全文获取类型
收费全文 | 84530篇 |
免费 | 1414篇 |
国内免费 | 700篇 |
专业分类
电工技术 | 1552篇 |
综合类 | 75篇 |
化学工业 | 13420篇 |
金属工艺 | 3717篇 |
机械仪表 | 2811篇 |
建筑科学 | 2042篇 |
矿业工程 | 550篇 |
能源动力 | 2120篇 |
轻工业 | 7787篇 |
水利工程 | 967篇 |
石油天然气 | 2328篇 |
武器工业 | 41篇 |
无线电 | 7720篇 |
一般工业技术 | 18459篇 |
冶金工业 | 13685篇 |
原子能技术 | 2668篇 |
自动化技术 | 6702篇 |
出版年
2022年 | 732篇 |
2021年 | 1152篇 |
2020年 | 888篇 |
2019年 | 1010篇 |
2018年 | 1850篇 |
2017年 | 1815篇 |
2016年 | 2073篇 |
2015年 | 1181篇 |
2014年 | 1936篇 |
2013年 | 4220篇 |
2012年 | 2875篇 |
2011年 | 3534篇 |
2010年 | 2892篇 |
2009年 | 3143篇 |
2008年 | 3158篇 |
2007年 | 3048篇 |
2006年 | 2598篇 |
2005年 | 2264篇 |
2004年 | 2137篇 |
2003年 | 2061篇 |
2002年 | 1960篇 |
2001年 | 1817篇 |
2000年 | 1798篇 |
1999年 | 1691篇 |
1998年 | 3807篇 |
1997年 | 2732篇 |
1996年 | 2030篇 |
1995年 | 1630篇 |
1994年 | 1424篇 |
1993年 | 1417篇 |
1992年 | 1075篇 |
1991年 | 1101篇 |
1990年 | 1118篇 |
1989年 | 1115篇 |
1988年 | 1000篇 |
1987年 | 931篇 |
1986年 | 919篇 |
1985年 | 994篇 |
1984年 | 831篇 |
1983年 | 817篇 |
1982年 | 722篇 |
1981年 | 730篇 |
1980年 | 697篇 |
1979年 | 673篇 |
1978年 | 647篇 |
1977年 | 799篇 |
1976年 | 962篇 |
1975年 | 610篇 |
1974年 | 573篇 |
1973年 | 561篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
J Hamamoto H Kohrogi O Kawano H Iwagoe K Fujii N Hirata M Ando 《Canadian Metallurgical Quarterly》1997,82(3):738-745
To investigate whether tachykinins are released in the airways in response to stimulation of the esophagus, we studied the airway plasma extravasation induced by intraesophageal HCl in the presence or absence of neutral endopeptidase inhibitor phosphoramidon and NK1-receptor antagonist FK-888 in anesthetized guinea pigs. The airway plasma leakage was evaluated by measuring extravasated Evans blue dye in the animals pretreated with propranolol and atropine. Infusion of 1 N HCl into the esophagus significantly increased plasma extravasation in the trachea. Phosphoramidon significantly potentiated plasma extravasation in the trachea and main bronchi, whereas FK-888 significantly inhibited that extravasation in a dose-related manner. In the capsaicin-treated animals, airway plasma extravasation was completely inhibited even in the presence of phosphoramidon. Tracheal plasma extravasation potentiated by phosphoramidon was significantly inhibited in the bilateral vagotomized animals. These results suggest that 1) tachykinin-like substances are released to cause plasma extravasation in the airways as a result of intraesophageal HCl stimulation and 2) there are neural pathways communicating between the esophagus and airways, including the vagus nerve. 相似文献
992.
We extend a dynamic approach of behavior generation to the representation of spatial information. Two levels of dynamics integrate dead-reckoning, dominant far from home bases, and piloting, dominant near home bases. When the view-based piloting system recognizes a home base, visual place information recalibrates the dead-reckoning system, inverting the hierarchical ordering of the two dynamic levels by time scale inversion. Reference views taken at discrete home bases are recognized invariantly under rotation of views. This process yields compass information. Continuous translational information is obtained as a neural place representation built from view correlations with a scattered set of local views. This self-calibrating cognitive map couples into a dynamics of heading direction integrating the behaviors of obstacle avoidance and target acquisition. Targets can be designated in terms of the cognitive map. We demonstrate the dynamical model in simulation. 相似文献
993.
Contact deposition of gold by a magnesium powder in a hydrodynamic mode in 0.001–0.005 M solutions of the system [Au(CN)2]?-CN? is investigated. It is found that the cementation rate of gold (V c ) is directly proportional tot he concentration of the [Au(CN)2]? complex and the area of the cementing agent. As the temperature is increased in the ranges 20–30 and 30–40°C, the increase in V c is 20–25 and 8–10%, respectively. The time dependence of degree of gold extraction on magnesium has an extreme character due to the increasing rate of the inverse process of leaching. In an ultrasonic field, the cementation rate and degree of gold extraction increase. This phenomenon is conditioned by destruction of the hydroxide film on the magnesium surface. The deposited gold has a film nature. 相似文献
994.
The structure and phase composition of the samples of foam aluminum based on the AMg6 alloy (Al-6%Mg-0.7%Mn) obtained in a high-energy planetary mill are investigated. Mechanical doping provides high dispersity and homogeneity of all structural components including particles of the foam agent TiH2, which allows one to obtain foam aluminum with a pore size of 1–5 mm at a density of 1.20–0.80 g/cm3. Mechanical properties of foam aluminum were estimated based on the results of compression tests. Based on preliminary investigations, an imitation model of foam formation is suggested that well describes the process of foam formation. 相似文献
995.
O. V. Anfalova A. I. Vorob’ev V. S. Kraev M. A. Chemerkin L. I. Osokin 《Atomic Energy》2006,100(6):389-393
The construction and basic technical characteristics of the TUK-84 assembly are described. The materials used to fabricate
the vessel parts and sealing components are presented, and the composition and operation of the system which monitors the
technical parameters are described. The construction of the rolled layers (courses) is discussed and their advantages are
shown.
__________
Translated from Atomnaya énergiya,Vol. 100, No. 6, pp. 419–422, June, 2006. 相似文献
996.
O. V. Konstantinova A. V. Kuz’mov V. V. Skorokhod M. B. Shtern 《Powder Metallurgy and Metal Ceramics》2007,46(1-2):25-31
A theoretical method for determining the percolation limit and effective conductivity of composites based on polydisperse
mixtures of insulator and conductor powders is proposed. The effect of the particle size ratio between the insulator and conductor
on the percolation limit and effective conductivity is studied. Numerical simulation of the microstructure, effective properties,
and percolation limit in composites is discussed.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 31–40, 2007. 相似文献
997.
S. O. Katrych V. M. Petyukh A. A. Bondar W. Steurer 《Powder Metallurgy and Metal Ceramics》2007,46(7-8):357-364
For alloys in the range Os-OsAl2-IrAl2.7-Ir, as-cast and annealed at 1400 °C (Os-OsAl-IrAl-Ir) and 1250°C (OsAl-OsAl2-IrAl2.7-IrAl), phase equilibria are studied by powder x-ray diffraction (PXRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). Between isostructural aluminides OsAl and IrAl there exists a continuous solid solution (Os,Ir)Al. Other unary and binary phases form terminal solid solutions: (Os), (Ir), (OsAl2), and (IrAl2.7). 相似文献
998.
Two-hundred and one strains classified under the (Pasteurella) haemolytica-complex isolated from cattle, sheep, deer, pigs, hares and rabbits were investigated by ribotyping. Fifty-nine of these strains were selected for further studies using multilocus enzyme electrophoresis (MEE). A correlation between the clusters identified by ribotyping and MEE was demonstrated and the results furthermore indicated that a genetic basis exists for most clusters previously outlined by the use of quantitative evaluation of phenotypic data. The taxonomic relevance of ornithine decarboxylase and fermentation of L-arabinose, D-sorbitol and glucosides for taxonomic delineation within the (P.) haemolytica-complex was supported. A taxonomic importance was further indicated for ONPG, ONPX, ONPF, meso-inositol, D-xylose, maltose, dextrine and NPG in relation to some of the taxa. Within the porcine taxon 15, however, differences in ornithine decarboxylase did not correspond to genetic clusters. Six lineages were revealed by MEE. Lineage A contained electrophoretic types (ETs) representing biogroups 1, 3A-3H, 8A and 9, indicating a genetic relationship between these groups--an observation which was supported by ribotyping. Lineage B included biogroup 8D, 3 strains from biogroup 10 and a single strain from biogroup 1 and taxon 18/biovar 1. Lineage C contained strains allocated to biogroup 6 from ruminants and the porcine taxon 15. The similarity between these two groups was accentuated by ribotyping. Lineage D and the single isolate in lineage E contained strains allocated to biogroups 7, 10, 8B and 8C, in addition to single strains from biogroups 6 and 9. The same strains were found in the heterogenous ribotype cluster 17. Lineage F contained strains representing the leprine taxon 20 and the ruminant (P.) granulomatis. Ribotyping indicated that the ruminant biogroup 3J was affiliated with both taxon 20 and (P.) granulomatis. 相似文献
999.
A class AB current-controlled grounded resistor based on a translinear loop implemented from bipolar transistors is described. Simulation results show that its value is tunable from 30 to ~100 kΩ with frequency responses up to 100 MHz and beyond. With 12.5 V supply voltages, the total harmonic distortion (THD) is <1% for peak to peak magnitudes of the input current >2.5 times the value of the control current. To illustrate its suitability, the results of a controlled amplifier, using this resistor and operating in current-mode, are also given 相似文献
1000.
M. O. Al-Hunaidi 《Journal of Nondestructive Evaluation》1996,15(2):71-82
The potential of using Spectral analysis of surface waves (SASW) for nondestructive testing of pavement and soil sites has been demonstrated in several publications. The usual SASW field testing and data analysis procedures and the assumption of a single propagation mode yield accurate results when there are no sharp changes in the stiffness of the site with depth. When this is not the case, however, difficulties arise in the interpretation of experimental data due to the participation of more than one mode in the wave field. In an earlier study, the multiple filter/crosscorrelation technique was suggested for analyzing multi-mode SASW signals. This technique, however, may not yield accurate results when propagation modes are closely spaced. A more general method using spectral analysis in the frequency wave-number domain is presented in this paper. Formulas are presented for determining a reasonably small number of surface measurements, and the accuracy of this method in resolving experimental dispersion curves is demonstrated for a pavement site. 相似文献