全文获取类型
收费全文 | 4660篇 |
免费 | 135篇 |
国内免费 | 9篇 |
专业分类
化学 | 3044篇 |
晶体学 | 157篇 |
力学 | 147篇 |
数学 | 428篇 |
物理学 | 1028篇 |
出版年
2023年 | 35篇 |
2022年 | 72篇 |
2021年 | 92篇 |
2020年 | 83篇 |
2019年 | 117篇 |
2018年 | 102篇 |
2017年 | 86篇 |
2016年 | 142篇 |
2015年 | 112篇 |
2014年 | 142篇 |
2013年 | 358篇 |
2012年 | 256篇 |
2011年 | 285篇 |
2010年 | 183篇 |
2009年 | 153篇 |
2008年 | 229篇 |
2007年 | 205篇 |
2006年 | 182篇 |
2005年 | 181篇 |
2004年 | 176篇 |
2003年 | 113篇 |
2002年 | 107篇 |
2001年 | 57篇 |
2000年 | 42篇 |
1999年 | 49篇 |
1998年 | 26篇 |
1997年 | 31篇 |
1996年 | 44篇 |
1995年 | 42篇 |
1993年 | 41篇 |
1992年 | 43篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 53篇 |
1988年 | 36篇 |
1987年 | 39篇 |
1986年 | 42篇 |
1985年 | 43篇 |
1984年 | 50篇 |
1983年 | 42篇 |
1982年 | 42篇 |
1981年 | 43篇 |
1980年 | 52篇 |
1979年 | 37篇 |
1978年 | 30篇 |
1977年 | 56篇 |
1976年 | 35篇 |
1975年 | 34篇 |
1974年 | 29篇 |
1973年 | 24篇 |
排序方式: 共有4804条查询结果,搜索用时 15 毫秒
1.
K. Batra V. Prasad M. Mohan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):191-198
The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction
of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented
for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters
are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na
Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered.
The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as
well as principal quantum number.
Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002 相似文献
2.
Beeranahally H Doreswamy Madegowda Mahendra Hirihally C Devarajegowda Venkatesh B Devaru Sridhar M Anandalwar Javaregowda S Prasad 《Analytical sciences》2004,20(2):407-408
The title compound was extracted from a natural product and its structure was characterized by an X-ray diffraction method. It crystallizes in the tetragonal space group P41 with cell parameters a = 15.832(10)A, c = 11.622(10)A, Z = 4; the final residual factor is R1 = 0.0769. The structure has both intra and intermolecular hydrogen bonds. 相似文献
3.
B. Sadashive Gowda G.S.V.L. Narasimham M.V. Krishna Murthy 《International Journal of Heat and Fluid Flow》1997,18(6):613-624
In this paper, a mathematical model for forced-air precooling of spherical food products in bulk is developed. The foods are arranged in horizontal layers stacked one above the other to form a rectangular parallelepiped with a vertical gap in between the product layers. The foods are cooled by chilled air blown along the height of the package. The governing equations for the conduction heat transfer in the foods, simultaneous heat and mass transfer at the food-air interface and in the air stream are solved numerically using finite-difference methods. A comprehensive numerical study is performed by varying the process parameters over a wide range. Typical results showing the variation of moist air properties along the height of the package and the effect of each parameter on the process time are presented. The ranges of parameters for advantageous operation of the precooling system are identified. Correlations are obtained for the process time based on the product center and mass-averaged temperatures in terms of process parameters. 相似文献
4.
P Rabindra Reddy P R Prasad Reddy M Harilatha Reddy 《Journal of Chemical Sciences》1987,99(5-6):297-303
Studies on interaction of La(III), Pr(III), Nd(III), Sm(III), Gd(III), Dy(III) and Er(III) with inosine and xanthosine in
a 1:1 ratio have been carried out by potentiometric equilibrium measurements at 35±0·1°C and 0·1 M (KNO3) ionic strength. Investigations were also made for the interaction of these metal ions and nucleosides with the biologically
important secondary ligands glycine and histidine. These investigations were undertaken with a view to assess the influence
of charge on the structure and stability of 1:1 metal-inosine/xanthosine systems.
DBT/India overseas Fellow at Harvard University (1986–88). 相似文献
5.
A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose. 相似文献
6.
Andrew Bach Xinglong Jiang Joseph Mckenna Kapa Prasad Oljan Repic Wen‐Chung Shieh 《Journal of heterocyclic chemistry》2004,41(4):637-640
An efficient approach has been developed for the synthesis of an isofervenulin analogue 1 employing a one‐pot condensation‐substitution reaction of a chlorocarboethoxytriazine (electrophile) with a urea (nucleophile). The resulting cyclization reaction resulted in the synthesis of a pyrimido‐heterocycle in good yield in either acidic or basic media. The former was assisted by utilizing trimethylsilyl chloride. 相似文献
7.
C. V. Yelamaggad Manoj Mathews Uma Hiremath Geetha Nair D. S. Shankar Rao S. Krishna Prasad 《Liquid crystals》2003,30(8):899-908
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
8.
We present exact numerical results for a symmetric layered medium (prism/Ag film/nonlinear dielectric/Ag film/prism) where
the middle dielectric slab is assumed to have a saturation-type nonlinearity. We show bistable behaviour in the power dependence
of the reflectivity ofp-polarized light under the condition when coupled surface modes are excited in the structure. Moreover, we study the effect
of saturation on the bistable behaviour to show that multivalued character is inhibited by saturation effects. The field distributions
corresponding to the minimum reflectivity states of the nonlinear structure are also presented. 相似文献
9.
10.