全文获取类型
收费全文 | 271篇 |
免费 | 14篇 |
专业分类
化学 | 204篇 |
力学 | 1篇 |
数学 | 7篇 |
物理学 | 73篇 |
出版年
2023年 | 3篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 10篇 |
2009年 | 4篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 7篇 |
2005年 | 2篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1963年 | 2篇 |
1919年 | 1篇 |
1880年 | 2篇 |
排序方式: 共有285条查询结果,搜索用时 46 毫秒
1.
Characterization of autocatalytic decomposition reactions is important
for the safe handling and storage of energetic materials. Isothermal differential
scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition
of energetic materials. However, isothermal DSC tests are time consuming and
the choice of experimental temperature is crucial. This paper shows that an
automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient
screening tool for the identification of autocatalytic decomposition behavior
of energetic materials.
Hydroxylamine nitrate (HAN) is an important
member of the hydroxylamine family. High concentrations of HAN are used as
liquid propellants, and low concentrations of HAN are used primarily in the
nuclear industry for decontamination of equipment. Because of its instability
and autocatalytic decomposition behavior, HAN has been involved in several
incidents. 相似文献
2.
Tracy Huziak‐Clark Stephen J. Van Hook Julie Nurnberger‐Haag Lena Ballone‐Duran 《School science and mathematics》2007,107(8):311-324
This article focuses on the impact a collaborative project between university graduate fellows and K‐12 classroom teachers had on improved pedagogy in the classroom and in the future at the university. Nine teams participated in a yearlong professional development project to improve pedagogy and communication skills of the participants. This study shows that the participants, the fellows and the K‐12 teacher partners, made changes in planning, implementation, and even motivation for using inquiry‐based methods in their classroom. External observations of the teams further support the individuals' claims of improved pedagogy using inquiry and impact on student conceptual understanding. The Horizon Classroom Observation instrument was used for these observations. The teams showed an overall increase in scores, as well as overall effective and exemplarily implementation of their planning. The program design, the implementation, and the results of this three‐year study will be elaborated in this article. 相似文献
3.
4.
Held GA Solina DH Solina H Keane DT Haag WJ Horn PM Grinstein G 《Physical review letters》1990,65(9):1120-1123
5.
6.
7.
Siegers C Biesalski M Haag R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(11):2831-2838
Highly protein-resistant, self-assembled monolayers (SAMs) of dendritic polyglycerols (PGs) on gold can easily be obtained by simple chemical modification of these readily available polymers with a surface-active disulfide linker group. Several disulfide-functionalized PGs were synthesized by N,N'-dicyclohexylcarbodiimide-mediated ester coupling of thioctic acid. Monolayers of the disulfide-functionalized PG derivatives spontaneously form on a semitransparent gold surface and effectively prevent the adsorption of proteins, as demonstrated by surface plasmon resonance (SPR) kinetic measurements. A structure-activity relationship relating the polymer architecture to its ability to effectuate protein resistance has been derived from results of different surface characterization techniques (SPR, attenuated total reflectance infrared (ATR-IR), and contact-angle measurements). Dendritic PGs combine the characteristic structural features of several highly protein-resistant surfaces: a highly flexible aliphatic polyether, hydrophilic surface groups, and a highly branched architecture. PG monolayers are as protein resistant as poly(ethylene glycol) (PEG) SAMs and are significantly better than dextran-coated surfaces, which are currently used as the background for SPR spectroscopy. Due to the higher thermal and oxidative stability of the bulk PG as compared to the PEG and the easy accessibility of these materials, dendritic polyglycerols are novel and promising candidates as surface coatings for biomedical applications. 相似文献
8.
A reinvestigation of 2-methylacetophenone ( 1 ) by ns flash photolysis has provided detailed evidence for the reaction sequence of photoenolization. The triplet reaction proceeds adiabatically from the lowest excited triplet state of the ketone, 3 K (1) , to the enol excited triplet state, 3 E (1) , which decays both to enol and ketone ground state. The Z- and E-isomers of the photoenol, Z- E (1) and E- E (1) are formed in about equal yield by the triplet pathway, while direct enolization from the lowest excited singlet state of 1 yields (predominantly) the Z-isomer. Intramolecular reketonization from Z- E (1) to 1 proceeds at a rate of ca. 108s?1 in cyclohexane, but can be retarded to ca. 104s?1 in hydrogen-bond-acceptor solvents. The proposed mechanism is summarized in Scheme 1 and rationalized on the basis of a state correlation diagram, Scheme 2. 3,3,6,8-Tetramethyl-1-tetralone ( 2 ) was used as a reference compound with fixed conformational position of the carbonyl group, and some results from a brief investigation of 2,4-dimethylbenzophenone ( 3 ) are also reported. 相似文献
9.
10.
Gianini M Forster A Haag P von Zelewsky A Stoeckli-Evans H 《Inorganic chemistry》1996,35(17):4889-4895
cis-Bis-homoleptic platinum(II) complexes, with predetermined helical chirality at the metal center, can be obtained by using strongly sterically interacting ligands. With this aim, two new ligands, (8R,10R)-2-(2'-thienyl)-4,5-pinenopyridine, th4,5ppy (2), and (8R,10R)-2-(2'-thienyl)-5,6-pinenopyridine, th5,6ppy (4), were synthesized and coordinated to platinum. The structures of the resulting complexes, Pt(th4,5ppy)(2) (5) and Pt(th5,6ppy)(2) (6), were determined by X-ray diffraction, and it was found that they both crystallize with a Delta-cis configuration. Thermal oxidative additions (TOA) of alkyl halides were performed with both complexes leading, in the case of 5, to a mixture of isomers and, in the case of 6, to isomerically pure products. The predetermination of chirality at the metal center is therefore preserved in the octahedral (OC-6) platinum(IV) complexes. Crystals of Pt(th4,5ppy)(2) (5) are orthorhombic, of space group P2(1)2(1)2(1), with a = 12.973(1) ?, b = 13.619(2) ?, c = 17.665(2) ?, alpha = beta = gamma = 90 degrees, and Z = 4. Final R = 0.0268 and R(w) = 0.0424 for 3101 observed reflections. Crystals of Pt(th5,6ppy)(2) (6) are hexagonal, of space group P6(1), with a = 11.5465(4) ?, b = 11.5465(4) ?, c = 35.356(3) ?, alpha = beta = 90 degrees, gamma = 120 degrees, and Z = 6. Final R = 0.0424 and R(w) = 0.0845 for 2660 observed reflections. Neither molecule possesses a crystallographic C(2) symmetry. 相似文献