全文获取类型
收费全文 | 1712篇 |
免费 | 80篇 |
国内免费 | 11篇 |
专业分类
化学 | 1173篇 |
晶体学 | 11篇 |
力学 | 53篇 |
数学 | 269篇 |
物理学 | 297篇 |
出版年
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 40篇 |
2020年 | 34篇 |
2019年 | 24篇 |
2018年 | 26篇 |
2017年 | 34篇 |
2016年 | 58篇 |
2015年 | 43篇 |
2014年 | 57篇 |
2013年 | 93篇 |
2012年 | 140篇 |
2011年 | 168篇 |
2010年 | 54篇 |
2009年 | 53篇 |
2008年 | 118篇 |
2007年 | 122篇 |
2006年 | 117篇 |
2005年 | 119篇 |
2004年 | 78篇 |
2003年 | 61篇 |
2002年 | 71篇 |
2001年 | 20篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有1803条查询结果,搜索用时 15 毫秒
991.
Lawrence NS 《Talanta》2006,69(2):385-392
The determination of methane is of strong interest to the analytical community due to its natural abundance, its potential to cause explosions and its known greenhouse effect. The current report gives a brief overview into the environmental significance of methane and an account of the existing detection protocols for methane in air and environmental samples. 相似文献
992.
Acyl carrier proteins are critical components of fatty acid and polyketide biosynthesis. Their primary function is to shuttle intermediates between active sites via a covalently bound phosphopantetheine arm. Small molecules capable of acylating this prosthetic group will provide a simple and reversible means of introducing novel functionality onto carrier protein domains. A series of N-activated β-lactams are prepared to examine site-specific acylation of the phosphopantetheine-thiol. In general, β-lactams are found to be significantly more reactive than our previously studied β-lactones. Selectivity for the holo over apo-form of acyl carrier proteins is demonstrated indicating that only the phosphopantetheine-thiol is modified. Incorporation of an N-propargyloxycarbonyl group provides an alkyne handle for conjugation to fluorophores and affinity labels. The utility of these groups for mechanistic interrogation of a critical step in polyketide biosynthesis is examined through comparison to traditional probes. In all, we expect the probes described in this study to serve as valuable and versatile tools for mechanistic interrogation. 相似文献
993.
Ana L. Aguirre Nathan L. Loud Dr. Keywan A. Johnson Prof. Daniel J. Weix Dr. Ying Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(51):12981-12986
High-throughput experimentation (HTE) methods are central to modern medicinal chemistry. While many HTE approaches to C−N and Csp2−Csp2 bonds are available, options for Csp2−Csp3 bonds are limited. We report here how the adaptation of nickel-catalyzed cross-electrophile coupling of aryl bromides with alkyl halides to HTE is enabled by AbbVie ChemBeads technology. By using this approach, we were able to quickly map out the reactivity space at a global level with a challenging array of 3×222 micromolar reactions. The observed hit rate (56 %) is competitive with other often-used HTE reactions and the results are scalable. A key to this level of success was the finding that bipyridine 6-carboxamidine (BpyCam), a ligand that had not previously been shown to be optimal in any reaction, is as general as the best-known ligands with complementary reactivity. Such “cryptic” catalysts may be common and modern HTE methods should facilitate the process of finding these catalysts. 相似文献
994.
André Seco Dr. Shilin Yu Dr. Arnaud Tron Dr. Nathan D. McClenaghan Prof. Fernando Pina Prof. A. Jorge Parola Dr. Nuno Basílio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16512-16522
A linear double pyridinium-terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV-Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensitive. Switching from the neutral chalcone to the cationic flavylium form upon irradiation at 365 nm under acidic conditions provided an enhanced CB7 association (K1:1 increases from 1.2×105 M−1 to 1.5×108 M−1), limiting spontaneous on-thread cucurbituril shuttling. This co-conformational change in the [2]pseudorotaxane is reversible in the dark with kobs=4.1×10−4 s−1. Threading the flavylium moiety into CB7 leads to a dramatic increase in the fluorescence quantum yield, from 0.29 in the free axle to 0.97 in the [2]pseudorotaxane and 1.0 in the [3]pseudorotaxane. 相似文献
995.
Dr. Chengxiang Xiang Dr. Adam Z. Weber Prof. Shane Ardo Dr. Alan Berger YiKai Chen Prof. Robert Coridan Dr. Katherine T. Fountaine Prof. Sophia Haussener Prof. Shu Hu Dr. Rui Liu Prof. Nathan S. Lewis Dr. Miguel A. Modestino Dr. Matthew M. Shaner Prof. Meenesh R. Singh Dr. John C. Stevens Dr. Ke Sun Dr. Karl Walczak 《Angewandte Chemie (International ed. in English)》2016,55(42):12974-12988
An integrated cell for the solar‐driven splitting of water consists of multiple functional components and couples various photoelectrochemical (PEC) processes at different length and time scales. The overall solar‐to‐hydrogen (STH) conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as on the component integration, overall device architecture, and system operating conditions. This Review focuses on the modeling‐ and simulation‐guided development and implementation of solar‐driven water‐splitting prototypes from a holistic viewpoint that explores the various interplays between the components. The underlying physics and interactions at the cell level is are reviewed and discussed, followed by an overview of the use of the cell model to provide target properties of materials and guide the design of a range of traditional and unique device architectures. 相似文献
996.
H2 Formation on Cosmic Grain Siliceous Surfaces Grafted with Fe+: A Silsesquioxanes‐Based Computational Model 下载免费PDF全文
Cosmic siliceous dust grains are involved in the synthesis of H2 in the inter‐stellar medium. In this work, the dust grain siliceous surface is represented by a hydrogen Fe‐metalla‐silsesquioxane model of general formula: [Fe(H7Si7O12?n)(OH)n]+ (n=0,1,2) where Fe+ behaves like a single‐site heterogeneous catalyst grafted on a siliceous surface synthesizing H2 from H. A computational analysis is performed using two levels of theory (B3LYP‐D3BJ and MP2‐F12) to quantify the thermodynamic driving force of the reaction: [Fe‐T7H7]++4H→[Fe‐T7H7(OH)2]++H2. The general outcomes are: 1) H2 synthesis is thermodynamically strongly favored; 2) Fe‐H / Fe‐H2 barrier‐less formation potential; 3) chemisorbed H‐Fe leads to facile H2 synthesis at 20≤T≤100 K; 4) relative spin energetics and thermodynamic quantities between the B3LYP‐D3BJ and MP2‐F12 levels of theory are in qualitative agreement. The metalla‐silsesquioxane model shows how Fe+ fixed on a siliceous surface can potentially catalyze H2 formation in space. 相似文献
997.
998.
N. M. L. Nathan 《Acta Analytica》2005,20(3):3-6
Direct Realists believe that perception involves direct awareness of an object not dependent for its existence on the perceiver.
Howard Robinson rejects this doctrine in favour of a Sense-Datum theory of perception. His argument against Direct Realism
invokes the principle ‘same proximate cause, same immediate effect’. Since there are cases in which direct awareness has the
same proximate cerebral cause as awareness of a sense datum, the Direct Realist is, he thinks, obliged to deny this causal
principle. I suggest that although Direct Realism is in more than one respect implausible, it does not succumb to Robinson’s
argument. The causal principle is true only if ‘proximate cause’ means ‘proximate sufficient cause’, and the Direct Realist
need not concede that there is a sufficient cerebral cause for direct awareness of independent objects. 相似文献
999.
This paper deals with two-dimensional composites made of several isotropic linearly conducting phases in prescribed volume fractions. The primary focus is on the three-phase case; the generalization to a larger number of phases is straightforward.A class of high- but finite-rank laminates is introduced. The laminates saturate the known inequality bounds—due to the work of Hashin and Shtrikman, Lurie and Cherkaev, Tartar, and Murat and Tartar—on the effective conductivity tensor of any composite. These bounds depend only on the constituent material properties and volume fractions and not on the placement of these materials in the composite. The bounds are known not to be optimal for all admissible choices of the conductivities and volume fractions. However, they are now known to be realizable in a much larger range of these parameters than was previously known.The range of effective properties of our multiphase laminates strictly includes those corresponding to the composites found earlier by Milton and Kohn, Lurie and Cherkaev, and Gibiansky and Sigmund. The new optimal laminates are found in a systematic fashion by satisfying sufficient conditions on the fields in each layer. This leads to a simple algorithm for generating optimal laminates.In addition a new supplementary bound for multiphase structures is also proven which must be satisfied by composites with smooth interfaces. 相似文献
1000.
Simultaneous measurements of the release of atomic sodium, particle diameter and particle temperature for a single burning coal particle 总被引:1,自引:0,他引:1
P.J. van Eyk P.J. Ashman Z.T. Alwahabi G.J. Nathan 《Proceedings of the Combustion Institute》2009,32(2):2099-2106
The temporal history of the release of volatile alkali species during coal combustion is a significant, but poorly understood factor in the fouling and corrosion of heat transfer surfaces within industrial coal-fired boilers. We present new results of the simultaneous measurement of particle temperature, particle size and the atomic sodium concentration in the plume of a burning coal particle. During the char phase, the sodium concentration in the plume was found to be linearly dependent on the inverse of particle diameter, but during the ash phase the sodium concentration was found to decay exponentially with decreasing particle temperature. The centreline decay of Na within the plume above the burning particle consists of one region controlled by a first order chemical reaction and a second region controlled by diffusion. 相似文献