全文获取类型
收费全文 | 195023篇 |
免费 | 1919篇 |
国内免费 | 614篇 |
专业分类
化学 | 107833篇 |
晶体学 | 3296篇 |
力学 | 7819篇 |
综合类 | 4篇 |
数学 | 18366篇 |
物理学 | 60238篇 |
出版年
2016年 | 2270篇 |
2015年 | 1684篇 |
2014年 | 2395篇 |
2013年 | 7842篇 |
2012年 | 5256篇 |
2011年 | 6622篇 |
2010年 | 4429篇 |
2009年 | 4359篇 |
2008年 | 5995篇 |
2007年 | 6160篇 |
2006年 | 5911篇 |
2005年 | 5407篇 |
2004年 | 4944篇 |
2003年 | 4422篇 |
2002年 | 4298篇 |
2001年 | 5772篇 |
2000年 | 4389篇 |
1999年 | 3511篇 |
1998年 | 2744篇 |
1997年 | 2779篇 |
1996年 | 2724篇 |
1995年 | 2516篇 |
1994年 | 2393篇 |
1993年 | 2285篇 |
1992年 | 2784篇 |
1991年 | 2666篇 |
1990年 | 2613篇 |
1989年 | 2639篇 |
1988年 | 2584篇 |
1987年 | 2587篇 |
1986年 | 2404篇 |
1985年 | 3269篇 |
1984年 | 3285篇 |
1983年 | 2716篇 |
1982年 | 2910篇 |
1981年 | 2847篇 |
1980年 | 2756篇 |
1979年 | 2897篇 |
1978年 | 3139篇 |
1977年 | 2963篇 |
1976年 | 2895篇 |
1975年 | 2755篇 |
1974年 | 2701篇 |
1973年 | 2715篇 |
1972年 | 1759篇 |
1971年 | 1467篇 |
1968年 | 1931篇 |
1967年 | 2130篇 |
1966年 | 1920篇 |
1965年 | 1499篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
282.
Images of the surface ordering of 4-n-octyl-4'-cyanobiphenyl, a room temperature smectic liquid crystal deposited upon graphite, have been obtained by scanning tunnelling microscopy. The microscope was operated in air using the constant-current mode. Under certain tunnelling conditions it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported conformations have been observed: an overlapping bilayer structure with spacing 3.7 nm, and a monolayer structure with spacing 2.4 nm. The latter structure may represent the first visual evidence for a surface polar ordered structure. 相似文献
283.
J. H. Koolen 《European Journal of Combinatorics》2002,23(8):987
Bannai and Ito conjectured in a 1987 paper that there are finitely many distance-regular graphs with fixed degree that is greater than two. In a series of papers they showed that their conjecture held for distance-regular graphs with degrees 3 or 4. In this paper we prove that the Bannai–Ito conjecture holds for degrees 5–7. 相似文献
284.
H. M. Soroush 《The Journal of the Operational Research Society》1994,45(3):287-300
The classical PERT approach uses the path with the largest expected duration as the critical path to estimate the probability of completing a project by a given deadline. However, in general, such a path is not the ‘most critical’ path and does not provide the smallest estimate for the probability of completion time. This paper studies the ‘most critical path’ problem and formulates it as an optimal path problem in a deterministic network with a two-attribute fractional objective function. An exact solution approach is presented for the optimal path problem which also gives the solution to the most critical path problem. The illustrative examples as well as our computational results demonstrate that the proposed algorithm provides estimates for the probabilities of completion time that are much more accurate than those of the classical approach. 相似文献
285.
286.
S. M. Lenzi C. H. Dasso M. A. Nagarajan H. M. Sofia A. Vitturi 《Acta Physica Hungarica A》1997,6(1-4):95-98
The existence of a neutron skin in neutron-rich nuclei is discussed in connection with the excitation of isovector dipole and quadrupole giant modes via isoscalar nuclear probes. In the case of large neutron excess, important contributions are obtained from the nuclear excitation, which may even become predominant according to proper kinematical conditions. At variance with the usual situation encountered in inelastic processes, constructive interference can be found between nuclear and Coulomb contributions. 相似文献
287.
We calculate the energy momentum tensor to orderE 4 in chiral perturbation theory. New terms not present in previous work enter the effective Lagrangian. We describe these and estimate the values of the new coupling constants, using the results of a disperisve analysis of the π andK energy momentum tensors and relying on tensor meson dominance for the spin two component. In addition, we compare our findings with the predictions of known scalar meson dominance models of the conformal anomaly. 相似文献
288.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. L. Seaman Y. Dalichaouch M. B. Maple J. D. Garrett 《Hyperfine Interactions》1991,64(1-4):517-522
We have performed both zero field and high transverse field measurements at dilution refrigerator temperatures on a number of heavy electron systems, examining the superconducting and magnetic properties of these interesting materials. Among the materials studied to date are UBe13, URu2Si2 and U6Fe. The magnetic field penetration depth in the superconducting state of UBe13 is greater than 10000 Å, as no increase in the transverse field relaxation rate is observed belowT c . A sharp increase in the precession frequency is seen, starting atT c . This frequency shift shows little temperature dependence at low temperature; we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we have observed relaxation in high transverse field due to the formation of a flux lattice in U6Fe, a material where the electron effective mass is rather lighter than in other heavy fermion systems. The relaxation exhibits a sharp onset atT c=3.9 K, and is flat at low temperatures as expected for a conventional superconductor. 相似文献
289.
Recent studies have established that side chain polymeric liquid crystals composed of mesogenic and non-mesogenic side groups keep their liquid-crystalline properties even for a low proportion of mesogens. We show that the detailed structures of three kinds of new diluted liquid crystal polysiloxanes depend on the nature of the co-substituent as well as on the proportion of the silicon sites occupied by the mesogenic groups. Mixtures of these systems with low molar mass liquid crystals were also investigated in terms of compatibility and/or stabilization of smectic A phases. 相似文献
290.