全文获取类型
收费全文 | 47335篇 |
免费 | 4429篇 |
国内免费 | 3045篇 |
学科分类
工业技术 | 54809篇 |
出版年
2024年 | 168篇 |
2023年 | 764篇 |
2022年 | 1032篇 |
2021年 | 1304篇 |
2020年 | 1450篇 |
2019年 | 1226篇 |
2018年 | 1190篇 |
2017年 | 1575篇 |
2016年 | 1836篇 |
2015年 | 1817篇 |
2014年 | 2701篇 |
2013年 | 2844篇 |
2012年 | 3120篇 |
2011年 | 3820篇 |
2010年 | 2808篇 |
2009年 | 2734篇 |
2008年 | 2601篇 |
2007年 | 2985篇 |
2006年 | 2756篇 |
2005年 | 2842篇 |
2004年 | 2317篇 |
2003年 | 1771篇 |
2002年 | 1261篇 |
2001年 | 1127篇 |
2000年 | 959篇 |
1999年 | 907篇 |
1998年 | 805篇 |
1997年 | 660篇 |
1996年 | 643篇 |
1995年 | 529篇 |
1994年 | 465篇 |
1993年 | 414篇 |
1992年 | 298篇 |
1991年 | 224篇 |
1990年 | 187篇 |
1989年 | 154篇 |
1988年 | 124篇 |
1987年 | 73篇 |
1986年 | 62篇 |
1985年 | 61篇 |
1984年 | 60篇 |
1983年 | 32篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
2.
卫星电视上行站信号自动监测系统 总被引:1,自引:0,他引:1
鄂志东 《信息安全与通信保密》2006,(3):84-85
每个卫星电视上行站都必须对卫星转发器上的电视信号进行监测,才能及时发现卫星电视上行信号的异常变化,准确处理异常突发干扰。为实现自动、连续、实时监测,就需要建立卫星电视上行站射频信号自动监测系统。文章详细介绍了一个自动监测系统的设计及实现。 相似文献
3.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions. 相似文献
4.
5.
This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests. 相似文献
7.
8.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
9.
Analysis of non-stationary electrochemical oscillations emerges utilization of the techniques allowing an observation of time evolution of their parameters such as instantaneous frequency, amplitude or frequency band. An algorithm of extraction of these parameters can be based on one of linear or quadratic time-frequency representations of oscillations record. In this paper, the authors present representatives of such transformations (Choi-Williams and Cone-shaped) originating from one of the most popular joint time-frequency energy distribution—Wigner-Ville distribution. Short introduction to the mathematics of the topic discussed is provided, then the authors present an example of application in the analysis of current oscillations of copper dissolution process. 相似文献
10.
吐哈油田部分区块地层压力系数小于0.9,常规水基压井液对储层伤害大,若使用油基压井液成本高,环境污染严重。通过实验优选出了一种低密度水基微泡沫压井液。该压井液具有密度低、泡沫强度高、稳定性好、携砂能力强等优点。现场应用表明,低密度微泡沫压井液稳定时间大于48 h,密度在0.70~0.99 g/cm3之间可调,抗油污染能力强,抗油大于8%,抗温在100℃以上,岩心污染后渗透率恢复值大于80%;并且施工方便,成本低,具有储层保护能力,使用微泡沫压井液的井表皮系数在0.20~2.34之间。 相似文献