全文获取类型
收费全文 | 5552篇 |
免费 | 460篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 74篇 |
综合类 | 16篇 |
化学工业 | 1110篇 |
金属工艺 | 151篇 |
机械仪表 | 245篇 |
建筑科学 | 186篇 |
矿业工程 | 1篇 |
能源动力 | 217篇 |
轻工业 | 354篇 |
水利工程 | 36篇 |
石油天然气 | 7篇 |
无线电 | 1061篇 |
一般工业技术 | 1210篇 |
冶金工业 | 573篇 |
原子能技术 | 30篇 |
自动化技术 | 763篇 |
出版年
2024年 | 6篇 |
2023年 | 44篇 |
2022年 | 67篇 |
2021年 | 140篇 |
2020年 | 115篇 |
2019年 | 129篇 |
2018年 | 179篇 |
2017年 | 188篇 |
2016年 | 187篇 |
2015年 | 180篇 |
2014年 | 234篇 |
2013年 | 382篇 |
2012年 | 307篇 |
2011年 | 408篇 |
2010年 | 310篇 |
2009年 | 333篇 |
2008年 | 312篇 |
2007年 | 286篇 |
2006年 | 249篇 |
2005年 | 182篇 |
2004年 | 172篇 |
2003年 | 164篇 |
2002年 | 161篇 |
2001年 | 107篇 |
2000年 | 100篇 |
1999年 | 102篇 |
1998年 | 195篇 |
1997年 | 142篇 |
1996年 | 97篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 61篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 42篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1973年 | 5篇 |
排序方式: 共有6034条查询结果,搜索用时 375 毫秒
41.
Significant amounts of bismuth can be removed from magnesium-lead alloys by crystallization of the intermetallic compounds
Mg0. 6573Pb0. 3427 and Mg0.662Pb0.338in the Mg2Pb, magnesium plumbide phase field of the Pb-Mg-Bi system. The results of the previous studies have been used to develop a
process for debismuthizing lead using controlled conditions for the crystallization of magnesium plumbide from alloys containing
0.03 to 0.06 wt Pct bismuth and magnesium whose concentration is determined by the relationship wt Pct Mg = 2.9 + 20 x wt
Pct Bi. A flow diagram showing the sequence of operations is presented together with a material balance, which was established
from data obtained from individual experiments simulating the previously mentioned unit operations, with a final product containing
less than 0.0010 wt Pct Bi. The process also includes the recycling of magnesium recovered by vacuum distillation. Additional
procedures are included to extend the process to treat alloys containing up to 1.5 wt pct bismuth. 相似文献
42.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
43.
44.
Cross-phase-modulation-induced nonlinear phase noise in WDM direct-detection DPSK systems 总被引:3,自引:0,他引:3
Hoon Kim 《Lightwave Technology, Journal of》2003,21(8):1770-1774
In direct-detection differential-phase-shift-keying (DPSK) systems, the signal-spontaneous emission beat noise introduces phase noise due to Kerr nonlinearity. In wavelength-division-multiplexed (WDM) systems, this nonlinear phase noise comes not only from the channel itself through self-phase modulation (SPM) but also from the other channels through cross-phase modulation (XPM). In this paper, we theoretically and experimentally investigate XPM-induced nonlinear phase noise. We calculate the performance degradation of DPSK systems caused by XPM-induced nonlinear phase noise in addition to SPM-induced phase noise and experimentally verify it using a 600-km nonzero-dispersion-shifted-fiber link. 相似文献
45.
Hoon C. Park Chahngmin Cho Sung W. Lee 《International journal for numerical methods in engineering》1995,38(24):4101-4122
The present paper describes an assumed strain finite element model with six degrees of freedom per node designed for geometrically non-linear shell analysis. An important feature of the present paper is the discussion on the spurious kinematic modes and the assumed strain field in the geometrically non-linear setting. The kinematics of deformation is described by using vector components in contrast to the conventional formulation which requires the use of trigonometric functions of rotational angles. Accordingly, converged solutions can be obtained for load or displacement increments that are much larger than possible with the conventional formulation with rotational angles. In addition, a detailed study of the spurious kinematic modes and the choice of assumed strain field reveals that the same assumed strain field can be used for both geometrically linear and non-linear cases to alleviate element locking while maintaining kinematic stability. It is strongly recommended that the element models, described in the present paper, be used instead of the conventional shell element models that employ rotational angles. 相似文献
46.
A set of chaotic attractors is observed on a boost converter model. The union of their Poincare maps is strange. The attractors are densely packed such that they are sensitive to initial conditions. However every attractor in the set is stable with a finite (may be long) period 相似文献
47.
KA McGovern JS Schoeniger JP Wehrle CE Ng JD Glickson 《Canadian Metallurgical Quarterly》1993,29(2):196-204
Oxygenation is a major determinant of the physiological state of cultured cells. 19F NMR can be used to determine the oxygen concentration available to cells immobilized in a gel matrix by measuring the relaxation rate (1/T1) of perfluorocarbons (PFC) incorporated into the gel matrix. In calcium alginate gel beads without cells the relaxation rate (1/T1) of the trifluoromethyl group of perfluorotripropylamine (FTPA) varies linearly with oxygen concentration, with a slope of 1.26 +/- 0.15 x 10(-3) s-1 microM-1 and an intercept of 0.50 +/- 0.04 s-1. During perfusion with medium equilibrated with 95%/5% O2/CO2, changes in PFC T1s indicate that the average oxygen concentration was reduced from 894 +/- 102 microM in the absence of cells to 476 +/- 65 microM and 475 +/- 50 microM in the presence of 0.7 x 10(8) EMT6/Ro and RIF-1 murine tumor cells per milliliter of gel, respectively. The presence of 0.2 microliters of FTPA/ml of gel had no effect on the energy status of the cells as indicated by 31P NMR spectra. To calculate oxygen gradients within the beads from the average PFC T1 of the sample, a mathematical model was used assuming that oxygen is the limiting nutrient for cell metabolism and that the cellular oxygen consumption rate is independent of oxygen concentration. Data for EMT6/Ro cells were fit using experimentally determined perfusion parameters together with literature values for cell volume and oxygen consumption rate.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
48.
A numerical simulation model for random large amplitude vibration control of composite plate using piezoelectric material is presented. The H∞ control design is employed to suppress the large amplitude vibrations of composites plates under random loading. The numerical simulation model is developed and based on the finite element method. The finite element governing equation includes fully coupled structural and electrical nodal degrees of freedom, and consider the von Karman large amplitude vibration. The modal reduction method using the structural modes is adopted to reduce the finite element equations into a set of modal equations with fewer degrees of freedom. The modal equations are then employed for controller design and time domain simulation. In the simulations without control, the value of the linear mode to the nonlinear deflection is quantified; and the minimum number of linear modes needed for accurate model is obtained. In the simulations with control, it is shown that the truncated modes, which are neglected in the control design, deteriorate the controller performance. Generally, the vibration reduction level is not monotonically increasing with the size of the piezoelectric actuator. The optimal piezoelectric actuator size depends on the excitation level. For higher excitation level, optimal actuator size is larger. The H∞ controller based on the linear finite element formulation gives better vibration reduction for small amplitude vibration, but it still gives reasonable performance for large amplitude vibration provided that the piezoelectric actuator is big and powerful enough. 相似文献
49.
An integral method is investigated and developed in the current work. The effects of the parameters of inlet distortions
on the trend of downstream flow feature in compressor are simulated. Other than the drag-to-lift ratio of the blade and the
inlet incidence angle, it is found that the distorted inlet velocity is another essential parameter to control the distortion
in propagation. Based on this study, a novel critical distortion line and corresponding critical distortion factor are proposed
to express the effect of the two essential inlet parameters on the propagation of distortion, namely, the inlet incidence
angle and the distorted inlet velocity. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion
is further described by a compressor critical performance and its critical characteristic. The results present a useful physical
insight to an axial flow compressor behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the
active role of compressor in determining the velocity distribution when compressor responds to an inlet flow distortion.
Received: 20 December 2001 / Accepted: 21 August 2002
The authors would like to thank HQ RSAF for permission to publish this work, their financial support and encouragement. The
first author wants to acknowledge Prof. Frank Marble of California Institute of Technology, for bringing the problem to the
author's attention and for his helpful discussion. 相似文献