全文获取类型
收费全文 | 35492篇 |
免费 | 4385篇 |
国内免费 | 2933篇 |
专业分类
化学 | 18063篇 |
晶体学 | 315篇 |
力学 | 1563篇 |
综合类 | 110篇 |
数学 | 2921篇 |
物理学 | 9398篇 |
综合类 | 10440篇 |
出版年
2024年 | 150篇 |
2023年 | 661篇 |
2022年 | 1143篇 |
2021年 | 1166篇 |
2020年 | 1105篇 |
2019年 | 1043篇 |
2018年 | 913篇 |
2017年 | 834篇 |
2016年 | 1326篇 |
2015年 | 1367篇 |
2014年 | 1705篇 |
2013年 | 2082篇 |
2012年 | 2712篇 |
2011年 | 2770篇 |
2010年 | 1888篇 |
2009年 | 1833篇 |
2008年 | 2048篇 |
2007年 | 1873篇 |
2006年 | 1699篇 |
2005年 | 1507篇 |
2004年 | 1142篇 |
2003年 | 861篇 |
2002年 | 859篇 |
2001年 | 709篇 |
2000年 | 722篇 |
1999年 | 1048篇 |
1998年 | 967篇 |
1997年 | 976篇 |
1996年 | 941篇 |
1995年 | 789篇 |
1994年 | 692篇 |
1993年 | 532篇 |
1992年 | 533篇 |
1991年 | 481篇 |
1990年 | 375篇 |
1989年 | 373篇 |
1988年 | 277篇 |
1987年 | 232篇 |
1986年 | 152篇 |
1985年 | 100篇 |
1984年 | 53篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
21.
22.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
23.
Hang Sun 《Tetrahedron letters》2004,45(3):615-617
A versatile and efficient sequence was developed for the synthesis of 1-desoxy-Δ8-THC analogues and is demonstrated by the synthesis of sulfonamide analogues with an acetylene group at the C-2′ position in the side chain. In this procedure the 1-desoxy-Δ8- THC ring structure is built first and the synthesis of the side chain is then developed. 相似文献
24.
Ion-exchange resins, especially chelating resins are used for pre-concentration of metal ions in trace analysis as well as
for radiochemical separations following neutron activation of a variety of environmental samples. As part of a systematic
study of the sorption characteristics of chelating resins, sorption of Zn(II) and Cd(II) by three chelating resins were studied
for various acid conditions in nitrate and chloride media. Both Zn(II) and Cd(II) showed similar behavior. Under higher acid
conditions, maximum sorption occurred in 3M HCl solutions. Under low acid conditions, the sorption increased with pH. Chelex
100 gave the highest sorption among the three resins.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
Fang‐Chyou Chiu Sun‐Mou Lai Jong‐Wu Chen Pei‐Hsien Chu 《Journal of Polymer Science.Polymer Physics》2004,42(22):4139-4150
The melt mixing technique was used to prepare various polypropylene (PP)‐based (nano)composites. Two commercial organoclays (denoted 20A and 30B) served as the fillers for the PP matrix, and two different maleated (so‐called) compatibilizers (denoted PP‐MA and SMA) were employed as the third component. The results from X‐ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that 190 °C was an adequate temperature for preparing the nanocomposites. Nanocomposites were achieved only if specific pairs of organoclay and compatibilizer were simultaneously incorporated in the PP matrix. For example, PP/20A(5 wt %)/PP‐MA(10 wt %) and PP/30B(5 wt %)/SMA(5 wt %) composites exhibited nanoscaled dispersion of 20A or 30B in the PP matrix. Differential scanning calorimetry (DSC) results indicated that the organoclays served as nucleation agents for the PP matrix. Generally, their nucleation effectiveness increased with the addition of compatibilizers. The thermal stability enhancement of PP after adding 20A was confirmed with thermogravimetric analysis (TGA). The enhancement became more evident as a suitable compatibilizer was further added. However, for the 30B‐included composites, thermal stability enhancement was not evident. The dynamic mechanical properties (i.e., storage modulus and loss modulus) of PP increased as the nanocomposites were formed; the properties increment corresponded to the organoclay dispersion status in the matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4139–4150, 2004 相似文献
26.
Xiaohui Yang Xiaoying Sun Jiajia Shao Yunhang Liu Xinling Wang 《Journal of Polymer Science.Polymer Physics》2004,42(22):4195-4198
A series of polymer electrolytes based on multiarm polymers and lithium salt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and impedance measurement. The relationships of conductivity with salt concentration, temperature, and arm numbers are discussed. It is suggested that the star polymer has a higher solvency and ion transfer ability on lithium salts than on linear polymers. The conductivity maximum appeared at a higher salt concentration ([EO]/[Li] = 4). Impedance measurement suggested that the optimum conductivity was 2 × 10?4 s · cm?1. The conductivity increased with temperature and the dependence of ionic conductivity on temperature fits the Arrhenius equation. Among the studied systems, the star polymer with a five arm number performs better than other structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4195–4198, 2004 相似文献
27.
28.
研究铲磨机各种运动和控制要求,设计出继电控制与PC控制相结合的电气控制系统。此系统在电路设计、电气柜安装、调试维修和操作等方面满足了设计要求。铲磨加工过程的PC控制解决了转轮流道三维表面成形运动的控制难题。PC控制程序基本满足了铲磨工艺要求。 相似文献
29.
30.
研究了电子线路的数值化设计方法.它是一种自动化程度高、通用性强、精度高的电路设计方法。介绍了电子线路数值优化设计软件系统YJX—1.它具有广泛的通用性和快速收敛的特点。 相似文献