全文获取类型
收费全文 | 21506篇 |
免费 | 1854篇 |
国内免费 | 1163篇 |
专业分类
电工技术 | 298篇 |
技术理论 | 1篇 |
综合类 | 2453篇 |
化学工业 | 890篇 |
金属工艺 | 1529篇 |
机械仪表 | 1542篇 |
建筑科学 | 6289篇 |
矿业工程 | 452篇 |
能源动力 | 266篇 |
轻工业 | 292篇 |
水利工程 | 355篇 |
石油天然气 | 348篇 |
武器工业 | 148篇 |
无线电 | 3932篇 |
一般工业技术 | 3321篇 |
冶金工业 | 591篇 |
原子能技术 | 1096篇 |
自动化技术 | 720篇 |
出版年
2024年 | 54篇 |
2023年 | 178篇 |
2022年 | 315篇 |
2021年 | 414篇 |
2020年 | 531篇 |
2019年 | 469篇 |
2018年 | 438篇 |
2017年 | 561篇 |
2016年 | 576篇 |
2015年 | 653篇 |
2014年 | 1148篇 |
2013年 | 1192篇 |
2012年 | 1502篇 |
2011年 | 1716篇 |
2010年 | 1268篇 |
2009年 | 1437篇 |
2008年 | 1355篇 |
2007年 | 1576篇 |
2006年 | 1384篇 |
2005年 | 1171篇 |
2004年 | 971篇 |
2003年 | 864篇 |
2002年 | 732篇 |
2001年 | 647篇 |
2000年 | 559篇 |
1999年 | 477篇 |
1998年 | 418篇 |
1997年 | 349篇 |
1996年 | 296篇 |
1995年 | 240篇 |
1994年 | 222篇 |
1993年 | 152篇 |
1992年 | 124篇 |
1991年 | 112篇 |
1990年 | 94篇 |
1989年 | 71篇 |
1988年 | 64篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 18篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Peter Rez 《Journal of research of the National Institute of Standards and Technology》2002,107(6):487-495
To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V. 相似文献
82.
岩壁梁是一种新型结构,为通过一定深度的锚杆将钢筋混凝土梁固定在地下厂房两侧的岩壁上,而吊车荷载则通过锚杆和钢筋混凝土与岩石接触面的摩擦力传到岩体上,形成岩壁梁和岩体共同受力的结构。岩壁梁是地下厂房施工和运行的核心建筑物,岩壁梁锚杆和混凝土的施工质量是直接关系到岩壁梁成败的关键,所以施工技术和施工质量均要求极高,是地下厂房系统施工的重点和难点。本文介绍了瀑布沟水电站地下厂房岩壁梁锚杆和混凝土施工的关键技术及质量控制经验,可供同类工程借鉴参考。 相似文献
83.
某跨线桥施工支架方案设计 总被引:1,自引:0,他引:1
结合某大桥的概况,根据梁体施工工艺要求、现场实地勘察情况确定跨线施工方案,支架采用布架灵活、搭拆方便、承载力大的WDJ碗扣式多功能钢支架,部分预应力现浇连续箱梁采用支墩加纵梁预留门洞的支架现浇,取得良好效果。 相似文献
84.
85.
86.
An approach to solving a linear interpolation problem in a fuzzy information space is proposed. Two different schemes of interpolation
are outlined: a heuristic one, based on the geometrical interpretation of operations, and an optimization one, based on the
expansion principle. The results obtained allow performing fuzzy linear prediction.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 55–68, March–April 2006. 相似文献
87.
The dynamic properties of high-cis (98%) and cis-trans (42% cis) polybutadienes, crosslinked with 0.1 to 1.0% of crosslinking agent, have been studied using a torsion pendulum method over the temperature range ?170 to +20°C. For the high-cis rubber plots of damping factor (tan δ) against temperature showed the expected peak in the glass-transition region with an additional peak in the neighbourhood of 0°C attributable to crystallization. The cis-trans rubber showed two damping maxima in the transition region, separated by 30 to 40°C (depending on the degree of crosslinking), suggesting incipient phase separation of the component structures. The rebound resilience of the high-cis rubber at room temperature exceeded that of the cis-trans, reaching 92% at the highest crosslink density. Plots of resilience versus temperature for both rubbers showed a single minimum in the glass transition region. 相似文献
88.
F. D. McDaniel B. L. Doyle C. H. Seager D. S. Walsh G. Vizkelethy D. K. Brice C. Yang P. Rossi M. Nigam M. El Bouanani G. V. Ravi Prasad J. C. Schwartz L. T. Mitchell J. L. Duggan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):1-10
A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino. 相似文献
89.
90.
T. D. M. Weijers H. Timmers R. G. Elliman 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):397-401
The impact of the pulse height deficit effect in gas ionization detectors on the accurate extraction of depth information from heavy ion elastic recoil detection spectra has been investigated. Thin GaN films and GexSi1−x/Si heterostructures have been analyzed with a 200 MeV 197Au beam. Employing an empirical parameterisation of the pulse height deficit, a global energy calibration of the detector can be achieved. Energy spectra have been compared, calibrated with either a constant or a full energy-dependent compensation for the deficit. A constant compensation results in significant distortion of the extracted depth profile for heavier ions, whereas an energy-dependent compensation yields true concentration–depth profiles. 相似文献