全文获取类型
收费全文 | 4015篇 |
免费 | 113篇 |
国内免费 | 35篇 |
专业分类
化学 | 2559篇 |
晶体学 | 48篇 |
力学 | 161篇 |
数学 | 642篇 |
物理学 | 753篇 |
出版年
2022年 | 89篇 |
2021年 | 109篇 |
2020年 | 74篇 |
2019年 | 74篇 |
2018年 | 74篇 |
2017年 | 41篇 |
2016年 | 109篇 |
2015年 | 77篇 |
2014年 | 95篇 |
2013年 | 223篇 |
2012年 | 171篇 |
2011年 | 238篇 |
2010年 | 126篇 |
2009年 | 129篇 |
2008年 | 159篇 |
2007年 | 193篇 |
2006年 | 187篇 |
2005年 | 194篇 |
2004年 | 156篇 |
2003年 | 136篇 |
2002年 | 140篇 |
2001年 | 65篇 |
2000年 | 55篇 |
1999年 | 34篇 |
1998年 | 37篇 |
1997年 | 40篇 |
1996年 | 54篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 43篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 48篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 51篇 |
1981年 | 62篇 |
1980年 | 48篇 |
1979年 | 36篇 |
1978年 | 32篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 33篇 |
1974年 | 33篇 |
1973年 | 36篇 |
排序方式: 共有4163条查询结果,搜索用时 15 毫秒
11.
12.
G.Biju Kumar Hetal.V Patel Amrish C Shah Markus Trenkle Christine J Cardin 《Tetrahedron: Asymmetry》1996,7(12):3391-3396
N-Arylsulfonamides of (R)- and (S)-2-amino-1-butanol, on condensation with aromatic aldehydes produced diastereomerically pure 2-aryl-3-arenesulfonyl 4-ethyl-1,3-oxazolidines. The absolute configurations of one enantiomeric pair have been determined from two fully refined X-ray structures, supplemented by nmr data. 相似文献
13.
14.
15.
16.
17.
18.
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
19.
The problem treated in this paper concerns calculating the evolution of the pressure in a single-phase, slightly compressible fluid in a porous medium consisting of communicating layers. The fluid is produced through a point sink located on the side of an otherwise sealed cylindrical wellbore. This location of the sink causes the flow around the wellbore to be azimuthally asymmetric.The problem is solved through successive application of Laplace, finite Fourier and finite Hankel transforms. Although apparently straightforward, this approach leads to serious numerical difficulties. The published form of the inversion formula for the finite Hankel transform leads to inaccurate computation for the higher azimuthal modes even with 128 bit arithmetic. An alternative form is developed which enables accurate evaluation of the solution with the more practical 64 bit arithmetic. The technique for two-layer solution presented here can be directly extended to a problem with a larger number of communicating layers. This is the first instance of successful application of the finite Hankel transform to an azimuthally asymmetric diffusion problem. 相似文献
20.
In the study of integrable systems of ODE's arising from a Lax pair with a parameter, the constants of the motion occur as spectral curves. The specific curves depend upon the representation of the Lie algebra. In this paper a Galois theory of spectral curves is given that classifies the spectral curves from an integrable system. The spectral curves correspond to conjugacy classes of certain subgroups of the Weyl group for the Lie algebra. The theory is illustrated with the periodic Toda lattice.Partially supported by a Louisiana Education Quality Support Fund grant LEQSF (87-89)-RD-A-8 相似文献