全文获取类型
收费全文 | 10104篇 |
免费 | 440篇 |
国内免费 | 35篇 |
专业分类
化学 | 6448篇 |
晶体学 | 45篇 |
力学 | 270篇 |
数学 | 2082篇 |
物理学 | 1734篇 |
出版年
2023年 | 89篇 |
2022年 | 124篇 |
2021年 | 230篇 |
2020年 | 222篇 |
2019年 | 226篇 |
2018年 | 224篇 |
2017年 | 198篇 |
2016年 | 367篇 |
2015年 | 356篇 |
2014年 | 390篇 |
2013年 | 636篇 |
2012年 | 733篇 |
2011年 | 802篇 |
2010年 | 454篇 |
2009年 | 402篇 |
2008年 | 641篇 |
2007年 | 597篇 |
2006年 | 529篇 |
2005年 | 527篇 |
2004年 | 427篇 |
2003年 | 329篇 |
2002年 | 335篇 |
2001年 | 122篇 |
2000年 | 87篇 |
1999年 | 106篇 |
1998年 | 81篇 |
1997年 | 96篇 |
1996年 | 90篇 |
1995年 | 73篇 |
1994年 | 62篇 |
1993年 | 45篇 |
1992年 | 44篇 |
1991年 | 51篇 |
1990年 | 44篇 |
1989年 | 31篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 29篇 |
1985年 | 55篇 |
1984年 | 51篇 |
1983年 | 32篇 |
1982年 | 56篇 |
1981年 | 39篇 |
1980年 | 56篇 |
1979年 | 44篇 |
1978年 | 45篇 |
1977年 | 39篇 |
1976年 | 35篇 |
1975年 | 33篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
61.
In this paper the distribution of the zeros of the error function for bestL
1-approximation by rational functions fromR
n,m
is considered. It is shown that the maximal distance between such zeros isO(1/(n–m)), ifn > m.Communicated by Edward B. Saff. 相似文献
62.
Summary Bhattacharya, Chernoff and Yang (1983) proposed a nonparametric estimate for the slope of a regression lineY =
o
X + V subjected to the truncationYy
0. The estimate corresponds to the zero-crossing of a random functionS
n
(). In this paper an estimate for the asymptotic variance of the estimate of the slope is proposed and the rate of convergence is given. The proofs rest heavily on the local behavior ofS
n
() in the neighborhood of the true value o. 相似文献
63.
Dupieux P Alard JP Augerat J Babinet R Bastid N Brochard F Charmensat P De Marco N Fanet H Fodor Z Fraysse L Girard J Gorodetzky P Gosset J Laspalles C Lemaire MC L'Hôte D Lucas B Marroncle J Montarou G Parizet MJ Poitou J Qassoud D Racca C Schimmerling W 《Physics letters. [Part B]》1988,200(1-2):17-21
Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed. 相似文献
64.
65.
Szantai E Ronai Z Szilagyi A Sasvari-Szekely M Guttman A 《Journal of chromatography. A》2005,1079(1-2):41-49
The investigation of the genetic background and phenotype structures of complex diseases, such as cardiovascular or psychiatric disorders and tumors, is one of the most scrutinized fields of the post genomic era. Besides the multiplex analysis of genetic markers and polymorphisms throughout the whole genome, more and more attention is focused on the interaction between the etiological factors of these traits. Haplotype determination, rather than multiplex genotyping seems to be one of the first building blocks of this endeavor. This review focuses on the importance and theoretical background of haplotyping, and summarizes the recent examples of novel and emerging haplotyping techniques by capillary gel electrophoresis based DNA fragment analysis, a powerful tool for the examination of the inheritance of complex traits. 相似文献
66.
Gáti T Simon A Tóth G Magiera D Moeller S Duddeck H 《Magnetic resonance in chemistry : MRC》2004,42(7):600-604
Adducts of four phosphine chalcogenides with the chiral dirhodium complex ([Rh-Rh]) were investigated by variable-temperature 1H and 31P NMR spectroscopy in order to compare their properties as axial ligands. Whereas the selenide (1) and the sulfide (2) are strong ligands with electrostatic attraction and, in addition, a significant orbital (HOMO-LUMO) interaction, the phosphine oxide compounds (P=O) bind primarily via electrostatic attraction and are relatively weak donors. Moreover, the overall bond strength in these adducts depends on steric congestion around the P=O group. 相似文献
67.
Andersson I Gorzsás A Pettersson L 《Dalton transactions (Cambridge, England : 2003)》2004,(3):421-428
A detailed study of the quaternary aqueous H+/H2VO4-/H2O2/picolinate (Pi-) system has been performed at 25 degrees C in 0.150 M Na(Cl) medium using quantitative 51 V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4-/Pi- system, six complexes have been found in the pH region 1-10. In the quaternary H+/H2VO4-/H2O2/Pi- system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 1)C NMR data and available crystal structures. 相似文献
68.
Riedl Z Kövér P Soós T Hajós G Egyed O Fábián L Messmer A 《The Journal of organic chemistry》2003,68(14):5652-5659
2-Arylsulfanyl and 2-benzylsulfanylpyridinium N-arylimides (2) easily prepared from 3-aryltetrazolopyridinium salts (1) with aryl and benzylthiolates, respectively, reacted with various dipolarophiles yielding cycloadducts that underwent transformation to give tetrahydropyrrolo[3,2-b]pyridines (5, 6, and 8) in good yields. A similar rearrangement (formation of 15) was also observed in the case of parent derivatives being unsubstituted in position 2 (12). The abscence of any significant solvent effect, comparison of the sulfur and non-sulfur analogues, as well as the stereoselective nature of the observed ring transformation seem to support a sigmatropic mechanism. Structure elucidation of the products has been carried out by single-crystal X-ray diffraction and (1)H NMR experiments. 相似文献
69.
Thomas P J Linsinger Alexander Bernreuther Philippe Corbisier Marta Dabrio Håkan Emteborg Andrea Held Andrée Lamberty Gaida Lapitajs Marina Ricci Gert Roebben Stefanie Trapmann Franz Ulberth Hendrik Emons 《Accreditation and quality assurance》2007,12(3-4):167-174
The potential approaches for third-party assessment of reference material producers are revisited and the activities of the
Reference Materials (RM) Unit of the Institute for Reference Materials and Measurements (IRMM) to obtain accreditation to
ISO Guide 34 and ISO 17025 are described. Accreditation was related to the Unit as all matrix RM activities of the institute
are concentrated there. A management system was established that allows sufficient flexibility to be applicable to a wide
range of RMs while being precise enough to ensure compliance with ISO Guides 30, 31 and especially 34 and 35. Accreditation
was achieved in 2004 with independent scopes for testing and RM production and was confirmed and extended in 2005. The key
aspects of the RM Unit's management system for RM production are presented.
Presented at BERM-10, April 2006, Charleston, SC, USA 相似文献
70.