全文获取类型
收费全文 | 467988篇 |
免费 | 5681篇 |
国内免费 | 2063篇 |
专业分类
电工技术 | 8848篇 |
技术理论 | 5篇 |
综合类 | 1242篇 |
化学工业 | 74781篇 |
金属工艺 | 23474篇 |
机械仪表 | 16338篇 |
建筑科学 | 10170篇 |
矿业工程 | 4898篇 |
能源动力 | 9030篇 |
轻工业 | 33444篇 |
水利工程 | 6348篇 |
石油天然气 | 16178篇 |
武器工业 | 269篇 |
无线电 | 44793篇 |
一般工业技术 | 102015篇 |
冶金工业 | 73634篇 |
原子能技术 | 14619篇 |
自动化技术 | 35646篇 |
出版年
2021年 | 4836篇 |
2019年 | 4438篇 |
2018年 | 7954篇 |
2017年 | 8208篇 |
2016年 | 8722篇 |
2015年 | 5434篇 |
2014年 | 9032篇 |
2013年 | 20009篇 |
2012年 | 13837篇 |
2011年 | 17674篇 |
2010年 | 14234篇 |
2009年 | 15495篇 |
2008年 | 16357篇 |
2007年 | 16139篇 |
2006年 | 13733篇 |
2005年 | 12028篇 |
2004年 | 11236篇 |
2003年 | 10646篇 |
2002年 | 10605篇 |
2001年 | 10454篇 |
2000年 | 10009篇 |
1999年 | 9450篇 |
1998年 | 18969篇 |
1997年 | 14434篇 |
1996年 | 10998篇 |
1995年 | 8587篇 |
1994年 | 7991篇 |
1993年 | 8019篇 |
1992年 | 6585篇 |
1991年 | 6451篇 |
1990年 | 6586篇 |
1989年 | 6464篇 |
1988年 | 6139篇 |
1987年 | 5651篇 |
1986年 | 5560篇 |
1985年 | 6092篇 |
1984年 | 5933篇 |
1983年 | 5622篇 |
1982年 | 5143篇 |
1981年 | 5317篇 |
1980年 | 5109篇 |
1979年 | 5436篇 |
1978年 | 5551篇 |
1977年 | 5673篇 |
1976年 | 6882篇 |
1975年 | 5056篇 |
1974年 | 4972篇 |
1973年 | 5001篇 |
1972年 | 4400篇 |
1971年 | 4023篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Quasi-static stress fields for a crack inclined to the property gradation in functionally graded materials 总被引:3,自引:0,他引:3
Summary. Quasi-static stress fields for a crack inclined to the direction of property gradation in functionally graded materials (FGMs)
are obtained through an asymptotic analysis coupled with Westergaard's stress function approach. The elastic modulus of the
FGM is assumed to vary exponentially along the gradation direction. The mode mixity due to the inclination of the property
gradient is accommodated in the analysis through superposition of opening and shear modes. The first four terms in the expansion
of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field.
Using these stress field contours of constant maximum shear stress, constant maximum principal stress, constant first stress
invariant and constant out of plane displacement are generated, and the effect of inclination of the property gradation direction
on these contours is discussed.
Received September 22, 2002
Published online: May 20, 2003
The financial support of National Science Foundation (NSF) under grant no. CMS 99000138 is gratefully acknowledged. 相似文献
23.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
24.
This study investigates the citation patterns in the journal, Medical Principles and Practice from its inception in 1989 through 2000 (volumes 1-9). The data set includes 4740 references appended to the 221 original
research articles. All of the citations were entered into a ProCite database for analysis. Specifically, this study addresses:
(1) bibliometric patterns of cited works in terms of publication format, subject scatter, authorship characteristics, age
of citations, geographic distribution, and language distribution; (2) productivity of journal titles; (3) the role of self-citation;
and (4) how selected bibliometric indicators apply. Some of the findings include: journal articles are most frequently cited;
English language publications dominate the literature; there is a trend of multiple authorship; and the pattern of aging is
below the norm for medical literature. The results of the study can provide a benchmark to measure the user behavior of a
particular group of researchers as well as for the provision of collection development and management decisions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
25.
To enhance the understanding of the behavior and effects of the precipitation of MnO2 particles in the subsurface generated during in situ chemical oxidation (ISCO) using permanganate, laboratory batch experiments were completed to examine the influence that varied reaction matrix conditions have on the generation and properties of manganese oxides. The conditions examined include organic material type and concentration, permanganate concentration, pH, and the presence of calcium (as a representative divalent cation) in solution. Experimental studies included: (1) spectrophotometric examination of permanganate depletion and manganese oxides generation over time during reactions with trichloroethene; (2) scanning electron microscopy analyses of manganese particle morphology; (3) particle size distribution (filtration) characterization studies; and (4) optical particle sizing and numeration studies. Bench-scale, batch experiments were conducted to focus on fundamental chemical properties affecting particle development under varied potential environmental conditions. The amount of manganese oxides particles that develop, grow, and potentially settle as a result of permanganate ISCO of organic contaminants is a function of the particle size and concentration, the time allowed for particle development, and the impact of matrix conditions on the ability of particles to agglomerate. 相似文献
26.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
27.
28.
L. Vu‐Quoc V. Srinivas Y. Zhai 《International journal for numerical methods in engineering》2003,58(3):397-461
We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
29.
30.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions. 相似文献