全文获取类型
收费全文 | 31276篇 |
免费 | 4057篇 |
国内免费 | 3357篇 |
专业分类
化学 | 22681篇 |
晶体学 | 399篇 |
力学 | 1503篇 |
综合类 | 242篇 |
数学 | 3929篇 |
物理学 | 9936篇 |
出版年
2024年 | 50篇 |
2023年 | 476篇 |
2022年 | 533篇 |
2021年 | 839篇 |
2020年 | 1014篇 |
2019年 | 1022篇 |
2018年 | 875篇 |
2017年 | 829篇 |
2016年 | 1239篇 |
2015年 | 1282篇 |
2014年 | 1480篇 |
2013年 | 2146篇 |
2012年 | 2533篇 |
2011年 | 2766篇 |
2010年 | 1912篇 |
2009年 | 1879篇 |
2008年 | 2121篇 |
2007年 | 1943篇 |
2006年 | 1715篇 |
2005年 | 1524篇 |
2004年 | 1197篇 |
2003年 | 1007篇 |
2002年 | 952篇 |
2001年 | 814篇 |
2000年 | 679篇 |
1999年 | 628篇 |
1998年 | 548篇 |
1997年 | 478篇 |
1996年 | 519篇 |
1995年 | 415篇 |
1994年 | 401篇 |
1993年 | 377篇 |
1992年 | 343篇 |
1991年 | 300篇 |
1990年 | 242篇 |
1989年 | 217篇 |
1988年 | 180篇 |
1987年 | 136篇 |
1986年 | 161篇 |
1985年 | 163篇 |
1984年 | 113篇 |
1983年 | 66篇 |
1982年 | 76篇 |
1981年 | 54篇 |
1980年 | 52篇 |
1979年 | 60篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 41篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
The products from the condensation of acetone-anils ( 1 ) and TCNE reaction were characterized after separation. The main products, tricyanoethylene derivatives ( 7–9 ) were isolated with the malonodinitrile derivatives ( 10–12 ), respectively. The [2+2] cycloaddition product ( 13 ), namely 5-methoxy-3,4-(2′,2′,3′,3′-tetracyanocyclobutano)-l,2-dihydro-2,2,4-trimethylquinoline also has been isolated. The distribution of these three products is substituent dependent. 相似文献
85.
Jing Zhang Dan Shan Shaolin Mu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5573-5582
A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007 相似文献
86.
87.
Chii-Wann Lin Kuo-Ping Chen Ming-Chii Su Chih-Kung Lee Chih-Chung Yang 《Optical and Quantum Electronics》2005,37(13-15):1423-1437
We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure. 相似文献
88.
Richard Becker Mladen Prester Ping Hui Lin Mats Johnsson Ivica Zivkovic 《Journal of solid state chemistry》2007,180(3):1051-1059
Two new isostructural cobalt selenite halides Co5(SeO3)4Cl2 and Co5(SeO3)4Br2 have been synthesized. They crystallize in the triclinic system space group P−1 with the following lattice parameters for Co5(SeO3)4Cl2: a=6.4935(8) Å, b=7.7288(8) Å, c=7.7443(10) Å, α=66.051(11)°, β=73.610(11)°, γ=81.268(9)°, and Z=1. The crystal structures were solved from single-crystal X-ray data, R1=3.73 and 4.03 for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively. The new compounds are isostructural to Ni5(SeO3)4Br2.Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range. The anisotropic susceptibility is quantitatively interpreted within the zero-field splitting schemes for Co2+ and Ni2+ ions. Sharp low-temperature susceptibility features, at TN=18 and 20 K for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively, are ascribed to antiferromagnetic ordering in a minority magnetic subsystem. In isostructural Ni5(SeO3)4Br2 magnetically ordered subsystem represents a majority fraction (TN=46 K). Nevertheless, anisotropic susceptibility of Ni5(SeO3)4Br2 is dominated at low temperatures by a minority fraction, subject to single-ion anisotropy effects and increasing population of Sz=0 (singlet) ground state of octahedrally coordinated Ni2+. 相似文献
89.
90.
长江中下游的主要防洪工程是长江干堤 ,长江堤防线路长、工程浩大、堤基工程地质水文地质条件复杂 ,涉及大量的已有地质数据和资料。今后在整治加固堤防的工程地质勘察工作中 ,还需随时进行数据的收集、存储、检索、分析、统计和维护 ,随时调用这些数据进行综合处理、编制报告和图件 ;在防汛期间可以针对堤防险工险段的险情 ,随时查询和调用有关的资料、数据或者图件 ,提供采取抢险措施决策的地质依据。这既提高了地质数据的利用价值和利用率 ,又保证了信息的准确性、完整性和共享性。因此 ,建立合理的长江堤防工程地质信息处理模型及其成熟的技术方法具有重要的意义。 相似文献