全文获取类型
收费全文 | 25047篇 |
免费 | 1290篇 |
国内免费 | 429篇 |
专业分类
电工技术 | 847篇 |
综合类 | 495篇 |
化学工业 | 3771篇 |
金属工艺 | 754篇 |
机械仪表 | 858篇 |
建筑科学 | 1153篇 |
矿业工程 | 171篇 |
能源动力 | 616篇 |
轻工业 | 2727篇 |
水利工程 | 309篇 |
石油天然气 | 293篇 |
武器工业 | 75篇 |
无线电 | 3066篇 |
一般工业技术 | 3437篇 |
冶金工业 | 4565篇 |
原子能技术 | 319篇 |
自动化技术 | 3310篇 |
出版年
2024年 | 74篇 |
2023年 | 246篇 |
2022年 | 518篇 |
2021年 | 792篇 |
2020年 | 557篇 |
2019年 | 550篇 |
2018年 | 623篇 |
2017年 | 603篇 |
2016年 | 656篇 |
2015年 | 613篇 |
2014年 | 874篇 |
2013年 | 1329篇 |
2012年 | 1209篇 |
2011年 | 1409篇 |
2010年 | 1078篇 |
2009年 | 1019篇 |
2008年 | 1089篇 |
2007年 | 1005篇 |
2006年 | 821篇 |
2005年 | 737篇 |
2004年 | 603篇 |
2003年 | 561篇 |
2002年 | 563篇 |
2001年 | 512篇 |
2000年 | 462篇 |
1999年 | 518篇 |
1998年 | 1504篇 |
1997年 | 936篇 |
1996年 | 712篇 |
1995年 | 481篇 |
1994年 | 422篇 |
1993年 | 419篇 |
1992年 | 234篇 |
1991年 | 218篇 |
1990年 | 206篇 |
1989年 | 220篇 |
1988年 | 177篇 |
1987年 | 148篇 |
1986年 | 153篇 |
1985年 | 200篇 |
1984年 | 145篇 |
1983年 | 134篇 |
1982年 | 111篇 |
1981年 | 127篇 |
1980年 | 121篇 |
1979年 | 114篇 |
1977年 | 153篇 |
1976年 | 220篇 |
1975年 | 70篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
This paper describes the application of an expert system for the evaluation of the short-term thermal rating and temperature rise of overhead conductors. The expert system has been developed using a database and Leonardo expert system shell which is gaining popularity among commercial tools for developing expert system applications. The expert system has been found to compare well when evaluated against site tests. A practical application is given to demonstrate the usefulness of the expert system developed 相似文献
72.
The specific surface areas (A) of different clay mineral powders were measured by both the BET method and by thin layer wicking. The values of A for the BET and the wicking experiments coincided within a few percent. Thus, the simple and inexpensive thin layer wicking approach may well suffice to obtain reliable specific surface area values for most powders. From the wicking data it is also possible to obtain a rough estimate of the average particle size. 相似文献
73.
74.
Kamper M.J. Van der Merwe F.S. Williamson S. 《Energy Conversion, IEEE Transaction on》1996,11(3):547-555
The finite element analysis method is used directly in optimisation algorithms to optimise in multidimensions the design of the cageless reluctance synchronous machine. Two optimisation methods are evaluated to minimise or maximise the function value. These are the direction set method of Powell and the quasi-Newton algorithm. Both methods proved to be successful, with some advantages and disadvantages. Using these methods at a power level below 10 kW, results are given of structures of the reluctance synchronous machine which have been optimised according to specific criteria. Calculated and measured results show that the maximum torque optimum designed reluctance synchronous machine has the advantages of high power density and high efficiency 相似文献
75.
A. Benati M.A. Butturi C. Capperdoni M.C. Carotta G. Martinelli M. Merli L. Passari G. Sartori R. Van Steenwinkel G.M. Youssef 《Solar Energy Materials & Solar Cells》1996,43(2):183
The newly developed ingot growing techniques, as the three-grain and the columnar multigrain ingot processes, are now offering the possibility of slicing thinner wafers (≤ 100 μm). In this paper we present the results obtained on p type large area (≥ 100 cm2) and 100 μm thick wafers by using both conventional and reverse cell manufacturing technologies.The conventional cells are provided with aluminium or boron BSF plus screen-printed silver mirror or a silver-aluminium net; the reverse cells have a FSF and the deep back junction completely covered by a screen-printed or CVD silver layer.The constructing parameters have been chosen on the base of one and two dimensions modeling and both raw material and devices have been completely characterized.This work shows that very thin wafers do not introduce serious problems for the conventional manufacturing of solar cells. The efficiencies of the normal and of the reverse cells are found to be comparable and are of the same order than those of thicker cells, however at a significant lower cost. The main obtained result has to be related to the demonstration of a cell manufacturing feasibility starting from very thin wafers. 相似文献
76.
Kuppens S.J.M. Van Eijkelenborg M.A. Schrama C.A. Van Exter M.P. Woerdman J.P. 《Quantum Electronics, IEEE Journal of》1996,32(3):383-387
We have measured the quantum-limited linewidths of small HeNe 3.39 μm and HeXe 3.51 μm lasers. In contrast to the expected Schawlow-Townes behaviour strong deviations from the inverse power dependence are observed, leading to a double-valued relation between the linewidth and the output power. This phenomenon is analyzed in terms of the increase of spontaneous emission, by a factor Nsp, due to incompleteness of the inversion. Our analysis shows that typically Nsp has a value ranging from 1-10. Combining existing models for the pump power dependence of the level populations with measurements of the small signal gain, we are able to explain the observed double-valued linewidth behaviour in a quantitative way 相似文献
77.
Activation of macrophages by T cells is considered an initiating event in glomerular crescent formation. Since interferon-gamma (INF gamma) is a key mediator in T-cell-mediated activation of macrophages, we decided to test its role in a model of crescentic glomerulonephritis. An anti-glomerular basement membrane (GBM) serum was injected intravenously in presensitized wild-type or IFN gamma receptor deficient (IFN gamma(R)-/-) mice. Glomerulonephritis with glomerular crescents and tubulointerstitial inflammation developed in both strains, even though most evaluated morphological parameters and proteinuria indicated a less severe pathology in the mutant mice compared to the wild type. Thus, IFN gamma is not essential either for glomerular crescent formation or for tubulointerstitial involvement in anti-GBM glomerulonephritis in mice. In conclusion, the role of macrophages in this model might have been overestimated, or other cytokines may compensate for deficient IFN gamma signaling in the activation of macrophages. 相似文献
78.
Ferdinand P. Ferragu O. Lechien J.L. Lescop B. Magne S. Marty V. Rougeault S. Kotrotsios G. Neuman V. Depeursinge Y. Michel J.B. Van Uffelen M. Varelas D. Berthou H. Pierre G. Renouf C. Jarret B. Verbandt Y. Stevens W. Voet M.R.H. Toscano D. 《Lightwave Technology, Journal of》1995,13(7):1303-1313
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging 相似文献
79.
We present a theory for passive mode-locking in semiconductor laser structures using a semiconductor laser amplifier and absorber. The mode-locking system is described in terms of the different elements in the semiconductor laser structure. We derive mode-locking conditions and show how other mode-locking parameters, like pulse width and pulse energy, are determined by the mode-locking system. System parameters, like bandwidth, dispersion, and self-phase modulation are shown to play an important role in mode-locking conditions and results. We also discuss the effects of pulse collisions and positions of the mode-locking elements inside the cavity on mode-locking stability and show that these effects can be easily included in the presented model. Finally, we give a number of design rules and recommendations for fabricating passively mode-locked lasers 相似文献
80.
The network interconnection and its regulation consist in solving the following dilemma: increase competition and preserve the universal service through access charges, which symbolizes today institutional organization within the telecommunication industry. This paper presents some of the economic and social factors that drive the interconnection policies namely ona (open network architecture) in the United States, or onp (open network provision) in Europe. In the first section, we list some social and economical issues related to open network policies. In the second section, we study the different answers brought up by the regulator through alternative interconnection price formulas. In conclusion, we discuss the stakes and risks of interconnection, while the technological evolution of network introduces intelligent software in switching équipement and implements the tremendous abilities of the digital broadband networks. 相似文献