全文获取类型
收费全文 | 9275篇 |
免费 | 1098篇 |
国内免费 | 564篇 |
专业分类
化学 | 2674篇 |
晶体学 | 56篇 |
力学 | 514篇 |
综合类 | 279篇 |
数学 | 3737篇 |
物理学 | 3677篇 |
出版年
2024年 | 15篇 |
2023年 | 90篇 |
2022年 | 204篇 |
2021年 | 281篇 |
2020年 | 242篇 |
2019年 | 229篇 |
2018年 | 250篇 |
2017年 | 353篇 |
2016年 | 397篇 |
2015年 | 285篇 |
2014年 | 590篇 |
2013年 | 674篇 |
2012年 | 545篇 |
2011年 | 600篇 |
2010年 | 473篇 |
2009年 | 571篇 |
2008年 | 602篇 |
2007年 | 598篇 |
2006年 | 517篇 |
2005年 | 461篇 |
2004年 | 397篇 |
2003年 | 366篇 |
2002年 | 297篇 |
2001年 | 240篇 |
2000年 | 240篇 |
1999年 | 202篇 |
1998年 | 191篇 |
1997年 | 182篇 |
1996年 | 153篇 |
1995年 | 112篇 |
1994年 | 89篇 |
1993年 | 77篇 |
1992年 | 55篇 |
1991年 | 52篇 |
1990年 | 45篇 |
1989年 | 26篇 |
1988年 | 34篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 8篇 |
1982年 | 28篇 |
1981年 | 17篇 |
1980年 | 5篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A new consistency measure, the harmonic consistency index, is obtained for any positive reciprocal matrix in the analytic hierarchy process. We show how this index varies with changes in any matrix element. A tight upper bound is provided for this new consistency measure when the entries of matrix are at most 9, as is often recommended. Using simulation, the harmonic consistency index is shown to give numerical values similar to the standard consistency index but it is easier to compute and interpret. In addition, new properties of the column sums of reciprocal matrices are obtained. 相似文献
82.
Duan-zhi ZHANG School of Mathematical Sciences Peking University Beijing China 《中国科学A辑(英文版)》2007,50(6):761-772
In this paper, we study the Maslov-type index theory for linear Hamiltonian systems with brake orbits boundary value conditions and its applications to the existence of multiple brake orbits of nonlinear Hamiltonian systems. 相似文献
83.
激光标线的原理和实验 总被引:1,自引:1,他引:0
根据几何光学知识分析了激光标线原理.理论和实验表明:激光标线长度与激光光束形状、光学元件形状及材料折射率有关.并讨论了激光标线向两侧扩展的原因. 相似文献
84.
基于BP神经网络的企业未来获利能力智能综合评价 总被引:3,自引:0,他引:3
分析了相关分析——多指标综合评价法在确定企业未来获利能力方面的优点和不足 ;并在其基础上提出了基于 BP神经网络的多指标综合评价法 ;仿真试验证明了基于 BP神经网络的多指标综合评价法的有效性 相似文献
85.
J. A. Morrison 《Queueing Systems》1991,9(1-2):191-213
In this paper the steady-state behavior of a closed queueing network with multiple classes and large populations is investigated. One of the two nodes of the network simply introduces random delays and the discipline in the other node is discriminatory processor sharing. The network is not product-form, so not even the steady-state behavior is known. We assume that the usage is moderately heavy, and obtain two-term asymptotic approximations to the mean number of jobs, and the mean sojourn time, of each class of jobs in the processor node. We also obtain the leading term in the asymptotic approximation to the joint distribution of the number of jobs in the processor node, which is a zero-mean multivariate Gaussian distribution around a line through the origin. 相似文献
86.
平衡规划问题的熵函数方法及其在混合交通流中的应用 总被引:1,自引:0,他引:1
将参变极值问题的极大熵函数方法应用到求解平衡规划问题中,通过先验分布信息和Kullback熵概念,给出了平衡规划问题基于Kullback熵表示的熵函数求解方法,并将平衡规划的极大熵函数方法应用于求解混合交通平衡分配问题. 相似文献
87.
A scheme for vehicle density and velocity estimation in a stretch of highway based on a modified cell transmission model [C.
F. Daganzo, Transportation Research, Part B, 28B(4),269–287, 1994. Elsevier is presented. The scheme is intended for use with on-ramp metering control algorithms, providing
local knowledge of densities and velocities that is helpful to improve on-ramp metering control performance. Estimation of
density is obtained by nonlinear estimators, while velocity estimation is obtained by gradient algorithms. There is one density–velocity
estimator for free traffic flow and other for congested traffic flow. Both estimator schemes work in parallel. The final estimation
of density and velocity results from a convex combination of the predictions of the two estimators. This combination depends
on occupancy or density measurements at the boundaries of the stretch and is produced by a fuzzy inference system. Stability
and convergence of the density and velocity estimation scheme is proved by Lyapunov based techniques. Simulation results comparing
measured and estimated traffic data are presented. They confirm good performance of the estimators.
Research sponsored by grants UNAM PAPIIT IN110403 and CONACYT 47583. 相似文献
88.
89.
分析了几种相关结构函数(Copula)表示的相关结构模型,给出了用相关结构函数对金融资产间的相关结构进行建模的方法.结果表明混合Gumbel(M-Gumbel)相关结构函数能较全面地描述上海深圳两证券指数的相关结构,模拟计算VaR的结果支持了实证分析的结论. 相似文献
90.
The attention of the present paper was devoted to nondestructive evaluation of masonry structures with a Focal Plane Array infrared camera. Tests were carried out in laboratory on specimens, which simulated one- and two-layer structures, with defects of different geometry and nature and located at different depths. The defects detection was analysed through a cause/effect relationship between the characteristics of defects and hosting material and the observed defect thermal signature, or contrast, on the hosting material. 相似文献