全文获取类型
收费全文 | 39872篇 |
免费 | 2296篇 |
国内免费 | 1881篇 |
专业分类
化学 | 22249篇 |
晶体学 | 233篇 |
力学 | 3924篇 |
综合类 | 535篇 |
数学 | 8105篇 |
物理学 | 9003篇 |
出版年
2024年 | 66篇 |
2023年 | 378篇 |
2022年 | 1067篇 |
2021年 | 1066篇 |
2020年 | 1016篇 |
2019年 | 979篇 |
2018年 | 873篇 |
2017年 | 1100篇 |
2016年 | 1480篇 |
2015年 | 1120篇 |
2014年 | 1589篇 |
2013年 | 2772篇 |
2012年 | 2270篇 |
2011年 | 2050篇 |
2010年 | 1762篇 |
2009年 | 2261篇 |
2008年 | 2218篇 |
2007年 | 2519篇 |
2006年 | 2080篇 |
2005年 | 1884篇 |
2004年 | 1827篇 |
2003年 | 1521篇 |
2002年 | 1168篇 |
2001年 | 957篇 |
2000年 | 933篇 |
1999年 | 837篇 |
1998年 | 785篇 |
1997年 | 707篇 |
1996年 | 646篇 |
1995年 | 624篇 |
1994年 | 548篇 |
1993年 | 454篇 |
1992年 | 421篇 |
1991年 | 361篇 |
1990年 | 327篇 |
1989年 | 216篇 |
1988年 | 218篇 |
1987年 | 136篇 |
1986年 | 117篇 |
1985年 | 141篇 |
1984年 | 112篇 |
1983年 | 58篇 |
1982年 | 94篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 74篇 |
1978年 | 33篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.
102.
103.
Dimensional analysis is presented as a powerful tool in the study of the paste boriding process. In particular, a dimensional method is used to study the growth kinetics of the boride layers FeB and Fe2B. Experiments were performed in AISI 1045 steel and AISI M2 steel, to test the suggested model. Samples of 1045 steel were prepared and treated using boron paste thickness of 3-5 mm, at temperatures of 1193, 1223 and 1273 K, with 2, 4 and 6 h of treatment time. The M2 specimens had boron paste thickness of 3 and 4 mm and temperatures of 1223, 1253 and 1273 K for 2 and 6 h. Results indicate that the growth of boron layers obeys power laws of the form y = αxβ, where α and β constants are a function of the material and the interface of interest. Validation of the model was carried out using experimental data with an average error percentage of 7.6% for Fe2B in 1045 steel, 15.8% for FeB and 3.4% for Fe2B in M2 steel. 相似文献
104.
105.
This paper examines the performance of Commodity Trading Advisors (CTAs) using fixed and variable benchmarking models. In
order to avoid the troublesome passive and active commodity and managed futures benchmarks (indices) when examining the performance
of CTAs, we innovate by using data envelopment analysis (DEA). Because this alternative class has non-linear returns due to
long/short positions, and derivatives (i.e., dynamic trading strategies), DEA can alleviate the problems usually associated
with these indices. The effectiveness of using benchmarking models in a DEA setting will provide investors with an alternative
technique in assessing the performance and identifying efficient CTAs. 相似文献
106.
We consider the M(t)/M(t)/m/m queue, where the arrival rate λ(t) and service rate μ(t) are arbitrary (smooth) functions of time. Letting pn(t) be the probability that n servers are occupied at time t (0≤ n≤ m, t > 0), we study this distribution asymptotically, for m→∞ with a comparably large arrival rate λ(t) = O(m) (with μ(t) = O(1)). We use singular perturbation techniques to solve the forward equation for pn(t) asymptotically. Particular attention is paid to computing the mean number of occupied servers and the blocking probability
pm(t). The analysis involves several different space-time ranges, as well as different initial conditions (we assume that at t = 0 exactly n0 servers are occupied, 0≤ n0≤ m). Numerical studies back up the asymptotic analysis.
AMS subject classification: 60K25,34E10
Supported in part by NSF grants DMS-99-71656 and DMS-02-02815 相似文献
107.
本文我们给出一个修正的非线性扩散方程模型,与Cotte Lions和Morel的模型相比该模型有许多实质上的优点。主要的想法是把原来去噪声部分:卷积Gauss过程替代为解一个有界区域上的线性抛物方程问题,因此避开了对初始数值如何全平面延拓的问题。我们从数学上的证明该问题解的存在性和适定性,同时给出对矩形域情况的解的级数形式。最后我们给基于本模型的数值计算差分模型,并且给出几个具体图像在该模型下处理结果。 相似文献
108.
Alexander Ya. Kruger 《Set-Valued Analysis》2006,14(2):187-206
The paper continues investigations of stationarity and regularity properties of collections of sets in normed spaces. It contains
a summary of different characterizations (both primal and dual) of regularity and a list of sufficient conditions for a collection
of sets to be regular. 相似文献
109.
Huai-Chun Zhou Yu-Bo HouDong-Lin Chen Chu-Guang Zheng 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(5):605-620
A parallel-plane space filled with absorbing, emitting, isotropically scattering, gray medium is studied in this paper. The boundary intensity and boundary temperature profiles are calculated for the inverse analysis. For the simultaneous estimation of temperature, absorption and scattering coefficient profiles in the medium, the sum of residuals of boundary intensity and temperature after being weighted by a balance factor is minimized through using a Newton-type iteration algorithm and the least-squares method. To avoid over-updating for the parameters, the relative updating magnitude during the iteration process is constrained not to be >0.5. It is shown that the boundary intensity measurement alone is not enough to estimate simultaneously the temperature (source) and the radiative properties (both absorption and scattering coefficients) when the measurement data contain sensitive random errors. The boundary temperature measurement can serve as a necessary supplementation to the boundary intensity to make this kind of inverse radiative transfer problem resolvable. It was shown that a compensation relationship between absorption and scattering coefficients makes it difficult to fix them accurately. Parabolic profiles for the three parameters are used to validate the estimation method. When the optical thickness approaches 4.0, the results for the radiative properties are not acceptable, although the result for temperature profile is reasonable. This means the method needs further improvements. 相似文献
110.