全文获取类型
收费全文 | 141697篇 |
免费 | 7836篇 |
国内免费 | 15618篇 |
专业分类
化学 | 74287篇 |
晶体学 | 1181篇 |
力学 | 3316篇 |
综合类 | 1080篇 |
数学 | 18713篇 |
物理学 | 21722篇 |
综合类 | 44852篇 |
出版年
2024年 | 219篇 |
2023年 | 1055篇 |
2022年 | 2517篇 |
2021年 | 2625篇 |
2020年 | 3057篇 |
2019年 | 3035篇 |
2018年 | 2693篇 |
2017年 | 3800篇 |
2016年 | 4124篇 |
2015年 | 3930篇 |
2014年 | 5144篇 |
2013年 | 8768篇 |
2012年 | 8901篇 |
2011年 | 7879篇 |
2010年 | 6455篇 |
2009年 | 8140篇 |
2008年 | 8545篇 |
2007年 | 9984篇 |
2006年 | 9265篇 |
2005年 | 8101篇 |
2004年 | 7474篇 |
2003年 | 6265篇 |
2002年 | 7065篇 |
2001年 | 4664篇 |
2000年 | 4326篇 |
1999年 | 3947篇 |
1998年 | 3248篇 |
1997年 | 2738篇 |
1996年 | 2393篇 |
1995年 | 2203篇 |
1994年 | 1978篇 |
1993年 | 1692篇 |
1992年 | 1568篇 |
1991年 | 1229篇 |
1990年 | 1012篇 |
1989年 | 989篇 |
1988年 | 770篇 |
1987年 | 556篇 |
1986年 | 430篇 |
1985年 | 305篇 |
1984年 | 297篇 |
1983年 | 171篇 |
1982年 | 242篇 |
1981年 | 204篇 |
1980年 | 215篇 |
1979年 | 214篇 |
1978年 | 189篇 |
1977年 | 138篇 |
1976年 | 114篇 |
1973年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
New thiazole derivatives were synthesized and fully characterized, then coordinated with PtCl4 salt. Also, the newly synthesized Pt(IV) complexes were investigated analytically (elemental and thermogravimetric analyses), spectrally (infrared, UV–visible, mass, 1H NMR, 13C NMR, X‐ray diffraction) as well as theoretically (kinetics, modeling and docking). The data extracted led to the establishment of the best chemical and structural forms. Octahedral geometry was the only formula proposed for all complexes, which is favorable for d6 systems. The molecular ion peaks from mass spectral analysis coincide with all analytical data, confirming the molecular formula proposed. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) allowed discrimination of features between crystalline particles and other amorphous morphology. By applying Gaussian09 as well as HyperChem 8.2 programs, the best structural forms were obtained, as well as computed significant parameters. Computed parameters such as softness, hardness, surface area and reactivity led us towards application in two opposing pathways: tumor inhibition and oxidation activation. The catalytic oxidation for CO was conducted over PtO2, which was yielded from calcination of the most reactive complex. The success of catalytic role for synthesized PtO2 was due to its particulate size and surface morphology, which were estimated from XRD patterns and SEM images, respectively. The antitumor activity was tested versus HCT‐116 and HepG‐2 cell lines. Mild toxicity was recorded for two of the derivatives and their corresponding complexes. This degree of toxicity is more favorable in most cases, due to exclusion of serious side effects, which is coherently attached with known antitumor drugs. 相似文献
42.
设A,B均为正规矩阵,关于正规矩阵的特征值扰动,有结论 (n∑i=1︱μτ(i)-λi︱2)(1/2)≤n(1/2)‖E‖F,其中λi,μi分别为A,B的特征值.通过新的方法证明给出特征值扰动上界的新估计,并改进了以上结论. 相似文献
43.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
44.
A string of four new hetero binuclear Ru(III) complexes of ferrocenecarboxaldehyde-4(N)-substituted thiosemicarbazones were synthesized and characterized by various spectral (infrared, ultraviolet–visible, Electron Paramagnetic Resonance (EPR) and High Resolution Mass Spectrometry (HR-MS) techniques. The binding abilities of the ligands/complexes with nucleic acid (calf thymus DNA, CT-DNA) and bovine serum albumin (BSA) were analyzed by absorption and emission titration methods. The complexes exhibited better DNA binding affinity than their parent ligands. The interaction with CT-DNA was found to be intercalative and with BSA static quenching mechanism was observed. All the synthesized Ru(III) complexes were subjected to study their in vitro cytotoxicity against MCF-7 (human breast cancer) and HT-29 (human colon cancer) cell lines. Among the four complexes, complex 3 [RuCp (FF-etsc)PPh3]Cl exhibited the highest cytotoxicity in MCF-7 cells and complex 4 [RuCp (FF-ptsc)PPh3]Cl was the most active on HT-29 cells. 相似文献
45.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
46.
一个基于Exchange的企业办公自动化系统的实现 总被引:1,自引:0,他引:1
介绍了一个基于Exchange的企业办公自动化系统的实现,其中包括系统目标、开发平台和工具的选择、系统的功能模块、关键技术以及系统的安全机制。 相似文献
47.
杨茂财 《太原理工大学学报》2003,34(3):381-382
就相关熵的性质进行了讨论,证明了在pp密度逼近中使用的作为“距离”的相关熵不满足距离定义中的第三个条件,并给出了三角不等式成立的条件。 相似文献
48.
Theory and controls parameters affecting the output pressure and flow rate of the packed-bed electroosmotic pump (p-EOP), including zeta potential ζ, electric intensity E, length of the column L, cross-section area of the column A, dielectric constant ε and viscosity coefficient η of the liquid being pumped, are discussed concisely. And also, the fabrication and application of the p-EOP are introduced. 相似文献
49.
50.
The use of supercritical fluid carbon dioxide (SF-CO_2) in extraction of lanolin and its alcohol issuperior to the conventional solvent extractionmethod. Its distinctive advantages include highextractive ratio, nontoxic and nonflammablesolvents, and minimal by-product pollution. The 相似文献