首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   82918篇
  免费   1058篇
  国内免费   699篇
电工技术   1515篇
综合类   60篇
化学工业   12898篇
金属工艺   3575篇
机械仪表   2744篇
建筑科学   2116篇
矿业工程   550篇
能源动力   2051篇
轻工业   7181篇
水利工程   949篇
石油天然气   2341篇
武器工业   41篇
无线电   7696篇
一般工业技术   17616篇
冶金工业   14500篇
原子能技术   2723篇
自动化技术   6119篇
  2022年   653篇
  2021年   1019篇
  2020年   790篇
  2019年   873篇
  2018年   1654篇
  2017年   1665篇
  2016年   1882篇
  2015年   1052篇
  2014年   1713篇
  2013年   3984篇
  2012年   2625篇
  2011年   3166篇
  2010年   2639篇
  2009年   2939篇
  2008年   2980篇
  2007年   2898篇
  2006年   2486篇
  2005年   2166篇
  2004年   2065篇
  2003年   2018篇
  2002年   1911篇
  2001年   1827篇
  2000年   1813篇
  1999年   1709篇
  1998年   3786篇
  1997年   2715篇
  1996年   2052篇
  1995年   1660篇
  1994年   1459篇
  1993年   1475篇
  1992年   1129篇
  1991年   1140篇
  1990年   1180篇
  1989年   1172篇
  1988年   1056篇
  1987年   989篇
  1986年   998篇
  1985年   1081篇
  1984年   912篇
  1983年   881篇
  1982年   806篇
  1981年   818篇
  1980年   751篇
  1979年   771篇
  1978年   740篇
  1977年   876篇
  1976年   1018篇
  1975年   667篇
  1974年   640篇
  1973年   641篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
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   
982.
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   
983.
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   
984.
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   
985.
Two eyetracking experiments examined the interaction among syntactic parsing preferences, thematically based comprehension preferences, and plausibility in the early stages of reading a sentence. Results from 64 adults support the pattern of results reported by L. Stowe (1989) when looking at the disambiguating region of a sentence. However, the results for earlier regions suggest that the postverbal noun phrase was initially taken as direct object of an ergative verb even when the subject was inanimate. It appears that the inanimacy of the subject may not have guided the initial syntactic analysis, but rather facilitated the revision of an initial misanalysis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
986.
We present T 1 measurements performed in liquid and solid 3 He confined in sintered silver. In the liquid case, we find a close to linear relationship between T 1 and the applied magnetic field, similar to other (non metallic) systems, and up to higher frequencies (corresponding to 11 T) than previously reported. In the solid, the relaxation rate is found to increase spectacularly at large polarizations, which may indicate a polarization dependence of the exchange motion. Now atNow at  相似文献   
987.
A set of standard equipments is considered for reproducing seismic oscillation parameters that have been developed at the Mendeleev All-Union Metrology Research Institute.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 36–38, August, 1993.  相似文献   
988.
Examined publishing practices of the American Psychological Association (APA) in the alcohol and drug area. Although the total number of articles published by APA increased only 7.6% between 1984 and 1990, the number of alcohol and drug articles more than doubled. Despite the disproportionate growth of alcohol and drug articles between 1984 and 1990, only 3.8% of 1,408 APA articles published in 1990 addressed alcohol and drug use issues. An earlier investigation by M. O. Howard and D. A. Howard (1992) reported that 541 articles published in 1984 in 12 alcohol and drug specialty journals received an average of 3.48 citations by the end of 1988. Alcohol and drug articles published by APA in 1984 received more than 4 times as many citations during this period. Also, alcohol and drug articles published by APA received significantly more citations between 1984 and 1988 than those published in specialty journals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
989.
This study focused on the self-representations of suicidal adolescent. Twenty-six Israeli suicidal inpatients, 24 nonsuicidal inpatients, and 24 control participants completed scales on suicidal tendencies, the hedonic value of self-representations, the complexity (differentiation, integration) of these self-representations, and the discrepancies among self domains (actual, ideal, ought). Suicidal adolescents showed more negative self-representations, a less differentiated and less integrated organization of self-attributes, and more discrepancies between the 3 assessed domains of the self than did control participants. In addition, compared with psychiatric nonsuicidal participants, suicidal adolescents showed a less complex organization of self-attributes and a higher discrepancy between ideal self and ought self. Results were discussed in terms of the vulnerable self of suicidal adolescents, characterized by uneven processing of positive and negative information, confusion, and simplicity.  相似文献   
990.
The solutions of the direct and inverse problems of electromagnetic diagnostics of laminated materials with the use of a rectangular waveguide as a radiator are presented. The direct problem, i.e., the problem of finding the coefficient of reflection of electromagnetic waves, is solved by using a method based on the computation of the energy flow through the aperture of a waveguide. The method of global minimization was applied to solve the inverse problem, i.e., to find the parameters of the material for given reflection coefficients measured at various frequencies.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 2, pp. 26–33, March–April, 1994.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号