全文获取类型
收费全文 | 1288篇 |
免费 | 50篇 |
国内免费 | 35篇 |
专业分类
化学 | 845篇 |
晶体学 | 6篇 |
力学 | 41篇 |
数学 | 223篇 |
物理学 | 258篇 |
出版年
2021年 | 7篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 12篇 |
2016年 | 33篇 |
2015年 | 19篇 |
2014年 | 22篇 |
2013年 | 55篇 |
2012年 | 69篇 |
2011年 | 55篇 |
2010年 | 27篇 |
2009年 | 42篇 |
2008年 | 79篇 |
2007年 | 76篇 |
2006年 | 65篇 |
2005年 | 60篇 |
2004年 | 52篇 |
2003年 | 52篇 |
2002年 | 54篇 |
2001年 | 34篇 |
2000年 | 29篇 |
1999年 | 18篇 |
1998年 | 7篇 |
1997年 | 17篇 |
1996年 | 27篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 16篇 |
1971年 | 7篇 |
1969年 | 9篇 |
1968年 | 11篇 |
排序方式: 共有1373条查询结果,搜索用时 111 毫秒
101.
Necessary conditions for optimality in control problems with differential-inclusion dynamics have recently been developed
in the non-convex case by Clarke, Vinter, and others. Using appropriate reparametrizations of the time variable, we extend
these results to systems whose dynamics involve a differential inclusion where a vector-valued measure appears. An auxiliary
result central to our proof is an extension of existing free end-time necessary conditions to Clarke’s stratified framework. 相似文献
102.
Branca RT Jenista ER Warren WS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(2):347-351
Intermolecular dipolar interactions between proton and carbon spins can be used to indirectly detect carbon spectra with high sensitivity. In this communication, we present a modified sequence that, in addition to the high sensitivity of heteronuclear intermolecular multiple quantum coherence (iMQC) experiments, retains the line narrowing capability characteristic of homonuclear zero-quantum coherences. We demonstrate that this sequence can be used to obtain high resolution (13)C spectra in the presence of magnetic field inhomogeneities, both for thermal and hyperpolarized samples, and discuss applications to water-hyperpolarized carbon imaging. 相似文献
103.
Let m, m′, r, r′, t, t′ be positive integers with r, r′ ? 2. Let \(\mathbb{L}_r \) denote the ring that is universal with an invertible 1×r matrix. Let \(M_m (\mathbb{L}_r^{ \otimes t} )\) denote the ring of m × m matrices over the tensor product of t copies of \(\mathbb{L}_r \) . In a natural way, \(M_m (\mathbb{L}_r^{ \otimes t} )\) is a partially ordered ring with involution. Let \(PU_m (\mathbb{L}_r^{ \otimes t} )\) denote the group of positive unitary elements. We show that \(PU_m (\mathbb{L}_r^{ \otimes t} )\) is isomorphic to the Brin-Higman-Thompson group tV r,m ; the case t=1 was found by Pardo, that is, \(PU_m (\mathbb{L}_r )\) is isomorphic to the Higman-Thompson group V r,m . We survey arguments of Abrams, Ánh, Bleak, Brin, Higman, Lanoue, Pardo and Thompson that prove that t′V r′,m′ ≌ tV r,m if and only if r′ =r, t′ =t and gcd(m′, r′?1) = gcd(m, r?1) (if and only if \(M_{m'} (\mathbb{L}_{r'}^{ \otimes t'} )\) and \(M_m (\mathbb{L}_r^{ \otimes t} )\) are isomorphic as partially ordered rings with involution). 相似文献
104.
105.
H. N. Warren und Clemens Winkler 《Fresenius' Journal of Analytical Chemistry》1890,29(1):445-446
Ohne Zusammenfassung 相似文献
106.
107.
Glen A. Warren Robert C. Runkle 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):829-833
The Radiation Detection and Nuclear Sciences Group at Pacific Northwest National Laboratory has a long history in conducting measurements of radioisotopes for various applications. This experience includes ultra-low background measurements, arrays of germanium detectors, automated sampling and measurement systems and coincidence measurement systems. A recent lab-supported effort has been studying how these capabilities, both in terms of hardware and experience, can be leveraged to enable environmental sampling measurements. One area of interest is the release of fission products and actinides into the environment from a reactor incident. While the initial survey of this area is still under way, one isotope of interest that surfaced early in the study is 238Pu. Existing techniques to assay this isotope suffer from measurement challenges. In alpha counting, there can be significant interference with 241Am, while in mass spectrometry, there can be interference with 238U. The authors are developing the concept for a detector that through coincidence counting techniques can distinguish 238Pu and 241Am. In addition, we will design the system to conduct radiometric measurements of other plutonium isotopes to enable a direct comparison of those isotopes. We will present our concept of the detector system for 238Pu, as well as discuss other radiometric measurements of fission products and actinides with which we intend to advance the state of the art for environmental measurements. 相似文献
108.
Kaustubh Joshi Warren Batchelor Khairunnisaa Abd Rasid 《Cellulose (London, England)》2011,18(6):1407-1421
No reliable method exists for measuring the cellulose fiber–fiber shear bond strength in paper. This paper reports a simple
method for measuring the fiber–fiber shear bond strength by weakening the fibers independently of the bonds in a sheet of
paper, using acid vapor, until all the fibers break across the fracture line. The bond strength is then calculated from the
fiber strength, as measured by the zero span test, at the point where the fibers first are weakened such that they all break.
The method was used to calculate the average bond strength of handsheets made out of two different pulps. The first pulp was
a never dried, 60% yield, unbleached radiata pine. The bond strength was 25.0 ± 3.3 MPa. Drying the fibers before reslushing
and making sheets reduced the bond strength by up to 33%, with the reduction depending on the severity of the drying treatment.
The second pulp was a bleached dried softwood kraft and was used to investigate the effect of low consistency refining on
bond strength. The bond strength increased from 13.7 ± 1.0 MPa for the sheets made from the unrefined pulp to 37.0 ± 1.0 MPa,
for the sheets made from the most heavily refined pulp. The bond strength measurements are considerably higher than previous
literature estimates for the shear bond strength. The causes for the discrepancy include stress concentrations in tests of
single fiber–fiber bonds. 相似文献
109.
David S. Wragg Benjamin Le Ouay Matthew G. O’Brien John E. Warren Russell E. Morris 《Journal of solid state chemistry》2010,183(7):1625-3071
We have prepared isostructural aluminium and gallium phosphate chains by ionothermal reactions in 1-ethyl-3-methylimidazolium bromide and 1-ethylpyridinium bromide under a variety of conditions. The chains can be prepared as pure phases or along with three dimensional framework phases. The chains are favoured at shorter heating times and the crystallinity can be improved by addition of transition metal acetates and amines which are not included in the final structure. The chain can be prepared with or without the presence of hydrofluoric acid. 相似文献
110.