全文获取类型
收费全文 | 21639篇 |
免费 | 944篇 |
国内免费 | 314篇 |
专业分类
电工技术 | 475篇 |
综合类 | 543篇 |
化学工业 | 3840篇 |
金属工艺 | 534篇 |
机械仪表 | 759篇 |
建筑科学 | 903篇 |
矿业工程 | 180篇 |
能源动力 | 597篇 |
轻工业 | 2179篇 |
水利工程 | 251篇 |
石油天然气 | 176篇 |
武器工业 | 27篇 |
无线电 | 2467篇 |
一般工业技术 | 2956篇 |
冶金工业 | 3738篇 |
原子能技术 | 179篇 |
自动化技术 | 3093篇 |
出版年
2023年 | 103篇 |
2022年 | 185篇 |
2021年 | 509篇 |
2020年 | 282篇 |
2019年 | 352篇 |
2018年 | 407篇 |
2017年 | 384篇 |
2016年 | 452篇 |
2015年 | 376篇 |
2014年 | 560篇 |
2013年 | 1103篇 |
2012年 | 865篇 |
2011年 | 1050篇 |
2010年 | 800篇 |
2009年 | 872篇 |
2008年 | 851篇 |
2007年 | 873篇 |
2006年 | 766篇 |
2005年 | 650篇 |
2004年 | 726篇 |
2003年 | 934篇 |
2002年 | 1218篇 |
2001年 | 1032篇 |
2000年 | 605篇 |
1999年 | 545篇 |
1998年 | 1354篇 |
1997年 | 885篇 |
1996年 | 644篇 |
1995年 | 444篇 |
1994年 | 332篇 |
1993年 | 360篇 |
1992年 | 201篇 |
1991年 | 159篇 |
1990年 | 150篇 |
1989年 | 138篇 |
1988年 | 137篇 |
1987年 | 111篇 |
1986年 | 114篇 |
1985年 | 153篇 |
1984年 | 90篇 |
1983年 | 98篇 |
1982年 | 84篇 |
1981年 | 103篇 |
1980年 | 100篇 |
1979年 | 64篇 |
1978年 | 49篇 |
1977年 | 100篇 |
1976年 | 192篇 |
1975年 | 52篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
101.
A. Bianconi Y. Busby M. Fratini V. Palmisano L. Simonelli M. Filippi S. Sanna F. Congiu A. Saccone M. Giovannini S. De Negri 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):495-501
Here we report synthesis and characterization of high quality samples of the superconducting system Mg1−x
Al
x
B2, with a novel optimized preparation method, in a wide range of Al concentration. All the physical properties of the samples
can be tuned continuously with increasing Al content. We have characterized the samples for their structural, morphological
and magnetic properties with high resolution XRD, SEM-EDS and susceptibility measurements. We have prepared a large number
of Al doped MgB2 in the range 0<x<0.57. All the samples are bulk superconductors and the critical temperature show a smooth and regular behavior as a function
of x.
This work was supported by European project 517039 “Controlling Mesoscopic Phase Separation” (COMEPHS) (2005).
An erratum to this article can be found at 相似文献
102.
Recent years have witnessed major governmental initiatives regarding critical infrastructure protection (CIP). During that same time, critical infrastructures (CIs) have undergone massive institutional restructuring under the headings of privatization, deregulation and liberalization. Little research has gone into understanding the interactions between these two developments. In this article, we outline the consequences of institutional restructuring for the changing ways in which CIs ensure the reliability and security of their networks and services. Neither Normal Accident Theory nor High‐Reliability Theory can account for reliability under these conditions. We then investigate the implications of these findings for CIP. 相似文献
103.
104.
可实现性k-ε模型在水轮机流场计算中的应用 总被引:9,自引:1,他引:8
本文针对目前水轮机转轮内部流场计算中存在的偏工况计算困难的问题,探讨了一种不同于标准k-ε模型的可实现性k-ε模型(Realizablek-ε在水轮机偏工况计算中的应用。文章首先对该模型的优点进行了分析。然后针对某混流式转轮进行了计算,计算与实验结果比较表明,二者在设计工况附近时十分接近;在小开底小流量下,对转轮的主要特征的预测也是成功的。但小开度下计算值与实测值之间的差别也表明,在水轮机偏工况计算中,该湍流模型有待进一步改进。 相似文献
105.
As an alternative to previously developed catalytic FeCrAlloy fibre mat burners based on perovskite catalysts, new catalytic burners have been developed based on Pd catalyst on lantana-stabilised Al2O3 and different fibre structures (NIT100A, NIT100S and NIT200S by ACOTECH NV). All development steps are considered, shifting from catalyst preparation (based on combustion synthesis of γ-Al2O3) to the optimisation of lantana and Pd loadings, from the definitions of the best catalyst-deposition conditions (washcoating) to the catalytic burners performances, determined in an ad hoc developed combustion chamber. The results show almost half pollutants emissions and better performance compared to various non-catalytic counterparts, especially as far as CO and NOx emissions are concerned. Some flame instability problems were though registered, especially for one of the catalytic burner mattresses employed, at low specific power inputs and excesses of air (<375 kW/m2 and <12%, respectively). Further, PdO/Pd transition is shown to influence the dynamic behaviour of the catalytic burners. 相似文献
106.
框架结构焦仓的定向倒塌爆破 总被引:4,自引:1,他引:3
介绍了框架结构焦仓定向爆破拆除的设计与施工,着重介绍了爆破参烽的选取及安全防护措施。达到预期的爆破效果。 相似文献
107.
The key synchronization aspects in the system design of a QQPSK (quadrature-quadrature phase-shift-keying) modem are addressed. The sensitivity of the data demodulator to synchronization errors is discussed, and contextually the performances of some IF and baseband carrier phase and symbol timing recovery schemes are evaluated both theoretically and by computer simulations. In particular, a fourth-power IF carrier/clock regenerator and two baseband clock recovery schemes, with and without the aid of data decisions, respectively, are taken into account. The analysis shows on the one hand the substantial robustness of QQPSK to carrier phase errors and the adequacy of the examined carrier extraction scheme. On the other hand, the remarkable sensitivity of QQPSK to symbol timing inaccuracy is stressed and the need to resort to the newly proposed decision-aided baseband clock recovery scheme is pointed out 相似文献
108.
109.
110.
We have studied the short term C mineralization of six wastes from important food industries, one sludge from a biogas plant and three composts. All the wastes were characterized chemically and fractionated according to the Van Soest method. The fresh wastes were incubated under controlled environment conditions to determine the C mineralization rate. Based on first order mineralization kinetics, we calculated the hypothetical amount of stable C in the wastes as the amount of C that would not be mineralized within one year under field conditions. The percentage of stable organic C in the organic matter was in general much larger in the composts than in the other wastes, but when expressed on dry matter, the non-composted wastes had comparable or larger amounts of stable organic C than the composts and have a considerable potential for supplying organic matter to soils, and hence for C sequestration. The amount of stable organic C could best be predicted by the total N content of the wastes (R
a
2 = 0.855), whereas the results of the fractionation had very little predictive power, probably due to problems related to the high ash content of some of the wastes. An index that combined stable organic C and N and P content in the wastes was calculated to assess possible limitations for applying these wastes in agriculture. Under current nutrient legislation in Western Europe, a number of these wastes will only be usable in small amounts, but these and other food industry wastes could still prove to be valuable soil amendments in nutrient poor situations, for increasing soil organic C content and supplying nutrients. 相似文献