全文获取类型
收费全文 | 168674篇 |
免费 | 8974篇 |
国内免费 | 4486篇 |
专业分类
电工技术 | 6484篇 |
技术理论 | 9篇 |
综合类 | 7787篇 |
化学工业 | 25795篇 |
金属工艺 | 9379篇 |
机械仪表 | 8184篇 |
建筑科学 | 8602篇 |
矿业工程 | 3009篇 |
能源动力 | 3684篇 |
轻工业 | 9344篇 |
水利工程 | 2918篇 |
石油天然气 | 4784篇 |
武器工业 | 911篇 |
无线电 | 19814篇 |
一般工业技术 | 26616篇 |
冶金工业 | 6809篇 |
原子能技术 | 1343篇 |
自动化技术 | 36662篇 |
出版年
2024年 | 429篇 |
2023年 | 1524篇 |
2022年 | 3026篇 |
2021年 | 3951篇 |
2020年 | 2970篇 |
2019年 | 2453篇 |
2018年 | 16826篇 |
2017年 | 16058篇 |
2016年 | 12338篇 |
2015年 | 4193篇 |
2014年 | 4599篇 |
2013年 | 5463篇 |
2012年 | 8637篇 |
2011年 | 15097篇 |
2010年 | 13223篇 |
2009年 | 10420篇 |
2008年 | 11500篇 |
2007年 | 12124篇 |
2006年 | 4677篇 |
2005年 | 4943篇 |
2004年 | 3809篇 |
2003年 | 3642篇 |
2002年 | 3004篇 |
2001年 | 2335篇 |
2000年 | 2218篇 |
1999年 | 2159篇 |
1998年 | 1830篇 |
1997年 | 1559篇 |
1996年 | 1310篇 |
1995年 | 1100篇 |
1994年 | 822篇 |
1993年 | 678篇 |
1992年 | 562篇 |
1991年 | 430篇 |
1990年 | 305篇 |
1989年 | 290篇 |
1988年 | 235篇 |
1987年 | 137篇 |
1986年 | 118篇 |
1985年 | 111篇 |
1984年 | 51篇 |
1983年 | 48篇 |
1982年 | 60篇 |
1981年 | 41篇 |
1968年 | 46篇 |
1966年 | 48篇 |
1965年 | 50篇 |
1959年 | 38篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
讲述了参观Semicon/west94′展览会及考察美国和西德的5个公司、1所大学所了解到的投影光刻技术、电子束曝光技术、透镜面形测试技术的发展。 相似文献
202.
本文介绍了汉英机器翻译系统中从中间媒介语言生成英语的生成系统的词汇结构和功能,描述了生成系统各个层次之间的转换原理。为了说明清楚,在叙述中注意了列举从中间媒介中间媒介语言到目标语句的生成实例。 相似文献
203.
本文利用可控平均冷却速度的单向凝固实验炉测定了45号钢在不同平均冷却速度下的冷却曲线,由此得到其在凝固期间的平均冷却速度R,相应地测量了不同平均冷却速度下试样的二次枝晶臂间距S2,通过回归,得到了如下关系式:S2=727R-0.41,并将引式成功地应用于实际生产中。 相似文献
204.
Porous silica glass was prepared by sol-gel process from tetraethoxysilane (TEOS). The effects of solvents (water, ethanol), drying condition, heat treatment temperature on specific surface area and pore size distribution of porous silica were investigated. Gelation process accelerates with an increase of H2O content, while retards with the increase of ethanol amount. Structure changes during heat treatment were studied by means of DTA, XRD. TEM micrographs show that the gel particles shrink after heated at 500°C, thus the average pore size decreases. 相似文献
205.
文章通过对洋浦电厂海水冷却箱涵沟槽预裂(深孔)爆破技术的研究,提出了复杂地质条件下合理的控制爆破参数及微差起爆方式。针对砂层地段难以钻、爆的特点。笔者进行了有益的探讨。 相似文献
206.
Images stored in resist for soft X-ray lithography or microradiography were found to show a background noise which limits the resolution. This is due to the statistically variable spatial distribution of the photons incident on the resist surface. An estimate of the fundamental noise-limited resolution has been made from the experimental measurement of photon flux incident on the surface and the accurate development rate curves. Monochromatic radiation from a synchrotron source was used. 相似文献
207.
扫描电子显微研究表明,化学汽相沉积的金刚石薄膜中晶粒大小比较均匀。但随着沉积时间和薄膜厚度的增加,晶粒逐渐变大,且每一层内,存在少量的大金刚石颗粒,讨论了晶粒尺寸变化和大晶粒形成的原因和机制。 相似文献
208.
Apoptosis in the failing human heart 总被引:1,自引:0,他引:1
G Olivetti R Abbi F Quaini J Kajstura W Cheng JA Nitahara E Quaini C Di Loreto CA Beltrami S Krajewski JC Reed P Anversa 《Canadian Metallurgical Quarterly》1997,336(16):1131-1141
BACKGROUND: Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. METHODS: Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. RESULTS: Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonstration of DNA-strand breaks in myocyte nuclei was coupled with the documentation of chromatin condensation and fragmentation by confocal microscopy. All these findings reflect apoptosis of myocytes. The percentage of myocytes labeled with BCL2 (which protects cells against apoptosis) was 1.8 times as high in the hearts of patients with cardiac failure as in the normal hearts, whereas labeling with BAX (which promotes apoptosis) remained constant. The near doubling of the expression of BCL2 in the cardiac tissue of patients with heart failure was confirmed by Western blotting. CONCLUSIONS: Programmed death of myocytes occurs in the decompensated human heart in spite of the enhanced expression of BCL2; this phenomenon may contribute to the progression of cardiac dysfunction. 相似文献
209.
210.
The effect of DC flux on the core loss is examined for the practical range of power and frequency. Relevant core loss equations are derived and applied to an optimization algorithm to determine the minimum core loss at a given ratio of s (DC flux density to AC peak flux density). It has been found that the curves of hysteresis loss density versus the ratio of s exhibit a peak at a critical ratio. Below or above this critical ratio, the loss density decreases drastically. On the other hand, the curves of eddy-current loss density versus the ratio of s exhibits a minimum point at a critical ratio. Below or above this critical ratio, the loss density increases gradually 相似文献