全文获取类型
收费全文 | 38374篇 |
免费 | 4558篇 |
国内免费 | 3645篇 |
专业分类
电工技术 | 3227篇 |
技术理论 | 2篇 |
综合类 | 6698篇 |
化学工业 | 1733篇 |
金属工艺 | 816篇 |
机械仪表 | 2657篇 |
建筑科学 | 2628篇 |
矿业工程 | 780篇 |
能源动力 | 771篇 |
轻工业 | 2404篇 |
水利工程 | 1028篇 |
石油天然气 | 852篇 |
武器工业 | 486篇 |
无线电 | 5186篇 |
一般工业技术 | 3764篇 |
冶金工业 | 854篇 |
原子能技术 | 487篇 |
自动化技术 | 12204篇 |
出版年
2024年 | 166篇 |
2023年 | 513篇 |
2022年 | 921篇 |
2021年 | 998篇 |
2020年 | 1037篇 |
2019年 | 959篇 |
2018年 | 986篇 |
2017年 | 1181篇 |
2016年 | 1294篇 |
2015年 | 1357篇 |
2014年 | 2048篇 |
2013年 | 2309篇 |
2012年 | 2673篇 |
2011年 | 2889篇 |
2010年 | 2282篇 |
2009年 | 2466篇 |
2008年 | 2563篇 |
2007年 | 2951篇 |
2006年 | 2628篇 |
2005年 | 2330篇 |
2004年 | 1943篇 |
2003年 | 1610篇 |
2002年 | 1335篇 |
2001年 | 1133篇 |
2000年 | 989篇 |
1999年 | 830篇 |
1998年 | 670篇 |
1997年 | 578篇 |
1996年 | 531篇 |
1995年 | 468篇 |
1994年 | 404篇 |
1993年 | 286篇 |
1992年 | 258篇 |
1991年 | 214篇 |
1990年 | 194篇 |
1989年 | 172篇 |
1988年 | 113篇 |
1987年 | 68篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
牛肉眼肌图像的分割是牛肉自动分级的重要步骤。基于水平集的C-V模型采用两个具有不同均值的分块连续区域分割图像,在迭代过程中,为了约束水平集保持为符号距离函数,必须对其进行重新初始化,大大增加了计算量,降低了曲线演化速度。为此,通过加入边缘检测函数和惩罚项因子,提出了改进的C-V水平集模型,并用于牛肉图像分割,同时与模糊C均值聚类、阈值分割法进行了对比。结果表明:采用改进的C-V模型对牛肉图像进行分割,准确提取了眼肌边缘,分割出了脂肪和肌肉区域,准确率高;曲线演化过程中无需对水平集函数符号初始化,加快了曲线演化速度。 相似文献
992.
Sangmun Shin Nguyen Khoa Viet Truong Byung Rae Cho Sung Hoon Hong 《Computers & Industrial Engineering》2011
Robust design (RD) and tolerance design (TD) have received much attention from researchers and practitioners for more than two decades, and a number of methodologies for modeling and optimizing the RD and TD processes have been studied. However, there is ample room for improvement. Because most existing research considers RD and TD as separate research fields, the primary objective of this paper is to develop a sequential robust–tolerance design method to jointly determine the best factor settings and the closed-form solutions for the optimal specification limits. We then apply the proposed method to a destructive quality characteristic. Finally, a case study and sensitivity analyses are performed for verification purposes, and further studies are discussed. 相似文献
993.
This paper studies a discrete-time single-server infinite-capacity queueing system with correlated arrivals, geometrically distributed service times and negative customers. Positive customers are generated by a Bernoulli bursty source, with geometrically distributed lengths of the on-periods and off-periods. Negative customers arrive to the system according to a geometrical arrival process which is independent of the positive arrival process. A negative customer removes a positive customer in service if any, but has no effect on the system if it finds the system empty. We analyze the Markov chain underlying the queueing system and evaluate the performance of the system based on generating functions technique. Closed-form expressions of some performance measures of the system are obtained, such as stationary probability generating functions of queue length, unfinished work, sojourn time distribution and so on. Finally, the effect of several parameters on the system is shown numerically. 相似文献
994.
The discrete ordered median location model is a powerful tool in modeling classic and alternative location problems that have been applied with success to a large variety of discrete location problems. Nevertheless, although hub location models have been analyzed from the sum, maximum and coverage point of views, as far as we know, they have never been considered under an alternative unifying point of view. In this paper we consider new formulations, based on the ordered median objective function, for hub location problems with new distribution patterns induced by the different users’ roles within the supply chain network. This approach introduces some penalty factors associated with the position of an allocation cost with respect to the sorted sequence of these costs. First we present basic formulations for this problem, and then develop stronger formulations by exploiting properties of the model. The performance of all these formulations is compared by means of a computational analysis. 相似文献
995.
The Burr type III distribution allows for a wider region for the skewness and kurtosis plane, which covers several distributions including the log-logistic, and the Weibull and Burr type XII distributions. However, outliers may occur in the data set. The robust regression method such as an M-estimator with symmetric influence function has been successfully used to diminish the effect of outliers on statistical inference. However, when the data distribution is asymmetric, these methods yield biased estimators. We present an M-estimator with asymmetric influence function (AM-estimator) based on the quantile function of the Burr type III distribution to estimate the parameters for complete data with outliers. The simulation results show that the M-estimator with asymmetric influence function generally outperforms the maximum likelihood and traditional M-estimator methods in terms of the bias and root mean square errors. One real example is used to demonstrate the performance of our proposed method. 相似文献
996.
In the present work, we investigate the Dirichlet problem for a three-dimensional (3D) elliptic equation with two singular coefficients. We find four fundamental solutions of the equation, containing hypergeometric functions of Appell. Then using an “a-b-c” method, the uniqueness for the solution of the Dirichlet problem is proved. Applying a method of Green’s function, we are able to find the solution of the problem in an explicit form. Moreover, decomposition formulas, formulas of differentiation and some adjacent relations for Appell’s hypergeometric functions were used in order to find the explicit solution for the formulated problem. 相似文献
997.
Qinjiao Gao Zongmin WuShenggang Zhang 《Computers & Mathematics with Applications》2011,62(12):4356-4361
In this paper, we propose a novel scheme for simulating geometric active contours (geometric flow) of one kind, applying multiquadric (MQ) quasi-interpolation. We first represent the geometric flow in its parametric form. Then we obtain the numerical scheme by using the derivatives of the quasi-interpolation to approximate the spatial derivative of each dependent variable and a forward difference to approximate the temporal derivative of each dependent variable. The resulting scheme is simple, efficient and easy to implement. Also images with complex boundaries can be more easily proposed on the basis of the good properties of the MQ quasi-interpolation. Several biomedical and astronomical examples of applications are shown in the paper. Comparisons with other methods are included to illustrate the validity of the method. 相似文献
998.
M.K. Aouf 《Computers & Mathematics with Applications》2011,62(9):3575-3580
In this paper, we obtain some subordination and superordination-preserving results of analytic functions involving the Liu-Owa integral operator. Sandwich-type result is also obtained. 相似文献
999.
Joan Goh Ahmad Abd. MajidAhmad Izani Md. Ismail 《Computers & Mathematics with Applications》2011,62(12):4492-4498
In the present paper, the cubic B-splines method is considered for solving one-dimensional heat and wave equations. A typical finite difference approach had been used to discretize the time derivative while the cubic B-spline is applied as an interpolation function in the space dimension. The accuracy of the method for both equations is discussed. The efficiency of the method is illustrated by some test problems. The numerical results are found to be in good agreement with the exact solution. 相似文献
1000.
M.A. Jafari A. Aminataei 《Computers & Mathematics with Applications》2011,62(3):1091-1097
In this paper an algorithm, based on a new modified homotopy perturbation method (MHPM), is presented to obtain approximate solutions of multi-term diffusion-wave equations of fractional order. To illustrate the method some examples are provided. The results show the simplicity and the efficiency of the algorithm. 相似文献