全文获取类型
收费全文 | 42134篇 |
免费 | 580篇 |
国内免费 | 788篇 |
专业分类
电工技术 | 724篇 |
综合类 | 51篇 |
化学工业 | 6378篇 |
金属工艺 | 3094篇 |
机械仪表 | 1386篇 |
建筑科学 | 863篇 |
矿业工程 | 151篇 |
能源动力 | 1429篇 |
轻工业 | 2266篇 |
水利工程 | 356篇 |
石油天然气 | 1386篇 |
无线电 | 3976篇 |
一般工业技术 | 10665篇 |
冶金工业 | 7218篇 |
原子能技术 | 788篇 |
自动化技术 | 2771篇 |
出版年
2021年 | 340篇 |
2020年 | 276篇 |
2019年 | 374篇 |
2018年 | 665篇 |
2017年 | 657篇 |
2016年 | 743篇 |
2015年 | 539篇 |
2014年 | 807篇 |
2013年 | 2387篇 |
2012年 | 1405篇 |
2011年 | 1884篇 |
2010年 | 1489篇 |
2009年 | 1781篇 |
2008年 | 1624篇 |
2007年 | 1768篇 |
2006年 | 1400篇 |
2005年 | 1226篇 |
2004年 | 1178篇 |
2003年 | 1078篇 |
2002年 | 1066篇 |
2001年 | 1119篇 |
2000年 | 964篇 |
1999年 | 999篇 |
1998年 | 2115篇 |
1997年 | 1657篇 |
1996年 | 1440篇 |
1995年 | 983篇 |
1994年 | 757篇 |
1993年 | 774篇 |
1992年 | 597篇 |
1991年 | 572篇 |
1990年 | 524篇 |
1989年 | 485篇 |
1988年 | 369篇 |
1987年 | 402篇 |
1986年 | 364篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1972年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
R. Z. Gataulin 《Chemical and Petroleum Engineering》1992,28(8):519-521
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 8, pp. 31–32, August, 1992. 相似文献
192.
193.
The corrosion mechanism and microstructural characteristics of yttria (Y2 O3 ) exposed to uranium hexafluoride (UF4 ) and uranium tetrafluoride gases at temperatures above 900°C were investigated. Processed yttria samples were exposed for times ranging from 5 to 40 min. A weight increase was observed after each test exposure. An outer corrosion scale composed of UO2 and YF3 , and an inner corrosion layer of YF3 , were observed following the UF6 reaction at nearly 1200 K. During the UF4 exposure, an outer layer containing a liquid mixture of fluoride, oxygen, yttrium, uranium compounds, a secondary reaction layer of UO2 followed by an inner layer composed of a solution of Y2 O3 and YF3 , possibly in the form of YOF inner layer, were observed. It was found that the corrosion process is controlled by the diffusion which is evidenced by the parabolic growth rate of the secondary layer. After completion of the solidification process, the formation of a eutectic region and dendrites were observed throughout the outer scale. In general, at temperatures above 1173 K, high corrosion rates were observed, and yttria did not appear to be a viable containment material for UF4 and UF6 . 相似文献
194.
By using a mRNA differential display technique to search for salicylate suppressible genes, we identified a cDNA in human foreskin fibroblasts, which by GenBankTM DNA data base search shows sequence homology to the recently reported cullin/Cdc53 (CUL) family genes, especially CUL-3. We have cloned the full-length human CUL-3 (Hs-CUL-3) cDNA. It encodes a 768-amino acid polypeptide and has a predicted molecular weight of 88,939. The amino acid sequence of Hs-CUL-3 shows 46% homology to that of its Caenorhabditis elegans ortholog, Ce-CUL-3, and 27 and 23% to that of Hs-CUL-1 and Hs-CUL-2, respectively. Northern blot analysis showed that phorbol 12-myristate 13-acetate increased the expression of Hs-CUL-3 mRNA in a concentration- and time-dependent manner, and this increase was inhibited by sodium salicylate. Hs-CUL-3 widely expressed in human tissues and its expression in cultured COLO205 colon cancer cells was increased when compared with that in normal colon cells. It is likely that Hs-CUL-3 is involved in cell proliferation control. 相似文献
195.
196.
To investigate the association of human leukocyte antigen (HLA) with susceptibility and clinical manifestations of sarcoidosis. Fifty-five patients with sarcoidosis were studied by using allele group specific polymerase chain reaction technique (PCR). Our data show that: (1) the gene frequency of HLA-DR5 is significantly increased in patients with sarcoidosis, but that of HLA-DR7 decreased. (2) Gene frequencies of HLA-DR9 and HLA-DR5 are relatively increased in male patients and in patients with stage I and stage IIa, respectively. The results suggest that HLA-DR gene might contribute to the susceptibility as well as to the difference of clinical manifestations in sarcoidosis. 相似文献
197.
Channel crosstalk effects in wavelength-multiplexed subcarrier-multiplexing video transmission systems due to cross-phase modulation are investigated. The crosstalk level depends on the spacing of optical channels. For analogue CATV transmissions in the 1.5 μm window using normal singlemode fibre, it is shown that the number of achievable optical channels is severely limited by cross-phase modulation for typical system parameters 相似文献
198.
199.
200.
It is possible to optimize the performance of the inorganic-organic composites dispersing the inorganic component in the organic matrix on a nanomiter length scale. If dry the inorganic phase cannot be intimately dispersed during the incorporation in the matrix. When the particle surface is organically modified, and the incorporation is made starting from a liquid dispersion (particles in polymer solution), the resulting composites exhibit an excellent homogeneity. Here, monolithic [poly(methyl methacrylate)/monodisperse silica particles] nanocomposites have been prepared and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), micro-hardness, and differential scanning calorimetry (DSC). 相似文献