全文获取类型
收费全文 | 4982篇 |
免费 | 239篇 |
国内免费 | 18篇 |
专业分类
化学 | 3364篇 |
晶体学 | 56篇 |
力学 | 99篇 |
数学 | 648篇 |
物理学 | 1072篇 |
出版年
2023年 | 43篇 |
2022年 | 31篇 |
2021年 | 69篇 |
2020年 | 89篇 |
2019年 | 105篇 |
2018年 | 50篇 |
2017年 | 51篇 |
2016年 | 157篇 |
2015年 | 179篇 |
2014年 | 179篇 |
2013年 | 265篇 |
2012年 | 309篇 |
2011年 | 346篇 |
2010年 | 187篇 |
2009年 | 158篇 |
2008年 | 284篇 |
2007年 | 233篇 |
2006年 | 202篇 |
2005年 | 199篇 |
2004年 | 181篇 |
2003年 | 140篇 |
2002年 | 123篇 |
2001年 | 90篇 |
2000年 | 102篇 |
1999年 | 64篇 |
1998年 | 73篇 |
1997年 | 63篇 |
1996年 | 86篇 |
1995年 | 75篇 |
1994年 | 72篇 |
1993年 | 72篇 |
1992年 | 56篇 |
1991年 | 41篇 |
1990年 | 42篇 |
1989年 | 34篇 |
1988年 | 34篇 |
1987年 | 39篇 |
1986年 | 36篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 32篇 |
1982年 | 43篇 |
1981年 | 27篇 |
1980年 | 38篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 43篇 |
1976年 | 24篇 |
1974年 | 31篇 |
1973年 | 22篇 |
排序方式: 共有5239条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
H. G. Bohlen W. von Oertzen R. Kalpakchieva B. Gebauer S. M. Grimes A. Lenz T. N. Massey M. Milin Ch. Schulz Tz. Kokalova S. Torilov S. Thummerer 《Physics of Atomic Nuclei》2003,66(8):1494-1500
The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2?, and 3/2?, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C. 相似文献
5.
6.
Andrea Mühlbauer Stephan Seip Alexander Nowak VanSung Tran 《Helvetica chimica acta》2003,86(6):2065-2072
Chemical investigation of the roots of the Vietnamese plant Tacca paxiana resulted in the isolation of five new steroidal compounds, taccalonolide R ( 6 ), S ( 7 ), T ( 8 ), U ( 9 ), and V ( 10 ). Their structures were established on the basis of NMR and mass‐spectral data. In addition, the five known taccalonolides A ( 1 ), B ( 2 ), E ( 3 ), K ( 4 ), and N ( 5 ) were also isolated and identified. 相似文献
7.
8.
Stephan Kreutzer 《Annals of Pure and Applied Logic》2004,130(1-3):61-78
We study the relationship between least and inflationary fixed-point logic. In 1986, Gurevich and Shelah proved that in the restriction to finite structures, the two logics have the same expressive power. On infinite structures however, the question whether there is a formula in IFP not equivalent to any LFP-formula was left open.
In this paper, we answer the question negatively, i.e. we show that the two logics are equally expressive on arbitrary structures. We give a syntactic translation of IFP-formulae to LFP-formulae such that the two formulae are equivalent on all structures.
As a consequence of the proof we establish a close correspondence between the LFP-alternation hierarchy and the IFP-nesting depth hierarchy. We also show that the alternation hierarchy for IFP collapses to the first level, i.e. the complement of any inflationary fixed point is itself an inflationary fixed point. 相似文献
9.
We present a systematic comparison of the correlation contribution at the level of the second-order polarization propagator approximation (SOPPA ) and MP 2 to the static dipole polarizability of (1) Be, BeH?, BH, CH+, MgH?, AIH, SiH+, and GeH+; (2) BH3, CH4, NH3, H2O, HF, BF, and F2; and (3) N2, CO, CN?, HCN, C2H2, and HCHO . Fairly extended basis sets were used in the calculations. We find that the agreement with experimental values is improved in SOPPA and MP .2 over the results at the SCF level. The signs and magnitudes of the correlation contribution in SOPPA are similar to those obtained in analytical derivative MP 2 calculations. However, it is not possible to say, in general, which method gives the largest correlation contribution or the best agreement with experiment, nor is it possible to make a priori prediction of the sign of the correlation contribution. For the first group of molecules, which have a quasi-degenerate ground state, additional CCDPPA and CCSDPPA calculations were performed and compared with polarizabilities obtained as analytical/numerical derivatives of the CCD and CCSD energies. The CCSDPPA results were found to be in better agreement with other calculations than were the SOPPA results, demonstrating the necessity of using methods based on infinite-order perturbation theory for these systems. © 1994 John Wiley & Sons, Inc. 相似文献
10.
We introduce a new technique for imaging oxygen concentrations in fuel/air mixtures that takes advantage of the different
responses of toluene and 3-pentanone to collisional quenching by molecular oxygen. Since laser-induced fluorescence signals
from both tracers upon excitation at 248 nm are spectrally well separated, simultaneous detection is possible. The technique
is first applied to instantaneous imaging in turbulent mixing processes of interacting seeded air and nitrogen flows.
Received: 1 August 2001 / Revised version: 29 October 2001 / Published online: 29 November 2001 相似文献