全文获取类型
收费全文 | 5044篇 |
免费 | 184篇 |
国内免费 | 24篇 |
专业分类
化学 | 3573篇 |
晶体学 | 42篇 |
力学 | 110篇 |
数学 | 711篇 |
物理学 | 816篇 |
出版年
2023年 | 32篇 |
2022年 | 57篇 |
2021年 | 119篇 |
2020年 | 85篇 |
2019年 | 81篇 |
2018年 | 70篇 |
2017年 | 74篇 |
2016年 | 184篇 |
2015年 | 128篇 |
2014年 | 152篇 |
2013年 | 301篇 |
2012年 | 373篇 |
2011年 | 410篇 |
2010年 | 222篇 |
2009年 | 182篇 |
2008年 | 349篇 |
2007年 | 323篇 |
2006年 | 277篇 |
2005年 | 314篇 |
2004年 | 237篇 |
2003年 | 213篇 |
2002年 | 186篇 |
2001年 | 73篇 |
2000年 | 70篇 |
1999年 | 34篇 |
1998年 | 57篇 |
1997年 | 36篇 |
1996年 | 71篇 |
1995年 | 35篇 |
1994年 | 38篇 |
1993年 | 51篇 |
1992年 | 29篇 |
1991年 | 33篇 |
1990年 | 41篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 35篇 |
1986年 | 22篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 3篇 |
排序方式: 共有5252条查询结果,搜索用时 31 毫秒
21.
We derive the action of 2D gravity from the two-cocycle of the Virasoro group by using a previously introduced method for constructing a dynamical system from a Lie group. A natural construction and explanation of the hidden SL(2,
)-Kac-Moody symmetry, of general applicability, is provided. We also show how the proper quantization goes beyond the ordinary co-adjoint orbit method, and the possible connection with the Poisson-Lie groups. 相似文献
22.
Rafael Ortega 《Journal of Dynamics and Differential Equations》1992,4(4):651-665
This paper gives sufficient conditions for the existence of periodic solutions of twist type of a time-dependent differential equation of the second order. The concept of periodic solution of twist type is defined in terms of the corresponding Birkhoff normal form and, in particular, implies that the solution is Lyapunov stable. Some applications to nonlocal problems are given. 相似文献
23.
Stereoselectivity in the intermolecular Pauson-Khand reaction of electron-deficient terminal alkynes
A family of terminal alkyne dicobalthexacarbonyl complexes bearing groups with a range of electron-withdrawing abilities has been synthesized. After submitting these complexes to the intermolecular Pauson-Khand reaction with norbornadiene, electron-deficient substrates afforded up to 26% of the unexpected endo-cyclopentenone. 相似文献
24.
A linear inequality system with infinitely many constraints is polynomial (analytical) if its index set is a compact interval
of the real line and all its coefficients are polynomial (analytical, respectively) functions of the index on this interval.
This paper provides an example of analytical system whose solution set cannot be the solution set of any polynomial system.
Research supported by DGES of Spain and FEDER of UE, Grant BFM2002-04114-C02-01.
Research supported by CONACyT of Mexico, Grant 130036.
Research partially supported by CONACyT of Mexico, Grant 44003. 相似文献
25.
Miguel A. Arcones 《Annals of the Institute of Statistical Mathematics》1998,50(1):87-117
We consider exact weak and strong Bahadur-Kiefer representations of the least absolute deviation estimator for the linear regression model. The precise behavior of these representations is obtained under minimal conditions. 相似文献
26.
P.R.S. Gomes I. Padron E. Crema O.A. Capurro J.O. Fernández Niello G.V. Marti A. Arazi M. Trotta J. Lubian M.E. Ortega A.J. Pacheco M.D. Rodríguez J.E. Testoni R.M. Anjos L.C. Chamon M. Dasgupta D.J. Hinde K. Hagino 《Physics letters. [Part B]》2006
Complete and incomplete fusion cross sections for the 9Be + 144Sm reaction have been measured at near-barrier energies, using the delayed X-ray detection technique. At above-barrier energies these show a suppression of complete fusion for this weakly bound projectile on an intermediate mass target. The suppression factor, attributed to 9Be break-up, was deduced from a comparison of complete fusion yields with coupled-channels calculations, and appears consistent with measured incomplete fusion product yields. At ∼10%, it is considerably smaller than the value of ∼30% previously found for a 208Pb target. Simultaneous measurements of elastic and inelastic scattering permit a clearer picture of the reaction mechanisms. 相似文献
27.
28.
We show that the racemic states of the B 2 phase of liquid crystals composed of banana-shaped molecules do not satisfy the Curie principle. Thus it is argued that these states cannot exist in bulk samples and the homochiral states constitute the only stable microscopic structures. A reinterpretation of the racemic states with the same macroscopic optical behaviour is proposed in terms of mixtures of the homochiral structures. 相似文献
29.
Large-scale production of cellulose-binding domains. Adsorption studies using CBD-FITC conjugates 总被引:1,自引:0,他引:1
Ricardo Pinto Joana Carvalho Manuel Mota Miguel Gama 《Cellulose (London, England)》2006,13(5):557-569
A method for the gram-scale production of cellulose-binding domains (CBD) through the proteolytic digestion of a commercial enzymatic preparation (Celluclast) was developed. The CBD obtained, isolated from Trichoderma reesei cellobiohydrolase I, is highly pure and heavily glycosylated. The purified peptide has a molecular weight of 8.43 kDa, comprising the binding module, a part of the linker, and about 30% glycosidic moiety. Its properties may thus be different from recombinant ones expressed in bacteria. CBD-fluorescein isothiocyanate conjugates were used to study the CBD-cellulose interaction. The presence of fluorescent peptides adsorbed on crystalline and amorphous cellulose fibers suggests that amorphous regions have a higher concentration of binding sites. The adsorption is reversible, but desorption is a very slow process. 相似文献
30.
Miguel Angel Javaloyes Paolo Piccione 《Differential Geometry and its Applications》2006,24(5):521-541
We study the singularities of the exponential map in semi Riemannian locally symmetric manifolds. Conjugate points along geodesics depend only on real negative eigenvalues of the curvature tensor, and their contribution to the Maslov index of the geodesic is computed explicitly. We prove that degeneracy of conjugate points, which is a phenomenon that can only occur in semi-Riemannian geometry, is caused in the locally symmetric case by the lack of diagonalizability of the curvature tensor. The case of Lie groups endowed with a bi-invariant metric is studied in some detail, and conditions are given for the lack of local injectivity of the exponential map around its singularities. 相似文献