全文获取类型
收费全文 | 4561篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 101篇 |
金属工艺 | 3篇 |
机械仪表 | 33篇 |
建筑科学 | 26篇 |
矿业工程 | 5篇 |
能源动力 | 17篇 |
轻工业 | 84篇 |
水利工程 | 13篇 |
石油天然气 | 4篇 |
无线电 | 46篇 |
一般工业技术 | 118篇 |
冶金工业 | 4062篇 |
原子能技术 | 2篇 |
自动化技术 | 65篇 |
出版年
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 36篇 |
2012年 | 8篇 |
2011年 | 15篇 |
2010年 | 17篇 |
2009年 | 10篇 |
2008年 | 26篇 |
2007年 | 30篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 24篇 |
2002年 | 16篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 143篇 |
1998年 | 1314篇 |
1997年 | 774篇 |
1996年 | 501篇 |
1995年 | 255篇 |
1994年 | 183篇 |
1993年 | 243篇 |
1992年 | 29篇 |
1991年 | 51篇 |
1990年 | 55篇 |
1989年 | 53篇 |
1988年 | 62篇 |
1987年 | 44篇 |
1986年 | 42篇 |
1985年 | 38篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 25篇 |
1980年 | 39篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 83篇 |
1976年 | 197篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1966年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有4581条查询结果,搜索用时 0 毫秒
1.
ML Martínez-Frías E Bermejo Sánchez E Rodríguez Pinilla A Villa 《Canadian Metallurgical Quarterly》1997,46(6):593-596
INTRODUCTION: Even though there are few epidemiological studies evaluating the birth weights of different groups of malformed babies with chromosomal abnormalities, it is widely known that infants with trisomy 18, and to a lesser degree those with trisomy 13 and other chromosomal alterations, have low birth weights. PATIENTS AND METHODS: In this study we present the analysis of the birth weights and gestational ages of a large sample of babies (23,155 malformed and a similar number of nonmalformed babies), separating the different groups of chromosomal anomalies and comparing the weight in the clinical groups of malformed infants. RESULTS: Most of the groups with chromosomal abnormalities present lower birth weights in comparison to the other groups. CONCLUSIONS: The results of our study support the conclusion that the relationship between chromosomal alterations and low birth weight is sufficiently important that such a low birth weight in children with minor or major anomalies should be considered as one more indication to perform chromosomal analysis. 相似文献
2.
3.
4.
5.
Effect of starting particle size on hot-pressing of magnesium oxide (MgO) powder was examined using seven kinds of MgO powders
prepared by a vapour-phase oxidation process; the average primary particle sizes were 11, 25, 32, 44, 57, 107 and 261 nm.
These compressed powders (compacts) were hot-pressed at a temperature between 900 and 1300°C. The densifications of these
compacts during the hot-pressing proceeded via (i) the sintering of primary particles within secondary particles and the rearrangement
of secondary particles/grains (900°C), (ii) the gradual grain growth controlled by the pore migration (900∼1100°C) and (iii)
the rapid grain growth due to the active mass transfer (1300°C); the grain sizes of MgO compacts hot-pressed at and below
1100°C were <1 μm, while those at 1300°C attained 20∼30 μm. The transluscent compact with the relative density of 99.7% could
be obtained when the compressed powder with the average primary particle size of 44 nm was hot-pressed at a temperature as
low as 1100°C for 1 h.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
6.
GM Gazzaniga G Angelini G Pastorino E Santoro M Lucchini ML Dal Prà 《Canadian Metallurgical Quarterly》1993,78(3):271-275
Four hundred forty-six patients with Tourette Syndrome (TS) and/or their parents completed a 52-item self-report survey about vocal and motor tics, and the frequency of associated co-morbid conditions of aggression, obsessions and compulsions, attentional problems, sleep disturbance, mood disturbance, anxiety, and self-mutilative behaviours which have been frequently reported in the literature on TS. Respondents also responded to an open-ended question regarding the most disabling aspects of TS. Results were analyzed within two age groups; under 18 years of age (N = 245) and 18 years of age or older (N = 177). Tics and associated conditions were the most frequently reported disabling aspect by both age groups. Subjects under age 18, however, reported significantly more frequent problems with hyperactivity, temper control, aggressive behaviours and sleepwalking than adults with TS. 相似文献
7.
R. H. Howell P. A. Sterne M. J. Fluss J. H. Kaiser K. Kitazawa H. Kojima 《Journal of Superconductivity and Novel Magnetism》1994,7(1):169-173
High-statistics (>4 × 108 counts), room-temperature measurements of the electron-positron momentum density of La2?x Sr x CuO4 have been performed for samples with Sr concentrations of x=0.0, 0.1, 0.13, and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron-positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane. 相似文献
8.
9.
A Nu?ez C De la Roza ML Rodrigo-Angulo W Bu?o F Reinoso-Suárez 《Canadian Metallurgical Quarterly》1997,754(1-2):1-11
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters. 相似文献
10.
Ehrlichia spp. from human and equine sources in the northeastern Unites States were detected by PCR, isolated, and propagated in the HL-60 promyelocytic leukemia cell line. Growth of Ehrlichia from both equine and human sources was enhanced by addition of retinoic acid, which causes granulocytic differentiation of the HL-60 cells. DNA sequencing of a portion of the 16S rDNA gene supported the hypothesis that the same pathogen was responsible for both equine and human granulocytic ehrlichiosis. 相似文献