全文获取类型
收费全文 | 18601篇 |
免费 | 2950篇 |
国内免费 | 2610篇 |
专业分类
化学 | 14447篇 |
晶体学 | 244篇 |
力学 | 951篇 |
综合类 | 157篇 |
数学 | 2203篇 |
物理学 | 6159篇 |
出版年
2024年 | 39篇 |
2023年 | 241篇 |
2022年 | 556篇 |
2021年 | 541篇 |
2020年 | 582篇 |
2019年 | 693篇 |
2018年 | 567篇 |
2017年 | 585篇 |
2016年 | 817篇 |
2015年 | 933篇 |
2014年 | 1084篇 |
2013年 | 1439篇 |
2012年 | 1705篇 |
2011年 | 1670篇 |
2010年 | 1228篇 |
2009年 | 1208篇 |
2008年 | 1360篇 |
2007年 | 1152篇 |
2006年 | 1075篇 |
2005年 | 984篇 |
2004年 | 878篇 |
2003年 | 650篇 |
2002年 | 703篇 |
2001年 | 562篇 |
2000年 | 403篇 |
1999年 | 333篇 |
1998年 | 300篇 |
1997年 | 278篇 |
1996年 | 247篇 |
1995年 | 185篇 |
1994年 | 194篇 |
1993年 | 140篇 |
1992年 | 106篇 |
1991年 | 99篇 |
1990年 | 109篇 |
1989年 | 68篇 |
1988年 | 62篇 |
1987年 | 37篇 |
1986年 | 50篇 |
1985年 | 42篇 |
1984年 | 28篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 23篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Tian-Ling Ren Lin-Tao Zhang Li-Tian Liu Zhi-Jian Li 《Journal of Sol-Gel Science and Technology》2002,24(3):271-274
A novel silicon-based PbTiO3/Pb(Zr,Ti)O3/PbTiO3 (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 C/cm2 respectively. The current density is less than 5 × 10–9 A/cm2 below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 × 109 read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications. 相似文献
43.
[Chemical reaction: See text] We have developed a general, efficient, and inexpensive catalyst system for arylation of amines by using 10 mol % of CuI as the copper source, 20 mol % of diphenyl pyrrolidine-2-phosphonate (DPP) as the ligand, K3PO4 as the base, and DMF containing 2% water (v/v) as the solvent. 相似文献
44.
A two-tiered organizing scheme with multiple-length scales for construction of dandelion-like hollow CuO microspheres has been elucidated: (1) mesoscale formation of rhombic building units from smaller nanoribbons via oriented aggregation and (2) macroscopic organization of these units into the CuO microspheres. This self-assembly concept may also be applicable to other metal oxides by creating geometric constraints for constructional units. 相似文献
45.
W. Ren 《Colloid and polymer science》1992,270(10):990-998
Inverse relaxation is studied for hard elastic polypropylene (HEPP), rubber and non-elastic polypropylene. The results show that contractive stress, stress, and internal friction are three essential factors related to the phenomenon. A three-element model in which each element has a definite meaning is proposed to describe this phenomenon. The results also show that, in the first cyclic deformation, relaxation time increases with the increase of recovery for all the materials, which indicates that recovery viscosity increases with the increase of recovery, but the stress rising amplitude (SRA) of inverse relaxation has a maximum in the recovery range. Analysis indicates that SRA equals recovery internal friction (RIF) for ideal material in which stress is solely a function of strain, independent of paths, and approximately equals RIF for non-ideal material at a given strain. From this principle it is found that the order of the work counteracted by RIF for the four materials is the same as that of their second hysteresis loop, and the RIF of HEPP has a sudden increase at the later recovery range. 相似文献
46.
47.
用水热法合成了云母蒙脱石,并与羟基铝齐聚物交联,DTA和IR结果表明,由于柱的引进,高温焙烧时层内八面体上羟基脱除变得较为容易。由NH_3-TPD和吡啶吸附测得的表面酸性表明Al-CLS具有较SMM更多的弱酸和强酸中心。催化剂上弱酸中心有利于醇的脱水,而吸附在强酸中心上的NH_3有利于醇的胺化。 相似文献
48.
Can one join both ends of a helix? A helical aromatic oligoamide was macrocyclized into a saddle-shaped bifunctional clip molecule that self-assembles into discrete circular dodecamers in the solid state and shows great potential for binding aromatic acid guests in solution. The cyclization step requires that the helix is only partly denatured in the reaction medium. 相似文献
49.
绿色合成氧化剂高铁酸盐 总被引:13,自引:0,他引:13
高铁酸盐是绿色、无污染、高选择性和高活性的强氧化剂,其氧化性能比KMn04、O3和Cl还强,可以氧化醇类、含氮化合物、甚至烃类等有机化合物,高铁酸盐在有机物氧化合成中的应用具有很好的发展前景。本文介绍了有关高铁酸盐的制备方法、性质及有机物氧化合成方面的研究进展。 相似文献
50.
Synthesis, Structure and Conductivity of the New Charge-transfer Salt (ET)_2(CH_2=CH-CH_2-SO_3)·H_2O
Zhi LIU Qi FANG* Wen Tao YU Min Hua JIANG De Qing ZHANG Dao Ben ZHU State Key Laboratory of Crystal Materials Shandong University Jinan Institute of Chemistry The Chinese Academy of Sciences Beijing 《中国化学快报》2003,14(4)
ET is one of the most famous electron-donor molecules, which forms charge-transfer complexes (abbr. CT-complexes) with various types of counterions. These complexes have received intense attention because a wide range of physical properties such as conductivity and superconductivity1, ferromagnetism2-4 and nonlinear optical properties5 was found in these materials. Although the majority of the ET-based CT-complexes were prepared by combining with inorganic counterions, CT-complexes with o… 相似文献