全文获取类型
收费全文 | 53081篇 |
免费 | 6020篇 |
国内免费 | 7392篇 |
专业分类
化学 | 40340篇 |
晶体学 | 718篇 |
力学 | 2177篇 |
综合类 | 489篇 |
数学 | 7056篇 |
物理学 | 15713篇 |
出版年
2024年 | 69篇 |
2023年 | 615篇 |
2022年 | 1148篇 |
2021年 | 1470篇 |
2020年 | 1417篇 |
2019年 | 1517篇 |
2018年 | 1268篇 |
2017年 | 1363篇 |
2016年 | 1997篇 |
2015年 | 1984篇 |
2014年 | 2362篇 |
2013年 | 3743篇 |
2012年 | 4177篇 |
2011年 | 4540篇 |
2010年 | 3137篇 |
2009年 | 3407篇 |
2008年 | 3634篇 |
2007年 | 3367篇 |
2006年 | 3059篇 |
2005年 | 2832篇 |
2004年 | 2717篇 |
2003年 | 2063篇 |
2002年 | 2055篇 |
2001年 | 1518篇 |
2000年 | 1333篇 |
1999年 | 1133篇 |
1998年 | 886篇 |
1997年 | 784篇 |
1996年 | 802篇 |
1995年 | 667篇 |
1994年 | 582篇 |
1993年 | 571篇 |
1992年 | 548篇 |
1991年 | 428篇 |
1990年 | 386篇 |
1989年 | 337篇 |
1988年 | 308篇 |
1987年 | 235篇 |
1986年 | 257篇 |
1985年 | 279篇 |
1984年 | 233篇 |
1983年 | 164篇 |
1982年 | 146篇 |
1981年 | 127篇 |
1980年 | 113篇 |
1979年 | 102篇 |
1978年 | 73篇 |
1977年 | 68篇 |
1976年 | 64篇 |
1974年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
131.
JiangMinCHEN LuLingWU XianHUANG 《中国化学快报》2004,15(2):143-144
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process. 相似文献
132.
The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module 总被引:1,自引:0,他引:1
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported. 相似文献
133.
The first hyperpolarizabilities of a series of novel azulenic-barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolarizabilities of chromophores holds the same tendency as the experimental results. In addition, the static first hyperpolarizability β0 of molecules was calculated by means of the Sum-Over-States (SOS) expression and the two-level formula respectively. The results show that these molecules possess large static first hyperpolarizabilities and the, β0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the β0 value. 相似文献
134.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
135.
Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity. 相似文献
136.
WeiMinSHI JianWU YiFengWU KaiXianQIAN 《中国化学快报》2004,15(12):1427-1429
A mono-funtionalised tetraphenylporphyrin (TPP) bearing valine moiety at the phenyl ring was synthesized for photocytotoxicity examination in four steps, starting from regiospecific mono-nitration of TPP at the phenyl ring. The in vitro photocytotoxicitic effect against SPC-Al adenocarcinona cell line was tested. 相似文献
137.
The paper discusses the relationship between weights and control vertices of two rational NURBS curves of degree two or three with all weights larger than zero when they represent the same curve parametrically and geometrically, and gives sufficient and necessary conditions for coincidence of two rational NURBS curves in non-degeneracy case. 相似文献
138.
139.
Thermal oxidation of polyethylene filled with dispersed copper and containing an amine antioxidant was studied. The concentration ranges in which the catalytic effect of the metal on the polymer oxidation or the stabilizing effect of the antioxidant prevails were determined. Under certain conditions, dispersed copper enhances the stabilizing effect of the antioxidant. 相似文献
140.
Francesc Carreras M. Dolors Llongueras Antonio Magaña 《Annals of Operations Research》2005,137(1):67-89
A partnership in a cooperative game is a coalition that possesses an internal structure and, simultaneously, behaves as an
individual member. Forming partnerships leads to a modification of the original game which differs from the quotient game
that arises when one or more coalitions are actually formed.
In this paper, the Shapley value is used to discuss the convenience to form either coalitions or partnerships. To this end,
the difference between the additive Shapley value of the partnership in the partnership game and the Shapley alliance value
of the coalition, and also between the corresponding value of the internal and external players, are analysed. Simple games
are especially considered.
Research partially supported by Grant BFM 2003-01314 of the Science and Technology Spanish Ministry and the European Regional
Development Fund. 相似文献