全文获取类型
收费全文 | 7969篇 |
免费 | 905篇 |
国内免费 | 439篇 |
专业分类
化学 | 1254篇 |
晶体学 | 22篇 |
力学 | 826篇 |
综合类 | 161篇 |
数学 | 3163篇 |
物理学 | 3887篇 |
出版年
2024年 | 11篇 |
2023年 | 78篇 |
2022年 | 148篇 |
2021年 | 174篇 |
2020年 | 215篇 |
2019年 | 152篇 |
2018年 | 159篇 |
2017年 | 295篇 |
2016年 | 338篇 |
2015年 | 259篇 |
2014年 | 465篇 |
2013年 | 571篇 |
2012年 | 428篇 |
2011年 | 421篇 |
2010年 | 355篇 |
2009年 | 453篇 |
2008年 | 475篇 |
2007年 | 504篇 |
2006年 | 425篇 |
2005年 | 398篇 |
2004年 | 329篇 |
2003年 | 375篇 |
2002年 | 312篇 |
2001年 | 264篇 |
2000年 | 262篇 |
1999年 | 222篇 |
1998年 | 205篇 |
1997年 | 169篇 |
1996年 | 151篇 |
1995年 | 148篇 |
1994年 | 84篇 |
1993年 | 83篇 |
1992年 | 71篇 |
1991年 | 40篇 |
1990年 | 46篇 |
1989年 | 25篇 |
1988年 | 34篇 |
1987年 | 31篇 |
1986年 | 25篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1976年 | 6篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有9313条查询结果,搜索用时 390 毫秒
101.
Francis J. Narcowich Joseph D. Ward Holger Wendland. 《Mathematics of Computation》2005,74(250):743-763
In this paper we discuss Sobolev bounds on functions that vanish at scattered points in a bounded, Lipschitz domain that satisfies a uniform interior cone condition. The Sobolev spaces involved may have fractional as well as integer order. We then apply these results to obtain estimates for continuous and discrete least squares surface fits via radial basis functions (RBFs). These estimates include situations in which the target function does not belong to the native space of the RBF.
102.
The paper deals with a singularly perturbed reaction diffusionmodel problem. The focus is on reliable a posteriori error estimatorsfor the H1 seminorm that can be applied to anisotropic finiteelement meshes. A residual error estimator and a local problemerror estimator are proposed and rigorously analysed. They arelocally equivalent, and both bound the error reliably. Threemodifications of these estimators are introduced and discussed. Much attention is given to the performance of the error estimatorin numerical experiments. This helps to identify those estimatorsthat are suitable for practical applications. 相似文献
103.
104.
The 3-D modeling of heads by using optical triangulation techniques is of great interest in the context of virtual reality, telecommunication and computer animation. This paper presents a structured light-based system mainly for human heads. It is named “3-D Laser Color Scanner” (3DLCS). A 3-D model is obtained with a cylindrical scan. The laser beam is switched on and off using a “light valve” and two successive CCD frames are captured, one with the laser line showing and one without. We can simplify the laser line extracting by subtracting these two images.In this system, two CCD cameras are used to avoid occlusion problems. Color information is read from the CCD when the laser light is absent. Since traditional laser scanner will miss the range data in the low-reflectance areas such as the hair area of human head, a shape from silhouette algorithm is presented to overcome this problem. Finally, we give some results using our system. The resulting model is suitable for many applications. 相似文献
105.
Vladimir E. Bondarenko 《Complexity》2005,11(2):39-52
Information processing and two types of memory in an analog neural network model with time delay that produces chaos similar to the human and animal EEGs are considered. There are two levels of information processing in this neural network: the level of individual neurons and the level of the neural network. Similar to the state of brain, the state of chaotic neural network is defined. It is characterized by two types of memories (memory I and memory II) and correlation structure between the neurons. In normal (unperturbed) state, the neural network generates chaotic patterns of averaged neuronal activities (memory I) and patterns of oscillation amplitudes (memory II). In the presence of external stimulation, the activity patterns change, showing changes in both types of memory. As in experiments on stimulation of the brain, the neural network model shows synchronization of neuronal activities due to stimulus measured by Pearson's correlation coefficient. An increase in neural network asymmetry (increase of the neural network excitability) leads to the phenomenon similar to the epilepsy. Modeling of brain injury, Parkinson's disease, and dementia is performed by removing and weakening interneuron connections. In all cases, the chaotic neural network shows a decrease of the degree of chaos and changes in both types of memory similar to those observed in experiments with healthy human subjects and patients with Parkinson's disease and dementia. © 2005 Wiley Periodicals, Inc. Complexity 11:39–52, 2005 相似文献
106.
107.
Recoil proton tracks in nuclear emulsion are counted by scanning them using strip, square or circular field of view of optical microscope. In this paper, the overestimate due to the edge effects in counting recoil proton tracks at different neutron energies produced from the T(d,n)4He reaction has been determined by measuring the true track density in NTA film. The overestimate has also been calculated using the measured value of the mean projected track length (L) in the film. The percentage of measured overestimates has been compared with those obtained by calculation and the results agree reasonably well. Fading effect in NTA film has been studied and found to be 22% more in the summer than in the winter season. A great reduction in fading rate could be achieved if the films are desiccated and sealed in highly pure dry nitrogen maintained at an over-pressure of 1000 Pa to reduce water vapour ingress. After the edge effect correction, the sensitivity of NTA film has been calculated from (1.72±0.08)×10−3 tracksn−1 to (1.97±0.16)×10−3 tracksn−1 in the neutron energy ranges from 15.91 to 18.88 MeV. The response was found to be from 0.24±0.02 trackscm−2 permSv to 0.26±0.01 trackscm−2 permSv in the same energy range. 相似文献
108.
109.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
110.
具有离散参数齐次随机场的线性预测(V) 总被引:1,自引:1,他引:0
本文提出并研究下列四类线性预测问题:2(n0),6(n0),5(NO,n0)及3(N0,n0).不仅求出了它们的预测误差,而且也求出了它们的预测值.因而不仅推广了而且也改进了[2-5]中的结果.本文还给出了场{X(m,n)}的一个新形式的表示式. 相似文献