全文获取类型
收费全文 | 314494篇 |
免费 | 29061篇 |
国内免费 | 18203篇 |
专业分类
电工技术 | 21231篇 |
技术理论 | 54篇 |
综合类 | 41076篇 |
化学工业 | 33014篇 |
金属工艺 | 10737篇 |
机械仪表 | 17572篇 |
建筑科学 | 40153篇 |
矿业工程 | 15673篇 |
能源动力 | 8303篇 |
轻工业 | 20903篇 |
水利工程 | 14419篇 |
石油天然气 | 12463篇 |
武器工业 | 3294篇 |
无线电 | 27155篇 |
一般工业技术 | 21986篇 |
冶金工业 | 15891篇 |
原子能技术 | 3098篇 |
自动化技术 | 54736篇 |
出版年
2024年 | 829篇 |
2023年 | 3707篇 |
2022年 | 6684篇 |
2021年 | 8218篇 |
2020年 | 8438篇 |
2019年 | 6930篇 |
2018年 | 6377篇 |
2017年 | 7936篇 |
2016年 | 9281篇 |
2015年 | 10494篇 |
2014年 | 18642篇 |
2013年 | 16910篇 |
2012年 | 21966篇 |
2011年 | 23287篇 |
2010年 | 18314篇 |
2009年 | 18941篇 |
2008年 | 17889篇 |
2007年 | 22715篇 |
2006年 | 21062篇 |
2005年 | 18341篇 |
2004年 | 15335篇 |
2003年 | 13693篇 |
2002年 | 11194篇 |
2001年 | 9269篇 |
2000年 | 7805篇 |
1999年 | 6335篇 |
1998年 | 4849篇 |
1997年 | 4181篇 |
1996年 | 3887篇 |
1995年 | 3248篇 |
1994年 | 2858篇 |
1993年 | 2162篇 |
1992年 | 1901篇 |
1991年 | 1423篇 |
1990年 | 1237篇 |
1989年 | 1062篇 |
1988年 | 863篇 |
1987年 | 576篇 |
1986年 | 443篇 |
1985年 | 381篇 |
1984年 | 359篇 |
1983年 | 265篇 |
1982年 | 231篇 |
1981年 | 186篇 |
1980年 | 154篇 |
1979年 | 118篇 |
1978年 | 68篇 |
1977年 | 75篇 |
1976年 | 61篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Yumio Yato 《Journal of Nuclear Science and Technology》2019,56(4):311-316
When UF6 is handled in leak tight system, the amount of uranium compound formed on the surface of containers, valves, and others in UF6 handling facilities is not so significant for a short term that special attention has not been given to this problem. The present work was done to throw some more light on this problem based on the recent experiment. We discuss the possibility that the intermolecular transfer of a fluorine atom from UF6 to UF5 may participate in the formation of uranium compound. The discussion includes also the unique features contained in the experimental result, the reaction processes assumed in this problem, and the derivation of a rate equation for expressing the deposition of uranium compound. Furthermore, we propose a new method for determining nonlinear parameters included in a governing differential equation having two variables for expressing the deposition of uranium compound from experimental raw data. 相似文献
132.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5. 相似文献
133.
The rate of penetration (ROP) model is of great importance in achieving a high efficiency in the complex geological drilling process. In this paper, a novel two-level intelligent modeling method is proposed for the ROP considering the drilling characteristics of data incompleteness, couplings, and strong nonlinearities. Firstly, a piecewise cubic Hermite interpolation method is introduced to complete the lost drilling data. Then, a formation drillability (FD) fusion submodel is established by using Nadaboost extreme learning machine (Nadaboost-ELM) algorithm, and the mutual information method is used to obtain the parameters, strongly correlated with the ROP. Finally, a ROP submodel is established by a neural network with radial basis function optimized by the improved particle swarm optimization (RBFNN-IPSO). This two-level ROP model is applied to a real drilling process and the proposed method shows the best performance in ROP prediction as compared with conventional methods. The proposed ROP model provides the basis for intelligent optimization and control in the complex geological drilling process. 相似文献
134.
针对现有混合入侵检测模型仅定性选取特征而导致检测精度较低的问题,同时为了充分结合误用检测模型和异常检测模型的优势,提出一种采用信息增益率的混合入侵检测模型.首先,利用信息增益率定量地选择特征子集,最大程度地保留样本信息;其次,采用余弦时变粒子群算法确定支持向量机参数构建误用检测模型,使其更好地平衡粒子在全局和局部的搜索能力,然后,选取灰狼算法确定单类支持向量机参数构建异常检测模型,以此来提高对最优参数的搜索效率和精细程度,综合提高混合入侵检测模型对攻击的检测效果;最后,通过两种数据集进行仿真实验,验证了所提混合入侵检测模型具有较好的检测性能. 相似文献
135.
A size-dependent governing equation is derived to investigate the torsional static behaviors of two-dimensionally functionally graded microtubes based on the modified couple stress theory. The shear modulus is assumed to vary along the tube’s length direction according to an exponential distribute function, and varies along the tube’s radius direction according to a power-law function. A generalized differential quadrature method is developed to determine the rotational angle and shear stresses. Some illustrative examples are given to investigate the effects of applied torques, the length scale parameter and various material compositions on the torsional angle and shear stresses. 相似文献
136.
This paper considers thermochemical recuperation (TCR) of waste-heat using natural gas reforming by steam and combustion products. Combustion products contain steam (H2O), carbon dioxide (CO2), and ballast nitrogen (N2). Because endothermic chemical reactions take place, methane steam-dry reforming creates new synthetic fuel that contains valuable combustion components: hydrogen (H2), carbon monoxide (CO), and unreformed methane (CH4). There are several advantages to performing TCR in the industrial furnaces: high energy efficiency, high regeneration rate (rate of waste-heat recovery), and low emission of greenhouse gases (CO2, NOx). As will be shown, the use of TCR is significantly increasing the efficiency of industrial furnaces – it has been observed that TCR is capable of reducing fuel consumption by nearly 25%. Additionally, increased energy efficiency has a beneficial effect on the environment as it leads to a reduction in greenhouse gas emissions. 相似文献
137.
以转基因水稻中最常用的CaMV35S启动子、NOS终止子、Cry1Ab/Ac基因、HPT基因及SPS水稻内标基因为研究对象,利用5 种不同的荧光信号(FAM、HEX、Taxas Red、Cy5、Cy5.5)进行多重实时聚合酶链式反应(real-time polymerase chain reaction,real-time PCR)检测方法的研究。通过引物组合筛选、反应体系优化、特异性测试、灵敏度测试、适用性测试等一系列实验,建立了5 重real-time PCR方法,灵敏度可达0.032%。此方法具有灵敏度高、结果准确、通量大等优点,可实现水稻中转基因成分的快速、高效检测。 相似文献
138.
针对电力市场用户群庞大,交易过程中售电套餐选择困难的问题,在Spark环境下设计了一种售电套餐推荐方法,同时也解决了售电套餐推荐过程中在大数据环境下的可扩展性及实时性问题。首先,计算出每个套餐属性的权重值,从而计算得到售电套餐综合相似度。然后,计及用户和套餐两方面提出一种售电套餐推荐方法,实现售电套餐的精准推荐。实验表明,提出的推荐方法能够明显提高推荐的准确度,并且在分布式环境下具有良好的推荐效率和可扩展性。 相似文献
139.
140.
为了解决被动雷达系统中的多发射源定位问题,提出了一种基于多重信号分类(MUSIC)算法和图像膨胀(IE)算法的直接定位方法。该方法结合了谱分析中的MUSIC思想,通过对接收量测协方差矩阵进行特征分析求解目标的位置。首先,在目标个数未知的前提下,利用Akaike信息准则(AIC)来确定模型阶数;然后,推导了基于MUSIC的定位代价函数;之后,利用图像膨胀算法处理得到的代价函数平面;最后,膨胀处理后的输出为目标个数及目标位置的估计值。提出的算法有效地解决了目标检测及提取的问题,能够确定多个目标的位置坐标,为后续的定位性能分析提供可能性,也保证了算法的完整性。进一步地分析了多个临近目标情况下影响目标提取性能的主要因素。 相似文献