全文获取类型
收费全文 | 2958篇 |
免费 | 99篇 |
国内免费 | 15篇 |
专业分类
化学 | 2123篇 |
晶体学 | 31篇 |
力学 | 36篇 |
数学 | 336篇 |
物理学 | 546篇 |
出版年
2023年 | 20篇 |
2022年 | 22篇 |
2021年 | 56篇 |
2020年 | 54篇 |
2019年 | 61篇 |
2018年 | 35篇 |
2017年 | 33篇 |
2016年 | 88篇 |
2015年 | 60篇 |
2014年 | 66篇 |
2013年 | 100篇 |
2012年 | 180篇 |
2011年 | 210篇 |
2010年 | 104篇 |
2009年 | 86篇 |
2008年 | 170篇 |
2007年 | 134篇 |
2006年 | 172篇 |
2005年 | 131篇 |
2004年 | 90篇 |
2003年 | 72篇 |
2002年 | 83篇 |
2001年 | 35篇 |
2000年 | 43篇 |
1999年 | 34篇 |
1998年 | 39篇 |
1997年 | 30篇 |
1996年 | 32篇 |
1995年 | 49篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 30篇 |
1990年 | 26篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 33篇 |
1980年 | 24篇 |
1978年 | 35篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1975年 | 22篇 |
1974年 | 28篇 |
1973年 | 26篇 |
1970年 | 21篇 |
排序方式: 共有3072条查询结果,搜索用时 768 毫秒
1.
In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox-active ligands with tunable H-bonding donors. The mononuclear Cu-anion complexes were oxidized to the corresponding “high-valent” intermediates by oxidation of the redox-active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H-atom abstraction. Thermodynamic analysis of the H-atom abstractions, which included reduction potential measurements, pKa determination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H-bonding donor did not lead to major differences in the reactivity of the “high-valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H+ and e− acceptor. 相似文献
2.
Lagrangian and Eulerian modelling approaches are compared for simulating turbulent dispersion and coalescence of droplets within a spray. Both models predict similar droplet dispersion rates and shifts in droplet size distribution due to coalescence within the spray, over a wide range of droplet and gas flows, and for sprays with different droplet-size distributions at the nozzle exit. The computer time required for simulating coalescence within a steady axisymmetric spray is of a similar order of magnitude regardless of which formulation, Eulerian or Lagrangian, is adopted. However, the Lagrangian formulation is more practical in terms of the range of applicability and ease of implementation. 相似文献
3.
The concept of strong interactions need not be limited to the sector of physics taken by QCD. While this domain is investigated by RHIC, LHC will be able to probe potential new strong interactions simultaneously: Finding the precise mechanism for electroweak symmetry breaking is one of the prime problems of physics. Intricately linked to this point is the question after the true nature or even the existence of the Higgs boson. Here, we present stronly interacting theories providing an explanation for the hierarchy problem and leading to a light composite Higgs boson, favoured by experimental data. Our variation of the standard model is consistent with precision data. We achieve this accordance by using technifermions in a higher representation of their gauge group. Anomaly conditions require at least one extra lepton family for some of the theories whereby they contain a natural dark matter candidate. We can accurately determine the masses of said leptons from experimental data. 相似文献
4.
Using ultra-high vacuum scanning tunneling microscopy (UHV-STM), we show that copper-phthalocyanine (CuPc) grows in a well ordered manner on hydrogen passivated vicinal silicon surfaces. CuPc grows one-dimensionally parallel to the monatomic steps on the vicinal silicon surface. Surprisingly, elongated clusters of the CuPc parallel to the step directions are formed even on the middle of the terraces well away from the step edges. The one-dimensional growth mode continues even after the full monolayer coverage on the substrate which results in strongly oriented growth mode of a thin film of CuPc on the vicinal silicon surfaces. 相似文献
5.
A new parallel storm surge model, the Parallel Environmental Model (PEM), is developed and tested by comparisons with analytic solutions. The PEM is a 2‐D vertically averaged, wetting and drying numerical model and can be operated in explicit, semi‐implicit and fully implicit modes. In the implicit mode, the propagation, Coriolis and bottom friction terms can all be treated implicitly. The advection and diffusion terms are solved with a parallel Eulerian–Lagrangian scheme developed for this study. The model is developed specifically for use on parallel computer systems and will function accordingly in either explicit of implicit modes. Storm boundary conditions are based on a simple exponential decay of pressure from the centre of a storm. The simulated flooding caused by a major Category 5 hurricane making landfall in the Indian River Lagoon, Florida is then presented as an example application of the PEM. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
Hamid R. Memarian Mohammad Bagheri Dietrich D?pp 《Monatshefte für Chemie / Chemical Monthly》2004,42(3):833-838
In continuation of previous work some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized and their photochemical behavior was studied under oxygen and argon atmosphere. Oxidation of the dihydropyridine ring and formation of pyridine derivatives was the result of the reaction. The presence of oxygen affects not only on the rate of oxidation, but also the formation of some unidentified by-products was observed on irradiation under this atmosphere. 相似文献
7.
8.
H. P. Gunnlaugsson K. Bharuth-Ram M. Dietrich M. Fanciulli H. O. U. Fynbo G. Weyer 《Hyperfine Interactions》2006,169(1-3):1315-1318
We report on the detection of Fe i –B pairs in heavily B doped silicon using 57Fe emission Mössbauer spectroscopy following implantation of radioactive 57Mn+ parent ions (T 1/2?=?1.5 min) at elevated temperatures >?850 K. The Fe i –B pairs are formed upon the dissociation of Fe i –V pairs during the lifetime of the Mössbauer state (T 1/2?=?100 ns). The resulting free interstitial Fei diffuses over sufficiently large distances during the lifetime of the Mössbauer state to encounter a substitutional B impurity atom, forming Fe i –B pairs, which are stable up to ~1,050 K on that time scale. 相似文献
9.
10.
A flow model in combination with a statistical-dynamical turbulence generator and a linearised Euler time-domain model for sound waves were used to simulate the effect of screen-induced turbulence on the noise level in the acoustical shadow of a screen in wind. Instead of simulating a great number of different frozen turbulence realisations, the concept of transient turbulence was successfully tested and applied. This concept is adequate to the time-domain model and reduces the computational demands. Several two-dimensional simulations allowed to isolate the individual effects of wind and screen on the propagation of 500 Hz sound waves over a 4-m high noise barrier. At a distance of 250 m from the source (240 m behind the screen) the sheltering effect of the screen and the refraction effect of the wind are in the order of 6 and 4 dB, respectively. The screen-induced turbulence leads to fluctuations in the noise level with a standard deviation of 1.2 dB and a maximum amplitude of 3 dB. However, the time averaged effect turned out to be in the order of merely 0.2 dB. The effect of the screen-induced turbulence on the average noise level behind the screen is therefore negligible. 相似文献