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971.
972.
Zhang AH Jiang N Gu W Ma J Wang YR Song YC Tan RX 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14479-14485
(-)-Alternarlactam [(-)-1], a new promising cytotoxin against two human cancer cell lines, was isolated from an endophyte culture and synthesized (along with (+)-1) from readily available starting materials. The absolute configuration, chirality-activity relevance and self-aggregation of (-)-1 were assigned by a combination of synthetic, spectroscopic and computational approaches. The full characterization of the new fungal cytotoxin may provide valuable information in the discovery of new antitumor agents. 相似文献
973.
Chao Zhao Konggang Qu Yujun Song Can Xu Jinsong Ren Prof. Xiaogang Qu Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(27):8147-8154
Here we report a reusable DNA single‐walled carbon nanotube (SWNT)‐based fluorescent sensor for highly sensitive and selective detection of Ag+ and cysteine (Cys) in aqueous solution. SWNTs can effectively quench the fluorescence of dye‐labeled single‐stranded DNA due to their strong π–π stacking interactions. However, upon incubation with Ag+, Ag+ can induce stable duplex formation mediated by C–Ag+–C (C=cytosine) coordination chemistry, which has been further confirmed by DNA melting studies. This weakens the interactions between DNA and SWNTs, and thus activates the sensor fluorescence. On the other hand, because Cys is a strong Ag+ binder, it can remove Ag+ from C–Ag+–C base pairs and deactivates the sensor fluorescence by rewrapping the dye‐labeled oligonucleotides around the SWNT. In this way, the fluorescence signal‐on and signal‐off of a DNA/SWNT sensor can be used to detect aqueous Ag+ and Cys, respectively. This sensing platform exhibits high sensitivity and selectivity toward Ag+ and Cys versus other metal ions and the other 19 natural amino acids, with a limit of detection of 1 nM for Ag+ and 9.5 nM for Cys. Based on these results, we have constructed a reusable fluorescent sensor by using the covalent‐linked SWNT–DNA conjugates according to the same sensing mechanism. There is no report on the use of SWNT–DNA assays for the detection of Ag+ and Cys. This assay is simple, effective, and reusable, and can in principle be used to detect other metal ions by substituting C–C base pairs with other native or artificial bases that selectively bind to other metal ions. 相似文献
974.
Fan Xia Dr. Xu Hou Liuxuan Cao Lin Wang Jianming Xue Prof. Guangzhao Zhang Prof. Yanlin Song Prof. Daoben Zhu Prof. Yugang Wang Prof. Lei Jiang Prof. 《Chemphyschem》2010,11(4):859-864
Herein we demonstrate a fully abiotic smart single‐nanopore device that rectifies ionic current in response to the temperature. The temperature‐responsive nanopore ionic rectifier can be switched between a rectifying state below 34 °C and a non‐rectifying state above 38 °C actuated by the phase transition of the poly(N‐isopropylacrylamide) [PNIPAM] brushes. On the rectifying state, the rectifying efficiency can be enhanced by the dehydration of the attached PNIPAM brushes below the LCST. When the PNIPAM brushes have sufficiently collapsed, the nanopore switches to the non‐rectifying state. The concept of the temperature‐responsive current rectification in chemically‐modified nanopores paves a new way for controlling the preferential direction of the ion transport in nanofluidics by modulating the temperature, which has the potential to build novel nanomachines with smart fluidic communication functions for future lab‐on‐chip devices. 相似文献
975.
976.
Zhishan Su Dr. Song Qin Dr. Changwei Hu Prof. Dr. Xiaoming Feng Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4359-4367
The mechanism of the hetero‐Diels–Alder reactions of Brassard’s diene and 1,3‐butadiene catalyzed by a titanium(IV) complex of a tridentate Schiff base was investigated by DFT and ONIOM methods. The calculations indicate that the mechanism of the reaction is closely related to the nucleophilicity–electrophilicity between diene and carbonyl substrates. A stepwise pathway is adopted for Brassard’s diene, and the step corresponding to the formation of the C? C bond is predicted to be the rate‐determining step with a free‐energy barrier of 8.4 kcal mol?1. For 1,3‐butadiene, the reaction takes place along a one‐step, two‐stage pathway with a free‐energy barrier of 14.9 kcal mol?1. For Brassard’s diene as substrate, the OCH3 and OSi(CH3)3 substituents may play a key role in the formation of the transition state and zwitterionic intermediate by participating in charge transfer from Brassard’s diene to formaldehyde. The combination of the phenyl groups at the amino alcohol moiety and the ortho‐tert‐butyl group of the salicylaldehyde moiety in the chiral tridentate Schiff base ligand plays an important role in the control of the stereoselectivity, which is in agreement with experimental observations. 相似文献
977.
Sun Hwa Lee Li Xu Dr. Byeong Kwon Park Yuri V. Mironov Dr. Soo Hyun Kim Young Ju Song Cheal Kim Prof. Dr. Youngmee Kim Dr. Sung‐Jin Kim Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4678-4685
Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H2O}4Re4Q4(CN)12]?4 CH3OH? 8 H2O (saloph=N,N′‐o‐phenylenebis(salicylidenaminato), Q=Se ( 1 ‐Se), Te ( 2 ‐Te)), have been synthesized by the diffusion of a methanolic solution of [PPh4]4[Re4Q4(CN)12] into a methanolic solution of [Mn(saloph)]+. The structure of 2 ‐Te has been determined by X‐ray crystallography. These rhenium cluster‐supported [MnIII(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta‐chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants MnV?O, MnIV?O, and MnIII? OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H218O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of MnV?O, MnIV?O, and MnIII? OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts. 相似文献
978.
Three pyridyl functionalized bis(pyrazol‐1‐yl)methanes, namely 2‐[(4‐pyridyl)methoxyphenyl] bis(pyrazol‐1‐yl)methane (L1), 2‐[(4‐pyridyl)methoxyphenyl]bis(3,5‐dimethylpyrazol‐1‐yl)methane (L2) and 2‐[(3‐pyridyl)methoxyphenyl]bis(pyrazol‐1‐yl)methane (L3) have been synthesized by the reactions of (2‐hydroxyphenyl)bis(pyrazol‐1‐yl)methanes with chloromethylpyridine. Treatment of these three ligands with R2SnCl2 (R = Et, n‐Bu or Ph) yields a series of symmetric 2:1 adducts of (L)2SnR2Cl2 (L = L1, L2 or L3), which have been confirmed by elemental analysis and NMR spectroscopy. The crystal structures of (L2)2Sn(n‐Bu)2Cl2·0.5C6H14 and (L3)2SnEt2Cl2 determined by X‐ray crystallography show that the functionalized bis(pyrazol‐1‐yl)methane acts as a monodentate ligand through the pyridyl nitrogen atom, and the pyrazolyl nitrogen atoms do not coordinate to the tin atom. The cytotoxic activity of these complexes for Hela cells in vitro was tested. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
979.
The kinetics of oxidation of 2-aminoethanol and 3-amino-1-propanol by diperiodatoargentate(III) (DPA) were carried out spectrophotometrically in alkaline medium in the temperature range of 293.2-308.2 K. The reaction showed first order with respect to [DPA] and each reductant. The observed rate constant (k obs) decreased with the increase of [IO4 -] and increased with the increase of [OH-]. Increasing ionic strength of the medium decreased the rate. Investigations of the reaction at different temperatures allowed the determination of the activation parameters for the slow step of proposed mechanism. The proposed mechanism and the derived rate laws found consistent with the observed kinetics. 相似文献
980.
Jin-Ping Song Yu-Jing Guo Shao-Min Shuang Chuan Dong 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(1-2):115-120
Multi-wall carbon nanotubes (CNTs)/Nafion composite membrane modified glassy carbon electrode (GCE) was fabricated to investigate the redox of brilliant cresyl violet (BCV) and its supramolecular system with γ-CD and hydroxypropyl-γ-CD (HP-γ-CD). The cyclic voltammetric results indicated that MWNTs/Nafion composite membrane was able to electrocatalyze the redox of BCV compared with bare GCE. Under optimal conditions, differential pulse voltammetry (DPV) was used to study the inclusion interaction of BCV with γ-CD and HP-γ-CD. The consequence demonstrated that the formation of complexes led to the rise of peak current and the shift of peak potential. The inclusion constants of BCV dimer with γ-CD, HP-γ-CD are 2,650 and 8,040 L/mol, respectively. UV–Vis spectra were also employed to confirm the formation of complexes. According to 1HNMR, the possible binding mode of BCV dimer with CDs was discussed. 相似文献