全文获取类型
收费全文 | 9439篇 |
免费 | 608篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 217篇 |
综合类 | 68篇 |
化学工业 | 2123篇 |
金属工艺 | 283篇 |
机械仪表 | 239篇 |
建筑科学 | 260篇 |
矿业工程 | 29篇 |
能源动力 | 411篇 |
轻工业 | 1335篇 |
水利工程 | 87篇 |
石油天然气 | 69篇 |
无线电 | 838篇 |
一般工业技术 | 1506篇 |
冶金工业 | 1287篇 |
原子能技术 | 109篇 |
自动化技术 | 1230篇 |
出版年
2024年 | 30篇 |
2023年 | 87篇 |
2022年 | 105篇 |
2021年 | 391篇 |
2020年 | 294篇 |
2019年 | 300篇 |
2018年 | 354篇 |
2017年 | 341篇 |
2016年 | 339篇 |
2015年 | 241篇 |
2014年 | 399篇 |
2013年 | 638篇 |
2012年 | 487篇 |
2011年 | 589篇 |
2010年 | 424篇 |
2009年 | 477篇 |
2008年 | 422篇 |
2007年 | 326篇 |
2006年 | 304篇 |
2005年 | 258篇 |
2004年 | 242篇 |
2003年 | 265篇 |
2002年 | 273篇 |
2001年 | 223篇 |
2000年 | 181篇 |
1999年 | 157篇 |
1998年 | 375篇 |
1997年 | 284篇 |
1996年 | 189篇 |
1995年 | 143篇 |
1994年 | 100篇 |
1993年 | 120篇 |
1992年 | 65篇 |
1991年 | 57篇 |
1990年 | 60篇 |
1989年 | 36篇 |
1988年 | 57篇 |
1987年 | 40篇 |
1986年 | 43篇 |
1985年 | 50篇 |
1984年 | 27篇 |
1983年 | 27篇 |
1982年 | 29篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 31篇 |
1976年 | 44篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
S. Danto P. Houizot C. Boussard‐Pledel X.‐H. Zhang F. Smektala J. Lucas 《Advanced functional materials》2006,16(14):1847-1852
Conditions of formation of bulk tellurium chalcogenide glasses, containing 70–80 at % Te associated to Ga and Ge are described. The characteristic temperatures are measured: the glass‐transition temperature, Tg, is situated in the range 140–185 °C and the difference Tx – Tg, where Tx is the onset crystallization temperature, is in the range 76–113 °C. Moreover, the optical transmission window is exceptional, ranging from 1.99 μm in the bandgap up to 28 μm in the phonon region. Developed within the framework of requirements for the Darwin mission (a search for and study of extrasolar planets), feasibility of infrared optical fibers formed from these glasses is studied. Drawing experiments are conducted with the glass Ga2‐Ge3Te15, which possesses the maximum Tx – Tg, and a first optical fiber is presented. 相似文献
62.
da Costa D.B. Yacoub M.D. Filho J.C.S.S. Fraidenraich G. Mendes J.R. 《Communications Letters, IEEE》2006,10(1):13-15
This paper provides simple, exact, new closed-form expressions for the generalized phase crossing rate of Nakagami-m fading channels. Sample numerical results obtained by simulation are presented that validate the formulations developed here. A special case of this formulation is the Rayleigh case, whose result agrees with that obtained elsewhere in the literature. In passing, several new closed-form results concerning the statistics of the envelope, its in-phase and quadrature components, phase, and their time derivatives are obtained. 相似文献
63.
X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces presents several problems related both to peak assignment and to degradation. In this work, we analyse extensively the question of XPS peak assignments in this kind of surfaces. We conclude that in this kind of surfaces using binding energy differences between fluorine and carbon is better than using absolute binding energies. Also a useful relation between fluorine photoelectron energy vs. polymer composition expressed through the atomic ratio fluorine/carbon (F/C) was found. A protocol for data treatment is proposed and applied to a XPS study of the degradation induced by X-ray on high-density polyethylene surfaces modified by direct fluorination. Results obtained for the degradation, namely the atomic ratio F/C obtained by two different methods, combined with angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to study the fluorine concentration profile in depth, producing self-consistent results. 相似文献
64.
This article raises various issues in the design of an efficient BCI system in multimedia applications. The main focus is on one specific modality, namely an electroencephalography (EEG)-based BCI. In doing so, we provide an overview of the most recent progress achieved in this field, with an emphasis on signal processing aspects. 相似文献
65.
The differentiation method of model reduction is shown to be equivalent to forming successive ratios of multipoint Taylor polynomial approximation of the numerator and denominator of the transfer function, respectively. This reformulation allows the method to be applied entirely through a Routh-type array structure. Strong links are seen to exist between the method and other stability preserving methods via this Routh-type structure 相似文献
66.
An experimental study of the effects produced by different parameters of the heat-quenching cycle permitted the optimization of the properties typical of these martensitic stainless steels: hardness and corrosion resistance. The results obtained demonstrate that the heating temperatures currently used in industrial quenching treatment of these steels should be modified. 相似文献
67.
R. Burlot R. Moncorgé H. Manaa G. Boulon Y. Guyot J. Garcia Solé D. Cochet-Muchy 《Optical Materials》1996,6(4):313-330
The polarized absorption and luminescence properties of Nd3+ doped isostructural LiNbO3, MgO:LiNbO3 and LiTaO3 nonlinear bulk single crystals are reported. Pump-probe experiments associated with the Judd-Ofelt approach are used to estimate two types of room temperature cross sections: polarized emission cross sections of the dominant 4F3/2 → 4I1//2 transition near 1085 and 1093 nm and polarized excited-state absorption cross sections in the same spectral domain and in the green spectral range corresponding to self frequency doubling. Self frequency-doubling results are also given in Nd:LiNbO3 and Nd:MgO:LiNbO3 versus sample temperature. 相似文献
68.
AF da Silva P McCollum T Szymanska L de Cossart 《Canadian Metallurgical Quarterly》1996,83(10):1370-1372
A total of 700 patients who had carotid endarterectomy (CEA) in the UK and Ireland during a 6-month interval between March and August 1994 were studied prospectively. Some 108 patients (15.4 per cent) had a contralateral internal carotid artery occlusion. Previous reports have shown an associated stroke rate of about 10 per cent in these patients. This study assessed complications and outcome for patients undergoing CEA with contralateral internal carotid artery occlusion compared with those without. The indications for surgery were comparable between the two groups although the patients with occlusion had a slightly higher incidence of arrhythmia and stroke. Intraoperative shunts were used in a significantly higher proportion of those with occlusion (83.3 versus 64.7 per cent, P = 0.0001). The combined death and stroke rate for patients with occlusion was 5.6 per cent compared with 2.4 per cent for the remainder (P not significant). On the basis of the present data, CEA with a contralateral carotid artery occlusion carries only a slight increase in the rate of postoperative stroke and death. This increase was not statistically significant and is lower than that reported previously. 相似文献
69.
B. Herreros G. Lifante A. Kling J.C. Soares M.F. da Silva P.D. Townsend P.J. Chandler J. Olivares J.M. Cabrera 《Optical Materials》1996,6(4):281-286
We present a structural study of two Nd3+/MgO codoped LiNbO3 waveguides fabricated by two different methods: ion-implantation and proton-exchange. Rutherford backscattering spectrometry in combination with channelling was used to study the influence of the waveguide fabrication method on the possible modification of the LiNbO3 crystal structure within the waveguiding layer. The results show that the ion-implanted waveguide mainly maintains the same properties as the virgin crystal, apart from a deterioration of a thin surface layer, whilst the proton-exchanged waveguide exhibits a quite different behaviour, although its surface is less damaged. 相似文献
70.
Y Yonemura H Kimura S Fushida K Tugawa Y Nakai M Kaji L Fonseca A Yamaguchi I Miyazaki 《Canadian Metallurgical Quarterly》1993,71(8):2448-2453
BACKGROUND: Proliferative activities of tumors are thought to be prognostic features of malignant tumors, but their value as measured by proliferating cell nuclear antigen (PCNA) labeling remains unclear in gastric cancer. METHODS: PCNA labeling rates (LR) were quantified in 121 paraffin-embedded biopsy specimens from primary tumors by immunocytochemistry. RESULTS: Immunohistochemical analyses have demonstrated that PCNA presents an intense staining in the nuclei of tumor cells and mucous neck cells of gastric glands. The PCNA LR ranged from 12% to 79% (mean +/- standard deviation), and a significant correlation was found between bromodeoxyuridine labeling indices and PCNA LR: PCNA LR were closely associated with tumor size, serosal invasion, and nodal involvement. The patients with tumors with high PCNA LR (greater than 40%) were dead significantly earlier than were those with tumors with low PCNA LR: When the PCNA LR and all the clinicopathologic parameters were entered into a Cox regression model, PCNA LR emerged as an independent prognostic factor. CONCLUSION: These results indicate that PCNA LR may be a potentially useful prognostic factor for gastric cancer. 相似文献