全文获取类型
收费全文 | 2770篇 |
免费 | 111篇 |
国内免费 | 7篇 |
专业分类
化学 | 2150篇 |
晶体学 | 8篇 |
力学 | 25篇 |
数学 | 347篇 |
物理学 | 358篇 |
出版年
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 32篇 |
2020年 | 61篇 |
2019年 | 42篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 85篇 |
2015年 | 75篇 |
2014年 | 91篇 |
2013年 | 131篇 |
2012年 | 171篇 |
2011年 | 183篇 |
2010年 | 99篇 |
2009年 | 95篇 |
2008年 | 158篇 |
2007年 | 133篇 |
2006年 | 140篇 |
2005年 | 138篇 |
2004年 | 141篇 |
2003年 | 95篇 |
2002年 | 103篇 |
2001年 | 51篇 |
2000年 | 46篇 |
1999年 | 37篇 |
1998年 | 31篇 |
1997年 | 44篇 |
1996年 | 38篇 |
1995年 | 40篇 |
1994年 | 49篇 |
1993年 | 43篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 28篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 33篇 |
1984年 | 19篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1973年 | 11篇 |
1972年 | 11篇 |
排序方式: 共有2888条查询结果,搜索用时 15 毫秒
991.
992.
Uwe Schön Josef Messinger Uwe Reinecker Manoj K.S. Prabhu 《Tetrahedron letters》2005,46(42):7111-7115
An efficient Pd(0)-catalyzed protocol for the rapid and efficient preparation of 3-aminoestrone via 3-benzylaminoestrone from estrone-triflate is described. The three step synthesis proceeds with an overall yield of about 55% using X-Phos as optimal ligand for the Pd(0)-catalyzed Buchwald-Hartwig amination. 相似文献
993.
Uwe Deininghaus 《Zeitschrift für Physik B Condensed Matter》1981,45(1):71-78
Squaric acid is a layered structure with an antiferrodistortive phase transition atT
c
=373 K. Vertex and Ising models are considered, leading to the conclusion that two-dimensional squaric acid is a realization of the2d X–Y model with a cubic anisotropy, belonging to the same universality class as the Baxter or symmetrical Ashkin-Teller model. Experimental evidence is briefly discussed. 相似文献
994.
Dr. Céline Cerutti‐Delasalle Dr. Mohamed Mehiri Dr. Cecilia Cagliero Prof. Dr. Patrizia Rubiolo Prof. Dr. Carlo Bicchi Prof. Dr. Uwe J. Meierhenrich Dr. Nicolas Baldovini 《Angewandte Chemie (International ed. in English)》2016,55(44):13719-13723
Frankincense (olibanum) is one of the oldest aromatic materials used by humans, but the key molecular constituents contributing to its characteristic odor remained unknown. Reported herein is the discovery that (1S,2S)‐(+)‐trans‐ and (1S,2R)‐(+)‐cis‐2‐octylcyclopropyl‐1‐carboxylic acids are highly potent and substantive odorants occurring in ppm amounts in all of the frankincense samples analyzed, even those showing radically different volatile compositions. These cyclopropyl‐derived acids provide the very characteristic old churchlike endnote of the frankincense odor. 相似文献
995.
Patrick Degen Anuj Shukla Uwe Boetcher Heinz Rehage 《Colloid and polymer science》2008,286(2):159-168
In a series of experiments, we coated iron oxide nanoparticles, which were originally stabilized with lauric acid, with a
polymer layer of Octadecyltrichlorosilane (OTS). Characterization of the different coated nanoparticles was accomplished by
Static and Dynamic Light Scattering, acoustic spectroscopy, and Atomic Force Microscopy. In various experiments, we systematically
investigated the effect of different parameters such as the OTS concentration and iron oxide content on the particle size
of the coated nanoparticles. It was recognized that the size of the coated nanoparticles mainly depend on the concentration
of OTS (C
OTS) measured with respect to the concentration of the iron oxide particles (C
mag.). Below a well-defined threshold value of C
OTS
/C
mag, we did not observe any adsorption of OTS on the surface of iron oxide nanoparticles. The particle size of OTS-coated iron
oxide nanoparticles increased rapidly at concentration ratios above the threshold concentration and reached a typical plateau
value for long periods of time. 相似文献
996.
The microwave heated Suzuki-Miyaura cross-coupling reaction of boronic acids, boronic esters and organotrifluoroborates served as a model reaction in a singlemode equipment. The reaction conditions were optimized with respect to temperature and reaction time and were transferred to multimode equipment which is well suited for multiparallel synthesis in a larger scale. The source of the Pd species chosen included immobilized Pd complexes and Pd particles. In fact the increased time to reach the required reaction time in multimode chambers suitable for 48 parallel reactions has to be taken into account. The nature of the boronic acid has no impact on the efficiency of the catalytic process. However, heterogenized Pd species perform less well in multimode chambers with larger vial volumes, which we ascribe to diffusion phenomena. 相似文献
997.
The syntheses of three water-soluble cruciform fluorophores (XF) carrying aniline- N, N-bisacetic acid, 2-hydroxyaniline- N, N, O-trisacetic acid, and 1,2-phenylenediamine- N, N, N', N'-tetrakisacetic acid are reported. The XF skeleton was synthesized by a Horner reaction to assemble the distyrylbenzene unit followed by a Sonogashira coupling to attach the phenyleneethynylene modules. The photophysics of both the sodium salts and the ethyl esters of the three carboxylated 1,4-bis(aminostyryl)-2,5-bis(phenylethynyl)benzenes were investigated in chloroform and in aqueous buffered solution at a pH of 7.0 and compared to that of 1,4-bis(dibutylaminostyryl)-2,5-bis(phenylethynyl)benzene (BDB). The attachment of the carboxylate units to the aniline nitrogens influenced the photophysics and the sensory responses of the XFs, as the combined effect of steric bulk and charge repulsion led to a blue-shifted absorption when compared to that of BDB. While the fluorescence of the water-soluble XFs is sensitive toward metal cations, the mode of sensing action is different from that of BDB, where direct complexation to the aniline nitrogen lowers the energy of the HOMO (but not of the LUMO), leading to a blue-shifted emission. In the case of the 2-hydroxyaniline- N, N, O-trisacetic acid and 1,2-phenylenediamine- N, N, N', N'-tetrakisacetic acid-functionalized XFs, interaction with metal cations in aqueous buffered solution is guided by a breakup of excimers that form in water at XF concentrations as low as 50 micromol x L (-1). 相似文献
998.
Gnichwitz JF Wielopolski M Hartnagel K Hartnagel U Guldi DM Hirsch A 《Journal of the American Chemical Society》2008,130(26):8491-8501
A series of novel supramolecular architectures were built around a tin tetraphenyl porphyrin platform 6--functionalized by a 2-fold 1-ethyl-3-3-(3-dimethylaminopropyl)carbodiimide (EDC) promoted condensation reaction--and chiral depsipeptide dendrons of different generations 1-4. Here, implementation of a Hamilton receptor provided the necessary means to keep the constituents together via strong hydrogen bonding. Characterization of all architectures has been performed, including 4 which is the fourth generation, on the basis of NMR and photophysical methods. In particular, several titration experiments were conducted suggesting positive cooperativity, an assessment that is based on association constants that tend to be higher for the second binding step than for the first step. Importantly, molecular modeling calculations reveal a significant deaggregation of the intermolecular network of 6 during the course of the first binding step. As a consequence, an improved accessibility of the second Hamilton receptor unit in 6 emerges and, in turn, facilitates the higher association constants. The features of the equilibrium, that is, the dynamic exchange of depsipeptide dendrons 1-4 with fullerene 5, was tested in photophysical reference experiments. These steady-state and time-resolved measurements showed the tunable excited-state deactivations of these complexes upon photoexcitation. 相似文献
999.
Morgana B. Dessuy Maria Goreti R. Vale Fábio G. Lepri Daniel L.G. Borges Bernhard Welz Márcia M. Silva Uwe Heitmann 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
The artifacts created in the measurement of phosphorus at the 213.6-nm non-resonance line by electrothermal atomic absorption spectrometry using line source atomic absorption spectrometry (LS AAS) and deuterium lamp background correction (D2 BC) have been investigated using high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). The absorbance signals and the analytical curves obtained by LS AAS without and with D2 BC, and with HR-CS AAS without and with automatic correction for continuous background absorption, and also with least-squares background correction for molecular absorption with rotational fine structure were compared. The molecular absorption due to the suboxide PO that exhibits pronounced fine structure could not be corrected by the D2 BC system, causing significant overcorrection. Among the investigated chemical modifiers, NaF, La, Pd and Pd + Ca, the Pd modifier resulted in the best agreement of the results obtained with LS AAS and HR-CS AAS. However, a 15% to 100% higher sensitivity, expressed as slope of the analytical curve, was obtained for LS AAS compared to HR-CS AAS, depending on the modifier. Although no final proof could be found, the most likely explanation is that this artifact is caused by a yet unidentified phosphorus species that causes a spectrally continuous absorption, which is corrected without problems by HR-CS AAS, but which is not recognized and corrected by the D2 BC system of LS AAS. 相似文献
1000.
Issle J Pla-Roca M Martínez E Hartmann U 《Langmuir : the ACS journal of surfaces and colloids》2008,24(3):888-893
Poly(dimethylsiloxane) (PDMS) stamps are widely used in soft lithographic methods. They are powerful tools for obtaining structures of soft material in the micrometer to nanometer range by printing techniques. In this contribution, a new application of h-PDMS stamps for nanobead deposition is introduced. Magnetite-polysaccharide particles of an average diameter of 150 nm are used. They can be biologically functionalized by attaching various molecular groups. Deposition of these particles on a carrier substrate results in well-reproducible structures. This is achieved by means of PDMS stamps with different patterns using a microfluidic approach on one hand and a printing approach on the other hand. Furthermore, magnetic substrates with particular domain structures have been used. The beads can then be arranged in rather complicated but well-defined geometrical structures along the domain walls. The magnetic interaction considerably increases the adhesion of the beads to the carrier substrate. All involved materials are biocompatible. Thus the setup can be used in cell culture experiments in order to investigate influences of different particle-bound proteins and particle patterns on cell growth and vitality. 相似文献