全文获取类型
收费全文 | 3115篇 |
免费 | 187篇 |
国内免费 | 10篇 |
专业分类
化学 | 2125篇 |
晶体学 | 17篇 |
力学 | 67篇 |
数学 | 487篇 |
物理学 | 616篇 |
出版年
2023年 | 37篇 |
2022年 | 29篇 |
2021年 | 61篇 |
2020年 | 119篇 |
2019年 | 89篇 |
2018年 | 53篇 |
2017年 | 52篇 |
2016年 | 136篇 |
2015年 | 108篇 |
2014年 | 110篇 |
2013年 | 124篇 |
2012年 | 172篇 |
2011年 | 174篇 |
2010年 | 114篇 |
2009年 | 86篇 |
2008年 | 141篇 |
2007年 | 114篇 |
2006年 | 112篇 |
2005年 | 87篇 |
2004年 | 59篇 |
2003年 | 61篇 |
2002年 | 76篇 |
2001年 | 32篇 |
2000年 | 44篇 |
1999年 | 31篇 |
1998年 | 44篇 |
1997年 | 28篇 |
1996年 | 33篇 |
1995年 | 50篇 |
1994年 | 39篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 32篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 32篇 |
1986年 | 30篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1982年 | 19篇 |
1981年 | 33篇 |
1980年 | 23篇 |
1978年 | 36篇 |
1977年 | 31篇 |
1976年 | 33篇 |
1975年 | 20篇 |
1974年 | 32篇 |
1973年 | 27篇 |
1970年 | 24篇 |
1967年 | 22篇 |
排序方式: 共有3312条查询结果,搜索用时 15 毫秒
11.
12.
A flow model in combination with a statistical-dynamical turbulence generator and a linearised Euler time-domain model for sound waves were used to simulate the effect of screen-induced turbulence on the noise level in the acoustical shadow of a screen in wind. Instead of simulating a great number of different frozen turbulence realisations, the concept of transient turbulence was successfully tested and applied. This concept is adequate to the time-domain model and reduces the computational demands. Several two-dimensional simulations allowed to isolate the individual effects of wind and screen on the propagation of 500 Hz sound waves over a 4-m high noise barrier. At a distance of 250 m from the source (240 m behind the screen) the sheltering effect of the screen and the refraction effect of the wind are in the order of 6 and 4 dB, respectively. The screen-induced turbulence leads to fluctuations in the noise level with a standard deviation of 1.2 dB and a maximum amplitude of 3 dB. However, the time averaged effect turned out to be in the order of merely 0.2 dB. The effect of the screen-induced turbulence on the average noise level behind the screen is therefore negligible. 相似文献
13.
14.
A test statistic is developed that checks the validity of the extreme value conditions without specifiying the shape parameter of the limiting extreme value distribution. 相似文献
15.
16.
17.
Hans-Detlev Gilsing Jürgen Angerer Dietrich Prescher 《Monatshefte für Chemie / Chemical Monthly》2005,1(10):795-801
The synthesis of an oxidative major metabolite of bis(2-ethylhexyl) phthalate is described. The target molecule and its ring-deuterated isomer were obtained via acylation of the appropriate -hydroxy benzyl ester or the corresponding carboxylate with phthalic anhydride or phthalic anhydride-d4. All transformation steps proceed with high yields. 相似文献
18.
Grell D. Grell E. Bugnon P. Dietrich B. Lehn J.-M. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):483-495
The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous
solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole
type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M-1. Affinities close to 105 M-1 are found for polyazacryptands (3 and 4) exhibiting F-/Cl- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which
is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The
binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free
energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable
entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
20.
Bulk properties and free interfaces of mixtures of charged platelike colloids and salt are studied within the density-functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model. The charges of the particles are concentrated in their center. The density functional is derived by functional integration of an extension of the Debye-Hückel pair distribution function with respect to the interaction potential. For sufficiently small macroion charges, the bulk phase diagrams exhibit one isotropic and one nematic phase separated by a first-order phase transition. With increasing platelet charge, the isotropic and nematic binodals are shifted to higher densities. The Donnan potential between the coexisting isotropic and nematic phases is inferred from bulk structure calculations. Nonmonotonic density and nematic order parameter profiles are found at a free interface interpolating between the coexisting isotropic and nematic bulk phases. Moreover, electrically charged layers form at the free interface leading to monotonically varying electrostatic potential profiles. Both the widths of the free interfaces and the bulk correlation lengths are approximately given by the Debye length. For fixed salt density, the interfacial tension decreases upon increasing the macroion charge. 相似文献