全文获取类型
收费全文 | 525666篇 |
免费 | 21669篇 |
国内免费 | 13474篇 |
专业分类
化学 | 302042篇 |
晶体学 | 7059篇 |
力学 | 23981篇 |
综合类 | 680篇 |
数学 | 62566篇 |
物理学 | 164481篇 |
出版年
2022年 | 5392篇 |
2021年 | 6287篇 |
2020年 | 6865篇 |
2019年 | 6656篇 |
2018年 | 6450篇 |
2017年 | 6017篇 |
2016年 | 10423篇 |
2015年 | 9428篇 |
2014年 | 12083篇 |
2013年 | 26897篇 |
2012年 | 23721篇 |
2011年 | 27531篇 |
2010年 | 17890篇 |
2009年 | 17728篇 |
2008年 | 23449篇 |
2007年 | 23076篇 |
2006年 | 22045篇 |
2005年 | 19749篇 |
2004年 | 17283篇 |
2003年 | 14905篇 |
2002年 | 14421篇 |
2001年 | 15578篇 |
2000年 | 12283篇 |
1999年 | 10169篇 |
1998年 | 8199篇 |
1997年 | 7888篇 |
1996年 | 7933篇 |
1995年 | 7198篇 |
1994年 | 6706篇 |
1993年 | 6221篇 |
1992年 | 6754篇 |
1991年 | 6493篇 |
1990年 | 5919篇 |
1989年 | 5633篇 |
1988年 | 5806篇 |
1987年 | 5377篇 |
1986年 | 5211篇 |
1985年 | 7382篇 |
1984年 | 7339篇 |
1983年 | 5978篇 |
1982年 | 6405篇 |
1981年 | 6307篇 |
1980年 | 6076篇 |
1979年 | 6118篇 |
1978年 | 6165篇 |
1977年 | 6110篇 |
1976年 | 6017篇 |
1975年 | 5892篇 |
1974年 | 5684篇 |
1973年 | 5910篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
321.
J. Schropp 《Numerische Mathematik》1997,78(1):87-101
Summary. We use the qualitative properties of the solution flow of the gradient equation to compute a local minimum of a real-valued function . Under the regularity assumption of all equilibria we show a convergence result for bounded trajectories of a consistent,
strictly stable linear multistep method applied to the gradient equation. Moreover, we compare the asymptotic features of
the numerical and the exact solutions as done by Humphries, Stuart (1994) and Schropp (1995) for one-step methods. In the
case of -stable formulae this leads to an efficient solver for stiff minimization problems.
Received July 10, 1995 / Revised version received June 27, 1996 相似文献
322.
Arno Jüschke Johannes Jahn Andreas Kirsch 《Computational Optimization and Applications》1997,7(3):261-276
In this paper we consider a special optimization problem withtwo objectives which arises in antenna theory. It is shown that thisabstract bicriterial optimization problem has at least one solution.Discretized versions of this problem are also discussed, and therelationships between these finite dimensional problems and the infinitedimensional problem are investigated. Moreover, we presentnumerical results for special parameters using a multiobjectiveoptimization method. 相似文献
323.
多级制造系统是现代制造业的主要加工方式,系统的每一级的加工速度和加工周期是系统设计的主要决策变量,正确确定这两个变量是系统得到优化的主要目标。本文导出了系统优化的基本模型,它包括系统各级的生产时间、等待时间、生产速度、生产成本以及系统的循环时间、总成本、产品利润和利润率等,并给出了一个应用实例。 相似文献
324.
Mössbauer spectroscopy was used to investigate the reactions of microbes with iron minerals in aqueous solutions and as components of rocks in banded iron formations and granite. A microbial biofilm that formed on a wall of an excavated granite vault in a deep underground laboratory initiated this research. At the aerobic face of the biofilm, iron was found in a form of ferrihydrite; in the anaerobic face against the rock, iron was found as very small siderite particles. Laboratory incubations of the biofilm microbial consortium showed different mineral species could be formed. When the microbial consortium from the biofilm was incubated with magnetite grains, up to about 10% of the iron was altered in three weeks to hematite. The ability of the consortium to precipitate iron both as Fe2+ and Fe3+ in close proximity may have a bearing on the deposition of banded iron formations. These reactions could also be important in microbially induced corrosion. 相似文献
325.
326.
We consider an optimal growth (multi-sector) model with nonconvex technology. Using the Clarke results on generalized gradients, we prove that the value function has left and right derivatives with respect to the initial capital stock, without requiring supermodularity assumptions. 相似文献
327.
328.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
329.
Summary It is shown that the outer automorphism group of a Coxeter groupW of finite rank is finite if the Coxeter graph contains no infinite bonds. A key step in the proof is to show that if the
group is irreducible andΠ
1 andΠ
2 any two bases of the root system ofW, thenΠ
2 = ±ωΠ
1 for some ω εW. The proof of this latter fact employs some properties of the dominance order on the root system introduced by Brink and
Howlett.
This article was processed by the author using the Springer-Verlag TEX PJour1g macro package 1991. 相似文献
330.