全文获取类型
收费全文 | 3807篇 |
免费 | 111篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 279篇 |
金属工艺 | 17篇 |
机械仪表 | 40篇 |
建筑科学 | 70篇 |
矿业工程 | 3篇 |
能源动力 | 35篇 |
轻工业 | 128篇 |
水利工程 | 15篇 |
石油天然气 | 8篇 |
无线电 | 308篇 |
一般工业技术 | 396篇 |
冶金工业 | 2276篇 |
原子能技术 | 24篇 |
自动化技术 | 285篇 |
出版年
2022年 | 15篇 |
2021年 | 22篇 |
2020年 | 27篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 28篇 |
2016年 | 28篇 |
2015年 | 46篇 |
2014年 | 37篇 |
2013年 | 119篇 |
2012年 | 49篇 |
2011年 | 81篇 |
2010年 | 55篇 |
2009年 | 42篇 |
2008年 | 72篇 |
2007年 | 57篇 |
2006年 | 56篇 |
2005年 | 57篇 |
2004年 | 59篇 |
2003年 | 52篇 |
2002年 | 50篇 |
2001年 | 36篇 |
2000年 | 47篇 |
1999年 | 100篇 |
1998年 | 686篇 |
1997年 | 393篇 |
1996年 | 260篇 |
1995年 | 152篇 |
1994年 | 155篇 |
1993年 | 146篇 |
1992年 | 52篇 |
1991年 | 50篇 |
1990年 | 62篇 |
1989年 | 46篇 |
1988年 | 44篇 |
1987年 | 45篇 |
1986年 | 50篇 |
1985年 | 53篇 |
1984年 | 23篇 |
1983年 | 41篇 |
1982年 | 29篇 |
1981年 | 34篇 |
1980年 | 36篇 |
1978年 | 21篇 |
1977年 | 59篇 |
1976年 | 115篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1972年 | 13篇 |
1970年 | 14篇 |
排序方式: 共有3922条查询结果,搜索用时 62 毫秒
1.
2.
AD Santin PL Hermonat JC Hiserodt J Fruehauf V Schranz D Barclay S Pecorelli GP Parham 《Canadian Metallurgical Quarterly》1997,64(3):477-480
Tumor cells from eight freshly isolated cervical cancers (i.e., four adenocarcinomas and four squamous carcinomas) were analyzed for their production of the immune-inhibitory cytokine transforming growth factor-beta (TGF-beta) in vitro. All fresh adenocarcinomas secreted significant levels of TGF-beta (mean 397, range between 207 and 782 pg/ml/10(5) cells/48 hr). In contrast, no detectable TGF-beta was present in the supernatants from the four fresh squamous carcinoma cultures (P < 0.001). These data suggest that major differences in the secretion of the immunoinhibitory cytokine TGF-beta exist between squamous cell carcinomas and adenocarcinomas of the uterine cervix. Furthermore, these findings suggest that at least some of the differences in the natural biologic behavior, as well as in the response to radiation treatment, between these two histologic types of cervical cancer could be related to differences in secretion of this immune-inhibitory cytokine. 相似文献
3.
4.
5.
6.
Anguilla is a UK overseas (non-independent) territory in the Caribbean. It is a small middle-income island with a population of 13 000, and recent statistics indicate that it is more dependent on tourism than any other country or territory in the world. Rapid population growth and development have placed more emphasis on the need for human health and environmental protection. For the first time, a systematic water-quality monitoring programme has been developed, based on the realities of the local situation, e.g. low resource base, limited capabilities, dependence on household rainwater catchment, storage cisterns, and a poor water-supply network. Development of the programme incorporated the key themes of pragmatic, realistic, incremental, responsive, and consultative approaches. 相似文献
7.
8.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration. 相似文献
9.
The current, most frequently employed, commercial route to produce hydroxyapatite prosthetic coatings is plasma spraying. However, this has several important limitations especially for textured surfaces. Low temperature methods of coating fabrication such as cathodic electrodeposition are attractive alternatives. However, quantitative characterisation of the phase composition of thin electrodeposited coatings can be problematic. An X-ray diffraction method, which provides quantitative compositional information without reference to external or internal standards, is introduced and validated. The method can also be applied when Bragg peaks from the supporting substrate are apparent within the data and preferred orientation can be tolerated. This method has been used to examine in detail the microstructure of electrodeposited coatings which are compared directly with those formed by a commercial plasma spraying process.We show that, unlike the plasma sprayed coatings, the electrodeposited material consists of a single crystalline phase (hydroxyapatite) and a significantly reduced amorphous phase. The electrodeposited coatings also possess significantly more microstrain and a smaller crystallite size than the corresponding plasma sprayed material. 相似文献
10.
Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles. 相似文献