全文获取类型
收费全文 | 334篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 182篇 |
晶体学 | 13篇 |
力学 | 3篇 |
数学 | 36篇 |
物理学 | 108篇 |
出版年
2019年 | 3篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 20篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1959年 | 2篇 |
1942年 | 2篇 |
1911年 | 2篇 |
排序方式: 共有342条查询结果,搜索用时 15 毫秒
31.
Dimitrios P. CatsoulacosBarry R. Steele Georgios A. HeropoulosMaria Micha-Screttas Constantinos G. Screttas 《Tetrahedron letters》2003,44(24):4575-4578
DAB-dendr-(NH2)32 has been modified to produce two novel dendrimeric P,N-ligands, DAB-dendr-[1,2-(NCHC6H4PPh2)]32 and DAB-dendr-[1,2-(NHCH2C6H4PPh2)]32. These were both found to activate electron rich aryl bromides in the Heck reaction. The reactions seem to proceed better in a novel solvent system consisting of an equimolar mixture of a tertiary amine with acetic acid. A marked dependence of the conversion on the [equivalents of dendrimeric ligand]/[Pd] ratio has been observed with conversion decreasing as the ratio of dendrimer equivalents to Pd increases. This phenomenon is attributed to interactions of the arms bearing the metal with neighboring ones within the dendrimer. 相似文献
32.
Shao Y Molnar LF Jung Y Kussmann J Ochsenfeld C Brown ST Gilbert AT Slipchenko LV Levchenko SV O'Neill DP DiStasio RA Lochan RC Wang T Beran GJ Besley NA Herbert JM Lin CY Van Voorhis T Chien SH Sodt A Steele RP Rassolov VA Maslen PE Korambath PP Adamson RD Austin B Baker J Byrd EF Dachsel H Doerksen RJ Dreuw A Dunietz BD Dutoi AD Furlani TR Gwaltney SR Heyden A Hirata S Hsu CP Kedziora G Khalliulin RZ Klunzinger P Lee AM Lee MS Liang W Lotan I Nair N Peters B Proynov EI Pieniazek PA Rhee YM 《Physical chemistry chemical physics : PCCP》2006,8(27):3172-3191
Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces. 相似文献
33.
Tang PH Miles MV Steele P Davidson BS Geraghty SR Morrow AL 《Biomedical chromatography : BMC》2006,20(12):1336-1343
An isocratic HPLC method was developed for the determination of coenzyme Q(10) (CoQ(10)) in human breast milk. After a single-step liquid-liquid extraction, the milk extract was injected directly into the HPLC system. The analytical method is based on pre-column inline treatment of CoQ(10). Chromatographic separation of CoQ(10) and coenzyme Q(9) (CoQ(9)) internal standard was achieved using a reversed-phase Microsorb-MV C(18) analytical column. CoQ(10) and CoQ(9) were monitored by an electrochemical detector (ECD). An excellent linearity (r = 0.999) was observed for CoQ(10) in the concentration range 0.06-2.5 micromol L(-1) in breast milk. The limit of quantitation (LOQ) was 60 nmol L(-1). Coefficients of variations (CVs) for intra-day and inter-day assay precisions were less than 5%. A total of 194 breast milk samples were analyzed for the CoQ(10) concentration; the mean value was 0.32 +/- 0.21 micromol L(-1). 相似文献
34.
Crowley JD Steele IM Bosnich B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(35):8935-8951
Ferrocene has been investigated as a platform for developing protonmotive electrostatic drivers for molecular motors. When two 3-pyridine groups are substituted to the (rapidly rotating) cyclopentadienyl (Cp) rings of ferrocene, one on each Cp, it is shown that the (Cp) eclipsed, pi-stacked rotameric conformation is preferred both in solution and in the solid state. Upon quaternization of both of the pyridines substituents, either by protonation or by alkylation, it is shown that the preferred rotameric conformation is one where the pyridinium groups are rotated away from the fully pi-stacked conformation. Electrostatic calculations indicate that the rotation is caused by the electrostatic repulsion between the charges. Consistently, when the pi-stacking energy is increased pi-stacked population increases, and conversely when the electrostatic repulsion is increased pi-stacked population is decreased. This work serves to provide an approximate estimate of the amount of torque that the electrostatically driven ferrocene platform can generate when incorporated into a molecular motor. The overall conclusion is that the electrostatic interaction energy between dicationic ferrocene dipyridyl systems is similar to the pi-stacking interaction energy and, consequently, at least tricationic systems are required to fully uncouple the pi-stacked pyridine substituents. 相似文献
35.
Nano titanium dioxide (nTiO2), generally considered to be toxicologically inert, is manufactured in large quantities and extensively applied in consumer products. The small size and large surface area endow them with an active group or intrinsic toxicity. Advances in instrumentation are making Raman spectroscopy the tool of choice for an increasing number of (bio) chemical applications. One of the great advantages of this technique is its ability to provide information on the concentration, structure and interaction of biochemical molecules in their microenvironments within intact cells and tissues, non-destructively. Zebrafish (Danio rerio), one of the most important vertebrate model organisms used in developmental biology, are increasingly used in biomedical research, particularly as a model of human disease. In the present work, an attempt is made to study the effect of titanium dioxide, both nano and bulk, on the microenvironment of the liver tissues of Zebrafish using FT-Raman spectroscopy. The results of the present study suggest that TiO2 exposure demonstrate a marked influence on the microenvironments of the liver tissues of Zebrafish. A shift to a higher wavenumber and an increase in the intensity of the band at ∼1087 cm−1 in the TiO2 exposed tissues suggest that some of the conformational changes resulting from the alkali recovery process takes place due to TiO2 exposure. The decreased intensity ratio (I3220/I3400) observed in the titanium-exposed tissues suggests a decreased water domain size, which could be interpreted in terms of weaker hydrogen-bonded molecular species of water in the TiO2 exposed tissues. The observed shift of COO− bands to higher frequencies shows the disruption of salt bridges as a result of a change in the oppositely charged partners and due to the enhanced random coil conformation. The variation in the intensity ratio of the tyrosyl doublet (I858/I825) indicates variation in the hydrogen bonding of the phenolic hydroxyl group due to TiO2 exposure. The results further suggest that the microenvironments are greatly altered due to titanium nano exposure when compared to titanium bulk. In conclusion, the results indicate that FT-Raman spectroscopy might be a useful tool for rapid assessment of nano particle biological interactions. 相似文献
36.
37.
Saha R Biswas S Steele IM Dey K Mostafa G 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3166-3175
The metal complexes, [M(Hdammthiol)(2)]Cl·3H(2)O [M = Cr(III) (1), Fe(III) (2)] [where H(2)dammthiol is the thiol form of the ligand, diacetylmonoxime morpholine N-thiohydrazone] were synthesized by metal template reactions of diacetylemonoxime with morpholine N-thiohydrazide in the presence of CrCl(3)·6H(2)O and FeCl(3)·6H(2)O. Both the complexes (1 and 2) were characterized by single crystal X-ray crystallography, spectroscopic (IR and UV-vis), M?ssbauer and TGA analyses. The single crystal X-ray studies of both complexes show that the supramolecular hosts, constructed by the discrete mononuclear complexes, form supramolecular channels along the c-axis which are filled up by water-chloride clusters. In both complexes, the 1D water-chloride chain with chair-like architecture within the supramolecular hosts presents novelty. The magnetic measurement study of Fe(III) complex shows a spin crossover from S = 1/2 at 2.5 K to S = 5/2 at 300 K. At very low temperature, the presence of strong cooperative hydrogen bonding interactions stabilizes the S = 1/2 state. 相似文献
38.
Speciation and Structural Properties of Hydrothermal Solutions of Sodium and Potassium Sulfate Studied by Molecular Dynamics Simulations 下载免费PDF全文
Dr. Joachim Reimer Prof. Dr. Frédéric Vogel Prof. Dr. Matthew Steele‐MacInnis 《Chemphyschem》2016,17(10):1446-1453
Aqueous solutions of salts at elevated pressures and temperatures play a key role in geochemical processes and in applications of supercritical water in waste and biomass treatment, for which salt management is crucial for performance. A major question in predicting salt behavior in such processes is how different salts affect the phase equilibria. Herein, molecular dynamics (MD) simulations are used to investigate molecular‐scale structures of solutions of sodium and/or potassium sulfate, which show contrasting macroscopic behavior. Solutions of Na?SO4 exhibit a tendency towards forming large ionic clusters with increasing temperature, whereas solutions of K?SO4 show significantly less clustering under equivalent conditions. In mixed systems (NaxK2?xSO4), cluster formation is dramatically reduced with decreasing Na/(K+Na) ratio; this indicates a structure‐breaking role of K. MD results allow these phenomena to be related to the characteristics of electrostatic interactions between K+ and SO42?, compared with the analogous Na+?SO42? interactions. The results suggest a mechanism underlying the experimentally observed increasing solubility in ternary mixtures of solutions of Na?K?SO4. Specifically, the propensity of sodium to associate with sulfate, versus that of potassium to break up the sodium–sulfate clusters, may affect the contrasting behavior of these salts. Thus, mutual salting‐in in ternary hydrothermal solutions of Na?K?SO4 reflects the opposing, but complementary, natures of Na?SO4 versus K?SO4 interactions. The results also provide clues towards the reported liquid immiscibility in this ternary system. 相似文献
39.
Gao Feng Ivan Djordjevic Vishal Mogal Richard O'Rorke Oleksandr Pokholenko Terry W. J. Steele 《Macromolecular bioscience》2016,16(7):1072-1082
Development of bioadhesive formulations for tissue fixation remains a challenge. The major drawbacks of available bioadhesives are low adhesion strength, toxic byproducts, and complexity of application onto affected tissues. In order to address these problems, this study has developed a hydrogel bioadhesive system based on poly amido amine (PAMAM) dendrimer, grafted (conjugated) with UV‐sensitive, 4‐[3‐(trifluoromethyl)‐3H‐diazirin‐3‐yl] benzyl bromide (PAMAM‐g‐diazirine). This particular diazirine molecule can be grafted to the surface amine groups of PAMAM in a one‐pot synthesis. Diazirine functionalities are carbene precursors that form covalent crosslinks with hydrated tissues after low‐power UV activation without necessity of free‐radical initiators. The rheological properties and adhesion strength to ex vivo tissues are highly controllable depending on diazirine grafting, hydrogel concentration, and UV dose intensity fitting variety types of tissues. Covalent bonds at the tissue/bioadhesive interface provide robust adhesive and mechanical strength in a highly hydrated environment. The free flowing hydrogel conversion to elastic adhesive after UV activation allows intimate contact with the ex vivo swine tissue surfaces with low in vitro cytotoxicity observed, making it a promising bioadhesive formulation toward clinical applications.
40.
A laboratory information management system (LIMS) can make a major contribution to the quality and therefore to the efficiency
and competitiveness of a laboratory. Since it can impact all aspects of a laboratory's organization it must be the key if
not the principal player of the laboratory's quality system. It should support the laboratory in establishing, maintaining
and applying quality procedures thereby enabling the laboratory to achieve its quality goals. As a tool, LIMS permits the
laboratory to input and use its own know-how and experience to optimize the total organization (internal and external) and
workflow of generated information. However, perceived "quality" in the context of an LIMS, can be viewed as being made up
of different facets such as the security, reliability and accessibility of information as well as its turn around time and
production cost. This paper reviews the role of a LIMS in the laboratory and the contribution that both system design and
functionality can have on "building quality ".
Received: 5 October 1998 · Accepted: 20 October 1998 相似文献