全文获取类型
收费全文 | 859篇 |
免费 | 13篇 |
国内免费 | 5篇 |
专业分类
化学 | 432篇 |
晶体学 | 3篇 |
力学 | 13篇 |
数学 | 166篇 |
物理学 | 263篇 |
出版年
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2016年 | 15篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 36篇 |
2012年 | 25篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 27篇 |
2008年 | 42篇 |
2007年 | 32篇 |
2006年 | 44篇 |
2005年 | 31篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 36篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1968年 | 4篇 |
1967年 | 6篇 |
排序方式: 共有877条查询结果,搜索用时 15 毫秒
91.
The degree of diastereoselectivity in the wrapping of four new chiral Salan ligands to form chiral-at-metal titanium complexes ranged from mild to perfect as a function of the ligands' N substituents; the enantiomerically pure complexes catalyzed the addition of diethyl zinc to benzaldehyde in 73-76% enantiomeric excess. 相似文献
92.
The coordination chemistry of amine tris(phenolate) ligands around V(III) and V(V) is described for the first time. Three amine tris(phenolate) ligands were employed featuring different steric and electronic influence exerted by the phenolate substituents in the ortho and para positions being either t-Bu, Me, or Cl. V(III) complexes of all ligands (1-3) were readily obtained by reaction between the ligand precursors and VCl3(THF)3 in the presence of triethylamine. The complexes obtained were pentacoordinate, a THF ligand completing the coordination sphere of the metal, which was found to be of almost perfect TBP geometry, as revealed by crystallography. V(V) oxo complexes of all the ligands (4-6) were readily obtained by a reaction between the ligand precursors and VO(OPr)3. The oxo complexes of the alkyl-bearing ligands (4 and 5) could also be synthesized by the air oxidation of the corresponding V(III) complexes (1 and 2); however, the attempted air oxidation of the V(III) complex bound to the electron-poor ligand (3) did not yield the corresponding oxo complex 6. 1H NMR and crystallographic analysis of complexes 4 and 5 supported their TBP structures. Complex 6, on the other hand, was found to be composed of a TBP complex (6a) and an octahedral complex (6b) in equilibrium, the octahedral complex being more stable at lower temperatures. An X-ray structure of 6b revealed a mononuclear oxo complex, the sixth coordination site being occupied by an aqua ligand to which two THF molecules are H-bonded. Complexes 4-6 catalyze the epoxidation of olefins by t-BuOOH, albeit slowly. These complexes may thus be considered as structural and functional models of vanadium-dependent haloperoxidase enzymes. 相似文献
93.
Within the context of mass-varying neutrinos, we construct a cosmological model that has a phase transition in the electromagnetic fine structure constant at a redshift of 0.5. The model accommodates hints of a time variable in quasar spectra and the nonobservance of such an effect at very low redshifts. It is consistent with limits from the recombination and primordial nucleosynthesis eras and is free of instabilities. 相似文献
94.
D. H. Brick A. M. Shapiro M. Widgoff E. D. Alyea Jr. T. Fuess E. S. Hafen P. Haridas R. I. Hulsizer C. Milstene I. A. Pless R. K. Yamamoto F. Grard R. Dolfini S. Ratti R. Di Marco M. Kalelkar R. J. Plano P. E. Stamer S. Dado J. Goldberg R. Heifetz A. Levy W. M. Bugg T. Handler E. L. Hart Y. Eisenberg U. Karshon 《Zeitschrift fur Physik C Particles and Fields》1986,32(1):59-63
The total hadron multiplicity and the multiplicity in the three-jet events ine + e ?-annihilation are considered. The formula for the total multiplicity (with account for the heavy quark contribution) agrees well with experiment. The value of the multiplicity for three-jet events is predicted. 相似文献
95.
William R. Dolbier Jr. Yian Zhai Wei Xu Will Wheelus Florian Dulong Efram Goldberg Ion Ghiviriga Merle A. Battiste 《Journal of fluorine chemistry》2008,129(12):1133-1138
When 4-nitro-AF4 is treated with nucleophiles such as alkoxides and cyanide, a novel ring opening, cyclophane destroying reaction is observed whereby, via an SNAr mechanism, the nucleophile attacks the bridgehead aryl carbon vicinal to the nitro group with subsequent aryl-CF2 bond cleavage. 相似文献
96.
We have examined and subjected to analysis an exhaustive number of consumer products, including but not limited to lotions and cosmetics, herbal supplements, household cleaners, food items, and beverages. As a result we describe all those consumer products herein, to our knowledge, that are appropriately labelled as “Chemical free”. 相似文献
97.
S. Yu. Torilov K. A. Gridnev V. I. Zherebchevsky M. Brenner L. I. Vinogradov V. Z. Goldberg T. V. Korovitskaya T. Lönnroth N. A. Maltsev M. Mutterer B. G. Novatskii M. Norrby J. M. K. Slotte Yu. G. Sobolev W. H. Trzaska G. P. Tyurin S. V. Khlebnikov 《JETP Letters》2011,94(1):6-10
High-spin states of the 22Ne nucleus in the excitation energy range of 15–30 MeV have been studied. The angular correlation method has been used to determine the spins of excited states. A number of new states with high angular momenta—20.0 MeV (9?), 20.7 MeV (11?), 21.6 MeV (9?), 22.2 MeV (12+), and 25.0 MeV (9?)—have been revealed. They are intensely populated in the reaction 14C(12C, α1)22Ne* → α2 + 18O and correspond to the rotational bands of various structures. 相似文献
98.
R.A. Vidal F. Bonetto J. Ferrón M.A. Romero Evelina A. García E.C. Goldberg 《Surface science》2011,605(1-2):18-23
In this paper we report measurements of the positive (H+) and negative (H?) ion fractions after H+ scattering from a highly oriented pyrolytic graphite (HOPG) surface. The experimental results show that for a fixed (large) exit angle the negative fraction is almost independent of the primary ion energy, while the positive fraction increases steadily. For a fixed incident energy, the H+ and H? fractions show a complementary behavior with exit angle. A dynamical quantum mechanical calculation, based on the localized and extended features of the atom–surface interaction, allows us to understand many of the features of the experimental results. 相似文献
99.
We prove that any planar 4-web defines a unique projective structure in the plane in such a way that the leaves of the web foliations are geodesics of this projective structure. We also find conditions for the projective structure mentioned above to contain an affine symmetric connection, and conditions for a planar 4-web to be equivalent to a geodesic 4-web on an affine symmetric surface. Similar results are obtained for planar d-webs, d>4, provided that additional d−4 second-order invariants vanish. 相似文献
100.
Moshe Goldberg Robert Guralnick W. A. J. Luxemburg 《Linear and Multilinear Algebra》2013,61(2):209-219
In this paper we continue our study of stability properties of subnorms on subsets of finite-dimensional, power-associative algebras over the real or the complex numbers. 相似文献