全文获取类型
收费全文 | 22545篇 |
免费 | 839篇 |
国内免费 | 123篇 |
专业分类
化学 | 14680篇 |
晶体学 | 235篇 |
力学 | 686篇 |
数学 | 2172篇 |
物理学 | 5734篇 |
出版年
2023年 | 131篇 |
2022年 | 104篇 |
2021年 | 499篇 |
2020年 | 428篇 |
2019年 | 433篇 |
2018年 | 382篇 |
2017年 | 360篇 |
2016年 | 675篇 |
2015年 | 577篇 |
2014年 | 815篇 |
2013年 | 1392篇 |
2012年 | 1699篇 |
2011年 | 1905篇 |
2010年 | 1206篇 |
2009年 | 1047篇 |
2008年 | 1605篇 |
2007年 | 1387篇 |
2006年 | 1431篇 |
2005年 | 1207篇 |
2004年 | 1066篇 |
2003年 | 870篇 |
2002年 | 706篇 |
2001年 | 481篇 |
2000年 | 400篇 |
1999年 | 248篇 |
1998年 | 157篇 |
1997年 | 169篇 |
1996年 | 229篇 |
1995年 | 176篇 |
1994年 | 191篇 |
1993年 | 198篇 |
1992年 | 147篇 |
1991年 | 119篇 |
1990年 | 113篇 |
1989年 | 97篇 |
1988年 | 64篇 |
1987年 | 71篇 |
1986年 | 49篇 |
1985年 | 74篇 |
1984年 | 50篇 |
1983年 | 42篇 |
1982年 | 63篇 |
1981年 | 61篇 |
1979年 | 46篇 |
1978年 | 45篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 36篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
M. Shamshi HassanYoung-Sic Kang Byoung-Suhk KimIck-Soo Kim Hak-Yong KimMyung-Seob Khil 《Superlattices and Microstructures》2011,50(2):139-144
Well-defined and uniform Pr6O11 nanofibers were synthesized by electrospinning of an aqueous sol-gel consisting of praseodymium nitrate hexa-hydrate and polyvinyl acetate. The synthesized Pr6O11 nanofibers mat was dried at 80 °C for 24 h under vacuum and finally annealed at 600 °C for 2 h in static air furnace. From crystalline properties, the synthesized Pr6O11 nanofibers XRD analysis revealed the typical cubic structure. The morphological observation showed that the synthesized Pr6O11 nanofibers composed of fibers length in several 100 nm and diameter of ∼20 nm. Similarly, transmission electron microscope (TEM) measurement revealed the good crystalline nature of the synthesized Pr6O11 nanofibers with the average diameter of ∼20 nm. Photoluminescence (PL) demonstrated a strong green-blue emission peak at 521 nm, suggesting that the Pr6O11 nanofiber exhibited good crystal quality with very less structural defects. 相似文献
992.
Kim HaRi Subok Ri Ilmyong Kim CheongsongFeng Yuling 《Physica B: Condensed Matter》2011,406(8):1459-1465
Making a revision of mistakes in Ref. [19], we present a detailed study of the competition and interplay between the d-density wave (DDW) and d-wave superconductivity (DSC) within the fluctuation-exchange (FLEX) approximation for the two-dimensional (2D) Hubbard model. In order to stabilize the DDW state with respect to phase separation at lower dopings a small nearest-neighbor Coulomb repulsion is included within the Hartree-Fock approximation. We solve the coupled gap equations for the DDW, DSC, and π-pairing as the possible order parameters, which are caused by exchange of spin fluctuations, together with calculating the spin fluctuation pairing interaction self-consistently within the FLEX approximation. We show that even when nesting of the Fermi surface is perfect, as in a square lattice with only nearest-neighbor hopping, there is coexistence of DSC and DDW in a large region of dopings close to the quantum critical point (QCP) at which the DDW state vanishes. In particular, we find that in the presence of DDW order the superconducting transition temperature Tc can be much higher compared to pure superconductivity, since the pairing interaction is strongly enhanced due to the feedback effect on spin fluctuations of the DDW gap. π-pairing appears generically in the coexistence region, but its feedback on the other order parameters is very small. In the present work, we have developed a weak-coupling theory of the competition between DDW and DSC in 2D Hubbard model, using the static spin fluctuation obtained within FLEX approximation and ignoring the self-energy effect of spin fluctuations. For our model calculations in the weak-coupling limit we have taken U/t=3.4, since the antiferromagnetic instability occurs for higher values of U/t. 相似文献
993.
Back Cover: Tailoring Intermolecular Interactions for Efficient Room‐Temperature Phosphorescence from Purely Organic Materials in Amorphous Polymer Matrices (Angew. Chem. Int. Ed. 42/2014) 下载免费PDF全文
Sungbaek Seo Jaehun Jung Prof. Dr. Jinsang Kim 《Angewandte Chemie (International ed. in English)》2014,53(42):11382-11382
994.
Pd nanoparticles immobilized on PNIPAM–halloysite: highly active and reusable catalyst for Suzuki–Miyaura coupling reactions in water 下载免费PDF全文
Myeng Chan Hong Hyunseok Ahn Myung Chan Choi Yongwoo Lee Jongsik Kim Hakjune Rhee 《应用有机金属化学》2014,28(3):156-161
Poly(N‐isopropylacrylamide)–halloysite (PNIPAM‐HNT) nanocomposites exhibited inverse temperature solubility with a lower critical solution temperature (LCST) in water. Palladium (Pd) nanoparticles were anchored on PNIPAM‐HNT nanocomposites with various amounts of HNT from 5 to 30 wt%. These Pd catalysts exhibited excellent reactivities for Suzuki–Miyaura coupling reactions at 50–70 °C in water. In particular, Pd anchored PNIPAM/HNT (95:5 w/w ratio) nanocomposites showed excellent recyclability up to 10 times in 96% average yield by simple filtration. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
995.
A.V. Bashinov A.A. Gonoskov A.V. Kim G. Mourou A.M. Sergeev 《The European physical journal. Special topics》2014,223(6):1105-1112
A short review of the Russian mega-science project XCELS and scientific problems to be solved are presented. We discuss the origin of multi-beam design to attain the highest field magnitude at optimal focusing. Then, we formulate particular physical problems of fundamental interest that can be solved within this project. 相似文献
996.
Dokyung Yoon Daekwang Woo Jung Heon Kim Moon Ki Kim Taesung Kim Eung-Soo Hwang Seunghyun Baik 《Journal of nanoparticle research》2011,13(6):2543-2551
The cytotoxicity of alumina nanoparticles (NPs) was investigated for a wide range of concentration (25–200 μg/mL) and incubation
time (0–72 h) using floating cells (THP-1) and adherent cells (J774A.1, A549, and 293). Alumina NPs were gradually agglomerated
over time although a significant portion of sedimentation occurred at the early stage within 6 h. A decrease of the viability
was found in floating (THP-1) and adherent (J774A.1 and A549) cells in a dose-dependent manner. However, the time-dependent
decrease in cell viability was observed only in adherent cells (J774A.1 and A549), which is predominantly related with the
sedimentation of alumina NPs in cell culture medium. The uptake of alumina NPs in macrophages and an increased cell-to-cell
adhesion in adherent cells were observed. There was no significant change in the viability of 293 cells. This in vitro test
suggests that the agglomeration and sedimentation of alumina NPs affected cellular viability depending on cell types such
as monocytes (THP-1), macrophages (J774A.1), lung carcinoma cells (A549), and embryonic kidney cells (293). 相似文献
997.
V. A. Baskov V. V. Kim B. I. Luchkov V. Yu. Tugaenko V. A. Khablo 《Bulletin of the Lebedev Physics Institute》2011,38(6):158-160
It is shown that the average charged particle multiplicity in electromagnetic showers induced by γ-rays with energies of 9–26 GeV in the tungsten crystal 1 mm thick (T = 77 K) oriented along the 〈111〉 axis approximately twofold increases in comparison with a misoriented crystal. 相似文献
998.
A Diels-Alder-based route to trans-fused angularly functionalized bicyclic structures has been developed. This transformation features the use of a tetrasubstituted dienophile in the cycloaddition step. 相似文献
999.
Young-Kil Chang Jaeheon Lee Moonsub Lee Han Kyong Kim Bo-Young Lee Kwan Soo Kim 《Tetrahedron》2010,66(30):5687-5691
An efficient large-scale synthesis of gemcitabine was achieved without chromatography or fractional crystallization. The key steps include stereospecific conversion of a novel β-ribofuranosyl phosphate into a highly crystalline α-ribofuranosyl bromide and coupling of the α-ribofuranosyl bromide and trimethylsilyl cytosine to produce a β-nucleoside. p-Phenylbenzoyl group was introduced for the protection of one of hydroxy groups in order to enhance the crystallinity of intermediates. Continuous removal of trimethylsilyl bromide, generated during the coupling reaction, by distillation from the reaction medium substantially enhanced the β-selectivity of the crucial coupling reaction. 相似文献
1000.