全文获取类型
收费全文 | 16371篇 |
免费 | 894篇 |
国内免费 | 1437篇 |
专业分类
化学 | 12921篇 |
晶体学 | 130篇 |
力学 | 325篇 |
综合类 | 10篇 |
数学 | 2217篇 |
物理学 | 3099篇 |
出版年
2023年 | 112篇 |
2022年 | 73篇 |
2021年 | 342篇 |
2020年 | 283篇 |
2019年 | 322篇 |
2018年 | 261篇 |
2017年 | 265篇 |
2016年 | 607篇 |
2015年 | 503篇 |
2014年 | 568篇 |
2013年 | 1242篇 |
2012年 | 1350篇 |
2011年 | 1455篇 |
2010年 | 833篇 |
2009年 | 1058篇 |
2008年 | 1023篇 |
2007年 | 993篇 |
2006年 | 847篇 |
2005年 | 888篇 |
2004年 | 1163篇 |
2003年 | 812篇 |
2002年 | 721篇 |
2001年 | 343篇 |
2000年 | 260篇 |
1999年 | 201篇 |
1998年 | 191篇 |
1997年 | 169篇 |
1996年 | 175篇 |
1995年 | 155篇 |
1994年 | 113篇 |
1993年 | 136篇 |
1992年 | 115篇 |
1991年 | 76篇 |
1990年 | 80篇 |
1989年 | 64篇 |
1988年 | 67篇 |
1987年 | 55篇 |
1986年 | 64篇 |
1985年 | 89篇 |
1984年 | 90篇 |
1983年 | 66篇 |
1982年 | 57篇 |
1981年 | 59篇 |
1980年 | 50篇 |
1979年 | 32篇 |
1978年 | 28篇 |
1977年 | 35篇 |
1976年 | 26篇 |
1975年 | 24篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Inside Cover: Stereoselective Synthesis of 1,3‐Diaminotruxillic Acid Derivatives: An Advantageous Combination of CH‐ortho‐Palladation and On‐Flow [2+2]‐Photocycloaddition in Microreactors (Chem. Eur. J. 1/2016) 下载免费PDF全文
42.
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
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
43.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes 下载免费PDF全文
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
44.
Prof. Antonio Molinaro Prof. Otto Holst Dr. Flaviana Di Lorenzo Dr. Maire Callaghan Dr. Alessandra Nurisso Dr. Gerardino D'Errico Dr. Alla Zamyatina Prof. Francesco Peri Dr. Rita Berisio Prof. Roman Jerala Prof. Jesús Jiménez‐Barbero Dr. Alba Silipo Prof. Sonsoles Martín‐Santamaría 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):500-519
In many Gram‐negative bacteria, lipopolysaccharide (LPS) and its lipid A moiety are pivotal for bacterial survival. Depending on its structure, lipid A carries the toxic properties of the LPS and acts as a potent elicitor of the host innate immune system via the Toll‐like receptor 4/myeloid differentiation factor 2 (TLR4/MD‐2) receptor complex. It often causes a wide variety of biological effects ranging from a remarkable enhancement of the resistance to the infection to an uncontrolled and massive immune response resulting in sepsis and septic shock. Since the bioactivity of lipid A is strongly influenced by its primary structure, a broad range of chemical syntheses of lipid A derivatives have made an enormous contribution to the characterization of lipid A bioactivity, providing novel pharmacological targets for the development of new biomedical therapies. Here, we describe and discuss the chemical aspects regarding lipid A and its role in innate immunity, from the (bio)synthesis, isolation and characterization to the molecular recognition at the atomic level. 相似文献
45.
46.
Dendronized Anionic Gold Nanoparticles: Synthesis,Characterization, and Antiviral Activity 下载免费PDF全文
Cornelia E. Peña‐González Pilar García‐Broncano Prof. M. Francesca Ottaviani Dr. Michela Cangiotti Dr. Alberto Fattori Margarita Hierro‐Oliva Prof. M. Luisa González‐Martín Dr. Jorge Pérez‐Serrano Dr. Rafael Gómez Prof. M. Ángeles Muñoz‐Fernández Dr. Javier Sánchez‐Nieves Dr. F. Javier de la Mata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):2987-2999
Anionic carbosilane dendrons decorated with sulfonate functions and one thiol moiety at the focal point have been used to synthesize water‐soluble gold nanoparticles (AuNPs) through the direct reaction of dendrons, gold precursor, and reducing agent in water, and also through a place‐exchange reaction. These nanoparticles have been characterized by NMR spectroscopy, TEM, thermogravimetric analysis, X‐ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, elemental analysis, and zeta‐potential measurements. The interacting ability of the anionic sulfonate functions was investigated by EPR spectroscopy with copper(II) as a probe. Different structures and conformations of the AuNPs modulate the availability of sulfonate and thiol groups for complexation by copper(II). Toxicity assays of AuNPs showed that those produced through direct reaction were less toxic than those obtained by ligand exchange. Inhibition of HIV‐1 infection was higher in the case of dendronized AuNPs than in dendrons. 相似文献
47.
48.
49.
Back Cover: Experimental and Theoretical Study of the Reactivity of Gold Nanoparticles Towards Benzimidazole‐2‐ylidene Ligands (Chem. Eur. J. 30/2016) 下载免费PDF全文
Dr. María Rodríguez‐Castillo Gustavo Lugo‐Preciado Dr. Danielle Laurencin Dr. Frederik Tielens Dr. Arie van der Lee Dr. Sébastien Clément Dr. Yannick Guari Dr. José M. López‐de‐Luzuriaga Dr. Miguel Monge Dr. Françoise Remacle Dr. Sébastien Richeter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10680-10680
50.
Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex 下载免费PDF全文
Lucía Piñeiro‐López Dr. Norma Ortega‐Villar Prof. Dr. M. Carmen Muñoz Dr. Gábor Molnár Dr. Jordi Cirera Prof. Dr. Rafael Moreno‐Esparza Prof. Dr. Víctor M. Ugalde‐Saldívar Dr. Azzedine Bousseksou Prof. Dr. Eliseo Ruiz Prof. Dr. José A. Real 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12741-12751
The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)2 (bztpen=N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) displays an S=1/2?S=3/2 spin crossover (SCO) behavior (T1/2=370 K, ΔH=12.48 kJ mol?1, ΔS=33 J K?1 mol?1) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0?S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120–420 K affording a detailed picture of how the electronic distribution of the t2g–eg orbitals modulates the structure of the {FeNO}7 bond, providing valuable magneto–structural and spectroscopic correlations and DFT analysis. 相似文献