全文获取类型
收费全文 | 1942篇 |
免费 | 34篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 288篇 |
金属工艺 | 49篇 |
机械仪表 | 62篇 |
建筑科学 | 63篇 |
矿业工程 | 5篇 |
能源动力 | 55篇 |
轻工业 | 127篇 |
水利工程 | 6篇 |
石油天然气 | 15篇 |
无线电 | 205篇 |
一般工业技术 | 312篇 |
冶金工业 | 550篇 |
原子能技术 | 13篇 |
自动化技术 | 212篇 |
出版年
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 9篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 103篇 |
2012年 | 32篇 |
2011年 | 71篇 |
2010年 | 49篇 |
2009年 | 45篇 |
2008年 | 54篇 |
2007年 | 53篇 |
2006年 | 58篇 |
2005年 | 58篇 |
2004年 | 50篇 |
2003年 | 44篇 |
2002年 | 38篇 |
2001年 | 45篇 |
2000年 | 45篇 |
1999年 | 44篇 |
1998年 | 162篇 |
1997年 | 109篇 |
1996年 | 74篇 |
1995年 | 57篇 |
1994年 | 61篇 |
1993年 | 68篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 12篇 |
排序方式: 共有1979条查询结果,搜索用时 420 毫秒
21.
Sample J.T. Ladner R. Shulman L. Ioup E. Petry F. Warner E. Shaw K. McCreedy F.P. 《Internet Computing, IEEE》2006,10(5):53-60
Using Web services, the authors have been able to increase the amount of data accessible through the Naval Research Laboratorys Geospatial Information Database (GIDB) portal. They created a Web crawler for Web Mapping Services (WMS) that harvests and adds data to the portal index and a translator that provides access to non-WMS data through the WMS interface. The Integrated Web Services Broker, using traditional Web services standards, provides automated access to meteorological and oceanographic data. 相似文献
22.
23.
Mechanical activation before carbothermic reduction can substantially enhance the formation of SiC from SiO2 and carbon mixtures. However, the morphology (e.g., particles or whiskers) of SiC formed from mechanically activated SiO2 and carbon mixtures is dependent of the degree of mechanical activation and the condition of the subsequent carbothermic reduction. These phenomena are investigated and rationalized based on the increased reactivity of the reactants and SiC formation mechanisms. 相似文献
24.
We demonstrate an erbium-doped fiber amplifier (EDFA) source for the fiber gyroscope with an overall mean wavelength stability of four parts per million. This source, which amplifies the gyroscope signal before detection, is shown to be more stable than a similar single-pass source in a standard configuration. The effects of varying the fiber temperature, pump power, pump wavelength, gyroscope feedback power and signal polarization state on the output mean wavelength are individually explored. Experimental results are in excellent agreement with simulations 相似文献
25.
NC Day PJ Shaw AL McCormack PJ Craig W Smith R Beattie TL Williams SB Ellis PG Ince MM Harpold D Lodge SG Volsen 《Canadian Metallurgical Quarterly》1996,71(4):1013-1024
The distribution of voltage-dependent calcium channel subunits in the central nervous system may provide information about the function of these channels. The present study examined the distribution of three alpha-1 subunits, alpha 1A, alpha 1B and alpha 1E, in the normal human hippocampal formation and parahippocampal gyrus using the techniques of in situ hybridization and immunocytochemistry. All three subunit mRNAs appeared to be similarly localized, with high levels of expression in the dentate granule and CA pyramidal layer. At the protein level, alpha 1A, alpha 1B and alpha 1E subunits were differentially localized. In general, alpha 1A-immunoreactivity was most intense in cell bodies and dendritic processes, including dentate granule cells, CA3 pyramidal cells and entorhinal cortex pre-alpha and pri-alpha cells. The alpha 1B antibody exhibited relatively weak staining of cell bodies but stronger staining of neuropil, especially in certain regions of high synaptic density such as the polymorphic layer of the dentate gyrus and the stratum lucidum and radiatum of the CA regions. The alpha 1E staining pattern shared features in common with both alpha 1A and alpha 1B, with strong immunoreactivity in dentate granule, CA3 pyramidal and entorhinal cortex pri-alpha cells, as well as staining of the CA3 stratum lucidum. These findings suggest regions in which particular subunits may be involved in synaptic communication. For example, comparison of alpha 1B and alpha 1E staining in the CA3 stratum lucidum with calbindin-immuno-reactivity suggested that these two calcium channels subunits may be localized presynaptically in mossy fibre terminals and therefore may be involved in neurotransmitter release from these terminals. 相似文献
26.
Pasricha S. Keppler M. Shaw S.R. Nehrir M.H. 《Energy Conversion, IEEE Transaction on》2007,22(3):746-754
Six steady-state fuel cell electrical terminal models are compared using experimental data from an Avista Laboratories SR-12 500 W proton exchange membrane (PEM) fuel cell. The paper begins by reviewing the physical effects in a fuel cell. The proposed electrical terminal models are introduced in terms of these physical effects, parameterized for identification and compared using the measured data. 相似文献
27.
28.
AU Teuscher M Lerch S Shaw G Pacini P Ferrari P Weidmann 《Canadian Metallurgical Quarterly》1998,16(9):1279-1284
OBJECTIVES: Elevated plasma endothelin (ET)-1 levels have been described in insulin-resistant states such as syndrome X, obesity, non-insulin-dependent diabetes mellitus, and in some studies in essential hypertension. To investigate whether increases in circulating ET-1 to levels observed in insulin-resistant states can modulate insulin levels and/or insulin sensitivity in humans, we assessed these variables during low, non-pressor-dose ET-1 compared with placebo infusion. DESIGN: In a randomized, single blind, crossover design, 10 lean normotensive male subjects received either an intravenous infusion of subpressor doses of ET-1 dissolved in polygeline or a control infusion of polygeline only (placebo). Using dynamic assessment by the minimal model approach with the modified frequent sampling intravenous glucose tolerance test (FSIGT) the following and other parameters were measured: insulin sensitivity; acute insulin response to glucose (AIR(G)) calculated as the average of the three peak values between 2 and 5 min after injection of glucose from which the basal insulin levels were subtracted; the initial area under the curve (AUC(1-19)) from insulin values between time 0 and 19 min and the first-phase insulin secretion (phi1) from insulin kinetics parameters. RESULTS: ET-1 infusion reduced AIR(G) (to 34.85 +/- 4.27 compared with 49.3 +/- 6.9 microU/ml during placebo, P=0.017) and the acute C-peptide response to glucose (to 2.33 +/- 0.41 compared with 3.1 +/- 0.44 ng/ml, P=0.018), decreased plasma insulin levels during the FSIGT compared with placebo (analysis of variance P<0.0001) and decreased the AUC(1-19) (to 2.1 +/- 0.2 compared with 2.9 +/- 0.3 U/l per 20 min, P<0.01) while phi1 tended to be lower. S1 measured during ET-1 infusion was unaltered (11.11 +/- 1.91 x 10(-4) versus 10.88 +/- 2.11 10(-4)/min per mU per l, NS). CONCLUSIONS: These findings demonstrate that an increase in circulating ET-1 to levels observed in insulin-resistant states acutely diminishes the insulin secretory response but does not significantly modify insulin sensitivity. 相似文献
29.
Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. 7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. 14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content. 相似文献
30.
Parallel electrocorticograms (ECoG) and electroencephalograms (EEG) were recorded during stun-recovery and stun-slaughter of eight calves 4-6 weeks old. Epochs of 8·2 s duration, derived from the ECoG and EEG signals pre-stun, during recovery and during exsanguination, were compared for differences in power content and frequency distribution using Fast Fourier Transform analysis. ECoG signals recorded during the quiescent phase post-stun had a markedly lower power content compared with pre-stun, whereas the EEG signal showed no such reduction in power content. During exsanguination, the mean rate of decline in the ECoG power content was 0·025 log units/s, three times faster than the mean rate of decline of the EEG at 0·008 log units/s. The duration of the electroplectic fit post-stun was detected equally well by the two techniques. The differences between EEG and ECoG traces in this study are thought to arise from differences in the signal-noise ratio of the two techniques and by artefacts in the EEG signal, caused by microscopic movement between EEG electrodes and the surrounding tissue. The slower rate of decline in the power content of the EEG during slaughter means that the time to onset of isoelectric cortical electrical activity will be longer if determined by EEG measurements than by ECoG recording. 相似文献