全文获取类型
收费全文 | 785199篇 |
免费 | 11181篇 |
国内免费 | 3415篇 |
专业分类
电工技术 | 14381篇 |
技术理论 | 5篇 |
综合类 | 3943篇 |
化学工业 | 118441篇 |
金属工艺 | 31897篇 |
机械仪表 | 23463篇 |
建筑科学 | 19624篇 |
矿业工程 | 4172篇 |
能源动力 | 19434篇 |
轻工业 | 66672篇 |
水利工程 | 8403篇 |
石油天然气 | 13770篇 |
武器工业 | 280篇 |
无线电 | 87468篇 |
一般工业技术 | 149688篇 |
冶金工业 | 140796篇 |
原子能技术 | 14275篇 |
自动化技术 | 83083篇 |
出版年
2021年 | 6688篇 |
2020年 | 4768篇 |
2019年 | 6005篇 |
2018年 | 23270篇 |
2017年 | 22018篇 |
2016年 | 19623篇 |
2015年 | 8128篇 |
2014年 | 12453篇 |
2013年 | 32576篇 |
2012年 | 22705篇 |
2011年 | 35753篇 |
2010年 | 28946篇 |
2009年 | 28610篇 |
2008年 | 30755篇 |
2007年 | 31422篇 |
2006年 | 21536篇 |
2005年 | 20296篇 |
2004年 | 19007篇 |
2003年 | 18563篇 |
2002年 | 17442篇 |
2001年 | 17130篇 |
2000年 | 16021篇 |
1999年 | 16654篇 |
1998年 | 41786篇 |
1997年 | 29626篇 |
1996年 | 22585篇 |
1995年 | 16895篇 |
1994年 | 14937篇 |
1993年 | 14577篇 |
1992年 | 10716篇 |
1991年 | 10079篇 |
1990年 | 9958篇 |
1989年 | 9738篇 |
1988年 | 9047篇 |
1987年 | 7961篇 |
1986年 | 7902篇 |
1985年 | 8789篇 |
1984年 | 8346篇 |
1983年 | 7446篇 |
1982年 | 6925篇 |
1981年 | 7150篇 |
1980年 | 6678篇 |
1979年 | 6709篇 |
1978年 | 6433篇 |
1977年 | 7456篇 |
1976年 | 9867篇 |
1975年 | 5681篇 |
1974年 | 5284篇 |
1973年 | 5440篇 |
1972年 | 4466篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
Theoretical and experimetal methods have been developed to characterize the effect of mechanical loading on the mesoscopic
and macroscopic mechanical state of polycrystalline materials. Ferritic and austenitic single-phase materials were first analyzed,
then phase interaction was studied in a multiductile phase material (austeno-ferritic duplex steel) and a natural reinforced
composite (pearlitic steel). The theoretical method is based on the self-consistent approach in which elastic and plastic
characteristics of the phases have been applied through the micromechanical behavior of single-crystal-using slip systems
and microscopic hardening. The effects of a crystallographic texture and phase interaction during loading and after unloading
were studied. The elastic and plastic anisotropy of the grains having the same crystallographic orientation were assessed
by diffraction strain analysis. The simulation was compared with the experiments performed using the X-ray diffraction technique.
In the considered duplex and pearlitic steels, it was observed that the ferrite stress state is much lower than the austenite
and cementite ones. The results of diffraction strain distribution have showed the pertinence of the models and give valuable
information, for example, for the yield stress and the hardening parameters of each phase in a two-phase material. 相似文献
992.
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
993.
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
994.
995.
I. M. Martynenko 《Journal of Engineering Physics and Thermophysics》2007,80(2):420-424
We have derived a Fredholm-type equation of the second kind for a directional derivative problem arising in the stationary
theory of heat conduction. One result of Ya. B. Lopatinskii has been refined.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 197–200, March–April, 2007. 相似文献
996.
Across 2 experiments, a new experimental procedure was used to investigate attentional capture by animal fear-relevant stimuli. In Experiment 1 (N = 34), unselected participants were slower to detect a neutral target animal in the presence of a spider than a cockroach distractor and in the presence of a snake than a large lizard distractor. This result confirms that phylogenetically fear-relevant animals capture attention specifically and to a larger extent than do non-fear-relevant animals. In Experiment 2 (N = 86), detection of a neutral target animal was slowed more in the presence of a feared fear-relevant distractor (e.g., a snake for snake-fearful participants) than in presence of a not-feared fear-relevant distractor (e.g., a spider for snake-fearful participants). These results indicate preferential attentional capture that is specific to phylogenetically fear-relevant stimuli and is selectively enhanced in individuals who fear these animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
M. Jayasankar 《Materials Letters》2007,61(3):790-793
Formation of aluminium titanate (AT) has been achieved at low temperature through sol-gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2-3 μm. 相似文献
998.
M. Meschke J. P. Pekola F. Gay R. E. Rapp H. Godfrin 《Journal of Low Temperature Physics》2004,134(5-6):1119-1143
We describe a systematic series of experiments on thermalization of electrons in lithographic metallic thin films at millikelvin temperatures using Coulomb blockade thermometry (CBT). Joule dissipation due to biasing of the CBT sensor tends to drive the electron system into non-equilibrium. Under all experimental conditions tested, the electron-electron relaxation is fast enough to ensure thermal electron distribution, which is also in agreement with the theoretical arguments we present. On the other hand, poor electron-phonon relaxation plays a dominant role in lifting the electron temperature above that of the bath. From a comparison of the results with the theoretical current-voltage characteristics of the thermometers we precisely determine the electron-phonon coupling constant for the common metals used. Our experiments show that it is a formidable task to attain thermal equilibrium with the bath using single-electron devices under non-zero bias conditions at 20–50 mK temperatures that are typically encountered in experiments. The conclusion concerning Coulomb blockade thermometry is more optimistic and two-fold: (1) One can now correct the errors due to bias heating in a satisfactory manner based on known material properties and the size of the metal films in the sensor. (2) Reliable thermometry down to 20 mK requires islands whose volumes are >10?15 m3, which is still acceptable both from the parameter (capacitance) and fabrication points of view. 相似文献
999.
As in other structurally disordered solids, the low temperature acoustic properties of poly-crystalline aluminium are governed by atomic two-level tunneling systems. The particular temperature variation of sound velocity and internal friction depends on the dynamical behaviour of these tunneling systems, which is expected to be determined by interaction with thermal phonons and conduction electrons as in metallic glasses. In earlier measurements on aluminium-wires no significant difference was found whether the sample was superconducting or kept in the normal state by a sufficiently high magnetic field and the concluding claim was ‘absence of electron-assisted relaxation for tunneling systems in poly-crystalline metals’. In this report, vibrating reed measurements are presented of pure poly-crystalline Al with a special sample shape that reduces the influence of the clamping. We in fact find significant differences between the sample being normal conducting or superconducting. The overall behaviour indeed resembles very closely that of metallic glasses and clearly demonstrates that also in Al tunneling systems couple to conduction electrons as expected. As a quantitative result we may state that the density of states of tunneling systems in poly-crystalline Al is considerably smaller than in metallic glasses. PACS numbers: 61.43.-j, 62.65.+k, 63.50.+x 相似文献
1000.