全文获取类型
收费全文 | 57828篇 |
免费 | 4948篇 |
国内免费 | 1495篇 |
专业分类
电工技术 | 1919篇 |
技术理论 | 2篇 |
综合类 | 2008篇 |
化学工业 | 11284篇 |
金属工艺 | 2169篇 |
机械仪表 | 2402篇 |
建筑科学 | 2930篇 |
矿业工程 | 745篇 |
能源动力 | 1571篇 |
轻工业 | 8220篇 |
水利工程 | 928篇 |
石油天然气 | 1561篇 |
武器工业 | 197篇 |
无线电 | 4391篇 |
一般工业技术 | 8452篇 |
冶金工业 | 6999篇 |
原子能技术 | 459篇 |
自动化技术 | 8034篇 |
出版年
2024年 | 235篇 |
2023年 | 864篇 |
2022年 | 1285篇 |
2021年 | 2036篇 |
2020年 | 1613篇 |
2019年 | 1583篇 |
2018年 | 2273篇 |
2017年 | 2220篇 |
2016年 | 2359篇 |
2015年 | 2166篇 |
2014年 | 2722篇 |
2013年 | 4194篇 |
2012年 | 3623篇 |
2011年 | 3705篇 |
2010年 | 3078篇 |
2009年 | 2833篇 |
2008年 | 2821篇 |
2007年 | 2654篇 |
2006年 | 2193篇 |
2005年 | 1862篇 |
2004年 | 1535篇 |
2003年 | 1562篇 |
2002年 | 1652篇 |
2001年 | 1413篇 |
2000年 | 1038篇 |
1999年 | 1001篇 |
1998年 | 2431篇 |
1997年 | 1696篇 |
1996年 | 1189篇 |
1995年 | 755篇 |
1994年 | 551篇 |
1993年 | 535篇 |
1992年 | 262篇 |
1991年 | 200篇 |
1990年 | 152篇 |
1989年 | 142篇 |
1988年 | 157篇 |
1987年 | 132篇 |
1986年 | 122篇 |
1985年 | 123篇 |
1984年 | 92篇 |
1983年 | 69篇 |
1982年 | 81篇 |
1981年 | 99篇 |
1980年 | 94篇 |
1979年 | 58篇 |
1977年 | 153篇 |
1976年 | 275篇 |
1975年 | 58篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
在油气井的试油测试资料中,压力恢复曲线有时会出现下滑现象,常被认为是施工失误所致。本文以实际资料为例,分析了“下滑恢复”的压力响应特征和影响因素,认为只在低渗透地层有可能产生“下滑恢复”现象,并提出了避免“下滑恢复”的施工建议。 相似文献
22.
通过对有线电视系统干扰信号产生原因的理论分析,提出在实际操作中的解决方案,以期达到使有线电视系统信号的输出更稳定、电视画面更清晰的目的。 相似文献
23.
24.
Presents an obituary and information about the life and accomplishments of Josef Maria Bro?ek. Born August 14, 1913, in the ancient town of Melnik, in central Bohemia, today the Czech Republic, Josef spent his childhood in Poland (Warsaw, 1913- 1915) and in Siberia (1915-1920). His education in Czechoslovakia culminated with a thesis on "Memory, Its Measurement and Structure" and a PhD awarded in June 1937. In the history of psychology, his lifetime project bore the title "Historiography of Psychology Around the World," and it covered about 20 geographical areas. Extensive attention was devoted to institutional and organizational developments as journals, academic settings, archives, museums, research groups, conferences, and institutes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
25.
M. Kaiarov E. Rudnayov J. Koval
ík J. Dusza M. Hnatko P. ajgalík A. Merstallinger 《Materialwissenschaft und Werkstofftechnik》2003,34(4):338-342
In the presented work some properties of a recently developed Si3N4/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si3N4 pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si3N4+SiC disc revealed that mechanical fracture was the wear controlling mechanism. Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism. 相似文献
26.
金属/Al2O3基纳米复合材料研究最新进展 总被引:2,自引:0,他引:2
金属/Al2O3纳米复合材料在保持原有金属的功能特性时,还可以获得 很好的力学性能,是有良好发展前景的一种纳米复合材料。本文回顾了近年来金属/Al2O3基纳米复合材料在制备工艺,微观结构和力学性能,增韧强化机理方面的最新进展,并指出了今后的研究方向。 相似文献
27.
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
28.
29.
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
30.
1. A total of 360 Japanese quail of 4 commercial meat-type lines and two diet treatments (260 and 216 g/kg or 238 and 195 g/kg of crude protein (CP) in the starter and grower diet, respectively) were used. 2. The positive effect of a high CP diet on body weight was significant only for the first 4 weeks after hatching. 3. The mean age at inflection point of the growth curve (t+) across lines and sexes was 1.4 d (0.6 to 2.8 d within line/sex groups) earlier for quail fed on a high CP diet than in quail receiving a low CP diet. The inflection (y+) and asymptotic (A) weights were similar under both dietary protein concentrations. Nevertheless, the shape of the growth curve, characterised by the ratio y+/A and parameter of the maturing rate k, was significantly influenced by diet. 4. A higher food intake and less efficient food conversion were found for quail fed on a high CP diet in the period from 15 to 28 d of age. 5. The fattening traits such as body weight, cumulative food intake and food conversion, were not affected by dietary CP content at the age of 5 weeks. 6. The effects of line on body weight, food intake and food conversion are discussed. 相似文献