全文获取类型
收费全文 | 4825篇 |
免费 | 799篇 |
国内免费 | 540篇 |
专业分类
化学 | 3350篇 |
晶体学 | 46篇 |
力学 | 347篇 |
综合类 | 24篇 |
数学 | 605篇 |
物理学 | 1792篇 |
出版年
2024年 | 18篇 |
2023年 | 102篇 |
2022年 | 129篇 |
2021年 | 183篇 |
2020年 | 199篇 |
2019年 | 192篇 |
2018年 | 178篇 |
2017年 | 137篇 |
2016年 | 269篇 |
2015年 | 220篇 |
2014年 | 254篇 |
2013年 | 368篇 |
2012年 | 472篇 |
2011年 | 456篇 |
2010年 | 308篇 |
2009年 | 286篇 |
2008年 | 306篇 |
2007年 | 250篇 |
2006年 | 243篇 |
2005年 | 211篇 |
2004年 | 185篇 |
2003年 | 158篇 |
2002年 | 132篇 |
2001年 | 111篇 |
2000年 | 94篇 |
1999年 | 100篇 |
1998年 | 73篇 |
1997年 | 73篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 27篇 |
1991年 | 38篇 |
1990年 | 35篇 |
1989年 | 26篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1944年 | 4篇 |
1942年 | 3篇 |
1941年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有6164条查询结果,搜索用时 31 毫秒
191.
Shuping Zhang Dr. Hongpan Rong Tianyi Yang Bing Bai Prof. Jiatao Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(18):4025-4031
Dilute alloy nanostructures have been demonstrated to possess distinct catalytic properties. Noble-metal-induced reduction is one effective synthesis strategy to construct dilute alloys and modify the catalytic performance of the host metal. Herein, we report the synthesis of ultrafine PtRu dilute alloy nanodendrites (PtRu NDs, molar ratio Ru/Pt is 1:199) by the reduction of RuIII ions induced by Pt metal. For the methanol oxidation reaction, PtRu NDs showed the highest forward peak current density (2.66 mA cm−2, 1.14 A/mgPt) and the best stability compared to those of pure-Pt nanodendrites (pure-Pt NDs), commercial PtRu/C and commercial Pt/C catalysts. 相似文献
192.
One‐Pot Synthesis of Pomegranate‐Structured Fe3O4/Carbon Nanospheres‐Doped Graphene Aerogel for High‐Rate Lithium Ion Batteries 下载免费PDF全文
Dr. Dafang He Lixian Li Fengjuan Bai Chenyang Zha Prof. Liming Shen Prof. Harold H. Kung Prof. Ningzhong Bao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4454-4459
A unique hierarchically nanostructured composite of iron oxide/carbon (Fe3O4/C) nanospheres‐doped three‐dimensional (3D) graphene aerogel has been fabricated by a one‐pot hydrothermal strategy. In this novel nanostructured composite aerogel, uniform Fe3O4 nanocrystals (5–10 nm) are individually embedded in carbon nanospheres (ca. 50 nm) forming a pomegranate‐like structure. The carbon matrix suppresses the aggregation of Fe3O4 nanocrystals, avoids direct exposure of the encapsulated Fe3O4 to the electrolyte, and buffers the volume expansion. Meanwhile, the interconnected 3D graphene aerogel further serves to reinforce the structure of the Fe3O4/C nanospheres and enhances the electrical conductivity of the overall electrode. Therefore, the carbon matrix and the interconnected graphene network entrap the Fe3O4 nanocrystals such that their electrochemical function is retained even after fracture. This novel hierarchical aerogel structure delivers a long‐term stability of 634 mA h g?1 over 1000 cycles at a high current density of 6 A g?1 (7 C), and an excellent rate capability of 413 mA h g?1 at 10 A g?1 (11 C), thus exhibiting great potential as an anode composite structure for durable high‐rate lithium‐ion batteries. 相似文献
193.
PG 1407+265 is a radio quiet quasar that has a relativistic jet.In this report,we show some peculiar properties of its optical and X-ray emissions,which indicate possible non-thermal origins produced from the jet.We use a simple synchrotron + synchrotron self Compton (SSC) model to fit the emissions with different ratios of energy densities between the magnetic field and electrons (η≡U B/U e),which predicts a different γ-ray luminosity.The First LAT AGN Catalog (1LAC) did not include PG 1407+265,which indic... 相似文献
194.
In order to solve large sparse linear complementarity problems on parallel multiprocessor systems, we construct modulus-based synchronous two-stage multisplitting iteration methods based on two-stage multisplittings of the system matrices. These iteration methods include the multisplitting relaxation methods such as Jacobi, Gauss–Seidel, SOR and AOR of the modulus type as special cases. We establish the convergence theory of these modulus-based synchronous two-stage multisplitting iteration methods and their relaxed variants when the system matrix is an H ?+?-matrix. Numerical results show that in terms of computing time the modulus-based synchronous two-stage multisplitting relaxation methods are more efficient than the modulus-based synchronous multisplitting relaxation methods in actual implementations. 相似文献
195.
Dr. Jiang Peng Jiakun Bai Xiumian Cao Jieting He Prof. Weiqing Xu Dr. Junhui Jia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):16036-16042
Elastic organic single crystals with light-emitting and multi-faceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT , which was easily crystallized and gained long needle-like crystals (centimeter-scale) in DCM/CH3OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle-like crystal showed reversible bending behaviour, showing the nature of multi-faceted bending. The average hardness (H) and elastic modulus (E) were 0.28±0.01 GPa and 4.56±0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C−H⋅⋅⋅π and C−H⋅⋅⋅C), H-bond (C−H⋅⋅⋅O) and π⋅⋅⋅π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm−1 (straight state) and 0.9 dBmm−1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm−1 (straight state) and 1.8 dBmm−1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices. 相似文献
196.
Cheng-Gang Li Jin-Cheng Zhou Yan-Fei Hu Bao-Zeng Ren Jun-Tao Bai Xian-Ke Hu Wen Yang 《Journal of Cluster Science》2018,29(3):459-468
Besides the size and structure, compositions also dramatically affect the properties of clusters. In fact, the increased degree of freedom poses much more challenges to determine the global minimum structure of multi-component clusters. In this thesis, based on the CALYPSO structure searching method, the global minimum structures are obtained for ScnNm (n + m=10) clusters at PW91/6-311+G(d) level. The growth behavior indicates that the cage unit tends to arrange into the compact configurations, and the occupied positions of N atoms shift from the surface towards the center of coordination site with the increasing number of Sc atoms. The relative stabilities have been discussed by analyzing the average binding energies and HOMO–LUMO gaps. In addition, the molecular orbitals, dipole moments, polarizability, hyperpolarizabilities, natural population, natural electron configuration, and Infared and Raman spectra calculations allow complete characterization of the electronic and vibrational properties for the global minimum structural clusters. 相似文献
197.
研究含汞土壤的修复问题,采用热解析和低温等离子体综合技术探究新途径,调整温度、添加剂、时间等因素来判断脱汞效果并探究其不同形态,分析工艺过程废料的内部联系,并对废气处理进行分析实验。结论如下:(1)通过改良技术的BCR连续萃取法,得出研究区汞的形态主要为有机结合态(53%)。之后依次是氧化物结合态(33%)、酸可提取态(8%)、残渣态(6%)。(2)温度对热解析程度影响较大。在500℃以上的热解析条件下,土壤中的汞浓度不足1.5 mg·kg-1。(3)当选用400℃的解析温度时,40 min汞去除总体完成。在低于1 700 mg·kg-1的浓度下,汞去除率随着土壤中的含量的增大而减小。(4)氯化钙对于热解析的促进作用最强,柠檬酸、升华硫也有一定作用,硫化钠对于汞去除形成阻滞。(5)低温等离子体的最佳状态是电源设置电压为22 kV,频率为660 Hz。整个系统的汞去除程度可达近90%。 相似文献
198.
199.
200.
Wen-Xing Yang Ai-Xi Chen Ting-Ting Zha Yanfeng Bai Ray-Kuang Lee 《Central European Journal of Physics》2014,12(10):737-743
We demonstrate the generation of two-mode continuous-variable (CV) entanglement in a V-type three-level atom trapped in a doubly resonant cavity using a microwave field driving a hyperfine transition between two upper excited states. By numerically simulating the dynamics of this system, our results show that the CV entanglement with large mean number of photons can be generated even in presence of the atomic relaxation and cavity losses. More interestingly, it is found that the intensity and period of entanglement can be enhanced significantly with the increasing of the atomic relaxation due to the existence of the perfect spontaneously generated interference between two atomic decay channels. Moreover, we also show that the entanglement can be controlled efficiently by tuning the intensity of spontaneously generated interference and the detuning of the cavity field. 相似文献