全文获取类型
收费全文 | 22625篇 |
免费 | 2318篇 |
国内免费 | 1513篇 |
专业分类
电工技术 | 1041篇 |
综合类 | 3239篇 |
化学工业 | 4870篇 |
金属工艺 | 2340篇 |
机械仪表 | 1055篇 |
建筑科学 | 1491篇 |
矿业工程 | 689篇 |
能源动力 | 758篇 |
轻工业 | 1149篇 |
水利工程 | 492篇 |
石油天然气 | 1050篇 |
武器工业 | 236篇 |
无线电 | 1265篇 |
一般工业技术 | 3071篇 |
冶金工业 | 1338篇 |
原子能技术 | 271篇 |
自动化技术 | 2101篇 |
出版年
2024年 | 68篇 |
2023年 | 263篇 |
2022年 | 418篇 |
2021年 | 631篇 |
2020年 | 654篇 |
2019年 | 621篇 |
2018年 | 542篇 |
2017年 | 692篇 |
2016年 | 779篇 |
2015年 | 795篇 |
2014年 | 1236篇 |
2013年 | 1440篇 |
2012年 | 1605篇 |
2011年 | 1698篇 |
2010年 | 1219篇 |
2009年 | 1316篇 |
2008年 | 1225篇 |
2007年 | 1485篇 |
2006年 | 1426篇 |
2005年 | 1216篇 |
2004年 | 1092篇 |
2003年 | 965篇 |
2002年 | 781篇 |
2001年 | 651篇 |
2000年 | 555篇 |
1999年 | 497篇 |
1998年 | 383篇 |
1997年 | 354篇 |
1996年 | 309篇 |
1995年 | 294篇 |
1994年 | 272篇 |
1993年 | 190篇 |
1992年 | 172篇 |
1991年 | 147篇 |
1990年 | 112篇 |
1989年 | 97篇 |
1988年 | 68篇 |
1987年 | 40篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1976年 | 2篇 |
1960年 | 1篇 |
1959年 | 3篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
42.
In this paper, we study a three-dimensional axisymmetric boundary-value problem of a slender cylinder composed of a nonlinearly elastic material subjected to an axial force. Starting from the field equations, after a transformation and proper scalings, we identify a small variable and two small parameters, which characterize the present problem. Then, by an approach involving compound series-asymptotic expansions, a nonlinear ODE is derived, which governs the axial strain (the first-term in the series expansion). By imposing the zero radial displacement conditions at two ends, we manage to get the analytical solution of the axial strain, from which all other physical quantities can be deduced and thus the three-dimensional displacement field can be determined. Graphical results are presented, which show that there are two boundary layers near the two ends while the middle part is in a state of almost uniform extension. The asymptotic structure of the analytical solution is derived, which offers clear explanations to the structure of the deformed configuration and shows that the thickness of both boundary layers is of the order of the radius. We also point out the relevance of the present results to the St. Venant’s problem. In particular, we obtain the explicit uniformly-valid exponentially small error term, when the obtained deformed configuration is compared to the configuration of a uniform extension. 相似文献
43.
化学还原法制备纳米铜粉的研究 总被引:18,自引:1,他引:17
本文采用KBH4在液相中化学还原CuSO4,并加入KOH和络合剂EDTA ,制得了纳米级的纯净的铜粉 ,通过调整反应物的浓度 ,可以消除Cu2 O等杂质。制备的纳米铜粉还存在一定程度的团聚 ,需试验加入分散剂来改善。 相似文献
44.
本文提出了求解非线性问题的一种新方法——逐次迭代法,本方法先是给出一个初始近似解,然后将这个近似解进行校正迭代,使之接近于真实解,把一个非线性问题转化为一个线性问题来解决。 相似文献
45.
Here, we describe the development of a reacting flow multi-species/combustion methodology, implemented as an extension to the differential reduced ejector analysis (DREA) computer program [Mathematical and computer modeling, vol. 31, 2000, p. 21; Appl. Math. Model. 25 (2001) 427; Comput. Math. Appl. 43(10–11); NASA Contractor Report, 1998]. Use of the single fluid IVP solver framework that was developed for the original DREA model has been directly coupled into the combustion formulation. With these modifications, the analysis has an elementary single step reaction Fuel+Oxidizer→Product combustion capability. Though approximate in nature, the simplicity and efficiency of the DREA formulation make it suitable for its original niche, namely design and preliminary design environments where more complex and expensive models may be inappropriate. 相似文献
46.
PVDF中空纤维滤膜的形态结构 总被引:3,自引:0,他引:3
用L-S相转换法制备了聚偏氟乙烯(PVDF)中空纤维不对称滤膜。铸膜液由聚合物、溶剂和添加剂组成。用电子显微镜(SEM)考察了聚合物浓度、添加剂用量及种类对膜形态结构的影响。实验结果表明,聚合物浓度对膜形态结构有显著影响,当铸膜液中聚合物浓度较低时,无论用什么种类添加剂,都能形成大、且多的孔,但孔的形状随添加剂不同而异。当恒定聚合物浓度时,添加剂的用量对膜形态结构有很大的影响,但孔的大小及多少与添加剂含量的多少不成正比。 相似文献
47.
利用Sobolev插值不等式和关于时间t的先验估计,研究了一类广义耦合的具有周期初值问题的KdV方程,得到了整体解和整体吸引子的存在性。 相似文献
48.
糠醛注水——润滑油糠醛精制装置的节能途径 总被引:3,自引:1,他引:2
介绍了用水稀释糠醛使润滑油糠醛精制装置节能的途径。通过注水——糠醛-水溶液(含水95%左右),可降低糠醛的气化沸点,增大换热系统的传热温差,改善换热效果,更多地回收能量,达到节约能源的目的。 相似文献
49.
非自喷井解释方法一直是困扰试井界的难题之一。自1995年底应用DKS2.0软件中DST压恢分析法先后处理了大港油田200多层实测资料以来,发现一部分井与常规分析法的处理结果完全不同。这些井多出现在均质无限大油藏,且其压力及压力导数曲线开口小、导数曲线驼峰较小。通过对DST压恢分析法在大港油田应用情况的分析,认为此方法适用于均质非自喷井,尤其是处理低渗且地层受污染井的结果比较符合地层的实际地质情况,其成果的应用对地层改造有一定的指导作用。 相似文献
50.
Evaluation of the Hubbell integral for an omnidirectional detector response to a rectangular plaque gamma emitting radiation source using a different numerical computation method on a personal computer was made. For a plaque consisting of several strip gamma emitters, exposure rates at different positions above the source were calculated using 'exact' evaluation and an approximate method. Optimization method is used to find source activity of each strip, so as to acquire desirable dose uniformity of the irradiated products. In uses of the Hubbell integral, by introducing appropriate programming, computation time can be saved. 相似文献