全文获取类型
收费全文 | 18371篇 |
免费 | 2070篇 |
国内免费 | 1355篇 |
专业分类
电工技术 | 3840篇 |
综合类 | 1948篇 |
化学工业 | 1141篇 |
金属工艺 | 390篇 |
机械仪表 | 1138篇 |
建筑科学 | 1065篇 |
矿业工程 | 480篇 |
能源动力 | 846篇 |
轻工业 | 326篇 |
水利工程 | 901篇 |
石油天然气 | 471篇 |
武器工业 | 151篇 |
无线电 | 1738篇 |
一般工业技术 | 1176篇 |
冶金工业 | 495篇 |
原子能技术 | 205篇 |
自动化技术 | 5485篇 |
出版年
2024年 | 86篇 |
2023年 | 208篇 |
2022年 | 476篇 |
2021年 | 522篇 |
2020年 | 553篇 |
2019年 | 532篇 |
2018年 | 474篇 |
2017年 | 570篇 |
2016年 | 640篇 |
2015年 | 752篇 |
2014年 | 1079篇 |
2013年 | 1091篇 |
2012年 | 1247篇 |
2011年 | 1507篇 |
2010年 | 1042篇 |
2009年 | 1183篇 |
2008年 | 1161篇 |
2007年 | 1374篇 |
2006年 | 1109篇 |
2005年 | 951篇 |
2004年 | 839篇 |
2003年 | 640篇 |
2002年 | 573篇 |
2001年 | 491篇 |
2000年 | 409篇 |
1999年 | 383篇 |
1998年 | 326篇 |
1997年 | 260篇 |
1996年 | 220篇 |
1995年 | 204篇 |
1994年 | 157篇 |
1993年 | 142篇 |
1992年 | 98篇 |
1991年 | 74篇 |
1990年 | 61篇 |
1989年 | 71篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1963年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
一种基于时间戳认证的零水印方案设计 总被引:1,自引:0,他引:1
零水印方法是一种新的数字水印方法。本文介绍了零水印的概念及零水印技术的关键问题,提出了一种基于时间戳认证的零水印方案。该方案很好地解决了非零水印的不可见性与鲁棒性之间的矛盾,具有可行性和通用性。 相似文献
52.
Abu Avi Lupa Israel 《AEUE-International Journal of Electronics and Communications》2005,59(5):307-310
This letter presents a general analysis of time jitter in sigma-delta synthesizer. One of the practical applications of 1-bit sigma-delta systems is a generation of high-resolution local oscillator (LO) signals. In order to generate LO signals, one may use a single-bit sigma-delta technique to encode sine waves. Today, direct generation of high-frequency sine wave using a clock with higher frequency, is possible. In this letter, we will analyze different LO signal generators and develop a practical way of computation to decide how to choose the best configuration under minimum degradation of signal-to-noise ratio (SNR) at the output. 相似文献
53.
AStudyontheModelofForecastingSystemabouttheActualTelephoneOccupationintheLeadDevelopment¥XieShichang;andXieXuemei(Departmento... 相似文献
54.
Isothermal melt spinning experiments have been conducted using two polyethylene melts of low density (LDPE) and high density
(HDPE) to produce steady state spinline profiles. The data revealed the threadline extensional viscosity exhibiting a contrasting
picture : extension thickening behavior for LDPE and extension thinning one for HDPE. A White-Metzner model having a strain
rate-dependent relaxation time was then found to be able to simulate this dichotomy in melt spinning fairly well: the fluids
whose relaxation times have smaller strain rate-dependence can fit LDPE data with extension thickening extensional viscosity
whereas the fluids whose relaxation times have larger strain rate-dependence can fit HDPE data with extension thinning extensional
viscosity. This dichotomous nature of viscoelastic fluids is also believed to be able to explain other similar contrasting
phenomena exhibited by polymer melts, such as vortex/no vortex in entry flows, cohesive/ductile fracture modes in extension,
and more/less stable draw resonance than Newtonian fluids. 相似文献
55.
56.
Bradley T. Ewing Jamie Brown Kruse Douglas A. Smith 《Journal of Wind Engineering & Industrial Aerodynamics》2007,95(3):209-219
This research examines the interdependence in time series wind speed data measured in the same location at four different heights. A multiple-equation system known as a vector autoregression is proposed for characterizing the time series dynamics of wind. Additionally, the recently developed method of generalized impulse response analysis provides insight into the cross-effects of the wind series and their responses to shocks. Findings are based on analysis of contemporaneous wind speed time histories taken at 13, 33, 70 and 160 ft above ground level with a sampling rate of 10 Hz. The results indicate that wind speeds measured at 70 ft was the most variable. Further, the turbulence persisted longer at the 70-ft measurement than at the other heights. The greatest interdependence is observed at 13 ft. Gusts at 160 ft led to the greatest persistence to an “own” shock and led to greatest persistence in the responses of the other wind series. 相似文献
57.
关于移动平均过程两系数的推导 总被引:1,自引:0,他引:1
杜德文 《石油化工高等学校学报》1995,(2)
对经济预测方法中两公式给出了证明,两公式的系数被显式推导出来,这两个公式是时间序列模型公式,广泛用于经济预测之中,但文献上很难找到推导过程,本文的证明是基本的,无需高深数学知识即可理解. 相似文献
58.
Berlin Wu 《Computational Economics》1994,7(1):37-53
In this paper, the methods of time series for nonlinearity are briefly surveyed, with particular attention paid to a new test design based on a neural network specification. The proposed integrated expert system contains two main components: an identification environment and a robust forecasting design. The identification environment can be viewed as a integrated dynamic design in which cognitive capabilities arise as a direct consequence of their self-organizational properties. The integrated framework used for discussing the similarities and differences in the nonlinear time series behavior is presented. Moreover, its performance in prediction proves to be superior than the former work. For the investigation of robust forecasting, we perform a simulation study to demonstrate the applicability and the forecasting performance. 相似文献
59.
60.
Abstract. A vector time series model of the form A(L)y(t) + B(L)x(t) =ε(t) is known as a vector autoregressive model with exogenous variables (VARX model) and involves a regressand vector y(t) and a regressor vector x(t). This paper provides a method for the recursive fitting of subset VARX models. It suggests the use of ascending recursions in conjunction with an order selection criterion to choose an 'optimum' subset VARX model. 相似文献