全文获取类型
收费全文 | 3342篇 |
免费 | 126篇 |
国内免费 | 4篇 |
专业分类
化学 | 2074篇 |
晶体学 | 30篇 |
力学 | 122篇 |
数学 | 623篇 |
物理学 | 623篇 |
出版年
2023年 | 33篇 |
2022年 | 39篇 |
2021年 | 38篇 |
2020年 | 64篇 |
2019年 | 72篇 |
2018年 | 75篇 |
2017年 | 66篇 |
2016年 | 137篇 |
2015年 | 105篇 |
2014年 | 129篇 |
2013年 | 371篇 |
2012年 | 150篇 |
2011年 | 175篇 |
2010年 | 120篇 |
2009年 | 114篇 |
2008年 | 143篇 |
2007年 | 139篇 |
2006年 | 143篇 |
2005年 | 115篇 |
2004年 | 104篇 |
2003年 | 94篇 |
2002年 | 83篇 |
2001年 | 53篇 |
2000年 | 33篇 |
1999年 | 45篇 |
1998年 | 39篇 |
1997年 | 43篇 |
1996年 | 37篇 |
1995年 | 35篇 |
1994年 | 33篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1985年 | 47篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 29篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1972年 | 13篇 |
排序方式: 共有3472条查询结果,搜索用时 31 毫秒
991.
992.
Michael Thompson Kenneth Mathieson Linda Owen Andrew P. Damant Roger Wood 《Accreditation and quality assurance》2009,14(2):73-78
In the FAPAS proficiency testing scheme, participants are asked to state whether the analytical method used was accredited
or not accredited. It is thus possible to compare the stated accreditation status with performance in the scheme. For this
purpose, fifty qualifying examples of analyte-test material combination were selected at random from the reports from the
year 2006. The accredited/non-accredited subsets of results from each example were subjected to a statistical analysis to
determine whether any significant differences between the distributions of results could be detected. Outliers were removed
from the datasets before the main statistical tests and considered separately. The inlying data were subjected to non-parametric
tests for differences in central tendency and dispersion. A few significant examples were found, but could be reasonably attributed
to chance. Among the inliers there were no grounds to reject the overall null hypothesis, that is, that accreditation has
no effect on performance. However, the proportion of outliers was about twice as high among the non-accredited group. 相似文献
993.
K. Kovnir M. Armbrüster D. Teschner T.V. Venkov L. Szentmiklósi F.C. Jentoft A. Knop-Gericke Yu. Grin R. Schl?gl 《Surface science》2009,603(10-12):1784-1792
The structurally well-defined intermetallic compound PdGa – a highly selective catalyst for the semi-hydrogenation of acetylene – was characterized by Fourier transform infrared spectroscopy (FTIR) in situ X-ray photoelectron spectroscopy and in situ prompt gamma activation analysis. A strong modification of the electronic states in PdGa compared to elemental Pd was revealed as well as the complete isolation of the Pd atoms on the surface of PdGa. In situ investigations proved the high stability of the surface, thus excluding segregation phenomena (common for alloys) or sub-surface chemistry involving C and/or H atoms (known for elemental Pd). By suppressing the sub-surface chemistry, the electronic modification as well as the site isolation lead to the high selectivity and long-term stability of PdGa in the semi-hydrogenation of acetylene. 相似文献
994.
Adriana Predoi-Cross Anildev V. Unni V. Malathy Devi Linda R. Brown 《Journal of Molecular Spectroscopy》2007,246(1):65-76
This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν2 + ν3 band of 12CH4. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm−1 resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν2 + ν3 transitions between 4410 and 4629 cm−1 are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm−1 atm−1 at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm−1 atm−1 at 296 K. 相似文献
995.
Every locally normal representation of a local chiral conformal quantum theory is covariant with respect to global conformal
transformations, if this theory is diffeomorphism covariant in its vacuum representation. The unitary, strongly continuous
representation implementing conformal symmetry is constructed; it consists of operators which are inner in a global sense
for the representation of the quantum theory. The construction is independent of positivity of energy and applies to all locally
normal representations irrespective of their statistical dimensions (index) 相似文献
996.
Dillmann I Kratz KL Wöhr A Arndt O Brown BA Hoff P Hjorth-Jensen M Köster U Ostrowski AN Pfeiffer B Seweryniak D Shergur J Walters WB;ISOLDE Collaboration 《Physical review letters》2003,91(16):162503
First beta- and gamma-spectroscopic decay studies of the N=82 r-process "waiting-point" nuclide 130Cd have been performed at CERN/ISOLDE using the highest achievable isotopic selectivity. Several nuclear-physics surprises have been discovered. The first one is the unanticipatedly high energy of 2.12 MeV for the [pi g(9/2) multiply sign in circle nu g(7/2)] 1(+) level in 130In, which is fed by the main Gamow-Teller transition. The second surprise is the rather high Q(beta) value of 8.34 MeV, which is in agreement only with recent mass models that include the phenomenon of N=82 shell quenching. Possible implications of these new results on the formation of the A approximately 130 r-process abundance peak are presented. 相似文献
997.
Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information. 相似文献
998.
J. Kurpeta A. Plochocki A. N. Andreyev J. Äystö A. De Smet H. De Witte A.-H. Evensen V. Fedoseyev S. Franchoo M. Górska H. Grawe M. Huhta M. Huyse Z. Janas A. Jokinen M. Karny E. Kugler W. Kurcewicz U. Köster J. Lettry A. Nieminen K. Partes M. Ramdhane H. L. Ravn K. Rykaczewski J. Szerypo K. Van de Vel P. Van Duppen L. Weissman G. Walter A. Wöhr 《The European Physical Journal A - Hadrons and Nuclei》2003,18(1):31-37
A new high-spin isomer in 215Bi, with a half-life of 36.9(6) s, has been identified at the PSB-ISOLDE on-line mass separator using the pulsed-release technique combined with the element selective RILIS source. A decay scheme of
Bi was constructed and complemented with the low-spinstructure observed in
Bi decay. The population of a cascade on top of the
level in 215Poprovides evidence for Gamow-Teller
-decay of the high-spin 215Bi isomer.Received: 3 March 2003, Revised: 10 June 2003, Published online: 9 October 2003PACS:
23.20.Lv
transitions and level energies - 27.80.+w
- 29.30.Kv X- and
-ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland. 相似文献
999.
B. Ramstein C. Mosbacher T. Hennino W. Augustyniak D. Bachelier H.G. Bohlen J.L. Boyard R. Dahl C. Ellegaard C. Gaarde J. Gosset J.C. Jourdain J.S. Larsen M.C. Lemaire D. L'Hôte H.P. Morsch M. Österlund J. Poitou P. Radvanyi M. Roy-Stephan T. Sams M. Skousen S. Tarlé-Rousteau P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):583-597
The exclusive 2H( 3He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected
in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ
excitation, the yield is less than 10% of the inclusive 2H( 3He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two
protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial
decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing
the NN and NΔ systems.
Received: 21 October 2002 / Accepted: 15 November 2002 / Published online: 11 March 2003
RID="a"
ID="a"e-mail: ramstein@ipno.in2p3.fr
RID="†"
ID="†"Deceased.
RID="†"
ID="†"Deceased.
RID="d"
ID="d"Present adress: School of Engineering, J?nk?ping University, P.O. Box 1026, S-551 11 J?nk?ping, Sweden.
Communicated by M. Gar?on 相似文献
1000.
Strawser D Karton A Zenkina OV Iron MA Shimon LJ Martin JM van der Boom ME 《Journal of the American Chemical Society》2005,127(26):9322-9323
The reaction between tetrakis(triethylphosphine)platinum(0) and 4-[trans-2-(4-bromophenyl)vinyl]pyridine (1) is examined. Initially, the metal center coordinates to the bridging double bond of 1. Complexes 2 and 3 were fully characterized, and their X-ray crystallography structures are presented. Upon heating, either in solution or in the solid state, complex 2 undergoes C-Br oxidative addition to give complex 3. Kinetic studies revealed that this conversion is unimolecular and does not involve dissociation of the metal center from the double bond. Density functional studies show that a plausible mechanism involves the metal center "walking" around the pi-system from the bridging C=C double bond to the C-Br bond. 相似文献