全文获取类型
收费全文 | 3093篇 |
免费 | 134篇 |
国内免费 | 112篇 |
专业分类
化学 | 2223篇 |
力学 | 32篇 |
数学 | 131篇 |
物理学 | 627篇 |
综合类 | 326篇 |
出版年
2024年 | 23篇 |
2023年 | 63篇 |
2022年 | 95篇 |
2021年 | 56篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 35篇 |
2017年 | 26篇 |
2016年 | 32篇 |
2015年 | 29篇 |
2014年 | 59篇 |
2013年 | 28篇 |
2012年 | 386篇 |
2011年 | 466篇 |
2010年 | 93篇 |
2009年 | 38篇 |
2008年 | 308篇 |
2007年 | 306篇 |
2006年 | 272篇 |
2005年 | 227篇 |
2004年 | 152篇 |
2003年 | 110篇 |
2002年 | 86篇 |
2001年 | 57篇 |
2000年 | 56篇 |
1999年 | 34篇 |
1998年 | 20篇 |
1997年 | 5篇 |
1996年 | 19篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 39篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
排序方式: 共有3339条查询结果,搜索用时 0 毫秒
71.
Our struggles and ultimate success in achieving a total synthesis of phomactin A are described. Our strategy features an intramolecular oxa-[3 + 3] annulation to construct its unique ABD-tricyclic manifold. Although the synthesis would constitute a distinctly new approach with the 12-membered D-ring of phomactin A being assembled simultaneously with the 1-oxadecalin at an early stage, the ABD-tricycle represents a unique structural topology that would pose a number of unprecedented challenges. One challenge concerned elaborating this tricycle to have oxygenation at the proper carbon atoms. To overcome this, we would utilize a Kornblum-DeLaMare ring-opening of a peroxide bridge as well as a challenging late-stage 1,3-allylic alcohol transposition. Further, the structural intricacies of the ABD-tricycle were uncovered by a conformational analysis that would be critical for the C5a-homologation. 相似文献
72.
To elucidate (i) the physicochemical properties of the {(η(5)-C(5)Me(5))[Ta(IV)](i-Pr)C(Me)N(i-Pr)}(2)(μ-η(1):η(1)-N(2)), I, [Ta(IV)](2)(μ-η(1):η(1)-N(2)), and {(η(5)-C(5)Me(5))[Ta(V)](i-Pr)C(Me)N(i-Pr)}(2)(μ-N)(2), II, [Ta(V)](2)(μ-N)(2), complexes; (ii) the mechanism of the I → II isomerization; and (iii) the reaction mechanism of these complexes with an H(2) molecule, we launched density functional (B3LYP) studies of model systems 1, 2, and 3 where the C(5)Me(5) and (i-Pr)C(Me)N(i-Pr) ligands of I (or II) were replaced by C(5)H(5) and HC(NCH(3))(2), respectively. These calculations show that the lower-lying electronic states of 1, [Ta(IV)](2)(μ-η(1):η(1)-N(2)), are nearly degenerate open-shell singlet and triplet states with two unpaired electrons located on the Ta centers. This finding is in reasonable agreement with experiments [J. Am Chem. Soc. 2007, 129, 9284-9285] showing easy accessibility of paramagnetic and diamagnetic states of I. The ground electronic state of the bis(μ-nitrido) complex 2, [Ta(V)](2)(μ-N)(2), is a closed-shell singlet state in agreement with the experimentally reported diamagnetic feature of II. The 1-to-2 rearrangement is a multistep and highly exothermic process. It occurs with a maximum of 28.7 kcal/mol free energy barrier required for the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(2)-N(2)) transformation step. Reaction of 1 with H(2) leading to the 1,4-addition product 3 proceeds with a maximum of 24.2 kcal/mol free energy barrier associated by the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The overall reaction 1 + H(2) → 3 is exothermic by 20.0 kcal/mol. Thus, the addition of H(2) to 1 is kinetically and thermodynamically feasible and proceeds via the rate-determining (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The bis(μ-nitrido) complex 2, [Ta(V)](2)(μ-N)(2), does not react with H(2) because of the large energy barrier (49.5 kcal/mol) and high endothermicity of the reaction. This conclusion is also in excellent agreement with the experimental observation [J. Am Chem. Soc. 2007, 129, 9284-9285]. 相似文献
73.
Liu Q Lu W Ma A Tang J Lin J Fang J 《Journal of the American Chemical Society》2005,127(15):5276-5277
In this communication, we report a successful synthesis of quasi-monodisperse In2O3 nanocrystals with high crystallinity in a high-temperature organic solution. The average size of nanocrystals can be tuned using a dynamic injection technique. TEM and XRD investigations indicate that each nanocrystal is a single crystal. The optical determination implies that the photoluminescence behavior of these In2O3 nanocrystals is different from that of the bulk, probably due to the combination of weak quantum-confinement-effects and the nature of high crystallinity in nanocrystals. 相似文献
74.
A sensitive and facile quartz crystal microbalance (QCM) biosensor for glucose detection in biological fluids was developed by means of a displacement-type assay mode between glucose and its analogy dextran for concanavalin A (ConA) binding sites on a graphene-based sensing platform. To construct such a displacement-based sensor, phenoxy-derived dextran (DexP) molecules were initially assembled onto the surface of graphene-coated QCM probe via π-π stacking interaction, and ConA molecules were then immobilized on the dextran through the dextran-ConA interaction. Upon addition of glucose, the analyte competed with the dextran for the ConA, and displaced it from the QCM probe, leading to a change in the frequency. Under optimal conditions, the frequency change relative to the basic resonant frequency was proportional to glucose concentration, and exhibited a dynamic range from 0.01 to 7.5 mM with a low detection limit (LOD) of 5.0 μM glucose (at 3σ). The relative standard deviations (RSDs) were below 6.2% and 9.0% for the reproducibility and selectivity of the QCM glucose sensors, respectively. In addition, the assay system was evaluated with glucose spiking samples into the distilled water and blank cattle serum, receiving in excellent correlation with the referenced values. 相似文献
75.
A facile one-pot method to high-quality Ag-graphene composite nanosheets for efficient surface-enhanced Raman scattering 总被引:2,自引:0,他引:2
Zhang Z Xu F Yang W Guo M Wang X Zhang B Tang J 《Chemical communications (Cambridge, England)》2011,47(22):6440-6442
Ag-graphene composite nanosheets (AGCN) with adjustable size and well-controlled densities of Ag nanoparticles (Ag NPs) using Poly(N-vinyl-2-pyrrolidone) (PVP) as a reductant and stabilizer are reported. The obtained AGCN substrate is extremely suitable for surface-enhanced Raman spectroscopy (SERS). 相似文献
76.
A novel approach towards 7b-aryl-indeno[1,2,3-jk]fluorene based on a nitrogen-containing core is reported. The acid-promoted Friedel-Crafts reaction of 9-(2-bromophenyl)-9-fluorenol with carbazole, triphenylamine or triindole afforded 9-(2-bromophenyl)fluorenyl-carbazole, -triphenylamine and -triindole derivatives, which were subsequently converted to 7b-aryl-fluoradenes via palladium-catalyzed intramolecular C-H direct arylation as a key step. 相似文献
77.
Baocai Du Renyong Geng Wenliang Tan Yuchao Mao Donghui Li Xue Zhang Dan Liu Weihua Tang Wenchao Huang Tao Wang 《Journal of Energy Chemistry》2021,(3):131-137
Molecular ordering within the photoactive layer plays a crucial role in determining the device performance of organic solar cells(OSCs).However,the simultaneous molecular ordering processes of polymer donors and non-fullerene acceptors(NFAs)during solution casting usually bring confinement effect,leading to insufficient structural order of photovoltaic components.Herein,the molecular packing of mINPOIC NFA is effectively formed through a heating induced aggregation strategy,with the aggregation of PBDB-T,which has a strong temperature dependence,is retarded by casting on a preheated substrate to reduce its interference toward m-INPOIC.A sequent thermal annealing treatment is then applied to promote the ordering of PBDB-T and achieve balanced aggregation of both donors and acceptors,resulting in the achievement of a maximum efficiency of 13.9% of PBDB-T:m-INPOIC binary OSCs.This work disentangles the interactions of donor polymer and NFA during the solution casting process and develops a rational strategy to enhance the molecular packing of NFAs to boost device performance. 相似文献
78.
Lianyi Shao Shige Wang Fangdan W u Xiaoyan Shi Zhipeng Sun Yuxin Tang 《Journal of Energy Chemistry》2021,(3):138-142
High-performance materials are the key to developing new alternative energy-storage systems[1-4].Sodium ion batteries(SIBs)are regarded as the promising large-scale electric energy storage owing to the high abundance and low cost of sodium resources[1,5-9].However,the sluggish kinetics of Na+caused by the large-sized Na+(1.02A)result in the lower energy density and unsatisfactory electrochemical properties[10-14]. 相似文献
79.
A protein array for cell detection was fabricated by spotting different antibodies on modified glass slides. Glass slides were modified to allow antibodies to be immobilized on it and to selectively bind antigens. Antibodies were specially selected with the cells to be detected as targets, which permitted target cells in samples to bind specifically to the array with little nonspecific binding. Results can be obtained by directly putting the samples onto the array for 1 h or a little longer to let the cells specifically interact with the antibodies. After washing the unbound samples away, images were observed with a microscope and captured with a CCD camera. The assessment of antibody-cell binding was evaluated by capturing red blood cells (RBCs) in human blood with blood group antibodies (anti-A and anti-B). Blood group antibodies were spotted on the modified glass slide and kept at 4<.deg> degrees C overnight for immobilization. Human blood samples diluted to different concentrations were used to examine the sensitivity and specificity of the method. 相似文献
80.
Liu B Yang Y Cui D Tang T Chen X Jing X 《Dalton transactions (Cambridge, England : 2003)》2007,(38):4252-4254
A lutetium bis(alkyl) complex stabilized by a flexible amino-phosphine ligand LLu(CH(2)Si(CH(3))(3))(2)(THF) (L = (2,6-C(6)H(3)(CH(3))(2))NCH(C(6)H(5))CH(2)P(C(6)H(5))(2)) was prepared which upon insertion of N,N'-diisopropylcarbodiimide led to C-H activation via metalation of the ligand aryl methyl followed by reduction of the C[double bond, length as m-dash]N double bond. 相似文献