全文获取类型
收费全文 | 3412篇 |
免费 | 158篇 |
国内免费 | 25篇 |
专业分类
化学 | 2363篇 |
晶体学 | 24篇 |
力学 | 76篇 |
数学 | 580篇 |
物理学 | 552篇 |
出版年
2023年 | 39篇 |
2022年 | 52篇 |
2021年 | 84篇 |
2020年 | 78篇 |
2019年 | 89篇 |
2018年 | 79篇 |
2017年 | 68篇 |
2016年 | 150篇 |
2015年 | 99篇 |
2014年 | 134篇 |
2013年 | 217篇 |
2012年 | 261篇 |
2011年 | 250篇 |
2010年 | 136篇 |
2009年 | 138篇 |
2008年 | 205篇 |
2007年 | 238篇 |
2006年 | 218篇 |
2005年 | 171篇 |
2004年 | 149篇 |
2003年 | 94篇 |
2002年 | 104篇 |
2001年 | 61篇 |
2000年 | 62篇 |
1999年 | 37篇 |
1998年 | 31篇 |
1997年 | 31篇 |
1996年 | 40篇 |
1995年 | 24篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有3595条查询结果,搜索用时 15 毫秒
1.
Dr. Joaquim Torra Dr. Felipe Viela Dr. Diego Megías Dr. Begoña Sot Prof. Cristina Flors 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(19):e202200026
CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45–55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo. 相似文献
2.
Experimental and Theoretical Studies on the Rearrangement of 2‐Oxoazepane α,α‐Amino Acids into 2′‐Oxopiperidine β2,3,3‐Amino Acids: An Example of Intramolecular Catalysis
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Diego Núñez‐Villanueva Dr. M. Ángeles Bonache Laura Lozano Dr. Lourdes Infantes Prof. José Elguero Prof. Ibon Alkorta Prof. M. Teresa García‐López Dr. Rosario González‐Muñiz Dr. Mercedes Martín‐Martínez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2489-2500
Enantiopure β‐amino acids represent interesting scaffolds for peptidomimetics, foldamers and bioactive compounds. However, the synthesis of highly substituted analogues is still a major challenge. Herein, we describe the spontaneous rearrangement of 4‐carboxy‐2‐oxoazepane α,α‐amino acids to lead to 2′‐oxopiperidine‐containing β2,3,3‐amino acids, upon basic or acid hydrolysis of the 2‐oxoazepane α,α‐amino acid ester. Under acidic conditions, a totally stereoselective synthetic route has been developed. The reordering process involved the spontaneous breakdown of an amide bond, which typically requires strong conditions, and the formation of a new bond leading to the six‐membered heterocycle. A quantum mechanical study was carried out to obtain insight into the remarkable ease of this rearrangement, which occurs at room temperature, either in solution or upon storage of the 4‐carboxylic acid substituted 2‐oxoazepane derivatives. This theoretical study suggests that the rearrangement process occurs through a concerted mechanism, in which the energy of the transition states can be lowered by the participation of a catalytic water molecule. Interestingly, it also suggested a role for the carboxylic acid at position 4 of the 2‐oxoazepane ring, which facilitates this rearrangement, participating directly in the intramolecular catalysis. 相似文献
3.
Condeixa Lucas Dias Silva Pierry Moah Diego Farias Brenda Leiras Adriana 《Central European Journal of Operations Research》2022,30(3):921-940
Central European Journal of Operations Research - Societal awareness and legislation changes concerning sustainability have affected how organizations generate value for stakeholders, as well as... 相似文献
4.
Design and development of a two‐dimensional system based on hydrophilic and reversed‐phase liquid chromatography with on‐line sample treatment for the simultaneous separation of excreted xenobiotics and endogenous metabolites in urine
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Diego García‐Gómez Encarnación Rodríguez‐Gonzalo Rita Carabias‐Martínez 《Biomedical chromatography : BMC》2015,29(8):1190-1196
In the present work we describe a two‐dimensional liquid chromatographic system (2D‐LC) with detection by mass spectrometry (MS) for the simultaneous separation of endogenous metabolites of clinical interest and excreted xenobiotics deriving from exposure to toxic compounds. The 2D‐LC system involves two orthogonal chromatographic modes, hydrophilic interaction liquid chromatography (HILIC) to separate polar endogenous metabolites and reversed‐phase (RP) chromatography to separate excreted xenobiotics of low and intermediate polarity. Additionally, the present proposal has the novelty of incorporating an on‐line sample treatment based on the use of restricted access materials (RAMs), which permits the direct injection of urine samples into the system. The work is focused on the instrumental coupling, studying all possible options and attempting to circumvent the problems of solvent incompatibility between the RAM device and the two chromatographic columns, HILIC and RP. The instrumental configuration developed, RAM‐HILIC‐RPLC‐MS/MS, allows the simultaneous assessment of urinary metabolites of clinical interest and excreted compounds derived from exposure to toxic agents with minimal sample manipulation. Thus, it may be of interest in areas such as occupational and environmental toxicology in order to explore the possible relationship between the two types of compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
Mejía Hugo Fernando Giraldo Jiménez-Piqué Emilio Valdés Matías Procaccini Raúl Pellice Sergio 《Journal of Solid State Electrochemistry》2020,24(10):2451-2460
Journal of Solid State Electrochemistry - A novel material was developed using sol-gel chemistry and an environmental-friendly grafting process of clay nanoparticles. In a previous work of our... 相似文献
6.
Maria Chudnovsky Jim Geelen Bert Gerards Luis Goddyn Michael Lohman Paul Seymour 《Combinatorica》2006,26(5):521-532
Let G=(V,E) be an oriented graph whose edges are labelled by the elements of a group Γ and let A⊂V. An A-path is a path whose ends are both in A. The weight of a path P in G is the sum of the group values on forward oriented arcs minus the sum of the backward oriented arcs in P. (If Γ is not abelian, we sum the labels in their order along the path.) We are interested in the maximum number of vertex-disjoint
A-paths each of non-zero weight. When A = V this problem is equivalent to the maximum matching problem. The general case also includes Mader's S-paths problem. We prove that for any positive integer k, either there are k vertex-disjoint A-paths each of non-zero weight, or there is a set of at most 2k −2 vertices that meets each of the non-zero A-paths. This result is obtained as a consequence of an exact min-max theorem.
These results were obtained at a workshop on Structural Graph Theory at the PIMS Institute in Vancouver, Canada. This research
was partially conducted during the period the first author served as a Clay Mathematics Institute Long-Term Prize Fellow. 相似文献
7.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
8.
Jim Foster 《Journal of Combinatorial Theory, Series A》2007,114(8):1515-1525
We show that for an n-gon with unit diameter to have maximum area, its diameter graph must contain a cycle, and we derive an isodiametric theorem for such n-gons in terms of the length of the cycle. We then apply this theorem to prove Graham's 1975 conjecture that the diameter graph of a maximal 2m-gon (m?3) must be a cycle of length 2m−1 with one additional edge attached to it. 相似文献
9.
I. Bretos J. Ricote R.J. Jiménez-Riobóo L. Pardo M.L. Calzada 《Applied Physics A: Materials Science & Processing》2007,89(4):967-973
A novel method to investigate the early formation stages of polycrystalline (Pb1-xCax)TiO3 (PCT) perovskite films by means of traditional Brillouin and micro-Brillouin spectroscopy (BS, mBS) is described in the present
work. The films were prepared by chemical solution deposition (CSD) onto oxidized (100)Si substrates and treated at temperatures
between 350–650 °C by rapid thermal processing (RTP). The elastic instability observed by Brillouin spectroscopy at the nano-structured
state of the PCT films was used here to determine their crystallization temperatures. Coexistence of different nanocrystalline
phases (e.g., pyrochlore, perovskite) in the films could also be detected by this technique. The reliability of these results
is demonstrated by complementary information obtained by X-ray diffraction (XRD) and scanning force microscopy (SFM). The
effects of the annealing temperature and of the Ca2+ content on the crystallization process of these films are also discussed.
PACS 78.35.+c; 77.84.-s; 61.82.Rx 相似文献
10.
It is shown that the condition υ > υp (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies
and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to
define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific
response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity
of light in the medium determines the existence of such general lower bound. 相似文献