全文获取类型
收费全文 | 3550篇 |
免费 | 122篇 |
国内免费 | 26篇 |
专业分类
化学 | 2494篇 |
晶体学 | 19篇 |
力学 | 55篇 |
数学 | 551篇 |
物理学 | 579篇 |
出版年
2024年 | 5篇 |
2023年 | 27篇 |
2022年 | 65篇 |
2021年 | 97篇 |
2020年 | 86篇 |
2019年 | 105篇 |
2018年 | 119篇 |
2017年 | 80篇 |
2016年 | 136篇 |
2015年 | 127篇 |
2014年 | 146篇 |
2013年 | 201篇 |
2012年 | 239篇 |
2011年 | 260篇 |
2010年 | 172篇 |
2009年 | 113篇 |
2008年 | 243篇 |
2007年 | 244篇 |
2006年 | 220篇 |
2005年 | 190篇 |
2004年 | 153篇 |
2003年 | 122篇 |
2002年 | 99篇 |
2001年 | 45篇 |
2000年 | 30篇 |
1999年 | 37篇 |
1998年 | 34篇 |
1997年 | 21篇 |
1996年 | 31篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有3698条查询结果,搜索用时 0 毫秒
931.
Coufal P Cihák M Suchánková J Tesarová E Bosáková Z Stulík K 《Journal of chromatography. A》2002,946(1-2):99-106
Monolithic capillary columns (320 microm I.D.) were prepared for capillary liquid chromatography (CLC) by radical polymerization of butylmethacrylate (BMA) and ethylenedimethacrylate (EDMA) in the presence of a porogen solvent containing propan-1-ol, butane-1,4-diol and water. The influence of the contents of the porogen solvent and EDMA in the polymerization mixture on the monolith porosity and column efficiency was investigated. The composition of the polymerization mixture was optimized to attain a minimum HETP of the order of tens of microm for test compounds with various polarities. The separation performance and selectivity of the most efficient monolithic column prepared was characterized by van Deemter curves, peak asymmetry factors and Walters hydrophobicity and silanol indices. It was demonstrated that the 320-microm I.D. monolithic column exhibited CLC separation performance similar to that observed for 100- and 150-microm I.D. monolithic columns reported in the literature; moreover, the 320-microm I.D. column was easier to operate in CLC and exhibited a higher sample loadability. 相似文献
932.
Tie‐Gen Chen Haolin Zhang Pavel K. Mykhailiuk Rohan R. Merchant Courtney A. Smith Tian Qin Phil S. Baran 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2476-2480
This work bridges a gap in the cross‐coupling of aliphatic redox‐active esters with aryl zinc reagents. Previously limited to primary, secondary, and specialized tertiary centers, a new protocol has been devised to enable the coupling of general tertiary systems using nickel catalysis. The scope of this operationally simple method is broad, and it can be used to simplify the synthesis of medicinally relevant motifs bearing quaternary centers. 相似文献
933.
Spacková N Cheatham TE Ryjácek F Lankas F Van Meervelt L Hobza P Sponer J 《Journal of the American Chemical Society》2003,125(7):1759-1769
An extended set of nanosecond-scale molecular dynamics simulations of DNA duplex sequences in explicit solvent interacting with the minor groove binding drug 4',6-diamidino-2-phenylindole (DAPI) are investigated for four different and sequence specific binding modes. Force fields for DAPI have been parametrized to properly reflect its internal nonplanarity. Sequences investigated include the binding modes observed experimentally, that is, AATT in d(CGCGAATTCGCG)(2) and ATTG in d(GGCCAATTGG)(2) and alternative shifted binding modes ATTC and AATT, respectively. In each case, stable MD simulations are obtained, well reproducing specific hydration patterns seen in the experiments. In contrast to the 2.4 A d(CGCGAATTCGCG)(2) crystal structure, the DAPI is nonplanar, consistent with its gas-phase geometry and the higher resolution crystal structure. The simulations also suggest that the DAPI molecule is able to adopt different conformational substates accompanied by specific hydration patterns that include long-residing waters. The MM_PBSA technology for estimating relative free energies was utilized. The most consistent free energy results were obtained with an approach that uses a single trajectory of the DNA-DAPI complex to estimate all free energy terms. It is demonstrated that explicit inclusion of a subset of bound water molecules shifts the calculated relative binding free energies in favor of both crystallographically observed binding modes, underlining the importance of structured hydration. 相似文献
934.
Klára Navrátilová Pavel Řezanka Michal Řezanka David Sýkora Jindřich Jindřich Vladimír Král 《Journal of separation science》2013,36(7):1270-1274
This work documents the influence of the position of single carboxymethyl group on the β‐cyclodextrin skeleton on the enantioselectivity. These synthesized monosubstituted carboxymethyl cyclodextrin (CD) derivatives, native β‐cyclodextrin, and commercially available carboxymethyl‐β‐cyclodextrin with degree of substitution approximately 3 were used as additives into the BGE consisting of phosphate buffer at 20 mmol/L concentration, pH 2.5, and several biologically significant low‐molecular‐mass chiral compounds were enantioseparated by CE. The results indicate that different substituent location on β‐cyclodextrin skeleton has a significant influence on the enantioseparation of the investigated enantiomers. The enantioselectivity of 2I‐O‐regioisomer was better than with native β‐cyclodextrin. Comparable results to native β‐cyclodextrin were obtained for 6I‐O‐ regioisomer and the enantioselectivity of 3I‐O‐regioisomer was even worse than with native β‐cyclodextrin. Commercially available derivative of CD provides better resolutions than the monosubstituted carboxymethyl CD derivatives for most of the investigated analytes. 相似文献
935.
936.
937.
938.
Tereza Košutová Lukáš Horák Artem Shelemin Mykhailo Vaidulych Jan Hanuš Hynek Biederman Ondřej Kylián Pavel Solař Miroslav Cieslar Andrei Choukourov Milan Dopita 《Surface and interface analysis : SIA》2020,52(12):1023-1028
Metal-polymer nanocomposites have gained increasing attention due to the wide potential applications field. Synthesis of nanoparticles from the gas phase is an intensively studied alternative to the chemical preparation methods. We present a one-step procedure that combines magnetron-based gas aggregation cluster source of silver nanoparticles and simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane (HMDSO). The key parameter of the process, significantly influencing the morphology and microstructure of studied nanoparticles, was found to be the amount of HMDSO added to the deposition chamber as witnessed by small angle X-ray scattering and X-ray diffraction methods combined with transmission electron microscopy and UV–Vis spectrophotometry. The presence of HMDSO in the chamber leads to changes in the size distribution and also in the architecture of prepared nanoparticles. The increasing amount of HMDSO induces the formation of individual core-shell nanoparticles, chains of core-shell nanoparticles, and for the highest concentration of HMDSO, the synthesis of multi-core-shell nanoparticles. The size of crystallites in the silver cores of nanoparticles decreases with addition of HMDSO, which prevents further aggregation. 相似文献
939.
Dr. Pavel A. Petrov Evgeny M. Kadilenko Dr. Taisiya S. Sukhikh Dr. Ilia V. Eltsov Prof. Artem L. Gushchin Prof. Vladimir A. Nadolinny Prof. Maxim N. Sokolov Prof. Nina P. Gritsan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(64):14688-14699
Interaction of the tetradentate redox-active 6,6′-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H4L) with TeCl4 leads to neutral diamagnetic compound TeL ( 1 ) in high yield. The molecule of 1 has a nearly planar TeN2O2 fragment, which suggests the formulation of 1 as TeIIL2−, in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp2] leads to quantitative formation of the paramagnetic salt [CoCp2]+[ 1 ].−, which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp2]+[ 1 ].− at room temperature features a quintet due to splitting on two equivalent 14N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the 125Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(14N) HFI constants and A∥(125Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1 .− is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1 .− can be regarded as the first example of a structurally characterised monomeric tellurium–nitrogen radical anion. 相似文献
940.
Dr. Roman L. Volkov Dr. Vladimir N. Kukin Dr. Pavel A. Kots Prof. Irina I. Ivanova Prof. Nikolay I. Borgardt 《Chemphyschem》2020,21(4):275-279
The article proposes a new way for visualization of mesopores and quantitative evaluation of the pore structure in zeolite crystals. The approach is based on platinum tracking inside the zeolite material after its incorporation from a gaseous precursor using an electron beam prior to preparing a TEM specimen by the focused ion beam technique. The pores in mesoporous silica and purely microporous zeolite Y were visualized in TEM images in a demonstration of the capabilities of the approach. Finally, platinum tracking was used for studying the pore structure of zeolite Y (CBV 720) containing mesopores both inside the crystal and those emerging at its surface, which were unambiguously distinguished from each other. The obtained sizes of the mesopores and the calculated material porosity are in good agreement with the results obtained by the low-temperature argon sorption isotherms method. 相似文献