全文获取类型
收费全文 | 685篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 488篇 |
力学 | 37篇 |
数学 | 46篇 |
物理学 | 131篇 |
出版年
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 13篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 27篇 |
2012年 | 31篇 |
2011年 | 56篇 |
2010年 | 28篇 |
2009年 | 16篇 |
2008年 | 39篇 |
2007年 | 29篇 |
2006年 | 37篇 |
2005年 | 47篇 |
2004年 | 38篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1948年 | 6篇 |
1924年 | 3篇 |
1914年 | 2篇 |
排序方式: 共有702条查询结果,搜索用时 15 毫秒
21.
Peter C. Roozemond Martin van Drongelen Zhe Ma Anne B. Spoelstra Daniel Hermida‐Merino Gerrit W. M. Peters 《Macromolecular rapid communications》2015,36(4):385-390
Flow‐induced structure formation is investigated with in situ wide‐angle X‐ray diffraction with high acquisition rate (30 Hz) using isotactic polypropylene in a piston‐driven slit flow with high wall shear rates (up to ≈900 s−1). We focus on crystallization within the shear layers that form in the high shear rate regions near the walls. Remarkably, the kinetics of the crystallization process show no dependence on either flow rate or flow time; the crystallization progresses identically regardless. Stronger or longer flows only increase the thickness of the layers. A conceptual model is proposed to explain the phenomenon. Above a certain threshold, the number of shish‐kebabs formed affects the rheology such that further structure formation is halted. The critical amount is reached already within 0.1 s under the current flow conditions. The change in rheology is hypothesized to be a consequence of the “hairy” nature of shish. Our results have large implications for process modelling, since they suggest that for injection molding type flows, crystallization kinetics can be considered independent of deformation history.
22.
Erwin R. van Rijssel Dr. Pieter van Delft Dr. Gerrit Lodder Prof. Herman S. Overkleeft Prof. Gijsbert A. van der Marel Dr. Dmitri V. Filippov Dr. Jeroen D. C. Codée 《Angewandte Chemie (International ed. in English)》2014,53(39):10381-10385
Lewis acid mediated substitution reactions using [D]triethylsilane as a nucleophile at the anomeric center of the four pentofuranoses, ribose, arabinose, xylose, and lyxose, all proceed with good to excellent stereoselectivity to provide the 1,2‐cis adducts. To unravel the stereoelectronic effects underlying the striking stereoselectivity in these reactions we have mapped the energy landscapes of the complete conformational space of the oxocarbenium ions of the four pentofuranoses. The potential energy surface maps provide a detailed picture of the influence of the differently oriented substituents and their mutual interactions on the stability of the oxocarbenium ions and the maps can be used to account for the observed stereoselectivities of the addition reactions. 相似文献
23.
In liquid-crystal elastomers, the simultaneous presence of rubber elasticity due to the crosslinked backbone chains and of optical birefringence due to the mesogens in the side chains lead to exceptional physical properties. An elastic deformation of the network influences the order of the mesogens and, therefore, the optical properties. A theory based on a Landau-de Gennes expansion of the free energy is proposed. In the opaque polydomain phase, the local orientation is given by a compromise between the external mechanical field and a local anchoring interaction. As the field is increased, it becomes energetically favorable for the mesogens to align parallel to the mechanical field, and a transition to a transparent monodomain structure occurs. Results for the average orientation, the stress and the chain conformation are given. 相似文献
24.
Gerrit L'Abb Wim Dehaen Lieve Bastin Jean-Paul Declercq J. Feneau-Dupont 《Journal of heterocyclic chemistry》1992,29(2):461-465
Methylation of the phenylhydrazone derived from 8-oxo-8H-indeno[1,2-d]-1,2,3-thiadiazole 5 with Meerwein's reagent furnishes the two methylated products 7 and 8. Single crystal X-ray analyses of these compounds reveal no significant S…NPh interaction, thus excluding a thiapentalene structure. 相似文献
25.
ABSTRACTMany proteins exhibit multiple binding patches. A patch may harbour a key chemical modification site, but may also simply act as a trap for the binding to another site. Here we consider the scenario in which one molecule (enzyme) binds another molecule (substrate) which contains two sites. We present microscopic expressions for the rate at which the enzyme binds to a particular site on the substrate, both for the scenario in which the enzyme directly binds the site without first visiting the other site, and for the case in which it may visit the other site an arbitrary number of times before binding to the site of interest. We also present the expressions for the corresponding dissociation reactions. These expressions can be used to compute in a single rare-event simulation of the dissociation pathway not only both the intrinsic and effective dissociation rate constants but also both association rate constants. 相似文献
26.
This study proposes and construct a primitive quantum arithmetic logic unit (qALU) based on the quantum Fourier transform (QFT). The qALU is capable of performing arithmetic ADD (addition) and logic NAND gate operations. It designs a scalable quantum circuit and presents the circuits for driving ADD and NAND operations on two-input and four-input quantum channels, respectively. By comparing the required number of quantum gates for serial and parallel architectures in executing arithmetic addition, it evaluates the performance. It also execute the proposed quantum Fourier transform-based qALU design on real quantum processor hardware provided by IBM. The results demonstrate that the proposed circuit can perform arithmetic and logic operations with a high success rate. Furthermore, it discusses in detail the potential implementations of the qALU circuit in the field of computer science, highlighting the possibility of constructing a soft-core processor on a quantum processing unit. 相似文献
27.
Hélène Beucher Dr. Sudhir Kumar Dr. Roopender Kumar Dr. Estíbaliz Merino Wei-Hsu Hu Gerrit Stemmler Sergio Cuesta-Galisteo Dr. Jorge A. González Léonard Bezinge Dr. Jakub Jagielski Dr. Chih-Jen Shih Prof. Dr. Cristina Nevado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(72):17604-17612
Efficient OLED devices have been fabricated using organometallic complexes of platinum group metals. Still, the high material cost and low stability represent central challenges for their application in commercial display technologies. Based on its innate stability, gold(III) complexes are emerging as promising candidates for high-performance OLEDs. Here, a series of alkynyl-, N-heterocyclic carbene (NHC)- and aryl-gold(III) complexes stabilized by a κ3-(N^C^C) template have been prepared and their photophysical properties have been characterized in detail. These compounds exhibit good photoluminescence quantum efficiency (ηPL) of up to 33 %. The PL emission can be tuned from sky-blue to yellowish green colors by variations on both the ancillary ligands as well as on the pincer template. Further, solution-processable OLED devices based on some of these complexes display remarkable emissive properties (ηCE 46.6 cd.A−1 and ηext 14.0 %), thus showcasing the potential of these motifs for the low-cost fabrication of display and illumination technologies. 相似文献
28.
Wei Peng Henriette S. de Bruijn Timo L. M. ten Hagen Go M. van Dam Jan L. N. Roodenburg Kristian Berg Max J. H. Witjes Dominic J. Robinson 《Photochemistry and photobiology》2020,96(3):708-717
Targeted photodynamic therapy (PDT) in head/neck cancer patients with a conjugate of the anti-epidermal growth factor receptor (EGFR) antibody, Cetuximab and a phthalocyanine photosensitizer IR700DX is under way, but the exact mechanisms of action are still not fully understood. In this study, the EGFR-overexpressing human head/neck OSC-19-luc2-cGFP tumor with transfected GFP gene was used in a skin-fold window chamber model in BALB/c nude mice. The uptake and localization of the conjugate in the tumor and its surrounding normal tissues were studied by an intravital confocal laser scanning microscopy with image analyses. The tumor was also irradiated with 690 nm laser light 24 h after conjugate administration. The vascular and tumor responses were examined by morphological evaluation and immunohistochemistry (IHC). The amount of conjugate in the tumor peaked at 24–48 h after injection. Image analyses of colocalization correlation parameters demonstrated a high fraction of the conjugate IR700DX colocalized in the GFP-expressing tumor cells. PDT-treated tumors showed extensive necrotic/apoptotic destruction with little vascular damage, while IHC showed no HIF-1α expression and decreased EGFR and Ki67 expression with activated caspase-3 overexpression, indicating a direct killing of tumor cells through both necrotic and apoptotic cell death. 相似文献
29.
Physics in Perspective - The concept of “fact” has a history. Over the past centuries, physicists have appropriated it in various ways. In this article, we compare Ernst Mach and Albert... 相似文献
30.
C. Athanasiou G. Marnellos J. E. ten Elshof P. Tsiakaras H. J. M. Bouwmeester M. Stoukides 《Ionics》1997,3(1-2):128-133
The catalytic and electrocatalytic behaviour of the La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) perovskite deposited on yttria stabilized zirconia (YSZ), was studied during the reaction of methane oxidation. Experiments
were carried out at atmospheric pressure, and at temperatures between 600 and 900 °C. When, instead of cofeeding with methane
in the gas phase, oxygen was electrochemically supplied as O2−, considerable changes in the methane conversion and product selectivity were observed. The non-faradaic effects (NEMCA) were
also studied and compared to those observed with metal catalysts.
Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997 相似文献