全文获取类型
收费全文 | 24856篇 |
免费 | 1323篇 |
国内免费 | 56篇 |
专业分类
电工技术 | 312篇 |
综合类 | 25篇 |
化学工业 | 4792篇 |
金属工艺 | 879篇 |
机械仪表 | 1298篇 |
建筑科学 | 432篇 |
矿业工程 | 6篇 |
能源动力 | 864篇 |
轻工业 | 1853篇 |
水利工程 | 91篇 |
石油天然气 | 18篇 |
无线电 | 3647篇 |
一般工业技术 | 4629篇 |
冶金工业 | 4736篇 |
原子能技术 | 291篇 |
自动化技术 | 2362篇 |
出版年
2024年 | 11篇 |
2023年 | 264篇 |
2022年 | 302篇 |
2021年 | 683篇 |
2020年 | 470篇 |
2019年 | 496篇 |
2018年 | 699篇 |
2017年 | 661篇 |
2016年 | 768篇 |
2015年 | 604篇 |
2014年 | 940篇 |
2013年 | 1390篇 |
2012年 | 1457篇 |
2011年 | 1789篇 |
2010年 | 1301篇 |
2009年 | 1332篇 |
2008年 | 1213篇 |
2007年 | 937篇 |
2006年 | 813篇 |
2005年 | 709篇 |
2004年 | 639篇 |
2003年 | 593篇 |
2002年 | 593篇 |
2001年 | 517篇 |
2000年 | 438篇 |
1999年 | 533篇 |
1998年 | 1779篇 |
1997年 | 1011篇 |
1996年 | 808篇 |
1995年 | 462篇 |
1994年 | 325篇 |
1993年 | 345篇 |
1992年 | 123篇 |
1991年 | 139篇 |
1990年 | 118篇 |
1989年 | 121篇 |
1988年 | 107篇 |
1987年 | 93篇 |
1986年 | 70篇 |
1985年 | 59篇 |
1984年 | 36篇 |
1983年 | 31篇 |
1982年 | 40篇 |
1981年 | 31篇 |
1980年 | 55篇 |
1979年 | 15篇 |
1977年 | 87篇 |
1976年 | 156篇 |
1975年 | 19篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
151.
152.
To determine the mechanism of measles virus-induced cell death, we studied the infection of Vero cells and monocytic cell lines with wild-type (Chicago-1) and vaccine (Edmonston) strains of measles virus. DNA fragmentation indicative of apoptosis was apparent by flow cytometry, agarose gel electrophoresis, and electron microscopy. Within syncytia, DNA strand breaks were demonstrated by end labeling with terminal transferase and then by visualization. 相似文献
153.
154.
155.
156.
157.
Dongwook Park Minnyeon Kim 《Quantum Electronics, IEEE Journal of》1996,32(8):1432-1440
This paper presents theoretical results on mode characteristics of surface-emitting (SE) lasers utilizing an active second-order grating section. Based on a coupled-mode approach, longitudinal modes and the associated space-harmonic transverse modes are calculated via a numerical technique. From these, the lasing-mode spectrum, near- and far-field patterns of the radiation mode, and the surface-emission power efficiency are obtained. Effects of the substrate reflector and the grating parameters are also investigated. Finally, comparisons are made with conventional, edge-emitting DFB lasers. The results indicate that with a suitable choice of structural parameter values, DFB SE lasers can be made to possess both the spectral discrimination of the conventional DFB lasers and the advantages of SE lasers at the same time and also that the second lowest longitudinal mode may be preferred over the fundamental longitudinal mode for many applications due to its symmetric field distribution 相似文献
158.
159.
In Kwon Kim Rae-Hong Park 《IEEE transactions on image processing》1996,5(4):587-597
In this paper, we propose a coding algorithm for still images using vector quantization (VQ) and fractal approximation, in which low-frequency components of an input image are approximated by VQ, and its residual is coded by fractal mapping. The conventional fractal coding algorithms indirectly used the gray patterns of an original image with contraction mapping, whereas the proposed fractal coding method employs an approximated and then decimated image as a domain pool and uses its gray patterns. Thus, the proposed algorithm utilizes fractal approximation without the constraint of contraction mapping. For approximation of an original image, we employ the discrete cosine transform (DCT) rather than conventional polynomial-based transforms. In addition, for variable blocksize segmentation, we use the fractal dimension of a block that represents the roughness of the gray surface of a region. Computer simulations with several test images show that the proposed method shows better performance than the conventional fractal coding methods for encoding still pictures. 相似文献
160.
Jeong-Woo Choi Jun Hyo Park Shin Chul Lee Dong-Il Kim Won Hong Lee 《Korean Journal of Chemical Engineering》1995,12(5):528-534
The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The
fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured
kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed
for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions
were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence
signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The
proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight
estimated by the structured kinetic model as well as by empirical correlation. 相似文献