全文获取类型
收费全文 | 8708篇 |
免费 | 382篇 |
国内免费 | 1916篇 |
专业分类
化学 | 5093篇 |
晶体学 | 6篇 |
力学 | 641篇 |
综合类 | 219篇 |
数学 | 1382篇 |
物理学 | 3665篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2016年 | 20篇 |
2015年 | 49篇 |
2014年 | 22篇 |
2013年 | 98篇 |
2012年 | 108篇 |
2011年 | 1341篇 |
2010年 | 689篇 |
2009年 | 686篇 |
2008年 | 115篇 |
2007年 | 123篇 |
2006年 | 191篇 |
2005年 | 436篇 |
2004年 | 1353篇 |
2003年 | 792篇 |
2002年 | 696篇 |
2001年 | 569篇 |
2000年 | 223篇 |
1999年 | 230篇 |
1998年 | 279篇 |
1997年 | 199篇 |
1996年 | 132篇 |
1995年 | 133篇 |
1994年 | 110篇 |
1993年 | 493篇 |
1992年 | 524篇 |
1991年 | 326篇 |
1990年 | 345篇 |
1989年 | 331篇 |
1988年 | 138篇 |
1987年 | 15篇 |
1986年 | 78篇 |
1985年 | 24篇 |
1984年 | 33篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1962年 | 2篇 |
1938年 | 3篇 |
1937年 | 2篇 |
1936年 | 2篇 |
1931年 | 2篇 |
1893年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
991.
MA Kang CHEN LinGen & SUN FengRui Postgraduate School Naval University of Engineering Wuhan China 《中国科学:化学》2010,(4)
An irreversible light-driven engine is described in this paper, in which the heat transfer between the working fluid and the environment obeys a linear phenomenological heat transfer law [ q ∝Δ(T -1)], with a working fluid composed of the bimolecular reacting system 2SO 3 F■S 2 O 6 F2. Piston trajectories maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. The optimal control theory is applied to determi... 相似文献
992.
YU YanLi BAI Wei ZHAO KongShuang& ZHOU YunLong College of Chemistry Beijing Normal University Beijing China College of Life Science 《中国科学:化学》2010,(3)
Dielectric spectroscopy(DS) was utilized to investigate the toxicity of the Cu2+ solution to Microcystis aeruginosa.It was found that 0.04 mM Cu2+ had no effect on dielectric increment,whereas the Cu2+ concentrations above 0.1 mM decreased the value of Δε/Δε intact.The toxic effect of Cu2+ on M.aeruginosa cells was time-dependent and concentration-dependent.There was a threshold concentration between 0.04 mM and 0.1 mM,which affected the cell membrane,suggesting that Cu2+ at the concentrations higher than 0... 相似文献
993.
空穴传输基团修饰的吡嗪铱配合物的合成及其发光性质 总被引:1,自引:0,他引:1
设计合成了空穴传输性咔唑基团修饰的吡嗪配体, 2,3-二(4-(9-咔唑基甲基)苯基)-5-甲基吡嗪(CzMPMP)及其铱配合物Ir(CzMPMP)2(acac)(acac: 乙酰丙酮). 用核磁共振(NMR)、质谱、元素分析等方法对其进行了表征, 并用紫外-可见吸收光谱、液相和固相光致发光光谱对其光学性质进行了研究. 通过与没有咔唑取代基的2,3-二苯基-5-甲基吡嗪铱配合物Ir(DPMP)2(acac)进行对照, 说明咔唑基团对配合物的光学性质有显著影响. 不含咔唑取代基的配合物Ir(DPMP)2(acac)的固态光致发光光谱中存在很强的激活双体(excimer)峰, 而Ir(CzMPMP)2(acac)的固态光致发光光谱中未发现有激活双体峰; 并且在溶液中, 含有咔唑取代基的配合物Ir(CzMPMP)2(acac)较Ir(DPMP)2(acac)的光致发光强度有显著提高. 这些结果说明咔唑基团的空间位阻可以有效阻止配合物成膜时产生激活双体, 从而消除发射峰红移现象并提高发光效率. 相似文献
994.
995.
996.
For a set A of nonnegative integers, the representation functions R2(A,n) and R3(A,n) are defined as the numbers of solutions to the equation n = a + a′ with a,a′∈ A, a < a′ and a a′, respectively. Let N be the set of nonnegative integers. Given n0 > 0, it is known that there exist A,A′■ N such that R2(A′,n) = R2(N \ A′,n) and R3(A,n) = R3(N \ A,n) for all n n0. We obtain several related results. For example, we prove that: If A ■ N such that R3(A,n) = R3(N \ A,n) for all n n0, then (1) for any n n0 we have... 相似文献
997.
FAN CuiLing LEI JianGuo & SHAN XiuLing School of Sciences Nantong University Nantong China College of Mathematics Information Science Hebei Normal University Shijiazhuang 《中国科学 数学(英文版)》2011,(1)
Difference systems of sets (DSSs) are combinatorial configurations which were introduced in 1971 by Levenstein for the construction of codes for synchronization. In this paper, we present two kinds of constructions of difference systems of sets by using disjoint difference families and a special type of difference sets, respectively. As a consequence, new infinite classes of optimal DSSs are obtained. 相似文献
998.
ZHANG Mei School of Mathematical Sciences Beijing Normal University Beijing China 《中国科学 数学(英文版)》2011,(2)
In this paper, we study the count of head runs up to a fixed time in a two-state stationary Markov chain. We prove that in total variance distance, the negative binomial, Poisson and binomial distributions are appropriate approximations according to the relation of the variance and mean of the count, generalizing earlier results in previous literatures. The proof is based on Stein’s method and coupling. 相似文献
999.
LI JunPing & LIU ZaiMing School of Mathematical Science Computing Technology Central South University Changsha China 《中国科学 数学(英文版)》2011,(5)
We consider a modified Markov branching process incorporating with both state-independent immigration-migration and resurrection. The effect of state-independent immigration-migration is firstly in- vestigated in detail. The explicit expressions for the extinction probabilities and mean extinction times are presented. The ergodicity and stability properties of the process incorporating with resurrection structure are then investigated. The conditions for recurrence, ergodicity and exponential ergodicity are... 相似文献
1000.
CHEN Meng School of Mathematical Sciences & LMNS Fudan University Shanghai China 《中国科学 数学(英文版)》2011,(8)
We investigate birationality of the anti-pluricanonical map Φ-m,the rational map defined by the anti-pluricanonical system |-mKX|,on weak Q-Fano 3-folds. 相似文献