全文获取类型
收费全文 | 2254篇 |
免费 | 49篇 |
国内免费 | 8篇 |
专业分类
化学 | 1602篇 |
晶体学 | 20篇 |
力学 | 52篇 |
数学 | 272篇 |
物理学 | 365篇 |
出版年
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 36篇 |
2019年 | 27篇 |
2018年 | 28篇 |
2017年 | 15篇 |
2016年 | 38篇 |
2015年 | 28篇 |
2014年 | 27篇 |
2013年 | 119篇 |
2012年 | 96篇 |
2011年 | 123篇 |
2010年 | 82篇 |
2009年 | 50篇 |
2008年 | 104篇 |
2007年 | 119篇 |
2006年 | 131篇 |
2005年 | 99篇 |
2004年 | 99篇 |
2003年 | 66篇 |
2002年 | 86篇 |
2001年 | 46篇 |
2000年 | 53篇 |
1999年 | 39篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 29篇 |
1995年 | 40篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 17篇 |
1991年 | 32篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 30篇 |
1981年 | 16篇 |
1980年 | 31篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1977年 | 29篇 |
1976年 | 14篇 |
1975年 | 22篇 |
1974年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有2311条查询结果,搜索用时 0 毫秒
1.
Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry 下载免费PDF全文
Victor A. Kusuma Elliot A. Roth William P. Clafshenkel Steven S. Klara Xu Zhou Surendar R. Venna Erik Albenze David R. Luebke Meagan S. Mauter Richard R. Koepsel Alan J. Russell David Hopkinson Hunaid B. Nulwala 《Journal of polymer science. Part A, Polymer chemistry》2015,53(13):1548-1557
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557 相似文献
2.
The Fermi and Coulomb holes of the 21
S state of the helium isoelectronic sequence are investigated. Several interesting differences between the results obtained and those which might be expected on the basis of the corresponding 23
S state are pointed out and discussed. 相似文献
3.
Szklarzewicz Janusz Samotus Alina Nowicka Beata Burgess John Fawcett John Russell David R. 《Transition Metal Chemistry》1999,24(2):177-182
The X-ray crystal structure of (bpyH2)2[W(CN)8]·4H2 O (bpyH2=2,2-bipyridinium) is described. The [W(CN)8]4– anion has an approximately square antiprismatic (D4d) conformation, seemingly imposed by strong anion–water–cation hydrogen-bonding interactions. Bond distances in the anion are: WC 2.150(5), 2.163(5); CN 1.128(6), 1.145(6)Å and the angles WCN are 177.6(5), 178.3(5)°. The dihydrate and the anhydrous salt are both intensely black solids, exhibiting ion-pair charge-transfer interaction between cation and anion. E.s.r. spectra indicate that 30% of the tungsten is present as WV in the solid state, but that in solution only the WIV complex is present. The electron withdrawing effect of the cation is discussed and compared with that in a series of salts with different bipyridinium cations. 相似文献
4.
Ningyi Chen Jiayi Xu Michael Reuman Xun Li Ronald K. Russell Zhihua Sui 《Tetrahedron letters》2006,47(33):5909-5913
Various substituents were introduced onto the methyl group in 4-methyl coumarins through lithiation, followed by reactions with a wide range of electrophiles. The presence of an alkoxy group on 6′-phenyl ring was found to be pivotal for the success of this reaction. This procedure provided a convenient synthetic pathway to elaborate the methyl group of 4-methylcoumarins. Application of this methodology was showcased with the synthesis of biologically important novel tetracyclic chromene ring systems (n = 1-3). 相似文献
5.
Protein tyrosine phosphatase 1B (PTP1B) functions by removing the phosphoryl group from tyrosinephosphorylated proteins in
insulin signaling and metabolism. The regeneration of the active site involves a sulphenylamide intermediate derived from
the intrastrand cross-linking between the catalytic serine and the neighboring backbone nitrogen. Two mechanisms have been
proposed for the formation of the sulphenylamide intermediate and the subsequent reactivation of the catalytic site. In the
current work, the proposed mechanisms have been investigated by the use of density functional theory calculations. Our results
suggest that these two mechanisms have similar overall energy barriers and that the preferred route will be determined by
the availability of hydrogen peroxide or other oxidizing reagents. 相似文献
6.
7.
Summary We consider a walk from a stateA
1 to a stateA
n+1 in which the probability of remaining atA
i
isp
i
, and the probability of progressing fromA
i
toA
i+1 is 1 –p
i
. The probabilityW
nk
of reachingA
n+1 fromA
1 in exactlyn + k steps can then be expressed as a polynomial of degreen + k in then variablesp
1,,p
n
. We determine the maximum value ofW
nk
and the (unique) choice (p
1,,p
n
) for which this extremum occurs.Dedicated to Professor Otto Haupt with best wishes on his 100th birthday 相似文献
8.
9.
Russell Lyons 《Inventiones Mathematicae》1986,83(3):605-616
Summary It is well-known that almost every number in [0, 1] is normal in base 2, in the sense of Lebesgue measure. Kahane and Salem asked whether the same is true with respect to any Borel measure whose Fourier-Stieltjes coefficients vanish at infinity — in other words, whether the set of non-normal numbers is a set of uniqueness in the wide sense. We show that this is not the case. In fact, we give best-possible conditions on the rate of decay of
in order that -almost every number be normal. The techniques include, on the one hand, probability measures with respect to which the binary digits in [0, 1] are independent only by blocks, rather than individually, and on the other hand, the strong law of large numbers for weakly correlated random variables.This work was partially supported by an NSF Graduate Fellowship, NSF Grant MCS-82-01602, and an AMS Research Fellowship. 相似文献
10.
The isothermal and temperature scanning calorimeters manufactured by Calorimetry Sciences Corporation are briefly described. Applications of calorimetry to determine thermodynamics and kinetics of reactions of interest in biotechnology are described with illustrative examples. 相似文献