全文获取类型
收费全文 | 1236篇 |
免费 | 23篇 |
国内免费 | 8篇 |
专业分类
化学 | 890篇 |
晶体学 | 7篇 |
力学 | 38篇 |
数学 | 135篇 |
物理学 | 197篇 |
出版年
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 66篇 |
2012年 | 62篇 |
2011年 | 71篇 |
2010年 | 28篇 |
2009年 | 26篇 |
2008年 | 58篇 |
2007年 | 63篇 |
2006年 | 62篇 |
2005年 | 90篇 |
2004年 | 61篇 |
2003年 | 49篇 |
2002年 | 55篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 9篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 20篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有1267条查询结果,搜索用时 314 毫秒
1.
A computer construction of the Monster is used to prove thatPSL(2, 59) is a subgroup of the Monster. 相似文献
2.
M. Tscherneck J. Kleinert C. Haimberger M. E. Holmes N. P. Bigelow 《Applied physics. B, Lasers and optics》2005,80(6):639-643
Ultracold molecules have been produced by photoassociation of Cs atoms trapped in a mirror magneto-optical trap. The molecules
were detected by resonantly enhanced multi-photon ionization followed by time-of-flight mass spectroscopy. The time-of-flight
ofatomic and molecular ions was investigated in the presence of a dc bias voltageapplied to the conducting mirror. This technique
provides a new tool for determining the distance between the cold molecules and the mirror surface.
This revised version was published online in August 2005 with a corrected cover date. 相似文献
3.
Dodecaynes 1a-d have been prepared via a convergent strategy that employs Sonogashira couplings as the carbon-carbon bond-forming tool. Due to the steric bulk of the DMTS groups, 1c adopts a nonplanar conformation, the dynamics of which have been probed by VT-NMR. The cobalt-catalyzed isomerization of 1a,b produced the new conjugated phenylenes 2a,b and 3a,b, respectively. [structure: see text] 相似文献
4.
5.
In this review paper, the NBS scale and its limitations are briefly discussed. The magnitude of liquid junction potentials and some calculated values are presented. The use of a molality scale for hydrogen electrode concentration cells at high temperatures is described, and results from measurements on ionization equilibria are summarized. Use of this scale is also recommended for certain circumstances with cells without liquid junction. As an alternative activity scale, use of the Pitzer ion-interaction treatment for ions is recommended for special cases. Finally, reference data are presented for ±HCl in HCl(aq) to 350°C and (HCl+NaCl)(aq) to 200°C that were derived by use of the Pitzer ion-interaction treatment.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991. 相似文献
6.
Jonathan S. Dordick K. C. Backman R. Balakrishnan R. Brent M. S. Ptashne L. P. Casson S. A. Goff A. L. Goldberg P. A. Cornelius R. M. Hochstrasser N. R. Kallenbach H. Rubin G. J. Todaro H. A. De Boer J. C. Delgoffe M. Lobmann N. ZyGraich L. Gehrke T. Kunkel A. Paau S. G. Platt L. Sequeira M. A. Palladino H. G. Roman D. Hultmark T. T. Rasmusan H. Steiner 《Applied biochemistry and biotechnology》1990,26(1):107-113
Protein engineering and site-directed mutagenesis is becoming immensely important in both fundamental studies and commercial applications involving proteins and enzymes in biocatalysis. Protein engineering has become a powerful tool to help biochemists and molecular enzymologists elucidate structure-function relationships in enzymic active sites, to understand the intricacies of protein folding and denaturation, and to alter the selectivity of enzymatic catalysis. Commercial applications of engineered enzymes are being developed to increase protein stability, widen or narrow substrate specificity, and to develop novel approaches for use of enzymes in organic synthesis, drug design, and clinical applications. In addition to protein engineering, novel expression systems have been designed to prepare large quantities of genetically engineered proteins. Recent US patents and scientific literature on protein engineering, site-directed mutagenesis, and protein expression systems related to protein engineering are surveyed. Patent abstracts are summarized individually and a list of literature references are given. 相似文献
7.
A paradox was observed in a previous study of the electrophoresis of linear DNA fragments in agarose gels (D. L. Holmes and N. C. Stellwagen, Electrophoresis 1990, 11, 5-15). The pore size of the agarose matrix was more accurately determined if the root-mean-square radius of gyration was used to measure DNA macromolecular size. However, the Ogston equations were obeyed and other gel parameters such as the apparent fiber radius and fiber volume appeared to be better described if the geometric mean radius was used to measure DNA size. This paradox can be resolved if relative mobilities (with respect to the smallest DNA molecule in the data set) are used to construct the Ferguson plots, instead of absolute mobilities. Using relative mobilities and the root-mean-square radius of gyration, the Ogston equations are obeyed and the pore size of the matrix is consistent with values determined by other methods. 相似文献
8.
9.
Valahovic MT Gunnoe TB Sabat M Harman WD 《Journal of the American Chemical Society》2002,124(13):3309-3315
A series of complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (Tp = hydridotris(pyrazolyl)borate) undergoes tandem electrophile/nucleophile addition reactions with a high degree of regiocontrol depending on the auxiliary ligand, L. When L = PMe(3), the reaction of the eta(2)-naphthalene complex with triflic acid followed by a silyl ketene acetal favors the 1,4-addition product, whereas when L = pyridine, N,N-dimethylaminopyridine, N-methylimidazole, or NH(3) the 1,2-addition product is favored. These reactions proceed with excellent stereocontrol: both electrophile (H(+), D(+)) and nucleophile (silyl ketene acetal) add anti to the face of metal coordination, and a single coordination diastereomer can be isolated for each reaction. One-electron oxidation of the Re complex affords the corresponding free dihydronaphthalene in good yield. 相似文献
10.
Dmitri V. Zagorevskii Yurii S. Nekrasov John L. Holmes 《Journal of the American Society for Mass Spectrometry》1993,4(3):216-222
The behavior of some substituted cyclopentadienylmanganese ions has been studied by tandem mass spectrometry. This metastable ion study showed that only C5H5Mn+ and (C5H4CN)Mn+ ions retain their nido-cluster structure (1), which is characterized by a simple metal-ligand bond cleavage. Other substituted ions, RXC5H4Mn+, rearrange to a different extent, depending on the nature of the substituent. The first rearrangement step is R radical migration to the central metal atom, leading to RMnC5H4X+-type ions (2). These ions decompose by elimination of X (for X=CO) or with formation of RMnX+, but further rearrangements can also occur. These are the reverse migration of R from the metal atom to the π-ligand (for R=H, Ph) and cyclopentadienyl ring expansion (for X=CH2). Collisional activation mass spectra contained an Mn+ ion peak, which can indicate the existence of stable type 1 structures for most cyclopentadienylmanganese ions. Carboxyl and hydroxymethyl derivatives exist, presumably as ions of type 2. The neutralization-reionization mass spectra of RXC5H4Mn+ ions are also discussed. 相似文献