全文获取类型
收费全文 | 777篇 |
免费 | 43篇 |
国内免费 | 10篇 |
专业分类
化学 | 484篇 |
晶体学 | 2篇 |
力学 | 31篇 |
数学 | 192篇 |
物理学 | 121篇 |
出版年
2023年 | 10篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 22篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 27篇 |
2015年 | 17篇 |
2014年 | 38篇 |
2013年 | 40篇 |
2012年 | 33篇 |
2011年 | 34篇 |
2010年 | 44篇 |
2009年 | 33篇 |
2008年 | 60篇 |
2007年 | 31篇 |
2006年 | 43篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1972年 | 3篇 |
1965年 | 4篇 |
1964年 | 4篇 |
1962年 | 3篇 |
1939年 | 3篇 |
1936年 | 4篇 |
1935年 | 3篇 |
排序方式: 共有830条查询结果,搜索用时 15 毫秒
1.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
2.
Arne Miller 《Radiation Physics and Chemistry》1993,42(4-6):581-584
The activities and services of the accredited Risø High Dose Reference Laboratory are described. The laboratory operates according to the European standard EN 45001 regarding Operation of Testing Laboratories, and it fulfills the requirements of being able to deliver traceable dose measurements for control of radiation sterilization. The accredited services include:
1. 1. Irradiation of dosimeters and test samples with cobalt-60 gamma rays.
2. 2. Irradiation of dosimeters and test samples with 10 MeV electrons.
3. 3. Issue of and measurement with calibrated dosimeters.
4. 4. Measurement of the dosimetric parameters of an irradiation facility.
5. 5. Measurement of absorbed dose distribution in irradiated products.
The paper describes these services and the procedures necessary for their execution. 相似文献
3.
Linear complexity and linear complexity profile are important characteristics of a sequence for applications in cryptography
and Monte-Carlo methods.
The nonlinear congruential method is an attractive alternative to the classical linear congruential method for pseudorandom
number generation.
Recently, a weak lower bound on the linear complexity profile of a general nonlinear congruential pseudorandom number generator
was proven by Gutierrez, Shparlinski and the first author. For most nonlinear generators a much stronger lower bound is expected.
Here, we obtain a much stronger lower bound on the linear complexity profile of nonlinear congruential pseudorandom number
generators with Dickson polynomials. 相似文献
4.
5.
Arne Barinka Stephan Dahlke Wolfgang Dahmen 《Advances in Computational Mathematics》2006,24(1-4):5-34
Recently adaptive wavelet methods have been developed which can be shown to exhibit an asymptotically optimal accuracy/work
balance for a wide class of variational problems including classical elliptic boundary value problems, boundary integral equations
as well as certain classes of noncoercive problems such as saddle point problems. A core ingredient of these schemes is the
approximate application of the involved operators in standard wavelet representation. Optimal computational complexity could
be shown under the assumption that the entries in properly compressed standard representations are known or computable in
average at unit cost. In this paper we propose concrete computational strategies and show under which circumstances this assumption
is justified in the context of elliptic boundary value problems.
Dedicated to Charles A. Micchelli on the occasion of his 60th birthday
Mathematics subject classifications (2000) 41A25, 41A46, 65F99, 65N12, 65N55.
This work has been supported in part by the Deutsche Forschungsgemeinschaft SFB 401, the first and third author are supported
in part by the European Community's Human Potential Programme under contract HPRN-CT-202-00286 (BREAKING COMPLEXITY). The
second author acknowledges the financial support provided through the European Union's Human Potential Programme, under contract
HPRN-CT-2002-00285 (HASSIP) and through DFG grant DA 360/4–1. 相似文献
6.
Richard P. Fischer Arne W. Fliflet 《International Journal of Infrared and Millimeter Waves》2002,23(9):1297-1313
This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements. 相似文献
7.
Arne Schirrmacher 《Physics in Perspective (PIP)》2003,5(1):4-20
David Hilbert (1862-1943) played an important role in establishing quantum physics in Göttingen. I analyze the ways in which his influence was decisive by comparison with Woldemar Voigt (1850-1919). Voigt was the leading Göttingen theoretical physicist before the arrival of Peter Debye (1884-1966), who was appointed to a new professorship in 1914 at Hilbert's instigation. I portray the Göttingen mathematicians, above all Hermann Minkowski (1864-1909) and David Hilbert, as planting the seeds for the blossoming of quantum physics under their student Max Born (1882-1970) in the 1920s. 相似文献
8.
The modified wave and scattering operators are shown to be bounded between weighted L
2-spaces for two-body Schrödinger operators with long range potentials. 相似文献
9.
The electron scattering pattern of gaseous dicyclopentadienylberyllium, Cp2Be, has been recorded from s = 2.00 to 39.00 Å−1 with a nozzle temperature of about 120°C. Molecular models of D5d symmetry or models containing one π-bonded and one σ-bonded Cp ring are not compatible with the data. The possibility the gaseous Cp2Be consists fo a mixture D5d and π-Cp, σ-Cp conformers is considered and rejected. A model of C5v symmetry can be brought into satisfactory agreement with the data. It is also found that a slip sandwich model obtained from the C5v model by moving sideways the ring which is at the greatest distance from Be, while keeping the two rings essentially parallel is compatible with the electron diffraction data. The best fit between experimental and calculated intensity curves is obtained with a model with a sideways slip of 0.8(1) Å. This model is similar to that indicated by the X-ray diffraction investigations by Wong and coworkers [4,5]. It is suggested that the potential energy of the molecule does not change much as the magnitude of the slip changes and that the molecule thus undergoes large amplitude vibration. 相似文献
10.
The effect of conformational preference on the chiroptical properties of α-substituted succinic acids and esters 2 has been investigated using variable-temperature CD in solvents of different polarity. All available evidence indicates that when R' in 2 is alkyl or halogen, the preferred conformation is 1e with the -CH2COOR group eclipsed by the CO bond, while when R' in 2 is hydroxy, methoxy or amino, the major conformer is 1d in which the heteroatom is eclipsed by the CO bond. In both cases, conformation 1f appears to be the least favored, mainly on steric grounds. The results when R' = chloro or bromo do not support previously proposed conclusions and an alternative explanation is advanced. In the resultant octant projection (Fig, 2) it is shown that the sign of the Cotton effect for 1 will be determined by the position of the groups X and Y in the back octants, and since one of these is always H in the two favored conformations, the sign is actually determined by the position of the other group. This octant projection predicts successfully the sign of the ellipticity of the n→π* transition for any α-substituted succinic acid or ester with the appropriate substituent R', and appears to apply also to simple alkanoic acids and esters with the same substituents. 相似文献