全文获取类型
收费全文 | 28711篇 |
免费 | 999篇 |
国内免费 | 1007篇 |
专业分类
化学 | 7876篇 |
晶体学 | 888篇 |
力学 | 788篇 |
综合类 | 70篇 |
数学 | 17267篇 |
物理学 | 3828篇 |
出版年
2024年 | 32篇 |
2023年 | 228篇 |
2022年 | 315篇 |
2021年 | 273篇 |
2020年 | 414篇 |
2019年 | 729篇 |
2018年 | 710篇 |
2017年 | 632篇 |
2016年 | 604篇 |
2015年 | 573篇 |
2014年 | 902篇 |
2013年 | 2523篇 |
2012年 | 1171篇 |
2011年 | 1840篇 |
2010年 | 1733篇 |
2009年 | 1915篇 |
2008年 | 2022篇 |
2007年 | 1999篇 |
2006年 | 1598篇 |
2005年 | 1236篇 |
2004年 | 1113篇 |
2003年 | 917篇 |
2002年 | 687篇 |
2001年 | 554篇 |
2000年 | 463篇 |
1999年 | 490篇 |
1998年 | 417篇 |
1997年 | 407篇 |
1996年 | 491篇 |
1995年 | 440篇 |
1994年 | 423篇 |
1993年 | 366篇 |
1992年 | 306篇 |
1991年 | 175篇 |
1990年 | 160篇 |
1989年 | 165篇 |
1988年 | 122篇 |
1987年 | 141篇 |
1986年 | 139篇 |
1985年 | 212篇 |
1984年 | 148篇 |
1983年 | 105篇 |
1982年 | 153篇 |
1981年 | 136篇 |
1980年 | 114篇 |
1979年 | 70篇 |
1978年 | 99篇 |
1977年 | 103篇 |
1976年 | 86篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
B. Gyires 《Periodica Mathematica Hungarica》1978,9(1-2):109-113
This paper contains applications of theorems of [1] for quadratic statistics which have constant regression on linear statistics. Two theorems are proved. The first is a sufficient condition which assumes that the characteristic function of a sample is an entire function. The second gives a new characterization of the normal distribution. 相似文献
62.
Many polysaccharide chains can adopt ordered helical and ribbon-like secondary structures. It seems however that these chains are often so stiff and extended that the cooperative interactions necessary for stability in the solvent environment can only be achieved when inter-chain as well as intra-chain interactions are favorable. Hence we commonly find two-or more-stranded associations of helices, of ribbons, or of helices with ribbons. These can be regarded as tertiary and higher levels of structure. The ordered secondary structure characteristically requires a regular repeating sequence of sugar residues, and the termination of this sequence by insertion of a residue of different type may also terminate the secondary structure and hence the association in which it is involved. This is the mechanism by which native polysaccharides may link up to form three dimensional networks, or gels, in which state they perform their natural roles in maintaining the hydration and integrity of biological tissues. For several polysaccharides there is evidence that the mechanism of biological control over the fine topology and properties of the gel network is mediated by enzymes which modify sugar residues at the polymer level to change the pattern of “interrupting” sugar residues. 相似文献
63.
Shie-Shien Yang 《Annals of the Institute of Statistical Mathematics》1981,33(1):463-470
Summary Let (X
1,Y
1), (X
2,Y
2),…, (X
n,Y
n) be i.i.d. as (X, Y). TheY-variate paired with therth orderedX-variateX
rn is denoted byY
rn and terms the concomitant of therth order statistic. Statistics of the form
are considered. The asymptotic normality ofT
n is established. The asymptotic results are used to test univariate and bivariate normality, to test independence and linearity
ofX andY, and to estimate regression coefficient based on complete and censored samples. 相似文献
64.
H. Groemer 《Aequationes Mathematicae》1981,22(1):215-222
In the euclidean planeE
2 letS
1,S
2, ... be a sequence of strips of widthsw
1,w
2, .... It is shown thatE
2 can be covered by translates of the stripsS
i if w
1
3/2
= . Further results concern conditions in order that a compact convex domain inE
2 can be covered by translates ofS
1,S
2, ....This research was supported by National Science Foundation Research Grant MCS 76-06111. 相似文献
65.
66.
B. Rendi 《Periodica Mathematica Hungarica》1977,8(3-4):225-228
Sans résumé
The article is the text of a talk given at the Symposium on Differential Geometry in Debrecen, Hungary, on August 28–September 3, 1975. 相似文献
67.
Frank J.S. Wang 《Stochastic Processes and their Applications》1977,5(2):173-193
Consider a population consisting of one type of individual living in a fixed region with area A. In [8], we constructed a stochastic population model in which the death rate is affected by the age of the individual and the birth rate is affected by the population density PA(t), i.e., the population size divided by the area A of the given region. In [8], we proposed a continuous deterministic model which in general is a nonlinear Volterra type integral equation and proved that under appropriate conditions the sequence PA(t) would converge to the solution P(t) of our integral equation in the sense that .In this paper, we obtain a “central limit theorem” for the random element √A(PA(t)?P(t)). We prove that under appropriate conditions √A(PA(t)?P(t)) will converge to a Gaussian process. (See Theorem 3.4 for the explicit formula of this Gaussian process.) 相似文献
68.
B. Gillot F. Bouton J.F. Ferriot F. Chassagneux A. Rousset 《Journal of solid state chemistry》1977,21(4):375-385
When Fe3+ ions are substituted by aluminum or chromium on magnetite octahedral sites, the ir spectrum shows the conversion of an inverse spinel to a normal spinel. Both broad bands of magnetite are gradually replaced by the four characteristic bands of normal spinels II–III. They are also observed for solid solutions, FeCr2O4FeAl2O4, with, however, a further band at 780 cm?1 which may be assigned to Al3+ ions on tetrahedral sites. Low-temperature (<400°C) oxidation of these compounds whose sizes are less than 2000 Å results in lacunar spinels III–III. The ir spectrum of these solids is characterized by two absorption bands (as for inverse spinels II–III) except for compounds close to pure γFe2O3 in which an order of vacancies could be put in evidence. 相似文献
69.
70.
Weakly bound linear and bent dimers, FH—X (where X = CO, OC, CNH, NCH, N2O and ON2), are investigated using the DFT B3LYP and ab initio MP2 methods with the same basis sets (6–311++G(3df,2pd)). The strengths of the H—C or H—N H‐bonds in dimers FH—CO, FH—CNH, and FH—N2O are compared with those of the H—O or H—N H‐bonds in dimers FH—OC, FH—NCH, and FH—ON2. The results obtained for the H‐bond distances, the elongation effect of the HF bond, the red shift of the HF stretching frequency, and the energy difference between the dimer and the charge transfer reveal that the H‐bonds of the first group of dimers are stronger than those of the second. The Gibbs energies calculated for the six dimer formations indicate that the weakly bound dimers are unstable at room temperature (T = 298 K) (FH—X's → FH + X's, ΔG < 0). 相似文献