全文获取类型
收费全文 | 39525篇 |
免费 | 4158篇 |
国内免费 | 2255篇 |
专业分类
电工技术 | 2738篇 |
技术理论 | 2篇 |
综合类 | 3350篇 |
化学工业 | 6056篇 |
金属工艺 | 2292篇 |
机械仪表 | 2404篇 |
建筑科学 | 2663篇 |
矿业工程 | 1187篇 |
能源动力 | 1317篇 |
轻工业 | 3517篇 |
水利工程 | 940篇 |
石油天然气 | 1784篇 |
武器工业 | 432篇 |
无线电 | 4310篇 |
一般工业技术 | 4368篇 |
冶金工业 | 2713篇 |
原子能技术 | 630篇 |
自动化技术 | 5235篇 |
出版年
2024年 | 243篇 |
2023年 | 768篇 |
2022年 | 1380篇 |
2021年 | 1726篇 |
2020年 | 1342篇 |
2019年 | 1126篇 |
2018年 | 1251篇 |
2017年 | 1262篇 |
2016年 | 1283篇 |
2015年 | 1630篇 |
2014年 | 1997篇 |
2013年 | 2364篇 |
2012年 | 2622篇 |
2011年 | 2856篇 |
2010年 | 2570篇 |
2009年 | 2378篇 |
2008年 | 2361篇 |
2007年 | 2351篇 |
2006年 | 2051篇 |
2005年 | 1798篇 |
2004年 | 1363篇 |
2003年 | 1257篇 |
2002年 | 1397篇 |
2001年 | 1256篇 |
2000年 | 903篇 |
1999年 | 728篇 |
1998年 | 747篇 |
1997年 | 610篇 |
1996年 | 507篇 |
1995年 | 377篇 |
1994年 | 266篇 |
1993年 | 231篇 |
1992年 | 164篇 |
1991年 | 113篇 |
1990年 | 85篇 |
1989年 | 75篇 |
1988年 | 68篇 |
1987年 | 50篇 |
1986年 | 49篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 13篇 |
1977年 | 56篇 |
1976年 | 100篇 |
1961年 | 8篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Kwong-Sak Leung Han-Bing Ji Yee Leung 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》1997,27(3):533-543
Associative-memory neural networks with adaptive weighted outer-product learning are proposed in this paper. For the correct recall of a fundamental memory (FM), a corresponding learning weight is attached and a parameter called signal-to-noise-ratio-gain (SNRG) is devised. The sufficient conditions for the learning weights and the SNRG's are derived. It is found both empirically and theoretically that the SNRG's have their own threshold values for correct recalls of the corresponding FM's. Based on the gradient-descent approach, several algorithms are constructed to adaptively find the optimal learning weights with reference to global- or local-error measure. 相似文献
22.
M Beksa? MS Beksa? VB Tipi HA Duru MU Karakás AN Cakar 《Canadian Metallurgical Quarterly》1997,30(3):145-150
The endothelium participates actively in homeostatic mechanisms such as the regulation of vascular tone and maintenance of a nonthrombotic environment, as well as directing biological responses such as leukocyte trafficking to inflammatory sites. Disruption of these processes leads to disease. In the antiphospholipid antibody syndrome autoantibodies provoke the endothelium to develop a prothrombotic surface. In systemic vasculitides associated with presence of antineutrophil cytoplasm antibodies, it is likely that the autoantibodies incite premature neutrophil activation, disrupted neutrophil-endothelium interactions and endothelial damage. This review considers how normal endothelial functions may be subverted in disease and how active endothelial responses may contribute to disease. 相似文献
23.
NW Tomkins NN Jonsson MP Young AN Gordon KA McColl 《Canadian Metallurgical Quarterly》1997,75(10):722-723
On the basis of clinical signs and histological findings eight 9-month-old male rusa deer (Cervus timorensis) were diagnosed with sheep associated-malignant catarrhal fever. Following a variable course involving rectal temperatures around 40.5 degrees C, depression, inappetence, diarrhoea, corneal opacity and hypopyon all animals died or were euthanased over a 5-week period. Severe multifocal vasculitis, mainly periglomerular and in the arcuate vessels were consistent histological findings which in the past have been adequate to confirm clinical diagnosis of sheep associated-malignant catarrhal fever. A nested polymerase chain reaction test has been used to detect a sheep associated-malignant catarrhal fever PRC product, 238 base-pairs in size, in DNA extracted from lymphocyte preparations. The result supported the diagnosis of sheep associated-malignant catarrhal fever in these deer. 相似文献
24.
AN Parkhomenko 《Canadian Metallurgical Quarterly》1997,69(6):55-59
The aim of the study was to discover determinants of the onset of life threatening ventricular tachyarrhythmia. 102 patients with acute myocardial infarction and 32 patients with postinfarction cardiosclerosis were examined. The data gained at programmed ventricular stimulation, high resolution ECG, Holter ECG monitoring, spectral analysis of cardiac rhythm variability and two-dimension echocardiography proved the importance of early postinfarction left ventricular dilatation in the onset of electrical cardiac instability, establishment of anatomic substrate of monomorphic ventricular tachycardias, low variability of cardiac rhythm. The findings evidence that MI patients with late ventricular potentials and end-diastolic left ventricular index above 100 ml/m2 in subacute period may be considered as a group of high risk in need of individual approach and further therapy. The discovered lowering of informative value of non-invasive methods in patients late after MI dictates the necessity of new approaches to detection of electrophysiological disturbances and sudden death risk in registration of postinfarction dilatation of the heart. 相似文献
25.
LG Westergaard PE Rasmussen S Maigaard HJ Ingerslev AN Andersen JF Larsen J Starup PJ Hornnes CY Andersen 《Canadian Metallurgical Quarterly》1993,155(33):2511-2514
Medical indications for in vitro fertilization and embryo transfer (IVF-ET) internationally and in Denmark are reviewed. Reports from large international centres document that tubal infertility, unexplained infertility, endometriosis and male infertility are equally good indications for IVF. Traditionally, tubal infertility has been the only medical indication qualifying for IVF treatment within the National Health Service in Denmark. Thus, in this country, couples with unexplained and male infertility and with endometriosis have to pay up to 25,000 D.Kr. per IVF-ET treatment in private fertility clinics. Since there is no scientific basis for this discrimination, it is urged that the present rules are changed, so that couples with unexplained and male infertility and endometriosis are also allowed IVF treatment free of charge in the public fertility clinics. 相似文献
26.
Voigt线型及其精确快速算法 总被引:1,自引:1,他引:0
通过把上半复平面分为4个区,并在每一区利用不同近似,建立了一种精确快速计算Voigt函数、修正的Voigt函数和Voigt函数偏导数的算法,其最大相对误差小于5×10-4.该算法是Line-by-Line大气透过率/辐射强度计算及其相关应用的有效算法. 相似文献
27.
ICA是一种含有中间件的网络软件体系结构,旨在以结构进化取得功能突破,据以全面支持来自用户的以及来自系统的各种应用需要。ICA的出台,表明国际上已建立起一种未来网定位新理念。ICA所代表的“信息通信”领域内的网络软件结构进化,立足于把未来网规范为三层结构,即“应用(Application)层”、“中间件(Middleware)层”和“基础(Baseware)层”。ICA的出现,对我国谋求新崛起是大好机遇,这不仅可以直接振兴我国网络软件产业,更可激励我国在新一轮的网络进化的进程中力争跻身“领潮国”的行列。“ICA融合了各种最新信息技术的长处”。ICA结构进化,标志着当今网络进化的时代特征。推进和实现基于ICA的未来网,有着较佳的可行性。 相似文献
28.
网格曲面中孔洞的光滑填充算法研究 总被引:14,自引:0,他引:14
三角网格模型是几何描述的一种重要形式,有着广泛的应用。但三角网络模型常常会存在孔洞缺陷。这些孔洞的存在一方面影响视觉效果,另一方面会影响许多后续的操作,如快速原型制造、有限元分析等,因此有必要对这些孔洞进行修补。目前绝大多数孔洞填充算法是将网格模型中的孔洞提取成空间多边形,并对孔洞多边形进行三角化。这种处理方法的主要缺陷是没有考虑网格曲面在孔洞附近的几何形态,因而填充部分不能与整个曲面光滑地融为一体。笔者提出了一种三角网格曲面中孔洞的光滑填充算法。该算法根据孔洞周围网格曲面的几何信息来增加孔洞内部的采样点,然后再对增加的采样点进行三角化,较好地解决了填充部分与整体曲面光滑连接的问题。 相似文献
29.
The deactivation characteristics of Pd/SiO2 in the selective hydrogenation of acetylene were correlated with changes in the amount of the C4 species produced. The amounts of butenes produced changed in parallel with the catalyst activity, indicating that the rate limiting step for butene production was the same as that for acetylene hydrogenation. On the other hand, the amount of 1,3-butadiene produced changed, showing a maximum with catalyst deactivation because 1,3-butadiene is an intermediate in the sequential reaction process which involves both the production and consumption of 1,3-butadiene. This was verified by a simultaneous TG/reaction experiment showing that 1,3-butadiene was a precursor of green oil. The catalyst showed a self-regenerative behavior in its activity and the amounts of C4 species produced during the early stage of deactivation because two opposite factors, which contributed to either the lowering or the promotion of activity, were involved in the process. A specific type of polymer species, produced during the initial period of deactivation, is proposed to be responsible for the promotion of catalyst activity. 相似文献
30.
H. Ji D. Chopp J. E. Dolbow 《International journal for numerical methods in engineering》2002,54(8):1209-1233
A hybrid numerical method for modelling the evolution of sharp phase interfaces on fixed grids is presented. We focus attention on two‐dimensional solidification problems, where the temperature field evolves according to classical heat conduction in two subdomains separated by a moving freezing front. The enrichment strategies of the eXtended Finite Element Method (X‐FEM) are employed to represent the jump in the temperature gradient that governs the velocity of the phase boundary. A new approach with the X‐FEM is suggested for this class of problems whereby the partition of unity is constructed with C1(Ω) polynomials and enriched with a C0(Ω) function. This approach leads to jumps in temperature gradient occurring only at the phase boundary, and is shown to significantly improve estimates for the front velocity. Temporal derivatives of the temperature field in the vicinity of the phase front are obtained with a projection that employs discontinuous enrichment. In conjunction with a finer finite difference grid, the Level Set method is used to represent the evolution of the phase interface. An iterative procedure is adopted to satisfy the constraints on the temperature field on the phase boundary. The robustness and utility of the method is demonstrated with several benchmark problems of phase transformation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献