全文获取类型
收费全文 | 2016篇 |
免费 | 123篇 |
国内免费 | 204篇 |
专业分类
化学 | 439篇 |
晶体学 | 9篇 |
力学 | 120篇 |
综合类 | 20篇 |
数学 | 1353篇 |
物理学 | 402篇 |
出版年
2023年 | 22篇 |
2022年 | 27篇 |
2021年 | 42篇 |
2020年 | 42篇 |
2019年 | 54篇 |
2018年 | 39篇 |
2017年 | 59篇 |
2016年 | 47篇 |
2015年 | 43篇 |
2014年 | 59篇 |
2013年 | 155篇 |
2012年 | 66篇 |
2011年 | 71篇 |
2010年 | 53篇 |
2009年 | 97篇 |
2008年 | 141篇 |
2007年 | 121篇 |
2006年 | 106篇 |
2005年 | 112篇 |
2004年 | 103篇 |
2003年 | 123篇 |
2002年 | 81篇 |
2001年 | 82篇 |
2000年 | 89篇 |
1999年 | 77篇 |
1998年 | 93篇 |
1997年 | 83篇 |
1996年 | 40篇 |
1995年 | 28篇 |
1994年 | 32篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2343条查询结果,搜索用时 31 毫秒
111.
可变形多孔介质渗透系数的测定方法 总被引:12,自引:1,他引:12
在Biot理论基础上给出可变形多孔介质耦合渗流基本方程;求出小试件一维定常耦合渗流问题的解答;表明在一维流固耦合情况下试件内部压力梯度有明显的非均匀性。因此通过实验确定可变形多孔介质渗透系数在数学上可归结为微分方程的反问题,传统的测试渗透系数的方法需要改进。介绍了可变形多孔介质渗透系数的测试原理和测试方法。对粒状多孔材料实验的结果表明,传统实验方法得到的渗透系数误差较大。 相似文献
112.
基于土拱效应的抗滑桩与护壁桩的桩间距分析 总被引:4,自引:0,他引:4
抗滑桩与护壁桩分别在滑坡治理和基坑支护中发挥着巨大的作用 ,其实施正是利用了土中的成拱效应 ,然而传统桩的设计虽考虑土拱效应的存在 ,但桩间距确定理论与方法并未建立起来。本文首先基于土体的极限平衡条件对滑坡推力作用下的土体中的成拱作用进行研究 ,得出了抗滑桩的最大桩间距公式 ,并以某一具体工程为例 ,对该最大桩间距的物理意义和可用性进行了讨论。在此基础上 ,给出了在考虑土拱效应的情况下合理桩间距的确定方法 ,并以此为据 ,对边坡加固设计提出一些建议. 相似文献
113.
In this paper, we deal with the critical problems in residue arithmetic. The reverse conversion from a Residue Number System (RNS) to positional notation is a main non-modular operation, and it constitutes a basis of other non-modular procedures used to implement various computational algorithms. We present a novel approach to the parallel reverse conversion from the residue code into a weighted number representation in the Mixed-Radix System (MRS). In our proposed method, the calculation of mixed-radix digits reduces to a parallel summation of the small word-length residues in the independent modular channels corresponding to the primary RNS moduli. The computational complexity of the developed method concerning both required modular addition operations and one-input lookup tables is estimated as , where k equals the number of used moduli. The time complexity is modular clock cycles. In pipeline mode, the throughput rate of the proposed algorithm is one reverse conversion in one modular clock cycle. 相似文献
114.
We derive many new identities involving the Ramanujan-Göllnitz-Gordon continued fraction H(q). These include relations between H(q) and H(q
n
) , which are established using modular equations of degree n. We also evaluate explicitly H(q) at
for various positive integers n. Using results of M. Deuring, we show that
are units for all positive integers n. 相似文献
115.
It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary. 相似文献
116.
Sufficient conditions for asymptotic normality for quadratic forms in {nt − npt} are given, where {nt} are the observed counts with expected cell means {npt}. The main result is used to derive asymptotic distributions of many statistics including the Pearson's chi-square. 相似文献
117.
118.
Diffusion in fluids is analyzed at non-classical conditions, intermediate between the Knudsen and Fickian limits. The fluid is considered in the framework of the Einstein’s diffusion evolution equation involving expansions of the density distribution in powers of displacement and time. The standard truncation of these expansions results in the classical model of diffusion; however, higher-order terms lead to a departure from classical behavior. This has not been studied or discussed adequately in the literature previously.Here, we present an exact solution of the Einstein’s diffusion evolution equation without truncation of the density expansions. This solution illustrates limitations in the classical truncations and demonstrates non-classical effects due to large mean free paths, λ. In particular, this new solution shows that, at large λ, there are significant quantitative deviations from classical diffusion profiles. In addition, this solution demonstrates a dramatic change in the diffusion mechanism from the state where the molecular motions are predominantly ballistic to one of molecular chaos. This has implications for fundamentals of fluids between the Knudsen and Fickian limits, and for a variety of fields where evolution of a system includes random, multi-scale displacement of particles, such as nanotechnology, vacuum techniques, turbulence, and astrophysics. 相似文献
119.
Let λ(n) be the n-th normalized Fourier coeficient of a holomorphic Hecke eigenform f(z) ∈ Sk(Γ) for the full modular group.In one of his papers,Sankaranarayanan mentioned that it is an open problem to give a non-trivial estimate for the sum of λ(n) over cubes,i.e.n x λ(n3).In this paper,we are able to use the analytic properties of symmetric power L-functions to solve his problem.More precisely,we prove that Σn≤zλ(n3) x(3/4 +ε),Σn≤zλ(n4) x(97+ε). 相似文献
120.