全文获取类型
收费全文 | 2630篇 |
免费 | 733篇 |
国内免费 | 253篇 |
专业分类
化学 | 792篇 |
晶体学 | 22篇 |
力学 | 290篇 |
综合类 | 34篇 |
数学 | 269篇 |
物理学 | 2209篇 |
出版年
2024年 | 3篇 |
2023年 | 22篇 |
2022年 | 38篇 |
2021年 | 49篇 |
2020年 | 62篇 |
2019年 | 82篇 |
2018年 | 64篇 |
2017年 | 102篇 |
2016年 | 120篇 |
2015年 | 120篇 |
2014年 | 173篇 |
2013年 | 209篇 |
2012年 | 171篇 |
2011年 | 203篇 |
2010年 | 187篇 |
2009年 | 159篇 |
2008年 | 190篇 |
2007年 | 183篇 |
2006年 | 170篇 |
2005年 | 118篇 |
2004年 | 107篇 |
2003年 | 143篇 |
2002年 | 132篇 |
2001年 | 140篇 |
2000年 | 127篇 |
1999年 | 85篇 |
1998年 | 77篇 |
1997年 | 60篇 |
1996年 | 70篇 |
1995年 | 46篇 |
1994年 | 32篇 |
1993年 | 24篇 |
1992年 | 16篇 |
1991年 | 27篇 |
1990年 | 8篇 |
1989年 | 21篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有3616条查询结果,搜索用时 15 毫秒
91.
A direct and efficient approach to 1‐aminoindolizines through three‐component one‐pot reaction of heteroaryl aldehydes, secondary amines and terminal alkynes catalyzed by CuI under solvent‐free conditions has been developed. This methodology provides a rapid access to substituted aminoindolizines with good yields (up to 97%). 相似文献
92.
Hua‐Wei Li Sabyasachi Kar Pinghui Jiang 《International journal of quantum chemistry》2013,113(10):1493-1497
The effects of Debye plasma on the frequency‐dependent polarizabilities of Li and Na atoms are investigated using symplectic algorithm within the framework of the pseudostate summation technique. Dynamic dipole polarizabilities of Li (2s 2S) and Na(3s 2S) as functions of scaled number density of the plasma electrons for arbitrary plasma temperature are presented. Screening effects on the resonance frequencies are also presented. In free‐atomic cases, our calculated results are comparable with the reported theoretical and experimental predictions. © 2012 Wiley Periodicals, Inc. 相似文献
93.
Water is an important component in living systems and deserves better understanding in chemistry and biology. However, due to the difficulty of investigating the water functions in protein structures, it is usually ignored in computational modeling, especially in the field of computer‐aided drug design. Here, using the potential of mean forces (PMFs) approach, we constructed a water PMF (wPMF) based on 3946 non‐redundant high resolution crystal structures. The extracted wPMF potential was first used to investigate the structure pattern of water and analyze the residue hydrophilicity. Then, the relationship between wPMF score and the B factor value of crystal waters was studied. It was found that wPMF agrees well with some previously reported experimental observations. In addition, the wPMF score was also tested in parallel with 3D‐RISM to measure the ability of retrieving experimentally observed waters, and showed comparable performance but with much less computational cost. In the end, we proposed a grid‐based clustering scheme together with a distance weighted wPMF score to further extend wPMF to predict the potential hydration sites of protein structure. From the test, this approach can predict the hydration site at the accuracy about 80% when the calculated score lower than ?4.0. It also allows the assessment of whether or not a given water molecule should be targeted for displacement in ligand design. Overall, the wPMF presented here provides an optional solution to many water related computational modeling problems, some of which can be highly valuable as part of a rational drug design strategy. © 2012 Wiley Periodicals, Inc. 相似文献
94.
Sandeep Kumar Singh Balkishen Razdan 《Journal of Dispersion Science and Technology》2013,34(4):538-545
This article looks at atomic force microscopy as an important aid to characterize the self-nanoemulsifying formulation of glibenclamide, lovastatin, and carvedilol in conjunction with other sophisticated technique, viz., transmission electron microscopy and photon correlation spectroscopy. Sizes obtained by processing the atomic force microscopy (AFM) image are comparable with those obtained from transmission electron microscope. Although in the present study, the mean particle size obtained from photon correlation spectroscopy does not correlate to the findings of atomic force microscopy and transmission electron microscopy, but the poly-disperse index values correlate well with the findings of AFM and transmission electron microscopy where uniform particle size was observed in aqueous dispersion of self-nanoemulsifying formulation of glibenclamide, lovastatin, and carvedilol. 相似文献
95.
Ewan Cruickshank Mirosław Salamończyk Damian Pociecha Grant J. Strachan John M. D. Storey Cheng Wang 《Liquid crystals》2013,40(10):1595-1609
ABSTRACTThe synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4?-[1,ω-alkanediylbis(thio)]bis-[1,1?-biphenyl]-4-carbonitriles (CBSnSCB), and 4?-({ω-[(4?-cyano[1,1?-biphenyl]-4-yl)oxy]alkyl}thio)[1,1?-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 34-{6-[(4?-cyano[1,1?-biphenyl]-4-yl)thio]-hexyl}[11,21:24,31-terphenyl]-14-carbonitrile (CT6SCB), is also reported and shows enantiotropic NTB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-NTB transition corresponds to 4 longitudinal molecular distances. 相似文献
96.
The paper studies a codimension-4 resonant homoclinic bifurcation with one orbit flip and two inclination flips, where the resonance takes place in the tangent direction of homoclinic orbit.Local active coordinate system is introduced to construct the Poincar′e returning map, and also the associated successor functions. We prove the existence of the saddle-node bifurcation, the perioddoubling bifurcation and the homoclinic-doubling bifurcation, and also locate the corresponding 1-periodic orbit, 1-homoclinic orbit, double periodic orbits and some 2n-homoclinic orbits. 相似文献
97.
Hong Shen 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1025-1028
The title CdII coordination polymer, [Cd(C10H8O4)(C12H12N6)0.5(H2O)]n, has been obtained by the hydrothermal method and studied by single‐crystal X‐ray diffraction, elemental analysis, thermogravimetric analysis, IR spectroscopy and fluorescence spectroscopy. The compound forms a novel three‐dimensional framework with 3,8‐connected three‐dimensional binodal {4.52}2{42.510.612.7.83} topology. An investigation of its photoluminescence properties shows that the compound exhibits a strong fluorescence emission in the solid state at room temperature. 相似文献
98.
Mikhail Y. Shalaginov Vadim V. Vorobyov Jing Liu Marcello Ferrera Alexey V. Akimov Alexei Lagutchev Andrey N. Smolyaninov Vasily V. Klimov Joseph Irudayaraj Alexander V. Kildishev Alexandra Boltasseva Vladimir M. Shalaev 《Laser \u0026amp; Photonics Reviews》2015,9(1):120-127
The broadband enhancement of single‑photon emission from nitrogen‐vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied experimentally. The metamaterial is fabricated as an epitaxial metal/dielectric superlattice consisting of CMOS‐compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (AlxSc1‐xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single‑photon emission and reduction of the excited‐state lifetime. Our results could have an impact on future CMOS‐compatible integrated quantum sources.
99.
100.
真空紫外光电离源(VUV-PI)是一种普适性的质谱软电离源,真空紫外光电离质谱谱图无碎片、易解析、灵敏度高,适合于在线快速分析。真空紫外光电离质谱根据分析对象不同可以直接采用单光子电离或添加掺杂剂实现化学电离,能实现气、液、固体分析,也可实现成像分析。该文介绍了真空紫外光电离源的电离原理、光源类型,分析了光电离质谱灵敏度的影响因素及其技术改进措施,并阐述了真空紫外光电离质谱技术在环境污染物、化工产物在线分析、国家安全分析以及生物医学分析中的相关应用研究。最后,总结了真空紫外光电离源的优缺点,并对真空紫外光电离技术在性能和应用方面的发展前景进行了展望。 相似文献