全文获取类型
收费全文 | 7175篇 |
免费 | 187篇 |
国内免费 | 13篇 |
专业分类
化学 | 4808篇 |
晶体学 | 55篇 |
力学 | 184篇 |
综合类 | 5篇 |
数学 | 765篇 |
物理学 | 1558篇 |
出版年
2023年 | 56篇 |
2022年 | 225篇 |
2021年 | 220篇 |
2020年 | 174篇 |
2019年 | 189篇 |
2018年 | 189篇 |
2017年 | 133篇 |
2016年 | 277篇 |
2015年 | 216篇 |
2014年 | 280篇 |
2013年 | 434篇 |
2012年 | 478篇 |
2011年 | 537篇 |
2010年 | 360篇 |
2009年 | 368篇 |
2008年 | 451篇 |
2007年 | 400篇 |
2006年 | 333篇 |
2005年 | 277篇 |
2004年 | 248篇 |
2003年 | 196篇 |
2002年 | 166篇 |
2001年 | 128篇 |
2000年 | 117篇 |
1999年 | 70篇 |
1998年 | 65篇 |
1997年 | 61篇 |
1996年 | 50篇 |
1995年 | 44篇 |
1994年 | 64篇 |
1993年 | 61篇 |
1992年 | 62篇 |
1991年 | 35篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有7375条查询结果,搜索用时 0 毫秒
91.
The susceptible-infected-susceptible (SIS) epidemics in a scale-free network in which each node is a square lattice itself is investigated through large-scale computer simulations. The model combines a local contact process among individuals in a node (or city) with stochastic long-range infections due to people traveling between cities interconnected by the national transportation scale-free network. A nonzero epidemic threshold is found and it is approached with a power-law behavior by the density of infected individuals, as observed in the small-world network of Watts and Strogatz. Also, the epidemic propagation follows a 1/f, hierarchical dynamics from the highly connected square lattices to the smaller degree nodes in outbreaks with sizes distributed accordingly a Gaussian function. 相似文献
92.
Cabral-de-Mello DC Silva FA de Cássia de Moura R 《Micron (Oxford, England : 1993)》2007,38(3):323-325
Eurysternus caribaeus was analyzed cytologically by conventional chromosomal staining. The species presents a diploid number of 2n=8, chromosomes with two arms and an XY sex determining mechanism. This is the first karyotype described for the genus Eurysternus and the tribe Eurysternini, and is also the smallest diploid number observed in the family Scarabaeidae and superfamily Scarabaeoidea. 相似文献
93.
94.
95.
Rosane Bassi Soares Denis Honorato Costa Walter Miyakawa Maria Goretti Temoteo Delgado Aguinaldo Silva Garcez Tania Mateus Yoshimura Martha Simões Ribeiro Silvia Cristina Nunez 《Photochemistry and photobiology》2020,96(3):618-624
Ventilator-associated pneumonia (VAP) is an infection that arises after endotracheal intubation affecting patients under intensive care. The presence of the endotracheal tube (ETT) is a risk factor since it is colonized by multispecies biofilm. Antimicrobial photodynamic therapy (aPDT) could be a strategy to decontaminate ETTs. We verify if methylene blue (MB) associated with external illumination of the ETT could be an alternative to destroy biofilm. We performed an in vitro and ex vivo study. In vitro study was performed with P. aeruginosa biofilm grew over ETT for 7 days. After treatment, the surviving cells were cultured for 3 days and the biofilm was analyzed by crystal violet absorbance. Ex vivo study employed ETT obtained from extubated patients. aPDT was performed with MB (100 µm ) and red LED (λ = 640±20 nm). We quantified the biofilm thickness and used scanning electron microscopy and fluorescence technique to verify morphological and functional changes after aPDT. Our results showed that bacteria remain susceptible to aPDT after sequential treatments. We also attested that aPDT can reduce biofilm thickness, disrupt biofilm attachment from ETT surface and kill microbial cells. These data suggest that aPDT should be investigated to decrease VAP incidence via ETT decontamination. 相似文献
96.
Nascimento M. C. Silva E.C. Costa J.C.M Pereira B.L. Passos R. R. Pocrifka L. A. 《Journal of Solid State Electrochemistry》2020,24(10):2543-2553
Journal of Solid State Electrochemistry - Manganese dioxide (MD) was synthesized by cyclic voltammetry using 0.5 mol L−1 MnSO4·6H2O as the precursor solution, with and... 相似文献
97.
Ribeiro Geyse Adriana Corrêa da Rocha Cláudia Quintino Veloso William Barros Dantas Luiza Maria Ferreira Richter Eduardo Mathias da Silva Iranaldo Santos Tanaka Auro Atsushi 《Journal of Solid State Electrochemistry》2020,24(8):1759-1768
Journal of Solid State Electrochemistry - Rapid methods using batch injection analysis (BIA) with amperometric detection were developed for the determination of quercetin extracted from the... 相似文献
98.
Weslley G. D. P. Silva Tamanna Poonia Prof. Jennifer van Wijngaarden 《Chemphyschem》2020,21(22):2515-2522
The highly variable conformational landscape of N-allylmethylamine (AMA) was investigated using Fourier transform microwave spectroscopy aided by high-level theoretical calculations to understand the energy relationship governing the interconversion between nine stable conformers. Spectroscopically, transitions belonging to four low energy conformers were identified and their hyperfine patterns owing to the 14N quadrupolar nucleus were unambiguously resolved. The rotational spectrum of the global minimum geometry, conformer I, shows an additional splitting associated with a tunneling motion through an energy barrier interconnecting its enantiomeric forms. A two-step tunneling trajectory is proposed by finding transition state structures corresponding to the allyl torsion and NH inversion. Natural bond orbital and non-covalent interaction analyses reveal that an interplay between steric and hyperconjugative effects rules the conformational preferences of AMA. 相似文献
99.
Clarissa O. Da Silva Fbio Eduardo C. Teixeira Jos Andr T. Azevedo Edilson C. Da Silva Marco Antonio Chaer Nascimento 《International journal of quantum chemistry》1996,60(1):433-438
The two lower-lying electronic states (3Σ− and 5Σ−) of the BeC, MgC, and CaC molecules were investigated using restricted Hartree-Fock (RHF), generalized valence bond (GVB), and configuration interaction (CI) calculations to establish the relative ordering of those states as a function of the size of the alkaline-earth element. It is shown that as a result of the competition between bonding effects, which predominate for the 3Σ− states, and exchange effects, which stabilize the 5Σ− states, the ordering of these states can be reversed as we move from the Be to the Ca atom. For both the BeC and MgC molecules, the ground state was found to be a triplet X3Σ− state, but for the CaC molecule, the high-spin X5Σ− becomes more stable. © 1996 John Wiley & Sons, Inc. 相似文献
100.
Diana C. G. A. Pinto Artur M. S. Silva Jos A. S. Cavaleiro 《Journal of heterocyclic chemistry》1996,33(6):1887-1893
One-pot syntheses of 5-hydroxy-2-(phenyl or styryl)chromones and the corresponding 6- and 8-monoiodo- and 6,8-diiodochromones have been developed. The procedures involve oxidative cyclization of 2′-benzyloxy-6′-hydroxychalcones and 2′-benzyloxy-6′-hydroxy-2-cinnamylideneacetophenones and electrophilic substitution processes on the chromone moieties; such procedures were also applied to the syntheses of 6,8-dibromochromone derivatives. 相似文献