全文获取类型
收费全文 | 7700篇 |
免费 | 1150篇 |
国内免费 | 997篇 |
专业分类
化学 | 5619篇 |
晶体学 | 48篇 |
力学 | 489篇 |
综合类 | 63篇 |
数学 | 840篇 |
物理学 | 2788篇 |
出版年
2024年 | 18篇 |
2023年 | 141篇 |
2022年 | 255篇 |
2021年 | 303篇 |
2020年 | 307篇 |
2019年 | 301篇 |
2018年 | 214篇 |
2017年 | 204篇 |
2016年 | 317篇 |
2015年 | 357篇 |
2014年 | 372篇 |
2013年 | 505篇 |
2012年 | 595篇 |
2011年 | 701篇 |
2010年 | 440篇 |
2009年 | 432篇 |
2008年 | 498篇 |
2007年 | 434篇 |
2006年 | 427篇 |
2005年 | 413篇 |
2004年 | 292篇 |
2003年 | 257篇 |
2002年 | 260篇 |
2001年 | 222篇 |
2000年 | 171篇 |
1999年 | 161篇 |
1998年 | 151篇 |
1997年 | 131篇 |
1996年 | 140篇 |
1995年 | 151篇 |
1994年 | 115篇 |
1993年 | 104篇 |
1992年 | 74篇 |
1991年 | 97篇 |
1990年 | 60篇 |
1989年 | 59篇 |
1988年 | 50篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9847条查询结果,搜索用时 15 毫秒
71.
Solventless Formation of G‐Quartet Complexes Based on Alkali and Alkaline Earth Salts on Au(111) 下载免费PDF全文
Chi Zhang Likun Wang Lei Xie Huihui Kong Prof. Dr. Qinggang Tan Liangliang Cai Qiang Sun Prof. Dr. Wei Xu 《Chemphyschem》2015,16(10):2099-2105
Template cations have been extensively employed in the formation, stabilization and regulation of structural polymorphism of G‐quadruplex structures in vitro. However, the direct addition of salts onto solid surfaces, especially under ultra‐high‐vacuum (UHV) conditions, to explore the feasibility and universality of the formation of G‐quartet complexes in a solventless environment has not been reported. By combining UHV‐STM imaging and DFT calculations, we have shown that three different G‐quartet‐M (M: Na/K/Ca) complexes can be obtained on Au(111) using alkali and alkaline earth salts as reactants. We have also identified the driving forces (intra‐quartet hydrogen bonding and electrostatic ionic bonding) for the formation of these complexes and quantified the interactions involved. Our results demonstrate a novel route to fabricate G‐quartet‐related complexes on solid surfaces, providing an alternative feasible way to bring metal elements to surfaces for constructing metal–organic systems. 相似文献
72.
All-solid-state sodium batteries with poly(ethylene oxide) (PEO)-based electrolytes have shown great promise for large-scale energy storage applications. However, the reported PEO-based electrolytes still suffer from a low Na+ transference number and poor ionic conductivity, which mainly result from the simultaneous migration of Na+ and anions, the high crystallinity of PEO, and the low concentration of free Na+. Here, we report a high-performance PEO-based all-solid-state electrolyte for sodium batteries by introducing Na3SbS4 to interact with the TFSI− anion in the salt and decrease the crystallinity of PEO. The optimal PEO/NaTFSI/Na3SbS4 electrolyte exhibits a remarkably enhanced Na+ transference number (0.49) and a high ionic conductivity of 1.33 × 10−4 S cm−1 at 45 °C. Moreover, we found that the electrolyte can largely alleviate Na+ depletion near the electrode surface in symmetric cells and, thus, contributes to stable and dendrite-free Na plating/stripping for 500 h. Furthermore, all-solid-state Na batteries with a 3,4,9,10-perylenetetracarboxylic dianhydride cathode exhibit a high capacity retention of 84% after 200 cycles and superior rate performance (up to 10C). Our work develops an effective way to realize a high-performance all-solid-state electrolyte for sodium batteries.A high-performance all-solid-state PEO/NaTFSI/Na3SbS4 electrolyte for sodium batteries is realized owing to the electrostatic interaction between TFSI− in the salt and Na3SbS4, which immobilizes TFSI− anions and promotes the dissociation of NaTFSI. 相似文献
73.
Lijun Cai Sarina Macfadyen Baozhen Hua Haochuan Zhang Wei Xu Yonglin Ren 《Molecules (Basel, Switzerland)》2022,27(6)
Monitoring and early detection of stored-grain insect infestation is essential to implement timely and effective pest management decisions to protect stored grains. We report a reliable analytical procedure based on headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS) to assess stored-grain infestation through the detection of volatile compounds emitted by insects. Four different fibre coatings were assessed; 85 µm CAR/PDMS had optimal efficiency in the extraction of analytes from wheat. The headspace profiles of volatile compounds produced by Tribolium castaneum (Herbst), Rhyzopertha dominica (Fabricius), and Sitophilus granarius (Linnaeus), either alone or with wheat, were compared with those of non-infested wheat grains. Qualitative analysis of chromatograms showed the presence of different volatile compound profiles in wheat with pest infestation compared with the wheat controls. Wheat-specific and insect-specific volatile compounds were identified, including the aggregation pheromones, dominicalure-1 and dominicalure-2, from R. dominica, and benzoquinones homologs from T. castaneum. For the first time, the presence of 3-hydroxy-2-butanone was reported from S. granarius, which might function as an alarm pheromone. These identified candidate biomarker compounds can be utilized in insect surveillance and monitoring in stored grain to safeguard our grain products in future. 相似文献
74.
75.
Chenggang Cai Guoli Chang Miaomiao Zhao Pinggu Wu Zhengyan Hu Dingguo Jiang 《Molecules (Basel, Switzerland)》2022,27(6)
The four polycyclic aromatic hydrocarbon markers (PAH4) of benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), and benzo[a]pyrene (BaP) are indicators showing polycyclic aromatic hydrocarbon (PAH) contamination levels in Chinese medicine raw materials (CMRMs), extracts and health food products; Samples of herbal medicine, herbal extracts, and food supplements were extracted with n-hexane, then cleaned up sequentially on Florisil and EUPAH solid-phase extraction (SPE) columns. A gas chromatography–mass spectrometry method for the determination of four polycyclic aromatic hydrocarbon markers in Chinese medicine raw material, extracts, and health food products was established; In spiked-recovery experiments, the average recovery was about 78.6–107.6% with a precision of 2.3–10.5%. The limit of quantification (LOQ) and limit of detection (LOD) of the PAH4 markers in this method were 2.0 μg/kg and 0.7 μg/kg, respectively. When the developed method was utilized to determine PAH4 contents in 12 locally available health food products, 3 samples contained over 10.0 μg/kg BaP, and 5 samples contained over 50.0 μg/kg PAH4. The European Union (EU) limits for BaP and PAH4 are 10 and 50.0 μg/kg, respectively; therefore, more attention must be drawn to the exposure risk of BaP and PAH4 in CMRMs, their extracts, and health food products. According to the risk assessment based on the Margin of Exposure (MOE) method, it is recognized that the products mentioned in this study pose a low risk. 相似文献
76.
We present a formulation of ab initio electronic structure calculations in a finite magnetic field, which retains the simplicity and efficiency of techniques widely used in first principles molecular dynamics simulations, based on plane-wave basis sets and Fourier transforms. In addition we discuss results obtained with this method for the energy spectrum of interacting electrons in quantum wells, and for the electronic properties of dense fluid deuterium in a uniform magnetic field. 相似文献
77.
B2O3-P2O5-SiO2 (BPS) three-dimensional (3D) high-organized polystyrene (PS) opals and inverse opals with large domain were fabricated and characterized. 相似文献
78.
Lin Zhang Ying-Hua LiYu-Ying Yu Xue-Mei LiYun Ma Cheng-Gang GuCheng-Da Dai Ling-Cang Cai 《Physica B: Condensed Matter》2011,406(22):4163-4169
The mean-field potential (MFP) approach is an efficient way to evaluate the free energy contribution of ion motions for both solid and liquid states. In this paper the MFP is generally constructed with a volume-dependent term and a shape function. The former is derived in accordance with quasi-harmonic approximation. The latter is given semi-empirically. Application to multiphase equations of state for β-, γ- and liquid-tin has been examined. The theoretical phase diagram and thermodynamic properties of isotherm, thermal expansion, heat capacity, Hugoniot states as well as phase transitions are all in excellent agreement with experiments. 相似文献
79.
用频谱分析法测量声光驻波调制器的调制度 总被引:1,自引:0,他引:1
从调制的基本概念出发,指出声光驻波调制器件为宽带频率调制型。讨论了调制度概念的成立条件和适用范围。理论上求出其成立条件为v<0.9(v=2πL△u/λ为衍射光强I(θ,t)中的自变量)。鉴于一般驻波型声光器件都是含有一定的行波成份,但行波声场和驻波声场在拉曼-奈斯衍射范围内衍射角均遵从sinθmi=土mλ/,故两者在空间上是无法分开的。文中给出了从频域上测量调制度M的一种新方法。并给出了零级和一般衍射光的测量值。 相似文献
80.
X. Cai X. M. Chen Z. Y. Liu Z. Y. Shen H. P. Liu X. W. Ma M. D. Hou 《Zeitschrift für Physik A Hadrons and Nuclei》1976,355(4):439-442
The double and single ionization cross section ratios of helium by partially stripped carbon, oxygen and fluorine ions are measured for projectile charge states ranging from +1 to +4 and impact energies from 1.5 MeV to 7.5 MeV. The effective charge effect in partially stripped ion-helium collisions is studied. It is found that the effective charge qeff increases as the impinging energy increases and q eff shows a modest dependence upon the projectile charge state in the present energy range. The projectile charge state, projectile energy, projectile and target electronic state dependences of the effective charge effect may be explained using orbital interpenetrating. 相似文献