全文获取类型
收费全文 | 18247篇 |
免费 | 752篇 |
国内免费 | 50篇 |
专业分类
化学 | 12845篇 |
晶体学 | 327篇 |
力学 | 641篇 |
综合类 | 1篇 |
数学 | 1242篇 |
物理学 | 3993篇 |
出版年
2024年 | 48篇 |
2023年 | 184篇 |
2022年 | 403篇 |
2021年 | 470篇 |
2020年 | 535篇 |
2019年 | 603篇 |
2018年 | 569篇 |
2017年 | 528篇 |
2016年 | 783篇 |
2015年 | 560篇 |
2014年 | 918篇 |
2013年 | 1631篇 |
2012年 | 1331篇 |
2011年 | 1366篇 |
2010年 | 892篇 |
2009年 | 715篇 |
2008年 | 944篇 |
2007年 | 920篇 |
2006年 | 721篇 |
2005年 | 646篇 |
2004年 | 527篇 |
2003年 | 436篇 |
2002年 | 358篇 |
2001年 | 199篇 |
2000年 | 175篇 |
1999年 | 134篇 |
1998年 | 92篇 |
1997年 | 123篇 |
1996年 | 134篇 |
1995年 | 96篇 |
1994年 | 102篇 |
1993年 | 121篇 |
1992年 | 124篇 |
1991年 | 101篇 |
1990年 | 111篇 |
1989年 | 101篇 |
1988年 | 78篇 |
1987年 | 80篇 |
1986年 | 73篇 |
1985年 | 101篇 |
1984年 | 103篇 |
1983年 | 83篇 |
1982年 | 78篇 |
1981年 | 68篇 |
1980年 | 75篇 |
1979年 | 83篇 |
1978年 | 65篇 |
1977年 | 81篇 |
1976年 | 60篇 |
1975年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
41.
A model of two interacting (chemically different) linear polymer chains is solved exactly using the real-space renormalization
group transformation on a family of Sierpinski gasket type fractals and on a truncated 4-simplex lattice. The members of the
family of the Sierpinski gasket-type fractals are characterized by an integer scale factorb which runs from 2 to ∞. The Hausdorff dimensiond
F of these fractals tends to 2 from below asb → ∞. We calculate the contact exponenty for the transition from the State of segregation to a State in which the two chains are entangled forb = 2-5. Using arguments based on the finite-size scaling theory, we show that forb→∞, y = 2 - v(b) d
F, wherev is the end-toend distance exponent of a chain. For a truncated 4-simplex lattice it is shown that the system of two chains
either remains in a State in which these chains are intermingled in such a way that they cannot be told apart, in the sense
that the chemical difference between the polymer chains completely drop out of the thermodynamics of the system, or in a State
in which they are either zipped or entangled. We show the region of existence of these different phases separated by tricritical
lines. The value of the contact exponenty is calculated at the tricritical points. 相似文献
42.
Absolute total electron scattering cross sections for carbon dioxide have been measured at low electron energies using a photoelectron
source. The measurements have been carried out at 27 electron energies varying from 0.91–9.14 eV with an accuracy of ±3%.
The cross sections obtained in the present experiment have been compared with other measurements and theoretical computations. 相似文献
43.
44.
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
45.
R.G. Abhilash Kumar K. Vinod U. Syamaprasad 《Applied Physics A: Materials Science & Processing》2007,88(2):243-247
MgB2/Fe wires were prepared by electrical self-heating of in situ powder-in-tube wires for the first time at ambient conditions.
Characterization of the wires processed at 750 °C, 800 °C and 850 °C for 15 min by XRD, SEM, ϱ–T, susceptibility and JC measurements shows that the MgB2 formed is of high quality particularly with respect to phase purity and transport JC. The method considerably reduces the overall energy consumption vis-à-vis the production cost, simplifies the complexity
of the fabrication procedure and is promising for manufacture of high-quality MgB2 superconducting wires.
PACS 74.70.Ad; 74.62.Bf; 74.25.Fy; 74.25.Ha; 81.20.Hy 相似文献
46.
K. Ravikumar B. Sridhar M. Mahesh V. V. Narayana Reddy 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):o574-o576
The crystal structures of pyranoquinolines 9‐fluoro‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline, C18H18FNO, and 9‐methyl‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline, C19H21NO, are isomorphous. In both structures, the pyran ring is exo to the six‐membered N‐heterocyclic ring formed in the cycloaddition step. The torsion angles across the phenyl linkage for the two structures are −91.2 (1) and −88.3 (2)°. The striking feature in both crystal packings is that they do not contain the expected conventional hydrogen bonds, in spite of the presence of good hydrogen‐bonding functionalities. Possible C—H⋯π interactions are, however, observed. 相似文献
47.
48.
Sherif Yehia C. Mitros Sanjeev Kumar S. Jha Glenn M. Julian R. A. Dunlap 《Hyperfine Interactions》1987,34(1-4):415-418
The systematics of hyperfine magnetic fields at sp impurities on the Z-sites in Co based Heusler alloys are investigated. New TDPAC measurements of Cd hyperfine fields are reported. 相似文献
49.
Mass transport due to electromigration can be estimated if the diffusion coefficientD and the electromigration effective charge numberZ* are known. Neutron activated tracer scanning method determine the radioactivity at different positions. An automatic scanning
system for determining the radioactive concentration profiles developed using a microprocessor is described in this paper.
Using the radioactive concentration profiles the electromigration shift is determined. From this shift the electromigration
effective charge numberZ* is calculated. The system developed was tested for tin thin films. 相似文献
50.
Arup Baksi Bidyut Kumar Roy Rasajit Kumar Bera 《Mathematical and Computer Modelling》2006,44(11-12):1069-1079
The fundamental equations of the problems of generalized thermoelasticity with one relaxation parameter including heat sources in infinite rotating magneto-thermo-viscoelastic media have been derived in the form of a vector matrix differential equation in the Laplace transform domain for a one dimensional problem. These equations have been solved by the eigenvalue approach to determine deformations, stress, and temperature. The results have been compared to those available in the existing literature. The graphs have been drawn to show the effect of rotation in the medium. 相似文献