全文获取类型
收费全文 | 1551篇 |
免费 | 89篇 |
国内免费 | 47篇 |
专业分类
化学 | 880篇 |
晶体学 | 23篇 |
力学 | 62篇 |
综合类 | 3篇 |
数学 | 272篇 |
物理学 | 447篇 |
出版年
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 21篇 |
2020年 | 34篇 |
2019年 | 49篇 |
2018年 | 44篇 |
2017年 | 41篇 |
2016年 | 62篇 |
2015年 | 39篇 |
2014年 | 50篇 |
2013年 | 149篇 |
2012年 | 104篇 |
2011年 | 96篇 |
2010年 | 103篇 |
2009年 | 88篇 |
2008年 | 123篇 |
2007年 | 88篇 |
2006年 | 62篇 |
2005年 | 64篇 |
2004年 | 64篇 |
2003年 | 75篇 |
2002年 | 44篇 |
2001年 | 46篇 |
2000年 | 34篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1970年 | 2篇 |
排序方式: 共有1687条查询结果,搜索用时 93 毫秒
81.
Gülhan Turan Begüm Nurpelin Sağlik Ulviye Acar Çevik Serkan Levent Betül Kaya Çavuşoğlu 《Phosphorus, sulfur, and silicon and the related elements》2020,195(6):491-497
AbstractIn this study, a novel series of benzothiazole-thiazolylhydrazine (3a–3i) was synthesized and their structures were characterized by 1H-NMR, 13C-NMR spectrometry, and mass spectroscopy. These compounds were evaluated as inhibitors of type A and type B monoamine oxidase (MAO) enzymes. The most active compound 3b (2-((2-(2-(4-(4-Nitrophenyl)thiazol-2-yl)hydrazineylidene)-2-phenylethyl)thio)benzothiazole) showed strong inhibitory activity at hMAO-A (IC50 of 0.095?±?0.004?µM). Furthermore, compound 3i (2-((2-(2-(4-(2,4-dichlorophenyl)thiazol-2-yl)hydrazineylidene)-2-phenylethyl)thio)benzothiazole) showed significant inhibition profile on hMAO-A with the IC50 values 0.141?±?0.006?µM. 相似文献
82.
Aye Ünlü Kerem Teral Zübeyde Uurlu Aydn Ali A. Dnmez Hasan Soliman Yusufolu hsan al 《Molecules (Basel, Switzerland)》2022,27(3)
Polygala species are frequently used worldwide in the treatment of various diseases, such as inflammatory and autoimmune disorders as well as metabolic and neurodegenerative diseases, due to the large number of secondary metabolites they contain. The present study was performed on Polygala inexpectata, which is a narrow endemic species for the flora of Turkey, and resulted in the isolation of nine known compounds, 6,3′-disinapoyl-sucrose (1), 6-O-sinapoyl,3′-O-trimethoxy-cinnamoyl-sucrose (tenuifoliside C) (2), 3′-O-(O-methyl-feruloyl)-sucrose (3), 3′-O-(sinapoyl)-sucrose (4), 3′-O-trimethoxy-cinnamoyl-sucrose (glomeratose) (5), 3′-O-feruloyl-sucrose (sibiricose A5) (6), sinapyl alcohol 4-O-glucoside (syringin or eleutheroside B) (7), liriodendrin (8), and 7,4′-di-O-methylquercetin-3-O-β-rutinoside (ombuin 3-O-rutinoside or ombuoside) (9). The structures of the compounds were determined by the spectroscopic methods including 1D-NMR (1H NMR, 13C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC), and HRMS. The isolated compounds were shown in an in silico setting to be accommodated well within the inhibitor-binding pockets of myeloperoxidase and inducible nitric oxide synthase and anchored mainly through hydrogen-bonding interactions and π-effects. It is therefore plausible to suggest that the previously established anti-inflammatory properties of some Polygala-derived phytochemicals may be due, in part, to the modulation of pro-inflammatory enzyme activities. 相似文献
83.
84.
可控粒径纳米Rh的液相还原法制备及其在甲醇重整制氢反应中的应用 总被引:3,自引:0,他引:3
采用液相还原法,通过控制溶液的pH值制备了一系列粒径可控的纳米Rh金属粒子.并用TEM和UV-Vis等技术对其进行了表征.结果表明.在不同pH值的还原溶液中得到的贵金属粒径有明显变化.溶液碱性越强,还原所得金属纳米粒子的粒径越小.当溶液pH值为13时,纳米Rh粒径最小.为6nm左右.采用浸渍法将得到的纳米粒子负载于γ-Al2O3上,以甲醇重整制氢为探针反应,考察了负载型Rh/γ-Al2O3中Rh粒子粒径与反应活性的关系.发现随纳米Rh粒径的减小.反应转化率与氢气选择性都有明显提高.由此可以推测,纳米粒子的尺寸效应是Rh/γ-Al2O3在重整反应中具有高活性的重要原因. 相似文献
85.
Hanİfe Saraçoğlu Alaaddin Cukurovali 《International journal of quantum chemistry》2012,112(6):1566-1578
The title molecule, 3‐{[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐indol‐2‐one (C22H20N4O1S1), was prepared and characterized by 1H NMR, 13C NMR, IR, UV–visible, and single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group P21 with a = 8.3401(5), b = 5.6976(3), c = 20.8155(14) Å, and β = 95.144(5)°. Molecular geometry from X‐ray experiment and vibrational frequencies of the title compound in the ground state has been calculated using the Hartree–Fock with 6‐31G(d, p) and density functional method (B3LYP) with 6‐31G(d, p) and 6‐311G(d, p) basis sets, and compared with the experimental data. The calculated results show that optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies values show good agreement with experimental data. Density functional theory calculations of the title compound and thermodynamic properties were performed at B3LYP/6‐31G(d, p) level of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
86.
采用氨气还原法制备了NaY分子筛负载的MoCo/Y、MoNi/Y双组氮化物催化剂,用XRD和EXAFS方法征了样品的结构,并测定了其在CH4+CO2重整反应中的活性,在氧化态时,MoCo/Y样品中主要存在CoMoO4和Co3O4两种物相,Mo的配位状态接近于CoMoO4,而Co的配位状态更接近于Co3O4,MoNi/Y样品中主要有NiMoO4和NiO两种物相,Mo的配位状态接近于MiMoO4,而Ni的配位状态可能是NiMoO4和NiO两种化合物中Ni配位状态的平均效果,Ni-Mo之间的朴素作用似乎比Co-Mo相对较强,在氮化态时,两种样品中Mo的配位状态较为相似,但即不同于MoO3,也不同于单组分γ-Mo2N.Co和Ni的配位状态都不同于各在氧化态下的状态,且都在相同的位置出现一个新强峰,这似乎表明MoCo和MoNi生成了结构相似的氮化物,在CH4+CO2重整反应中,氮化态MoCO/Y和MoNi/Y的活性大大超过非负载单组分γ-Mo2N催化剂,其中MoNi/Y的活性相对更好一些,且活性随Ni含量增加而提高。 相似文献
87.
正丁烷氧化制顺酐Ce基复合氧化物VPO催化剂研制 总被引:3,自引:0,他引:3
在用共沉淀方法制备的Ce-Fe复合氧化物中,加入VPO化剂制备复合VPO催化剂;井测试结构、氧化还原性能以及催化性能。实验结果表明,Ce-Fe复合氧化物的组成和数量均对复合VPO催化剂的结构产生较大的影响,Ce-Fe复合氧化物的加入,提高了复合VPO催化剂表面低温氧物种的活性,降低了品格氧物种的TPR出峰温度,无论在有无气相氧条件下,复合VPO催化剂的晶格氧均有良好的反应催化性能。 相似文献
88.
Dursun Ali K?se Hacali Necefo?lu Onur ?ahin Orhan Büyükgüng?r 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1233-1241
The mixed-ligand 3-hydroxybenzoic acid complex of Zn(II) with nicotinamide and N,N-diethylnicotinamide were synthesized and characterized (colorless single crystals, [Zn(3-hba)2(H2O)2(na)2] and [Zn(3-hba)2(H2O)2(dena)2]). The chemical, FT-IR, thermal, mass spectral analyses, and X-ray data results revealed that both of the compounds contain two water molecules, two 3-hydroxybenzoate (3-hba) and two nicotinamide (na) or two N,N-diethylnicotinamide (dena) ligands per formula unit. 3-hba and na or dena ligands bind to the Zn(II) ion monodentately through their acidic oxygen and pyridinic nitrogen atoms, respectively. The coordination of metal atoms are completed by two molecules of aqua ligands. The charge balance of complexes is accommodated by two molecules of 3-hba ions. The unit cell has two molecules coordination molecules and each of them was as settled to four surfaces of unit cell cage in na complex. There is one mole molecule that was occupied to center of unit cell cage in dena complex. The two dimensional network structure of the complex is like a hexagonal for na and square plane for dena complexes. The thermal decomposition takes place in three steps; first, dehydration of the two aqua ligands, second, elimination of the two nicotinamide ligands, finally, burning of the two benzoate ion ligands. 相似文献
89.
Photonic crystal behavior of a rotating Bose-Einstein condensate with a triangular vortex lattice is reviewed and a scheme for getting much wider band gaps is proposed. It is shown that photonic band gaps can be widened an order of magnitude more by using a Raman scheme of index enhancement, in comparison to previously considered upper level microwave scheme. 相似文献
90.
A. Zülfikaroǧlu Ç Yüksektepe H. Batı N. Çalışkan 《Russian Journal of Coordination Chemistry》2010,36(2):124-128
In the title complex, [Ni(C30H24N6O4)]2 · 4C3H7NO · H2O (I), the Ni(II) atoms are six-coordinated by two N atoms and one O atom of each of the two tridendate benzoylhydrazone ligands, leading
to a distorted octahedral geometry. In the environment of Ni(II) atoms, the equatorial planes are approximately perpendicular.
The structure is stabilized by O-H...O, O-H...N, and C-H...O intra- and intermolecular hydrogen bonding, resulting in the
formation of infinite chains running along the x axis of the triclinic cell. The structure of the compound was characterized by IR and UV spectra, elemental analyses, and
X-ray diffraction techniques. 相似文献