全文获取类型
收费全文 | 15305篇 |
免费 | 1257篇 |
国内免费 | 572篇 |
专业分类
电工技术 | 829篇 |
技术理论 | 1篇 |
综合类 | 1055篇 |
化学工业 | 2659篇 |
金属工艺 | 1011篇 |
机械仪表 | 1009篇 |
建筑科学 | 1195篇 |
矿业工程 | 562篇 |
能源动力 | 426篇 |
轻工业 | 845篇 |
水利工程 | 238篇 |
石油天然气 | 1126篇 |
武器工业 | 126篇 |
无线电 | 1424篇 |
一般工业技术 | 1817篇 |
冶金工业 | 883篇 |
原子能技术 | 147篇 |
自动化技术 | 1781篇 |
出版年
2024年 | 80篇 |
2023年 | 317篇 |
2022年 | 454篇 |
2021年 | 682篇 |
2020年 | 525篇 |
2019年 | 389篇 |
2018年 | 498篇 |
2017年 | 523篇 |
2016年 | 444篇 |
2015年 | 592篇 |
2014年 | 712篇 |
2013年 | 865篇 |
2012年 | 929篇 |
2011年 | 1036篇 |
2010年 | 865篇 |
2009年 | 807篇 |
2008年 | 802篇 |
2007年 | 762篇 |
2006年 | 800篇 |
2005年 | 708篇 |
2004年 | 474篇 |
2003年 | 464篇 |
2002年 | 497篇 |
2001年 | 432篇 |
2000年 | 355篇 |
1999年 | 402篇 |
1998年 | 322篇 |
1997年 | 259篇 |
1996年 | 238篇 |
1995年 | 217篇 |
1994年 | 155篇 |
1993年 | 98篇 |
1992年 | 97篇 |
1991年 | 63篇 |
1990年 | 59篇 |
1989年 | 52篇 |
1988年 | 43篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 2篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Although the photoacoustic effect is almost universally generated by radiation whose intensity is varied in time either by amplitude modulation of a continuous optical source or through the use of pulsed irradiation, it is possible to produce sound by movement of a continuous source in space. Here, the characteristics of sound production by movement of a light source in one dimension are discussed by solution to the wave equation for pressure. Solutions to the wave equation for the velocity potential, from which the acoustic pressure can be determined, are found using the D’Alembert integral and by Fourier transformation of the wave equation. The characteristics of the waveform generated by a Gaussian heat source moving uniformly in space are found to depend on the initial conditions for movement of the source. 相似文献
83.
84.
85.
Transcatheter aortic heart valves (TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate (PEGDA) hydrogels and anisotropic high-shrinkage polyethylene terephthalate/polyamide6 (PET-PA6) fabric (PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses (DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties (i.e., storage moduli ~23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ~9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic (contact angle ~41.6° ± 3.8°) and had low-fouling properties without platelet adhesion, suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area (1.75 cm2) and low regurgitation (3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore, PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future. 相似文献
86.
直升机超临界尾传动轴在跨临界转速时会产生剧烈的振动。限幅减振器是专门针对尾传动轴跨临界减振问题设计的一种复合式减振器。限幅减振器与尾传动轴组成的系统具有摩擦、碰撞等强非线性特征,动力学特性异常复杂。为揭示限幅减振器工作机理并指导减振器设计,建立了具有双间隙结构的限幅减振器与尾传动轴系统的弹簧-质量-阻尼等效模型。分别基于直接时间域积分和时频变换谐波平衡(Harmonic Balance Method with Alternating Frequency-Time Domain Technique)+数值延拓(Numerical Continuation)两种方法对控制方程进行了求解。计算结果表明,限幅减振器存在无作用、正常减振、异常减振、限位四种工作状态。其中,限位状态是针对故障工况下尾传动轴进行的临时限位保护。此外,进一步研究了减振器参数对减振和限位效果的影响,得到了传动轴与碰摩环之间间隙、碰撞刚度以及临界摩擦力对限幅减振器减振效果的影响规律。发现存在最优临界摩擦力,且最优临界摩擦力与传动轴不平衡量等有关。同时限位状态下,通过增加碰摩环与底座之间的碰撞刚度可以减小限位幅值,但也会产生... 相似文献
87.
Shijie Hu Xiaoyu Li Jiayu Bai Hang Lei Weizhong Qian Sunqiang Hu Cong Zhang Akpatsa Samuel Kofi Qian Qiu Yong Zhou Shan Yang 《计算机、材料和连续体(英文)》2023,74(2):2803-2815
When the Transformer proposed by Google in 2017, it was first used for machine translation tasks and achieved the state of the art at that time. Although the current neural machine translation model can generate high quality translation results, there are still mistranslations and omissions in the translation of key information of long sentences. On the other hand, the most important part in traditional translation tasks is the translation of key information. In the translation results, as long as the key information is translated accurately and completely, even if other parts of the results are translated incorrect, the final translation results’ quality can still be guaranteed. In order to solve the problem of mistranslation and missed translation effectively, and improve the accuracy and completeness of long sentence translation in machine translation, this paper proposes a key information fused neural machine translation model based on Transformer. The model proposed in this paper extracts the keywords of the source language text separately as the input of the encoder. After the same encoding as the source language text, it is fused with the output of the source language text encoded by the encoder, then the key information is processed and input into the decoder. With incorporating keyword information from the source language sentence, the model’s performance in the task of translating long sentences is very reliable. In order to verify the effectiveness of the method of fusion of key information proposed in this paper, a series of experiments were carried out on the verification set. The experimental results show that the Bilingual Evaluation Understudy (BLEU) score of the model proposed in this paper on the Workshop on Machine Translation (WMT) 2017 test dataset is higher than the BLEU score of Transformer proposed by Google on the WMT2017 test dataset. The experimental results show the advantages of the model proposed in this paper. 相似文献
88.
R. Bai C. L. Briant D. C. Paine J. R. Beresford 《Metallurgical and Materials Transactions A》1998,29(3):757-764
This article presents a study of the evolution of the annealing texture in hafnium, as measured by electron backscattering
diffraction patterns (EBSPs). It was found that the annealing texture of asreceived extruded rod depended on the annealing
temperature. After low-temperature recrystallization, the deformation axis was parallel to
or
and the basal planes were approximately parallel to the deformation axis. These orientations were deduced by the position
of the points in the standard stereographic triangle used to produce the inverse pole figure. As the annealing temperature
was raised to 1700 °C, the direction parallel to the rolling direction changed to
and the grain size increased. It appeared that the increase in grain size occurred by a process of abnormal grain growth,
and this abnormal grain growth appeared to be the cause of the change in the texture. Texture was also examined in samples
that had been warm rolled to thickness reductions between 10 and 90 pct and then annealed at 1700 °C. In these samples, the
main feature of the texture was that the basal plane became parallel to the rolling plane as the amount of rolling increased.
The maximum grain size was observed in samples that had been rolled to a reduction in thickness of 50 pct. 相似文献
89.
Molecular dynamic model of nanofluid between flat plates under shear flow conditions was built. The nanofluid model consisted
of 12 spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard–Jones
(LJ) potential function was adopted to deal with the interactions between atoms. Thus, the motion states of nanoparticles
during the process of flowing were obtained and the flow behaviors of nanofluid between flat plates at different moments could
be analyzed. The simulation results showed that an absorption layer of argon atoms existed surrounding each nanoparticle and
would accompany with the particle to move. The absorption layer contributed little to the flow of nanoparticles but much to
the heat transferring in nanofluids. Another phenomenon observed during shear flowing process was that the nanoparticles would
vibrate and rotate besides main flowing with liquid argon and these micro-motions could strengthen partial flowing in nanofluids. 相似文献
90.
Xiangjian Chen Di Li Yue Bai Zhijun Xu 《International Journal of Control, Automation and Systems》2011,9(6):1154-1163
This paper focuses on modeling and intelligent control of the new Eight-Rotor MAV which is used to solve the problem of low
coefficient proportion between lift and gravity for Quadrotor MAV. The dynamical and kinematical modeling for the Eight-Rotor
MAV was developed which has never been proposed before. Based on the achieved dynamic modeling, two types of controller were
presented. One type, a PID controller is derived in a conventional way with simplified dynamics and turns out to be quite
sensitive to sensor noise as well as external perturbation. The second type controller is the Neuro-Fuzzy adaptive controller
which is composed of two type-II fuzzy neural networks (TIIFNNs) and one PD controller: The PD controller is adopted to control
the attitude, one of the TIIFNNs is designed to learn the inverse model of Eight-Rotor MAV on-line, the other one is the copy
of the former one to compensate for model errors and external disturbances, both structure and parameters of T-IIFNNs are
tuned on-line at the same time, and then the stability of the Eight-Rotor MAV closed-loop control system is proved using Lyapunov
stability theory. Finally, the validity of the proposed control method has been verified through real-time experiments. The
experimental results show that the performance of Neuro-Fuzzy adaptive controller performs very well under sensor noise and
external disturbances, and has more superiority than traditional PID controller. 相似文献