全文获取类型
收费全文 | 353883篇 |
免费 | 8503篇 |
国内免费 | 5565篇 |
专业分类
化学 | 167948篇 |
晶体学 | 4812篇 |
力学 | 14752篇 |
综合类 | 306篇 |
数学 | 35880篇 |
物理学 | 99998篇 |
无线电 | 44255篇 |
出版年
2021年 | 3340篇 |
2020年 | 3635篇 |
2019年 | 3959篇 |
2018年 | 5523篇 |
2017年 | 5667篇 |
2016年 | 6940篇 |
2015年 | 4923篇 |
2014年 | 7241篇 |
2013年 | 14495篇 |
2012年 | 12883篇 |
2011年 | 14476篇 |
2010年 | 10855篇 |
2009年 | 11145篇 |
2008年 | 13585篇 |
2007年 | 13812篇 |
2006年 | 12978篇 |
2005年 | 14334篇 |
2004年 | 13017篇 |
2003年 | 10742篇 |
2002年 | 9152篇 |
2001年 | 9721篇 |
2000年 | 7883篇 |
1999年 | 6285篇 |
1998年 | 5624篇 |
1997年 | 5463篇 |
1996年 | 5027篇 |
1995年 | 4697篇 |
1994年 | 4771篇 |
1993年 | 4335篇 |
1992年 | 4738篇 |
1991年 | 4803篇 |
1990年 | 4610篇 |
1989年 | 4335篇 |
1988年 | 4328篇 |
1987年 | 3916篇 |
1986年 | 3712篇 |
1985年 | 4772篇 |
1984年 | 5024篇 |
1983年 | 4203篇 |
1982年 | 4299篇 |
1981年 | 4222篇 |
1980年 | 4158篇 |
1979年 | 4102篇 |
1978年 | 4413篇 |
1977年 | 4330篇 |
1976年 | 4386篇 |
1975年 | 4029篇 |
1974年 | 4111篇 |
1973年 | 4256篇 |
1972年 | 3015篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
82.
Yuhuan Sun Hongshuang Qin Zhengqing Yan Chuanqi Zhao Jinsong Ren Xiaogang Qu 《Advanced functional materials》2019,29(14)
Recently, quorum sensing (QS) inhibitors (QSIs) have been combined with antibiotics to enhance antibiofilm efficacy in vitro and in vivo. However, targeting QS signals alone is not enough to prevent bacterial infections. Drug resistance and recurrence of biofilms makes it difficult to eradicate. Herein, photodynamic therapy (PDT) is selected to unite QSIs and antibiotics. A synergistically antibiofilm system, which combines QSIs, antibiotics, and PDT based on hollow carbon nitride spheres (HCNSs) is envisaged. First, HCNS provides the multidrug delivering ability, enabling QSIs and antibiotics to be released in sequence. Subsequently, multistage releases sensitize bacteria effectively, potentiating the chemotherapeutic effects of the antibiotics. Finally, the integration of QSIs and PDT not only minimizes the possibility of drug resistance, but also overcomes the problem of limited mass and extension of PDT. Even after 48 h of incubation, the bacterial biofilm is obviously inhibited. And its biofilm disperse efficiency exceeds 48% (compared with QSI‐potentiated chemotherapy group) and 40% (compared with PDT group). Besides, the inhibition of the QS system influences phenotypes related to virulence factor production and surface hydrophobicity, which weaken biofilm invasion and formation. Eventually, this system is applied to disperse bacterial biofilm in vivo. Overall, PDT and QS modulation are devoted to eradicate drug resistance and recurrence of the biofilm. 相似文献
83.
Santosh S. Bhujbal Chawale Bhushankumar G. Kale Mayuri A. 《Journal of Analytical Chemistry》2022,77(4):473-483
Journal of Analytical Chemistry - HPTLC is a widely used tool in standardization of herbs because of its ability to estimate the presence of active components in samples. HPTLC-bioautography is a... 相似文献
84.
Kozhitov L. V. Kiselev B. G. Raykova T. B. Popkova A. V. Kostishin V. G. Muratov D. G. Yakushko E. V. Kosushkin V. G. Bebenin V. G. 《Russian Microelectronics》2019,48(8):599-612
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical... 相似文献
85.
Kazantsev Yu. N. Kraftmakher G. A. Mal’tsev V. P. 《Journal of Communications Technology and Electronics》2019,64(6):550-554
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice... 相似文献
86.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
87.
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the... 相似文献
88.
Differential Equations - We study a mixed problem for systems of one-dimensional semilinear hyperbolic equations with variable nonlinearity growth rate and nonlinear boundary conditions. Theorems... 相似文献
89.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
90.
Manjumol K. A. Jayasankar M. Vidya K. Mohamed A. Peer Nair Balagopal N. Warrier K. G. K. 《Journal of Sol-Gel Science and Technology》2015,74(1):161-167
Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel... 相似文献