全文获取类型
收费全文 | 19895篇 |
免费 | 2140篇 |
国内免费 | 1467篇 |
专业分类
化学 | 2801篇 |
晶体学 | 62篇 |
力学 | 1264篇 |
综合类 | 479篇 |
数学 | 9548篇 |
物理学 | 4244篇 |
无线电 | 5104篇 |
出版年
2024年 | 45篇 |
2023年 | 169篇 |
2022年 | 321篇 |
2021年 | 458篇 |
2020年 | 470篇 |
2019年 | 432篇 |
2018年 | 440篇 |
2017年 | 576篇 |
2016年 | 704篇 |
2015年 | 593篇 |
2014年 | 1014篇 |
2013年 | 1316篇 |
2012年 | 1056篇 |
2011年 | 1255篇 |
2010年 | 1125篇 |
2009年 | 1285篇 |
2008年 | 1315篇 |
2007年 | 1316篇 |
2006年 | 1291篇 |
2005年 | 1009篇 |
2004年 | 887篇 |
2003年 | 892篇 |
2002年 | 771篇 |
2001年 | 689篇 |
2000年 | 561篇 |
1999年 | 518篇 |
1998年 | 434篇 |
1997年 | 368篇 |
1996年 | 327篇 |
1995年 | 276篇 |
1994年 | 213篇 |
1993年 | 178篇 |
1992年 | 182篇 |
1991年 | 129篇 |
1990年 | 104篇 |
1989年 | 91篇 |
1988年 | 75篇 |
1987年 | 64篇 |
1986年 | 37篇 |
1985年 | 66篇 |
1984年 | 57篇 |
1983年 | 34篇 |
1982年 | 62篇 |
1981年 | 45篇 |
1980年 | 49篇 |
1979年 | 63篇 |
1978年 | 33篇 |
1977年 | 34篇 |
1976年 | 18篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
SHI Yan-rui CAO Pei-xia Shijiazhuang Post Telecommunication Technical College Shijiazhuang P.R. China. 《中国邮电高校学报(英文版)》2004,11(Z1)
1 Introduction ExpressMailService (EMS )wasopenedupbyChinaPostintheearly 80stomeettheneedsofeco nomicdevelopment.It sthemostcompetitiveoneofthepostservices.There recivilaviation ,Chinarail wayandotherprivateexpressdeliverycompaniesdomesticallyandUPS ,TNT ,DHLandTEDEXcompetingwithEMSintheinternationalmarket.OneofthemostpowerfulcompeteweaponofthesecompaniesisthelowerpricethanEMS[1 ] .BecauseofthefiercecompetitionEMSdeclinedfromthemo nopolistindomesticandinternationalmarketoftheear… 相似文献
23.
Recent years have witnessed a rapid growth of interest in the study of the dynamic behavior of replenishment rules of bullwhip effect. We prove that bullwhip effect and butterfly effect share a same the self-oscillation amplifying mechanism that is the ordering decisions the supplier self-oscillation amplify the perturbations brought by the errors in the processing of retailers' demand information. This results as an explicit self-similar structure of the sensitivity of the system to the initial values duty to the nonlinear mechanism. In this paper, the causes process of the bullwhip effect is described as the internal nonlinear mechanism and study on the complexity of bullwhip effect for order-up-to policy under demand signal processing. The methodology is based on fractal and chaotic theory and allows important insights to be gained about the complexity behavior of bullwhip effect. 相似文献
24.
多传感器目标的模糊识别 总被引:5,自引:0,他引:5
根据模糊理论,采用信息融合技术和模糊识别技术,讨论了在多类传感器网内进行多目标模糊识别的一般原理和方法。 相似文献
25.
非线性互补问题的一种全局收敛的显式光滑Newton方法 总被引:2,自引:0,他引:2
本针对Po函数非线性互补问题,给出了一种显式光滑Newton方法,该方法将光滑参数μ进行显式迭代而不依赖于Newton方向的搜索过程,并在适当的假设条件下,证明了算法的全局收敛性。 相似文献
26.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
27.
对由一类非线性抛物型变分不等方程所描述的无穷维动力系统,给出了存在全局吸引子及弱近似惯性流形的充分条件. 相似文献
28.
In electrodialysis using thin membranes and spacers, the compactness of the membrane cell-pairs leads to a small potential drop, and hence to energy saving. The spacer design itself has a great effect on the cost of the plants, since spacers act as turbulence promoters. A careful design, to increase the mass transfer coefficients, can reduce the membrane surface area required for a given application. Limiting current measurements, cell-pair resistance and pressure losses are presented for several thin spacers, for different flow-velocity values and feed water concentrations. It was possible to find an advantageous geometry of the separating mesh leading to substantial savings on investment and operation costs. 相似文献
29.
Zhong-Qing Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):374-403
An orthogonal system of rational functions is discussed. Some inverse inequalities, imbedding inequalities and approximation results are obtained. Two model problems are considered. The stabilities and convergences of proposed rational spectral schemes and rational pseudospectral schemes are proved. The techniques used in this paper are also applicable to other problems on the whole line. Numerical results show the efficiency of this approach. 相似文献
30.
采用封闭网络模型,按照电路元件参数,采用开路、短路和着色运算,将电路图逐层分解,得到网络展开图.给出网络展开图的概念和运算规则,指出网络展开图中从根到末稍每个路径的值就是网络行列式展开式中的一个有效项,从而由网络展开图得到符号网络函数.该方法直接对电路图进行运算,不需要建立任何形式的电路方程和行列式,适用于一般的有源电路,而且能生成各种类型的网络函数. 相似文献