全文获取类型
收费全文 | 48345篇 |
免费 | 5715篇 |
国内免费 | 3156篇 |
专业分类
电工技术 | 4168篇 |
综合类 | 4865篇 |
化学工业 | 4805篇 |
金属工艺 | 2061篇 |
机械仪表 | 6753篇 |
建筑科学 | 1917篇 |
矿业工程 | 1124篇 |
能源动力 | 1752篇 |
轻工业 | 983篇 |
水利工程 | 840篇 |
石油天然气 | 1833篇 |
武器工业 | 907篇 |
无线电 | 6198篇 |
一般工业技术 | 4571篇 |
冶金工业 | 1118篇 |
原子能技术 | 305篇 |
自动化技术 | 13016篇 |
出版年
2024年 | 87篇 |
2023年 | 653篇 |
2022年 | 1070篇 |
2021年 | 1379篇 |
2020年 | 1503篇 |
2019年 | 1295篇 |
2018年 | 1319篇 |
2017年 | 1716篇 |
2016年 | 2004篇 |
2015年 | 2218篇 |
2014年 | 3053篇 |
2013年 | 3009篇 |
2012年 | 3411篇 |
2011年 | 4036篇 |
2010年 | 2861篇 |
2009年 | 3129篇 |
2008年 | 3075篇 |
2007年 | 3639篇 |
2006年 | 3091篇 |
2005年 | 2635篇 |
2004年 | 2164篇 |
2003年 | 1938篇 |
2002年 | 1530篇 |
2001年 | 1265篇 |
2000年 | 1066篇 |
1999年 | 767篇 |
1998年 | 579篇 |
1997年 | 483篇 |
1996年 | 415篇 |
1995年 | 367篇 |
1994年 | 306篇 |
1993年 | 245篇 |
1992年 | 192篇 |
1991年 | 145篇 |
1990年 | 116篇 |
1989年 | 121篇 |
1988年 | 73篇 |
1987年 | 42篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 15篇 |
1956年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Irina Terekhova Iliya Kritskiy Mikhail Agafonov Roman Kumeev Carlos Martínez-Corts Horacio Prez-Snchez 《International journal of molecular sciences》2020,21(23)
The selectivity of encapsulation of leflunomide and teriflunomide by native α-, β- and γ-cyclodextrins was investigated through 1H NMR and molecular modeling. Thermodynamic analysis revealed the main driving forces involved in the binding. For α-cyclodextrin, the partial encapsulation was obtained while deep penetration was characterized for the other two cyclodextrins, where the remaining polar fragment of the molecule is located outside the macrocyclic cavity. The interactions via hydrogen bonding are responsible for high negative enthalpy and entropy changes accompanying the complexation of cyclodextrins with teriflunomide. These results were in agreement with the molecular modeling calculations, which provide a clearer picture of the involved interactions at the atomic level. 相似文献
82.
从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。 相似文献
83.
84.
85.
In this study, we proposed a model for the morphological structure of electrospun membranes; it was different from the random distribution of fibers in a nonwoven. On the basis of our observation and analysis of the jet path by a high‐speed camera and the electrospun membranes by scanning electron microscopy, we proposed the base circle/deposition circle model of electrospun membranes. The base circle was used to position the deposition circles. The deposition circles, distributed on or around the base circle at a specific proportion, represented the distribution of the electrospun fibers on the collector. The pore characteristics and fiber distribution were compared between the electrospun membrane and simulated membranes with different spinning times; this verified that they had similar distribution trends. A membrane was simulated with a similar magnification ratio to the actual membrane. This further verified the model. This model could be used for the homogeneity simulation of an electrospun membrane in multinozzle electrospinning, and this may be helpful for predicting electrospun membranes in practical applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45653. 相似文献
86.
ABSTRACTIn this article, we report on the lack of reliability of explicit user feedback and its interpretation in the light of system evaluation. It is known, that given feedback strongly depends on the situational context. But also when many contextual factors are held constant, user feedback still proves to be unreliable. This impacts the evaluation of predictive algorithms since it is not clear whether a deviation between a user response and its corresponding prediction can be seen as a flaw by the system or just as usual ‘human uncertainty’. As a result, the perspective on the evaluation of adaptive systems basically changes. The main goal of this article is to demonstrate that simply increasing the amount of explicit feedback is not the key to sustainable system design innovation, as long as that information is not appropriately evaluated. To this end, we will exploit a novel probabilistic approach of processing user feedback and identify biasing effects on accuracy metrics, error probabilities for system rankings as well as natural limitations of evaluation. Finally, we will discuss possible solution strategies and give advice for handling explicit user feedback that is associated with uncertainty. 相似文献
87.
Main challenges for developing data-based models lie in the existence of high-dimensional and possibly missing observations that exist in stored data from industry process. Variational autoencoder (VAE) as one of the deep learning methods has been applied for extracting useful information or features from high-dimensional dataset. Considering that existing VAE is unsupervised, an output-relevant VAE is proposed for extracting output-relevant features in this work. By using correlation between process variables, different weight is correspondingly assigned to each input variable. With symmetric Kullback–Leibler (SKL) divergence, the similarity is evaluated between the stored samples and a query sample. According to the values of the SKL divergence, data relevant for modeling are selected. Subsequently, Gaussian process regression (GPR) is utilized to establish a model between the input and the corresponding output at the query sample. In addition, owing to the common existence of missing data in output data set, the parameters and missing data in the GPR are estimated simultaneously. A practical debutanizer industrial process is utilized to illustrate the effectiveness of the proposed method. 相似文献
88.
89.
针对卫星激光通信粗跟踪系统的跟踪稳定精度指标要求高的特点,建立了基于永磁同步电机直接驱动的粗跟踪系统模型并进行了跟踪稳定误差分析。在采用传统PID控制策略存在跟踪误差较大、动态性能较差等不足的基础上,提出了一种基于粗跟踪系统的改进型前馈复合控制策略。从理论上分析了前馈复合控制策略提高了粗跟踪系统的动态性能,为降低跟踪稳定误差提供了改善方案。地面实验验证结果表明,与传统控制策略相比,改进型复合控制策略极大地降低了系统的动态跟踪误差,动态跟踪误差由606μrad降低至13μrad(1δ)。进一步的在轨实验也验证了改进型复合控制策略的合理性和先进性,总体指标满足了卫星激光通信终端的极高精度要求。本文所提出的控制策略对其他高性能跟踪伺服系统设计也具有较大的借鉴意义。 相似文献
90.
为提高现有数控机床空间误差分析方法的准确度,本文基于阿贝原则对齐次转换矩阵(HTM)几何误差补偿模型进行优化。首先,推导出XYFZ型三轴机床适用的HTM几何误差补偿模型并给出模型正确使用的前提条件;然后,基于阿贝原则分析了三轴机床的空间误差传递机理,指出阿贝误差对机床定位精度的影响,给出理论计算公式并在机床运动轴上进行实验验证;最后,基于阿贝原则和布莱恩原则对现有的HTM几何误差补偿模型进行优化,采用该模型拟合体对角线空间误差,并与实测机床体对角线误差进行对比验证。现有HTM几何补偿模型可将机床空间误差由41.15μm补偿至16.37μm,补偿率为60.22%;优化后的补偿模型可将机床空间误差补偿至5.32μm,补偿率为87.07%,提高了26.85%。实验结果表明,优化后的补偿模型更加合理,进一步改善了空间误差的补偿精度。 相似文献