全文获取类型
收费全文 | 26411篇 |
免费 | 4213篇 |
国内免费 | 4159篇 |
专业分类
化学 | 19419篇 |
晶体学 | 332篇 |
力学 | 1727篇 |
综合类 | 296篇 |
数学 | 3530篇 |
物理学 | 9479篇 |
出版年
2024年 | 75篇 |
2023年 | 568篇 |
2022年 | 939篇 |
2021年 | 1012篇 |
2020年 | 1089篇 |
2019年 | 1063篇 |
2018年 | 844篇 |
2017年 | 905篇 |
2016年 | 1385篇 |
2015年 | 1317篇 |
2014年 | 1555篇 |
2013年 | 1980篇 |
2012年 | 2223篇 |
2011年 | 2283篇 |
2010年 | 1676篇 |
2009年 | 1509篇 |
2008年 | 1705篇 |
2007年 | 1407篇 |
2006年 | 1376篇 |
2005年 | 1275篇 |
2004年 | 1078篇 |
2003年 | 912篇 |
2002年 | 987篇 |
2001年 | 834篇 |
2000年 | 636篇 |
1999年 | 658篇 |
1998年 | 483篇 |
1997年 | 385篇 |
1996年 | 433篇 |
1995年 | 355篇 |
1994年 | 352篇 |
1993年 | 249篇 |
1992年 | 199篇 |
1991年 | 211篇 |
1990年 | 197篇 |
1989年 | 113篇 |
1988年 | 104篇 |
1987年 | 68篇 |
1986年 | 91篇 |
1985年 | 71篇 |
1984年 | 37篇 |
1983年 | 45篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1974年 | 3篇 |
1957年 | 6篇 |
1936年 | 5篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
本文给出了在Re=50—400范围内二维圆柱后涡脱落的有序和混沌现象的一些初步实验结果。涡脱落由有序到混沌的转捩发生在Re=184.6—193.5之间,但是它不是通过准周期途径。在涡脱落频率与Re数的关系曲线上有两个间断。在Re=70处的间断可能对应于倾斜涡脱落模式的变化,在Re≈193.5处的第二间断对应于由有序到混沌状态的转捩。 相似文献
2.
3.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
5.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
6.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
7.
Qi Wang Huaxiang Yang Zhiqiang Fan Hong Xu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(5):1093-1099
Ethylisobutylaluminoxane (EBAO) and its analogues were synthesized by a reaction between an triethylaluminum (Et3Al)/triisobutylaluminum (i‐Bu3Al) mixture and 4‐fluorobenzeneboronic acid, phenylboronic acid, or n‐butaneboronic acid and subsequent hydrolysis with water. They were used as cocatalysts in ethylene polymerization catalyzed by an iron complex {[(ArN?C(Me))2C5H3N]FeCl2, where Ar is 2,6‐diisopropylphenyl}. Polyethylene with a high molecular weight and a narrow molecular weight distribution was prepared with modified EBAOs, and the performance of the iron complex at high polymerization temperatures was greatly improved. The activators for the iron complex also affected the polymerization activity and the molecular weight of the resultant polyethylene. It was suggested that the stereo and electronic effects of the substitute groups of aluminoxane contributed to the improved performance of the new activators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1093–1099, 2004 相似文献
8.
Raymond Mackay Jie Zhang Qi Wu Yuzhuo Li 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):343-348
The longitudinal relaxation times (T1) of water in concentrated silica and alumina slurries were measured as a function of solids content. It was shown that the results could be fit very well with a two-phase fast-exchange model between free and surface-bound water. As expected, values of T1 for bound water were in the order of 20–2000 times lower than that for free water, indicating a higher effective viscosity of the surface-bound water. The strength of the interaction depended on the particular surface, and all of the aluminas examined interacted more strongly with water than the two silicas studied, which themselves differed considerably. The chemical mechanical polishing (CMP) removal rate of tantalum by silica slurries was shown to be directly correlated with the interaction parameters, derived from the NMR relation times rather than with total surface hydroxyl group concentration. 相似文献
9.
Qing An WU Zhen Yuan XU Mei ZHENG Dan Qian XU Jun XU Yin Chu SHENCollege of Chemical Engineering Materials Zhejiang University of Technology Hangzhou 《中国化学快报》2004,(7)
Six new 13-O-acylavermectin Bl aglycones(3-8) were synthesized from avermectin B1 aglycone and their bioactivities were evaluated against Spodoptera exigua, Spodoptera eridania, Tetranychus urticae and Aphis fabae. 相似文献
10.
Zhong Hong YAN Chun Hao YANG Xi Han WU Yu Yuan XIEDivision of Chemistry Shanghai Second Medical University Shanghai Sate Key Laboratory of Drug Research Shanghai Institute of Materia Medica Shanghai Institutesfor Biological Sciences Shanghai 《中国化学快报》2004,(4)
The first and facile synthesis of (±)syringaresinol was described. 相似文献