全文获取类型
收费全文 | 23219篇 |
免费 | 2848篇 |
国内免费 | 1075篇 |
专业分类
电工技术 | 622篇 |
技术理论 | 2篇 |
综合类 | 1959篇 |
化学工业 | 3611篇 |
金属工艺 | 726篇 |
机械仪表 | 1994篇 |
建筑科学 | 7475篇 |
矿业工程 | 467篇 |
能源动力 | 1068篇 |
轻工业 | 443篇 |
水利工程 | 591篇 |
石油天然气 | 490篇 |
武器工业 | 555篇 |
无线电 | 562篇 |
一般工业技术 | 2856篇 |
冶金工业 | 527篇 |
原子能技术 | 318篇 |
自动化技术 | 2876篇 |
出版年
2024年 | 127篇 |
2023年 | 738篇 |
2022年 | 968篇 |
2021年 | 1304篇 |
2020年 | 1260篇 |
2019年 | 1006篇 |
2018年 | 722篇 |
2017年 | 823篇 |
2016年 | 812篇 |
2015年 | 864篇 |
2014年 | 1696篇 |
2013年 | 1565篇 |
2012年 | 1549篇 |
2011年 | 1887篇 |
2010年 | 1290篇 |
2009年 | 1347篇 |
2008年 | 1279篇 |
2007年 | 1406篇 |
2006年 | 1187篇 |
2005年 | 886篇 |
2004年 | 742篇 |
2003年 | 631篇 |
2002年 | 503篇 |
2001年 | 455篇 |
2000年 | 334篇 |
1999年 | 313篇 |
1998年 | 250篇 |
1997年 | 218篇 |
1996年 | 144篇 |
1995年 | 145篇 |
1994年 | 106篇 |
1993年 | 102篇 |
1992年 | 79篇 |
1991年 | 78篇 |
1990年 | 57篇 |
1989年 | 75篇 |
1988年 | 50篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1959年 | 8篇 |
1957年 | 2篇 |
1956年 | 2篇 |
1955年 | 5篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
31.
Because of the introduction of new processing parameters in water-assisted injection molding (WAIM), processes control has become more difficult. First, design of experiment (DOE) was carried out by using optimized Latin hypercubes (Opt LHS). On the basis of this, computational fluid dynamics (CFD) method was used to simulate and calculate hollowed core ratios and wall thickness differences of cooling water pipe at different positions. Then inverse radial basis function (RBF) neural network model reflecting the fitting relationship between processing parameters and molding quality was established, and accuracy of the model was detected by cross validation. Finally, expected molding quality was applied to predict processing parameters, and the obtained molding quality under the predicted processing parameters was verified by computer aided engineering (CAE) simulation and experimental methods. The results showed that mean relative precisions of processing parameters such as melt temperature, delay time, short shot size, water pressure, and mold temperature for inverse RBF model were 98.6%, 93.6%, 98.5%, 93.9%, and 97.9%, respectively, which met the accuracy requirements. Furthermore, compared with expected values of hollowed core ratios and wall thickness differences, the average errors of CAE and experiment were 2.3% and 4.9%, respectively. 相似文献
32.
Andrey A. Buglak Alexey V. Samokhvalov Anatoly V. Zherdev Boris B. Dzantiev 《International journal of molecular sciences》2020,21(22)
Aptamers are nucleic acid analogues of antibodies with high affinity to different targets, such as cells, viruses, proteins, inorganic materials, and coenzymes. Empirical approaches allow the design of in vitro aptamers that bind particularly to a target molecule with high affinity and selectivity. Theoretical methods allow significant expansion of the possibilities of aptamer design. In this study, we review theoretical and joint theoretical-experimental studies dedicated to aptamer design and modeling. We consider aptamers with different targets, such as proteins, antibiotics, organophosphates, nucleobases, amino acids, and drugs. During nucleic acid modeling and in silico design, a full set of in silico methods can be applied, such as docking, molecular dynamics (MD), and statistical analysis. The typical modeling workflow starts with structure prediction. Then, docking of target and aptamer is performed. Next, MD simulations are performed, which allows for an evaluation of the stability of aptamer/ligand complexes and determination of the binding energies with higher accuracy. Then, aptamer/ligand interactions are analyzed, and mutations of studied aptamers made. Subsequently, the whole procedure of molecular modeling can be reiterated. Thus, the interactions between aptamers and their ligands are complex and difficult to understand using only experimental approaches. Docking and MD are irreplaceable when aptamers are studied in silico. 相似文献
33.
《Journal of the European Ceramic Society》2020,40(13):4396-4402
The response of nanocrystalline silicon carbide (nc-SiC) to nanoindentation is investigated using molecular dynamics (MD) simulation. It is found that the hardness of the nc-SiC decreases with decreasing grain size, showing an inverse Hall-Petch relationship. The behavior is primarily attributed to the reduced number of intact covalent bonds with grain refinement. Dislocation nucleation and growth in nc-SiC are strongly suppressed by the grain boundaries (GBs). In addition to the dislocation region in the grains, the indentation-induced amorphization of nanograins proceeds preferentially from the GBs, leading to grain shrinkage until the grains are fully amorphized. The results provide an improved understanding of the mechanical properties in nc-SiC and other nanostructured covalent materials. 相似文献
34.
萃取塔因生产能力大、占地面积小、密闭性好等优点,在石油、化工、生物、医药和环境工程等多领域被广泛应用。本文从以下几个方面介绍了萃取塔近些年的研究进展:综述了传统萃取塔(脉冲萃取塔、转盘塔与Kühni塔等)的水力学、轴向扩散与传质模型的发展,分析比较了表面张力、传质方向、放大效应等因素对模型的影响;介绍了计算流体动力学(CFD)在萃取塔中单液滴、单相流模拟、液-液两相流模拟、外加能量模拟、与群体平衡模型(PBM)耦合模拟中的应用进展;介绍了国内外设计开发的新型萃取塔,包括改变传统塔的内构件和引入多种外场能量等方式来强化相间传质。研究表明,将先进实验研究方法、准确经验模型和可靠理论计算相结合,将会是萃取塔研究的重要手段和方向。 相似文献
35.
PDC钻头水力结构优化设计研究 总被引:9,自引:0,他引:9
在PDC钻头工作过程中,钻井液对钻头体表面的冲洗、冷却和润滑是保证钻头正常工作的一个非常重要的条件。对PDC钻头而言,水力结构(主要是中心水眼和冠部水道)设计的重要性尤其突出。以前,对钻头水力系统研究只能通过实验的方法进行,研究周期长、成本高、结构调整不方便,而数值模拟的方法在几年前还不成熟,甚至静态的复杂结构流场问题基本无法解决。为此,在提出PDC钻头水力结构优化设计原则的基础上,对PDC钻头的三维流场进行了数值模拟。模拟中考虑了钻头的喷嘴布置位置、直径、数量以及切削齿对流场的影响。计算结果表明,原设计在喷嘴布置位置和喷射角度上存在不足,以此为基础进行了水力结构的优化设计。文中的研究成果成功地应用在新型钻头水力结构的设计中,研究方法为PDC钻头水力结构优化分析奠定了理论基础。 相似文献
36.
37.
38.
A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited. 相似文献
39.
40.