全文获取类型
收费全文 | 104770篇 |
免费 | 7936篇 |
国内免费 | 3014篇 |
专业分类
电工技术 | 4163篇 |
技术理论 | 10篇 |
综合类 | 4551篇 |
化学工业 | 19658篇 |
金属工艺 | 4227篇 |
机械仪表 | 4583篇 |
建筑科学 | 6524篇 |
矿业工程 | 1883篇 |
能源动力 | 2805篇 |
轻工业 | 12136篇 |
水利工程 | 1664篇 |
石油天然气 | 3810篇 |
武器工业 | 527篇 |
无线电 | 9735篇 |
一般工业技术 | 14287篇 |
冶金工业 | 10050篇 |
原子能技术 | 866篇 |
自动化技术 | 14241篇 |
出版年
2024年 | 395篇 |
2023年 | 1507篇 |
2022年 | 2763篇 |
2021年 | 3978篇 |
2020年 | 3068篇 |
2019年 | 2685篇 |
2018年 | 3591篇 |
2017年 | 3601篇 |
2016年 | 3623篇 |
2015年 | 3810篇 |
2014年 | 4779篇 |
2013年 | 6703篇 |
2012年 | 6563篇 |
2011年 | 6931篇 |
2010年 | 5634篇 |
2009年 | 5291篇 |
2008年 | 5260篇 |
2007年 | 4884篇 |
2006年 | 4319篇 |
2005年 | 3718篇 |
2004年 | 2909篇 |
2003年 | 2614篇 |
2002年 | 2375篇 |
2001年 | 2030篇 |
2000年 | 2109篇 |
1999年 | 2465篇 |
1998年 | 4073篇 |
1997年 | 2892篇 |
1996年 | 2333篇 |
1995年 | 1686篇 |
1994年 | 1423篇 |
1993年 | 1124篇 |
1992年 | 681篇 |
1991年 | 526篇 |
1990年 | 453篇 |
1989年 | 411篇 |
1988年 | 340篇 |
1987年 | 264篇 |
1986年 | 210篇 |
1985年 | 193篇 |
1984年 | 154篇 |
1983年 | 108篇 |
1982年 | 125篇 |
1981年 | 137篇 |
1980年 | 128篇 |
1979年 | 56篇 |
1978年 | 56篇 |
1977年 | 150篇 |
1976年 | 275篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
一类Feistel密码的线性分析 总被引:5,自引:0,他引:5
该文提出一种新的求取分组密码线性偏差上界的方法,特别适用于密钥线性作用的Feistel密码.该分析方法的思路是,首先对密码体制线性偏差进行严格的数学描述,分别给出密码线性偏差与轮函数F及S盒的线性偏差的数学关系;然后通过求取线性方程组最小重量解,确定密码线性偏差的上界. 相似文献
44.
对己二腈工业反应器提出了两釜串联带回流的模型,通过模拟计算得出模型的级间返混系数 f=6的结论。该模型能较好地预测工业反应器中物料组分浓度变化和气、液两相的流动特性;指出了现工业反应器的鼓泡中和段体积偏小是造成己二酸浓度偏高的关键;提出了可以通过增加串连一个鼓泡预反应段的改造方案,能有效地降低己二酸的浓度,从7%降至4%左右,从而能较好地减缓腐蚀和结焦。 相似文献
45.
46.
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
47.
48.
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
49.
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
50.
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