全文获取类型
收费全文 | 950篇 |
免费 | 17篇 |
国内免费 | 6篇 |
专业分类
化学 | 615篇 |
晶体学 | 15篇 |
力学 | 12篇 |
数学 | 53篇 |
物理学 | 278篇 |
出版年
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 41篇 |
2012年 | 46篇 |
2011年 | 44篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 41篇 |
2007年 | 59篇 |
2006年 | 57篇 |
2005年 | 82篇 |
2004年 | 48篇 |
2003年 | 53篇 |
2002年 | 37篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1967年 | 8篇 |
1955年 | 3篇 |
排序方式: 共有973条查询结果,搜索用时 15 毫秒
1.
2.
Masamura Shinnosuke Iwamoto Tetsu Sugitani Yoshiki Konishi Keiji Hara Naoyuki 《Nonlinear dynamics》2020,99(4):3155-3168
Nonlinear Dynamics - The present study experimentally investigates amplitude death in delay-coupled double-scroll circuits with a time-varying network topology that randomly changes at a regular... 相似文献
3.
Phosphorescent Ruthenium Complexes with a Nitroimidazole Unit that Image Oxygen Fluctuation in Tumor Tissue 下载免费PDF全文
Dr. Aoi Son Atsushi Kawasaki Daiki Hara Dr. Takeo Ito Dr. Kazuhito Tanabe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2527-2536
Understanding oxygen fluctuation in a cancerous tumor is important for effective treatment, especially during radiotherapy. In this paper, ruthenium complexes bearing a nitroimidazole group are shown to report the oxygen status in tumor tissue directly. The nitroimidazole group was known to be accumulated in hypoxic tumor tissues. On the other hand, the ruthenium complex showed strong phosphorescence around 600 nm. The emission of ruthenium is quenched instantaneously by molecular oxygen due to energy transfer between triplet states of oxygen and ruthenium complex, but the emission is then recovered by the removal of oxygen. Thus, we could observe oxygen fluctuation in tumor tissue in a real‐time manner by monitoring the phosphorescence of the ruthenium complex. The versatility of the probe is demonstrated by monitoring oxygen fluctuation in living cells and tumor tissue planted in mice. The ruthenium complex promptly penetrated plasma membrane and accumulated in cells to emit its oxygen‐dependent phosphorescence. In vivo experiments revealed that the oxygen level in tumor tissue seems to fluctuate at the sub‐minute timescale. 相似文献
4.
Ruthenium‐Immobilized Periodic Mesoporous Organosilica: Synthesis,Characterization, and Catalytic Application for Selective Oxidation of Alkanes 下载免费PDF全文
Nobuhiro Ishito Dr. Hirokazu Kobayashi Dr. Kiyotaka Nakajima Yoshifumi Maegawa Dr. Shinji Inagaki Dr. Kenji Hara Prof. Dr. Atsushi Fukuoka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15564-15569
Periodic mesoporous organosilica (PMO) is a unique material that has a crystal‐like wall structure with coordination sites for metal complexes. A Ru complex, [RuCl2(CO)3]2, is successfully immobilized onto 2,2’‐bipyridine (BPy) units of PMO to form a single‐site catalyst, which has been confirmed by various physicochemical analyses. Using NaClO as an oxidant, the Ru‐immobilized PMO oxidizes the tertiary C?H bonds of adamantane to the corresponding alcohols at 57 times faster than the secondary C?H bonds, thereby exhibiting remarkably high regioselectivity. Moreover, the catalyst converts cis‐decalin to cis‐9‐decalol in a 63 % yield with complete retention of the substrate stereochemistry. The Ru catalyst can be separated by simple filtration and reused without loss of the original activity and selectivity for the oxidation reactions. 相似文献
5.
Crystal Structure of the Isopropylzinc Alkoxide of Pyrimidyl Alkanol: Mechanistic Insights for Asymmetric Autocatalysis with Amplification of Enantiomeric Excess 下载免费PDF全文
Dr. Arimasa Matsumoto Takaaki Abe Atsushi Hara Takayuki Tobita Taisuke Sasagawa Prof. Dr. Tsuneomi Kawasaki Prof. Dr. Kenso Soai 《Angewandte Chemie (International ed. in English)》2015,54(50):15218-15221
Asymmetric amplification during self‐replication is a key feature that is used to explain the origin of homochirality. Asymmetric autocatalysis of pyrimidyl alkanol in the asymmetric addition of diisopropylzinc to pyrimidine‐5‐carbaldehyde is a unique example of this phenomenon. Crystallization of zinc alkoxides of this 5‐pyrimidyl alkanol and single‐crystal X‐ray diffraction analysis of the alkoxide crystals reveal the existence of tetramer or higher oligomer structures in this asymmetric autocatalytic system. 相似文献
6.
Hironao Nakayama Masako Nakahara Erina Matsugi Midori Soda Tomoka Hattori Koki Hara Ayuki Usami Chiaki Kusumoto Shigeki Higashiyama Kiyoyuki Kitaichi 《Molecules (Basel, Switzerland)》2021,26(1)
Ferulic Acid (FA) is a highly abundant phenolic phytochemical which is present in plant tissues. FA has biological effects on physiological and pathological processes due to its anti-apoptotic and anti-oxidative properties, however, the detailed mechanism(s) of function is poorly understood. We have identified FA as a molecule that inhibits apoptosis induced by hydrogen peroxide (H2O2) or actinomycin D (ActD) in rat pheochromocytoma, PC12 cell. We also found that FA reduces H2O2-induced reactive oxygen species (ROS) production in PC12 cell, thereby acting as an anti-oxidant. Then, we analyzed FA-mediated signaling responses in rat pheochromocytoma, PC12 cells using antibody arrays for phosphokinase and apoptosis related proteins. This FA signaling pathway in PC12 cells includes inactivation of pro-apoptotic proteins, SMAC/Diablo and Bad. In addition, FA attenuates the cell injury by H2O2 through the inhibition of phosphorylation of the extracellular signal-regulated kinase (ERK). Importantly, we find that FA restores expression levels of brain-derived neurotrophic factor (BDNF), a key neuroprotective effector, in H2O2-treated PC12 cells. As a possible mechanism, FA increases BDNF by regulating microRNA-10b expression following H2O2 stimulation. Taken together, FA has broad biological effects as a neuroprotective modulator to regulate the expression of phosphokinases, apoptosis-related proteins and microRNAs against oxidative stress in PC12 cells. 相似文献
7.
This paper proposes a delayed feedback control (DFC) based on the act-and-wait concept, which reduces the dynamics of DFC
systems to that of discrete-time systems. Based on this concept, a delayed feedback controller is designed for a prototype
two-dimensional oscillator using a simple systematic procedure. This control has two advantages: the feedback delay time can
be large and it can obtain deadbeat behavior. A numerical example using a double-scroll circuit model demonstrates these theoretical
results. 相似文献
8.
Cadmium sulfide (CdS) nanoclusters were prepared by a freeze drying method from two types of cadmium carboxylates. One was cadmium methacrylates that were part of poly(methyl methacrylate) (PMMA) ionomer. The other was cadmium acetates that were dispersed in PMMA. X-ray diffraction was mainly used to study the formation and the size of nanoclusters. The size of CdS made from the ionomer was 0.9 nm, whereas that from the composite of cadmium acetate and PMMA was 2 nm. This was consistent with the size difference of the precursors of CdS: i.e., Cd carboxylate nanoclusters (ionic aggregates) were smaller in the ionomer than in the PMMA mixture, because ionic groups in the ionomer were constrained due to their connectivity to backbone chains and thus forming smaller ionic aggregates. Once stabilized, however, CdS nanocluster sizes were unchanged despite thermal treatments at up to 220 °C for 24 h for both systems. Structural transformations from a freeze dried cadmium carboxylate powder, to a CdS-containing powder, and to a heat-treated CdS-containing sample are speculated for both types of systems. 相似文献
9.
10.
Abstract The viscosity dependence of the isomerization process with comparatively low potential barrier was studied as a model of one-dimensional barrier crossing. We found that the ground-state isomerization of DODCI fails to fit the Kramers equation. We analyzed this non-Kramers behavior by means of an approach of frequency dependent friction. 相似文献