全文获取类型
收费全文 | 221901篇 |
免费 | 22100篇 |
国内免费 | 14685篇 |
专业分类
电工技术 | 16634篇 |
技术理论 | 1篇 |
综合类 | 19115篇 |
化学工业 | 27486篇 |
金属工艺 | 12822篇 |
机械仪表 | 13739篇 |
建筑科学 | 14558篇 |
矿业工程 | 7216篇 |
能源动力 | 5211篇 |
轻工业 | 21634篇 |
水利工程 | 6729篇 |
石油天然气 | 6273篇 |
武器工业 | 2198篇 |
无线电 | 21389篇 |
一般工业技术 | 18544篇 |
冶金工业 | 28070篇 |
原子能技术 | 3576篇 |
自动化技术 | 33491篇 |
出版年
2024年 | 948篇 |
2023年 | 2949篇 |
2022年 | 6978篇 |
2021年 | 9026篇 |
2020年 | 6564篇 |
2019年 | 4645篇 |
2018年 | 5244篇 |
2017年 | 5965篇 |
2016年 | 5867篇 |
2015年 | 8577篇 |
2014年 | 10465篇 |
2013年 | 12103篇 |
2012年 | 16574篇 |
2011年 | 17350篇 |
2010年 | 15320篇 |
2009年 | 14645篇 |
2008年 | 15001篇 |
2007年 | 14656篇 |
2006年 | 12407篇 |
2005年 | 13120篇 |
2004年 | 9856篇 |
2003年 | 7233篇 |
2002年 | 6227篇 |
2001年 | 5690篇 |
2000年 | 3942篇 |
1999年 | 2338篇 |
1998年 | 6844篇 |
1997年 | 4341篇 |
1996年 | 2969篇 |
1995年 | 1837篇 |
1994年 | 1345篇 |
1993年 | 1370篇 |
1992年 | 400篇 |
1991年 | 423篇 |
1990年 | 409篇 |
1989年 | 390篇 |
1988年 | 371篇 |
1987年 | 281篇 |
1986年 | 245篇 |
1985年 | 198篇 |
1984年 | 86篇 |
1983年 | 104篇 |
1982年 | 146篇 |
1981年 | 207篇 |
1980年 | 245篇 |
1979年 | 90篇 |
1978年 | 101篇 |
1977年 | 614篇 |
1976年 | 1326篇 |
1975年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
首次对茂金属聚丙烯(miPP)/齐格勒-纳塔聚丙烯(ziPP)共混体系的流动性进行了系统的研究。研究发现,在miPP/ziPP共混体系中,miPP含量的变化改变了共混体系的相结构,这种相结构会随着温度和剪切速率的变化而产生明显的变化,从而改变了体系的流动性能,且该共混体系在不同剪切速率下的流动曲线可以分别通过两个模型进行模拟。 相似文献
102.
103.
Jean-Fran?ois Blais Nathalie Meunier Guy Mercier Patrick Drogui Rajeshwar Dayal Tyagi 《Canadian Metallurgical Quarterly》2004,130(5):516-525
This research is related to a preindustrial pilot scale study of the performance of the simultaneous sewage sludge digestion and metal leaching (SSDML) process for decontamination and stabilization of sewage sludge. Ten batch tests were carried out in two 4?m3 bioreactors under various conditions of operation. Results indicated that the addition of 1.0 to 1.5?g?S0/L, which is the equivalent of approximately 30 to 50?kg?S0 per tons dry sludge, is sufficient to obtain conditions of acidity (pH<2.5) and oxido-reduction potential greater than 500 mV necessary for an effective solubilization of toxic metals. The final average of metal solubilization in the output sludge during the SSDML process varied in the following ranges: 25–78% Cd, 9–32% Cr, 48–100% Cu, 77–99% Mn, 15–53% Ni, 12–47% Pb, and 66–100% Zn. The N, P, and K contents were also preserved in the decontaminated sludge. Moreover, the use of low concentrations of elemental sulfur makes it possible to obtain decontaminated sludge with a low total sulfur content (1.4–1.5% S) compatible with agricultural use. The suspended solids removal calculated for the SSDML process was slightly lower, (2.5±0.4)% volatile suspended solids per day, than those reached using standard aerobic digestion. Finally, the SSDML process was found to be effective in removing bad odors and in the destruction (99–100%) of indicator bacteria. 相似文献
104.
设计管理信息系统的提出及其面临的问题 总被引:12,自引:2,他引:10
从管理和设计的两个方面出发,通过对现代企业产品设计管理信息系统的探讨,阐明了设计管理信息系统的概念和结构;并对其实施的条件及面临的困难进行了系统的分析。 相似文献
105.
Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性 总被引:5,自引:0,他引:5
Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料,可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同,它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0.8at%,分凝系数为0.8,与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0.78相当;用称重法测定其密度为5.00g/cm^3;用稳态纵向热流法测出其室温热导率为12.5W/mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。 相似文献
106.
107.
Branislav Radjenovi? Jae Koo Lee Marija Radmilovi?-Radjenovi? 《Computer Physics Communications》2006,174(2):127-132
Level set method [S. Osher, J. Sethian, J. Comput. Phys. 79 (1988) 12] is a highly robust and accurate computational technique for tracking moving interfaces in various application domains. It originates from the idea to view the moving front as a particular level set of a higher dimensional function, so the topological merging and breaking, sharp gradients and cusps can form naturally, and the effects of curvature can be easily incorporated. The resulting equations, describing interface surface evolution, are of Hamilton-Jacobi type and they are solved using techniques developed for hyperbolic equations. In this paper we describe an extension of the sparse field method for solving level set equations in the case of non-convex Hamiltonians, which are common in the simulations of the profile surface evolution during plasma etching and deposition processes. Sparse field method itself, developed by Whitaker [R. Whitaker, Internat. J. Comput. Vision 29 (3) (1998) 203] and broadly used in image processing community, is an alternative to the usual combination of narrow band and fast marching procedures for the computationally effective solving of level set equations. The developed procedure is applied to the simulations of 3D feature profile surface evolution during plasma etching process, that include the effects of ion enhanced chemical etching and physical sputtering, which are the primary causes of the Hamiltonian non-convexity. 相似文献
108.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
109.
110.
容灾系统中存储方案选择的研究 总被引:1,自引:0,他引:1
论文首先阐述了在容灾系统中存储方案的重要性,讨论了存储方案需要考虑的衡量指标,然后介绍了主要的存储方式,根据衡量指标划分了存储方式的特性范围,最后着重研究了容灾系统中存储方案的选择流程,并使用一个实例说明容灾系统中存储方案的选择流程。 相似文献