全文获取类型
收费全文 | 40579篇 |
免费 | 1160篇 |
国内免费 | 967篇 |
专业分类
化学 | 18350篇 |
晶体学 | 376篇 |
力学 | 1858篇 |
综合类 | 63篇 |
数学 | 10381篇 |
物理学 | 11678篇 |
出版年
2023年 | 152篇 |
2022年 | 170篇 |
2021年 | 268篇 |
2020年 | 319篇 |
2019年 | 333篇 |
2018年 | 1425篇 |
2017年 | 1697篇 |
2016年 | 1089篇 |
2015年 | 949篇 |
2014年 | 928篇 |
2013年 | 1329篇 |
2012年 | 3974篇 |
2011年 | 3280篇 |
2010年 | 2422篇 |
2009年 | 2189篇 |
2008年 | 1287篇 |
2007年 | 1303篇 |
2006年 | 1210篇 |
2005年 | 4955篇 |
2004年 | 4408篇 |
2003年 | 2727篇 |
2002年 | 867篇 |
2001年 | 608篇 |
2000年 | 355篇 |
1999年 | 373篇 |
1998年 | 268篇 |
1997年 | 204篇 |
1996年 | 216篇 |
1995年 | 170篇 |
1994年 | 191篇 |
1993年 | 144篇 |
1992年 | 285篇 |
1991年 | 248篇 |
1990年 | 239篇 |
1989年 | 186篇 |
1988年 | 187篇 |
1987年 | 116篇 |
1986年 | 110篇 |
1985年 | 130篇 |
1984年 | 97篇 |
1983年 | 94篇 |
1982年 | 67篇 |
1981年 | 63篇 |
1980年 | 59篇 |
1979年 | 63篇 |
1976年 | 116篇 |
1975年 | 71篇 |
1974年 | 88篇 |
1973年 | 92篇 |
1972年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Jue Lu Chang K. Hong Richard P. Wool 《Journal of Polymer Science.Polymer Physics》2004,42(8):1441-1450
Some discovery work was done on the synthesis of clay nanocomposites based on renewable plant oils. Functionalized triglycerides, such as acrylated epoxidized soybean oil, maleinized acrylated epoxidized soybean oil, and soybean oil pentaerythritol maleates, combined with styrene were used as the polymer matrix. The miscibility of these monomers and clay organomodifier was assessed by solubility parameters. The formation of nanocomposites was confirmed by both X‐ray data and transmission electron microscopy. The morphology showed a mix of intercalated and partially exfoliated sheets. The flexural modulus increased 30% at only 4 vol % clay content, but there was no significant effect on flexural strength, glass‐transition temperature, and thermal stability. Property enhancement was related to the degree of exfoliation that depends on both the polarity and flexibility of the monomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1441–1450, 2004 相似文献
42.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
43.
44.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
45.
46.
Gr-凝聚环的分次FP-内射维数 总被引:4,自引:0,他引:4
引进了分次FP-内射维数,对Gr-凝聚环的分次FP-内射维数作了刻划,将Stentrom等人的若干工作推广到分次环上. 相似文献
47.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
48.
J.S. Tsay H.W. Chang Y.L. Chiou K.T. Huang W.Y. Chan Y.D. Yao 《Journal of magnetism and magnetic materials》2006
Influences of oxygen exposure on the magnetic properties of Co/Ge(1 1 1) ultrathin films have been investigated by surface magneto-optic Kerr effect technique. As the oxygen exposure increases on Co/Ge(1 1 1) films, their magnetic properties could be modified. As an example for 15 ML Co/Ge(1 1 1) films, the coercivity increases from 730 to 920 Oe and the remanence Kerr intensity is reduced for 500 Langmuir (L) of oxygen exposure. Corresponding compositions analyzed by Auger electron spectroscopy measurement shows that the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. Oxygen distributes on the topmost layers of the film. The adsorbed oxygen influences the electronic density of states of Co and results in the changes of the magnetic properties. Besides, the appearance of O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of ultrathin Co/Ge(1 1 1) film is enhanced. 相似文献
49.
50.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献