全文获取类型
收费全文 | 168132篇 |
免费 | 17575篇 |
国内免费 | 11622篇 |
专业分类
电工技术 | 12848篇 |
技术理论 | 10篇 |
综合类 | 15397篇 |
化学工业 | 23084篇 |
金属工艺 | 10566篇 |
机械仪表 | 11288篇 |
建筑科学 | 13654篇 |
矿业工程 | 5734篇 |
能源动力 | 4555篇 |
轻工业 | 16461篇 |
水利工程 | 4632篇 |
石油天然气 | 6704篇 |
武器工业 | 1937篇 |
无线电 | 19270篇 |
一般工业技术 | 16983篇 |
冶金工业 | 7273篇 |
原子能技术 | 2552篇 |
自动化技术 | 24381篇 |
出版年
2024年 | 984篇 |
2023年 | 2746篇 |
2022年 | 5976篇 |
2021年 | 7902篇 |
2020年 | 5852篇 |
2019年 | 4315篇 |
2018年 | 4735篇 |
2017年 | 5238篇 |
2016年 | 4803篇 |
2015年 | 7068篇 |
2014年 | 8848篇 |
2013年 | 10630篇 |
2012年 | 12661篇 |
2011年 | 12943篇 |
2010年 | 11995篇 |
2009年 | 11578篇 |
2008年 | 11974篇 |
2007年 | 11786篇 |
2006年 | 10427篇 |
2005年 | 8842篇 |
2004年 | 6368篇 |
2003年 | 4576篇 |
2002年 | 4248篇 |
2001年 | 3783篇 |
2000年 | 3447篇 |
1999年 | 2642篇 |
1998年 | 1875篇 |
1997年 | 1548篇 |
1996年 | 1479篇 |
1995年 | 1229篇 |
1994年 | 1071篇 |
1993年 | 761篇 |
1992年 | 619篇 |
1991年 | 441篇 |
1990年 | 408篇 |
1989年 | 376篇 |
1988年 | 252篇 |
1987年 | 204篇 |
1986年 | 140篇 |
1985年 | 96篇 |
1984年 | 78篇 |
1983年 | 62篇 |
1982年 | 55篇 |
1981年 | 53篇 |
1980年 | 57篇 |
1979年 | 30篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1959年 | 22篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
连续法生产冷库板用组合聚醚的研制 总被引:1,自引:0,他引:1
针对国内板材厂家提出用连续法生产厚度在150 mm以上冷库板的要求,通过对聚醚体系、催化体系、发泡体系等进行调整,得到了适合于连续法生产厚度在150 mm以上冷库板的组合料,并成功地用于200 mm厚冷库板的连续化生产,未出现烧心开裂、变形等问题. 相似文献
62.
63.
64.
Wei-Cheng Tian Pang S.W. Chia-Jung Lu Zellers E.T. 《Journal of microelectromechanical systems》2003,12(3):264-272
The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 /spl mu/m (h)/spl times/50 /spl mu/m (w)/spl times/3000 /spl mu/m (l), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, /spl sim/200 /spl mu/m in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly. 相似文献
65.
66.
67.
68.
OBJECTIVE: To study the correlation of development and survival with amplification of c-erbB2 oncogene in endometrial carcinoma. METHODS: The amplification and expression of c-erbB2 oncogene were determined from formalin-fixed, paraffin-embedded tissues of 25 normal, 31 hyperplastic, and 72 malignant samples of the endometrium in 128 patients, using differential polymerase chain reaction (DPCR) and an immunohistochemical technique. RESULTS: Amplified c-erbB2 (2 to 12 copies) were found in two of 25 (8.0%) normal, 15 of 31 (48.4%) hyperplastic, and 45 of 72 (62.5%) malignant samples. When the results of DPCR were compared with those of the immunohistochemical method, the negative findings concide well with one another, i.e., nonamplification was associated with the absence of immunoreactivity. It was noted that the amplified c-erbB2 was found more significantly in complex and a typical hyperplasias than in simple hyperplasias. The high-level c-erbB2 amplification (at least five copies) was significantly correlated with the histological grade of endometrial carcinoma and vascular or lymphatic invasion. No correlation was seen between c-erbB2 amplification and overall survival in the present group of patients. CONCLUSIONS: The amplified c-erbB2 may play a potential role in the early development of some endometrial carcinomas. The high-level c-erbB2 amplification may identify a subset of aggressive endometrial carcinoma that involves vascular or lymphatic invasiveness and poor cell differentiation playing the role of a marker for clinical prognosis. 相似文献
69.
70.
Jianbo Lu & Robert E. Skelton 《Computer-Aided Civil and Infrastructure Engineering》1998,13(6):405-414
A new method for integrated design of passive and active elements is presented. Rather than the existing qualitative selection of parameters for passive elements, a quantitative approach is proposed that finds optimal active and passive parameters with respect to an H2 /H∞ performance requirement. This new approach automatically yields passive designs when the given performance limits are high enough and active (hybrid) designs when the given performance constraints are stringent. Furthermore, our algorithm finds the special performance requirement (the peak of the frequency response) that cannot be satisfied by any passive design. Hence this article shows how to determine when control is required rather than assuming a priori that it is or is not required. A simple design method given herein yields either passive, active, or hybrid designs depending only on the level of the performance constraints that are specified in the statement of the problem. 相似文献