全文获取类型
收费全文 | 1674篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 1125篇 |
晶体学 | 15篇 |
力学 | 75篇 |
数学 | 299篇 |
物理学 | 199篇 |
出版年
2023年 | 12篇 |
2022年 | 13篇 |
2021年 | 24篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 47篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 76篇 |
2012年 | 68篇 |
2011年 | 104篇 |
2010年 | 61篇 |
2009年 | 48篇 |
2008年 | 79篇 |
2007年 | 92篇 |
2006年 | 80篇 |
2005年 | 84篇 |
2004年 | 75篇 |
2003年 | 67篇 |
2002年 | 57篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 15篇 |
排序方式: 共有1713条查询结果,搜索用时 15 毫秒
951.
Sergio Di Liberto Franco Meddi Giorgio Romano Giovanni Rosa Claudio Sgarbi 《Nuclear Physics A》1978,296(3):519-532
The disintegration of aluminium nuclei by 800 MeV electrons is studied using plastic detectors. Angular and energy distributions of emitted Li, Be and B isotopes are presented. The compatibility of the results with a two-stage process (cascade and evaporation) is studied with the aid of a Monte Carlo calculation. 相似文献
952.
The conformation al geometries and the possible interconversion paths for bicyclo[4.1.0] heptane (norcarane) and cyclohexene epoxide have been studied by both quantum mechanical and molecular mechanics calculations. The half-chair conformation is the most stable in the two compounds even if conformational equilibria with other forms cannot be excluded. Theoretical results are compared with the experimental data of molecular geometry, heat of formation, rotational constants, dipole moment, molar Kerr constant and proton coupling constants. The results obtained by the force-field method are satisfactory and consequently the extension of the method to derivatives of this kind seems possible. 相似文献
953.
Giorgio Talenti 《Rendiconti del Circolo Matematico di Palermo》1983,32(2):272-280
Si migliorano i risultati di [7]. 相似文献
954.
Giorgio Malesani Gianfranco Chiarelotto Maria Grazia Ferlin Sergio Masiero 《Journal of heterocyclic chemistry》1981,18(3):613-617
Treatment of 4,7-dimethoxyindoles 1 and 9 with ethylmagnesium bromide and ethyl chloroformate in refluxing dry ether gives the corresponding indole-1-carboxylic acid ethyl esters 3 and 10 as major products, together, with minor amounts of indole-3-carboxylic acid ethyl esters 2 and 11 . Similar treatment of 4,7-dimethoxyindole ( 1 ) with ethylmagnesium bromide and chloroacetyl chloride affords the related 3-chloroacetyl derivative 13 . All of the new 4,7-dimethoxyindole compounds were dealkylated with anhydrous aluminium chloride in refluxing dry benzene. Transformation of these demethylated indoles into other interesting derivatives, in view of possible antimicrobial activity is also reported. 相似文献
955.
A modified version of the Eguchi-Kawai model is proposed. We show that this modified model is equivalent to U(N) gauge theory in the infinite volume when N → ∞. The argument is based on investigations both in the continuum and on a lattice. We show that our modified model does not suffer from the notorious spontaneous symmetry breaking. 相似文献
956.
Giorgio Letta 《Probability Theory and Related Fields》1963,2(1):69-74
Ohne ZusammenfassungHerrn Prof. Dr. H. Richter bin ich für Hinweise wÄhrend der Abfassung dieser Arbeit dankbar. 相似文献
957.
Adamus G Montaudo MS Montaudo G Kowalczuk M 《Rapid communications in mass spectrometry : RCM》2004,18(13):1436-1446
A series of aliphatic copolyesters was obtained from (R,S)-beta-butyrolactone and two isomeric hydroxy acids, 6-hydroxyhexanoic and (R,S)-2-hydroxyhexanoic acids. The reactions were conducted in bulk without catalyst. Electrospray ionization tandem mass spectrometry (ESI-MSn) was used for molecular characterization of these copolyester oligomers. The mass spectra of the copolyesters studied have enabled identification of their molecular structures including chemical nature of the end groups (hydroxyl and carboxylate). The compositions of the oligocopolyesters and their sequence distributions were determined based on measurement of the relative intensities of the individual oligocopolyester peaks in the ESI mass spectra. The mass spectra (MS1) provided information on composition and sequence distribution, and small deviations from Bernoulli statistics were detected. The arrangement of co-monomer structural units along the oligopolyester chains was verified by MS/MS experiments and investigation of the fragmentation pathways. 相似文献
958.
959.
Discretization of phase space usually nullifies chaos in dynamical systems. We show that if randomness is associated with discretization dynamical chaos may survive and be indistinguishable from that of the original chaotic system, when an entropic, coarse-grained analysis is performed. Relevance of this phenomenon to the problem of quantum chaos is discussed. 相似文献
960.
Aji A. Anappara Alessandro Tredicucci Fabio Beltram Giorgio Biasiol Lucia Sorba 《Superlattices and Microstructures》2007,41(5-6):308
We report the external control of the intersubband polariton coupling by manipulating the carrier density in quantum wells resonantly coupled to a GaAs/AlGaAs microcavity. The electrons in the wells were tuned by means of a depletion gate bias or by utilizing charge transfer between the energetically aligned ground subbands of asymmetric tunnel-coupled quantum wells. We propose the use of tunnel-assisted control of the polariton ground state in an asymmetrically coupled quantum well for implementing ultrafast modulation of intersubband polaritons. 相似文献