全文获取类型
收费全文 | 494470篇 |
免费 | 6157篇 |
国内免费 | 1417篇 |
专业分类
化学 | 233757篇 |
晶体学 | 6489篇 |
力学 | 18764篇 |
综合类 | 13篇 |
数学 | 49940篇 |
物理学 | 133168篇 |
无线电 | 59913篇 |
出版年
2021年 | 4118篇 |
2020年 | 4647篇 |
2019年 | 4979篇 |
2018年 | 6396篇 |
2017年 | 6212篇 |
2016年 | 9532篇 |
2015年 | 5878篇 |
2014年 | 9293篇 |
2013年 | 21488篇 |
2012年 | 16449篇 |
2011年 | 20259篇 |
2010年 | 14591篇 |
2009年 | 15177篇 |
2008年 | 19941篇 |
2007年 | 20295篇 |
2006年 | 18984篇 |
2005年 | 17286篇 |
2004年 | 16078篇 |
2003年 | 14381篇 |
2002年 | 14048篇 |
2001年 | 15776篇 |
2000年 | 12390篇 |
1999年 | 10031篇 |
1998年 | 8612篇 |
1997年 | 8280篇 |
1996年 | 7963篇 |
1995年 | 7211篇 |
1994年 | 7100篇 |
1993年 | 6739篇 |
1992年 | 7379篇 |
1991年 | 7475篇 |
1990年 | 7112篇 |
1989年 | 6787篇 |
1988年 | 6615篇 |
1987年 | 6002篇 |
1986年 | 5648篇 |
1985年 | 7187篇 |
1984年 | 7264篇 |
1983年 | 5814篇 |
1982年 | 5809篇 |
1981年 | 5795篇 |
1980年 | 5340篇 |
1979年 | 5659篇 |
1978年 | 5786篇 |
1977年 | 5678篇 |
1976年 | 5568篇 |
1975年 | 5141篇 |
1974年 | 5108篇 |
1973年 | 5116篇 |
1972年 | 3626篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Physics of Particles and Nuclei Letters - The problem of spontaneous isotopic symmetry breaking in Nambu–Jona-Lasinio quark models is considered. It is shown that, in models with light... 相似文献
183.
Alfredo M. Gravagnuolo Eden Morales‐Narváez Charlene Regina Santos Matos Sara Longobardi Paola Giardina Arben Merkoçi 《Advanced functional materials》2015,25(38):6084-6092
Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self‐assemble into chemically stable amphiphilic films, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and efficient glass functionalization by spontaneous self‐assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2‐coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fluorophore, anti‐immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self‐assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications. 相似文献
184.
185.
186.
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
187.
Ortiz Adolfo Yang Jianhua Coccolo Mattia Seoane Jesús M. Sanjuán Miguel A. F. 《Nonlinear dynamics》2020,102(4):2323-2337
Nonlinear Dynamics - The main purpose of this paper is to study both the underdamped and the overdamped dynamics of the nonlinear Helmholtz oscillator with a fractional-order damping. For that... 相似文献
188.
A zinc coordination polymer derived from pyridine-2,6-dicarboxylate (PDC), {[Zn2(PDC)2]}n, was successfully prepared via conventional, sonication and microwave-irradiation methods. The composition and characteristics of the obtained coordination polymers (CPs) were investigated by elemental analysis, TGA/DTA, X-ray diffraction and spectroscopic techniques. The so obtained CPs were heat-treated in the air at 600 °C for 2 h to produce ZnO of nanosized particles (NPs). It is of interest to note that the synthesis approach of the precursor greatly affects both the nanoparticle size and the structure of the resulting ZnO NPs. Moreover, the smallest particle size was associated with the sample derived from the ultrasonically prepared precursor. TEM analysis revealed that all samples have sphere-like morphologies. Structural analysis of the prepared ZnO samples was conducted and compared using Rietveld analysis of their PXRD patterns. Optical band gap calculations based on analysis of the UV–vis spectra of ZnO samples using Tauc's power law were achieved. The highest band gap of 3.63 eV was observed for ZnO sample obtained from the ultrasonically prepared precursor. Furthermore, the photocatalytic activity of ZnO NPs for the removal of Eosin Y color was monitored. The highest removal efficiency was recorded for ZnO originated from the ultrasonically synthesized precursor. Enhancement of removal efficiency that reached 98% was attained in only a period of 8 min. Its recycling test showed that it can be reused without structural changes over four cycling experiments. 相似文献
189.
Galia Pozina Elizaveta I. Girshova Konstantin M. Morozov Konstantin A. Ivanov Anton Yu. Egorov Mikhail A. Kaliteevski 《Annalen der Physik》2019,531(6)
Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures. 相似文献
190.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献