全文获取类型
收费全文 | 42329篇 |
免费 | 546篇 |
国内免费 | 790篇 |
专业分类
电工技术 | 735篇 |
综合类 | 52篇 |
化学工业 | 6402篇 |
金属工艺 | 3097篇 |
机械仪表 | 1387篇 |
建筑科学 | 864篇 |
矿业工程 | 151篇 |
能源动力 | 1431篇 |
轻工业 | 2283篇 |
水利工程 | 356篇 |
石油天然气 | 1386篇 |
无线电 | 3997篇 |
一般工业技术 | 10701篇 |
冶金工业 | 7245篇 |
原子能技术 | 790篇 |
自动化技术 | 2788篇 |
出版年
2021年 | 346篇 |
2020年 | 277篇 |
2019年 | 375篇 |
2018年 | 669篇 |
2017年 | 662篇 |
2016年 | 749篇 |
2015年 | 541篇 |
2014年 | 814篇 |
2013年 | 2393篇 |
2012年 | 1414篇 |
2011年 | 1897篇 |
2010年 | 1499篇 |
2009年 | 1785篇 |
2008年 | 1628篇 |
2007年 | 1769篇 |
2006年 | 1401篇 |
2005年 | 1229篇 |
2004年 | 1179篇 |
2003年 | 1078篇 |
2002年 | 1068篇 |
2001年 | 1120篇 |
2000年 | 965篇 |
1999年 | 1003篇 |
1998年 | 2122篇 |
1997年 | 1668篇 |
1996年 | 1445篇 |
1995年 | 983篇 |
1994年 | 762篇 |
1993年 | 780篇 |
1992年 | 599篇 |
1991年 | 575篇 |
1990年 | 526篇 |
1989年 | 487篇 |
1988年 | 371篇 |
1987年 | 403篇 |
1986年 | 364篇 |
1985年 | 382篇 |
1984年 | 307篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 298篇 |
1980年 | 350篇 |
1979年 | 343篇 |
1978年 | 295篇 |
1977年 | 416篇 |
1976年 | 632篇 |
1975年 | 311篇 |
1974年 | 294篇 |
1973年 | 313篇 |
1972年 | 276篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
35.
D. C. Peets R. Liang C. Stock W. J. L. Buyers Z. Tun L. Taillefer R. J. Birgeneau D. A. Bonn W. N. Hardy 《Journal of Superconductivity and Novel Magnetism》2002,15(6):531-534
We have grown cubic centimeter-size crystals of YBa2Cu3O x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y2BaCuO5 and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y2BaCuO5 concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were ~1° per crystal and ~2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and ~50 Å in the c-direction. 相似文献
36.
J.Z. ZhaoT.S. Chen 《International Journal of Heat and Mass Transfer》2002,45(11):2265-2276
The inertia effect on the onset of thermal instability in natural convection flow over heated horizontal and inclined flat plates embedded in fluid-saturated porous media is analyzed. The linear non-parallel flow model is employed in the instability analysis, which takes into account the streamwise variation as well as the transverse variation of the disturbance amplitude functions. The set of partial differential equations for the disturbance amplitude functions are converted to a system of homogeneous linear ordinary differential equations with homogeneous boundary conditions by the local non-similarity method. The resulting eigenvalue problem is then solved by an implicit finite-difference method. Representative neutral stability curves and critical Rayleigh numbers are presented. It has been found that as the angle of inclination relative to the horizontal increases, the surface heat transfer rate increases, whereas the flow becomes more stable to the vortex mode of instability. Also, as the inertia effect, expressed in terms of Forchheimer number, Fr, increases, the heat transfer rate decreases, but the flow becomes more stable. It is demonstrated that the non-parallel flow model predicts a more stable flow than the parallel flow model. 相似文献
37.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
38.
Triton polymers are commercial surfactants whose molecular weight distributions are conventionally determined by means of high-performance liquid chromatography (HPLC). However, in the case of the important octylphenol ethoxylates [p-C8H17-C6H4-O-(CH2CH2O)n-H], HPLC cannot resolve individual oligomers of high molecular weight Triton surfactants (e.g., greater than 2000 u or so; u = unified atomic mass unit). In this paper, we show that laser desorption Fourier transform ion cyclotron resonance mass spectrometry (LD/FT/ICR/MS) provides a simple and accurate measure of such Triton surfactant molecular weight distributions up to at least 3500 u, based on a single-shot laser pulse measurement of a few seconds duration. Comparison of LD/FT/ICR/MS and HPLC molecular weight distributions of low molecular weight surfactants shows that laser desorption/ionization produces minimal fragmentation and thus offers an accurate measure of the relative abundances of the neutral oligomers, without the need for prior chromatographic separation of the components. Moreover, for all Triton polymer molecular weight distributions (700-3000 u), LD/FT/ICR/MS provides much more highly resolved profiles of oligomer relative abundances. Finally, LD/FT/ICR/MS reveals the presence of poly(ethylene oxide) side products of the polymerization process, which are not observed by HPLC with conventional ultraviolet absorption detection. 相似文献
39.
This brief presents a necessary and sufficient condition for testing positive, real, imaginary, and negative rational functions. A related term, the positive, imaginary, and negative polynomial, is defined and two necessary and sufficient conditions for testing it are given. 相似文献
40.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献