全文获取类型
收费全文 | 25428篇 |
免费 | 2276篇 |
国内免费 | 801篇 |
专业分类
电工技术 | 1075篇 |
技术理论 | 1篇 |
综合类 | 1186篇 |
化学工业 | 4897篇 |
金属工艺 | 1312篇 |
机械仪表 | 1401篇 |
建筑科学 | 1481篇 |
矿业工程 | 429篇 |
能源动力 | 778篇 |
轻工业 | 2064篇 |
水利工程 | 404篇 |
石油天然气 | 1202篇 |
武器工业 | 209篇 |
无线电 | 3354篇 |
一般工业技术 | 3762篇 |
冶金工业 | 1449篇 |
原子能技术 | 272篇 |
自动化技术 | 3229篇 |
出版年
2024年 | 61篇 |
2023年 | 366篇 |
2022年 | 466篇 |
2021年 | 893篇 |
2020年 | 716篇 |
2019年 | 662篇 |
2018年 | 756篇 |
2017年 | 801篇 |
2016年 | 817篇 |
2015年 | 980篇 |
2014年 | 1210篇 |
2013年 | 1650篇 |
2012年 | 1572篇 |
2011年 | 1825篇 |
2010年 | 1495篇 |
2009年 | 1431篇 |
2008年 | 1334篇 |
2007年 | 1260篇 |
2006年 | 1264篇 |
2005年 | 1088篇 |
2004年 | 807篇 |
2003年 | 770篇 |
2002年 | 712篇 |
2001年 | 685篇 |
2000年 | 617篇 |
1999年 | 688篇 |
1998年 | 725篇 |
1997年 | 533篇 |
1996年 | 441篇 |
1995年 | 386篇 |
1994年 | 304篇 |
1993年 | 203篇 |
1992年 | 169篇 |
1991年 | 129篇 |
1990年 | 109篇 |
1989年 | 91篇 |
1988年 | 77篇 |
1987年 | 74篇 |
1986年 | 64篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 13篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 25篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
In this paper, a complete dynamic model on task space for a 6 degrees of freedom (DOF) Gough‐Stewart platform‐type computer numerical control (CNC) machine is derived. The rotation terms of the legs are included for those inertia effects cannot be negligible in the machine tool applications. The formulation derived by means of the Euler‐Lagrange method is convenient for designing the adaptive control law. Also, the average‐type force model for end milling process is derived and included in the dynamic model and control. A composite adaptive control scheme is developed by use of filtering dynamics technique. An appropriate estimator gain is designed in the parameter adaptation law that is useful for estimating the selected important cutting parameters. Experimental results verify the proposed adaptive control scheme can achieve good tracking performance. © 2004 Wiley Periodicals, Inc. 相似文献
992.
Huang YP Wang JS Huang KN Ho CT Huang JD Young MS 《The Review of scientific instruments》2007,78(6):065103
A novel microcomputer-based ultrasonic distance measurement system is presented. This study proposes an efficient algorithm which combines both the amplitude modulation (AM) and the phase modulation (PM) of the pulse-echo technique. The proposed system can reduce error caused by inertia delay and amplitude attenuation effect when using the AM and PM envelope square wave form (APESW). The APESW ultrasonic driving wave form causes a phase inversion phenomenon in the relative wave form of the receiver. The phase inversion phenomenon sufficiently identifies the "measurement pulse" in the received wave forms, which can be used for accurate time-of-flight (TOF) measurement. In addition, combining a countertechnique to compute the phase shifts of the last cycle for TOF, the presented system can obtain distance resolution of 0.1% of the wavelength corresponding to the 40 kHz frequency of the ultrasonic wave. The standard uncertainty of the proposed distance measurement system is found to be 0.2 mm at a range of 50-500 mm. The APESW signal generator and phase detector of this measuring system are designed on a complex programmable logic device, which is used to govern the TOF measurement and send the data to a personal computer for distance calibration and examination. The main advantages of this APESW system are high resolution, low cost, narrow bandwidth requirement, and ease of implementation. 相似文献
993.
Predicting fatigue life by numerical methods was almost impossible in the field of rubber materials. One of the reasons is
that there is not obvious fracture criteria caused by non-standardization of material and excessively various way of mixing
process. But, tearing energy as fracture factor can be applied to a rubber-like material regardless of different types of
fillers, relative to other fracture factors and the crack growth process of rubber could be considered as the whole fatigue
failure process by the existence of potential defects in industrial rubber components. This characteristic of fatigue failure
could make it possible to predict the fatigue life of rubber components in theoretical way. FESEM photographs of the surface
of industrial rubber components were analyzed for verifying the existence and distribution of potential defects. For the prediction
of fatigue life, theoretical way of evaluating tearing energy for the general shape of test-piece was proposed. Also, algebraic
expression for the prediction of fatigue life was derived from the rough cut growth rate equation and verified by comparing
with experimental fatigue lives of dumbbell fatigue specimen in various loading condition. 相似文献
994.
Dong Ho Bae Chul Han Kim Seon Young Cho Jung Kyun Hong Chon Liang Tsai 《Journal of Mechanical Science and Technology》2002,16(9):1054-1064
Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the
development or refinement of welded product designs. Various researchers have studied several thermal models associated with
the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated.
These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict
the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately
determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared.
Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts
wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results
in reasonable agreement with the experimental data. 相似文献
995.
996.
The role of higher cantilever modes is important to obtain some material contrast. The analysis of AFM subjected to a short-range force can improve greatly the studies of surface topography and interaction energies and interaction forces, especially for chemical and biological materials. When the tip-sample distance is in the order of inter-atomic spacing, the short-range tip-sample force is usually simulated by the Lennard-Jones model. In this study, the analytical method to determine the frequency shift of AFM subjected to the Lennard-Jones force is proposed. The closed-form solution of the partial differential equation with a nonlinear boundary condition is derived and then the corresponding frequency shifts of higher modes can be determined easily. Moreover, the conventional perturbation method is usually used to determine the frequency shift, but only for the first mode. This is because the original continuous beam system is transformed into a discrete lumped-masses model. Although the above disadvantages exist, the lumped-masses model is simple and intuitive. Using the principle of dynamic strain energy, the conventional perturbation method is revised successfully to determine the frequency shifts of higher modes. The assessment of the generalized perturbation method and the proposed method is made. Finally, the effects of several parameters on the first three frequency shifts are investigated. 相似文献
997.
Tae Jo Ko Jung Whan Park Hee Sool Kim Sun Ho Kim 《The International Journal of Advanced Manufacturing Technology》2007,32(7-8):739-746
Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional
tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop
floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which
has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting
laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed,
and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and
the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor
at a numerical control (NC) machining center. 相似文献
998.
999.
1000.
介绍了DMA4500型数字式密度仪测定牛羊油的密度,分析测量结果的影响因素,依据中华人民共和国国家计量技术规范JJF 1059-1999,对测量结果的不确定度进行评定和表示。其扩展不确定度U=1×10-4g/cm3,置信概率95%,满足我国现行标准要求。 相似文献