全文获取类型
收费全文 | 889篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
化学 | 483篇 |
晶体学 | 4篇 |
力学 | 10篇 |
数学 | 138篇 |
物理学 | 275篇 |
出版年
2021年 | 10篇 |
2018年 | 7篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 46篇 |
2012年 | 28篇 |
2011年 | 53篇 |
2010年 | 32篇 |
2009年 | 18篇 |
2008年 | 36篇 |
2007年 | 39篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 31篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 16篇 |
2000年 | 22篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 19篇 |
1995年 | 10篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 11篇 |
1975年 | 18篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1970年 | 5篇 |
1968年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有910条查询结果,搜索用时 796 毫秒
151.
152.
The concepts of a linear covering code and a covering set for the limited-magnitude-error channel are introduced. A number of covering-set constructions, as well as some bounds, are given. In particular, optimal constructions are given for some cases involving small-magnitude errors. A problem of Stein is partially solved for these cases. Optimal packing sets and the corresponding error-correcting codes are also considered for some small-magnitude errors. 相似文献
153.
Tracking controlled states over a large range of accessible parameters is a process which allows for the experimental continuation of unstable states in both chaotic and non-chaotic parameter regions of interest. In algorithmic form, tracking allows experimentalists to examine many of the unstable states responsible for much of the observed nonlinear dynamic phenomena. Here we present a theoretical foundation for tracking controlled states from both dynamical systems as well as control theoretic viewpoints. The theory is constructive and shows explicitly how to track a curve of unstable states as a parameter is changed. Applications of the theory to various forms of control currently used in dynamical system experiments are discussed. Examples from both numerical and physical experiments are given to illustrate the wide range of tracking applications. (c) 1997 American Institute of Physics. 相似文献
154.
Schwartz BD Moore CJ Rahm F Hayes PY Kitching W De Voss JJ 《Journal of the American Chemical Society》2008,130(44):14853-14860
The volatile components of the mandibular gland secretion generated by the Giant Ichneumon parasitoid wasp Megarhyssa nortoni nortoni Cresson are mainly spiroacetals and methyl ketones, and all have an odd number of carbon atoms. A biosynthetic scheme rationalizing the formation of these diverse components is presented. This scheme is based on the results of incorporation studies using (2)H-labeled precursors and [(18)O]dioxygen. The key steps are postulated to be decarboxylation of beta-ketoacid equivalents, beta-oxidation (chain shortening), and monooxygenase-mediated hydroxylation leading to a putative ketodiol that cyclizes to spiroacetals. The generality of the role of monooxygenases in spiroacetal formation in insects is considered, and overall, a cohesive, internally consistent theory of spiroacetal generation by insects is presented, against which future hypotheses will have to be compared. 相似文献
155.
Glycosaminoglycans are sulfated in complex and changing patterns that affect neural development. These sugars mediate interactions between macromolecules, and their biological contributions are of high interest. In this issue of Chemistry & Biology, Shipp and Hsieh-Wilson describe microarrays to probe these complex modifications. 相似文献
156.
Karp E Pecinovsky CS McNevin MJ Gin DL Schwartz DK 《Langmuir : the ACS journal of surfaces and colloids》2007,23(15):7923-7927
An amphiphilic photoisomerizable macrocycle has been prepared that forms stable Langmuir monolayers at the air-water interface. The hydrophilic core of the molecule switches between closed and open isomers upon irradiation by the appropriate wavelengths of light. Isotherm measurements, Brewster angle microscope images, and atomic force micrographs (of transferred Langmuir-Blodgett films) suggest a phase transition between a face-on to a tilted edge-on molecular orientation as a function of surface concentration. In the face-on phase, in situ photoisomerization results in a reversible increase in surface pressure due to greater molecular crowding in the open configuration. 相似文献
157.
158.
Erik Schwartz Vincenzo Palermo Dr. Chris E. Finlayson Dr. Ya‐Shih Huang Matthijs B. J. Otten Andrea Liscio Dr. Sara Trapani Irene González‐Valls Patrick Brocorens Dr. Jeroen J. L. M. Cornelissen Dr. Kalina Peneva Dr. Klaus Müllen Prof. Dr. Frank C. Spano Prof. Dr. Arkady Yartsev Prof. Sebastian Westenhoff Dr. Richard H. Friend Prof. Dr. David Beljonne Dr. Roeland J. M. Nolte Prof. Dr. Paolo Samorì Prof. Dr. Alan E. Rowan Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(11):2536-2547
Exciton migration! Spectroscopic analyses and extensive molecular dynamics studies revealed a well‐defined 41 helix in which the perylene molecules (see figure) form four “helter‐skelter‐like” overlapping pathways along which excitons and electrons can rapidly migrate.
159.
Cerveny S Schwartz GA Alegría A Bergman R Swenson J 《The Journal of chemical physics》2006,124(19):194501
The relaxation dynamics of dipropylene glycol and tripropylene glycol (nPG-n=2,3) water solutions on the nPG-rich side has been studied by broadband dielectric spectroscopy and differential scanning calorimetry in the temperature range of 130-280 K. Two relaxation processes are observed for all the hydration levels; the slower process (I) is related to the alpha relaxation of the solution whereas the faster one (II) is associated with the reorientation of water molecules in the mixture. Dielectric data for process (II) at temperatures between 150 and 200 K indicate the existence of a critical water concentration (x(c)) below which water mobility is highly restricted. Below x(c), nPG-water domains drive the dielectric signal whereas above x(c), water-water domains dominate the dielectric response at low temperatures. The results also show that process (II) at low temperatures is due to local motions of water molecules in the glassy frozen matrix. Additionally, we will show that the glass transition temperatures (T(g)) for aqueous PG, 2PG, and 3PG solutions do not extrapolate to approximately 136 K, regardless of the extrapolation method. Instead, we find that the extrapolated T(g) value for water from these solutions lies in the neighborhood of 165 K. 相似文献
160.
Halim Y Schwartz SJ Francis D Baldauf NA Rodriguez-Saona LE 《Journal of AOAC International》2006,89(5):1257-1262
Lycopene is a potent antioxidant that has been shown to play critical roles in disease prevention. Efficient assays for detection and quantification of lycopene are desirable as alternatives to time- and labor-intensive methods. Attenuated total reflectance infrared (ATR-IR) spectroscopy was used for quantification of lycopene in tomato varieties. Calibration models were developed by partial least-squares regression (PLSR) using quantitative measures of lycopene concentration from liquid chromatography as reference method. IR spectra showed a distinct marker band at 957 cm(-1) for trans Carbon-Hydrogen (CH) deformation vibration of lycopene. PLSR models predicted the lycopene content accurately and reproducibly with a correlation coefficient (sigma) of 0.96 and standard error of cross-validation <0.80 mg/100 g. ATR-IR spectroscopy allowed for rapid, simple, and accurate determination of lycopene in tomatoes with minimal sample preparation. Results suggest that the ATR-IR method is applicable for high-throughput quantitative analysis and screening for lycopene in tomatoes. 相似文献