全文获取类型
收费全文 | 2230篇 |
免费 | 126篇 |
国内免费 | 10篇 |
专业分类
化学 | 1539篇 |
晶体学 | 4篇 |
力学 | 58篇 |
数学 | 419篇 |
物理学 | 346篇 |
出版年
2023年 | 24篇 |
2022年 | 53篇 |
2021年 | 74篇 |
2020年 | 57篇 |
2019年 | 56篇 |
2018年 | 52篇 |
2017年 | 43篇 |
2016年 | 111篇 |
2015年 | 91篇 |
2014年 | 93篇 |
2013年 | 140篇 |
2012年 | 182篇 |
2011年 | 221篇 |
2010年 | 90篇 |
2009年 | 93篇 |
2008年 | 151篇 |
2007年 | 144篇 |
2006年 | 147篇 |
2005年 | 121篇 |
2004年 | 93篇 |
2003年 | 79篇 |
2002年 | 67篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 2篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有2366条查询结果,搜索用时 12 毫秒
931.
Dr. Pablo Labra-Vázquez Ricardo Flores-Cruz Aylin Galindo-Hernández Dr. Justo Cabrera-González Cristian Guzmán-Cedillo Dr. Arturo Jiménez-Sánchez Dr. Pascal G. Lacroix Dr. Rosa Santillan Dr. Norberto Farfán Dr. Rosario Núñez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16530-16540
A set of BODIPY-carboranyl dyads synthesized by a Sonogashira cross-coupling reaction, where different C-substituted ortho- and meta-carboranyl fragments have been linked to a BODIPY fluorophore is described. Chemical, photophysical and physicochemical analyses are presented, including NMR and single XRD experiments, optical absorption/emission studies and partition coefficient (log P) measurements. These studies, supported by DFT computations (M06-2X/6-31G**), provide an explanation to the largely divergent cell income that these fluorescent carboranyl-based fluorophores display, for which a structural or physicochemical explanation remains elusive. By studying the cell uptake efficiency and subcellular localization for our set of dyads on living HeLa cells, we tracked the origins of these differences to significant variations in their static dipole moments and partition coefficients, which tune their ability to interact with lipophilic microenvironments in cells. Remarkably, m-carboranyl-BODIPY derivatives with a higher lipophilicity are much better internalised by cells than their homologous with o-carborane, suggesting that m-isomers are potentially better theranostic agents for in vitro bioimaging and boron carriers for boron neutron capture therapy. 相似文献
932.
Inma P. Cabrera Pablo Cordero Emilio Muñoz-Velasco Manuel Ojeda-Aciego Bernard De Baets 《Mathematical Methods in the Applied Sciences》2020,43(9):5673-5680
Fuzzy-directed graphs are often chosen as the data structure to model and implement solutions to several problems in the applied sciences. Galois connections have also shown to be useful both in theoretical and in practical problems. In this paper, the notion of relational Galois connection is extended to be applied between transitive fuzzy directed graphs. In this framework, the components of the connection are crisp relations satisfying certain reasonable properties given in terms of the so-called full powering. 相似文献
933.
Dr. Uriel N. Morzan Dr. Pablo E. Videla Dr. Micheline B. Soley Dr. Erik T. J. Nibbering Prof. Victor S. Batista 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20219-20223
Ultrafast UV-pump/soft-X-ray-probe spectroscopy is a subject of great interest since it can provide detailed information about dynamical photochemical processes with ultrafast resolution and atomic specificity. Here, we focus on the photodissociation of ICN in the 1Π1 excited state, with emphasis on the transient response in the soft-X-ray spectral region as described by the ab initio spectral lineshape averaged over the nuclear wavepacket probability density. We find that the carbon K-edge spectral region reveals a rich transient response that provides direct insights into the dynamics of frontier orbitals during the I−CN bond cleavage process. The simulated UV-pump/soft-X-ray-probe spectra exhibit detailed dynamical information, including a time-domain signature for coherent vibration associated with the photogenerated CN fragment. 相似文献
934.
Nerea Ruiz del Árbol Carlos Sánchez-Sánchez Gonzalo Otero-Irurueta José I. Martínez Pedro L. de Andrés Ana C. Gómez-Herrero Pablo Merino Marten Piantek David Serrate Paolo Lacovig Silvano Lizzit José Alemán Gary J. Ellis María F. López José A. Martín-Gago 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23420-23427
On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1,4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures. 相似文献
935.
936.
Tailor‐made and chemically designed synthesis of coumarin‐containing benzoxazines and their reactivity study toward their thermosets 下载免费PDF全文
Pablo Froimowicz Carlos Rodriguez Arza Seishi Ohashi Hatsuo Ishida 《Journal of polymer science. Part A, Polymer chemistry》2016,54(10):1428-1435
Coumarins are used as a natural renewable resource to synthesize coumarin‐containing benzoxazine resins. The coumarin‐containing benzoxazines are fully characterized in terms of their chemical structure by Fourier‐transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. The influence of electronic effects caused by the substituents on the polymerization temperature is also evaluated. Thermal properties of the resulting thermosets are characterized by differential scanning calorimetry and thermogravimetric analysis, showing good stability and char yields higher than 50%. The coumarin‐containing polybenzoxazine thermosets show Tg values in the range between 160 and 190 °C. Thus, the herein presented coumarin‐containing benzoxazine resins are proven to be competitive monomers when compared with other petroleum‐based benzoxazine resins toward the generation of high‐performance thermoset. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1428‐1435 相似文献
937.
An immersed boundary method for unstructured meshes in depth averaged shallow water models 下载免费PDF全文
The representation of geometries as buildings, flood barriers or dikes in free surface flow models implies tedious and time‐consuming operations in order to define accurately the shape of these objects when using a body fitted numerical mesh. The immersed boundary method is an alternative way to define solid bodies inside the computational domain without the need of fitting the mesh boundaries to the shape of the object. In the direct forcing immersed boundary method, a solid body is represented by a grid of Lagrangian markers, which define its shape and which are independent from the fluid Eulerian mesh. This paper presents a new implementation of the immersed boundary method in an unstructured finite volume solver for the 2D shallow water equations. Moving least‐squares is used to transmit information between the grid of Lagrangian markers and the fluid Eulerian mesh. The performance of the proposed implementation is analysed in three test cases involving different flow conditions: the flow around a spur dike, a dam break flow with an isolated obstacle and the flow around an array of obstacles. A very good agreement between the classic body fitted approach and the immersed boundary method was found. The differences between the results obtained with both methods are less relevant than the errors because of the intrinsic shallow water assumptions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
938.
In Silico Olefin Metathesis with Ru‐Based Catalysts Containing N‐Heterocyclic Carbenes Bearing C60 Fullerenes 下载免费PDF全文
Juan Pablo Martínez Dr. Sai Vikrama Chaitanya Vummaleti Dr. Laura Falivene Prof. Dr. Steven P. Nolan Prof. Dr. Luigi Cavallo Prof. Dr. Miquel Solà Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6617-6623
Density functional theory calculations have been used to explore the potential of Ru‐based complexes with 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) ligand backbone ( A ) being modified in silico by the insertion of a C60 molecule ( B and C ), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A , B , and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron‐withdrawing N‐heterocyclic carbene improves the performance of unannulated complex A . The efficiency of complex B is only surpassed by complex A when the backbone of the N‐heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic‐donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A . Overall, this study indicates that such Ru‐based complexes B and C might have the potential to be effective olefin metathesis catalysts. 相似文献
939.
Pablo Sánchez-Moreno Juan Carlos Angulo Jesus S. Dehesa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(8):1-6
Phase drift is an inherent problem in one-way phase-encoded quantum key distribution (QKD) systems. Although combining passive with active phase compensation (APC) processes can effectively compensate for the phase drift, the security problems brought about by these processes are rarely considered. In this paper, we point out a security hole in the APC process and put forward a corresponding attack scheme. Under our proposed attack, the quantum bit error rate (QBER) of the QKD can be close to zero for some conditions. However, under the same conditions the ratio r of the key “0” and the key “1” which Bob (the legal communicators Alice and Bob) gets is no longer 1:1 but 2:1, which may expose Eve (the eavesdropper). In order to solve this problem, we modify the resend strategy of the attack scheme, which can force r to reach 1 and the QBER to be lower than the tolerable QBER. 相似文献
940.
Frontispiece: Self‐Immolative Linkers as Caps for the Design of Gated Silica Mesoporous Supports 下载免费PDF全文