全文获取类型
收费全文 | 22816篇 |
免费 | 2748篇 |
国内免费 | 2980篇 |
专业分类
化学 | 17890篇 |
晶体学 | 637篇 |
力学 | 152篇 |
综合类 | 131篇 |
数学 | 5594篇 |
物理学 | 4140篇 |
出版年
2023年 | 413篇 |
2022年 | 341篇 |
2021年 | 517篇 |
2020年 | 797篇 |
2019年 | 875篇 |
2018年 | 853篇 |
2017年 | 712篇 |
2016年 | 955篇 |
2015年 | 948篇 |
2014年 | 1269篇 |
2013年 | 1946篇 |
2012年 | 1355篇 |
2011年 | 1633篇 |
2010年 | 1313篇 |
2009年 | 1526篇 |
2008年 | 1553篇 |
2007年 | 1525篇 |
2006年 | 1284篇 |
2005年 | 1046篇 |
2004年 | 1017篇 |
2003年 | 906篇 |
2002年 | 945篇 |
2001年 | 608篇 |
2000年 | 522篇 |
1999年 | 475篇 |
1998年 | 380篇 |
1997年 | 287篇 |
1996年 | 286篇 |
1995年 | 333篇 |
1994年 | 279篇 |
1993年 | 220篇 |
1992年 | 217篇 |
1991年 | 126篇 |
1990年 | 114篇 |
1989年 | 87篇 |
1988年 | 87篇 |
1987年 | 58篇 |
1986年 | 66篇 |
1985年 | 79篇 |
1984年 | 68篇 |
1983年 | 29篇 |
1982年 | 72篇 |
1981年 | 68篇 |
1980年 | 51篇 |
1979年 | 62篇 |
1978年 | 56篇 |
1977年 | 39篇 |
1976年 | 48篇 |
1975年 | 28篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
构造了第孙中禹种强度不等的非对称三态叠加多模叠加态光场|ψ1(ABC)〉q.利用多模压缩态理论研究了态|ψ1(ABC)〉q第一正交分量高次和压缩.结果发现:①当构成态|ψ1(ABC)〉q的三个多模相干态光场的强度不相等时,在一定条件下,态|ψ1(ABC)〉q的第一正交分量可出现任意幂次的高次和压缩.②当上述的三个多模相干态光场强度相等时,态|ψ1(ABC)〉q的第一正交分量的高次和压缩现象消失.在这种情况下,态|ψ1(ABC)〉q的第一正交分量恒处于NH最小测不准态. 相似文献
92.
The Li oxides species formed on Li over-deposited V2O5 thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V2O5 system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li2O and Li2O2 compounds on the surface. The formation of Li2O2 causes to arise an emission line at about 11.3 eV in the valence band spectra. 相似文献
93.
Lin and Zhang (J. Roy. Statist. Soc. Ser. B 61 (1999) 381) proposed the generalized additive mixed model (GAMM) as a framework for analysis of correlated data, where normally distributed random effects are used to account for correlation in the data, and proposed to use double penalized quasi-likelihood (DPQL) to estimate the nonparametric functions in the model and marginal likelihood to estimate the smoothing parameters and variance components simultaneously. However, the normal distributional assumption for the random effects may not be realistic in many applications, and it is unclear how violation of this assumption affects ensuing inferences for GAMMs. For a particular class of GAMMs, we propose a conditional estimation procedure built on a conditional likelihood for the response given a sufficient statistic for the random effect, treating the random effect as a nuisance parameter, which thus should be robust to its distribution. In extensive simulation studies, we assess performance of this estimator under a range of conditions and use it as a basis for comparison to DPQL to evaluate the impact of violation of the normality assumption. The procedure is illustrated with application to data from the Multicenter AIDS Cohort Study (MACS). 相似文献
94.
O. N. Lyubenko I. G. Ermolenko L. D. Patsenker Krasovitskii I. N. Tur 《Chemistry of Heterocyclic Compounds》2003,39(4):511-519
The behavior of dimethylamino-substituted 7H-benzo[de]pyrazolo[5,1-a]isoquinoline-7-ones, synthesized for the first time, under conditions of the Vilsmeier-Haack reaction. It has been shown that, on heating with POCl3 and DMF, they are converted by electrophilic substitution at the position ortho to the dimethylamino group, followed by cyclization of the iminium adduct to a quinazolinium salt. When an acetyl group is present, the Arnold reaction, leading to the formation of a chloroaryl, accompanies the heterocyclization. The rates and proportion of the reaction products depend on the position of the dimethyl groups relative to the pyrazole ring. 相似文献
95.
《Solid State Communications》2003,127(11):703-706
In this work we present temperature dependent infrared reflectivity and absorption of Sr2FeWO6 between 700 and 17 K measured from 40 to 10000 cm−1. The reflectivity spectra show well defined phonon bands peaking at 143, 227, 377 and 625 cm−1 assigned to overlapping vibrational modes split from those active in cubic perovskite. We have also verified that this compound is structurally stable in the whole temperature range and that its optical gap at ∼750 cm−1 (95 meV) undergoes only a minor high temperature decrease ascribed to new thermally accessible levels. 相似文献
96.
研究了应用于锂二次电池正极的新型高能量密度存贮材料Li(AlxCo1-x)O2 (x=01—05)的磁性.发现Al3+的掺杂可导致Co3+中d电子自旋态发生变化,即有部分d电子进入高自旋态.伴随Co3+中电子状态的改变,材料结构演化也发生了相应变化,表现为c/a比增大明显减缓,较好地解释了材料结构对Vegard定律的正偏离.这对材料的微观结构与性能设计具有重要意义.
关键词:
锂电池材料
Li(AlxCo1-x)O2
磁性
自旋态
结构演化 相似文献
97.
98.
99.
F-H实验仪与光栅光谱仪连用观测253.7nm谱线 总被引:1,自引:0,他引:1
通过F-H实验仪和光栅光谱仪的连用,可实时观测汞原子从6s6s1So态激发到6s6sSP1态,退激时,辐射出能量为4.9eV的光量子,其波长为253.7nm. 相似文献
100.
Jin-Mok Hur Chung-Seok Seo Sun-Seok Hong Dae-Seung Kang Seong-Won Park 《Reaction Kinetics and Catalysis Letters》2003,80(2):217-222
The concept of a novel electrochemical reduction process for the treatment of spent nuclear fuels in Li2O-LiCl molten salt was proposed and fresh tests using U3O8 powder were carried out to elucidate the reaction mechanism and verify the feasibility of the process. Electrolysis of Li2O and reduction of U3O8 powder took place simultaneously at the cathode part of the electrolysis cell via a catalytic EC mechanism and the conversion of U3O8 to U metal was more than 99%.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献