全文获取类型
收费全文 | 23299篇 |
免费 | 855篇 |
国内免费 | 64篇 |
专业分类
化学 | 14998篇 |
晶体学 | 382篇 |
力学 | 737篇 |
综合类 | 1篇 |
数学 | 1826篇 |
物理学 | 6274篇 |
出版年
2023年 | 236篇 |
2022年 | 487篇 |
2021年 | 538篇 |
2020年 | 600篇 |
2019年 | 720篇 |
2018年 | 654篇 |
2017年 | 643篇 |
2016年 | 942篇 |
2015年 | 660篇 |
2014年 | 1072篇 |
2013年 | 1951篇 |
2012年 | 1598篇 |
2011年 | 1725篇 |
2010年 | 1133篇 |
2009年 | 953篇 |
2008年 | 1120篇 |
2007年 | 1104篇 |
2006年 | 876篇 |
2005年 | 755篇 |
2004年 | 594篇 |
2003年 | 477篇 |
2002年 | 427篇 |
2001年 | 257篇 |
2000年 | 245篇 |
1999年 | 187篇 |
1998年 | 127篇 |
1997年 | 155篇 |
1996年 | 181篇 |
1995年 | 170篇 |
1994年 | 166篇 |
1993年 | 182篇 |
1992年 | 217篇 |
1991年 | 159篇 |
1990年 | 149篇 |
1989年 | 160篇 |
1988年 | 139篇 |
1987年 | 137篇 |
1986年 | 115篇 |
1985年 | 165篇 |
1984年 | 182篇 |
1983年 | 134篇 |
1982年 | 143篇 |
1981年 | 132篇 |
1980年 | 141篇 |
1979年 | 145篇 |
1978年 | 148篇 |
1977年 | 133篇 |
1976年 | 95篇 |
1975年 | 92篇 |
1974年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The photocatalytic degradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid (2,4-D, 1), has been investigated in aqueous suspensions of titanium dioxide. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time in the presence of UV light source. The degradation kinetics was investigated under a variety of conditions, such as different types of TiO2, pH, catalyst and substrate concentrations. Higher photonic efficiencies were observed with Degussa P25 as compared with other photocatalysts. The degradation products were analysed by GC-MS and probable pathways for the formation of different products were proposed. 相似文献
42.
A triangulation of a connected closed surface is called weakly regular if the action of its automorphism group on its vertices
is transitive. A triangulation of a connected closed surface is called degree-regular if each of its vertices have the same
degree. Clearly, a weakly regular triangulation is degree-regular. In [8], Lutz has classified all the weakly regular triangulations
on at most 15 vertices. In [5], Datta and Nilakantan have classified all the degree-regular triangulations of closed surfaces
on at most 11 vertices.
In this article, we have proved that any degree-regular triangulation of the torus is weakly regular. We have shown that there
exists ann-vertex degree-regular triangulation of the Klein bottle if and only if n is a composite number ≥ 9. We have constructed two
distinctn-vertex weakly regular triangulations of the torus for eachn ≥ 12 and a (4m + 2)-vertex weakly regular triangulation of the Klein bottle for eachm ≥ 2. For 12 ≤n ≤ 15, we have classified all then-vertex degree-regular triangulations of the torus and the Klein bottle. There are exactly 19 such triangulations, 12 of which
are triangulations of the torus and remaining 7 are triangulations of the Klein bottle. Among the last 7, only one is weakly
regular. 相似文献
43.
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
44.
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
45.
46.
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
47.
48.
Applying tight-binding approximation and spin pairing of like charge carriers in a pair of excitons created in a lattice, the possibility of forming a bound exciton-exciton state is studied. It is found that, provided there exists strong exciton-lattice interaction, such a bound state may be formed and its energy may lie within the valence band deforming the material into a crystalline solid with no energy gap. Lowering of the energy is calculated in naphthalene and anthracene crystals where some experimental results are known. The excess energy released after the formation of such bound state can be adequate, depending on the material, to desorb neutral atoms or eject of electrons from surfaces. 相似文献
49.
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
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