全文获取类型
收费全文 | 422364篇 |
免费 | 14269篇 |
国内免费 | 6721篇 |
专业分类
电工技术 | 13426篇 |
技术理论 | 9篇 |
综合类 | 8938篇 |
化学工业 | 62948篇 |
金属工艺 | 23457篇 |
机械仪表 | 20285篇 |
建筑科学 | 15755篇 |
矿业工程 | 5776篇 |
能源动力 | 9268篇 |
轻工业 | 27471篇 |
水利工程 | 6239篇 |
石油天然气 | 14090篇 |
武器工业 | 1057篇 |
无线电 | 45845篇 |
一般工业技术 | 81283篇 |
冶金工业 | 52042篇 |
原子能技术 | 10003篇 |
自动化技术 | 45462篇 |
出版年
2023年 | 2709篇 |
2022年 | 5493篇 |
2021年 | 7704篇 |
2020年 | 5753篇 |
2019年 | 5476篇 |
2018年 | 14849篇 |
2017年 | 15763篇 |
2016年 | 11885篇 |
2015年 | 7794篇 |
2014年 | 10268篇 |
2013年 | 17586篇 |
2012年 | 16644篇 |
2011年 | 24083篇 |
2010年 | 20944篇 |
2009年 | 20445篇 |
2008年 | 20335篇 |
2007年 | 21633篇 |
2006年 | 12735篇 |
2005年 | 14338篇 |
2004年 | 11335篇 |
2003年 | 10911篇 |
2002年 | 9742篇 |
2001年 | 8914篇 |
2000年 | 8304篇 |
1999年 | 7958篇 |
1998年 | 13871篇 |
1997年 | 10222篇 |
1996年 | 8315篇 |
1995年 | 6340篇 |
1994年 | 5687篇 |
1993年 | 5247篇 |
1992年 | 4352篇 |
1991年 | 4066篇 |
1990年 | 3831篇 |
1989年 | 3815篇 |
1988年 | 3612篇 |
1987年 | 3137篇 |
1986年 | 2949篇 |
1985年 | 3316篇 |
1984年 | 3087篇 |
1983年 | 2873篇 |
1982年 | 2645篇 |
1981年 | 2768篇 |
1980年 | 2565篇 |
1979年 | 2732篇 |
1978年 | 2755篇 |
1977年 | 2982篇 |
1976年 | 3819篇 |
1975年 | 2417篇 |
1973年 | 2378篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
3.
Over tensile stress ranges giving creep lives up to 2000 hours at 373 to 463 K, the creep and creep fracture properties of
7010 are compared with results recorded for 7075 and other precipitation-hardened aluminum alloys. Using the ϕ methodology
to quantify the systematic variations in creep curve shape with changing test conditions, the behavior patterns displayed
by the different alloys are shown to depend on the extent to which precipitate coarsening causes a progressive loss of creep
strength with increasing test duration and temperature. The ϕ relationships also introduce new approaches for rationalization
and interpretation of creep data sets, based on the activation energy for lattice diffusion in the alloy matrices and the
yield stress or UTS at the creep temperatures. 相似文献
4.
P. B. Lovyrev A. I. Lavrov V. A. Babkin A. N. Aminov S. M. Melekhin Yu. P. Kazantsev P. M. Korol’kov 《Metallurgist》2006,50(3-4):152-157
Specifications require that all the welds in 12-m-diam. decomposers with a capacity of 3600 m3 be subjected to high-temperature tempering before going into service in order to alleviate the stresses from the welding
operation. Specialists at the organizations VNIIPTkhimnefteapparatury and VNIImontazhspetsstroi have proposed out-of-furnace
volumetric (complete) of the assembled decomposer with the use of special heaters. The use of this heating method has shortened
assembly operations while providing the welds with a highquality heat treatment and reducing the stresses overall (including
welding stresses, stresses from assembly of the decomposer, etc.) The technology ensures uniform heating of the housing of
the decomposer and provides for close control over the process. The experience gained in heat-treating decomposers can also
be used in the construction of other containers that come into contact with corrosive media.
__________
Translated from Metallurg, No. 3, pp. 61–64, March, 2006. 相似文献
5.
B. Schönfelder G. Gottstein L. S. Shvindlerman 《Metallurgical and Materials Transactions A》2006,37(6):1757-1771
While the motion of twist boundaries can be readily studied by atomistic simulations with molecular dynamics (MD) under the
action of an elastic driving force, the approach fails for tilt boundaries. This is due to the interaction of the elastic
stress with the grain boundary (GB) structure, which causes plastic strain by GB sliding. A novel concept, the orientation
correlated driving force, is introduced to circumvent this problem. It is shown that this concept can be successfully applied
to the study of the migration of tilt boundaries. The migration behavior of several twist and tilt GBs was investigated. The
transition from low-to high-angle boundaries can be captured, and a structural transition of tilt boundaries was found at
high temperatures, which also affected the migration behavior. The results compare well with experimental results of the motion
high-angle boundaries, but for low-angle boundaries, the agreement is poor.
This article is based on a presentation made in the “Hillert Symposium on Thermodynamics & Kinetics of Migrating Interfaces
in Steels and Other Complex Alloys,” December 2–3, 2004, organized by The Royal Institute of Technology in Stockholm, Sweden. 相似文献
6.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献
7.
N. I. Nikolaikin E. Yu. Barzilovich N. E. Nikolaikina 《Chemical and Petroleum Engineering》2006,42(5-6):332-338
The paper discusses optimal control of ecosystem state for observation of a generalized monotonically varying random parameter.
A model is proposed for the controlled vector random process, whose components are assigned acceptable ranges and the observations
are performed discretely.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 40–44, June, 2006. 相似文献
8.
9.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content
of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen
content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient,
the duration of the degassing operation, and the vacuum used in the treatment.
__________
Translated from Metallurg, No. 7, pp. 68–69, July, 2006. 相似文献
10.
Experimental studies of the bond response of three-wire strands and some influencing parameters 总被引:5,自引:0,他引:5
R. Gustavson 《Materials and Structures》2004,37(2):96-106
The bond behavior of prestressing strands is of great importance for the capacity of precast prestressed concrete structures. In the present study, the bond behavior of three-wire strands, and some influencing parameters, were examined by means of steel encased pull-through and push-in tests. The three mechanisms: adhesion, friction and other mechanical actions were found to be present at the strand-concrete interface at different slip values. The results from the experiments showed that the micro roughness of the strand surface strongly affected the initial bond response of the strand, that is the adhesion in the interface. The maximum bond capacity of indented three-wire strands was found to be directly connected to the geometric properties of the strand indents. The influence of the concrete strength on the bond capacity of the strand was hard to interpret. However, the density of the concrete matrix was found to be a better parameter for determine the influence of the concrete rather than the compressive strength. 相似文献