全文获取类型
收费全文 | 324篇 |
免费 | 10篇 |
国内免费 | 10篇 |
专业分类
化学 | 225篇 |
力学 | 8篇 |
数学 | 73篇 |
物理学 | 38篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 15篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 15篇 |
2008年 | 20篇 |
2007年 | 27篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 18 毫秒
331.
The Cotton effect of olefins in the pimaric acid series is discussed. The contribution of the vinyl group is important when it is near the endocyclic double bond and becomes negligible when the two double bonds are far apart. 相似文献
332.
Charles Z. Hotz Peter Kovacic Issam A. Khoury 《Journal of polymer science. Part A, Polymer chemistry》1983,21(9):2617-2628
Although polymerization of 2,5-dibromothiophene via coupling of the Grignard reagent with organonickel salts was reported in two earlier communications, a detailed examination of reaction variables was not done. This report provides results from variation in the following: time, amount of magnesium, amount of iodine, dilution, and variation in the halide of the monomer. The highest yield was obtained for reactions with 1:1 molar ratio of monomer to magnesium in more concentrated solutions of tetrahydrofuran for a reaction time of 4 h. For variation in the halogen of the monomer the following yield sequence was obtained: I > Br > Cl. The results are compared with the corresponding benzenoid system investigated by Yamamoto. In addition, polymerization studies were carried out with other brominated thiophene monomers. Use of an organic promoter (cis-1,4-dichloro-2-butene) in place of a nickel salt proved successful in the generation of poly(2,5-thienylene). 相似文献
333.
An Ordered Incidence Geometry, that is a geometry with certain axioms of incidence and order, is proposed as a minimal setting for the fundamental convexity theorems, which usually appear in the context of a linear vector space, but require only incidence, order (and for separation, completeness), and none of the linear structure of a vector space.Research supported by the National Science Foundation. 相似文献
334.
Adi Ben-Israel 《Numerical Algorithms》2000,25(1-4):37-46
A mapping :R
n
R
m
, nm, with Jacobian of full column-rank, has a local inverse that is analogous to the Moore–Penrose inverse of linear mappings. 相似文献
335.
Engel Y Dahan A Rozenshine-Kemelmakher E Gozin M 《The Journal of organic chemistry》2007,72(7):2318-2328
The syntheses of 1,10-phenanthroline fluorophore-based chemosensor 7 and its truncated analog 9 are reported. Interactions of these compounds with urea, thiourea, 1,3-dimethylurea, tetrahydropyrimidin-2(1H)-one, imidazolidin-2-one, and selected uronium salts were assessed by three-dimensional excitation-emission spectroscopy, UV-vis absorbance, and fluorescence titrations. Chemosensor 7 was found to be capable of distinguishing between neutral ureas and their salts, by producing a different optical response for each type of compounds. The complexation of urea by 7 was also studied by selective-NOE 1H NMR, 13C NMR (using 13C-labeled guest), and MALDI-TOF mass spectrometry. In addition, we performed DFT calculations (B3LYP 3-21g** level) for structures of complexes of 7 with urea, imidazolidin-2-one, and tetrahydropyrimidin-2(1H)-one. Development of chemosensor 7-type compounds in conjunction with differential excitation-emission spectroscopy represents an important step toward the development of novel tools for ureas and their salts analysis. 相似文献
336.
We elaborate on how to incorporate mesonic correlators into the worldline formalism. We consider possible applications to QCD-like theories in various dimensions. We focus on large-Nc two-dimensional QCD (the ?t Hooft model) and relate it to a single harmonic oscillator. We also discuss the dependence of the Peskin S-parameter on the number of massless flavors and their representation and compare our expression to the corresponding expression obtained at weak coupling. Finally, we use the worldline formalism to discuss how the Veneziano limit of QCD is realized in holography in the limit of small Nf/Nc. 相似文献
337.
Block copolymer micelles with bactericidal properties were designed to deactivate pathogens such as E. coli bacteria. The micelles of PS‐b‐PAA and PS‐b‐P4VP block copolymers were loaded with biocides TCMTB or TCN up to 20 or 30 wt.‐%, depending on the type of antibacterial agent. Bacteria were exposed to loaded micelles and bacterial deactivation was evaluated. The micelles loaded with TCN are bactericidal; bacteria are killed in less than two minutes of exposure. The most likely interpretation of the data is that the biocide is transferred to the bacteria by repeated micelle/bacteria contacts, and not via the solution.
338.
Following the advent of synthetic biology, several gene networks have been engineered to emulate digital devices, with the ability to program cells for different applications. In this work, we adapt the concept of logical stochastic resonance to a synthetic gene network derived from a bacteriophage λ. The intriguing results of this study show that it is possible to build a biological logic block that can emulate or switch from the AND to the OR gate functionalities through externally tuning the system parameters. Moreover, this behavior and the robustness of the logic gate are underpinned by the presence of an optimal amount of random fluctuations. We extend our earlier work in this field, by taking into account the effects of correlated external (additive) and internal (multiplicative or state-dependent) noise. Results obtained through analytical calculations as well as numerical simulations are presented. 相似文献
339.
Adi Azoulay Sapir Shekef Aloni Prof. Lidan Xing Ayelet Tashakory Prof. Yitzhak Mastai Prof. Menny Shalom 《Angewandte Chemie (International ed. in English)》2023,62(40):e202311389
The facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride-based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large-scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties. 相似文献
340.
West Douglas X. Billeh Issam S. Jasinski Jerry P. Jasinski John M. Butcher Ray J. 《Transition Metal Chemistry》1998,23(3):209-214
2-Formyl-, 2-acetyl- and 2-benzoylpyridine N(4)-cyclohexylsemicarbazone and N(4)-cyclohexylthiosemicarbazone complexes of cobalt(II, III), nickel(II) and copper(II) have been prepared and characterized
by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, coordination is
by the neutral ligand, the main exceptions being the cobalt(III) complexes of the three thiosemicarbazones and three of the
benzoylpyridine derivatives. Thus, bonding is via the pyridyl nitrogen, azomethine nitrogen and thione/thiolato sulfur. The five-coordinate copper(II) complex of 2-acetylpyridine
N(4)-cyclohexylthiosemicarbazone, [Cu(HAc4CHex)Cl2], approaches square pyramidal stereochemistry with the basal Cu—Cl bond significantly shorter than the apical Cu—Cl bond.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献