全文获取类型
收费全文 | 415篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 309篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 46篇 |
物理学 | 57篇 |
出版年
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 16篇 |
2012年 | 18篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 20篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 21篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1954年 | 1篇 |
1935年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有420条查询结果,搜索用时 15 毫秒
1.
Frans H.A. Rummens 《Chemical physics letters》1975,31(3):596-598
The use of the Bayliss-McRae theory on the solvent induced electronic frequency shifts for NMR dispersion shifts is criticized. It is suggested that the NMR shifts should actually be proportional to the square of the Bayliss-McRae function. It is shown that the methane gas-to-liquid shifts in eleven halo-methanes as solvents are indeed proportional to this squared function; ?σm(CH4) = 9.62 (n22?1)2/(2n22+1)2 ppm, where n2 is the refractive index of the solvent. The relation between this solvent factor and several existing continuum models for NMR medium shifts is discussed. 相似文献
2.
3.
Holland AE Engelbrecht MR Barentsz JO Heijstraten FM Goldfarb JW 《Magnetic resonance imaging》2002,20(3):261-269
The value of ECG-gated single-shot black-blood MR imaging for rapid visualization of the origin and course of the coronary arteries was investigated. The study population included 28 patients with known or suspected cardiac disease. ECG-gated single-shot black-blood MR acquisitions were acquired in the transverse, coronal, sagittal and LAO orientations, during free breathing and breath-holding. The origin of the left coronary artery was most frequently visualized in the coronal and LAO orientations and the origin of the right coronary artery was most frequently visualized in the LAO orientation. Overall, no significant difference was found for the visualization of the coronary artery segments and the overall image quality among acquisitions during breath-holding and free breathing. ECG-gated single-shot black-blood MR imaging (HASTE) appears to be a time-efficient and robust method for mapping of the entire coronary artery tree, without the need for breath-holding. The LAO orientation provides the most consistent visualization of the origins and major coronary artery segments. 相似文献
4.
We present a new Multiple-Observations (MO) helper data scheme for secret-key binding to an SRAM-PUF. This MO scheme binds a single key to multiple enrollment observations of the SRAM-PUF. Performance is improved in comparison to classic schemes which generate helper data based on a single enrollment observation. The performance increase can be explained by the fact that the reliabilities of the different SRAM cells are modeled (implicitly) in the helper data. We prove that the scheme achieves secret-key capacity for any number of enrollment observations, and, therefore, it is optimal. We evaluate performance of the scheme using Monte Carlo simulations, where an off-the-shelf LDPC code is used to implement the linear error-correcting code. Another scheme that models the reliabilities of the SRAM cells is the so-called Soft-Decision (SD) helper data scheme. The SD scheme considers the one-probabilities of the SRAM cells as an input, which in practice are not observable. We present a new strategy for the SD scheme that considers the binary SRAM-PUF observations as an input instead and show that the new strategy is optimal and achieves the same reconstruction performance as the MO scheme. Finally, we present a variation on the MO helper data scheme that updates the helper data sequentially after each successful reconstruction of the key. As a result, the error-correcting performance of the scheme is improved over time. 相似文献
5.
Frans G.T. Radloff Keith A. Hobson Alison J. Leslie 《Isotopes in environmental and health studies》2013,49(3):439-456
Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ13 C) and nitrogen (δ15 N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ13 C and δ15 N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods. 相似文献
6.
Denis D. Arslanov Marius Spunei Julien Mandon Simona M. Cristescu Stefan T. Persijn Frans J. M. Harren 《Laser \u0026amp; Photonics Reviews》2013,7(2):188-206
Over the past 10 years, with the advent of new crystals designs and a new generation of pump lasers, continuous‐wave (cw) optical parametric oscillators (OPOs) have developed into mature monochromatic light sources. Nowadays, cw OPOs can fulfill a wide variety of criteria for sensitive molecular gas sensing. It can access the mid‐infrared wavelength region, where many molecules have their fundamental rotational‐vibrational transitions, with high power. This high power combined with wide wavelength tuning and narrow linewidth creates excellent conditions for sensitive, high‐resolution spectroscopy. OPOs combined with robust methods, such as photoacoustic spectroscopy and cavity‐enhanced spectroscopy, are well suited for field measurements and remote‐sensing applications. The wide tunability of cw OPOs allows detection of larger molecules with broad absorption band structures, and its fast scanning capabilities allow rapid detection of trace gases, the latter is a demand for life‐science applications. After a short introduction about the physical principle of cw OPOs, with its most recent physical developments, this review focuses on sensitive molecular gas sensing with a variety of spectroscopic applications in atmospheric and life sciences. 相似文献
7.
Ann Hulsmans Koen Joris Nico Lambert Hans Rediers Priscilla Declerck Yasmine Delaedt Frans Ollevier Sven Liers 《Ultrasonics sonochemistry》2010,17(6):1004-1009
In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (Es) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment. 相似文献
8.
The “nonlinear superposition law” for systems of the Ermakov-type is generalized to systems of n + 1 second-order differential equations having n invariants, quadratic in the velocities. 相似文献
9.
Bilsen FA 《The Journal of the Acoustical Society of America》2006,120(2):594-596
Standing at the foot of the Mayan step pyramid at Chichen Itza in Mexico, one can produce a pitchy "chirp" echo by handclapping. As exposed by Declercq et al. [J. Acoust. Soc. Am. 116, 3328-3335 (2004)], an acoustic model based on optical Bragg diffraction at a periodic structure cannot explain satisfactorily the chirp-echo sonogram. Alternatively, considering the echo as a sequence of reflections, and given the dimensions of the pyramid and source-receiver position, the chirp is predicted correctly as a Repetition Pitch glide of which the pitch height is continuously decreasing within 177 ms from 796 to 471 Hz-equivalent. 相似文献
10.
Glycopeptides were isolated from functional units of two molluscan hemocyanins (Hcs). They were analyzed and localized in the sequences. A comparison with potential N-glycosylation sites of two other molluscan Hcs was made. An immunological cross-reactivity was observed between the beta-Hc and the alpha-macroglobulin of Helix pomotia. ELISA experiments with glycopeptide fractions indicated a competition. 相似文献