全文获取类型
收费全文 | 3429篇 |
免费 | 101篇 |
国内免费 | 24篇 |
专业分类
化学 | 2108篇 |
晶体学 | 15篇 |
力学 | 150篇 |
数学 | 519篇 |
物理学 | 762篇 |
出版年
2023年 | 35篇 |
2022年 | 79篇 |
2021年 | 118篇 |
2020年 | 104篇 |
2019年 | 83篇 |
2018年 | 58篇 |
2017年 | 50篇 |
2016年 | 132篇 |
2015年 | 93篇 |
2014年 | 138篇 |
2013年 | 171篇 |
2012年 | 227篇 |
2011年 | 255篇 |
2010年 | 148篇 |
2009年 | 126篇 |
2008年 | 202篇 |
2007年 | 195篇 |
2006年 | 213篇 |
2005年 | 194篇 |
2004年 | 150篇 |
2003年 | 129篇 |
2002年 | 130篇 |
2001年 | 52篇 |
2000年 | 23篇 |
1999年 | 31篇 |
1998年 | 32篇 |
1997年 | 39篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有3554条查询结果,搜索用时 15 毫秒
51.
52.
Stefano Capparelli 《Transactions of the American Mathematical Society》1996,348(2):481-501
We obtain a vertex operator construction of level 3 standard representations for the affine Lie algebra . As a corollary, we also get new conbinatorial identities.
53.
Stefano Serra 《BIT Numerical Mathematics》1996,36(1):135-142
In this paper we are concerned with the asymptotic behavior of the smallest eigenvalue
1
(n)
of symmetric (Hermitian)n ×n Toeplitz matricesT
n
(f) generated by an integrable functionf defined in [–, ]. In [7, 8, 11] it is shown that
1
(n)
tends to essinff =m
f
in the following way:
1
(n)
–m
f
1/n
2k
. These authors use three assumptions:A1)f –m
f
has a zero inx =x
0 of order 2k.A2)f is continuous and at leastC
2k
in a neighborhood ofx
0.A3)x =x
0 is the unique global minimum off in [–, ]. In [10] we have proved that the hypothesis of smoothnessA2 is not necessary and that the same result holds under the weaker assumption thatf L
1[–, ]. In this paper we further extend this theory to the case of a functionf L
1[–, ] having several global minima by suppressing the hypothesisA3 and by showing that the maximal order 2k of the zeros off –m
f
is the only parameter which characterizes the rate of convergence of
1
(n)
tom
f
. 相似文献
54.
Some results on configurations realizing minimum blocking sets of a finite projective plane are obtained by introducing a suitable attraction property.Dedicated to Professor M. Scafati Tallini on the occasion of her 65th birthday 相似文献
55.
56.
The complex formation between pyrophosphate (P(2)O(7)(4-)) and protonated methylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine, has been studied potentiometrically, in aqueous solution, at 25 degrees C. It was found that the species ALH(q)(A = amine, L = P(2)O(7)(4-)) are formed with q = 1 ... n(n = 3, 5, 6, 7, 7 and 8 for the above amines respectively). Mono- and di-amines form species A(p)LH(q) too. The stability of these species is quite high [e.g. H(4)A(4+) + HL(3-)ALH(5)(+): log K = 8.1 (A = pentaethylenehexamine)] and depends strictly on the charges involved in the formation reaction. Charges of reactants being equal, the stability trend is penten > tetren > trien > dien > en > meta and cationic mixed species are more stable than anionic ones. These results are discussed in relation to speciation problems in natural and biological fluids. 相似文献
57.
The optimal partition of energy between survival and reproduction is considered for a population subject to recurrent and potentially lethal critical events. The best strategy is found by maximizing fitness, a functional derived from the Lotka equation. The dynamics is governed by a second-order, age-varying, nonlinear system. The energy storage and the probability of survival are the state variables, while the amounts of energy placed into and withdrawn from the storage are the controls. The optimal life strategy is shown to be as follows: build up the storage at the very beginning of life, and then progressively deplete it to resist the critical events.This work was partially supported by MURST Project Ricerche sui Fondamenti della Conservazione della Natura. The authors would like to thank C. Ricci for suggesting the problem and C. Matessi for helpful discussion. 相似文献
58.
Copper(II) complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate) have been investigated in aqueous solution by means of pH-metric measurements at different temperatures, 5 = T = 45 degrees C, calorimetry and visible spectrophotometry. Potentiometric data, at all the considered temperatures in the range 2.5 = pH = 10.5, can be explained assuming the formation of the species CuLH(0), CuL(-), CuLH(2 -)(- 1), CuL(4 -)(2) and Cu(2)L(+). By using thermodynamic data and calculated electronic spectra for each complex a structural definition is proposed for the different species. Copper(II)-glyphosate complexes are quite stable and must be taken into account in the speciation of natural fluids. 相似文献
59.
Carlo Mealli Stefano Midollini Simonetta Moneti Thomas A. Albright 《Helvetica chimica acta》1983,66(2):557-569
The reaction of [(C3Ph3)Ni(PPh3)2]ClO4 with P(CH2CH2PPh2)3(pp3) and NaBPh4 yields the [(C3Ph3)Ni(pp3)]BPh4-complex. After long exposure of the solution of this compound in acetone/butanol to the air a new derivative [(C3Ph3)-Ni(pp2po)]BPh4· 0.5 C4H9OH, where pp2po is (Ph2PCH2CH2)2P(CH2 CH2POPh2), is obtained. Complete X-ray analysis has been carried out for the latter complex: a=18.303 (5); b=29.445 (6), c=13.305 (5) Å, β=112.70 (9)°; space group monoclinic, P21/a, Z=4. Disorder problems were encountered in the refinement of the structure. The best R is 0.093. One of the arms of the parent pp3-molecule, not coordinated to the metal, undergoes oxidation. The Ni-atom, coordinated by the three remaining P-atoms of the ligand, is also linked in a roughly η3-mode to the cyclopropenium ligand. The geometry of the molecule is examined in detail. Extended HMO-calculations were performed to interpret how the variation of P? Ni? P angles affects the bonding between the NiP3- and C3H3-fragments. The conclusion is that the overall energy of the complex may be lowered in spite of a weakening of the Ni-cyclopropenium linkage. Extensions are made to other systems containing a linkage between a metal and a X3-ring (X=P,As). 相似文献
60.