全文获取类型
收费全文 | 2722篇 |
免费 | 69篇 |
国内免费 | 19篇 |
专业分类
化学 | 1828篇 |
晶体学 | 12篇 |
力学 | 67篇 |
数学 | 458篇 |
物理学 | 445篇 |
出版年
2023年 | 20篇 |
2022年 | 29篇 |
2021年 | 39篇 |
2020年 | 61篇 |
2019年 | 51篇 |
2018年 | 19篇 |
2017年 | 28篇 |
2016年 | 77篇 |
2015年 | 75篇 |
2014年 | 86篇 |
2013年 | 123篇 |
2012年 | 150篇 |
2011年 | 195篇 |
2010年 | 104篇 |
2009年 | 127篇 |
2008年 | 183篇 |
2007年 | 168篇 |
2006年 | 162篇 |
2005年 | 124篇 |
2004年 | 135篇 |
2003年 | 93篇 |
2002年 | 97篇 |
2001年 | 40篇 |
2000年 | 40篇 |
1999年 | 41篇 |
1998年 | 31篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 26篇 |
1994年 | 13篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 22篇 |
1985年 | 11篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 13篇 |
1972年 | 12篇 |
排序方式: 共有2810条查询结果,搜索用时 0 毫秒
71.
Christoph Peschel Stefan van Wickeren Yves Preibisch Verena Naber Denis Werner Lars Frankenstein Dr. Fabian Horsthemke Prof. Dr. Urs Peuker Prof. Dr. Martin Winter Dr. Sascha Nowak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(22):e202200485
Herein we report on an analytical study of dry-shredded lithium-ion battery (LIB) materials with unknown composition. Samples from an industrial recycling process were analyzed concerning the elemental composition and (organic) compound speciation. Deep understanding of the base material for LIB recycling was obtained by identification and analysis of transition metal stoichiometry, current collector metals, base electrolyte and electrolyte additive residues, aging marker molecules and polymer binder fingerprints. For reversed engineering purposes, the main electrode and electrolyte chemistries were traced back to pristine materials. Furthermore, possible lifetime application and accompanied aging was evaluated based on target analysis on characteristic molecules described in literature. With this, the reported analytics provided precious information for value estimation of the undefined spent batteries and enabled tailored recycling process deliberations. The comprehensive feedstock characterization shown in this work paves the way for targeted process control in LIB recycling processes. 相似文献
72.
Dr. Ramasamy Jayarajan Tautvydas Kireilis Prof. Lars Eriksson Prof. Kálmán J. Szabó 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202202059
A broad range of aliphatic, aromatic, and heterocyclic boronic acids were successfully homologated using trifluorodiazoethane in the presence of BINOL derivatives to provide the corresponding chiral trifluoromethyl containing boronic acid derivatives in high yields and excellent enantioselectivity. The in situ conversion of the chiral transient boronic acids to the corresponding alcohols or β-CF3 carboxylates are also demonstrated. 相似文献
73.
Kristina Westerlund Anders Myrhammar Hanna Tano Maxime Gestin Amelie Eriksson Karlstrm 《Molecules (Basel, Switzerland)》2021,26(10)
Natural backbone-cyclized proteins have an increased thermostability and resistance towards proteases, characteristics that have sparked interest in head-to-tail cyclization as a method to stability-enhance proteins used in diagnostics and therapeutic applications, for example. In this proof-of principle study, we have produced and investigated a head-to-tail cyclized and HER2-specific ZHER2:342 Affibody dimer. The sortase A-mediated cyclization reaction is highly efficient (>95%) under optimized conditions, and renders a cyclic ZHER3:342-dimer with an apparent melting temperature, Tm, of 68 °C, which is 3 °C higher than that of its linear counterpart. Circular dichroism spectra of the linear and cyclic dimers looked very similar in the far-UV range, both before and after thermal unfolding to 90 °C, which suggests that cyclization does not negatively impact the helicity or folding of the cyclic protein. The cyclic dimer had an apparent sub-nanomolar affinity (Kd ~750 pM) to the HER2-receptor, which is a ~150-fold reduction in affinity relative to the linear dimer (Kd ~5 pM), but the anti-HER2 Affibody dimer remained a high-affinity binder even after cyclization. No apparent difference in proteolytic stability was detected in an endopeptidase degradation assay for the cyclic and linear dimers. In contrast, in an exopeptidase degradation assay, the linear dimer was shown to be completely degraded after 5 min, while the cyclic dimer showed no detectable degradation even after 60 min. We further demonstrate that a site-specifically DyLight 594-labeled cyclic dimer shows specific binding to HER2-overexpressing cells. Taken together, the results presented here demonstrate that head-to-tail cyclization can be an effective strategy to increase the stability of an Affibody dimer. 相似文献
74.
Dominik Raiser Dr. Hartmut Schubert Prof. Dr. Holger F. Bettinger Prof. Dr. Lars Wesemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):1981-1983
Halide and phenyl substituted germaborenes were shown to react with azides at room temperature and transfer a borylene moiety to give iminoboranes. This iminoborane synthesis based on a borylene transfer route was investigated computationally in the case of the phenyl substituted germaborene. 相似文献
75.
Dr. Dominik Raiser Dr. Klaus Eichele Dr. Hartmut Schubert Prof. Dr. Lars Wesemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):14073-14080
The reaction of the intramolecular germylene-phosphine Lewis pair (o-PPh2)C6H4GeAr* ( 1 ) with Group 15 element trichlorides ECl3 (E=P, As, Sb) was investigated. After oxidative addition, the resulting compounds (o-PPh2)C6H4(Ar*)Ge(Cl)ECl2 ( 2 : E=P, 3 : E=As, 4 : E=Sb) were reduced by using sodium metal or LiHBEt3. The molecular structures of the phosphine-stabilized phosphinidene (o-PPh2)C6H4(Ar*)Ge(Cl)P ( 5 ), arsinidene (o-PPh2)C6H4(Ar*)Ge(Cl)As ( 6 ) and stibinidene (o-PPh2)C6H4(Ar*)Ge(Cl)Sb ( 7 ) are presented; they feature a two-coordinate low-valent Group 15 element. After chloride abstraction, a cyclic germaphosphene [(o-PPh2)C6H4(Ar*)GeP] [B(C6H3(CF3)2)4] ( 8 ) was isolated. The 31P NMR data of the germaphosphene were compared with literature examples and analyzed by quantum chemical calculations. The phosphinidene was treated with [iBu2AlH]2, and the product of an Al−H addition to the low-valent phosphorus atom (o-PPh2)C6H4(Ar*)Ge(H)P(H)Al(C4H9)2 ( 9 ) was characterized. 相似文献
76.
The La0.6Sr0.4Co0.2Fe0.8O3 (LSCF48) cathode material was used as a protective-conducting coating on an interconnect made of Crofer 22 APU ferritic steel intended for application in intermediate-temperature solid oxide fuel cell (IT-SOFC) stacks. The LSCF48 coating was deposited on the surface of the steel via screen-printing followed by appropriate thermal treatment. The oxidation kinetics of the Crofer 22 APU steel—uncoated and coated with LSCF48—approximately obeys the parabolic rate law in air at 1,073 K under isothermal and cyclic oxidation conditions. The oxidation rate for uncoated steel is higher than that for coated steel. SEM–EDS and XRD investigations showed that the LSCF48 coating interacts with the steel during long-term oxidation in the afore-mentioned thermal conditions, and an intermediate multilayer interfacial zone is formed. This intermediate layer leads to lower area specific resistance in air at 1,073 K in comparison to the Crofer 22 APU steel without surface modification. 相似文献
77.
Eduard Hryha Henrik Borgström Karin Sterky Lars Nyborg 《Journal of Thermal Analysis and Calorimetry》2014,118(2):695-704
Binders present an important part of the powder metallurgy technology as they are vital to provide efficient powder agglomeration and/or lubrication during shaping. At the same time, they have to be easily removed from the compacts during initial stages of sintering without any harmful effect for the base material, as well as for the environment. Therefore, behavior of gelatin as a binder for stainless- and tool-steel gas-atomised powder compacts was studied by thermal analysis and electron microscopy. Thermal analysis showed that peak mass-loss occurred in the range between 340 and 370 °C, depending on the base powder and heating rate. Risk for base powder oxidation at temperatures below 425 °C was detected. Based on the obtained results, it is recommended to perform debinding at ~425 °C after applying a heating rate of around 7.5 °C min?1. Only in this way efficient enough binder removal can be obtained concurrently to avoiding base powder oxidation. 相似文献
78.
Andrew Marais Mikael S. Magnusson Thomas Joffre Erik L. G. Wernersson Lars Wågberg 《Cellulose (London, England)》2014,21(6):3941-3950
Polyelectrolytes have been used extensively in the papermaking industry for various purposes. Although recent studies have shown that polyamines can be efficient dry-strength additives, the mechanism governing the strength enhancement of paper materials following the adsorption of polyamines onto pulp fibres is still not well understood. In this study, the effect of the adsorption of polyallylamine hydrochloride (PAH) onto the surface of unbleached kraft pulp fibres was investigated on both the fibre and the network scale. Isolated fibre crosses were mechanically tested to evaluate the impact of the chemical additive on the interfibre joint strength on the microscopic scale and the effect was compared with that previously observed on the paper sheet scale. X-ray microtomography was used to understand structural changes in the fibrous network following the adsorption of a polyamine such as PAH. Using image analysis methods, it was possible to determine the number of interfibre contacts (or joints) per unit length of fibre as well as the average interfibre joint contact area. The results showed that the median interfibre joint strength increased by 18 % upon adsorption of PAH. This can be achieved both by a larger molecular contact area in the contact zones and by a stronger molecular adhesion. The addition of the polymer also increased the number of efficient interfibre contacts per sheet volume. This combination of effects is the reason why polyamines such as PAH can increase the dry tensile strength of paper materials. 相似文献
79.
Lars Müller Santina Hoof Matthias Keck Christian Herwig Prof. Dr. Christian Limberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(51):11851-11861
The design of biomimetic model complexes for the cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO) is reported, where the 3-His coordination of the iron ion is simulated by three pyrazole donors of a trispyrazolyl borate ligand (Tp) and protected cysteine and cysteamine represent substrate ligands. It is found that the replacement of phenyl groups—attached at the 3-positions of the pyrazole units in a previous model—by mesityl residues has massive consequences, as the latter arrange to a more spacious reaction pocket. Thus, the reaction with O2 proceeds much faster and afterwards the first structural characterization of an iron(II) η2-O,O-sulfinate product became possible. If one of the three Tp-mesityl groups is placed in the 5-position, an even larger reaction pocket results, which leads to yet faster rates and accumulation of a reaction intermediate at low temperatures, as shown by UV/Vis and Mössbauer spectroscopy. After comparison with the results of investigations on the cobalt analogues this intermediate is tentatively assigned to an iron(III) superoxide species. 相似文献
80.
Long Yang Ralf Steinbock Alexej Scheremetjew Rositha Kuniyil Lars H. Finger Antonis M. Messinis Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2020,59(27):11130-11135
A ruthenium‐catalyzed electrochemical dehydrogenative annulation reaction of imidazoles with alkynes has been established, enabling the preparation of various bridgehead N‐fused [5,6]‐bicyclic heteroarenes through regioselective electrochemical C?H/N?H annulation without chemical metal oxidants. Novel azaruthenabicyclo[3.2.0]heptadienes were fully characterized and identified as key intermediates. Mechanistic studies are suggestive of an oxidatively induced reductive elimination pathway within a ruthenium(II/III) regime. 相似文献