全文获取类型
收费全文 | 45449篇 |
免费 | 11741篇 |
国内免费 | 3138篇 |
专业分类
化学 | 48312篇 |
晶体学 | 554篇 |
力学 | 1239篇 |
综合类 | 114篇 |
数学 | 3203篇 |
物理学 | 6906篇 |
出版年
2024年 | 40篇 |
2023年 | 340篇 |
2022年 | 499篇 |
2021年 | 658篇 |
2020年 | 1788篇 |
2019年 | 3030篇 |
2018年 | 1465篇 |
2017年 | 1066篇 |
2016年 | 3886篇 |
2015年 | 4099篇 |
2014年 | 4096篇 |
2013年 | 4830篇 |
2012年 | 3954篇 |
2011年 | 3153篇 |
2010年 | 3515篇 |
2009年 | 3484篇 |
2008年 | 3003篇 |
2007年 | 2386篇 |
2006年 | 1980篇 |
2005年 | 2066篇 |
2004年 | 1728篇 |
2003年 | 1551篇 |
2002年 | 2261篇 |
2001年 | 1602篇 |
2000年 | 1510篇 |
1999年 | 602篇 |
1998年 | 242篇 |
1997年 | 214篇 |
1996年 | 215篇 |
1995年 | 146篇 |
1994年 | 153篇 |
1993年 | 113篇 |
1992年 | 102篇 |
1991年 | 96篇 |
1990年 | 89篇 |
1989年 | 87篇 |
1988年 | 61篇 |
1987年 | 57篇 |
1986年 | 32篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1957年 | 5篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Lan-Lan Zhang Dr. Wen-Ke Miao Dr. Li-Jun Ren Yu-Kun Yan Dr. Yue Lin Prof. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13396-13401
Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)—a polynorbornene backbone with inorganic polyoxometalate cluster pendants—upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application. 相似文献
52.
53.
54.
55.
56.
57.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
58.
Structural surface velocity distribution is often used to predict structural borne sound radiation. However the sampling interval of velocity should be chosen carefully to increase the prediction accuracy and to reduce the system cost. In this paper, several factors affecting the sampling interval are theoretically analyzed and discussed for a vibrating baffled rectangular plate. A new rule for the determination of the sampling interval is formulated. Using this rule, the results from both numerical simulations and experiments may be explained well. 相似文献
59.
60.