全文获取类型
收费全文 | 4941篇 |
免费 | 277篇 |
国内免费 | 18篇 |
专业分类
化学 | 3071篇 |
晶体学 | 22篇 |
力学 | 153篇 |
数学 | 933篇 |
物理学 | 1057篇 |
出版年
2023年 | 62篇 |
2022年 | 35篇 |
2021年 | 84篇 |
2020年 | 106篇 |
2019年 | 112篇 |
2018年 | 78篇 |
2017年 | 78篇 |
2016年 | 211篇 |
2015年 | 172篇 |
2014年 | 204篇 |
2013年 | 291篇 |
2012年 | 285篇 |
2011年 | 301篇 |
2010年 | 184篇 |
2009年 | 165篇 |
2008年 | 247篇 |
2007年 | 214篇 |
2006年 | 198篇 |
2005年 | 159篇 |
2004年 | 143篇 |
2003年 | 122篇 |
2002年 | 117篇 |
2001年 | 86篇 |
2000年 | 73篇 |
1999年 | 65篇 |
1998年 | 60篇 |
1997年 | 58篇 |
1996年 | 83篇 |
1995年 | 80篇 |
1994年 | 58篇 |
1993年 | 53篇 |
1992年 | 40篇 |
1991年 | 44篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1988年 | 29篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 49篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 30篇 |
1979年 | 29篇 |
1978年 | 31篇 |
1977年 | 34篇 |
1976年 | 26篇 |
1975年 | 23篇 |
1973年 | 26篇 |
排序方式: 共有5236条查询结果,搜索用时 15 毫秒
1.
2.
3.
Werner Leißner 《Results in Mathematics》1991,20(1-2):530-537
4.
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
5.
Hans Maaß 《Mathematische Annalen》1941,118(1):312-318
Ohne Zusammenfassung 相似文献
6.
7.
Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (Ea) of the segmental chain motion was lowest for dimeric maltose (Ea = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (Ea = 60.8 ± 1.8 kJ/mol). Subsequently, Ea leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the Ea dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher Ea values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004 相似文献
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.