全文获取类型
收费全文 | 2968篇 |
免费 | 103篇 |
国内免费 | 4篇 |
专业分类
化学 | 2140篇 |
晶体学 | 6篇 |
力学 | 38篇 |
数学 | 582篇 |
物理学 | 309篇 |
出版年
2021年 | 31篇 |
2020年 | 39篇 |
2019年 | 36篇 |
2018年 | 25篇 |
2016年 | 81篇 |
2015年 | 65篇 |
2014年 | 74篇 |
2013年 | 92篇 |
2012年 | 119篇 |
2011年 | 139篇 |
2010年 | 80篇 |
2009年 | 87篇 |
2008年 | 108篇 |
2007年 | 105篇 |
2006年 | 107篇 |
2005年 | 70篇 |
2004年 | 95篇 |
2003年 | 61篇 |
2002年 | 71篇 |
2001年 | 42篇 |
2000年 | 46篇 |
1999年 | 42篇 |
1998年 | 47篇 |
1997年 | 32篇 |
1996年 | 28篇 |
1995年 | 44篇 |
1994年 | 35篇 |
1993年 | 38篇 |
1992年 | 35篇 |
1991年 | 40篇 |
1990年 | 29篇 |
1989年 | 46篇 |
1988年 | 38篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 46篇 |
1984年 | 35篇 |
1983年 | 41篇 |
1982年 | 30篇 |
1981年 | 22篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 27篇 |
1977年 | 36篇 |
1976年 | 23篇 |
1975年 | 18篇 |
1973年 | 16篇 |
1971年 | 19篇 |
1934年 | 27篇 |
1933年 | 17篇 |
排序方式: 共有3075条查询结果,搜索用时 15 毫秒
41.
Jörg Fridgen Georg Eickerling Ana M. Santos 《Journal of organometallic chemistry》2004,689(17):2752-2761
Novel chiral 2′-pyridinyl alcohols derived from isopropylidene-protected carbohydrates are reported. They show different characteristics at the hydroxy group, but are all suitable ligands for chiral molybdenum(VI) complexes of the type MoO2L2 (L = chiral 2′-pyridinyl alcoholate). MoO2(acac)2 served as starting material in the complex syntheses. The structure of one ligand and one dioxo complex were exemplary established by X-ray crystallography. For catalytic runs in the enantioselective epoxidation catalysis trans-methylstyrene was used as model substrate, tert-butylhydroperoxide and cumolhydroperoxide, resp., as the oxidant. 相似文献
42.
43.
44.
The performance of a new separation technique for metal-speciation — capillary electrophoresis (CE) — is presented. Polyhydroxy compounds such as polyphenols and organic tanning agents can be determined in the g/L range. Certain complexes of these compounds with iron (III) ions may also be directly or indirectly verified. The work has shown that it is possible to determine certain complexes existing in beverages (tea and coffee) by decomplexation with chelating agents (CDTA). The ligands released can be separated by CE and identified by their migration time and UV/VIS absorption spectra. 相似文献
45.
It is shown that for certain classes of infinite block Toeplitz matricesT(a)=[a
j-k
]
0
the Moore-Penrose inverses of the finite sectionT
n
(a)=[a
j-k
]
0
n–1
converge to the Moore-Penrose inverse ofT(a). Furthermore the convergence for modified finite section methods and the finite section method for Wiener-Hopf integral and related operators are studied. 相似文献
46.
Georg Keller 《Communications in Mathematical Physics》1994,161(2):311-322
It is shown how the differential flow equation (or, equivalently, the continous renormalization group) method can be employed to give an astonishingly easy proof of the local Borel summability of the renormalized perturbative Euclidean massive
4
4
.Supported by NSF grant # DMS-9100383 相似文献
47.
Christoph Meingast Frank Gugenberger Georg Roth Miro Haluška Hans Kuzmany 《Zeitschrift für Physik B Condensed Matter》1994,95(1):67-71
The thermal expansion of vapor-grownC
70 single crystals ahs been investigated using high-resolution capacitance dilatometry from 5–380 K. Measurements were made both parallel and perpendicular to the hexagonalc-axis. Three first-order phase transitions which we associate with the consecutive disordering of theC
70 molecules are observed upon heating at 280 K (long-axis spinning), 300 K (long-axis precession) and 355 K (quasi-free rotation), respectively. The highest-temperature transition exhibits a very large (50 K) thermal hysteresis. Powder and single-crystal X-ray diffraction show that the crystals are predominantly hexagonal-close-packed (HCP) with an idealc/a1.63 above 360 K andc/a1.84 at 295 K. 相似文献
48.
The present paper studies the properties of Hubbard-like models in high spatial dimensionsD. In a first par the limit of infinite dimension and its main features-i.e.i) the mapping onto a generalized atomic model with an additional auxiliary field andii) the validity of the local approximation for the self-energy-are worked out in a systematic (1/D)-expansion. Since the hopping matrix elements have to be properly scaled with the dimensionD, the (1/D)-expansion is also an expansion in the hopping amplitude. Thus for small hopping theD-limit may serve as a proper approximation for finite-dimensional systems. The second part of the paper adopts the hybridisation-perturbation theory of the single impurity Anderson model in order to construct a perturbation theory for the auxiliary field of the generalized atom which can also be interpreted as an expansion in the hopping amplitude. The non-crossing approximation (NCA) is used to study the antiferromagnetic phase transtion of theD-Hubbard model in the case of half filling: the critical temperature, the antiferromagnetic order parameter and the free energy of the lattice system are calculated. The NCA-results are in quite good agreement with recent results from the imaginary-time discretisation method. 相似文献
49.
Two-photon excitation spectra of naphthalene and acenaphthene have been measured up to 50000 cm?1. In naphthalene. three two-photon allowed states are observed for which the symmetry assignment is confirmed by polarization. The corre- sponding transitions are also seen in acenaphthene. The experimental data are in excellent agreement with theoretical predictions. 相似文献
50.
Walter Fischer Cyril A. Grob Reinhard Hanreich Georg von Sprecher Adrian Waldner 《Helvetica chimica acta》1981,64(7):2298-2311
The solvolysis rates and products of the 6-exo-substituted 2-exo- 1a - 1u , and 2-endo-norbornyl p-toluenesulfonates 2a - 2u , have been determined. In general, the rate constants for 1 and 2 (log k) correlate well with the inductive constants σ of the substitutents at C(6); however, their sensitivity to σ is much larger in the 2-exo-series 1 than in the 2-endo-series 2 . This differential transmission of polar effects is the cause of decreasing 2-exo/2-endo rate ratios from 2388 for R = t-C4H9 to 0.37 for R = Br, i. e. with increasing electron attraction by the substituent. The high sensitivity of the rate constants for the 2-exo-p-toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)-atom, i. e. to 1,3-bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3-bridging, lead to faster reactions and to the formation of 2-exo substitution products. Conversely, acceptor substituents reduce 1,3-bridging, decrease rates and facilitate the formation of 2-endo substitution products. Graded 1,3-bridging is discussed in the light of Winstein's nonclassical ion concept. 相似文献