全文获取类型
收费全文 | 15100篇 |
免费 | 1387篇 |
国内免费 | 1164篇 |
专业分类
电工技术 | 320篇 |
综合类 | 604篇 |
化学工业 | 3060篇 |
金属工艺 | 1781篇 |
机械仪表 | 2193篇 |
建筑科学 | 238篇 |
矿业工程 | 103篇 |
能源动力 | 261篇 |
轻工业 | 738篇 |
水利工程 | 37篇 |
石油天然气 | 206篇 |
武器工业 | 90篇 |
无线电 | 2909篇 |
一般工业技术 | 3367篇 |
冶金工业 | 356篇 |
原子能技术 | 1049篇 |
自动化技术 | 339篇 |
出版年
2024年 | 34篇 |
2023年 | 261篇 |
2022年 | 343篇 |
2021年 | 470篇 |
2020年 | 455篇 |
2019年 | 473篇 |
2018年 | 425篇 |
2017年 | 529篇 |
2016年 | 513篇 |
2015年 | 480篇 |
2014年 | 606篇 |
2013年 | 904篇 |
2012年 | 842篇 |
2011年 | 1128篇 |
2010年 | 797篇 |
2009年 | 832篇 |
2008年 | 907篇 |
2007年 | 894篇 |
2006年 | 822篇 |
2005年 | 740篇 |
2004年 | 622篇 |
2003年 | 565篇 |
2002年 | 523篇 |
2001年 | 344篇 |
2000年 | 375篇 |
1999年 | 328篇 |
1998年 | 297篇 |
1997年 | 296篇 |
1996年 | 276篇 |
1995年 | 214篇 |
1994年 | 162篇 |
1993年 | 153篇 |
1992年 | 154篇 |
1991年 | 131篇 |
1990年 | 122篇 |
1989年 | 113篇 |
1988年 | 82篇 |
1987年 | 71篇 |
1986年 | 68篇 |
1985年 | 63篇 |
1984年 | 74篇 |
1983年 | 54篇 |
1982年 | 57篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
钙—铈氟碳酸盐矿物中BmSn型新多型的发现及其微结构研究 总被引:7,自引:2,他引:5
利用Philips CM-12分析型透射电镜对四川昌北大型稀土矿床中钙铈氟碳酸盐矿物进行了研究。除证实氟碳钙铈矿(BS)存在3R和6R2种多型外,首次发现和研究了氟碳钙铈矿(BS)存在4H、12H、18R、24R、30R和36R6种新多型;伦琴矿(BS_2)1种6R新多型和B_2S新规则混层矿物2H、12R和24R3种中新多型。电子衍射和晶格象分析表明:该类矿物中众多新多型的产生,主要是由于矿物结构单元层沿(?)轴有序堆垛和[CO_3]的定向周期性变化所致。 相似文献
93.
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
94.
电子辐照加速器大功率工频高压电源 总被引:1,自引:0,他引:1
文章介绍目前两种用于烟气脱硫加速器的不同形式直流高压电源,分析了它们各自的特点。针对它们存在的不足之处,提出了一种全新的倍压型桥式整流线路,并对此线路进行了理论推导和计算机模拟仿真。 相似文献
95.
Ziegler-Natta烯烃聚合催化剂进展 总被引:1,自引:0,他引:1
综述了Ziegler-Natta催化剂在乙烯聚合和丙烯聚合方面的研究开发现状,重点介绍了采用新型二醚化合物作为内给电子体的丙烯聚合催化剂的进展。随着合成树脂向功能化方向发展,开发综合性能优越的新型催化剂及给电子体将是今后的研究方向。 相似文献
96.
A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness
profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness
profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with
distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp
decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve
into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser
and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that
microhardness can be considered as an index of the contamination resulting from metal-mould reaction. 相似文献
97.
本文描述用离子束透过钽金属膜进行混合和快速热处理方法来形成钽的硅化物.用溅射方法在P型硅衬底上淀积一层金属钽,然后用砷离子束透过钽金属模进行混合,采用快速热处理后形成了平整的硅化钽薄层.使用厚度为500埃的钽金属膜,得到钽的硅化物薄层电阻为5.5Ω/□.研究了砷离子能量、剂量及钽膜厚度对钽的硅化物薄层电阻的影响.用透射电镜和台阶仪对所形成的硅化钽进行了分析和厚度测量. 相似文献
98.
氟碳铈矿/直氟碳钙铈矿混层结构中新规则混层矿物的超微结构研究 总被引:4,自引:0,他引:4
用电子衍射和晶格像技术研究了钙稀土氟碳酸盐矿物中的氟碳铈矿(B)/直氟碳钙铈矿(S)混层结构,发现并确定了B_4S_4、B_8S_6、B_1S_6、B_7S_4和B_2S_15种新规则混层矿物的对称性、晶胞参数及理论晶体化学式。根据所获得的高分辨晶格像真实而直观地揭示出该类B_mS_n(m>n)型新规则混层矿物的长周期有序堆垛结构特征及变化规律。 相似文献
99.
A new surface characterization technique: RIMAPS (Rotated Image with Maximum Average Power Spectrum)
This work introduces a new imaging technique, Rotated Image with Maximum Average Power Spectrum (RIMAPS), for use in determining orientation and characteristics of surface topography. It consists of computing the maximum value of the averaged power spectrum, given by one step of the two‐dimensional Fourier transform, for each angle of rotation of a digitized image. The basic measurement science of this technique is described and different cases are studied. The characterization of simple geometrical figures explains the meaning of peaks and their angular positions given by RIMAPS analysis. A known surface pattern made on a sample of pure copper, mechanically ground, is used to study reproducibility, dependence on image quality and topography scale relative to pixel size and magnification. Samples of pure zinc, mechanically ground and chemically etched, were used to show the main features of RIMAPS analysis when characterizing a more complicated pattern on a real surface. All the studies performed under different conditions for observation and acquisition of images give strong evidence of the stability and robustness of RIMAPS as a technique for the characterization of topography. 相似文献
100.
Brefeldin A (BFA) has been reported to cause disassembly of the Golgi. We have used three-dimensional (3-D) high-resolution scanning electron microscopy (HRSEM) to investigate these effects in human skin fibroblast cells. The spontaneous reassembly during prolonged exposure to BFA and some effects of forskolin were observed. A BFA concentration of 5μg/ml caused Golgi complexes to become vesicular, resulting in a progressive decrease in the size of the Golgi. Morphologic changes were visible within 2 min of BFA incubation, and by 30 min no identifiable Golgi could be found. Spontaneous reassembly of the Golgi apparatus upon the removal of the BFA or with continued long-term exposure with BFA could not be confirmed. Preliminary experiments with forskolin were not effective in reversing or inhibiting the effects of BFA in human fibroblast cells grown in culture. This inability for spontaneous reassembly and nonreversal by forskolin may reflect a differential effect of BFA in various cell types. HRSEM has proven to be useful for observing 3-D morphologic effects of BFA in Golgi. 相似文献