全文获取类型
收费全文 | 7664篇 |
免费 | 1154篇 |
国内免费 | 1001篇 |
专业分类
化学 | 5572篇 |
晶体学 | 46篇 |
力学 | 484篇 |
综合类 | 61篇 |
数学 | 838篇 |
物理学 | 2818篇 |
出版年
2024年 | 18篇 |
2023年 | 140篇 |
2022年 | 241篇 |
2021年 | 297篇 |
2020年 | 308篇 |
2019年 | 294篇 |
2018年 | 211篇 |
2017年 | 203篇 |
2016年 | 314篇 |
2015年 | 359篇 |
2014年 | 371篇 |
2013年 | 504篇 |
2012年 | 592篇 |
2011年 | 690篇 |
2010年 | 441篇 |
2009年 | 431篇 |
2008年 | 495篇 |
2007年 | 435篇 |
2006年 | 427篇 |
2005年 | 408篇 |
2004年 | 289篇 |
2003年 | 255篇 |
2002年 | 254篇 |
2001年 | 220篇 |
2000年 | 176篇 |
1999年 | 166篇 |
1998年 | 156篇 |
1997年 | 141篇 |
1996年 | 144篇 |
1995年 | 156篇 |
1994年 | 118篇 |
1993年 | 108篇 |
1992年 | 76篇 |
1991年 | 97篇 |
1990年 | 60篇 |
1989年 | 60篇 |
1988年 | 48篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9819条查询结果,搜索用时 0 毫秒
101.
A comparative study has been carried out between experimentally and naturally weathered pyrites. Both were found to share similar species of weathering products and a similar weathering mechanism. The weathering products could be divided into sulphur-bearing or iron-bearing groups. The sulphur-bearing group was comprised of sulphate, sulphite, thiosulphate, elemental sulphur, polysulphide, and mono-sulphide. The iron-bearing group was comprised of goethite, hematite or magnetite, and iron sulphate. The weathering structural profile was also similar for both types of weathering, being composed of a surficial layer and a transitional layer. The surficial layer was made up of both the sulphur-bearing and the iron-bearing products, while the transitional layer was comprised of goethite, and hematite or magnetite. The inward migration of the weathering interface was stimulated by the diffusion of oxygen and moisture. The oxygen was considered to preferably squeeze the iron to form goethite, and the ferric ions of goethite to have acted as a bridge for electron transfer between the oxygen and bulk S22− and Fe2+ of pyrite. 相似文献
102.
103.
104.
Shuhai Lin Hongde Liu Basem Kanawati Liangfeng Liu Jiyang Dong Min Li Jiandong Huang Philippe Schmitt-Kopplin Zongwei Cai 《Analytical and bioanalytical chemistry》2013,405(15):5105-5117
In the wake of genomics, metabolomics characterizes the small molecular metabolites revealing the phenotypes induced by gene mutants. To address the metabolic signatures in the hippocampus of the amyloid-beta (Aβ) peptides produced in transgenic (Tg) CRND8 mice, high-field ion cyclotron resonance–Fourier transform mass spectrometry supported by LC-LTQ-Orbitrap was introduced to profile the extracted metabolites. More than 10,000 ions were detected in the mass profile for each sample. Subsequently, peak alignment and the 80 % rule followed by feature selection based on T score computation were performed. The putative identification was also conducted using the highly accurate masses with isotopic distribution by interfacing the MassTRIX database as well as MS/MS fragmentation generated in the LTQ-Orbitrap after chromatographic separation. Consequently, 58 differentiating masses were tentatively identified while up to 44 differentiating elemental compositions could not be biologically annotated in the databases. Nonetheless, of the putatively annotated masses, eicosanoids in arachidonic acid metabolism, fatty acid beta-oxidation disorders as well as disturbed glucose metabolism were highlighted as metabolic traits of Aβ toxicity in Tg CRND8 mice. Furthermore, a web-based bioinformatic tool was used for simulation of the metabolic pathways. As a result of the obtained metabolic signatures, the arachidonic acid metabolism dominates the metabolic perturbation in hippocampal tissues of Tg CRND8 mice compared to non-Tg littermates, indicating that Aβ toxicity functions neuroinflammation in hippocampal tissue and new theranostic opportunities might be offered by characterization of altered arachidonic acid metabolism for Alzheimer’s disease. 相似文献
105.
The azido sugar,GalNAz,was successfully used for imaging and perturbing protein glycosylation in triple-negative breast cancer cell line,MDA-MB-231.After the incorporation of GalNAz in the triple-negative breast cancer cell line,the tumorigenicity of these cells was decreased.Results from gene analysis and drug treatment suggest that the tumorigenicity decrease may be attributed to the reduction of cancer stem cell population.Possible mechanisms of GalNAz induced cancer stem cells(CSCs) proportion change are discussed. 相似文献
106.
A new reagent, Ammonium chlorochromate adsorbed on silica gel, suitable for the oxidation of alcohols and benzoins to the corresponding carbonyl compounds is described. 相似文献
107.
Preparation and characterization of ZrCO/C composite aerogels 总被引:1,自引:0,他引:1
Li Ye Wenfeng Qiu Hao Li Aijun Zhao Tao Cai Tong Zhao 《Journal of Sol-Gel Science and Technology》2013,65(2):150-159
Zr-containing organic aerogels were synthesized by ligand substitution reaction of polyzirconoxone and 2, 4-dihydroxybenzoic acid, followed by polymerization with formaldehyde, and then supercritical drying using CO2. After carbonization and carbothermal reduction under an argon atmosphere, ZrCO/C composite aerogels with controllable zirconium content (47.8–78.6 wt%) were obtained. The carbothermal reduction was substantially completed at 1,500 °C, and the obtained ZrCO/C composite aerogels exhibit low oxygen contents (9.4–6.7 wt%) and high surface areas (589–147 m2/g). Pore morphologies of the ZrCO/C composite aerogels were investigated in detail by nitrogen sorption measurements, scanning electron microscopy and its associated energy-dispersive X-ray microanalysis measurements. The results show that the aerogels are composed of carbon framework and Zr-conglomerations, and the surface area of aerogel is severely affected by its zirconium content. The presence of reductive ZrC crystals can greatly enhance the oxidation resistance ability of amorphous carbon framework and prevent collapse. 相似文献
108.
Background
Hylocereus polyrhizus and Hylocereus undatus are two varieties of the commonly called pitaya fruits, and pitaya fruits have gained popularity in many countries all over the world. However, studies on chemical composition and the nutritional quality of pitaya flesh peel are limited.Results
Extracts of pitaya (H. polyrhizus and H. undatus) peel were extracted by supercritical carbon dioxide extraction, and analyzed by gas chromatography–mass spectrometry analysis. Their cytotoxic and antioxidant activities were investigated. The main components of H. polyrhizus extract were β-amyrin (15.87%), α-amyrin (13.90%), octacosane (12.2%), γ-sitosterol (9.35%), octadecane (6.27%), 1-tetracosanol (5.19%), stigmast-4-en-3-one (4.65%), and campesterol (4.16%), whereas H. undatus were β-amyrin (23.39%), γ-sitosterol (19.32%), and octadecane (9.25%), heptacosane (5.52%), campesterol (5.27%), nonacosane (5.02%), and trichloroacetic acid, hexadecyl ester (5.21%). Both of the two extracts possessed good cytotoxic activities against PC3, Bcap-37, and MGC-803 cells (IC50 values ranging from 0.61 to 0.73 mg/mL), and the activities of their main components were also studied. Furthermore, these extracts also presented some radical scavenging activities, with IC50 values of 0.83 and 0.91 mg/mL, respectively.Conclusion
This paper provides evidence for studying the chemical composition of supercritical carbon dioxide extracts of pitaya peel and their biological activity. 相似文献109.
An innovative thermostable 2-D layered Zn(II) compound, chemical terms are written as [Zn(3-pysa)2(H2O)2]n (1, 3-Hpysa = 3-pyridinesulfonic acid), has been generated from the solvothermal reactions of 3-Hpysa and Zn(NO3)2·6H2O. Its single crystal analysis was implemented via the single crystal X-ray diffraction analysis together with the powder X-ray diffraction, elemental analysis and thermogravimetric analysis. The crystal framework is of monoclinic P21/n space group and its crystal cell figures: a = 7.7499(5), b = 10.9923(6), c = 8.3430(5) Å, α = 90, β = 96.924(6), γ = 90°, V = 705.55(7) Å3, Z = 4. The 2D layers were finally combined to a 3-D supramolecular conformation through intermolecular H-bonds existing between coordinated H2O molecules and sulfonate oxygen atoms from adjacent layer. Its practical role in pulpitis treatment was estimated and the relevant mechanism was studied in the meantime. 相似文献
110.
Cai Mengmeng Yao Lijuan Zhu Man Tao Peng Nan Ruihua Jian Zengyun 《Journal of Thermal Analysis and Calorimetry》2021,143(4):2911-2918
Journal of Thermal Analysis and Calorimetry - Differential scanning calorimetry was used to investigate the non-isothermal crystallization kinetics of the Fe76.5Nb3B20Cu0.5 glassy alloys. The... 相似文献