全文获取类型
收费全文 | 100814篇 |
免费 | 10015篇 |
国内免费 | 6784篇 |
专业分类
电工技术 | 7892篇 |
技术理论 | 3篇 |
综合类 | 8286篇 |
化学工业 | 14132篇 |
金属工艺 | 6530篇 |
机械仪表 | 7046篇 |
建筑科学 | 8208篇 |
矿业工程 | 3276篇 |
能源动力 | 3132篇 |
轻工业 | 7136篇 |
水利工程 | 2575篇 |
石油天然气 | 4742篇 |
武器工业 | 1284篇 |
无线电 | 12244篇 |
一般工业技术 | 10524篇 |
冶金工业 | 3983篇 |
原子能技术 | 1538篇 |
自动化技术 | 15082篇 |
出版年
2024年 | 437篇 |
2023年 | 1313篇 |
2022年 | 2681篇 |
2021年 | 3907篇 |
2020年 | 2903篇 |
2019年 | 2440篇 |
2018年 | 2626篇 |
2017年 | 3101篇 |
2016年 | 2908篇 |
2015年 | 4259篇 |
2014年 | 5462篇 |
2013年 | 6322篇 |
2012年 | 7509篇 |
2011年 | 8291篇 |
2010年 | 7757篇 |
2009年 | 7442篇 |
2008年 | 7502篇 |
2007年 | 7253篇 |
2006年 | 6762篇 |
2005年 | 5387篇 |
2004年 | 3988篇 |
2003年 | 3246篇 |
2002年 | 3165篇 |
2001年 | 2682篇 |
2000年 | 2106篇 |
1999年 | 1516篇 |
1998年 | 928篇 |
1997年 | 787篇 |
1996年 | 639篇 |
1995年 | 525篇 |
1994年 | 406篇 |
1993年 | 314篇 |
1992年 | 212篇 |
1991年 | 170篇 |
1990年 | 128篇 |
1989年 | 116篇 |
1988年 | 68篇 |
1987年 | 65篇 |
1986年 | 57篇 |
1985年 | 25篇 |
1984年 | 27篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 12篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1959年 | 17篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
结合广西田阳县生态扶贫产业核心示范区一期工程补水泵站实际情况,通过方案比选,采用河流入江口东岸布置方案,并对泵站进行了设计介绍,总结技术特点,为类似工程提供参考。 相似文献
82.
83.
In this paper, we address a new problem of noisy images which present in the procedure of relevance feedback for medical image retrieval. We concentrate on the noisy images, caused by the users mislabeling some irrelevant images as relevant ones, and a noisy-smoothing relevance feedback (NS-RF) method is proposed. In NS-RF, a two-step strategy is proposed to handle the noisy images. In step 1, a noisy elimination algorithm is adopted to identify and eliminate the noisy images. In step 2, to further alleviate the influence of noisy images, a fuzzy membership function is employed to estimate the relevance probabilities of retained relevant images. After noisy handling, the fuzzy support vector machine, which can take into account different relevant images with different relevance probabilities, is adopted to re-rank the images. The experimental results on the IRMA medical image collection demonstrate that the proposed method can deal with the noisy images effectively. 相似文献
84.
聚萘二甲酸乙二醇酯(PEN)的研究及发展 总被引:8,自引:0,他引:8
综述了聚萘二甲酸乙二醇酯(PEN)的发展历史,合成工艺,应用领域及其与PET的性能比较。 相似文献
85.
Lijin Xie Junfeng Ma Jun Zhou Zhongqiang Zhao Hua Tian Yonggang Wang Jiantao Tao Xiaoyi Zhu 《Journal of the American Ceramic Society》2006,89(5):1717-1720
Well-crystallized bismuth tungstate (Bi2 WO6 ) powders with different morphologies were successfully synthesized via a low-temperature molten salt method. The powders were characterized by X-ray diffraction, transmission electron microscopy, and UV-Vis, respectively. It was found that the variation of morphology of the obtained Bi2 WO6 powder mainly depends on the different reaction temperatures and the weight ratio of LiNO3 –NaNO3 salt to precursor. In addition, the UV-Visible absorption spectra showed that the synthesized powders had strong light absorption properties not only in the ultraviolet light but also in the visible light region. 相似文献
86.
Changhui Ni Jun Yan Gengdong Cheng Xu Guo 《Structural and Multidisciplinary Optimization》2014,50(1):113-128
The present paper studies the integrated size and topology optimization of skeletal structures under natural frequency constraints. It is found that, unlike the conventional compliance-oriented topology optimization problems, the considered problem may be strongly singular in the sense that the corresponding feasible domain may be disconnected and the global optimal solutions are often located at the tips of some separated low dimensional sub-domains when the cross-sectional areas of the structural components are used as design variables. As in the case of stress-constrained topology optimization, this unpleasant behavior may prevent the gradient-based numerical optimization algorithms from finding the true optimal topologies. To overcome the difficulties posed by the strongly singular optima, some particular forms of area/moment of inertia-density interpolation schemes, which can restore the connectedness of the feasible domain, are proposed. Based on the proposed optimization model, the probability of finding the strongly singular optimum with gradient-based algorithms can be increased. Numerical examples demonstrate the effectiveness of the proposed approach. 相似文献
87.
88.
采用结合丙烯腈含量为26%的NBR、分子量适中的悬浮法Ⅲ型PVC和BR共混,制得了综合性能较PVC/NBR并用胶优异的弹性体。优选的工艺条件为:PVC/NBR/BR=30/60/10(质量比);补强剂选用炭黑40份,超细碳酸钙50份,轻质碳酸钙20份;硫化体系选用过氧化物加少量硫磺;混炼温度为140—170℃,混炼时间为10—15min。通过电子显微镜和动态力学分析,弹性体存在两个T,PVC为分散相,橡胶为连续相。 相似文献
89.
本文针对电子政务信息系统的特点,设计了基于安全隔离的边界防护体系。将安全隔离技术应用到电子政务中,实现了数据的安全高效实时传输,形成了多方位的安全边界防护体系架构。 相似文献
90.
The supermolecular structure of photocross-linked polyethylene (XLPE) has been studied by small-angle light scattering (SALS). The data show that the spherulitic structure of XLPE gradually deteriorates with increasing degree of cross-linking and increasing irradiation temperature from well-developed spherulites to rodlike aggregates and disordered lamellar structures. A photocross-linked sample of PE has lower crystallinity, smaller crystallites, and smaller spherulites than does the original sample. At high degrees of cross-linking, the SALS patterns show little or no spherulitic structure. Results with photocross-linked polyethylene demonstrate that the overall effect of cross-linking on the morphological structure is similar to that of an increase in molecular weight of the polymer. © 1993 John Wiley & Sons, Inc. 相似文献