全文获取类型
收费全文 | 16046篇 |
免费 | 625篇 |
国内免费 | 140篇 |
专业分类
化学 | 10838篇 |
晶体学 | 103篇 |
力学 | 435篇 |
数学 | 2755篇 |
物理学 | 2680篇 |
出版年
2023年 | 140篇 |
2022年 | 255篇 |
2021年 | 330篇 |
2020年 | 402篇 |
2019年 | 386篇 |
2018年 | 256篇 |
2017年 | 224篇 |
2016年 | 606篇 |
2015年 | 478篇 |
2014年 | 566篇 |
2013年 | 869篇 |
2012年 | 1123篇 |
2011年 | 1315篇 |
2010年 | 675篇 |
2009年 | 584篇 |
2008年 | 987篇 |
2007年 | 942篇 |
2006年 | 934篇 |
2005年 | 837篇 |
2004年 | 726篇 |
2003年 | 504篇 |
2002年 | 521篇 |
2001年 | 177篇 |
2000年 | 146篇 |
1999年 | 150篇 |
1998年 | 118篇 |
1997年 | 129篇 |
1996年 | 170篇 |
1995年 | 106篇 |
1994年 | 112篇 |
1993年 | 120篇 |
1992年 | 86篇 |
1991年 | 93篇 |
1990年 | 71篇 |
1989年 | 72篇 |
1988年 | 84篇 |
1987年 | 72篇 |
1986年 | 67篇 |
1985年 | 99篇 |
1984年 | 105篇 |
1982年 | 115篇 |
1981年 | 122篇 |
1980年 | 97篇 |
1979年 | 84篇 |
1978年 | 113篇 |
1977年 | 92篇 |
1976年 | 73篇 |
1975年 | 71篇 |
1974年 | 64篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
A Tin Analogue of Carbenoid: Isolation and Reactivity of a Lithium Bis(imidazolin‐2‐imino)stannylenoid 下载免费PDF全文
Tatsumi Ochiai Dr. Daniel Franz Dr. Xiao‐Nan Wu Dr. Elisabeth Irran Prof. Dr. Shigeyoshi Inoue 《Angewandte Chemie (International ed. in English)》2016,55(24):6983-6987
The lithium bis(imino)stannylenoid (NIPr)2Sn(Li)Cl ( 1 ; NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) was prepared by the reaction of LiNIPr with 0.5 equiv of SnCl2?diox (diox=1,4‐dioxane) and the ambiphilic character of the compound was demonstrated by investigations into its reactivity. Treatment of 1 with I2 or MeI yielded the oxidative addition products (NIPr)2SnI2 and (NIPr)2Sn(Me)I, respectively. In contrast, the reaction of 1 with one equivalent of Me3SiCl resulted in the formation of Me3SiNIPr and the chlorostannylene dimer [NIPrSnCl]2. Moreover, the substitution reaction of compound 1 with MeLi led to the formation of the methyl‐substituted stannate (NIPr)2Sn(Li)Me. 相似文献
972.
Coordination Chemistry of Diiodine and Implications for the Oxidation Capacity of the Synergistic Ag+/X2 (X=Cl,Br, I) System 下载免费PDF全文
Dr. Przemysław J. Malinowski Dr. Daniel Himmel Prof. Dr. Ingo Krossing 《Angewandte Chemie (International ed. in English)》2016,55(32):9262-9266
The synergistic Ag+/X2 system (X=Cl, Br, I) is a very strong, but ill‐defined oxidant—more powerful than X2 or Ag+ alone. Intermediates for its action may include [Agm(X2)n]m+ complexes. Here, we report on an unexpectedly variable coordination chemistry of diiodine towards this direction: ( A )Ag‐I2‐Ag( A ), [Ag2(I2)4]2+( A ?)2 and [Ag2(I2)6]2+( A ?)2?(I2)x≈0.65 form by reaction of Ag( A ) ( A =Al(ORF)4; RF=C(CF3)3) with diiodine (single crystal/powder XRD, Raman spectra and quantum‐mechanical calculations). The molecular ( A )Ag‐I2‐Ag( A ) is ideally set up to act as a 2 e? oxidant with stoichiometric formation of 2 AgI and 2 A ?. Preliminary reactivity tests proved this ( A )Ag‐I2‐Ag( A ) starting material to oxidize n‐C5H12, C3H8, CH2Cl2, P4 or S8 at room temperature. A rough estimate of its electron affinity places it amongst very strong oxidizers like MF6 (M=4d metals). This suggests that ( A )Ag‐I2‐Ag( A ) will serve as an easily in bulk accessible, well‐defined, and very potent oxidant with multiple applications. 相似文献
973.
Nicolas Tielker Daniel Tomazic Jochen Heil Thomas Kloss Sebastian Ehrhart Stefan Güssregen K. Friedemann Schmidt Stefan M. Kast 《Journal of computer-aided molecular design》2016,30(11):1035-1044
We predict cyclohexane–water distribution coefficients (log D 7.4) for drug-like molecules taken from the SAMPL5 blind prediction challenge by the “embedded cluster reference interaction site model” (EC-RISM) integral equation theory. This task involves the coupled problem of predicting both partition coefficients (log P) of neutral species between the solvents and aqueous acidity constants (pK a) in order to account for a change of protonation states. The first issue is addressed by calibrating an EC-RISM-based model for solvation free energies derived from the “Minnesota Solvation Database” (MNSOL) for both water and cyclohexane utilizing a correction based on the partial molar volume, yielding a root mean square error (RMSE) of 2.4 kcal mol?1 for water and 0.8–0.9 kcal mol?1 for cyclohexane depending on the parametrization. The second one is treated by employing on one hand an empirical pK a model (MoKa) and, on the other hand, an EC-RISM-derived regression of published acidity constants (RMSE of 1.5 for a single model covering acids and bases). In total, at most 8 adjustable parameters are necessary (2–3 for each solvent and two for the pK a) for training solvation and acidity models. Applying the final models to the log D 7.4 dataset corresponds to evaluating an independent test set comprising other, composite observables, yielding, for different cyclohexane parametrizations, 2.0–2.1 for the RMSE with the first and 2.2–2.8 with the combined first and second SAMPL5 data set batches. Notably, a pure log P model (assuming neutral species only) performs statistically similarly for these particular compounds. The nature of the approximations and possible perspectives for future developments are discussed. 相似文献
974.
Maheshkumar Prakash Patil Ashish Anirudh Rokade Daniel Ngabire Gun-Do Kim 《Journal of Cluster Science》2016,27(5):1737-1750
The green synthesis of silver nanoparticles (AgNPs) has been proposed as a simple, eco-friendly and cost effective alternative to chemical and physical methods. The Rhus chinensis plant is one of the well studied medicinal plant and its galls find excellent clinical and therapeutic applications. The present study reports the use of water extract from galls of R. chinensis as a reducing agent and formation of AgNPs from silver nitrate solution by a green synthesis route. The AgNPs formation was observed visually by color change and the absorbance peak at 450 nm was observed by UV–Visible spectrophotometer. The shape, size, and morphology of synthesized AgNPs were monitored by transmission electron microscopy and field-emission scanning electron microscopy. The face centered cubic structure of AgNPs was confirmed by X-ray diffraction pattern and element composition by energy dispersive X-ray analysis. The Fourier transform infrared spectroscopy spectrum revealed that the presence of components acts as a reducing and capping agent. The antibacterial activity was performed using the agar well diffusion method. Minimum inhibitory concentration and minimum bactericidal concentration were determined by broth dilution and spread plate method respectively. Synthesized nanoparticles were spotted as triangular and hexagonal shape and the particle size was around 150 nm. 相似文献
975.
Engineering a Chemical Switch into the Light‐driven Proton Pump Proteorhodopsin by Cysteine Mutagenesis and Thiol Modification 下载免费PDF全文
Dr. Daniel Harder Stephan Hirschi Zöhre Ucurum Roland Goers Prof. Dr. Wolfgang Meier Prof. Dr. Daniel J. Müller Prof. Dr. Dimitrios Fotiadis 《Angewandte Chemie (International ed. in English)》2016,55(31):8846-8849
For applications in synthetic biology, for example, the bottom‐up assembly of biomolecular nanofactories, modules of specific and controllable functionalities are essential. Of fundamental importance in such systems are energizing modules, which are able to establish an electrochemical gradient across a vesicular membrane as an energy source for powering other modules. Light‐driven proton pumps like proteorhodopsin (PR) are excellent candidates for efficient energy conversion. We have extended the versatility of PR by implementing an on/off switch based on reversible chemical modification of a site‐specifically introduced cysteine residue. The position of this cysteine residue in PR was identified by structure‐based cysteine mutagenesis combined with a proton‐pumping assay using E. coli cells overexpressing PR and PR proteoliposomes. The identified PR mutant represents the first light‐driven proton pump that can be chemically switched on/off depending on the requirements of the molecular system. 相似文献
976.
977.
Dr. Marco Taddei Daniel Antti Steitz Prof. Dr. Jeroen Anton van Bokhoven Dr. Marco Ranocchiari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3245-3249
Metal–organic frameworks are having a tremendous impact on novel strategic applications, with prospective employment in industrially relevant processes. The development of such processes is strictly dependent on the ability to generate materials with high yield efficiency and production rate. We report a versatile and highly efficient method for synthesis of metal–organic frameworks in large quantities using continuous flow processing under microwave irradiation. Benchmark materials such as UiO‐66, MIL‐53(Al), and HKUST‐1 were obtained with remarkable mass, space–time yields, and often using stoichiometric amounts of reactants. In the case of UiO‐66 and MIL‐53(Al), we attained unprecedented space–time yields far greater than those reported previously. All of the syntheses were successfully extended to multi‐gram high quality products in a matter of minutes, proving the effectiveness of continuous flow microwave technology for the large scale production of metal–organic frameworks. 相似文献
978.
Exploring Coordination Modes: Late Transition Metal Complexes with a Methylene‐bridged Macrocyclic Tetra‐NHC Ligand 下载免费PDF全文
Philipp J. Altmann Dr. Daniel T. Weiss Christian Jandl Prof. Dr. Fritz E. Kühn 《化学:亚洲杂志》2016,11(10):1597-1605
A tetranuclear silver(I) N‐heterocyclic carbene (NHC) complex bearing a macrocyclic, exclusively methylene‐bridged, tetracarbene ligand was synthesized and employed as transmetalation agent for the synthesis of nickel(II), palladium(II), platinum(II), and gold(I) derivatives. The transition metal complexes exhibit different coordination geometries, the coinage metals being bound in a linear fashion forming molecular box‐type complexes, whereas the group 10 metals adapt an almost ideal square planar coordination geometry within the ligand's cavity, resulting in saddle‐shaped complexes. Both the AgI and the AuI complexes show ligand‐induced metal–metal contacts, causing photoluminescence in the blue region for the gold complex. Distinct metal‐dependent differences of the coordination behavior between the group 10 transition metals were elucidated by low‐temperature NMR spectroscopy and DFT calculations. 相似文献
979.
Dr. Lukiana L. Anka‐Lufford Kierra M. M. Huihui Dr. Nicholas J. Gower Dr. Laura K. G. Ackerman Prof. Dr. Daniel J. Weix 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11564-11567
Cross‐electrophile coupling of aryl halides with alkyl halides has thus far been primarily conducted with stoichiometric metallic reductants in amide solvents. This report demonstrates that the use of tetrakis(dimethylamino)ethylene (TDAE) as an organic reductant enables the use of non‐amide solvents, such as acetonitrile or propylene oxide, for the coupling of benzyl chlorides and alkyl iodides with aryl halides. Furthermore, these conditions work for several electron‐poor heterocycles that are easily reduced by manganese. Finally, we demonstrate that TDAE addition can be used as a control element to ‘hold’ a reaction without diminishing yield or catalyst activity. 相似文献
980.
On the Ambiphilic Reactivity of Geometrically Constrained Phosphorus(III) and Arsenic(III) Compounds: Insights into Their Interaction with Ionic Substrates 下载免费PDF全文
Thomas P. Robinson Siu‐Kwan Lo Daniel De Rosa Simon Aldridge Jose M. Goicoechea 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15712-15724
The ambiphilic nature of geometrically constrained Group 15 complexes bearing the N,N‐bis(3,5‐di‐tert‐butyl‐2‐phenolate)amide pincer ligand (ONO3?) is explored. Despite their differing reactivity towards nucleophilic substrates with polarised element–hydrogen bonds (e.g., NH3), both the phosphorus(III), P(ONO) ( 1 a ), and arsenic(III), As(ONO) ( 1 b ), compounds exhibit similar reactivity towards charged nucleophiles and electrophiles. Reactions of 1 a and 1 b with KOtBu or KNPh2 afford anionic complexes in which the nucleophilic anion associates with the pnictogen centre ([(tBuO)Pn(ONO)]? (Pn=P ( 2 a ), As ( 2 b )) and [(Ph2N)Pn(ONO)]? (Pn=P ( 3 a ), As ( 3 b )). Compound 2 a can subsequently be reacted with a proton source or benzylbromide to afford the phosphorus(V) compounds (tBuO)HP(ONO) ( 4 a ) and (tBuO)BzP(ONO) ( 5 a ), respectively, whereas analogous arsenic(V) compounds are inaccessible. Electrophilic substrates, such as HOTf and MeOTf, preferentially associate with the nitrogen atom of the ligand backbone of both 1 a and 1 b , giving rise to cationic species that can be rationalised as either ammonium salts or as amine‐stabilised phosphenium or arsenium complexes ([Pn{ON(H)O}]+ (Pn=P ( 6 a ), As ( 6 b )) and [Pn{ON(Me)O}]+ (Pn=P ( 7 a ), As ( 7 b )). Reaction of 1 a with an acid bearing a nucleophilic counteranion (such as HCl) gives rise to a phosphorus(V) compound HPCl(ONO) ( 8 a ), whereas the analogous reaction with 1 b results in the addition of HCl across one of the As?O bonds to afford ClAs{(H)ONO} ( 8 b ). Functionalisation at both the pnictogen centre and the ligand backbone is also possible by reaction of 7 a / 7 b with KOtBu, which affords the neutral species (tBuO)Pn{ON(Me)O} (Pn=P ( 9 a ), As ( 9 b )). The ambiphilic reactivity of these geometrically constrained complexes allows some insight into the mechanism of reactivity of 1 a towards small molecules, such as ammonia and water. 相似文献