全文获取类型
收费全文 | 873篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
化学 | 541篇 |
晶体学 | 2篇 |
力学 | 17篇 |
数学 | 77篇 |
物理学 | 280篇 |
出版年
2023年 | 7篇 |
2022年 | 22篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 45篇 |
2015年 | 40篇 |
2014年 | 44篇 |
2013年 | 56篇 |
2012年 | 66篇 |
2011年 | 67篇 |
2010年 | 21篇 |
2009年 | 31篇 |
2008年 | 63篇 |
2007年 | 69篇 |
2006年 | 41篇 |
2005年 | 46篇 |
2004年 | 46篇 |
2003年 | 38篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1970年 | 1篇 |
1952年 | 1篇 |
1940年 | 1篇 |
1938年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有917条查询结果,搜索用时 312 毫秒
81.
Rosa M. Miró-Roig 《Rendiconti del Circolo Matematico di Palermo》1938,62(1):153-164
The goal of this paper is to demonstrate that all non-singular rational normal scrolls \(S(a_0,\ldots ,a_k)\subseteq \mathbb P ^N\), \(N =\sum _{i=0}^k(a_i)+k\), (unless \(\mathbb P ^{k+1}=S(0,\ldots ,0,1)\), the rational normal curve \(S(a)\) in \(\mathbb P ^a\), the quadric surface \(S(1,1)\) in \(\mathbb P ^3\) and the cubic scroll \(S(1,2)\) in \(\mathbb P ^4\)) support families of arbitrarily large rank and dimension of simple Ulrich (and hence indecomposable ACM) vector bundles. Therefore, they are all of wild representation type unless \(\mathbb P ^{k+1}\), \(S(a)\), \(S(1,1)\) and \(S(1,2)\) which are of finite representation type. 相似文献
82.
83.
84.
Miró P Pierrefixe S Gicquel M Gil A Bo C 《Journal of the American Chemical Society》2010,132(50):17787-17794
Uranyl-peroxide nanoclusters display different topologies based on square, pentagonal and hexagonal building blocks. Computed complexation energies of different cations (Li(+), Na(+), K(+), Rb(+), and Cs(+)) with [UO(2)(O(2))(H(2)O)](n) (n = 4, 5, and 6) macrocycles suggest a strong cation templating effect. The inherent bent structure of a U-O(2)-U model dimer is demonstrated and justified through the analysis of its electronic structure, as well as of the inherent curvature of the four-, five-, and six-uranyl macrocyles. The curvature is enhaced by cation coordination, which is suggested to be the driving force for the self-assembly of the nanocapsules. 相似文献
85.
A simple, rapid and efficient sample preparation technique, dispersive liquid-liquid microextraction, coupled with gas chromatography-flame ionization detection has been developed to determine N-methylpyrrolidine in cefepime. The effect of various experimental factors on the preparation procedure, such as the nature and volume of extraction and disperser solvents, extraction time, the nature of buffer and its pH, and salt effect, was investigated, optimized and the following results were obtained: extraction solvent, chloroform; dispersive solvent and solvent for dissolving cefepime, a mixture of methanol/water (88:12, v/v); salting out agent, NaCl; and buffer, carbonate/bicarbonate (C=0.5?M, pH=12). The optimized conditions were applied to the real sample (cefepime) for the extraction and determination of N-methylpyrrolidine. The calibration graph is linear from 0.02 to 850?mg/L with the square of correlation coefficient 0.999. LOD and LOQ are 6.4 and 21.2?μg/L in solution, respectively, and 0.2 (2×10(-5) ) and 0.6 (6×10(-5) ) μg/g (%, w/w) in cefepime powder, respectively, using sample size 50?mg. Repeatability of the method is good and RSD% for six repeated experiments (C=170?mg/L) is 6.35%. 相似文献
86.
We first analyse the anti-BRST and double BRST structures of a certain higher derivative theory that has been known to possess
BRST symmetry associated with its higher derivative structure. We discuss the invariance of this theory under shift symmetry
in the Batalin–Vilkovisky (BV) formalism. We show that the action for this theory can be written in a manifestly extended
BRST invariant manner in superspace formalism using one Grassmann coordinate. It can also be written in a manifestly extended
BRST invariant manner and on-shell manifestly extended anti-BRST invariant manner in superspace formalism using two Grassmann
coordinates. 相似文献
87.
In this paper we consider a class of polynomials P(z) = a0+∑n v=t a v z v, t ≥ 1not vanishing in |z|k, k≥1 and investigate the dependence of max|z|=1|P(Rz)-P(rz)on max|z|=1|P(z)|, where 1 ≤ r R. Our result generalizes and refines some know polynomial inequalities. 相似文献
88.
89.
90.
The purpose of this study was to examine the efficiency with which rice bran (treated or untreated) removes heavy metals, especially Cr(III) and Hg(II), from acidic solution. Sorption assays were done in shaken flasks in the presence of rice bran. Different experimental conditions such as pH, volume of solution, bran weight, particle size, exchange time and stirring time were improved. The efficiency of bran was studied before and after treatments. For treatment, solutions of acid, alkali and salt were used. The results show that after treating with 4 M sodium chloride solution, its efficiency in removal of Cr(III) and Hg(II) was improved. Kinetic measurements of chromium and mercury removal by bran have revealed that sorption equilibrium was obtained after 10 min of contact. Sorption experiments done with various granulometric fractions of rice bran have shown that this sorbent has the same efficiencies in meshes higher than 20. Further research is necessary in order to determine a mechanism for cations removal by the bran. It is mentioned that the process of making polished rice from brown rice discharges rice bran; therefore, it is very inexpensive, with a cost of 1/50 ? 1/40 of that of synthetic sorbent, and thus its use would significantly lower the cost of wastewater treatment. 相似文献