全文获取类型
收费全文 | 89027篇 |
免费 | 1462篇 |
国内免费 | 518篇 |
专业分类
电工技术 | 1018篇 |
综合类 | 2513篇 |
化学工业 | 12395篇 |
金属工艺 | 4970篇 |
机械仪表 | 3206篇 |
建筑科学 | 2510篇 |
矿业工程 | 615篇 |
能源动力 | 1401篇 |
轻工业 | 4037篇 |
水利工程 | 1365篇 |
石油天然气 | 519篇 |
武器工业 | 4篇 |
无线电 | 9837篇 |
一般工业技术 | 17062篇 |
冶金工业 | 3016篇 |
原子能技术 | 276篇 |
自动化技术 | 26263篇 |
出版年
2023年 | 95篇 |
2022年 | 175篇 |
2021年 | 228篇 |
2020年 | 177篇 |
2019年 | 185篇 |
2018年 | 14625篇 |
2017年 | 13543篇 |
2016年 | 10154篇 |
2015年 | 811篇 |
2014年 | 454篇 |
2013年 | 623篇 |
2012年 | 3465篇 |
2011年 | 9798篇 |
2010年 | 8593篇 |
2009年 | 5866篇 |
2008年 | 7045篇 |
2007年 | 7999篇 |
2006年 | 351篇 |
2005年 | 1394篇 |
2004年 | 1254篇 |
2003年 | 1321篇 |
2002年 | 733篇 |
2001年 | 239篇 |
2000年 | 281篇 |
1999年 | 116篇 |
1998年 | 147篇 |
1997年 | 101篇 |
1996年 | 101篇 |
1995年 | 69篇 |
1994年 | 69篇 |
1993年 | 50篇 |
1992年 | 35篇 |
1991年 | 35篇 |
1988年 | 27篇 |
1984年 | 23篇 |
1969年 | 24篇 |
1968年 | 45篇 |
1967年 | 34篇 |
1966年 | 42篇 |
1965年 | 46篇 |
1963年 | 31篇 |
1962年 | 22篇 |
1961年 | 19篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 37篇 |
1956年 | 34篇 |
1955年 | 65篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate
Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate have been carried out.
The dielectric constant has been measured as a function of frequency in the range 2 kHz–1 MHz and temperature range 30–300 °C.
The dielectric constant increases with temperature, attains a peak near 215 °C, and then decreases as the temperature exceeds
215 °C. The dielectric anomaly at 215 °C is suggested to be due to phase transition brought about in the material. The dielectric
behaviour of the material is correlated with the results on thermal analysis. Thermogravimetric and differential thermal analysis
have been used to study the thermal characteristics of the material. The experimental results show that the material is thermally
stable up to 200 °C. The decomposition process occurs in two stages until ytterbium oxide is formed at 700 °C. The non-isothermal
kinetic parameters e.g., activation energy and the frequency factor have been evaluated for each stage of thermal decomposition
by using the integral method, applying the Coats–Redfern approximation. 相似文献
82.
Christian P. Romero Jonathan I. Avila Edgardo Cisternas Guerau B. Cabrera Alejandro L. Cabrera Kristiaan Temst Margriet J. Van Bael 《Journal of Materials Science》2007,42(18):7667-7672
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of
4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made
by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under
ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity
at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen
TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there
are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately
8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained
for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure. 相似文献
83.
Alexander Katsman Shalom Cohen Menachem Bamberger 《Journal of Materials Science》2007,42(16):6996-7003
This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved
by precipitation of binary phases such as MgZn2 and Mg2Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening
in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking
into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’
evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation
interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters
of the model, R
N
i and k
σ i
, were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The
effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated
from the hardness maximum positions on the aging curves. 相似文献
84.
The aim of the present paper is to review the recent progress in the synthesis of in situ particle reinforced aluminum composites
using thermal, mechanical and combined mechanical-thermal activation of aluminothermic reduction reactions. The combination
of combustion synthesis (CS) and mechanosynthesis (MS) is the most recent development in the processing of advanced materials
like micro and nano aluminum based composites. The combined mechanical thermal synthesis (MTS) has widened the possibilities
for both CS and MS. MTS holds great potential for commercial viability and offers exciting processing route for the synthesis
of advanced materials. Enhanced reaction kinetics and extended concentration limits in MTS are demonstrated by illustrating
the synthesis of aluminum based nanocomposite involving Al–CeO2. 相似文献
85.
Hideo Sawada Hiroshi Kakehi Masashi Koizumi Yoshihiro Katoh Masashi Miura 《Journal of Materials Science》2007,42(17):7147-7153
Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)
n
-RF] reacted with tetraethoxysilane (TEOS) and silica nanoparticles in the presence of low-molecular weight biocides such as
hibitane, hinokitiol, and hinokioil under alkaline conditions to afford RF-(DOBAA)
n
-RF/silica nanocomposites-encapsulated these biocides in excellent to moderate isolated yields. Fluoroalkyl end-capped N,N-dimethylacrylamide oligomer [RF-(DMAA)
n
-RF] and acrylic acid oligomer [RF-(ACA)
n
-RF]/silica nanocomposites-encapsulated hibitane were obtained under similar conditions. Dynamic light scattering measurements
showed that the size of these fluorinated nanocomposites-encapsulated biocides thus obtained is nanometer size-controlled.
Additionally, these fluorinated nanocomposites were shown to have a good dispersibility and stability in methanol and water.
Of particular interest, these fluorinated nanocomposites-encapsulated biocides were found to have a good antibacterial activity
against Staphylococcus aureus, and these nanocomposites were applied to the surface modification of traditional organic polymers such as poly(methyl methacrylate). 相似文献
86.
87.
Saeed Kazemi Najafi Alireza Abbasi Marasht Ghanbar Ebrahimi 《Journal of Materials Science》2007,42(3):789-793
Ultrasonic wave velocities were determined at parallel and perpendicular to manufacturing direction and at the interval angles
of 15° in clockwise and counterclockwise directions of particleboard and fiberboard. The experimental results were compared
with the predicted values using some empirical formulae such as Hankinson and Jacoby equations. The results showed that the
ultrasonic wave velocity were the highest in parallel direction in particleboard and fiberboard and decreases with increase
of angle and the lowest values occurred in perpendicular direction. The predicted ultrasonic velocity using Hankinson and
Jacoby equations are in close agreement with the measured values. Relationship between ultrasonic wave velocities and particles
and fibers angle could be successfully presented by cubic and quadratic regression equations as well. 相似文献
88.
89.
90.
Mamiko Hori Cécile Pagnoux Jean-François Baumard Masayuki Nogami 《Journal of Materials Science》2007,42(1):80-86
A new method is proposed to produce gold nanoparticles (GNP) by in situ reduction of a gold salt dissolved in water. The reducing
agent used is Tiron instead of the citrate anion most often mentioned in literature. The influence of various parameters has
been investigated, such as the content of Tiron with respect to that of the precursor of gold HAuCl4, or the initial pH of the solution after mixing of reactants. It is shown that Tiron also exerts a positive influence as
a dispersant, which impedes agglomeration of gold nanoparticles. The typical average size of GNP synthesized in the present
work is close to 7 nm. 相似文献