全文获取类型
收费全文 | 69230篇 |
免费 | 5701篇 |
国内免费 | 3047篇 |
专业分类
电工技术 | 3962篇 |
技术理论 | 11篇 |
综合类 | 4569篇 |
化学工业 | 11600篇 |
金属工艺 | 3642篇 |
机械仪表 | 3934篇 |
建筑科学 | 5417篇 |
矿业工程 | 1843篇 |
能源动力 | 1940篇 |
轻工业 | 5324篇 |
水利工程 | 1307篇 |
石油天然气 | 3703篇 |
武器工业 | 529篇 |
无线电 | 8319篇 |
一般工业技术 | 8561篇 |
冶金工业 | 3439篇 |
原子能技术 | 726篇 |
自动化技术 | 9152篇 |
出版年
2024年 | 313篇 |
2023年 | 1185篇 |
2022年 | 2107篇 |
2021年 | 2918篇 |
2020年 | 2278篇 |
2019年 | 1806篇 |
2018年 | 2061篇 |
2017年 | 2162篇 |
2016年 | 2109篇 |
2015年 | 2699篇 |
2014年 | 3366篇 |
2013年 | 3926篇 |
2012年 | 4345篇 |
2011年 | 4757篇 |
2010年 | 3914篇 |
2009年 | 3752篇 |
2008年 | 3717篇 |
2007年 | 3485篇 |
2006年 | 3315篇 |
2005年 | 2878篇 |
2004年 | 2146篇 |
2003年 | 1895篇 |
2002年 | 1752篇 |
2001年 | 1555篇 |
2000年 | 1692篇 |
1999年 | 2009篇 |
1998年 | 1713篇 |
1997年 | 1403篇 |
1996年 | 1391篇 |
1995年 | 1146篇 |
1994年 | 1007篇 |
1993年 | 697篇 |
1992年 | 545篇 |
1991年 | 397篇 |
1990年 | 339篇 |
1989年 | 308篇 |
1988年 | 220篇 |
1987年 | 154篇 |
1986年 | 112篇 |
1985年 | 82篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 52篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 13篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
水和甲醇存在下MAMS的消失反应动力学研究 总被引:1,自引:0,他引:1
通过实验研究了甲基丙烯酰胺硫酸盐(MAMS)与甲醇、水进行反应的动力学,并对该反应的机理进行了探讨。 相似文献
123.
124.
In (J. Comput. Phys. 229: 8105–8129, 2010), Li and Qiu investigated the hybrid weighted essentially non-oscillatory (WENO) schemes with different indicators for Euler
equations of gas dynamics. In this continuation paper, we extend the method to solve the one- and two-dimensional shallow
water equations with source term due to the non-flat bottom topography, with a goal of obtaining the same advantages of the
schemes for the Euler equations, such as the saving computational cost, essentially non-oscillatory property for general solution
with discontinuities, and the sharp shock transition. Extensive simulations in one- and two-dimensions are provided to illustrate
the behavior of this procedure. 相似文献
125.
A Radiating Gradient Vector Flow (RGVF) Snake aiming at accurate extraction of both the nucleus and cytoplasm from a single-cell cervical smear image is proposed. After preprocessing, the areas in the image are roughly clustered into nucleus, cytoplasm and the background by a spatial K-means clustering algorithm. After initial contours are extracted, the image is segmented using RGVF. RGVF involves a new edge map computation method and a stack-based refinement, and is thus robust to contaminations and can effectively locate the obscure boundaries. The boundaries can also be correctly traced even if there are interferences near the cytoplasm and nucleus regions. Experiments performed on the Herlev dataset, which contains 917 images show the effectiveness of the proposed algorithm. 相似文献
126.
Survival analysis is widely applied to develop injury risk curves from biomechanical data. To obtain more accurate estimation of confidence intervals of parameters, bootstrap method was evaluated by a designed simulation process. Four censoring schemes and various sample sizes were considered to investigate failure time parameters corresponding to low-level injury probabilities. In the numerical simulations, the confidence interval ranges developed by bootstrapping were about two-third of the corresponding ranges calculated by asymptotical normal approximation and showed highest reduction for censored datasets with smaller sample size (≤ 40). In analysis of two experimental datasets with reduced sample sizes and mixed censored data, it was shown that the bootstrapping reduce significantly the confidence intervals as well. The results presented in this study recommend using bootstrapping in development of more accurate confidence intervals for risk curves in injury biomechanics, which consequently will lead to better regulations and safer vehicle designs. 相似文献
127.
In this article, we solve the problem of global stabilization for a chain of integrators in the presence of input saturation and disturbances. A novel and elegant approach to solve this problem, in the absence of disturbances, was proposed by Teel (1992) using saturation functions and coordinate transformation. With Teel’s work as a foundation, many results have been proposed to improve the performance of controllers for a chain of integrators. Naturally, all such approaches also inherited the limitations of Teel’s approach. Most importantly, in the presence of uncertainties and disturbances, the transformation introduced in Teel (1992) would considerably shrink the region where the controller is unsaturated and, severely limit the level of uncertainties and disturbances which can be tolerated. In order to overcome these difficulties, a conceptually different approach which does not rely on the coordinate transformation is presented in this work. Specifically, modified saturation functions are directly applied to the tracking error of actual states as opposed to transformed fictitious states to develop a globally stable controller. The proposed controller is less conservative in terms of the level of uncertainties and disturbances which can be handled. In addition, arbitrarily good disturbance rejection in the unsaturated region can be achieved theoretically. Comparative simulation studies performed on a third order integrator chain verified the effectiveness of the proposed scheme. 相似文献
128.
何永佳 《武汉理工大学学报(材料科学英文版)》2013,28(3):544-547
Porous haydite used as waste filter medium was prepared by dreging lake sludge to help solve the treatment problem of sludge and realize its reclamation. Several calcination regimes were considered and their effects on the pore structure and the properties such as the strength, the density, the filtering ability and the phosphate absorption ability of the haydite were investigated. For the mixture of 60% lake sludge and 40% fly ash in this experiment, the calcination regime with a pre-calcination period at about 600 °C, a temperature keeping period at 1 200 °C and a moderate cooling rate are recommended to prepare haydite with reasonable pore structure and good performances for its usage as the waste water filter media. 相似文献
129.
海面高程的传递是水准测量中的难题.以宁波市象山县某围堤工程变形测量为例,对全站仪进行跨海面高程测量进行了成功应用,并用GPS拟合高程测量方法和平均海平面法进行了验证,结果合理. 相似文献
130.
正交频分复用技术由于具有频带利用率高和抗多径干扰能力强等优点,近年来在无线音频广播、无线视频广播、无线局域网等方面得到广泛的应用。然而,对OFDM系统进行准确的信道估计一直是其技术难点之一;加之MIMO技术虽然能有效的提高系统容量,但是同时也大大提高了系统的复杂度,这就进一步加大了对MIMO-OFDM系统进行信道估计的难度。在前人工作的基础上,对目前各常用信道评估方法实现复杂度与准确度进行分析,经过模拟仿真选择最适宜MIMO-OFDM系统评估手段进行研究。同时,由于OFDM系统本身对于信号同步性与正交性的苛刻要求,尤其在高容量高速率的实际应用中,其硬件实现往往需要付出高昂的成本代价;拟通过另一角度,研究在低成本、允许一定系统延迟、相对系统容量较低、传输速度不高的应用中,例如:短信业务、同区域语言服务等,仅搭建相应的软件平台实现真实仿真。 相似文献