | 623篇 |
专业分类
电工技术 | 731篇 |
综合类 | 1093篇 |
化学工业 | 2140篇 |
金属工艺 | 580篇 |
机械仪表 | 551篇 |
建筑科学 | 1426篇 |
矿业工程 | 327篇 |
能源动力 | 491篇 |
轻工业 | 304篇 |
水利工程 | 413篇 |
石油天然气 | 488篇 |
武器工业 | 110篇 |
无线电 | 915篇 |
一般工业技术 | 1803篇 |
冶金工业 | 364篇 |
原子能技术 | 184篇 |
自动化技术 | 1404篇 |
出版年
2024年 | 37篇 |
2023年 | 177篇 |
2022年 | 271篇 |
2021年 | 326篇 |
2020年 | 341篇 |
2019年 | 322篇 |
2018年 | 287篇 |
2017年 | 375篇 |
2016年 | 407篇 |
2015年 | 437篇 |
2014年 | 631篇 |
2013年 | 753篇 |
2012年 | 781篇 |
2011年 | 823篇 |
2010年 | 693篇 |
2009年 | 689篇 |
2008年 | 596篇 |
2007年 | 746篇 |
2006年 | 650篇 |
2005年 | 579篇 |
2004年 | 516篇 |
2003年 | 450篇 |
2002年 | 344篇 |
2001年 | 326篇 |
2000年 | 246篇 |
1999年 | 210篇 |
1998年 | 193篇 |
1997年 | 176篇 |
1996年 | 146篇 |
1995年 | 120篇 |
1994年 | 95篇 |
1993年 | 81篇 |
1992年 | 63篇 |
1991年 | 88篇 |
1990年 | 69篇 |
1989年 | 45篇 |
1988年 | 49篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1959年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
A semi-analytic boundary element method for parabolic problems 总被引:1,自引:0,他引:1
A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems. 相似文献
32.
33.
Wenhui MA Gang XIE Hua WANGFaculty of Materials Metallurgical Engineering Kunming University of Science Technology Kunming China Manuscript received January in revised form May 《材料科学技术学报》2002,18(3):286-287
The thermal expansion behavior of La1-xSrxMn1-yCoyO3-δ (x=0.2-0.4, y=0.1-0.3) perovskites in air has been investigated. The average linear thermal expansion coefficients increased with increasing Sr content up to 40 mole fraction or Co content up to 30 mole fraction. The expansion is generally attributed to an increase in the average cation radius as some of the cations in the perovskite are reduced in valence when oxygen ions are removed from the structure. 相似文献
34.
Kurt F. J. Heinrich 《Journal of research of the National Institute of Standards and Technology》2002,107(6):483-485
Quantitative electron probe analysis is based on models based on the physics or x-ray generation, empirically adjusted to the analyses of specimens of known composition. Their accuracy can be estimated by applying them to a set of specimens of presumably well-known composition. 相似文献
35.
川中地区上三叠统天然气地球化学特征及成藏过程探讨 总被引:3,自引:0,他引:3
川中地区上三叠统是一套自生自储的天然气成藏系统,天然气中甲烷含量为88%~96%,重烃(C2+)含量一般在6%~9%之间,二氧化碳和硫化氢等非烃气体含量普遍较低;天然气干燥系数(C1/C2+)为5~15,并且随深度增加而呈现升高的趋势;天然气和凝析油轻烃中的甲基环己烷、庚烷和异庚烷值变化表明天然气主要来源于腐殖型母质;天然气甲烷和乙烷碳同位素分别为-39.00‰~-41.00‰和-25.00‰~-27.00‰,具有典型煤成气特征。川中地区上三叠统烃源岩在燕山期持续沉降埋藏过程中,达到高成熟早期阶段;在喜山期,该地区大约2500m地层的剥蚀,使地层温度和压力大幅度降低,故储层中早期低成熟残余天然气的卸压膨胀作用和水溶气的脱溶作用为晚期天然气聚集成藏提供了重要的气源,同时也使气藏中甲烷碳同位素变轻。 相似文献
36.
Larry Wos 《Journal of Automated Reasoning》1987,3(4):433-435
This article is the fourth of a series of articles discussing various open research problems in automated reasoning. The problem proposed for research focuses on finding criteria that would enable an automated reasoning program to expand or contract definitions wisely. For evaluating a proposed solution to this research problem, we include suggestions concerning possible test problems.This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38. 相似文献
37.
38.
After the break-up of Czechoslovakia in 1993 the primary metrological standards authority almost fully remained in Slovakia. So we had to build our primary vacuum metrology anew. But we could do it using uptodate techniques that are more effective and they enable us to fulfil our task more effectively and in a shorter time.The steady demand to widen the lower pressure range and a steady demand for maximal accuracy collide with the financial possibilities open to a small country. So it is impossible to follow the classical pattern for the vacuum standards: liquid columns, static expansion system and dynamic expansion system. But it is possible to utilize contemporary progress in construction of piston manometers. This enables us to discard liquid column and static expansion techniques in favour of piston technique [Tesar J, Prazak D. Vacuum 2002; 67: 311, Tesar J, Prazak D, Krajicek Z. In:Proceedings of international symposium on Pressure and Vacuum, 2003. p. 169, Tesar J, Repa P, Prazak D, Krajicek Z, Peksa L. Vacuum 2004; 76: 491.]. Such system fulfils all the needs of a little industrial country and is economically acceptable. 相似文献
39.
Argyris G. Kagiannas Thanassis Didis Dimitris Th. Askounis John Psarras 《国际能源研究杂志》2003,27(2):173-186
The needs that an energy supply system must meet are constantly changing, due to technological, social and political reasons. Effective energy planning is a dynamic process that is repeated periodically and adjusts to changing conditions. Energy decision makers and planners are no longer able to rely on inductive decision making since they have to investigate the effect of various decision parameters and possible future changes. To help in this process, models have been developed where estimates of future load growth, candidate power plants, fuels and other key factors can be introduced, from which the planners can evaluate decision parameters and the available alternatives. The paper presents the different methodologies and practices that are used by 11 energy models for energy demand forecasting, supply side management and generation expansion planning, demand side management and integrated resource planning. The paper concludes to the presentation of a strategic appraisal of the examined energy models appropriate for energy planning in Mozambique. Three models are proposed for conducting demand forecasting, generation expansion planning and demand side management. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
40.
This study addresses the rolling and lifting probabilities for sediment entrainment by incorporating the probabilistic features of the turbulent fluctuation and bed grain geometry. The lognormally distributed instantaneous velocity and uniformly distributed initial grain position, along with a relation between lift coefficient and particle Reynolds number, are used to extend the theoretical formulation of the entrainment probabilities in smooth-bed flows. The two threshold conditions identified herein enable us to precisely define the probabilities of entrainment in the rolling and lifting modes. The results obtained in this study coincide well with the published data. The lifting probability increases monotonously with the dimensionless shear stress θ, which is consistent with the earlier results yet displays improved agreement with the experimental data. The maximum value of rolling probability, with a magnitude of 0.25, occurs at θ ≈ 0.15. For θ<0.05 (or θ>0.6), the rolling (or lifting) probability makes up more than 90% of the total entrainment probability and thus can be used as an approximation to the total probability of entrainment. The proposed rolling and lifting probabilities are further linked to the two separate criteria for incipient motion to explore the critical entrainment probabilities. The results reveal that a consistent probability corresponding to the critical state of sediment entrainment cannot be found. 相似文献