全文获取类型
收费全文 | 491469篇 |
免费 | 47423篇 |
国内免费 | 36636篇 |
专业分类
电工技术 | 37877篇 |
技术理论 | 58篇 |
综合类 | 54050篇 |
化学工业 | 67429篇 |
金属工艺 | 18689篇 |
机械仪表 | 27484篇 |
建筑科学 | 55091篇 |
矿业工程 | 18070篇 |
能源动力 | 14140篇 |
轻工业 | 38161篇 |
水利工程 | 18781篇 |
石油天然气 | 16430篇 |
武器工业 | 4525篇 |
无线电 | 48959篇 |
一般工业技术 | 40238篇 |
冶金工业 | 21879篇 |
原子能技术 | 5762篇 |
自动化技术 | 87905篇 |
出版年
2024年 | 986篇 |
2023年 | 5746篇 |
2022年 | 10201篇 |
2021年 | 13654篇 |
2020年 | 13517篇 |
2019年 | 11705篇 |
2018年 | 10896篇 |
2017年 | 14010篇 |
2016年 | 16016篇 |
2015年 | 18433篇 |
2014年 | 27304篇 |
2013年 | 28109篇 |
2012年 | 34971篇 |
2011年 | 38135篇 |
2010年 | 29304篇 |
2009年 | 30056篇 |
2008年 | 29887篇 |
2007年 | 36233篇 |
2006年 | 34355篇 |
2005年 | 29641篇 |
2004年 | 25235篇 |
2003年 | 21572篇 |
2002年 | 17441篇 |
2001年 | 13942篇 |
2000年 | 11653篇 |
1999年 | 9462篇 |
1998年 | 6909篇 |
1997年 | 5792篇 |
1996年 | 5288篇 |
1995年 | 4592篇 |
1994年 | 3999篇 |
1993年 | 2970篇 |
1992年 | 2571篇 |
1991年 | 1952篇 |
1990年 | 1665篇 |
1989年 | 1402篇 |
1988年 | 1107篇 |
1987年 | 760篇 |
1986年 | 584篇 |
1985年 | 590篇 |
1984年 | 531篇 |
1983年 | 382篇 |
1982年 | 409篇 |
1981年 | 262篇 |
1980年 | 235篇 |
1979年 | 137篇 |
1978年 | 80篇 |
1977年 | 99篇 |
1976年 | 71篇 |
1975年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
AbstractDifferent drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders. 相似文献
102.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification. 相似文献
103.
104.
针对EDEM自动划分网格较稀疏问题,采用Hypermesh划分仿真模型网格,利用Herz-Mindlin接触理论的Archard磨损模型对转载溜槽磨损问题进行仿真,在网格单元上提取出漏斗和溜管衬板的接触能量和磨损量,分析了磨损量与接触能量的关系。假设转载溜槽衬板磨损深度为物料与溜槽衬板的使用时间为线性函数,根据现场衬板磨损量的测量值,将衬板的磨损系数关系的看作隐式的单变量方程,应用EDEM软件的仿真结果求解出磨损系数的标定值。分析了漏斗和溜管的磨损机理。该方法可用于转载溜槽的磨损预测。 相似文献
105.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
106.
在受到陀螺效应、动框架效应等影响后产生的磁力非线性问题是磁悬浮控制力矩陀螺(MSCMG)高速转子位置精度下降的主要因素。为解决以上问题,提高转子位置精度,本文分析了转子所受磁力的特性,建立了转子系统非线性动力学模型,提出了神经网络滑模控制方法。设计滑模控制律,采用径向基函数神经网络逼近控制律中的非线性模型,自适应算法根据误差在线调整神经网络的权值,同时可以保证整个系统的稳定性。仿真和实验结果表明,所提出方法的转子位置精度达到99%,稳态误差为0.000 2 mm。神经网络滑模控制可以实现MSCMG转子系统的高精度位置控制。 相似文献
107.
108.
Gerd J. Hahn 《国际生产研究杂志》2020,58(5):1425-1441
The Fourth Industrial Revolution – also known as Industry 4.0 (i4.0) – comprises the digitalisation of the industrial sector. This paper uses the theoretical lens of supply chain innovation (SCI) to investigate the implications of i4.0 on supply chain management. For these purposes, the method of structured content analysis is applied to more than 200 use cases of i4.0-enabled SCI introduced by both established and startup companies. i4.0-enabled SCI manifests along three dimensions: process, technology, and business architecture. The key findings of this study can be summarised as follows: first, i4.0-enabled SCI extends the initial focus on productivity improvements in SC processes towards scalability and flexibility. Second, extant i4.0 solutions rely mostly on analytics and smart things while omitting smart people technology and the human-centric approach associated with the i4.0 paradigm. Third, established companies adopt i4.0 merely to sustain their existing business architectures while startup companies radically change their operating models, relying heavily on data analytics and the platform economy. Consequently, established companies pursue a problem-driven, engineering-based approach to SCI while startup companies follow an ‘asset-light’, business-driven approach. Lastly, there are two distinct approaches to digitalising operational SC processes: platform-based crowdsourcing of standard processes and on-demand provision of customised services. 相似文献
109.
针对异构计算节点组成的大规模多状态计算系统的容错性能分析问题,提出了一种计算系统容错性能的评估方法。该方法采用自定义的两级容错性能形式化描述框架进行系统描述,通过构造多值决策图(Multi-value Decision Diagram,MDD)模型对系统进行容错性能建模,并基于构造的模型高效地计算出部件故障的条件下计算系统在特定性能水平上运行的概率,减少了计算的冗余性。实验结果表明,该方法在模型的大小和构建时间上均优于传统方法。该方法的提出将对系统操作员或程序设计者具有重要意义,使其确保系统适合预期应用。 相似文献
110.
AbstractData mining techniques have been successfully utilized in different applications of significant fields, including medical research. With the wealth of data available within the health-care systems, there is a lack of practical analysis tools to discover hidden relationships and trends in data. The complexity of medical data that is unfavorable for most models is a considerable challenge in prediction. The ability of a model to perform accurately and efficiently in disease diagnosis is extremely significant. Thus, the model must be selected to fit the data better, such that the learning from previous data is most efficient, and the diagnosis of the disease is highly accurate. This work is motivated by the limited number of regression analysis tools for multivariate counts in the literature. We propose two regression models for count data based on flexible distributions, namely, the multinomial Beta-Liouville and multinomial scaled Dirichlet, and evaluated the proposed models in the problem of disease diagnosis. The performance is evaluated based on the accuracy of the prediction which depends on the nature and complexity of the dataset. Our results show the efficiency of the two proposed regression models where the prediction performance of both models is competitive to other previously used regression models for count data and to the best results in the literature. 相似文献