全文获取类型
收费全文 | 181360篇 |
免费 | 17977篇 |
国内免费 | 10169篇 |
专业分类
电工技术 | 14483篇 |
技术理论 | 8篇 |
综合类 | 18883篇 |
化学工业 | 17804篇 |
金属工艺 | 7308篇 |
机械仪表 | 16280篇 |
建筑科学 | 20710篇 |
矿业工程 | 6856篇 |
能源动力 | 8021篇 |
轻工业 | 13340篇 |
水利工程 | 7680篇 |
石油天然气 | 9173篇 |
武器工业 | 2170篇 |
无线电 | 11680篇 |
一般工业技术 | 17599篇 |
冶金工业 | 6795篇 |
原子能技术 | 2646篇 |
自动化技术 | 28070篇 |
出版年
2024年 | 538篇 |
2023年 | 2131篇 |
2022年 | 4333篇 |
2021年 | 5394篇 |
2020年 | 5573篇 |
2019年 | 4733篇 |
2018年 | 4562篇 |
2017年 | 5587篇 |
2016年 | 6787篇 |
2015年 | 7225篇 |
2014年 | 11622篇 |
2013年 | 11790篇 |
2012年 | 13616篇 |
2011年 | 15046篇 |
2010年 | 10762篇 |
2009年 | 11067篇 |
2008年 | 10338篇 |
2007年 | 12408篇 |
2006年 | 10747篇 |
2005年 | 9033篇 |
2004年 | 7623篇 |
2003年 | 6459篇 |
2002年 | 5234篇 |
2001年 | 4322篇 |
2000年 | 3683篇 |
1999年 | 3086篇 |
1998年 | 2628篇 |
1997年 | 2225篇 |
1996年 | 1844篇 |
1995年 | 1531篇 |
1994年 | 1362篇 |
1993年 | 998篇 |
1992年 | 920篇 |
1991年 | 678篇 |
1990年 | 580篇 |
1989年 | 492篇 |
1988年 | 408篇 |
1987年 | 277篇 |
1986年 | 239篇 |
1985年 | 223篇 |
1984年 | 258篇 |
1983年 | 253篇 |
1982年 | 203篇 |
1981年 | 102篇 |
1980年 | 102篇 |
1979年 | 69篇 |
1978年 | 56篇 |
1977年 | 48篇 |
1976年 | 44篇 |
1959年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
S. R. Reid T. X. Yu J. L. Yang G. G. Corbett 《International Journal of Impact Engineering》1996,18(7-8)
This paper is concerned with the problem of pipe whip, the dynamic response of a high pressure piping system subjected to an end force as the result of a pipe break which releases a jet of fluid from the broken section. Both experimental and theoretical results are presented concerning the dynamic elastic-plastic behaviour of cantilever pipes subjected to a transverse force pulse at the free end. Comparisons between experimental data and theoretical predictions are made for mild-steel pipes with outer diameter-to-thickness ratios of 19.5, 28 and 32. It is demonstrated that, for these geometries, the whipping pipes display three characteristically different responses, viz. elastic, plastic hardening behaviour for thick pipes, elastic, plastic hardening-softening behaviour for moderately thick pipes and elastic, plastic hardening-softening-collapse behaviour for thinner pipes. The experimental data taken from a series of high-speed films are compared with the predictions of the instantaneous shapes of the whipping pipes derived from both a rigid, perfectly-plastic, large deflection, dynamic beam model and a more comprehensive model which incorporates the effects of elasticity and plastic hardening and softening, the details of which are presented in the paper. 相似文献
972.
高层结构几何非线性分析的QR法 总被引:3,自引:1,他引:2
本文利用QR法分析高层建筑结构几何非线性问题,建立了新的计算格式。该法不仅未知量的数目少,精度高,而且输入简单,计算速度快,可以用微机分析复杂问题。 相似文献
973.
岩心分析过程中的取心间隔并非完全相同,这就形成了非等间距的岩心分析数据。测井曲线的数据一般都是采样等间距的,为了使岩心数据与测井数据更好地进行匹配,对岩心分析数据进行插值处理,使分析数据形成等距的形式,然后对插值后的数据根据不同的测井曲线进行滤波,使得岩心分析数据与测井数据的分辨率相匹配,利用处理后的数据建立模型或数据分析才可得到较为准确的模型。克里金插值和分形插值均为非线性的数学插值方法,它们与一般的数学插值方法相比较,能更好地反映数据的内在分布规律。文中分别利用克里金插值和分形插值的理论对岩心数据的插值进行了深入的研究,根据两种插值方法的理论建立了相应的插值方法。经过对两种插值理论的实例对比分析,得到了两种非线性插值方法的优缺点,为进一步的深入研究奠定了一定基础。 相似文献
974.
The adsorption and thermal analysis of 1-propanamine has been compared over MFI zeolites which contain H, Ga, and In cations. In the case of H+-containing materials, NH3 and propene are simultaneously desorbed above 600 K. This behavior, is well known and characteristic of the Hofmann elimination reaction. However, a distinctly different mode of reaction is observed in the case of Ga and In containing materials. NH3 is released below 600 K, propene and other products are released above 600 K, and a stable residue remains above 800 K. It is suggested that such behavior results from Lewis acid interactions of Ga or In cations with propanamine.On leave from the Bulgarian Academy of Sciences, Institute of Organic Chemistry. 相似文献
975.
976.
977.
The solution behaviour of a new mesogenic side group polyacrylate in tetrahydrofuran and toluene has been investigated by static and dynamic light scattering. In the dilute regime the polymer behaves as typical polydisperse linear chains in good solvent and the dynamics is dominated by a single fast mode. Cluster formation was detected starting at a concentration around 50 g l−1. It seems to be independent of the solvent as well as of polymer molecular weight. In the semidilute regime, the behaviour of the reduced osmotic modulus leads to the conclusion that repulsion between the chains is stronger than in linear macromolecules. The appearance of larger clusters was revealed above a characteristic concentration and is slightly dependent on the polyacrylate molecular weight. The dynamics was generally characterised by a fast mode related to the cooperative diffusion and by a slow mode associated with large clusters. The existence of a network of multiconnected clusters is envisaged with increasing solution concentration. 相似文献
978.
The present work quantifies the relations between the structure of a chemical reaction kinetic model, its valid parameter range, and the truncation error tolerance of the model. General methods are presented to solve the three important problems of valid parameter range analysis: (1) identification of the valid parameter range of a kinetic model, (2) estimation of the error tolerance required when applying a kinetic model over a specified parameter range, and (3) improvement of existing model generation algorithms to construct more robust models. Finally, the relationship between a model's structure, its valid parameter range, and the truncation error tolerance are illustrated by the flexibility-tolerance-model graph. The new methods are applied to pyrolysis of methane/ethane mixtures. 相似文献
979.
980.
吴连生 《理化检验(物理分册)》1998,34(1):15-19
简叙了电站装备失效分析程序、失效原因及其失效机理。大量的各种各样的失效,常常涉及一种或多种的失效机理。在众机理中,主要是:腐蚀失效、环境断裂失效、变形失效和断理解失效。 相似文献