全文获取类型
收费全文 | 360篇 |
免费 | 9篇 |
专业分类
化学 | 223篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 32篇 |
物理学 | 87篇 |
出版年
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 24篇 |
2011年 | 43篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 20篇 |
2007年 | 21篇 |
2006年 | 26篇 |
2005年 | 16篇 |
2004年 | 19篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1934年 | 1篇 |
1866年 | 2篇 |
排序方式: 共有369条查询结果,搜索用时 15 毫秒
1.
Graham R. Knox Peter L. Pauson Debra Willison 《Journal of organometallic chemistry》1993,450(1-2):177-184
Phenylazoferrocene undergoes nickelation and palladation exclusively on the phenyl group. Lithium phenylazocyclopentadienide has been converted into derivatives of Mo, Mn, Fe, Ru and Rh. 相似文献
2.
3.
Tshakane Tshepe Johan F. Prins Michael J. R. Hoch 《Czechoslovak Journal of Physics》1996,46(5):2439-2440
We have investigated low-temperature electrical transport mechanisms in the surface layer of a type IIa diamond which has been heavily implanted with boron-ions at low temperatures and then annealed at high temperatures. The boron atoms occupy substitutional sites giving rise to a heavily doped wide-bandgap semiconductor. The dc-conductivity results suggest that for the maximum boron doping that has been achieved, the diamond sample is close to the insulator-metal transition. A model to account for the observed increase in activated boron centres with ion dose is presented. On the insulating side of the transition, the data are interpreted in terms of variable-range hopping laws. 相似文献
4.
The use of continuous-flow isotope-ratio mass spectrometry (CF-IRMS) as a tool in soil analysis has been assessed as part of a larger study using a number of geological techniques applied in a forensic context. Carbon and nitrogen isotopic ratios, delta13C and delta15N, have been analysed to investigate situations which have arisen from crime casework. Three questions have been addressed: the role of spatial variation found over the short-scale (less than 20 m), temporal variation over a period of almost 2 years, and the variation found between source soils and soil transferred to footwear soles during a simple one-stage transfer process. Results are presented for the three experiments. The use of carbon and nitrogen isotopes has been shown to be useful in discriminating between soil types and sample locations, even when sampling occurs at a different time (as might be the case with a crime scene). In cases of primary transfer (from a source soil by a one-stage transfer to another surface, in this case, shoes and boots), the combination of carbon and nitrogen isotope ratios is a valuable tool in discriminating between sites and in showing the relationship of the transferred samples to the relevant source soils. Used in combination with other analytical techniques, isotopic analysis may prove to be a useful tool in a forensic context. 相似文献
5.
Zusammenfassung DurchEMK-Messungen und Röntgenbeugungsaufnahmen wurden die thermodynamischen und strukturellen Eigenschaften von Ni1–xTe untersucht. Die Phase Ni1–xTe reicht von NiTe (x=0) mit dem Strukturtype des NiAs bis zu Ni0,5Te mit dem Strukturtyp des CdJ2. Das Phasenfeld zwischen den beiden Verbindungen ist homogen und zeigt umx=0,25 einen Übergang zweiter Ordnung. Bei dieser Zusammensetzung ändert sich der Anstieg der Kurve Ni-Aktivität gegen Zusammensetzung. Auch der Gitterparameterc
0 ändert sich drastisch, und Beugungslinien der geordneten CdJ2-Struktur beginnen aufzutreten. Die Intensität der Beugungslinien ändert sich von der NiAs-Struktur bis zur CdJ2-Struktur gleichmäßig. Istx<0,2, so stimmen die Intensitäten mit denen überein, die man für die NiAs-Struktur berechnet, fürx>0,4 mit denen der CdJ2-Struktur. Aus den Aktivitätsmessungen wurde die Fehlstellenwechselwirkungsenergie berechnet. In dem Strukturtyp NiAs ist die Wechselwirkungsenergie zwischen zwei Leerstellen gleich Null. Die Leerstellen stoßen einander also weder ab noch ziehen sie einander an, sie sind also statistisch verteilt. Im Bereich der CdJ2-Struktur ist die Wechselwirkungsenergie zwischen zwei Leerstellen positiv, und zwarE
11=26,5 kcal/Mol. Die Leerstellen stoßen einander ab, und dac
0/2 kleiner ist alsa
0, trachten die Leerstellen, benachbarte Schichten zu vermeiden, und bilden so die CdJ2-Struktur.
Mit 9 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Diese Arbeit wurde zum Teil durch die National Aeronautics and Space Administration mit dem Grant NSG (T) 43 1101-020 unterstützt. 相似文献
Thermodynamics and Structure of Ni1–xTe
The thermodynamic properties and structural properties of Ni1–xTe have been studied using galvanic cell and X-ray diffraction techniques. The Ni1–xTe phase extends from NiTe (x=0) which has a NiAs type structure to Ni0.5Te (x=0.5) which has the CdI2 structure. The phase field between the two compounds is continuous and a second order type transition is taking place aroundx=0.25. At that composition the Ni-activity vs. composition curve changes slope. Thec o lattice parameter also changes drastically and diffraction lines due to the ordered CdI2 structure start to appear. The intensity of diffraction lines varies smoothly from the NiAs structure to the CdI2 structure. The intensities agree with that calculated for NiAs whenx<0.2, it agrees with the CdI2 intensity whenx>0.4. From the activity measurement, the defect interaction energy was calculated. In the NiAs type structure, the vacancyvacancy interaction energy is zero, the vacancies do not repel or attract each other and thus are random. In the CdI2 structure region the vacancy-vacancy interaction energy is positiveE 11=26.5 kcal/mole. The vacancies repel each other and asc 0/2 is smaller thana 0 the vacancies tend to avoid adjacent layers and thus form the CdI2 structure.
Mit 9 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Diese Arbeit wurde zum Teil durch die National Aeronautics and Space Administration mit dem Grant NSG (T) 43 1101-020 unterstützt. 相似文献
6.
In contrast to the histone-modifying action of other complexes of the type CpML(n)R, the compound obtained by linking the phenyl rings of two CpW(CO)(3)Ph moieties to the DNA-binding agent spermine selectively cleaves DNA in DNA-histone assemblies. 相似文献
7.
[reaction: see text] The palladium-catalyzed coupling of a range of enol triflates with amides, carbamates, and sulfonamides has been developed. This offers a simple and widely applicable synthesis of enamides, which may not be readily available by other means. 相似文献
8.
9.
Marcantonio KM Frey LF Liu Y Chen Y Strine J Phenix B Wallace DJ Chen CY 《Organic letters》2004,6(21):3723-3725
[reaction: see text] The palladium-catalyzed cyanation reaction is known to be sensitive to dissolved cyanide. Investigation into some causes of high levels of dissolved cyanide is presented here, along with a robust solution to this problem. 相似文献
10.
Long JW Logan MS Rhodes CP Carpenter EE Stroud RM Rolison DR 《Journal of the American Chemical Society》2004,126(51):16879-16889
We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties. 相似文献