全文获取类型
收费全文 | 584篇 |
免费 | 14篇 |
国内免费 | 4篇 |
专业分类
化学 | 353篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 69篇 |
物理学 | 171篇 |
出版年
2023年 | 4篇 |
2020年 | 3篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 23篇 |
2012年 | 22篇 |
2011年 | 39篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 26篇 |
2007年 | 32篇 |
2006年 | 31篇 |
2005年 | 25篇 |
2004年 | 26篇 |
2003年 | 23篇 |
2002年 | 34篇 |
2001年 | 35篇 |
2000年 | 22篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1937年 | 2篇 |
1932年 | 2篇 |
1917年 | 2篇 |
1908年 | 2篇 |
排序方式: 共有602条查询结果,搜索用时 765 毫秒
51.
[reaction: see text] A series of diimide-based macrocycles have been prepared using Mitsunobu-mediated alkylation as the macrocyclization step. These macrocycles could not be incorporated into [2]catenanes using previously established building blocks and coupling methodology. However, when one of the macrocycle syntheses was conducted in the presence of a dinaphtho crown ether, catenane formation was achieved. This result is discussed in terms of the ability of the components to establish intermolecular C-H...O hydrogen-bonding contacts. 相似文献
52.
Czerski L Vinogradova O Sanders CR 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,142(1):111-119
A method for measuring site-specific amide hydrogen-deuterium exchange rates for membrane proteins in bilayers is reported and evaluated. This method represents an adaptation and extension of the approach of Dempsey and co-workers (Biophys. J. 70, 1777-1788 (1996)) and is based on reconstituting (15)N-labeled membrane proteins into phospholipid bilayers, followed by lyophilization and rehydration with D(2)O or H(2)O (control). Following incubation for a time t under hydrated conditions, samples are again lyophilized and then solubilized in an organic solvent system, where (1)H-(15)N HSQC spectra are recorded. Comparison of spectra from D(2)O-exposed samples to spectra from control samples yields the extent of the H-D exchange which occurred in the bilayers during time t. Measurements are site specific if specific (15)N labeling is used. The first part of this paper deals with the search for a suitable solvent system in which to solubilize complex membrane proteins in an amide "exchange-trapped" form for NMR quantitation of amide peak intensities. The second portion of the paper documents application of the overall procedure to measuring site-specific amide exchange rates in diacylglycerol kinase, a representative integral membrane protein. Both the potential usefulness and the significant limitations of the new method are documented. 相似文献
53.
S.J.Sanders 《中国物理 C》2007,31(12):1137-1140
Identified particle elliptic flow results are presented for the Au+Au reaction at sNN=200GeV as a function of transverse momentum and pseudorapidity. Data at pseudorapidities η≈0,1, and 3.4 were obtained using the two BRAHMS spectrometers. Differential v2 (η,pt) values for a given particle type are
found to be essentially constant over the covered pseudorapidity range, in contrast to the integral v2 values which have previously been observed to decrease at forward rapidities. A softening of the particle spectra at forward angles is found to account for at least part of the integral v2 falloff. The data are found to be consistent with existing constituent quark scaling systematics. 相似文献
54.
55.
BAGHERI GH Azar 《中国化学》2009,27(6):1073-1078
The complexation of zinc(II) with dopamine has been investigated by spectrophotometric measurements in mixed solvent system at an ionic strength of 0.2 mol•dm-3 sodium chloride, employed at at (15±0.1), (25±0.1), (35±0.1) ℃ at inin a pH range of ca. 6 to ca. 7 with a high ratio of ligand to metal. The effect of solvent systems on protonation and complexation are was was discussed. Linear relationships are werewere observed by plotting lg K versus 1/D, where K and D show stability and dielectric constants, respectively. 相似文献
56.
Sanders LD Zobel BH Freyman RL Keen R 《The Journal of the Acoustical Society of America》2011,129(1):301-309
To gain information from complex auditory scenes, it is necessary to determine which of the many loudness, pitch, and timbre changes originate from a single source. Grouping sound into sources based on spatial information is complicated by reverberant energy bouncing off multiple surfaces and reaching the ears from directions other than the source's location. The ability to localize sounds despite these echoes has been explored with the precedence effect: Identical sounds presented from two locations with a short stimulus onset asynchrony (e.g., 1-5 ms) are perceived as a single source with a location dominated by the lead sound. Importantly, echo thresholds, the shortest onset asynchrony at which a listener reports hearing the lag sound as a separate source about half of the time, can be manipulated by presenting sound pairs in contexts. Event-related brain potentials elicited by physically identical sounds in contexts that resulted in listeners reporting either one or two sources were compared. Sound pairs perceived as two sources elicited a larger anterior negativity 100-250 ms after onset, previously termed the object-related negativity, and a larger posterior positivity 250-500 ms. These results indicate that the models of room acoustics listeners form based on recent experience with the spatiotemporal properties of sound modulate perceptual as well as later higher-level processing. 相似文献
57.
Xinliang An Andrew W. Caswell Scott T. Sanders 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(14):2355-2362
A novel technique for selecting wavelengths that optimize the temperature precision of absorption-based thermometry is developed. A single universal objective function considering continuous spectral lower-state energy , spectral absorbance intensities and an experimental noise level is derived and applied in a brute-force approach to analyze two-wavelength, Doppler-broadened H2O vapor-absorbance thermometry in the 1.33-1.37 μm range. The results reveal the top wavelength pairs and their temperature precisions over a wide temperature range from 280 to 2800 K. Although the spectral database used includes over thousands of transitions in this spectral range, the top pairs are composed of only 12 unique wavelengths. This wavelength selection technique is able to help researchers choose key wavelengths that will perform well in practical applications. 相似文献
58.
Autler-Townes splitting (ATS) and electromagnetically induced transparency (EIT) both yield transparency in an absorption profile, but only EIT yields strong transparency for a weak pump field due to Fano interference. Empirically discriminating EIT from ATS is important but so far has been subjective. We introduce an objective method, based on Akaike's information criterion, to test ATS vs EIT from experimental data for three-level atomic systems and determine which pertains. We apply our method to a recently reported induced-transparency experiment in superconducting-circuit quantum electrodynamics. 相似文献
59.
Quantum-enhanced metrology infers an unknown quantity with accuracy beyond the standard quantum limit (SQL). Feedback-based metrological techniques are promising for beating the SQL but devising the feedback procedures is difficult and inefficient. Here we introduce an efficient self-learning swarm-intelligence algorithm for devising feedback-based quantum metrological procedures. Our algorithm can be trained with simulated or real-world trials and accommodates experimental imperfections, losses, and decoherence. 相似文献
60.