全文获取类型
收费全文 | 47116篇 |
免费 | 9094篇 |
国内免费 | 15947篇 |
专业分类
化学 | 34222篇 |
晶体学 | 1804篇 |
力学 | 3582篇 |
综合类 | 1734篇 |
数学 | 7708篇 |
物理学 | 23107篇 |
出版年
2024年 | 118篇 |
2023年 | 455篇 |
2022年 | 1640篇 |
2021年 | 1587篇 |
2020年 | 1591篇 |
2019年 | 1693篇 |
2018年 | 1530篇 |
2017年 | 2148篇 |
2016年 | 1724篇 |
2015年 | 2479篇 |
2014年 | 2930篇 |
2013年 | 3886篇 |
2012年 | 3830篇 |
2011年 | 4182篇 |
2010年 | 4186篇 |
2009年 | 4235篇 |
2008年 | 4731篇 |
2007年 | 4240篇 |
2006年 | 4204篇 |
2005年 | 3473篇 |
2004年 | 2826篇 |
2003年 | 2026篇 |
2002年 | 2111篇 |
2001年 | 2021篇 |
2000年 | 2129篇 |
1999年 | 1211篇 |
1998年 | 648篇 |
1997年 | 489篇 |
1996年 | 461篇 |
1995年 | 388篇 |
1994年 | 386篇 |
1993年 | 376篇 |
1992年 | 321篇 |
1991年 | 267篇 |
1990年 | 235篇 |
1989年 | 208篇 |
1988年 | 208篇 |
1987年 | 188篇 |
1986年 | 135篇 |
1985年 | 98篇 |
1984年 | 104篇 |
1983年 | 100篇 |
1982年 | 57篇 |
1981年 | 51篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 21篇 |
1977年 | 15篇 |
1965年 | 25篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
72.
A G 4.0 dendrimer-like poly (amido amine) (PAMAM) based on silica nanoparticles was fabricated via a divergent approach.It was built from γ-aminopropyi silica nanoparfides (APSN) core via repetitive addition of acrylate (MA) and hexylenediamine (HDA). FT-IR and EA were used to monitor the progress of dendrimer during each step. The amino group content of the resulting product increased from 0.49 to 3.72 mmol/g after the 4th generation. In addition, the percentage of grafting increased with increasing generation and reached to 65.9% after 4th generation. It was found that the resulting silica nanoparticles could be dispersed in methanol with a mean hydrodynamic particle diameter of 152.7 nm although the silica nanoparticles had agglomerated during the storage period. 相似文献
73.
74.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
75.
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectroscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6·12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of well-defined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA) and ascorbic acid (AA), and the electrocatalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0–10.0 mmol·L?1 (for DA) or 0.5–20.0 mmol·L?1 (for AA). 相似文献
76.
77.
相对论重离子碰撞实验中混合事件方法的研究 总被引:1,自引:0,他引:1
把RQMD(Relativistic Quantum Molecular Dynamics)产生器产生的数据输入作为原始事例取样,讨论了在比较复杂的背景情况下,一种新的混合事件方法,用以证实在相对论重离子碰撞实验中高能量激发共振态的存在.并以共振态重子Δ++为例演示了这一方法的应用. 相似文献
78.
模糊关系矩阵传递闭包的Warshall算法 总被引:8,自引:2,他引:6
通过对照关系的传递闭包和模糊关系的传递闭包,把求关系矩阵的传递闭包的算法完整地推广到模糊关系矩阵上。 相似文献
79.
80.
分子生物学中基因无方向的反向基因组重排问题在数学上已被证明是一个NP困难问题.基于断点图的概念,给出一个时间复杂性为O(max{b^(π),nb(π)}),空间复杂性为0(n)的求其近似最优解的算法.其中n为基因组中基因个数,π=(π1,π2,…,πn)表示n个基因的一种排列,b(π)表示排列π中的断点数.数据实验的结果表明,该近似算法可以求得较好的结果. 相似文献