全文获取类型
收费全文 | 5654篇 |
免费 | 269篇 |
国内免费 | 24篇 |
专业分类
化学 | 4108篇 |
晶体学 | 53篇 |
力学 | 116篇 |
数学 | 418篇 |
物理学 | 1252篇 |
出版年
2024年 | 6篇 |
2023年 | 29篇 |
2022年 | 98篇 |
2021年 | 142篇 |
2020年 | 118篇 |
2019年 | 117篇 |
2018年 | 81篇 |
2017年 | 69篇 |
2016年 | 184篇 |
2015年 | 179篇 |
2014年 | 207篇 |
2013年 | 332篇 |
2012年 | 467篇 |
2011年 | 503篇 |
2010年 | 276篇 |
2009年 | 249篇 |
2008年 | 379篇 |
2007年 | 339篇 |
2006年 | 302篇 |
2005年 | 297篇 |
2004年 | 249篇 |
2003年 | 202篇 |
2002年 | 196篇 |
2001年 | 120篇 |
2000年 | 109篇 |
1999年 | 103篇 |
1998年 | 75篇 |
1997年 | 44篇 |
1996年 | 61篇 |
1995年 | 53篇 |
1994年 | 58篇 |
1993年 | 50篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 36篇 |
1989年 | 24篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 7篇 |
排序方式: 共有5947条查询结果,搜索用时 15 毫秒
991.
Young Min Ahn Won‐Woong Lee Jee H. Jung Sang‐Gi Lee Jongki Hong 《Journal of mass spectrometry : JMS》2009,44(12):1698-1708
Five glucosylceramides (GlcCers) were isolated by reversed phase high‐performance liquid chromatography from the MeOH extracts of a marine sponge, Haliclona (Reniera) sp., collected from the coast of Ulleung Island, Korea, and analyzed by fast atom bombardment mass spectrometry (FAB–MS) in positive‐ion mode. FAB‐mass spectra of these compounds included protonated molecules [M + H]+ and abundant sodiated molecules [M + Na]+ from a mixture of m‐NBA and NaI. The structures of these GlcCers, which were similar, were elucidated by FAB‐linked scan at constant B/E. To find diagnostic ions for their characterization, the GlcCers were analyzed by collision‐induced dissociation (CID) linked scan at constant B/E. The CID‐linked scan at constant B/E of [M + H]+ and [M + Na]+ precursor ions resulted in the formation of numerous characteristic product ions via a series of dissociative processes. The product ions formed by charge‐remote fragmentation provided important information for the characterization of the fatty N‐acyl chain moiety and the sphingoid base, commonly referred to as the long‐chain base. The product ions at m/z 203 and 502 were diagnostic for the presence of a sodiated sugar ring and β‐D ‐glucosylsphinganine, respectively. For further confirmation of the structure of the fatty N‐acyl chain moiety in each GlcCer, fatty acid methyl esters were obtained from the five GlcCers by methanolysis and analyzed by FAB–MS in positive‐ion mode. On the basis of these dissociation patterns, the structures of the five GlcCers from marine sponge were elucidated. In addition, the accurate mass measurement was performed to obtain the elemental composition of the GlcCers isolated from marine sponge. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
992.
Ji-Eun Lee Hyonchol Jang Eun-Jung Cho Hong-Duk Youn 《Experimental & molecular medicine》2009,41(7):471-477
Down syndrome critical region 1 (DSCR1), an oxidative stress-response gene, interacts with calcineurin and represses its phosphatase activity. Recently it was shown that hydrogen peroxide inactivates calcineurin by proteolytic cleavage. Based on these facts, we investigated whether oxidative stress affects DSCR1-mediated inactivation of calcineurin. We determined that overexpression of DSCR1 leads to increased proteolytic cleavage of calcineurin. Convertsely, knockdown of DSCR1 abolished calcineurin cleavage upon treatment with hydrogen peroxide. The PXIIXT motif in the COOH-terminus of DSCR1 is responsible for both binding and cleavage of calcineurin. The knockdown of overexpressed DSCR1 in DS fibroblast cells also abrogated calcineurin proteolysis by hydrogen peroxide. These results suggest that DSCR1 has the ability to inactivate calcineurin by inducing proteolytic cleavage of calcineurin upon oxidative stress. 相似文献
993.
Sang-Bok Ma Kyung-Wan Nam Won-Sub Yoon Seong-Min Bak Xiao-Qing Yang Byung-Won Cho Kwang-Bum Kim 《Electrochemistry communications》2009,11(8):1575-1578
Nano-sized lithium manganese oxide (LMO) dispersed on carbon nanotubes (CNT) has been synthesized successfully via a microwave-assisted hydrothermal reaction at 200 °C for 30 min using MnO2-coated CNT and an aqueous LiOH solution. The initial specific capacity is 99.4 mAh/g at a 1.6 C-rate, and is maintained at 99.1 mAh/g even at a 16 C-rate. The initial specific capacity is also maintained up to the 50th cycle to give 97% capacity retention. The LMO/CNT nanocomposite shows excellent power performance and good structural reversibility as an electrode material in energy storage systems, such as lithium-ion batteries and electrochemical capacitors. This synthetic strategy opens a new avenue for the effective and facile synthesis of lithium transition metal oxide/CNT nanocomposite. 相似文献
994.
Kaoru Honda Jaeheung Cho Prof. Dr. Takahiro Matsumoto Dr. Jungyun Roh Hideki Furutachi Dr. Takehiko Tosha Dr. Minoru Kubo Dr. Shuhei Fujinami Prof. Takashi Ogura Prof. Teizo Kitagawa Prof. Masatatsu Suzuki Prof. 《Angewandte Chemie (International ed. in English)》2009,48(18):3304-3307
In the nick(el) of time : Bis(μ‐oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H2O2, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3 . Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ‐η2:η2‐peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.
995.
Soyoung Jung Won Cho Hee Jung Lee Moonhyun Oh Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(8):1338-1338
Hexagonal tubes and rings with unusual shapes were generated through a unique self‐template‐directed growth mechanism. As described by M. Oh and co‐workers in the Communication on page 1459 ff., initially formed solid coordination polymer particles (CPPs) act as templates for the growth of the final hexagonal tubes and rings. Simple calcination of these unusually shaped CPPs results in the spontaneous formation of ZnO particles while the unique shape is maintained.
996.
Shabi Abbas Zaidi Kyoung Moon Han Sung Soon Kim Dong Guk Hwang Won Jo Cheong 《Journal of separation science》2009,32(7):996-1001
An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin. 相似文献
997.
Yutaek Seo Dr. Jong‐Won Lee Dr. Rajnish Kumar Dr. Igor L. Moudrakovski Dr. Huen Lee Prof. John A. Ripmeester Dr. 《化学:亚洲杂志》2009,4(8):1266-1274
Gas hydrates represent an attractive way of storing large quantities of gas such as methane and carbon dioxide, although to date there has been little effort to optimize the storage capacity and to understand the trade‐offs between storage conditions and storage capacity. In this work, we present estimates for gas storage based on the ideal structures, and show how these must be modified given the little data available on hydrate composition. We then examine the hypothesis based on solid‐solution theory for clathrate hydrates as to how storage capacity may be improved for structure II hydrates, and test the hypothesis for a structure II hydrate of THF and methane, paying special attention to the synthetic approach used. Phase equilibrium data are used to map the region of stability of the double hydrate in P–T space as a function of the concentration of THF. In situ high‐pressure NMR experiments were used to measure the kinetics of reaction between frozen THF solutions and methane gas, and 13C MAS NMR experiments were used to measure the distribution of the guests over the cage sites. As known from previous work, at high concentrations of THF, methane only occupies the small cages in structure II hydrate, and in accordance with the hypothesis posed, we confirm that methane can be introduced into the large cage of structure II hydrate by lowering the concentration of THF to below 1.0 mol %. We note that in some preparations the cage occupancies appear to fluctuate with time and are not necessarily homogeneous over the sample. Although the tuning mechanism is generally valid, the composition and homogeneity of the product vary with the details of the synthetic procedure. The best results, those obtained from the gas–liquid reaction, are in good agreement with thermodynamic predictions; those obtained for the gas–solid reaction do not agree nearly as well. 相似文献
998.
The purpose of this work is to introduce a hybrid projection method for finding a common element of the set of a generalized equilibrium problem, the set of solutions to a variational inequality and the set of fixed points of a strict pseudo-contraction in a real Hilbert space. 相似文献
999.
In this paper, we apply an intuitionistic fuzzy quasi-metric version of a fixed point theorem, to obtain the existence of solution for a recurrence equation associated with the analysis of Quicksort algorithms. 相似文献
1000.
When a dispersive wave system is subject to forcing by a moving external disturbance, a maximum or minimum of the phase speed is associated with a critical forcing speed at which the linear response is resonant. Nonlinear effects can play an important part near such resonances, and the salient characteristics of the nonlinear response depend on whether the maximum or minimum of the phase speed is realized in the long-wave limit (zero wavenumber) or at a finite wavenumber. The focus here is on the latter case that, among other physical systems, applies to gravity–capillary waves on water of finite or infinite depth. The analysis, for simplicity, is based on a forced–damped fifth-order Korteweg–de Vries equation, a model problem that features a phase-speed minimum at a finite wavenumber. When damping is not too strong compared with forcing, multiple subcritical finite-amplitude steady-solution branches coexist with the small-amplitude response predicted by linear theory. For forcing speed well below critical, the transient response from rest approaches the small-amplitude state, but at speeds close to critical, jump phenomena can occur, and reaching a time-periodic state that involves shedding of wavepacket solitary waves is also possible. 相似文献