全文获取类型
收费全文 | 3731篇 |
免费 | 471篇 |
国内免费 | 156篇 |
专业分类
化学 | 285篇 |
晶体学 | 2篇 |
力学 | 352篇 |
综合类 | 96篇 |
数学 | 2674篇 |
物理学 | 949篇 |
出版年
2024年 | 7篇 |
2023年 | 48篇 |
2022年 | 60篇 |
2021年 | 118篇 |
2020年 | 94篇 |
2019年 | 89篇 |
2018年 | 74篇 |
2017年 | 147篇 |
2016年 | 169篇 |
2015年 | 91篇 |
2014年 | 247篇 |
2013年 | 340篇 |
2012年 | 180篇 |
2011年 | 195篇 |
2010年 | 181篇 |
2009年 | 215篇 |
2008年 | 234篇 |
2007年 | 214篇 |
2006年 | 178篇 |
2005年 | 181篇 |
2004年 | 137篇 |
2003年 | 109篇 |
2002年 | 108篇 |
2001年 | 113篇 |
2000年 | 103篇 |
1999年 | 94篇 |
1998年 | 95篇 |
1997年 | 66篇 |
1996年 | 65篇 |
1995年 | 57篇 |
1994年 | 35篇 |
1993年 | 35篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 35篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 25篇 |
1986年 | 11篇 |
1985年 | 38篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有4358条查询结果,搜索用时 31 毫秒
181.
In this paper the optimization of additively decomposed discrete functions is investigated. For these functions genetic algorithms have exhibited a poor performance. First the schema theory of genetic algorithms is reformulated in probability theory terms. A schema defines the structure of a marginal distribution. Then the conceptual algorithm BEDA is introduced. BEDA uses a Boltzmann distribution to generate search points. From BEDA a new algorithm, FDA, is derived. FDA uses a factorization of the distribution. The factorization captures the structure of the given function. The factorization problem is closely connected to the theory of conditional independence graphs. For the test functions considered, the performance of FDA—in number of generations till convergence—is similar to that of a genetic algorithm for the OneMax function. This result is theoretically explained. 相似文献
182.
183.
In this note we propose a nonstandard technique for constructing global a posteriori error estimates for the stationary convection–reaction–diffusion equation. In order to estimate the approximation error in appropriate weighted energy norms, which measures the overall quality of the approximations, the underlying bilinear form is decomposed into several terms which can be directly computed or easily estimated from above using elementary tools of functional analysis. Several auxiliary parameters are introduced to construct such a splitting and tune the resulting upper error bound. It is demonstrated how these parameters can be chosen in some natural and convenient way for computations so that the weighted energy norm of the error is almost recovered, which shows that the estimates proposed are, in fact, quasi-sharp. The presented methodology is completely independent of numerical techniques used to compute approximate solutions. In particular, it is applicable to approximations which fail to satisfy the Galerkin orthogonality, e.g., due to an inconsistent stabilization, flux limiting, low-order quadrature rules, round-off and iteration errors etc. Moreover, the only constant that appears in the proposed error estimates is of global nature and comes from the Friedrichs–Poincaré inequality. 相似文献
184.
For neural networks with all the parameters unknown, we focus on the global robust synchronization between two coupled neural networks with time-varying delay that are linearly and unidirectionally coupled. First, we use Lyapunov functionals to establish general theoretical conditions for designing the coupling matrix. Neither symmetry nor negative (positive) definiteness of the coupling matrix are required; under less restrictive conditions, the two coupled chaotic neural networks can achieve global robust synchronization regardless of their initial states. Second, by employing the invariance principle of functional differential equations, a simple, analytical, and rigorous adaptive feedback scheme is proposed for the robust synchronization of almost all kinds of coupled neural networks with time-varying delay based on the parameter identification of uncertain delayed neural networks. Finally, numerical simulations validate the effectiveness and feasibility of the proposed technique. 相似文献
185.
The effects of absolute energy calibration on BESⅢ physics are discussed in detail,which mainly involve the effects on τ mass measurement,cross section scan measurement,and generic error determination in other measurements. 相似文献
186.
We consider the kernel estimation of a multivariate regression function at a point. Theoretical choices of the bandwidth are possible for attaining minimum mean squared error or for local scaling, in the sense of asymptotic distribution. However, these choices are not available in practice. We follow the approach of Krieger and Pickands (Ann. Statist.9 (1981) 1066–1078) and Abramson (J. Multivariate Anal.12 (1982), 562–567) in constructing adaptive estimates after demonstrating the weak convergence of some error process. As consequences, efficient data-driven consistent estimation is feasible, and data-driven local scaling is also feasible. In the latter instance, nearest-neighbor-type estimates and variance-stabilizing estimates are obtained as special cases. 相似文献
187.
盛其荣 《新疆大学学报(理工版)》1987,(4)
本文讨论半线性Klein—Gordon方程Cauchy问题。对初值φ(x)、ψ(x),对空间维数n及半线性项加以适当限制,在Sobolev空间框架下、用不动点原理得到了整体解的存在唯一性。 相似文献
188.
189.
Revenue management (RM) enhances the revenues of a company by means of demand-management decisions. An RM system must take into account the possibility that a booking may be canceled, or that a booked customer may fail to show up at the time of service (no-show). We review the Passenger Name Record data mining based cancellation rate forecasting models proposed in the literature, which mainly address the no-show case. Using a real-world dataset, we illustrate how the set of relevant variables to describe cancellation behavior is very different in different stages of the booking horizon, which not only confirms the dynamic aspect of this problem, but will also help revenue managers better understand the drivers of cancellation. Finally, we examine the performance of the state-of-the-art data mining methods when applied to Passenger Name Record based cancellation rate forecasting. 相似文献
190.
The Monte Carlo study evaluates the relative accuracy of Warm's (1989) weighted likelihood estimate (WLE) compared to the maximum likelihood estimate (MLE) using the nominal response model. And the results indicate that WLE was more accurate than MLE. 相似文献