全文获取类型
收费全文 | 293036篇 |
免费 | 21594篇 |
国内免费 | 11123篇 |
专业分类
电工技术 | 15462篇 |
技术理论 | 31篇 |
综合类 | 17493篇 |
化学工业 | 50675篇 |
金属工艺 | 16905篇 |
机械仪表 | 18490篇 |
建筑科学 | 23010篇 |
矿业工程 | 9529篇 |
能源动力 | 7981篇 |
轻工业 | 18518篇 |
水利工程 | 4802篇 |
石油天然气 | 20294篇 |
武器工业 | 2239篇 |
无线电 | 31648篇 |
一般工业技术 | 34841篇 |
冶金工业 | 15360篇 |
原子能技术 | 2871篇 |
自动化技术 | 35604篇 |
出版年
2024年 | 1229篇 |
2023年 | 4702篇 |
2022年 | 7983篇 |
2021年 | 11547篇 |
2020年 | 8591篇 |
2019年 | 7300篇 |
2018年 | 8221篇 |
2017年 | 9264篇 |
2016年 | 8069篇 |
2015年 | 11219篇 |
2014年 | 13840篇 |
2013年 | 16537篇 |
2012年 | 17836篇 |
2011年 | 19502篇 |
2010年 | 16840篇 |
2009年 | 15983篇 |
2008年 | 15526篇 |
2007年 | 15163篇 |
2006年 | 16050篇 |
2005年 | 14196篇 |
2004年 | 9105篇 |
2003年 | 7970篇 |
2002年 | 7375篇 |
2001年 | 6526篇 |
2000年 | 7136篇 |
1999年 | 8538篇 |
1998年 | 6895篇 |
1997年 | 5846篇 |
1996年 | 5485篇 |
1995年 | 4543篇 |
1994年 | 3802篇 |
1993年 | 2655篇 |
1992年 | 2152篇 |
1991年 | 1610篇 |
1990年 | 1180篇 |
1989年 | 942篇 |
1988年 | 769篇 |
1987年 | 532篇 |
1986年 | 401篇 |
1985年 | 278篇 |
1984年 | 195篇 |
1983年 | 127篇 |
1982年 | 137篇 |
1909年 | 97篇 |
1908年 | 102篇 |
1907年 | 101篇 |
1906年 | 94篇 |
1905年 | 118篇 |
1904年 | 150篇 |
1903年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Identification of gaps in mangrove forests with airborne LIDAR 总被引:2,自引:0,他引:2
Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m2 account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics. 相似文献
102.
Pattern search algorithms for nonlinear inversion of high-frequency Rayleigh-wave dispersion curves 总被引:1,自引:0,他引:1
Inversion of Rayleigh wave dispersion curves is challenging for most local-search methods due to its high nonlinearity and to its multimodality. In this paper, we implemented and tested a Rayleigh wave dispersion curve inversion scheme based on GPS Positive Basis 2N, a commonly used pattern search algorithm. Incorporating complete poll and complete search strategies based on GPS Positive Basis 2N into the inverse procedure greatly enhances the performance of pattern search algorithms because the two steps can effectively locate the promising areas in the solution space containing the global minima and significantly reduce the computation cost, respectively.The proposed inverse procedure was applied to nonlinear inversion of fundamental-mode Rayleigh wave dispersion curves for a near-surface shear (S)-wave velocity profile. The calculation efficiency and stability of the inversion scheme are tested on three synthetic models and a real example from a roadbed survey in Henan, China. Effects of the number of data points, the reduction of the frequency range of the considered dispersion curve, errors in P-wave velocities and density, the initial S-wave velocity profile as well as the number of layers and their thicknesses on inversion results are also investigated in the present study to further evaluate the performance of the proposed approach.Results demonstrate that pattern search algorithms applied to nonlinear inversion of high-frequency surface wave data should be considered good not only in terms of accuracy but also in terms of the computation effort due to their global and deterministic search process. 相似文献
103.
论文介绍了一种针对铁水鱼雷罐车铁水液位检测的较为可行的低成本方案。采用车上间接称重、远红外非接触传输信号方式,解决了对移动铁水罐车进行实时监测的难题。 相似文献
104.
介绍了利用ASP技术对图书馆主页上的光盘数据库进行远程维护,给出整个实施过程的步骤及部分程序的源程序。 相似文献
105.
一种协调的科技文献分类方法 总被引:1,自引:0,他引:1
科技文献之间的相互引证关系反映了一种科学交流活动,显示了科学文献之间(甚至是学科之间)的内在联系,而通过追溯文献之间的这种关系,可以改善和提高传统的基于内容的科技文献的分类的方法。论文利用有相互引证关系,有同引关系,以及有耦合关系的两篇文献一般是属于同一类的这一特点,提出了文献之间的引用相似度,同引相似度,耦合相似度这三个概念,再利用这三个概念生成了文献之间的“结构相似度”,并将它用于K-NN分类法中得出一种基于结构的分类法。最后,论文将这种基于结构的分类法和基于内容的NaveBayes分类法结合起来提出了一种新的协调分类法。 相似文献
106.
Huiping Hu Qiyuan Chen Zhoulan Yin Pingmin Zhang Lusheng Ye 《Metallurgical and Materials Transactions A》2003,34(13):793-797
The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA)
at the heating rate of 10 K min−1 in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T
di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface
area (S
G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray
diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the
specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time,
but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The
results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated
galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the
production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in
the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed. 相似文献
107.
钼酸盐阻燃抑烟剂研发现状 总被引:2,自引:1,他引:1
简要地叙述了钼酸盐类阻燃抑烟剂 ,如八钼酸铵、钼酸锌、钼酸钙、钼酸钴和三氧化钼等阻燃抑烟剂的研发现状 相似文献
108.
109.
根据生产实践 ,结合PLC的技术特点和 385m2 凯利式叶滤机的电气联锁特性 ,阐述了应用PLC技术 ,可进一步提高 385m2 凯利式叶滤机的运转率和自动化水平。 相似文献
110.
介绍了天津天铁冶金集团有限公司炼钢厂转炉出钢口袖砖工艺的开发过程,主要工艺参数的制定,实践证明,该工艺的应用取得了良好的使用效果。 相似文献