全文获取类型
收费全文 | 18728篇 |
免费 | 1383篇 |
国内免费 | 467篇 |
专业分类
电工技术 | 263篇 |
技术理论 | 1篇 |
综合类 | 1542篇 |
化学工业 | 1662篇 |
金属工艺 | 146篇 |
机械仪表 | 412篇 |
建筑科学 | 717篇 |
矿业工程 | 191篇 |
能源动力 | 186篇 |
轻工业 | 11745篇 |
水利工程 | 428篇 |
石油天然气 | 513篇 |
武器工业 | 51篇 |
无线电 | 314篇 |
一般工业技术 | 1198篇 |
冶金工业 | 435篇 |
原子能技术 | 86篇 |
自动化技术 | 688篇 |
出版年
2024年 | 144篇 |
2023年 | 416篇 |
2022年 | 640篇 |
2021年 | 913篇 |
2020年 | 931篇 |
2019年 | 853篇 |
2018年 | 780篇 |
2017年 | 695篇 |
2016年 | 774篇 |
2015年 | 720篇 |
2014年 | 1025篇 |
2013年 | 1298篇 |
2012年 | 1277篇 |
2011年 | 1217篇 |
2010年 | 834篇 |
2009年 | 723篇 |
2008年 | 645篇 |
2007年 | 950篇 |
2006年 | 953篇 |
2005年 | 790篇 |
2004年 | 601篇 |
2003年 | 586篇 |
2002年 | 488篇 |
2001年 | 335篇 |
2000年 | 356篇 |
1999年 | 262篇 |
1998年 | 219篇 |
1997年 | 166篇 |
1996年 | 151篇 |
1995年 | 154篇 |
1994年 | 113篇 |
1993年 | 98篇 |
1992年 | 81篇 |
1991年 | 74篇 |
1990年 | 53篇 |
1989年 | 48篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1964年 | 4篇 |
1959年 | 5篇 |
1958年 | 4篇 |
1957年 | 3篇 |
1955年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Jozef P H Linssen Anneloes L G M Janssens Hanneke C E Reitsma Wender L P Bredie Jacques P Roozen 《Journal of the science of food and agriculture》1993,61(4):457-462
Taste recognition threshold concentrations (TRTC) of styrene were determined in samples of oil-in-water emulsions (30–300 g kg?1 oil) and yoghurts (1–30 g kg?1 fat), spiked with styrene. The observed TRTC increased linearly with increasing fat content and ranged from 0–3 to 2–1 mg kg?1 for the emulsions and from 36 to 171 g kg?1 for the yoghurts. Styrene equilibrium partition coefficients between emulsions and their respective vapour phases were determined. The concentrations of styrene in the continuous aqueous phase of the emulsions and yoghurts were calculated at the TRTC. The styrene concentrations in the continuous phase had constant values of about 15 g kg?1 indicating that perception of styrene for oil-in–water emulsions is determined by the aqueous phase of the emulsion. The concentrations of styrene in the vapor phases above the emulsions and yoghurts were also calculated and were found to be constant at the TRTC. This relationship probably resulted from the equilibrium of distribution of styrene between the respective phases. Commercial yoghurt packed in polystyrene beakers contained styrene levels in the range 2–11 g kg?1, much lower then the TRTC reported. 相似文献
92.
对长石、石英、龙岩土、莱阳土4种因素各取4个水平,用正交表L16(45)安排16个试验,分析了这16个试验产品的吸水率、白度、热稳定性与每种因素各水平之间的关系.得出了白瓷坯料的最佳配方。其中,长石19,石英21,龙岩土21.莱阳土0. 相似文献
93.
《Landscape Research》2007,32(5):533-557
Within the lifetime of a generation of people now involved in work in the cattle and beef industry in South Dakota, the landscapes of social reproduction that support and give shape to life for people there have been rearranged. Many of the social and physical relationships that developed to support smaller-scale, diverse farms and their surrounding communities are being made redundant by a new system of beef production and retailing. The costs of these redundancies are felt in dwindling small towns and an ever sparser rural population. Considering these changes as parts of landscapes of social reproduction is a means to connect the political and corporate logic driving our food systems to the spatial production of difference in the conditions for livelihood, as well as the spatial production of livelihood itself for both producers and consumers. Such an analysis is necessary in order to address the injustices inherent within our current food system. 相似文献
94.
Ioannis D. Moscholios Michael D. Logothetis 《International Journal of Communication Systems》2006,19(1):67-93
We consider a single link loss system of quasi‐random input, described by the Engset multirate loss model (EnMLM). Blocked calls may once reattempt to be connected to the system requiring less bandwidth; then the system is described by the single retry model for finite sources (f‐SRM). The EnMLM and the f‐SRM are extended with the single threshold finite source model (f‐STM), where calls may attempt to be connected to the system with less bandwidth requirements, according to the link occupancy, before blocking occurs. We focus on CBP equalization in the EnMLM, f‐SRM and f‐STM, under the bandwidth reservation (BR) policy. For this analysis, we apply two approximate methods, the Roberts' method and the method of reverse transition rates (RTR), which lead to a recursive CBP calculation. We evaluate the accuracy of the above models under the BR policy by comparing the analytical with simulation CBP results, based on the relative approximation errors (RAE). The results are highly satisfactory because they show that the proposed models (formulas) lead to small RAE. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
95.
96.
螺旋弹簧的非线性理论及实验研究 总被引:3,自引:0,他引:3
本文通过对经典的圆柱螺旋弹簧理论的修正,给出了非线性理论解析公式.还通过对螺旋弹簧的精确测量和处理,验证了本文的非线性理论. 相似文献
97.
将圆柱形螺旋弹簧设计中的部分常用公式组合成一组仅与弹簧指数C有关的公式,并将C=4~14代入计算而获得一套参数表,由此,可提高圆柱形螺旋弹簧的设计效率。 相似文献
98.
In 1853 Sylvester stated and proved an elegant formula that expresses the polynomial subresultants in terms of the roots of the input polynomials. Sylvester’s formula was also recently proved by Lascoux and Pragacz using multi-Schur functions and divided differences. In this paper, we provide an elementary proof that uses only basic properties of matrix multiplication and Vandermonde determinants. 相似文献
99.
100.
准确估算集群系统所需无线信道数是工程设计中的一个重要的关键环节。本文从讨论系统业务、系统话务量出发,提出了一种正确使用爱尔兰—B公式(或巴姆表)确定集群系统中无线信道数的新方法。继而,较为详细地定量分析了集群方式对系统话务量的影响。最后,针对实际工程设计,推荐了一个集群系统容量计算的经验公式。 相似文献