全文获取类型
收费全文 | 4850篇 |
免费 | 132篇 |
国内免费 | 29篇 |
专业分类
化学 | 3164篇 |
晶体学 | 15篇 |
力学 | 222篇 |
数学 | 809篇 |
物理学 | 801篇 |
出版年
2023年 | 25篇 |
2022年 | 74篇 |
2021年 | 80篇 |
2020年 | 68篇 |
2019年 | 74篇 |
2018年 | 56篇 |
2017年 | 59篇 |
2016年 | 130篇 |
2015年 | 122篇 |
2014年 | 153篇 |
2013年 | 269篇 |
2012年 | 332篇 |
2011年 | 390篇 |
2010年 | 212篇 |
2009年 | 218篇 |
2008年 | 277篇 |
2007年 | 288篇 |
2006年 | 301篇 |
2005年 | 290篇 |
2004年 | 233篇 |
2003年 | 226篇 |
2002年 | 206篇 |
2001年 | 75篇 |
2000年 | 73篇 |
1999年 | 49篇 |
1998年 | 60篇 |
1997年 | 69篇 |
1996年 | 63篇 |
1995年 | 45篇 |
1994年 | 52篇 |
1993年 | 37篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 26篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1973年 | 10篇 |
排序方式: 共有5011条查询结果,搜索用时 0 毫秒
91.
Jocelyn D Laughton Philippe Bittar Yves Charnay Luc Pellerin Enikö Kovari Pierre J Magistretti Constantin Bouras 《BMC neuroscience》2007,8(1):35
Background
For a long time now, glucose has been thought to be the main, if not the sole substrate for brain energy metabolism. Recent data nevertheless suggest that other molecules, such as monocarboxylates (lactate and pyruvate mainly) could be suitable substrates. Although monocarboxylates poorly cross the blood brain barrier (BBB), such substrates could replace glucose if produced locally. 相似文献92.
Pump−probe experiments at the TEMPO beamline using the low‐α operation mode of Synchrotron SOLEIL 下载免费PDF全文
Mathieu G. Silly Tom Ferté Marie Agnes Tordeux Debora Pierucci Nathan Beaulieu Christian Chauvet Federico Pressacco Fausto Sirotti Horia Popescu Victor Lopez-Flores Marina Tortarolo Maurizio Sacchi Nicolas Jaouen Philippe Hollander Jean Paul Ricaud Nicolas Bergeard Christine Boeglin Bharati Tudu Renaud Delaunay Jan Luning Gregory Malinowski Michel Hehn Cédric Baumier Franck Fortuna Damjan Krizmancic Luigi Stebel Rudi Sergo Giuseppe Cautero 《Journal of synchrotron radiation》2017,24(4):886-897
The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low‐α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low‐α mode of the experimental set‐ups developed at the TEMPO beamline to perform pump–probe experiments with soft X‐rays based on photoelectron or photon detection are presented. A 282 kHz repetition‐rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two‐dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time‐resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high‐time‐resolution pump–probe experiments compared and discussed. 相似文献
93.
Ben Ali K Lafon O Zimmermann H Guittet E Lesot P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,187(2):205-215
We describe several homo- and heteronuclear 2D NMR strategies dedicated to the analysis of anisotropic (2)H spectra of a mixture of dideuterated unlike/like stereoisomers with two remote stereogenic centers, using weakly orienting chiral liquid crystals. To this end, we propose various 2D correlation experiments, denoted "D(H)(n)D" or "D(H)(n)C" (with n=1, 2), that involve two heteronuclear polarization transfers of INEPT-type with one or two proton relays. The analytical expressions of correlation signals for four pulse sequences reported here were calculated using the product-operators formalism for spin I=1 and S=1/2. The features and advantages of each scheme are presented and discussed. The efficiency of these 2D sequences is illustrated using various deuterated model molecules, dissolved in organic solutions of polypeptides made of poly-gamma-benzyl-L-glutamate (PBLG) or poly-epsilon-carbobenzyloxy-L-lysine (PCBLL) and NMR numerical simulations. 相似文献
94.
Parthey CG Matveev A Alnis J Bernhardt B Beyer A Holzwarth R Maistrou A Pohl R Predehl K Udem T Wilken T Kolachevsky N Abgrall M Rovera D Salomon C Laurent P Hänsch TW 《Physical review letters》2011,107(20):203001
We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb. 相似文献
95.
Diaz F Lee MS Rejeaunier X Lehoucq G Goudail F Loiseaux B Bansropun S Rollin J Debes E Mils P 《Optics letters》2011,36(3):418-420
Imaging systems that combine a phase mask in the pupil and digital postprocessing may have better performance than conventional ones. We have built such a system to enhance the depth of field of an uncooled thermal camera. The phase masks are binary, their structures are optimized thanks to an image quality criterion, and they have been realized with three different technologies that give equivalent results. The deconvolution postprocessing is performed in real time with a graphics processing unit. A significant increase of the depth of field of a factor 3 has been obtained. 相似文献
96.
Summary In this paper we study infinitesimal automorphisms of finiteL
2-norm for harmonic Riemannian and Kähler foliations admitting a complete bundle-like metric. The results generalize facts established recently in the compact case.1980 Mathematics Subject Classification: Primary 57 R 30, Secondary 58 E 20.Work supported in part by a grant from the National Science Foundation. 相似文献
97.
Analytical modelling of the work flow through flexible manufacturing systems (FMSs), based on closed queueing network models, has been successfully applied to the early stages of design and analysis of FMSs. This paper describes the advantages of using multiple job-class closed queueing networks for modelling realistic situations occurring in FMSs. The general modelling of FMSs by closed queueing networks is first reviewed. The way Solberg's CAN-Q—a single job-class queueing-based package—deals with several part types is clarified. A new model called MULTIQ, allowing multiple pallet types, each of which is used by several part types, is proposed. Results are derived using the data from an existing FMS. The use of the MULTIQ model for optimization purposes is suggested by some examples. 相似文献
98.
The absorption spectrum of CO2 in the 4.82-μm region has been observed with a high-resolution spectrometer. The (1110, 0310)I-0000 transition and the “hot” transitions (1220, 0420)I-0110 and (2000, 0400)I-0110 have been calibrated. The effective rotational constants of the upper levels have been deduced with good accuracy. 相似文献
99.
Philippe Bertani Jsus Raya Pierre Reinheimer Rgis Gougeon Luc Delmotte Jrme Hirschinger 《Solid state nuclear magnetic resonance》1999,13(4):255-229
19F/29Si Hartmann–Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated 29Si–19F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si–F internuclear distance, r=2.62±0.05 Å, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69±0.04 Å recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of 14 kHz is shown to be necessary for an effective suppression of 19F–19F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account. 相似文献
100.
This paper provides a characterization of the storage needs of a quadtree when used as an index to access large volumes of 2-dimensional data. It is shown that the page occupancy for data in random order approaches 33%. A precise mathematical analysis that involves a modicum of hypergeometric functions and dilogarithms, together with some computer algebra is presented.A brief survey of the analysis of storage usage in tree structures is included. The 33% ratio for quadtrees is to be compared to the figures for binary search trees (50%), tries (69%), and quadtries (46%).The research of this author was done while visiting INRIA, Rocquencourt, France under support from the Ministry of Education of Japanese Government.Work of this author was supported in part by the Basic Research Action of the E.C. under contract No. 3075 (Project ALCOM). 相似文献