全文获取类型
收费全文 | 3002篇 |
免费 | 156篇 |
国内免费 | 14篇 |
专业分类
化学 | 2261篇 |
晶体学 | 31篇 |
力学 | 89篇 |
数学 | 223篇 |
物理学 | 568篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 76篇 |
2021年 | 89篇 |
2020年 | 75篇 |
2019年 | 82篇 |
2018年 | 53篇 |
2017年 | 59篇 |
2016年 | 95篇 |
2015年 | 87篇 |
2014年 | 133篇 |
2013年 | 210篇 |
2012年 | 254篇 |
2011年 | 276篇 |
2010年 | 151篇 |
2009年 | 132篇 |
2008年 | 225篇 |
2007年 | 183篇 |
2006年 | 181篇 |
2005年 | 142篇 |
2004年 | 146篇 |
2003年 | 95篇 |
2002年 | 118篇 |
2001年 | 42篇 |
2000年 | 52篇 |
1999年 | 25篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 22篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有3172条查询结果,搜索用时 20 毫秒
901.
Choi EY Park K Yang CM Kim H Son JH Lee SW Lee YH Min D Kwon YU 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(21):5535-5540
In this paper, we report two metal-organic frameworks [Co3(ndc)3(bipyen)(1.5)]H2O (1) and [Co2(ndc)2bipyen)]C6H6.H2O (2) (bipyen=trans-1,2-bis(4-pyridyl)ethylene, H2ndc=2,6-naphthalenedicarboxylic acid). These compounds were both synthesized from identical hydrothermal reaction conditions except that benzene was added to the reaction for 2. Crystal structures show that the two compounds have triply interpenetrated three-dimensional frameworks and these frameworks have the same primary structure of a two-dimensional network of interconnected [Co2(O2CR)(4/2)] (R=naphthalene group) paddle-wheels and bridging bipyen ligands. Both compounds have guest water molecules and, in addition, 2 has guest benzene molecules. Structural transformations of the host accompanied guest removal, which can be monitored by powder X-ray diffraction. N2 adsorption data of 2 show that there are two different types of pores corresponding to the benzene and water pores. Upon exposure to vapors of several organic molecules, the heat-treated sample of 2 adsorbs benzene and cyclohexene, but does not adsorb toluene, (o-, m-, and p-)xylenes, cycloheptatriene, or cyclohexane. 相似文献
902.
Delta(12)-Prostaglandin (PG) J(2) is known to elicit an anti-neoplastic effects via apoptosis induction. Previous study showed Delta(12)-PGJ(2)-induced apoptosis utilized caspase cascade through cytochrome c-dependent pathways in HeLa cells. In this study, the cellular mechanism of Delta(12)-PGJ(2)- induced apoptosis in HeLa cells, specifically, the role of two mitochondrial factors; bcl-2 and apoptosis-inducing factor (AIF) was investigated. Bcl-2 attenuated Delta(12)-PGJ(2)-induced caspase activation, loss of mitochondrial transmembrane potential (Deltapsi(m)), nuclear fragmentation, DNA laddering, and growth curve inhibition for approximately 24 h, but not for longer time. AIF was not released from mitochondria, even if the Deltapsi(m) was dissipated. One of the earliest events observed in Delta(12)-PGJ(2)-induced apoptotic events was dissipation of Deltapsi(m), the process known to be inhibited by bcl-2. Pre-treatment of z-VAD- fmk, the pan-caspase inhibitor, resulted in the attenuation of ym depolarization in Delta(12)-PGJ(2)-induced apoptosis. Up-regulation of Sox-4 protein by Delta(12)-PGJ(2) was observed in HeLa and bcl-2 overexpressing HeLa B4 cell lines. Bcl-2 overexpression did not attenuate the expression of Sox-4 and its expression coincided with other apoptotic events. These results suggest that Delta(12)-PGJ(2) induced Sox-4 expression may activate another upstream caspases excluding the caspase 9-caspase 3 cascade of mitochondrial pathway. These and previous findings together suggest that Delta(12)-PGJ(2)-induced apoptosis in HeLa cells is caspase-dependent, AIF-independent events which may be affected by Sox-4 protein expression up-regulated by Delta(12)-PGJ(2). 相似文献
903.
904.
905.
This paper deals with the bilinear symmetrization problem associated with Sobolev inner products. Let 007B;Q
n
}
n=0
be the sequence of monic polynomials orthogonal with respect to a Sobolev inner product of order 1 when one of the measures is discrete and the other one is a nondiscrete positive Borel measure. Furthermore, assume that the supports of such measures are symmetric with respect to the origin so that the corresponding odd moments vanish. We consider the orthogonality properties of the sequences of monic polynomials 007B;P
n
}
n=0
and {R
n
}
n=0
such that Q
2n
(x)=P
n
(x
2), Q
2n+1(x)=xR
n
(x
2). Moreover, recurrence relations for {P
n
}
n=0
and {R
n
}
n=0
are obtained as well as explicit algebraic relations between them. 相似文献
906.
We study resonance patterns of a spiral-shaped dielectric microcavity with chaotic ray dynamics. Many resonance patterns of this microcavity, with refractive indices n=2 and 3, exhibit strong localization of simple geometric shape, and we call them quasiscarred resonances in the sense that there is, unlike conventional scarring, no underlying periodic orbits. It is shown that the formation of a quasiscarred pattern can be understood in terms of ray dynamical probability distributions and wave properties like uncertainty and interference. 相似文献
907.
Schwanda C Abe K Abe K Abe T Adachi I Aihara H Akatsu M Asano Y Aushev T Bahinipati S Bakich AM Ban Y Banas E Bay A Bizjak I Bondar A Bozek A Bracko M Browder TE Chang MC Chao Y Cheon BG Choi Y Choi YK Chuvikov A Cole S Danilov M Dash M Dong LY Drutskoy A Eidelman S Eiges V Gabyshev N Gershon T Gokhroo G Golob B Hazumi M Higuchi I Hinz L Hokuue T Hoshi Y Hou WS Huang HC Iijima T Inami K Ishikawa A Itoh R Iwasaki H Iwasaki M Kang JH Kang JS Kapusta P Katayama N Kawai H Kichimi H Kim HJ 《Physical review letters》2004,93(13):131803
We have searched for the decay B+-->omegal(+)nu (l=e or mu) in 78 fb(-1) of Upsilon(4S) data (85x10(6)BB events) accumulated with the Belle detector. The final state is fully reconstructed using the omega decay into pi(+)pi(-)pi(0), combined with detector hermeticity to estimate the neutrino momentum. A signal of 414+/-125 events is found in the data, corresponding to a branching fraction of (1.3+/-0.4+/-0.2+/-0.3)x10(-4), where the first two errors are statistical and systematic, respectively. The third error reflects the estimated form-factor uncertainty. 相似文献
908.
In this paper, we demonstrate that C. madurensis embryonic axes can withstand cryopreservation using the encapsulation-dehydration technique. Up to 57.5 % survival was achieved using a standard encapsulation-dehydration protocol, which included pregrowth of encapsulated axes for 16 h in medium containing 0.8 M sucrose + 1 M glycerol, desiccation of beads to around 30 % moisture content (fresh weight basis) followed by rapid freezing. A slightly higher survival percentage (65 %) was obtained using a modified encapsulation-dehydration protocol, which included pretreatment of axes with 2 M glycerol + 0.6 M sucrose for 1 h, concomitantly with their encapsulation in 3 % calcium alginate beads, followed by desiccation of the beads to around 30 % moisture content. 相似文献
909.
The desiccation and freezing tolerance of seeds, with and without testas, and embryonic axes of Citrus aurantifolia were investigated. Seeds were desiccated with silica gel, under the laminar air flow cabinet or by placing them on a laboratory bench. Whatever the desiccation method employed, survival before and after cryopreservation was higher for seeds without testas. When freezing intact seeds, the highest survival percentage (41.3 %) was achieved after desiccation to 7.3 % moisture content (fresh weight basis) on the laboratory bench. Survival of seeds cryopreserved without testas could reach up to 85 % after desiccation under the laminar air flow cabinet or on the laboratory bench, corresponding to moisture contents of 7.1 and 4.5 %, respectively. After desiccation with silica gel, survival reached a maximum of 60.0 %, for a seed moisture content of 3.3 %. Survival of control embryonic axes was high (80-100 %) whatever the sucrose concentration in the preculture medium and the duration of the desiccation period. After cryopreservation, no survival was noted with embryonic axes, which had not been precultured nor desiccated. Survival of non-desiccated embryonic axes after cryopreservation increased progressively in line with increasing sucrose concentrations in the preculture medium, from 7.5 % with 0.1 M sucrose to 77.5 % with 0.7 M sucrose. Survival of desiccated and cryopreserved embryos was always high, whatever the preculture treatment and desiccation period, ranging from 55.8 % to 92.5 %. 相似文献
910.
Broadband quasi-phase-matched second-harmonic generation in MgO-doped periodically poled LiNbO_3 at the communications band 总被引:2,自引:0,他引:2
A novel scheme for broadband second-harmonic generation was developed with type I quasi phase matching by use of an off-digital nonlinear optical coefficient d(31) . This was achieved by matching of the group velocities of the second harmonic and the fundamental, while the phase velocities were quasi phase matched. The desired group-velocity dispersion could be obtained with LiNbO(3) doped with 5 mol. % of MgO. Efficient second-harmonic generation with a bandwidth of 52 nm was obtained for the fundamental wavelength centered at 1566 nm in MgO-doped periodically poled LiNbO(3) , compared with a bandwidth of 1.3 nm for the conventional scheme using d(33) . Efficient frequency doubling of an ultrafast pulse is expected without group-velocity walk-off or pulse distortion. 相似文献