全文获取类型
收费全文 | 599篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
化学 | 387篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 49篇 |
物理学 | 164篇 |
出版年
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 21篇 |
2011年 | 40篇 |
2010年 | 17篇 |
2009年 | 9篇 |
2008年 | 30篇 |
2007年 | 31篇 |
2006年 | 26篇 |
2005年 | 26篇 |
2004年 | 36篇 |
2003年 | 28篇 |
2002年 | 23篇 |
2001年 | 11篇 |
2000年 | 4篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1956年 | 3篇 |
排序方式: 共有608条查询结果,搜索用时 656 毫秒
131.
A. Markiewicz D. V. Balbachas R. J. Fleming 《Journal of Thermal Analysis and Calorimetry》1991,37(6):1137-1152
Thermally stimulated luminescence (TSL) and thermally stimulated depolarization current (TSD) measurements were made simultaneously on low density polyethylene samples 0.175 mm thick, carrying evaporated gold electrodes. The samples were dc-polarized at room temperature at a field strength of 90 kV/cm, cooled to –190°C and X-irradiated with the field still applied, and then heated in short-circuit at 3 deg/min. Comparing the TSL and TSD data, particularly the effects of oxidizing the samples and immersing them in fuming nitric acid, it was shown that (1) the space-charge transport component of the TSD current between –190 and 30°C is negligible, (2) charge injection begins around –10°C (for evaporated gold electrodes) and increases rapidly with increasing temperature, and (3) all the injected charge is transported through the sample to the opposite electrode. Such transport takes place only through the amorphous regions of the sample.
Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60th birthday 相似文献
Zusammenfassung Es wurden simultane TSL- und TSD-Messungen an 0.175 mm starken, über aufgedampfte Goldelektroden verfügende Polyethylenproben geringer Dichte durchgeführt. Die Proben wurden bei Raumtemperatur und einer Feldstärke von 90 kV/cm gleichstrompolarisiert, auf –190°C abgekühlt, bei noch anliegendem Feld röntgenbestrahlt und dann unter Kurzschluß mit 3 Grad/min erhitzt. Durch einen Vergleich der TSL- und TSD-Daten, insbesondere der Wirkung der Oxydation der Proben bzw. des Eintauchens in rauchende Salpetersäure, zeigten, daß (1) die Raumladungstransport-Komponente des TSD-Stromes zwischen –190 und 30°C vernachlässigbar ist, (2) die Ladungsinjektion bei etwa — 10°C beginnt (für aufgedampfte Goldelektroden) und mit steigender Temperatur schnell anwächst und (3) die gesamte injezierte Ladung durch die Probe hindurch an die gegenüberliegende Elektrode transportiert wird. Ein derartiger Transport erfolgt nur in den amorphen Regionen der Probe.
Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60th birthday 相似文献
132.
This paper introduces the thermal column or the cold neutron guide beam of the 20 MW NBSR at the National Institute of Standards and Technology as a directk
o measurement facility. Measurement ofk
o at this facility not only produces accurate values, but avoids the additional correction factors needed in other measurement methods. Thek
o of Sb, Ag and Cr with respect to Sc as monitor have been measured and their values are comparable to values based on tabulated nuclear constants and to those measured by other researchers. 相似文献
133.
Wendell H. Fleming 《Applied Mathematics and Optimization》1980,6(1):271-285
This paper is concerned with the optimal control of continuous-time Markov processes. The admissible control laws are based on white-noise corrupted observations of a function on the state processes. A separated control problem is introduced, whose states are probability measures on the original state space. The original and separated control problems are related via the nonlinear filter equation. The existence of a minimum for the separated problem is established. Under more restrictive assumptions it is shown that the minimum expected cost for the separated problem equals the infimum of expected costs for the original problem with partially observed states.This research was supported in part by the Air Force Office of Scientific Research under AF-AFOSR 77-3063, and in part by the National Science Foundation MCS76-07261.Paper presented at the Workshop on Stochastic Processes in Infinite Dimensional Spaces and Random Fields, UCLA April, 1979. 相似文献
134.
135.
Prall BS Parkinson DY Ishikawa N Fleming GR 《The journal of physical chemistry. A》2005,109(48):10870-10879
We exploit a coherently excited nuclear wave packet to study nuclear motion modulation of electronic structure in a metal bridged phthalocyanine dimer, lutetium bisphthalocyanine, which displays two visible absorption bands. We find that the nuclear coordinate influences the energies of the underlying exciton and charge resonance states as well as their interaction; the interplay of the various couplings creates unusual anti-correlated spectral motion in the two bands. Excited state relaxation dynamics are the same regardless of which transition is pumped, with decay time constants of 1.5 and 11 ps. The dynamics are analyzed using a three-state kinetic model after relaxation from one or two additional states faster than the experimental time resolution of 50-100 fs. 相似文献
136.
A method was developed to analyze and quantitate volatile fatty acids such as acetic, propionic, butyric, iso-butyric, valeric, and iso-valeric acid from samples of biological origin. A capillary column system including an automatic on-column injection device as well as a precolumn of larger internal diameter than the analytical column was elaborated for this purpose. In order to obtain well resolved and correctly quantifiable chromatographic peaks it turned out to be essential to work under acidic/aqueous conditions. To achieve a better sample transfer into the chromatographic system an organic solvent had to be used together with the aqueous milieu, thus improving wetting properties of the liquid sample plug introduced into the column. Cold on-column injection was applied in order to avoid discrimination of the various acids due to sample splitting and the automatic technique was chosen in view of the large number of samples from biological extractions which had to be analyzed. 相似文献
137.
Yves Fleming Tom WirtzUrs Gysin Thilo GlatzelUrs Wegmann Ernst MeyerUrs Maier Jörg Rychen 《Applied Surface Science》2011,258(4):1322-1327
With the breakthroughs in lateral resolution with regards to secondary ion mass spectroscopy in recent years, new areas of research with much promise have opened up to the scientific community. Even though the much improved lateral resolution of 50 nm can effectively deliver more accurate 3D-images, the traditional 3D reconstructions, consisting of compiling previously acquired successive secondary ion mass spectrometry images into a 3D-stack, do not represent the real localized chemical distribution of the sputtered volume. Based on samples initially analyzed on the Cameca NanoSIMS 50 instrument, this paper portrays the advantages of combining the topographical information from atomic force microscopy and the chemical information from secondary ion mass spectrometry. Taking account of the roughness evolution within the analyzed zone, 3D reconstructions become a lot more accurate and allow an easier interpretation of results. On the basis of an Al/Cu sample, a comparison between traditional 3D imaging and corrected 3D reconstructions is given and the advantages of the newly developed 3D imaging method are explained. 相似文献
138.
139.
The fundamental parameter (FP) method was extended to account for the geometrical details of experimental x‐ray fluorescence (XRF) detection. In the traditional FP method the primary fluorescence photons have parallel pathways towards the detector. In the new approach the primary fluorescence photons can travel in any direction which allows them to reach the detector if not absorbed or scattered. The derived XRF signal equation explicitly depends on the length of the collimator in front of the detector, the detector size, position and orientation. An algorithm which numerically calculates the XRF signal for any set of parameters was developed and implemented for the Kα XRF signal of arsenic in skin. Optimal positions and orientations of the detector and collimator ensemble which maximize the XRF signal were found. Results and limitations of the method were also discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
140.
We say a matrix is simple if it is a (0,1)-matrix with no repeated columns. Given m and a k×l (0,1)-matrix F we define forb(m,F) as the maximum number of columns in a simple m-rowed matrix A for which no k×l submatrix of A is a row and column permutation of F. In set theory notation, F is a forbidden trace. For all k-rowed F (simple or non-simple) Füredi has shown that forb(m,F) is O(m
k
). We are able to determine for which k-rowed F we have that forb(m,F) is O(m
k−1) and for which k-rowed F we have that forb(m,F) is Θ(m
k
). 相似文献