全文获取类型
收费全文 | 18251篇 |
免费 | 547篇 |
国内免费 | 51篇 |
专业分类
化学 | 10641篇 |
晶体学 | 127篇 |
力学 | 466篇 |
综合类 | 2篇 |
数学 | 3154篇 |
物理学 | 4459篇 |
出版年
2023年 | 135篇 |
2022年 | 259篇 |
2021年 | 373篇 |
2020年 | 300篇 |
2019年 | 295篇 |
2018年 | 353篇 |
2017年 | 366篇 |
2016年 | 808篇 |
2015年 | 604篇 |
2014年 | 690篇 |
2013年 | 1425篇 |
2012年 | 1023篇 |
2011年 | 1104篇 |
2010年 | 788篇 |
2009年 | 690篇 |
2008年 | 817篇 |
2007年 | 719篇 |
2006年 | 614篇 |
2005年 | 464篇 |
2004年 | 427篇 |
2003年 | 405篇 |
2002年 | 369篇 |
2001年 | 278篇 |
2000年 | 273篇 |
1999年 | 220篇 |
1998年 | 215篇 |
1997年 | 189篇 |
1996年 | 205篇 |
1995年 | 193篇 |
1994年 | 161篇 |
1993年 | 152篇 |
1992年 | 150篇 |
1991年 | 143篇 |
1990年 | 123篇 |
1989年 | 111篇 |
1988年 | 147篇 |
1987年 | 127篇 |
1986年 | 124篇 |
1985年 | 189篇 |
1984年 | 166篇 |
1983年 | 132篇 |
1982年 | 123篇 |
1981年 | 119篇 |
1980年 | 148篇 |
1979年 | 131篇 |
1978年 | 140篇 |
1977年 | 135篇 |
1976年 | 128篇 |
1974年 | 130篇 |
1973年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Dr. Marcelo M. Pedroso Prof. James A. Larrabee Dr. Fernanda Ely Shuhui E. Gwee Dr. Nataša Mitić Prof. David L. Ollis Prof. Lawrence R. Gahan Prof. Gerhard Schenk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):999-1009
The diesterase Rv0805 from Mycobacterium tuberculosis is a dinuclear metallohydrolase that plays an important role in signal transduction by controlling the intracellular levels of cyclic nucleotides. As Rv0805 is essential for mycobacterial growth it is a promising new target for the development of chemotherapeutics to treat tuberculosis. The in vivo metal‐ion composition of Rv0805 is subject to debate. Here, we demonstrate that the active site accommodates two divalent transition metal ions with binding affinities ranging from approximately 50 nm for MnII to about 600 nm for ZnII. In contrast, the enzyme GpdQ from Enterobacter aerogenes, despite having a coordination sphere identical to that of Rv0805, binds only one metal ion in the absence of substrate, thus demonstrating the significance of the outer sphere to modulate metal‐ion binding and enzymatic reactivity. CaII also binds tightly to Rv0805 (Kd≈40 nm ), but kinetic, calorimetric, and spectroscopic data indicate that two CaII ions bind at a site different from the dinuclear transition‐metal‐ion binding site. CaII acts as an activator of the enzymatic activity but is able to promote the hydrolysis of substrates even in the absence of transition‐metal ions, thus providing an effective strategy for the regulation of the enzymatic activity. 相似文献
992.
Jan Turek Zdeňka Růžičková Eva Tloušťová Helena Mertlíková‐Kaiserová Jana Günterová Lubomír Rulíšek Aleš Růžička 《应用有机金属化学》2016,30(5):318-322
Two gold(I) complexes of the (NHC)AuX type bearing a triazole‐based N‐heterocyclic carbene (NHC) ligand (1‐tert‐butyl‐4‐(4‐methylphenyl)‐3‐phenyl‐1H‐1,2,4‐triazol‐4‐ium‐5‐ylidene) and various halide ligands (X = Br, I) were synthesized and characterized in solution using NMR spectroscopy as well as in the solid state using X‐ray diffraction techniques. The cytotoxic properties of both compounds and the precursor, (NHC)AuCl, were screened against a panel of human tumour cell lines including liver cancer (HepG2), cervical cancer (HeLa S3) and leukaemia (CCRF‐CEM, HL‐60) and compared to cisplatin and auranofin. It was found that the activities of the chloro and bromo derivatives were generally superior to that of cisplatin and slightly less effective compared to auranofin, except for HepG2 cells where auranofin was not as effective. In addition, the ability to induce membrane phosphatidyl serine externalization as a hallmark of apoptosis in CCRF‐CEM leukaemic cells was investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
993.
Rocío Velasco Dr. Carlos Silva López Dr. Olalla Nieto Faza Prof. Dr. Roberto Sanz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15058-15068
By carefully controlling the reaction temperature, treatment of aryl benzyl ethers with tBuLi selectively leads to α‐lithiation, generating stable organolithiums that can be directly trapped with a variety of selected electrophiles, before they can undergo the expected [1,2]‐Wittig rearrangement. This rearrangement has been deeply studied, both experimentally and computationally, with aryl α‐lithiated benzyl ethers bearing different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron‐poor aryl groups that favor the anionic pathway. 相似文献
994.
Dr. Flávio Figueira Igor Marques Dr. Andreia S. F. Farinha Prof. Dr. Augusto C. Tomé Prof. Dr. José A. S. Cavaleiro Prof. Dr. Artur M. S. Silva Prof. Dr. Jonathan Sessler Prof. Dr. Vítor Félix Prof. Dr. João P. C. Tomé 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14349-14355
A novel sapphyrin derivative was obtained from the reaction between a free‐base sapphyrin and dimethyl acetylenedicarboxylate (DMAD). The formation of the new compound involved a double aza‐Michael addition of two pyrrolic NH groups to a DMAD molecule, with the formation of a disubstituted ethano bridge. The NMR spectral data reveal a product with an unsymmetrical structure; DFT calculations provided support for a structure in which the ethano bridge links two adjacent pyrrole units. The present study provides a seemingly unprecedented example of an N,N′‐dinucleophile reacting with DMAD to form a heterocyclic compound in which the two N‐atoms are linked to the two sp3 carbon atoms derived from a substituted acetylene. 相似文献
995.
João Medeiros‐Silva Deni Mance Mark Daniëls Shehrazade Jekhmane Dr. Klaartje Houben Prof. Marc Baldus Dr. Markus Weingarth 《Angewandte Chemie (International ed. in English)》2016,55(43):13606-13610
1H detection can significantly improve solid‐state NMR spectral sensitivity and thereby allows studying more complex proteins. However, the common prerequisite for 1H detection is the introduction of exchangeable protons in otherwise deuterated proteins, which has thus far significantly hampered studies of partly water‐inaccessible proteins, such as membrane proteins. Herein, we present an approach that enables high‐resolution 1H‐detected solid‐state NMR (ssNMR) studies of water‐inaccessible proteins, and that even works in highly complex environments such as cellular surfaces. In particular, the method was applied to study the K+ channel KcsA in liposomes and in situ in native bacterial cell membranes. We used our data for a dynamic analysis, and we show that the selectivity filter, which is responsible for ion conduction and highly conserved in K+ channels, undergoes pronounced molecular motion. We expect this approach to open new avenues for biomolecular ssNMR. 相似文献
996.
997.
Dr. Ernst‐Christian Koch Prof. Dr. Stanisław Cudziło 《Angewandte Chemie (International ed. in English)》2016,55(49):15439-15442
The potential of phosphorus(V) nitride, P3N5 , as a replacement for red phosphorus, PR, in pyrotechnic obscurants has been theoretically and experimentally investigated. P3N5 can be safely mixed with KNO3 and even KClO3 and KClO4 . The corresponding formulations are surprisingly insensitive to friction and only mildly impact‐sensitive. P3N5 /KNO3 pyrolants with ξ=20–80 wt % P3N5 burn 200 times faster than the corresponding mixtures based on PR and generate a dense smoke. Hence obscurants based on P3N5 /KNO3 have a figure of merit that by far exceeds that of current state‐of‐the‐art PR‐based obscurants. Furthermore, unlike PR, which slowly degrades in moist air to phosphoric acids and phosphine (PH3), P3N5 is stable under these conditions and does not produce any acids or PH3 . P3N5 is hence a safe, stable, and powerful replacement for PR for use in insensitive munitions. 相似文献
998.
A Variety of Phase‐Transition Behaviors in a Niccolite Series of [NH3(CH2)4NH3][M(HCOO)3]2 下载免费PDF全文
Ran Shang Sa Chen Ke‐Li Hu Prof. Bing‐Wu Wang Prof. Zhe‐Ming Wang Prof. Song Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6199-6203
A niccolite series of [bnH22+][M(HCOO)3]2 (bnH22+=1,4‐butyldiammonium) shows four kinds of metal‐dependent phase transitions, from high temperature para‐electric phases to low‐temperature ferro‐, antiferro‐, glass‐like, and para‐electric phases. The conformational flexibility of bnH22+ and the different size, mass, and bonding character of the metal ion lead to various disorder‐order transitions of bnH22+ in the lattice and relevant framework modulations, thus different phase transitions and dielectric responses. The magnetic members display a coexistence or combination of electric and magnetic orderings in the low‐temperature region. 相似文献
999.
Dr. Ondřej Jankovský Alena Libánská Daniel Bouša Prof. David Sedmidubský Dr. Stanislava Matějková Prof. Zdeněk Sofer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8627-8634
Partially hydrogenated graphene materials, synthesized by the chemical reduction/hydrogenation of two different graphene oxides using zinc powder in acidic environment or aluminum powder in alkaline environment, exhibit high electrocatalytic activities, as well as electrochemical sensing properties. The starting graphene oxides and the resultant hydrogenated graphenes were characterized in detail. Their electrocatalytic activity was examined in the oxygen reduction reaction, whereas sensing properties towards explosives were tested by using picric acid as a redox probe. Findings indicate that the high electrocatalytic performance originates not only from the hydrogenation of graphene, but also from unintentional contamination of graphene with manganese and other metals during synthesis. A careful evaluation of the obtained data and a detailed chemical analysis are necessary to identify the origin of this anomalous electrocatalytic activity. 相似文献
1000.
Matúš Durec Francesco Zaccaria Dr. Célia Fonseca Guerra Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10912-10922
Repetitive guanine‐rich nucleic acid sequences play a crucial role in maintaining genome stability and the cell life cycle and represent potential targets for regulatory drugs. Recently, it has been demonstrated that guanine‐based ligands with a porphyrin core can be used as markers of G‐quadruplex assemblies in cell tissues. Herein, model systems of guanine‐based ligands are explored by DFT methods. The energies of formation of modified guanine tetrads and those of modified tetrads stacked on the top of natural guanine tetrads have been calculated. The interaction energy has been decomposed into contributions from hydrogen bonding, stacking, and ion coordination and a twist–rise potential energy scan has been performed to find the individual local minima. Energy decomposition analysis reveals the impact of various substituents (F, Cl, Br, I, Me, NMe2) on individual energy terms. In addition, cooperative reinforcement in forming the modified and stacked tetrads, as well as the frontier orbitals participating in the hydrogen‐bonding framework involving the HOMO–LUMO gap between the occupied σHOMO on the proton‐accepting C=O and =N? groups and unoccupied σLUMO on the N?H groups, has been studied. The investigated systems are demonstrated to have a potential in ligand development, mainly due to stacking enhancement compared with natural guanine, which is used as a reference. 相似文献