全文获取类型
收费全文 | 67868篇 |
免费 | 13865篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 895篇 |
综合类 | 20篇 |
化学工业 | 22987篇 |
金属工艺 | 805篇 |
机械仪表 | 1269篇 |
建筑科学 | 2565篇 |
矿业工程 | 61篇 |
能源动力 | 1526篇 |
轻工业 | 12243篇 |
水利工程 | 603篇 |
石油天然气 | 188篇 |
武器工业 | 1篇 |
无线电 | 7825篇 |
一般工业技术 | 15933篇 |
冶金工业 | 6513篇 |
原子能技术 | 95篇 |
自动化技术 | 8232篇 |
出版年
2024年 | 67篇 |
2023年 | 333篇 |
2022年 | 534篇 |
2021年 | 1171篇 |
2020年 | 2176篇 |
2019年 | 3891篇 |
2018年 | 4136篇 |
2017年 | 4371篇 |
2016年 | 4952篇 |
2015年 | 4708篇 |
2014年 | 4836篇 |
2013年 | 7179篇 |
2012年 | 4526篇 |
2011年 | 4064篇 |
2010年 | 3957篇 |
2009年 | 3699篇 |
2008年 | 3275篇 |
2007年 | 3018篇 |
2006年 | 2449篇 |
2005年 | 2049篇 |
2004年 | 1969篇 |
2003年 | 1895篇 |
2002年 | 1760篇 |
2001年 | 1465篇 |
2000年 | 1366篇 |
1999年 | 804篇 |
1998年 | 2105篇 |
1997年 | 1337篇 |
1996年 | 823篇 |
1995年 | 470篇 |
1994年 | 367篇 |
1993年 | 372篇 |
1992年 | 125篇 |
1991年 | 96篇 |
1990年 | 83篇 |
1989年 | 74篇 |
1988年 | 99篇 |
1987年 | 99篇 |
1986年 | 88篇 |
1985年 | 93篇 |
1984年 | 71篇 |
1983年 | 45篇 |
1982年 | 44篇 |
1981年 | 71篇 |
1980年 | 66篇 |
1979年 | 40篇 |
1977年 | 113篇 |
1976年 | 221篇 |
1975年 | 37篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
F Abadía-Molina R Calvente R Carmona R Luján F Abadía-Fenoll 《Canadian Metallurgical Quarterly》1993,8(2):297-304
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described. 相似文献
23.
24.
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
25.
SA Khotimchenko VM Kodentsova IA Alekseeva SG Vlaskina OA Vrzhesinskaia AA Sokol''nikov LA Kharitonchik IP Aleshko-Ozhevskií LV Sheviakova 《Canadian Metallurgical Quarterly》1997,43(3):158-164
Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells. 相似文献
26.
27.
28.
29.
R Herruzo-Cabrera L Malo-González ME Calle Purón MJ Vizcaíno-Alcaide J Del Rey-Calero 《Canadian Metallurgical Quarterly》1993,9(4):442-446
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program. 相似文献
30.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献