全文获取类型
收费全文 | 20945篇 |
免费 | 1938篇 |
国内免费 | 4937篇 |
专业分类
化学 | 16744篇 |
晶体学 | 500篇 |
力学 | 1727篇 |
综合类 | 249篇 |
数学 | 3042篇 |
物理学 | 5558篇 |
出版年
2024年 | 21篇 |
2023年 | 195篇 |
2022年 | 314篇 |
2021年 | 592篇 |
2020年 | 602篇 |
2019年 | 470篇 |
2018年 | 510篇 |
2017年 | 610篇 |
2016年 | 658篇 |
2015年 | 599篇 |
2014年 | 879篇 |
2013年 | 1650篇 |
2012年 | 1775篇 |
2011年 | 1249篇 |
2010年 | 980篇 |
2009年 | 1278篇 |
2008年 | 1379篇 |
2007年 | 1485篇 |
2006年 | 1416篇 |
2005年 | 1343篇 |
2004年 | 1238篇 |
2003年 | 1066篇 |
2002年 | 929篇 |
2001年 | 730篇 |
2000年 | 724篇 |
1999年 | 635篇 |
1998年 | 621篇 |
1997年 | 547篇 |
1996年 | 484篇 |
1995年 | 452篇 |
1994年 | 404篇 |
1993年 | 308篇 |
1992年 | 362篇 |
1991年 | 248篇 |
1990年 | 221篇 |
1989年 | 157篇 |
1988年 | 134篇 |
1987年 | 89篇 |
1986年 | 102篇 |
1985年 | 88篇 |
1984年 | 63篇 |
1983年 | 28篇 |
1982年 | 55篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
将稀土配合物Eu(asprin)_3phen掺杂到导电聚合物PVK中,制成结构分别为ITO/PVK:RE配合物/LiF/AI(1),ITO/PVK:RE配合物/PBD/LiF/AI(2)的电致发光(EL)器件。发现二者的电致发光谱存在着较大的差别:在器件(1)中,来自Eu~(3 )的位于594nm(~5D_0→~7F_1)和614nm(~5D_0→~7F_2)处的发光强度大致相当,而在器件(2)中,EL主要来自Eu~(3 )位于614nm的发光,594nm处的发光很弱,与薄膜状态下的光致发光谱(PL)一致。并针对此现象进行了初步讨论。 相似文献
73.
74.
Margherita De RosaMaria Rosaria Acocella Rosaria VillanoAnnunziata Soriente Arrigo Scettri 《Tetrahedron letters》2003,44(32):6087-6090
Initial concentration of enantioenriched or enantiopure catalysts proved to be an important factor for the achievement of a more pronounced amplification of ee's in the Ti(IV)/BINOL-catalyzed aldol reaction of an O-silyldienolate. 相似文献
75.
E. E. Ergozhin N. A. Bektenov A. K. Mekebaeva N. N. Chopabaeva 《Chemistry of Natural Compounds》2003,39(3):299-302
Phosphorus-containing cellulose cation exchangers were synthesized by reaction of wood cellulose with orthophosphoric acid and the ternary polymer from glycidylmethacrylate, styrene, and maleic anhydride. The effects of the ratio of reactants, temperature, and duration of the reaction on the phosphorylation and exchange capacity of the modified cellulose material were studied. 相似文献
76.
本文讨论了复调和函数在无穷远点的性质,揭示出有界区域上复调和函数的两类表示式之间的关系. 相似文献
77.
Douglas R. White Jason Owen-Smith James Moody Walter W. Powell 《Computational & Mathematical Organization Theory》2004,10(1):95-117
Social action is situated in fields that are simultaneously composed of interpersonal ties and relations among organizations, which are both usefully characterized as social networks. We introduce a novel approach to distinguishing different network macro-structures in terms of cohesive subsets and their overlaps. We develop a vocabulary that relates different forms of network cohesion to field properties as opposed to organizational constraints on ties and structures. We illustrate differences in probabilistic attachment processes in network evolution that link on the one hand to organizational constraints versus field properties and to cohesive network topologies on the other. This allows us to identify a set of important new micro-macro linkages between local behavior in networks and global network properties. The analytic strategy thus puts in place a methodology for Predictive Social Cohesion theory to be developed and tested in the context of informal and formal organizations and organizational fields. We also show how organizations and fields combine at different scales of cohesive depth and cohesive breadth. Operational measures and results are illustrated for three organizational examples, and analysis of these cases suggests that different structures of cohesive subsets and overlaps may be predictive in organizational contexts and similarly for the larger fields in which they are embedded. Useful predictions may also be based on feedback from level of cohesion in the larger field back to organizations, conditioned on the level of multiconnectivity to the field. 相似文献
78.
As predicted by Haldane, spin, S=1 one-dimensional (1D) Heisenberg antiferromagnet (HAF) has an energy gap between the singlet ground state and first excited triplet. On application of magnetic field, the triplet state Zeeman splits and the energy of one of the triplet state becomes zero at a critical field, Hc. Above Hc the system recovers magnetism. Then, we expect that a quasi-1D HAF will show a magnetic long-range ordering (LRO) at low temperatures due to the inter-chain coupling. This field-induced LRO has not been observed before due to complication of the crystal structure in the materials studied so far and/or technical difficulty.From a heat capacity measurement on a single crystal of an S=1 quasi-Q1D HAF, Ni(C5H14N2)2N3(PF6), we found an anomaly at a temperature in finite fields indicating a field-induced phase transition. A magnetic LRO is confirmed by a neutron diffraction measurement on the same sample. The temperature versus magnetic field phase diagram of this compound is constructed and discussed. 相似文献
79.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
80.
It has been observed that a quantum theory need not be Hermitian to have a real spectrum. We study the non-Hermitian relativistic quantum theories for many complex potentials, and obtain the real relativistic energy eigenvalues and corresponding eigenfunctions of a Dirac-charged particle in complex statically and spherically symmetric potentials. Complex Dirac–Eckart, complex Dirac–Rosen–Morse II, complex Dirac–Scarf and complex Dirac–Poschl–Teller potential are investigated. 相似文献