全文获取类型
收费全文 | 9344篇 |
免费 | 588篇 |
国内免费 | 433篇 |
专业分类
化学 | 1513篇 |
晶体学 | 20篇 |
力学 | 449篇 |
综合类 | 42篇 |
数学 | 4004篇 |
物理学 | 1779篇 |
综合类 | 2558篇 |
出版年
2024年 | 12篇 |
2023年 | 50篇 |
2022年 | 128篇 |
2021年 | 131篇 |
2020年 | 134篇 |
2019年 | 280篇 |
2018年 | 295篇 |
2017年 | 158篇 |
2016年 | 166篇 |
2015年 | 255篇 |
2014年 | 448篇 |
2013年 | 579篇 |
2012年 | 475篇 |
2011年 | 722篇 |
2010年 | 589篇 |
2009年 | 625篇 |
2008年 | 655篇 |
2007年 | 742篇 |
2006年 | 587篇 |
2005年 | 422篇 |
2004年 | 377篇 |
2003年 | 327篇 |
2002年 | 281篇 |
2001年 | 201篇 |
2000年 | 218篇 |
1999年 | 192篇 |
1998年 | 162篇 |
1997年 | 143篇 |
1996年 | 130篇 |
1995年 | 117篇 |
1994年 | 104篇 |
1993年 | 125篇 |
1992年 | 88篇 |
1991年 | 76篇 |
1990年 | 49篇 |
1989年 | 59篇 |
1988年 | 53篇 |
1987年 | 39篇 |
1986年 | 29篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 11篇 |
1976年 | 4篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 834 毫秒
71.
强混合样本下回归加权估计的一致渐近正态性 总被引:5,自引:0,他引:5
在强混合样本下,讨论固定设计回归模型的加权函数估计的一致渐近正态性,给出一致渐近正态性的收敛速度,这个速度接近n-1/6. 相似文献
72.
73.
In this paper, we study the central limit theorem and its weak invariance principle for sums of a stationary sequence of random
variables, via a martingale decomposition. Our conditions involve the conditional expectation of sums of random variables
with respect to the distant past. The results contribute to the clarification of the central limit question for stationary
sequences.
Magda Peligrad is supported in part by a Charles Phelps Taft research support grant at the Univeristy of Cincinnati and the
NSA grant H98230-05-1-0066. 相似文献
74.
Takashi Seo 《Journal of multivariate analysis》2006,97(9):1976-1983
In this paper, we consider simultaneous confidence intervals for all contrasts in the means when the observations are missing at random in the intraclass correlation model. An exact test statistic for the equality of the means and Scheffé, Bonferroni and Tukey types of simultaneous confidence intervals are given by an extension of Bhargava and Srivastava [On Tukey's confidence intervals for the contrasts in the means of the intraclass correlation model, J. Royal Statist. Soc. B35 (1973) 147-152] when the missing observations are of the monotone type. Finally, numerical results of simultaneous confidence intervals are presented. 相似文献
75.
Debora Di Caprio 《Topology and its Applications》2006,153(14):2680-2702
We introduce and study some completeness properties for systems of open coverings of a given topological space. A Hausdorff space admitting a system of cardinality κ satisfying one of these properties is of type Gκ. Hence, we define several new variants of the ?ech number and use elementary submodels to determine further results. We introduce M-hulls and M-networks, for M elementary submodel. As an application, we give estimates for both the tightness and the Lindelöf number of a generic upper hyperspace. Two recent results of Costantini, Holá and Vitolo on the tightness of co-compact hyperspaces follow from ours as corollaries. 相似文献
76.
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids 总被引:1,自引:0,他引:1
The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation ( LES)
approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited
by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability
is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar
are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and
other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability. 相似文献
77.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons
is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we
estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second. 相似文献
78.
为借助激光全息进行无损检测,获得位相物体的信息,对位相物体激光全息二次曝光法无损检测进行了研究,指出一般的二次曝光法测位相物体典型光路的缺点,提出了物光波2次通过样品的改进方案。利用此方案对一些位相物体(如普通玻璃和有机玻璃)作了无损检测实验,得到了较满意的实验结果。与普通检测方法相比,该方法具有精度高、结果直接可靠、不损伤物体等诸多优点。对改进方案稍作改动,即可用于塑料制品和玻璃制品生产线对加工产品进行在线产品质量监控。 相似文献
79.
Bandcrossing in 31 rotational bands of 25 different odd-A nuclei in the rare-earth region has been analysed by using a two-band mixing formalism with a constant band interaction within
the framework of the effective decoupling picture. The interband interaction strengthV between the one-quasiparticle band and the three-quasiparticle band exhibits a variation with the neutron number which is
not different from the oscillatory behaviour observed in even-even nuclei and does not show signs of any appreciable phase
shifting as predicted by theory. However, the overall range of variation ofV is greater than that observed in even-even systems. 相似文献
80.
Extension of a combined analytical/numerical initial value problem solver for unsteady periodic flow
Here we describe analytical and numerical modifications that extend the Differential Reduced Ejector/ mixer Analysis (DREA), a combined analytical/numerical, multiple species ejector/mixing code developed for preliminary design applications, to apply to periodic unsteady flow. An unsteady periodic flow modelling capability opens a range of pertinent simulation problems including pulse detonation engines (PDE), internal combustion engine ICE applications, mixing enhancement and more fundamental fluid dynamic unsteadiness, e.g. fan instability/vortex shedding problems. Although mapping between steady and periodic forms for a scalar equation is a classical problem in applied mathematics, we will show that extension to systems of equations and, moreover, problems with complex initial conditions are more challenging. Additionally, the inherent large gradient initial condition singularities that are characteristic of mixing flows and that have greatly influenced the DREA code formulation, place considerable limitations on the use of numerical solution methods. Fortunately, using the combined analytical–numerical form of the DREA formulation, a successful formulation is developed and described. Comparison of this method with experimental measurements for jet flows with excitation shows reasonable agreement with the simulation. Other flow fields are presented to demonstrate the capabilities of the model. As such, we demonstrate that unsteady periodic effects can be included within the simple, efficient, coarse grid DREA implementation that has been the original intent of the DREA development effort, namely, to provide a viable tool where more complex and expensive models are inappropriate. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献