全文获取类型
收费全文 | 478篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 342篇 |
力学 | 6篇 |
数学 | 33篇 |
物理学 | 108篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 26篇 |
2012年 | 14篇 |
2011年 | 26篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 23篇 |
2007年 | 33篇 |
2006年 | 17篇 |
2005年 | 25篇 |
2004年 | 11篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有489条查询结果,搜索用时 31 毫秒
481.
482.
K. Shukla A. Paskin D.O. Welch G.J. Dienes 《Journal of Physics and Chemistry of Solids》1985,46(1):83-96
The self-consistent average phonon (SCAP) approximation was successful in describing the thermodynamic properties of monatomic solids. This formalism was extended to ionic crystals (specifically sodium chloride) at two levels of approximation: (1) the phonon frequencies replaced by a single average frequency, and (2) the phonon frequencies replaced by two average frequencies corresponding to the usual acoustic and optic phonons. In order to compare with earlier calculations and with experiments various forms of the interatomic potential (with polarization neglected) were used. The SCAP calculation is in good agreement with experiment at low and medium temperatures but underestimates the high temperature thermal expansion. It is concluded that the SCAP formalism with polarization included should give a good approximation to the thermodynamic properties of simple ionic crystals over the entire temperature range. 相似文献
483.
This paper studies the robustness of the Bayes discriminant procedure with respect to data which do not follow a Gaussian (normal) probability distribution. The authors present descriminant criteria based on the beta, gamma, and lognormal distribution functions as alternatives to the usual Gaussian rule. These procedure are compared on both actual and simulated data. We find that Bayesian discrimination is sensitive to the incorrect use of the normal distribution. 相似文献
484.
485.
Sajonz P Schafer W Gong X Shultz S Rosner T Welch CJ 《Journal of chromatography. A》2007,1145(1-2):149-154
The suitability of the Eksigent Express 800 microfluidic eight-channel HPLC instrument for multiparallel normal-phase chiral analysis in support of high-throughput pharmaceutical process research was investigated. Analysis of test mixtures containing the two enantiomers of benzoin and the closely related (R,S)-dihydrobenzoin, was carried out in a 96-well microplate, affording rapid (<2 h) and accurate assessment of enantiopurity. In a second example, use of the instrument to support high-throughput catalyst screening of the asymmetric hydrogenation of a prochiral unsaturated ester is presented, in which method development (gradient screening of four columns and two eluents, followed by optimization to afford a fast analytical method) and analysis of a 96-well microplate was carried out within a single working day. This represents a considerable improvement over conventional analysis techniques that usually take several days to complete. 相似文献
486.
This study was designed to examine the impact of participating in an after‐school robotics competition on high school students' attitudes toward science. Specifically, this study used the Test of Science‐Related Attitude to measure students' social implications of science, normality of scientists, attitude toward scientific inquiry, adoption of scientific attitudes, enjoyment of science lessons, leisure interest in science, and career interest in science. Results indicated that students who participated in a robotic competition had a more positive attitude toward science and science‐related areas in four of the seven categories examined: social implications of science, normality of scientists, attitude toward scientific inquiry, and adoption of scientific attitudes. Implications of results on students' attitudes are discussed. 相似文献
487.
We demonstrate parametric generation of a new coherent field with a polarization orthogonal to the signal field via an all-resonant four-wave mixing process in a double-ladder system. We show that the generation of the coherent field is an efficient resonantly enhanced process that can be realized with a fairly dilute medium and relatively weak drive fields. The large parameter domain that exists in this system provides good control for both the weak probe and the generated field. Potential applications in optical communication are outlined. 相似文献
488.
David Welch Norman J. Kleiman Peter C. Arden Christine L. Kuryla Manuela Buonanno Brian Ponnaiya Xuefeng Wu David J. Brenner 《Photochemistry and photobiology》2023,99(1):168-175
Far-UVC radiation, typically defined as 200–235 nm, has similar or greater anti-microbial efficacy compared with conventional 254-nm germicidal radiation. In addition, biophysical considerations of the interaction of far-UVC with tissue, as well as multiple short-term safety studies in animal models and humans, suggest that far-UVC exposure may be safe for skin and eye tissue. Nevertheless, the potential for skin cancer after chronic long-term exposure to far-UVC has not been studied. Here, we assessed far-UVC induced carcinogenic skin changes and other pathological dermal abnormalities in 96 SKH-1 hairless mice of both sexes that were exposed to average daily dorsal skin doses of 400, 130 or 55 mJ cm−2 of 222 nm far-UVC radiation for 66 weeks, 5 days per week, 8 h per day, as well as similarly-treated unexposed controls. No evidence for increased skin cancer, abnormal skin growths or incidental skin pathology findings was observed in the far-UVC-exposed mice. In addition, there were no significant changes in morbidity or mortality. The findings from this study support the long-term safety of long-term chronic exposure to far-UVC radiation, and therefore its potential suitability as a practical anti-microbial approach to reduce airborne viral and bacterial loads in occupied indoor settings. 相似文献
489.
Lingqi Qiu Mousumi Saha Dr. Stefan Kraft Dr. Eric T. Dziekonski Dr. Christopher J. Welch Dr. Yumin Dai Dr. Andreas Kaerner Dr. R. Graham Cooks 《Angewandte Chemie (International ed. in English)》2023,62(47):e202310884
This study uses a rapid tandem mass-spectrometry method to determine water content in complex organic solutions. Emphasis is placed on trace-water analysis by a fast and accurate alternative to the Karl–Fischer method. In this new method, water is captured by a charge-labeled molecular probe. Water binds strongly with high specificity to the strongly electrophilic aldehyde site in a charge-labelled molecule (N-methylpyridinium); competitive binding by other analytes is effectively discriminated against in the mass-measurement step. Quantitative determinations are made over a wide concentration range, 0.001 % (10 ppm) to 99 %, with better than 10 % relative standard deviation, along with short (1 min) analysis times using small sample volumes (several μL). Applications include water measurement in simple organic solvents, for example, deuterated solvents, as well as in complex mixtures, for example, organic reaction mixtures. Additionally, this method allows for water monitoring in levitated droplets. Mechanistic investigations into the impact of water on important chemical processes in organic synthesis and environmental science are reported. 相似文献