全文获取类型
收费全文 | 3631篇 |
免费 | 145篇 |
国内免费 | 17篇 |
专业分类
化学 | 2735篇 |
晶体学 | 33篇 |
力学 | 69篇 |
数学 | 418篇 |
物理学 | 538篇 |
出版年
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 77篇 |
2020年 | 81篇 |
2019年 | 70篇 |
2018年 | 54篇 |
2017年 | 40篇 |
2016年 | 107篇 |
2015年 | 83篇 |
2014年 | 92篇 |
2013年 | 164篇 |
2012年 | 225篇 |
2011年 | 335篇 |
2010年 | 144篇 |
2009年 | 113篇 |
2008年 | 275篇 |
2007年 | 237篇 |
2006年 | 256篇 |
2005年 | 216篇 |
2004年 | 179篇 |
2003年 | 157篇 |
2002年 | 147篇 |
2001年 | 48篇 |
2000年 | 38篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 36篇 |
1993年 | 31篇 |
1992年 | 24篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1980年 | 18篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 13篇 |
1970年 | 13篇 |
排序方式: 共有3793条查询结果,搜索用时 265 毫秒
21.
Two problems in projectiles are discussed which generate interestingloci. 相似文献
22.
We show that the isotropy types of the singularities of Riemannian orbifolds are not determined by the Laplace spectrum. Indeed,
we construct arbitrarily large families of mutually isospectral orbifolds with different isotropy types. Finally, we show
that the corresponding singular strata of two isospectral orbifolds may not be homeomorphic.
Received: 6 October 2005 相似文献
23.
Generalized solutions are defined for stochastic evolution equations of the formdY
t
=A
*
Y
t
dt + dZ
t
on the nuclear triplel(R
d
) L2(R
d
) l(R
d
), whereA does not mapl(R
d
) into itself. One case which is treated in detail involvesA = –(–)
/2
,0 < < 2. This example arises as the Langevin equation for the fluctuation limit of a system of particles migrating according to a symmetric stable process and undergoing critical branching in a random medium.The research of D. A. Dawson was supported by the Natural Sciences and Engineering Research Council of Canada. L. G. Gorostiza's research was supported in part by CONACyT Grants PCEXCNA-040319 and 140102 G203-006, Mexico. 相似文献
24.
Elizabeth M. Holt Balawant S. Joshi Dilip H. Gawad S. William Pelletier 《Journal of chemical crystallography》1990,20(3):261-264
The crystal and molecular structure of 1-ethyl-4-methoxy-9H-pyrido[3,4b]indole (crenatine) carbonate C14H14N2O·H2CO3, (MS, m/z 226)M
R
288.3, a-carboline alkaloid, has been determined from X-ray diffraction data. The compound crystallizes in the space group Pbca with cell parameters:a=11.616(4),b=18.450(8),c=12.992(5)Å,V=2784(2)Å3,Z=8,D
calc=1.375 g cm–3, (MoK)=0.71069Å,(Mo K)=0.94 cm–1,F(000)=1216,R/R
w
=8.2/10.3% for 1099 reflections. The ring system of the-carboline nucleus is planar. The title compound shows a two center hydrogen bond between the indole N-H group and the oxygen atom of a carbonate group. The structure does not display hydrogen bonding between-carboline groups but rather a bonding network involving the carbonate group. 相似文献
25.
Kochocki JA Allison WW Alner GJ Ambats I Ayres DS Balka LJ Barr GD Barrett WL Benjamin D Border P Brooks CB Cobb JH Cockerill DJ Coover K Courant H Dahlin B DasGupta U Dawson JW Edwards VW Fields TH Kirby-Gallagher LM Garcia-Garcia C Giles RH Goodman MC Heller K Heppelman S Hill N Hoftiezer JH Jankowski DJ Johns K Joyce T Kafka T Litchfield PJ Lopez FV Lowe M Mann WA Marshak ML May EN McMaster L Milburn RH Miller W Napier A Oliver WP Pearce GF Perkins DH Peterson EA Price LE Roback D Rosen DB 《Physical review D: Particles and fields》1990,42(9):2967-2973
26.
27.
28.
29.
Margaret C. Gerthoffer Sikai Wu Bo Chen Tao Wang Steven Huss Shalisa M. Oburn Vincent H. Crespi John V. Badding Elizabeth Elacqua 《Chemical science》2020,11(42):11419
Limited supramolecular strategies have been utilized to synthesize sequence-defined polymers, despite the prominence of noncovalent interactions in materials design. Herein, we illustrate the utility of ‘sacrificial’ aryl-perfluoroaryl supramolecular synthons to synthesize sp3-hybridized nanothreads from sp2-enriched reactants. Our strategy features A–B reactant pairs in the form of a phenol:pentafluorophenol co-crystal that is preorganized for an electronically-biased and sequence-defined polymerization. The polymerization, initiated at 12 GPa, affords an alternating copolymer featuring exogenous –OH functionalities. The external substitution is confirmed through IR spectroscopy. Importantly, the inclusion of the functional unit provides the first experimental glimpse at reaction mechanism: keto–enol tautomerization that can only occur during cycloaddition is observed through IR spectroscopy. Our approach realizes the first example of a functionalized nanothread and attains sequence definition through sacrificial supramolecular preorganization and presents a further approach for de novo design of complex nanothreads.Supramolecular synthons are exploited to synthesize –OH functionalized sp3-rich sequence-defined nanothreads using pressure-induced polymerization of a phenol:pentafluorophenol co-crystal. 相似文献
30.
Walstrom A Pink M Yang X Tomaszewski J Baik MH Caulton KG 《Journal of the American Chemical Society》2005,127(15):5330-5331
Replacement of chloride in (PNP)RuCl, PNP = (tBu2PCH2SiMe2)2N, by Me3SiN3 gives a pre-redox adduct that, already at -30 degrees C, releases N2 to produce the mononuclear nonplanar Ru(IV) nitride (PNP)RuN, characterized by spectroscopic and X-ray methods. DFT calculations show the planar structure to be only 1.6 kcal/mol less stable, which explains the time-averaged simplicity of the 1H NMR spectrum, as well as the large vibrational amplitude of the nitride ligand. 相似文献