全文获取类型
收费全文 | 5593篇 |
免费 | 229篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 54篇 |
综合类 | 3篇 |
化学工业 | 753篇 |
金属工艺 | 142篇 |
机械仪表 | 188篇 |
建筑科学 | 67篇 |
矿业工程 | 2篇 |
能源动力 | 134篇 |
轻工业 | 304篇 |
水利工程 | 20篇 |
石油天然气 | 8篇 |
无线电 | 693篇 |
一般工业技术 | 741篇 |
冶金工业 | 2311篇 |
原子能技术 | 28篇 |
自动化技术 | 388篇 |
出版年
2024年 | 9篇 |
2023年 | 25篇 |
2022年 | 60篇 |
2021年 | 119篇 |
2020年 | 88篇 |
2019年 | 67篇 |
2018年 | 115篇 |
2017年 | 115篇 |
2016年 | 123篇 |
2015年 | 101篇 |
2014年 | 145篇 |
2013年 | 232篇 |
2012年 | 215篇 |
2011年 | 254篇 |
2010年 | 188篇 |
2009年 | 195篇 |
2008年 | 188篇 |
2007年 | 155篇 |
2006年 | 132篇 |
2005年 | 96篇 |
2004年 | 92篇 |
2003年 | 90篇 |
2002年 | 58篇 |
2001年 | 94篇 |
2000年 | 74篇 |
1999年 | 143篇 |
1998年 | 718篇 |
1997年 | 449篇 |
1996年 | 277篇 |
1995年 | 193篇 |
1994年 | 174篇 |
1993年 | 183篇 |
1992年 | 44篇 |
1991年 | 61篇 |
1990年 | 41篇 |
1989年 | 49篇 |
1988年 | 57篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 31篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 58篇 |
1976年 | 134篇 |
1975年 | 5篇 |
排序方式: 共有5836条查询结果,搜索用时 0 毫秒
21.
RG Wilde JT Billheimer SJ Germain EA Hausner PC Meunier DA Munzer JK Stoltenborg PJ Gillies DL Burcham SM Huang JD Klaczkiewicz SS Ko RR Wexler 《Canadian Metallurgical Quarterly》1996,4(9):1493-1513
Acyl-CoA:cholesterol acyltransferase (ACAT) is the enzyme largely responsible for intracellular cholesterol esterification. A systemic inhibitor of ACAT is believed to be able to slow or even reverse the atherosclerotic process. Towards that goal, a series of cyclic sulfides, derived from the hetero-Diels-Alder reaction of thioaldehydes with 1,3-dienes, and bearing carboxamide substituents, were prepared and evaluated for in vitro (in several tissues and species) and ex vivo ACAT inhibition. Minor changes in subsequent structure were found to have a significant effect in optimization of the biological activity of this series of compounds. 相似文献
22.
23.
This study focuses on how to assess the optimal environmental investment decisions under economic and ecological uncertainty, and establishes the continuous time model using the real option approach to optimize environmental pollution policy. Unlike traditional cost benefit analysis, this work extends the model of [Pindyck, R.S., 2002. Optimal timing problems in environmental economics. Journal of Economic Dynamics and Control 26(9–10), 1677–1697], and attempts to identify the storage threshold of pollution stocks and the optimal timing for implementing environmental pollution decisions. 相似文献
24.
Takuma Suzuki Hang-Ju Ko Agus Setiawan Jung-Jin Kim Koh Saitoh Masami Terauchi Takafumi Yao 《Materials Science in Semiconductor Processing》2003,6(5-6):519-521
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar. 相似文献
25.
Dynamic RSVP protocol 总被引:5,自引:0,他引:5
Geng-Sheng Kuo Po-Chang Ko 《Communications Magazine, IEEE》2003,41(5):130-135
RSVP is a resource reservation setup protocol that can be used by a host to request specific QoS for multicast multimedia flows on the Internet. Multiprotocol label switching (MPLS) architecture also needs RSVP. The fact that the resolutions of the display system used in different receiver nodes might have different, multi-resolution characteristics is supported in the MPEG-4 standard, and the EZW compression algorithm can cease decoding at any point in the bitstream. However, RSVP does not provide a more flexible mechanism. In this article we propose an extension of RSVP to provide the needed mechanism, coined dynamic RSVP (DRSVP), to dynamically adjust reserved resources on nodes without much effort. It provides different video resolutions to different receiver nodes with different needed reserved resources. Therefore, it does not waste precious Internet resources to transmit unnecessary multimedia packets. 相似文献
26.
A reinjection experiment has been conducted in an attempt to sustain reservoir pressure and steam production and to extract remaining heat energy in the superheated reservoir in the Matsukawa vapor-dominated geothermal field. This experiment was undertaken because the increase in superheat of produced steam and the decline of steam production are the current major issues for stable operation of the power plant. Almost all the reinjected fluid into well MR 1 was recovered from well M5, and the steam production of well M5 has increased by approximately 67%. 相似文献
27.
28.
The pattern of expression of the simian virus 40 (SV40) T antigen gene and resultant dysplasia were re-examined in a line of transgenic mice in which the T antigen gene was under the control of the SV40 early promoter. We found that T antigen expression in the kidney, and resulting dysplastic lesions, occurred exclusively in the distal convoluted tubules and the ascending limbs of Henle. Epidermal growth factor (EGF) expression in the kidney of normal mice was similarly immunolocalized. The correlation between high EGF immunoreactivity in normal mouse tissues and T antigen expression in the transgenic counterpart was also seen in the choroid plexus epithelium and in the submandibular glands of male mice. T antigen was not found in the submandibular gland of transgenic females. Similarly, EGF was only rarely detected in the normal female submandibular gland. In contrast to the correlation between T antigen expression in the transgenic mice and EGF expression in the corresponding tissues of the normal mice, within the dysplastic lesions of the transgenic mice EGF expression was severely diminished. Adenocarcinomas of the male submandibular gland from another line of transgenic mice that expresses the Int-1 transgene, showed similarly reduced levels of immunostaining for EGF. Thus, reduced expression of EGF might be a general feature of dysplasia and tumorigenesis in those tissues that normally express EGF. 相似文献
29.
30.
Two residues that may ligate Ca2+ in transmembrane domain six of the plasma membrane Ca(2+)-ATPase 总被引:1,自引:0,他引:1
AO Adebayo A Enyedi AK Verma AG Filoteo JT Penniston 《Canadian Metallurgical Quarterly》1995,270(46):27812-27816
In order to identify Ca2+ ligands in the putative transmembrane domain 6 of the plasma membrane Ca2+ pump, amino acids Asn879, Met882, Asp883, and Ser887 were singly altered. Asn879, Met882, and Asp883 were chosen because the corresponding amino acids have been proposed as Ca2+ ligands in the sarcoplasmic reticulum Ca2+ pump (Clarke, D. M., Loo, T. W., and MacLennan, D. H. (1990) J. Biol. Chem. 265, 6262-6267). For the alterations, a fully active truncated version of the pump was used, because the interaction of Ca2+ with the pump could be studied without interference from calmodulin binding. The mutants at Asn and Asp did not carry out ATP-supported Ca2+ uptake and formed no acylphosphate from [gamma-32P]ATP, suggesting that, like the corresponding amino acids in the sarcoplasmic reticulum Ca2+ pump, these two are Ca2+ ligands. However, all the mutants at the position of Met882 showed some activity. Indeed, the Met882--> Ile mutant was fully active at a saturating Ca2+ concentration and only the K1/2 for Ca2+ activation was shifted slightly upward. Converting the Met to Thr (which is the corresponding residue in the sarcoplasmic reticulum Ca2+ pump) reduced the activity to 20% of the wild type, further emphasizing the differences between the two Ca2+ pumps. The mutant Ser887--> Ala was expressed in greater amounts than, and had a specific activity about 50% higher than, the wild type, indicating that this serine also could not be a Ca2+ ligand and could not replace the missing Thr at position Met882. 相似文献