全文获取类型
收费全文 | 17380篇 |
免费 | 1748篇 |
国内免费 | 777篇 |
专业分类
化学 | 11255篇 |
晶体学 | 813篇 |
力学 | 242篇 |
综合类 | 47篇 |
数学 | 104篇 |
物理学 | 7444篇 |
出版年
2024年 | 16篇 |
2023年 | 127篇 |
2022年 | 241篇 |
2021年 | 335篇 |
2020年 | 400篇 |
2019年 | 347篇 |
2018年 | 302篇 |
2017年 | 345篇 |
2016年 | 547篇 |
2015年 | 475篇 |
2014年 | 614篇 |
2013年 | 1353篇 |
2012年 | 1056篇 |
2011年 | 1074篇 |
2010年 | 928篇 |
2009年 | 1133篇 |
2008年 | 1129篇 |
2007年 | 1380篇 |
2006年 | 1250篇 |
2005年 | 912篇 |
2004年 | 917篇 |
2003年 | 779篇 |
2002年 | 592篇 |
2001年 | 461篇 |
2000年 | 419篇 |
1999年 | 359篇 |
1998年 | 361篇 |
1997年 | 265篇 |
1996年 | 320篇 |
1995年 | 281篇 |
1994年 | 262篇 |
1993年 | 192篇 |
1992年 | 156篇 |
1991年 | 112篇 |
1990年 | 97篇 |
1989年 | 64篇 |
1988年 | 61篇 |
1987年 | 31篇 |
1986年 | 40篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
P. P. Onys'ko T. V. Kim E. I. Kiseleva A. D. Sinytsa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):73-76
Abstract Allylic and heteroallylic compounds are classical objects of organic chemistry and can serve as models in the investigation of various theoretical problems. The anions and 1,3-dipoles generated from azaallylic derivatives are widely used in the synthesis of cyclic and acyclic nitrogen-containing compounds. 相似文献
892.
Abstract The results of investigation of the quasi-Cherenkov (parametric) X-ray emission of 4.5 GeV electrons in diamond and quartz crystals are presented. A noticeable increase in X-ray photons yield has been observed under the influence of external factors (acoustic waves, temperature gradient). 相似文献
893.
A simple model is proposed to take into account secondary X-ray fluorescence and absorption effects near the interface. This model is based on the investigation of the shape change of the first derivative equation that can fit the sigmoidal EDS profile obtained when a high vacuum electron beam passes through the interface of two adjacent materials. The contribution of the photoelectric absorption of primary X-rays (characteristic and Bremsstrahlung) and the secondary fluorescence on the degradation of the X-ray spatial resolution can be easily quantified. The close agreement between the simulated (Monte Carlo simulation using the Casino software) and the experimental data serves to assess the reliability of this developed model. 相似文献
894.
《Journal of Coordination Chemistry》2012,65(1-2):131-134
Abstract The complex ion [Co(1,3-pd3a)NO2]? (pd3a=trimethylenediamine-N,N,N′-triacetate ion) was prepared from equatorial-skew-[Co(1,3-pd3a)H2 O]. The absorption spectrum and the 13C NMR spectrum show the nitro product to be a polar isomer. The diamine backbone ring is believed to have the chair conformation. 相似文献
895.
The zero field cooled (ZFC) and field cooled (FC) low-field magnetic moment m of a dense frozen ferrofluid containing Fe55Co45 particles of size 4.6nm in hexane exhibits irreversibility at temperatures T?T b≈ 30?K. FC in μ 0 H ≤ 1?T gives rise to shifted minor hysteresis loops below T b. At T c≈ 10?K, sharp peaks of m ZFC and of the ac susceptibility χ ′, a kink of the thermoremanent magnetic moment m TRM, a sizeable reduction of the coercive field H c, and the appearance of a spontaneous moment m SFM indicate a phase transition with near mean-field critical behaviour of both m SFM and χ ′ . These features are explained within a core-shell model of nanoparticles, whose strongly disordered shells gradually become blocked below T b, while their soft ferromagnetic cores couple dipolarly and become superferromagnetic (SFM) below T c. 相似文献
896.
Felix Katzsch Tobias Gruber Edwin Weber 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(9):679-684
The syntheses of three bis(benzo[b]thiophen‐2‐yl)methane derivatives, namely bis(benzo[b]thiophen‐2‐yl)methanone, C17H10OS2, (I), 1,1‐bis(benzo[b]thiophen‐2‐yl)‐3‐(trimethylsilyl)prop‐2‐yn‐1‐ol, C22H20OS2Si, (II), and 1,1‐bis(benzo[b]thiophen‐2‐yl)prop‐2‐yn‐1‐ol, C19H12OS2, (III), are described and their crystal structures discussed comparatively. The conformation of ketone (I) and the respective analogues are rather similar for most of the compounds compared. This is true for the interplanar angles, the Caryl—Cbridge—Caryl angles and the dihedral angles. The best resemblance is found for a bioisotere of (I), viz. 2,2′‐dinaphthyl ketone, (VII). By way of interest, the crystal packings also reveal similarities between (I) and (VII). In (I), the edge‐to‐face interactions seen between two napthyl residues in (VII) are substituted by S…π contacts between the benzo[b]thiophen‐2‐yl units in (I). In the structures of the bis(benzo[b]thiophen‐2‐yl)methanols, i.e. (II) and (III), the interplanar angles are also quite similar compared with analogues and related active pharmaceutical ingredients (APIs) containing the dithiophen‐2‐ylmethane scaffold, though the dihedral angles show a larger variability and produce unsymmetrical molecules. 相似文献
897.
《应用有机金属化学》2017,31(11)
A series of new sterically modulated chlorocoumarin‐substituted (benz)imidazolium salts and their bis‐N‐heterocyclic carbene silver(I) complexes were prepared and characterized. The complexes were prepared in good yields following the in situ deprotonation method by treating azolium salts with silver(I) oxide in the dark. All the compounds were characterized using various spectroscopic and analytical methods. Additionally, one of the benzimidazolium salts was characterized using single‐crystal X‐ray diffraction technique. In this salt, intermolecular π–π stacking interactions operate between benzimidazole as well as coumarin heterocyclic systems with adjacent molecules. In the preliminary antibacterial studies, the silver complexes were found more active than the corresponding salts against a panel of bacterial strains. Interestingly, the complexes displayed improved antibacterial efficacy against Escherichia coli strain, comparable with that of the standard drug ampicillin. 相似文献
898.
Jorge Castellanos-Soriano Allen T. Ekubo Mark R. J. Elsegood Nuria Lastra-Calvo Aman Mantry Arturo Martinez-Insua-Rodriguez 《Phosphorus, sulfur, and silicon and the related elements》2017,192(5):570-575
New tetraalkylaminophosphonium chlorides were readily prepared by four-fold condensation of commercially available [P(CH2OH)4]Cl with a range of fifteen aryl based primary amines, in EtOH, at ambient temperature. All compounds have been characterized by FT–IR spectroscopy and elemental analysis. Solution 31P{1H} NMR studies of these chloride salts reveal their instability with respect to various PIII/PV species. The structures of three examples have been determined by single crystal X-ray diffraction and confirm the pseudotetrahedral arrangement around the PV center. Extensive N–H···Cl hydrogen bonding is observed. 相似文献
899.
《Molecular physics》2012,110(17):2111-2135
We report a detailed reinvestigation of the ν2?+?2ν3 combination band of methane 12CH4 centred at (7510.3378?±?0.003)?cm?1 ((225.154263?±?0.0001)?THz) within the icosad of the overtone absorption. A new experimental setup is described, allowing us to carry out cw-laser cavity ring-down spectroscopy (cw-CRDS) at instrumental resolution in the MHz range in seeded supersonic jet expansions down to rotational temperature of 7?K compared to previous cw-CRDS measurements in our group achieving about 50?K in expansions of neat CH4. We provide a careful re-analysis on the basis of our new experimental results for the Q and R branch transitions including data obtained between about 7 and 300?K under various conditions. We resolve previously observed discrepancies of assignments and are able to present a definitive assignment for lines involving angular momentum quantum numbers up to J?=?4. The analysis of relative intensities in spectra taken at rotational and effective translational temperatures between about 50?K and less than 10?K indicate conservation of nuclear spin symmetry upon supersonic jet expansion, in agreement with previous results using other techniques and covering other spectral ranges. 相似文献
900.
S. Ravy P. A. Albouy S. Megtert R. Moret J. P. Pouget R. Comes 《Phase Transitions》2013,86(1-4):193-210
X-Ray diffuse scattering from a series of examples where the reason for the existence of incommensurable features is fairly well understood, is described. They include in particular non stoichiometric compounds such as [DIPS Φ4(l3)0.76] and such as intercalated graphite RbC24. and quasi one dimensional conductors. A particular emphasis is given on various 1 - D conductors and to the relation of the incommensurability to the characteristics of the electron conduction bands. 相似文献