全文获取类型
收费全文 | 4445篇 |
免费 | 123篇 |
国内免费 | 21篇 |
专业分类
化学 | 2747篇 |
晶体学 | 23篇 |
力学 | 240篇 |
数学 | 890篇 |
物理学 | 689篇 |
出版年
2023年 | 21篇 |
2022年 | 28篇 |
2021年 | 121篇 |
2020年 | 88篇 |
2019年 | 67篇 |
2018年 | 71篇 |
2017年 | 65篇 |
2016年 | 147篇 |
2015年 | 128篇 |
2014年 | 102篇 |
2013年 | 230篇 |
2012年 | 245篇 |
2011年 | 310篇 |
2010年 | 169篇 |
2009年 | 160篇 |
2008年 | 255篇 |
2007年 | 285篇 |
2006年 | 200篇 |
2005年 | 188篇 |
2004年 | 175篇 |
2003年 | 144篇 |
2002年 | 122篇 |
2001年 | 72篇 |
2000年 | 37篇 |
1999年 | 56篇 |
1998年 | 43篇 |
1997年 | 49篇 |
1996年 | 54篇 |
1995年 | 45篇 |
1994年 | 51篇 |
1993年 | 64篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 40篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 59篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 35篇 |
1981年 | 39篇 |
1980年 | 32篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 31篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 26篇 |
排序方式: 共有4589条查询结果,搜索用时 622 毫秒
71.
Giovanni Monegato 《Numerical Algorithms》1996,11(1):271-283
We consider the numerical solution of second kind integral equations of the form $$u(y) - \int\limits_0^1 {k(y/x)\frac{{u(x)}}{x}dx = f(y), 0 \le y \le 1,} $$ for some given kernelk(t). These equations, usually indicated as of Mellin type, arise in a variety of applications. In particular, we examine a Nyström interpolant based on the following product quadrature rule: $$\int\limits_0^1 {k(y/x)\frac{{u(x)}}{x}dx \approx \sum\limits_{i = 0}^n {w_{ni} (y)u(x_{mi} ).} } $$ This rule is obtained by interpolatingu(x) by the Lagrange polynomial associated with the set of Gauss-Radau nodes {x ni}. Under certain assumptions on the kernelk(t), we are able to prove the stability of our interpolant and derive convergence estimates. 相似文献
72.
A (k,k)-current T on an open subset of CN is plurisubharmonic if is positive. Positive plurisubharmonic currents admit Lelong numbers; we prove here that they are independent on the coordinates system. Moreover, if Y is an analytic subset of pure dimension, then the Lelong numbers of T on Y are given by a non negative weakly plurisubharmonic function. 相似文献
73.
74.
75.
Giovanni Gaiffi 《manuscripta mathematica》1996,91(1):83-94
Let
be the complexified Coxeter arrangement of hyperplanes of typeA
n−1. In this paper we construct anS
n+1 extension of the naturalS
n action on the complex cohomology ring of the complement ofA
n−1. Recurrence formulas connecting characters with respect to theS
n and theS
n+1 action are given. 相似文献
76.
77.
A. Badalá R. Barbera A. Palmeri G. S. Pappalardo F. Riggi A. C. Russo 《Zeitschrift für Physik A Hadrons and Nuclei》1993,344(4):455-467
Several global variables were tested with the aim to determine the impact parameter in nucleus-nucleus collisions producing pions at incident energies around 100 MeV/nucleon. The experimental set-up includes the MEDEA multidetector, part of which is used as a
0 spectrometer, and an additional hodoscope of plastic scintillators to cover very forward angles. A statistical model was used to generate bothinclusive and pion-triggered events. Selection ofwell measured events was made through the measured total parallel momentum. Among the different global variables which were tested, the average parallel velocity was seen to give the best correlation with the impact parameter. 相似文献
78.
Di-2-pyridylketone semicarbazone as ligand in metal complexes: synthesis and X-ray crystal structure
Luigi P. Battaglia Pier Giovanni Berzolla Anna Bonamartini Corradi Corrado Pelizzi 《Journal of chemical crystallography》1993,23(12):973-979
A series of complexes of di-2-pyridylketone semicarbazone (Hdips) and Mn(II), Co(II), Co(III), Ni(II) and Cu(II) nitrates were synthesized and characterized by means of IR spectroscopy and for cobalt and nickel by X-ray crystal structures. The results are in agreement with the formulae: Mn(Hdips)2(NO3)2·2H2O, [Co(Hdips)2](NO3)2·H2O (I), [Ni(Hdips)2](NO3)2·H2O (II), Cu(Hdips)(NO3)2·2H2O, [Co(dips)2](NO3)·2H2O (III). The structure of I and II are monoclinic, space groupP21/c, with, I,a=15.980(4),b=11.531(2),c=16.170(2)Å;=104.20(2)°,Z=4,R=0.032; II,a=16.109(5),b=11.480(3),c=16.135(6)Å;=104.15(2)°,Z=4,R=0.069. Compound III is also monoclinic, space groupP21/c witha=12.173(5),b=15.619(5),c=15.338(8)Å;=111.40(4)°,Z=4,R=0.059. In these complexes the ligand is tridentate via carbonylic oxygen, semicarbazone and pyridine nitrogens forming each two five membered chelate rings with the metal in a distorted octahedral geometry. 相似文献
79.
Armentano D De Munno G Mastropietro TF Julve M Lloret F 《Journal of the American Chemical Society》2005,127(31):10778-10779
Intermolecular proton transfer in solid phase from the hydroxo bridge to a water molecule occurs in a new mu-hydroxo iron(III) compound of formula {EtNH3[Fe2(ox)2Cl2(mu-OH)].2H2O}n leading to a still crystalline compound in which the mu-oxo bridge replaces the mu-hydroxo one. Both three-dimensional compounds exhibit magnetic ordering at Tc ca. 70 K due to a spin canting. 相似文献
80.
Silvio Aime Mauro Botta Giancarlo Cravotto Luca Frullano GiovanniB. Giovenzana Simonetta GeninattiCrich Giovanni Palmisano Massimo Sisti 《Helvetica chimica acta》2005,88(3):588-603
Four new ligands for lanthanide ions based on the H3do3a (=1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) structure and bearing one N‐sulfonylacetamide arm were synthesized, i.e., H4dota‐NHSO2R=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acids 1a – e . A 15N‐NMR study of the 15N‐labelled Eu3+ complex of one such ligands, 1d , showed that the coordination of the N‐sulfonylacetamide arm involves the carbonyl O‐atom rather than the N‐atom. The relaxometric properties of the corresponding Gd3+ complexes were investigated as a function of pH and temperature. These complexes have relaxivities in the range 4.5–5.3 mM ?1 s?1, at 20 MHz and 25°, and are characterized by a single H2O molecule in their inner coordination sphere. The mean residence lifetime of this molecule is relatively long (500–700 ns) compared to other anionic complexes. The slow rate of H2O exchange can be justified by the extensive delocalization of the negative charge on the N‐sulfonylacetamide arm. The long residence time of the coordinated H2O allowed the observation of the effect of the prototropic exchange on the relaxivity. The study of the interaction between the complex [Gd( 1e )]‐ and HSA revealed a weak affinity constant highlighting the importance of a localized negative charge on the complex to promote a strong interaction with the protein. 相似文献