全文获取类型
收费全文 | 33875篇 |
免费 | 2796篇 |
国内免费 | 1788篇 |
专业分类
化学 | 11372篇 |
晶体学 | 197篇 |
力学 | 8974篇 |
综合类 | 364篇 |
数学 | 6717篇 |
物理学 | 10835篇 |
出版年
2024年 | 48篇 |
2023年 | 320篇 |
2022年 | 759篇 |
2021年 | 798篇 |
2020年 | 841篇 |
2019年 | 748篇 |
2018年 | 749篇 |
2017年 | 865篇 |
2016年 | 974篇 |
2015年 | 916篇 |
2014年 | 1274篇 |
2013年 | 2255篇 |
2012年 | 1573篇 |
2011年 | 1802篇 |
2010年 | 1410篇 |
2009年 | 1917篇 |
2008年 | 1958篇 |
2007年 | 1992篇 |
2006年 | 1853篇 |
2005年 | 1408篇 |
2004年 | 1429篇 |
2003年 | 1297篇 |
2002年 | 1231篇 |
2001年 | 1019篇 |
2000年 | 957篇 |
1999年 | 872篇 |
1998年 | 821篇 |
1997年 | 666篇 |
1996年 | 575篇 |
1995年 | 511篇 |
1994年 | 458篇 |
1993年 | 438篇 |
1992年 | 491篇 |
1991年 | 331篇 |
1990年 | 285篇 |
1989年 | 231篇 |
1988年 | 207篇 |
1987年 | 191篇 |
1986年 | 169篇 |
1985年 | 166篇 |
1984年 | 165篇 |
1983年 | 90篇 |
1982年 | 177篇 |
1981年 | 209篇 |
1980年 | 200篇 |
1979年 | 196篇 |
1978年 | 182篇 |
1977年 | 103篇 |
1976年 | 118篇 |
1973年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
62.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 相似文献
63.
64.
We discuss the problem of transmitting polarized pulses along optical fibers with variable dispersion. The dissipation and mean dispersion are assumed to be zero, which allows using the model of the vector nonlinear Schrödinger equation. We consider an optical fiber consisting of arms of equal length, which is assumed to be large. We propose an asymptotic recursive procedure for calculating the amplitude and the phase of an optical pulse propagating along the optical cable with variable dispersion. 相似文献
65.
Vincenzo Santagada Ferdinando FiorinoElisa Perissutti Beatrice SeverinoSara Terracciano Giuseppe CirinoGiuseppe Caliendo 《Tetrahedron letters》2003,44(6):1145-1148
A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating. 相似文献
66.
67.
The turbulent flow in a compound meandering channel with a rectangular cross section is one of the most complicated turbulent flows, because the flow behaviour is influenced by several kinds of forces, including centrifugal forces, pressure‐driven forces and shear stresses generated by momentum transfer between the main channel and the flood plain. Numerical analysis has been performed for the fully developed turbulent flow in a compound meandering open‐channel flow using an algebraic Reynolds stress model. The boundary‐fitted coordinate system is introduced as a method for coordinate transformation in order to set the boundary conditions along the complicated shape of the meandering open channel. The turbulence model consists of transport equations for turbulent energy and dissipation, in conjunction with an algebraic stress model based on the Reynolds stress transport equations. With reference to the pressure–strain term, we have made use of a modified pressure–strain term. The boundary condition of the fluctuating vertical velocity is set to zero not only for the free surface, but also for computational grid points next to the free surface, because experimental results have shown that the fluctuating vertical velocity approaches zero near the free surface. In order to examine the validity of the present numerical method and the turbulent model, the calculated results are compared with experimental data measured by laser Doppler anemometer. In addition, the compound meandering open channel is clarified somewhat based on the calculated results. As a result of the analysis, the present algebraic Reynolds stress model is shown to be able to reasonably predict the turbulent flow in a compound meandering open channel. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
68.
两部美国大学物理教材对我们教学改革的启示 总被引:9,自引:1,他引:8
介绍了美国两部大学物理教材的特点,分析了美国教材在教学内容、教学方法、教学手段现代化方面的特色,为我们的教学改革提供一些可供借鉴的经验。 相似文献
69.
相对论重离子碰撞实验中混合事件方法的研究 总被引:1,自引:0,他引:1
把RQMD(Relativistic Quantum Molecular Dynamics)产生器产生的数据输入作为原始事例取样,讨论了在比较复杂的背景情况下,一种新的混合事件方法,用以证实在相对论重离子碰撞实验中高能量激发共振态的存在.并以共振态重子Δ++为例演示了这一方法的应用. 相似文献
70.
车前子中多糖含量的测定 总被引:12,自引:1,他引:11
采用蒽酮-硫酸法比色测定,用精制车前子多糖测得车前子多糖对葡萄糖的换算因子,对我国同属不同品种的车前子不同采集时间及炮制前后其多糖含量进行了比较研究。结果表明:此测定方法简便可行。供试液在8h内显色稳定,重现性较好,平均回收率为97.8%,RSD=1.41%(n=5)。江西吉安产大粒车前子生品多糖含量在9.15%~9.83%之间,炮制后其多糖含量在6.29%~6.81%之间;南昌新祺周车前GAP标准基地的大粒车前子生品多糖含量为7.85%~8.38%,炮制后其多糖含量为6.01%~6.64%;东北产的小粒车前子生品多糖含量为6.61%,炮制后其多糖含量为6.45%。 相似文献