全文获取类型
收费全文 | 14300篇 |
免费 | 2002篇 |
国内免费 | 1838篇 |
专业分类
化学 | 4039篇 |
晶体学 | 54篇 |
力学 | 789篇 |
综合类 | 303篇 |
数学 | 9358篇 |
物理学 | 3597篇 |
出版年
2024年 | 15篇 |
2023年 | 167篇 |
2022年 | 201篇 |
2021年 | 319篇 |
2020年 | 433篇 |
2019年 | 420篇 |
2018年 | 365篇 |
2017年 | 430篇 |
2016年 | 526篇 |
2015年 | 447篇 |
2014年 | 765篇 |
2013年 | 1055篇 |
2012年 | 710篇 |
2011年 | 913篇 |
2010年 | 802篇 |
2009年 | 1010篇 |
2008年 | 1087篇 |
2007年 | 1110篇 |
2006年 | 920篇 |
2005年 | 849篇 |
2004年 | 699篇 |
2003年 | 717篇 |
2002年 | 603篇 |
2001年 | 456篇 |
2000年 | 492篇 |
1999年 | 456篇 |
1998年 | 425篇 |
1997年 | 353篇 |
1996年 | 273篇 |
1995年 | 166篇 |
1994年 | 176篇 |
1993年 | 113篇 |
1992年 | 100篇 |
1991年 | 76篇 |
1990年 | 60篇 |
1989年 | 39篇 |
1988年 | 48篇 |
1987年 | 28篇 |
1986年 | 32篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 15篇 |
1982年 | 39篇 |
1981年 | 20篇 |
1980年 | 26篇 |
1979年 | 28篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Piezoelectric cat-eye modulating retro-reflector (MRR) is the core component of an acousto-optic retro-identification system. The influence of the optical parameters (link distance l, lens focal length f and the detector diameter r) to the cat-eye effect was analyzed theoretically and experimentally. A piezoelectric cat-eye retro-identification (PCERI) system was built, and an information transmission ratio of 2 kHz was achieved which can satisfy an access control system. 相似文献
92.
93.
In this paper, based on the theory of variable exponent spaces, we study the higher integrability for a class of nonlinear elliptic equations with variable growth and discontinuous coefficients. Under suitable assumptions, we obtain a local gradient estimate in Orlicz space for weak solution. 相似文献
94.
95.
Paul Kautny Dorian Bader Dr. Berthold Stöger Prof. Dr. Georg A. Reider Prof. Dr. Johannes Fröhlich Dr. Daniel Lumpi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18887-18898
To shed light on intramolecular charge‐transfer phenomena in 1,2,3‐triazole‐linked materials, a series of 1,2,3‐triazole‐linked push–pull chromophores were prepared and studied experimentally and computationally. Investigated modifications include variation of donor and/or acceptor strength and linker moiety as well as regioisomers. Photophysical characterization of intramolecular charge‐transfer features revealed ambipolar behavior of the triazole linker, depending on the substitution position. Furthermore, non‐centrosymmetric materials were subjected to second‐harmonic generation measurements, which revealed the high nonlinear optical activity of this class of materials. 相似文献
96.
97.
Computational Insights into the Charge Relaying Properties of β‐Turn Peptides in Protein Charge Transfers 下载免费PDF全文
Ru Zhang Dr. Jinxiang Liu Dr. Hongfang Yang Shoushan Wang Meng Zhang Prof. Dr. Yuxiang Bu 《Chemphyschem》2015,16(2):436-446
Density functional theory calculations suggest that β‐turn peptide segments can act as a novel dual‐relay elements to facilitate long‐range charge hopping transport in proteins, with the N terminus relaying electron hopping transfer and the C terminus relaying hole hopping migration. The electron‐ or hole‐binding ability of such a β‐turn is subject to the conformations of oligopeptides and lengths of its linking strands. On the one hand, strand extension at the C‐terminal end of a β‐turn considerably enhances the electron‐binding of the β‐turn N terminus, due to its unique electropositivity in the macro‐dipole, but does not enhance hole‐forming of the β‐turn C terminus because of competition from other sites within the β‐strand. On the other hand, strand extension at the N terminal end of the β‐turn greatly enhances hole‐binding of the β‐turn C terminus, due to its distinct electronegativity in the macro‐dipole, but does not considerably enhance electron‐binding ability of the N terminus because of the shared responsibility of other sites in the β‐strand. Thus, in the β‐hairpin structures, electron‐ or hole‐binding abilities of both termini of the β‐turn motif degenerate compared with those of the two hook structures, due to the decreased macro‐dipole polarity caused by the extending the two terminal strands. In general, the high polarity of a macro‐dipole always plays a principal role in determining charge‐relay properties through modifying the components and energies of the highest occupied and lowest unoccupied molecular orbitals of the β‐turn motif, whereas local dipoles with low polarity only play a cooperative assisting role. Further exploration is needed to identify other factors that influence relay properties in these protein motifs. 相似文献
98.
How Does Peripheral Functionalization of Ruthenium(II)–Terpyridine Complexes Affect Spatial Charge Redistribution after Photoexcitation at the Franck–Condon Point? 下载免费PDF全文
Julia Preiß Dr. Michael Jäger Prof. Dr. Sven Rau Prof. Dr. Benjamin Dietzek Prof. Dr. Jürgen Popp Prof. Dr. Todd Martínez Dr. Martin Presselt 《Chemphyschem》2015,16(7):1395-1404
Ruthenium polypyridine‐type complexes are extensively used sensitizers to convert solar energy into chemical and/or electrical energy, and they can be tailored through their metal‐to‐ligand charge‐transfer (MLCT) properties. Much work has been directed at harnessing the triplet MLCT state in photoinduced processes, from sophisticated molecular architectures to dye‐sensitized solar cells. In dye‐sensitized solar cells, strong coupling to the semiconductor exploits the high reactivity of the (hot) singlet/triplet MLCT state. In this work, we explore the nature of the 1MLCT states of remotely substituted RuII model complexes by both experimental and theoretical techniques. Two model complexes with electron‐withdrawing (i.e. NO2) and electron‐donating (i.e. NH2) groups were synthesized; these complexes contained a phenylene spacer to serve as a spectroscopic handle and to confirm the contribution of the remote substituent to the 1MLCT transition. [Ru(tpy)2]2+‐based complexes (tpy=2,2′:6′,2′′‐terpyridine) were further desymmetrized by tert‐butyl groups to yield unidirectional 1MLCTs with large transition dipole moments, which are beneficial for related directional charge‐transfer processes. Detailed comparison of experimental spectra (deconvoluted UV/Vis and resonance Raman spectroscopy data) with theoretical calculations based on density functional theory (including vibronic broadening) revealed different properties of the optically active bright 1MLCT states already at the Franck–Condon point. 相似文献
99.
Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push–Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD‐DFT Computational Study 下载免费PDF全文
Dr. Benedetta Carlotti Dr. Enrico Benassi Prof. Vincenzo Barone Dr. Giuseppe Consiglio Prof. Fausto Elisei Dr. Alessandra Mazzoli Prof. Anna Spalletti 《Chemphyschem》2015,16(7):1440-1450
Three (donor–π–acceptor)+ systems with a methyl pyridinium or quinolinium as the electron‐deficient group, a dimethyl amino as the electron‐donor group, and an ethylene or butadiene group as the spacer have been investigated in a joint spectroscopic and TD‐DFT computational study. A negative solvatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by considering the variation in the permanent dipole moment modulus and orientation upon photoexcitation. The fluorescence efficiency decreases upon increasing solvent polarity, in agreement with the excited‐state optimized geometries (planar in low‐polarity media and twisted in high‐polarity media). Femtosecond transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Considering the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promising NLO materials. 相似文献
100.
Photophysics of a Ruthenium 4H‐Imidazole Panchromatic Dye in Interaction with Titanium Dioxide 下载免费PDF全文
Julian Schindler Dr. Stephan Kupfer Dr. Maria Wächtler Dr. Julien Guthmuller Prof. Dr. Sven Rau Prof. Dr. Benjamin Dietzek 《Chemphyschem》2015,16(5):1061-1070
The photophysics of bis(4,4′‐di‐tert‐butyl‐2,2′‐bipyridine‐κ2N,N′)[2‐(4‐carboxyphenyl)‐4,5‐bis(p‐tolylimino‐κN)imidazolato]ruthenium(II) hexafluorophosphate is investigated, both in solution and attached to a nanocrystalline TiO2 film. The studied substitution pattern of the 4H‐imidazole ligand is observed to block a photoinduced structural reorganization pathway within the 4H‐imidazole ligand that has been previously investigated. Protonation at the 4H‐imidazole ring decreases the excited‐state lifetime in solution. When the unprotonated dye is anchored to TiO2, photoinduced electron injection occurs from thermally nonrelaxed triplet metal‐to‐ligand charge transfer (3MLCT) states with a characteristic time constant of 0.5 ps and an injection efficiency of roughly 25 %. Electron injection from the subsequently populated thermalized 3MLCT state of the dye does not take place. The energy of this state seems to be lower than the conduction band edge of TiO2. 相似文献