全文获取类型
收费全文 | 1487篇 |
免费 | 77篇 |
国内免费 | 3篇 |
专业分类
化学 | 1137篇 |
晶体学 | 7篇 |
力学 | 8篇 |
数学 | 158篇 |
物理学 | 257篇 |
出版年
2023年 | 16篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 31篇 |
2019年 | 31篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 57篇 |
2015年 | 31篇 |
2014年 | 47篇 |
2013年 | 76篇 |
2012年 | 111篇 |
2011年 | 127篇 |
2010年 | 64篇 |
2009年 | 50篇 |
2008年 | 93篇 |
2007年 | 89篇 |
2006年 | 95篇 |
2005年 | 74篇 |
2004年 | 72篇 |
2003年 | 54篇 |
2002年 | 37篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有1567条查询结果,搜索用时 15 毫秒
81.
Trettin R Knöller K Loosli HH Kowski P 《Isotopes in environmental and health studies》2002,38(2):103-119
Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as 834S, delta18O-H2O, deltaD, tritium, and 85K5r. delta34S values of the groundwater sulfate vary between -19...+ 37 per thousand CDT. No simple correlation exists between sulfate concentrations and delta34S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and 14C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable delta18O and 8D, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling. 相似文献
82.
Frieder Knüppel 《Geometriae Dedicata》1999,76(3):253-264
Let V be a finite-dimensional vector-space. A linear mapping on V is called simple if V( - 1) is 1-dimensional. Let S be a set of simple bijections on V. We discuss conditions entraining that each element of S is orthogonal (respectively symplectic) under an appropriate symmetric (respectively symplectic) bilinear form on V. 相似文献
83.
Anirban Sen Gupta Stephanie T. Lopina 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4906-4915
Tyrosine‐derived pseudo‐polypeptides have recently been established as potential biomaterials. The bulk production of these polymers is dependant upon the convenient synthesis of tyrosine‐derived diphenolic monomers. Suitable solution phase methods for the synthesis of such monomers, with transient activated esters, have been reported previously by Kohn, J.; Langer, R. In Biomaterials Science: An Introduction to Materials in Medicine; Ratner, B. D.; Hoffman, A. S.; Schoen, F. J.; Lemons, J. E., Eds.; Academic Press: New York, 1996; pp 64–72. However, for all the methods reported by them, purification and isolation of the diphenol monomer involves rigorous extraction, column purification, or an extensive aqueous workup. These may lead to the incorporation of solvent‐based as well as inorganic impurities and also may lead to difficulties in the process scale‐up. In this article, an alternate and relatively more convenient method for the synthesis of tyrosine‐based diphenol monomers is reported. This involved the investigation of polymer resin‐bound carbodiimide in the solid‐phase synthesis of L‐tyrosine‐based diphenolic monomers. This method was found to eliminate the need for rigorous purification processes and was found to maintain reasonable yield as well as maintain purity of the final monomer product. The monomer was able to produce polymers of a reasonably high‐molecular‐weight and a narrow polydispersity. The amide bond formation by such a polymer‐tethered reagent can be described to follow a reverse‐Merrifield sense and the method is relatively convenient to scale up. The L‐tyrosine‐based diphenolic monomeric compound formed by this method was analyzed by NMR, Fourier transform infrared, and elemental microanalysis techniques for chemical structure and composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4906–4915, 2004 相似文献
84.
G. Kühler D. Meuer S. Müller A. Richter E. Spamer O. Titze W. Knüpfer 《Physics letters. [Part B]》1981,104(3):189-193
Low momentum transfer, high-resolution inelastic electron scattering on 208Pb has been used to study the distribution of E1 and E2 strength in the region of excitation energy Ex = 8?12MeV. The E1 and E2 strength is very fragmented and the EWSR strength amounts to (10+7?6)% and (29+11?8)% in the investigated energy region, respectively. The E2 strength found is less than most current theoretical predictions but agrees qualitatively with a 1p - 1h +2p - 2h model calculation presented in this paper. The E2 strength is also smaller than what is known from hadron scattering and the shape of the strength distribution is also markedly different in electron and hadron scattering. 相似文献
85.
D. Bender G. Eulenberg A. Richter E. Spamer B.C. Metsch W. Knüpfer 《Nuclear Physics A》1983,398(3):408-414
Following the studies of the distribution of M1 strength in the even-even N = 28 isotones 48Ca, 50Ti, 52Cr and 54Fe by inelastic electron scattering, the result of a search for M1 transitions in the odd-even N = 28 nucleus 51V is reported. No strong M1 excitation has been detected, in contrast to a recent (p, p') experiment. There is no immediate explanation for this discrepancy. Shell-model calculations indicate that a part of it might be accounted for by an interference between the spin and orbital term of the electromagnetic transition operator in the (e, e') experiment. 相似文献
86.
W. Nitsche G. J. Wagner K. T. Knöpfle P. Grabmayr H. Riedesel 《Zeitschrift für Physik A Hadrons and Nuclei》1981,300(1):109-110
At 26 MeV/A, inelastic scattering of6Li ions from28Si proceeds predominantly via direct one-nucleon removal, while inelasticα scattering leads, in addition, to excitation of the target nucleus. 相似文献
87.
The reactions 17O(d, t) 16O and 17O(d, τ)16N have been investigated at Ed = 52 MeV. Energy spectra of tritons and τ-particles have been measured simultaneously up to excitation energies of 22 MeV in 16O and 10 MeV in 16N, respectively. Spectroscopic factors have been obtained by a DWBA analysis of the measured angular distributions. From the comparison of the t- and τ-spectra analog (T = 1) states in 16O could be identified and the distribution of T = 0 and T = 1 spectroscopic strengths could be deduced. Nearly the total and hole strengths have been found and the particle-hole multiplets could be located both for T = 0 and T = 1. The average residual interactions in both shell-model configurations turned out to be strikingly different. 相似文献
88.
89.
Tamm-Dancoff calculations including the complete 1p and 2s-1d shells are presented for non-normal parity states of nuclei with mass 15, 16 and 17. The basis is confined to ?ω excitations. Spurious states have been eliminated. The particle-particle and hole-hole interactions were taken from previous work. The particle-hole interaction was represented by 80 matrix elements from Kuo, eight of which were varied to fit 30 selected levels with a rms deviation of 310 keV. Spectroscopic factors and electromagnetic transition rates generally agree quite well with the experimental data. It is shown that the inclusion of the 1p and 1d. shells is essential even at low excitation energies in these nuclei. 相似文献
90.
O.?Docenko M.?Tamanis R.?FerberEmail author A.?Pashov H.?Kn?ckel E.?Tiemann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,36(1):49-55
We present a detailed experimental study of the D1Π state of the
NaRb molecule by means of Fourier transform spectroscopy of laser induced
fluorescence. The entire data field for the D1Π state of Na85Rb
and Na87Rb consists of rovibrational levels with v′=0-39 and
J′=1-200. The data were incorporated into a direct fit of a
single potential energy curve to the level energies using the Inverted
Perturbation Approach method. The D1Π state q factors, which
describe the Λ-doubling, have been obtained in a wide range of
rotational and vibrational quantum numbers. Analysis revealed several
perturbation regions in the D1Π state.
Electronic supplementary material Online Material 相似文献