全文获取类型
收费全文 | 4749篇 |
免费 | 611篇 |
国内免费 | 478篇 |
专业分类
化学 | 3463篇 |
晶体学 | 42篇 |
力学 | 199篇 |
综合类 | 54篇 |
数学 | 684篇 |
物理学 | 1396篇 |
出版年
2024年 | 16篇 |
2023年 | 110篇 |
2022年 | 171篇 |
2021年 | 180篇 |
2020年 | 197篇 |
2019年 | 203篇 |
2018年 | 182篇 |
2017年 | 157篇 |
2016年 | 249篇 |
2015年 | 236篇 |
2014年 | 305篇 |
2013年 | 345篇 |
2012年 | 400篇 |
2011年 | 390篇 |
2010年 | 277篇 |
2009年 | 251篇 |
2008年 | 291篇 |
2007年 | 239篇 |
2006年 | 223篇 |
2005年 | 177篇 |
2004年 | 150篇 |
2003年 | 127篇 |
2002年 | 150篇 |
2001年 | 126篇 |
2000年 | 73篇 |
1999年 | 72篇 |
1998年 | 61篇 |
1997年 | 47篇 |
1996年 | 39篇 |
1995年 | 46篇 |
1994年 | 49篇 |
1993年 | 38篇 |
1992年 | 35篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1971年 | 5篇 |
1962年 | 3篇 |
排序方式: 共有5838条查询结果,搜索用时 0 毫秒
991.
Jian-Liang Zhou Jing-Jing An Ping Li Hui-Jun Li Yan Jiang Jie-Fei Cheng 《Journal of chromatography. A》2009,1216(12):2394-2403
We present herein a novel bioseparation/chemical analysis strategy for protein–ligand screening and affinity ranking in compound mixtures, designed to increase screening rates and improve sensitivity and ruggedness in performance. The strategy is carried out by combining on-line two-dimensional turbulent flow chromatography (2D-TFC) with liquid chromatography–mass spectrometry (LC–MS), and accomplished through the following steps: (1) a reversed-phase TFC stage to separate the protein/ligand complex from the unbound free molecules, (2) an on-line dissociation process to release the bound ligands from the complexes, and (3) a second mixed-mode cation-exchange/reversed-phase TFC stage to trap the bound ligands and to remove the proteins and salts, followed by LC–MS analysis for identification and determination of the binding affinities. The technique can implement an ultra-fast isolation of protein/ligand complex with the retention time of a complex peak in about 5 s, and on-line prepare the “clean” sample to be directly compatible with the LC–MS analysis. The improvement in performance of this 2D-TFC/LC–MS approach over the conventional approach has been demonstrated by determining affinity-selected ligands of the target proteins acetylcholinesterase and butyrylcholinesterase from a small library with known binding affinities and a steroidal alkaloid library composed of structurally similar compounds. Our results show that 2D-TFC/LC–MS is a generic and efficient tool for high-throughput screening of ligands with low-to-high binding affinities, and structure-activity relationship evaluation. 相似文献
992.
Catalytic dehydration of 2‐propanol and that of 1‐butanol were performed at atmospheric pressure and 150–300°C over ZrO2 and sulfated ZrO2 (S/ZrO2) in a fixed‐bed, tubular reactor. The catalysts were characterized with XRD, elemental analysis, FT‐IR, N2 physisorption, TG/DTA, TPD, and TPR. The main structures of ZrO2 and S/ZrO2 were monoclinic and tetragonal, respectively. As ZrO2 was modified with sulfuric acid, its surface area and acid amount were greatly increased, whereas the pore volume, the pore diameter, and the particle size were reduced. Both samples owned weak basicity. For both reactions, only dehydration products of alkene and ether were obtained. The alcohol conversion enhanced remarkably with the catalyst acid amount and the surface area as well as the reaction temperature. In addition, the ether selectivity on S/ZrO2 decreased with raising the reaction temperature. The activation energy was 81.0 kJ/mol in the propene formation from 2‐propanol over S/ZrO2. The corresponding value was 94.4 kJ/mol for the dehydration of 1‐butanol. 相似文献
993.
With the given special structures, the CD bonded stationary phases are expected to have complementary retention properties with conventional C18 stationary phase, which will be helpful to enhance the polar selectivity in RP mode separation. In this work, two β-cyclodextrin (β-CD) bonded stationary phases for reversed-phase HPLC, including 1, 12-dodecyldiol linked β-CD stationary phase (CD1) and olio (ethylene glycol) (OEG) linked β-CD stationary phase (CD2), have been synthesized via click chemistry. The resulting materials were characterized with FT-IR and elemental analysis, which proved the successful immobilization of ligands. The similarities and differences in retention characteristics between the CD and C18 stationary phases have been elucidated by using comparative linear solvation energy relationships (LSERs). The force related to solute McGowan volume has no significant difference, while the hydrogen bonding and dipolar interactions between solutes and CD stationary phases are stronger than between solutes and C18, which is attributed to the special structures (CD and triazole groups) of CD stationary phases. Chemical origins are interpreted by comparison between CD1 and CD2. Similar dispersive interactions of CD1 and CD2 are attributed to their similar length of spacer arms. CD2 which contains OEG spacer arm has relative weaker HBD acidity but stronger HBA basicity. CD stationary phases display no serious different methylene selectivity and higher polar selectivity than in the case of C18. Higher acid selectivity and lower basic selectivity are observed on CD2 than on CD1. Distinctive retention properties and good complementary separation selectivity to C18 make the novel CD bonded stationary phases available for more application in RPLC. 相似文献
994.
The ionic liquids containing Cd and Zn, which served as the metal-chalcogenides precursors, were synthesized and reacted with
Na2S to synthesize the ionic-liquid-capped semiconductors. The products were detected by XRD and TEM. The results demonstrated
that the CdS was composed of 5–6 nm monodispersed nanocrystals. At the same time, the ZnO composed of 1 μm hexagonal-disk
nanostructure was prepared under the same experimental condition. The difference of the morphology and structures between
Zn and Cd systems was discussed by thermodynamics and crystallography. The fluorescence of as-prepared ZnO and CdS showed
the excellent photoluminescence. 相似文献
995.
Jing Yang Yanyan Zhao Ray L. Frost 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):398-403
Infrared spectroscopy has been used to study nano- to micro-sized gallium oxyhydroxide α-GaO(OH), prepared using a low temperature hydrothermal route. Rod-like α-GaO(OH) crystals with average length of 2.5 μm and width of 1.5 μm were prepared when the initial molar ratio of Ga to OH was 1:3. β-Ga2O3 nano and micro-rods were prepared through the calcination of α-GaO(OH). The initial morphology of α-GaO(OH) is retained in the β-Ga2O3 nanorods.The combination of infrared and infrared emission spectroscopy complimented with dynamic thermal analysis were used to characterise the α-GaO(OH) nanotubes and the formation of β-Ga2O3 nanorods. Bands at around 2903 and 2836 cm−1 are assigned to the –OH stretching vibration of α-GaO(OH) nanorods. Infrared bands at around 952 and 1026 cm−1 are assigned to the Ga–OH deformation modes of α-GaO(OH). A significant number of bands are observed in the 620–725 cm−1 region and are assigned to GaO stretching vibrations. 相似文献
996.
Low-cost sensors with high sensitivity and selectivity for chemical and biological detection are of high scientific and economic
importance. Silica nanoparticles (NPs) have shown vast promise in sensor applications by virtue of their controllable surface
modification, good chemical stability, and biocompatibility. This mini-review summarizes our recent development of silica
NP-based assays for chemical and biological detection, where silica NPs serve as the substrate for probe immobilization, target
recognition, and separation. The assay performance is further improved through the introduction of conjugated polyelectrolyte
to amplify the detection signal. The assays have been demonstrated to be successful for the detection of DNA, small molecules,
and proteins. They could be generalized for other targets based on specific interactions, such as DNA hybridization, antibody-antigen
recognition, and target-aptamer binding. 相似文献
997.
Wang Y Li YS Wu J Zhang Z An D 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):2637-2644
Surface-enhance Raman (SER) spectra of pyrazinamide (PZA), isoniazid (INAZ), and isonicotiamide (INCT) in silver sols have been studied over a range of solution concentration and pH. A linear calibration curve has been obtained for each of the sample molecules, and the lower limits of detection are estimated to be 5 ng for PZA and INAZ, and 10 ng for INCA. The variation of SER intensity with the sample solution pH is explained in terms of the charge of the sample species and the stability of the sols. The normal Raman and infrared spectra for the pure drug samples have also been collected, from which some vibration assignments for the molecules are given. The absorption behaviors of the molecules on the silver particle surfaces are also suggested. 相似文献
998.
构造了一类Hartogs域的具有最小体积的外切Hermite椭球.作为一个应用,得到了从这类Hartogs域到单位球的Carathéodory极值映射.并且给出了计算极值的显式公式. 相似文献
999.
Rieter WJ Taylor KM An H Lin W Lin W 《Journal of the American Chemical Society》2006,128(28):9024-9025
Nanoscale metal-organic frameworks (NMOFs) based on Gd3+ centers and benzenedicarboxylate and benzenetricarboxylate bridging ligands were synthesized using reverse microemulsions and characterized using SEM, PXRD, and TGA. These NMOFs exhibit extraordinarily large R1 and R2 relaxivities because of the presence of up to tens of millions of Gd3+ centers in each nanoparticle and are thus efficient T1 and T2 contrast agents for MRI. The NMOFs can also be made highly luminescent by doping with Eu3+ or Tb3+ centers. The results from this work suggest that NMOFs can be used as potential contrast agents for multimodal imaging. 相似文献
1000.
We show that densification of silica glass at ambient pressure as observed in irradiation experiments can be attributed to defect generation and subsequent structure relaxation. In our molecular dynamics simulations, defects are created by randomly removing atoms, by displacing atoms from their nominal positions in an otherwise intact glass, and by assigning certain atom excess kinetic energy (simulated ion implantation). The former forms vacancies; displacing atoms and ion implantation produce both vacancies and "interstitials." Appreciable densification is induced by these defects after equilibration of the defective glasses. The structural and vibrational properties of the densified glasses are characterized, displaying resembling features regardless of the means of densification. These results indicate that relaxation of high free-energy defects into metastable amorphous structures enriched in atomic coordination serves as a common mechanism for densification of silica glass at ambient pressure. 相似文献