全文获取类型
收费全文 | 540333篇 |
免费 | 7619篇 |
国内免费 | 1857篇 |
专业分类
电工技术 | 10156篇 |
综合类 | 503篇 |
化学工业 | 82762篇 |
金属工艺 | 21140篇 |
机械仪表 | 17590篇 |
建筑科学 | 12479篇 |
矿业工程 | 2525篇 |
能源动力 | 14717篇 |
轻工业 | 45533篇 |
水利工程 | 5301篇 |
石油天然气 | 8478篇 |
武器工业 | 24篇 |
无线电 | 65212篇 |
一般工业技术 | 107489篇 |
冶金工业 | 98851篇 |
原子能技术 | 11035篇 |
自动化技术 | 46014篇 |
出版年
2021年 | 4840篇 |
2020年 | 3705篇 |
2019年 | 4813篇 |
2018年 | 7964篇 |
2017年 | 7957篇 |
2016年 | 8514篇 |
2015年 | 5647篇 |
2014年 | 9126篇 |
2013年 | 26415篇 |
2012年 | 14716篇 |
2011年 | 19500篇 |
2010年 | 15513篇 |
2009年 | 17451篇 |
2008年 | 18107篇 |
2007年 | 18066篇 |
2006年 | 16045篇 |
2005年 | 14479篇 |
2004年 | 13834篇 |
2003年 | 13615篇 |
2002年 | 13049篇 |
2001年 | 12845篇 |
2000年 | 12105篇 |
1999年 | 12570篇 |
1998年 | 30732篇 |
1997年 | 21567篇 |
1996年 | 16853篇 |
1995年 | 12714篇 |
1994年 | 11240篇 |
1993年 | 11183篇 |
1992年 | 8353篇 |
1991年 | 7902篇 |
1990年 | 7859篇 |
1989年 | 7553篇 |
1988年 | 7122篇 |
1987年 | 6321篇 |
1986年 | 6185篇 |
1985年 | 7046篇 |
1984年 | 6502篇 |
1983年 | 5969篇 |
1982年 | 5509篇 |
1981年 | 5517篇 |
1980年 | 5106篇 |
1979年 | 4991篇 |
1978年 | 4900篇 |
1977年 | 5680篇 |
1976年 | 7340篇 |
1975年 | 4274篇 |
1974年 | 3952篇 |
1973年 | 4066篇 |
1972年 | 3381篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
T. Connolley M. J. Starink P. A. S. Reed 《Metallurgical and Materials Transactions A》2004,35(3):771-783
Notches were machined in specimens of INCONEL 718 by a broaching process, where differing broaching runs led to differing
extents of subsurface deformation and surface roughness. Fatigue tests were carried out at 600 °C with a trapezoidal loading
waveform at 0.25 Hz. The broaching process that led to the more severe subsurface deformation (but lower surface roughness)
showed the worst fatigue performance. Analysis of total strain amplitude in the notch root with the aid of an elastoplastic
finite-element (FE) model showed that the work hardening related to the subsurface deformation caused by the different broaching
can account for the difference in fatigue lives. Differences in initiation and growth behavior were seen for the two broached
finishes as well as for broached and subsequently polished samples. These differences are discussed in terms of a change in
crack growth initiation and growth mechanisms due to the presence of the work-hardened layer. 相似文献
982.
Cyclic oxidation response of multiphase niobium-based alloys 总被引:4,自引:0,他引:4
Kwai S. Chan 《Metallurgical and Materials Transactions A》2004,35(2):589-597
Cyclic oxidation tests were performed on multiphase Nb-based alloys containing silicide, Laves, and Nb solid solution phases.
In particular, the oxidation resistance of six alloys with various compositions (Nb, Ti, Hf, Cr, Ge, and Si) and microstructures
was characterized by thermal cycling from ambient temperature to a peak temperature that ranges from 900 °C to 1400 °C. Weight
change data were obtained and the corresponding spalled oxides were collected and identified by X-ray diffraction. The results
indicated that Nb-based alloys formed a mixture of CrNbO4, Nb2O5, and Nb2O5 · TiO2, with possibly small amounts of SiO2 or GeO2. The oxidation resistance was improved when CrNbO4 formed instead of Nb2O5 and Nb2O5 · TiO2. These results were used to assess the influence of microstructure and composition on the oxidation resistance of multiphase
Nb-based alloys. 相似文献
983.
Today's mobile communications market is very competitive, with wireless service providers making every effort to improve the performance of their network to retain subscribers. Coupled with the proliferation of radio-frequency signals in the environment due to the growth of all forms of wireless communication, this leads to a very challenging task - namely, to provide ubiquitous high-quality service in spite of ever-increasing interference levels. One of the tools at the disposal of the network operator to provide such service is a cryogenically cooled receiver front end for base stations, wherein each receive path consists of a high-temperature superconducting (HTS) bandpass filter followed by a cryogenically cooled low-noise amplifier. There are two primary benefits achieved by the use of this front end. The first is improved receiver sensitivity through the reduction of electrical noise generated by the front end itself. The second is the significant reduction in the effects of out-of-band interference through the highly selective filtering made possible by the use of HTS materials. While this paper addresses both receiver-sensitivity and filter-selectivity benefits, the focus is on improved out-of-band interference rejection through enhanced filter selectivity. 相似文献
984.
985.
986.
Outgassing from stainless steel and the effects of the gauges 总被引:1,自引:0,他引:1
The true outgassing from surfaces is often masked by the production of gases and pumping within the measuring gauge. Quadrupole mass analysers have been used to measure the outgassing from carefully prepared samples of stainless steel. By using an isolation pressure rise technique coupled to non-evaporable getter pumping, the problem of production of methane by the gauge is overcome and it has been possible to measure the outgassing of methane to very low levels. The specific outgassing rate of methane from 316 L stainless steel is found to be ?5×10−22 mbar l s−1 cm−2. The outgassing of the other gases has been measured using several gauges. The specific outgassing of hydrogen is found to be 4.5×10−15 mbar l s−1 cm−2 and the total of all other gasses amounted to no more than 10% of this figure. Although the measurements of the other gases are more ambiguous than those for methane, it is concluded that, in all probability, only hydrogen is outgassed from stainless steel. 相似文献
987.
Recently, there has been much interest in wide band-gap wurtzite semiconductors such as group-III nitrides (GaN, AlGaN, and InGaN) and ZnO. Ion-beam-defect processes are considerably more complex in these wurtzite semiconductors than in the case of both elemental and group-III-V cubic semiconductors. This brief review focuses on our recent studies of the following aspects of ion-beam-defect processes: (i) effects of implanted species and the density of collision cascades, (ii) the nature of ion-beam-produced planar defects in GaN, (iii) defect production in GaN by swift heavy ions, (iv) blistering of H-implanted GaN, (v) electrical isolation of GaN and ZnO, (vi) the effect of Al and In content on defect processes in III-nitrides, and (vii) structural damage in ZnO with an intriguing effect of the formation of an anomalous defect peak. Emphasis is given to unusual ion-beam-defect processes and to the physical mechanisms underlying them. 相似文献
988.
In the present study a continuum model for one-dimensional plane Couette-Poiseuille flow is implemented to turbomolecular pumps in different flow regimes. Pumping performance of various turbomolecular pumps including 6 single rotors, a rotor-stator row, a rotor-stator-rotor row, and a multi-row with 13 alternative rotor-stator rows is considered here. The obtained results show that the model provides good quantitative values for pumping performance of turbomolecular pumps over the whole regimes ranging from molecular flow to transition to slip flow. 相似文献
989.
We have fabricated and tested a high-Tc dc-SQUID magnetometer patterned on a YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77 K showed that the magnetometer has a white noise of 333 fT/Hz1/2 without superconducting shield, corresponding to a flux sensitivity of 14.5 μΦ0/Hz1/2. We constructed a test system for eddy current non-destructive evaluation of conducting aluminum plates by using the magnetometer. Flaws over 10 mm below the surface can be clearly identified. By mapping the magnetic field distribution, we can locate the flaw position. The signals caused by flaw were expanded due to the use of double-D type driving coil with a wider central slit. The experimental results confirmed that this test system could operate in a magnetic unshielded environment. 相似文献
990.
ZnS, ZnSe, and CdTe polycrystals are experimentally investigated. Mechanisms are treated which restrict the thermal conductivity in samples prepared by recrystallization pressing and by deposition from the vapor phase and subjected to additional strain. Anomalies are observed on the temperature dependences of the thermal resistance of investigated samples, which are due to the special features of their phonon spectra and to the variation of the contribution made by longitudinal and transverse phonon branches to the heat transfer in the Debye temperature region and higher. 相似文献