全文获取类型
收费全文 | 125987篇 |
免费 | 10113篇 |
国内免费 | 13288篇 |
专业分类
化学 | 78186篇 |
晶体学 | 2616篇 |
力学 | 3308篇 |
综合类 | 1202篇 |
数学 | 31374篇 |
物理学 | 32702篇 |
出版年
2023年 | 1278篇 |
2022年 | 1620篇 |
2021年 | 2892篇 |
2020年 | 3228篇 |
2019年 | 3709篇 |
2018年 | 3271篇 |
2017年 | 3546篇 |
2016年 | 3953篇 |
2015年 | 3813篇 |
2014年 | 5121篇 |
2013年 | 9341篇 |
2012年 | 6278篇 |
2011年 | 7997篇 |
2010年 | 6758篇 |
2009年 | 8247篇 |
2008年 | 8505篇 |
2007年 | 8579篇 |
2006年 | 7430篇 |
2005年 | 6109篇 |
2004年 | 5701篇 |
2003年 | 4882篇 |
2002年 | 4129篇 |
2001年 | 3461篇 |
2000年 | 2907篇 |
1999年 | 2562篇 |
1998年 | 2193篇 |
1997年 | 1964篇 |
1996年 | 2191篇 |
1995年 | 2127篇 |
1994年 | 1973篇 |
1993年 | 1685篇 |
1992年 | 1560篇 |
1991年 | 1032篇 |
1990年 | 790篇 |
1989年 | 741篇 |
1988年 | 684篇 |
1987年 | 570篇 |
1986年 | 539篇 |
1985年 | 692篇 |
1984年 | 553篇 |
1983年 | 322篇 |
1982年 | 555篇 |
1981年 | 737篇 |
1980年 | 609篇 |
1979年 | 585篇 |
1978年 | 498篇 |
1977年 | 407篇 |
1976年 | 340篇 |
1974年 | 140篇 |
1973年 | 216篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
92.
93.
节能减排已成为当今社会发展的主题,对节约能源、提高太阳能的高效综合利用的新型窗用透明隔热材料的理论设计和研究尤其重要.本文采用基于密度泛函理论的计算方法,研究了六方相三氧化钨Ti掺杂前、后的晶格参数、电子能带结构、形成能和光学性质.研究结果表明,Ti掺杂后晶格体积增大,系统能量降为负值,体系具有更好的稳定性;掺杂后电子能带结构发生很大的变化,但材料仍保持n型电导率;随之,其光学性质也发生改变,掺杂前h-WO3无近红外吸收性能,掺杂后的Ti0.33WO3具有很强的近红外吸收性能.在此基础上研究了Ti掺杂h-WO3前、后的太阳辐射屏蔽性能,掺杂前无太阳辐射屏蔽性能;掺杂后的Ti0.33WO3薄膜具有可见光高透明、近红外屏蔽的性能.计算结果为Ti掺杂h-WO3在窗用透明隔热材料方面的研究提供了理论依据. 相似文献
94.
ABSTRACT Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag+ and Fe3+, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field. 相似文献
95.
96.
LI Yuan LI Ruizhe LI Zhenhua WEI Weiqin OUYANG Shuxin YUAN Hong ZHANG Tierui 《高等学校化学研究》2020,36(6):1006-1012
Photothermal Fischer-Tropsch synthesis(FTS) has been extensively studied, but few reports were focused on systematically exploring the influence of support on catalytic performance. Herein, a series of Fe5C2-based catalysts with different supports was fabricated via a one-step wet-chemical method for photothermal conversion of syngas to lower olefins. Under light irradiation, the optimized Fe5C2/α-Al2O3 catalyst demonstrated remarkable photothermal FTS activity, delivering selectivity to lower olefins of 50.3% with a CO conversion rate of 52.5%. Characterization studies using X-ray diffraction and Mössbauer spectroscopy analysis revealed that the active catalyst mainly contained Fe5C2 nanoparticles on α-Al2O3 support. It was found that the weak interaction between active phase and α-Al2O3 could promote the formation of Fe5C2, which contributed to the high selectivity to lower olefins. 相似文献
97.
98.
Jerry Ray Dias 《Molecular physics》2020,118(12)
Cycloparaphenylene ([r]CPP) and cyclacene ([r]CA) series are models for short carbon nanotubes. It is shown that armchair edges in model cycloparaphenylenes possess greater aromaticity and cyclic conjugation than do zigzag edges in model cyclacenes. According to Aihara’s bond resonance energy (BRE) and Bosanac and Gutman energy effect (ef) measurements, cycloparaphenylenes are twice as aromatic as cyclacenes. The general solution of all eigenvalues of all members of the cycloparaphenylene series is given. The origin of the recurrence of some eigenvalues are determined. 相似文献
99.
A. Othman Almatroud Amina-Aicha Khennaoui Adel Ouannas Giuseppe Grassi M. Mossa Al-sawalha Ahlem Gasri 《Entropy (Basel, Switzerland)》2020,22(12)
This article proposes a new fractional-order discrete-time chaotic system, without equilibria, included two quadratic nonlinearities terms. The dynamics of this system were experimentally investigated via bifurcation diagrams and largest Lyapunov exponent. Besides, some chaotic tests such as the 0–1 test and approximate entropy (ApEn) were included to detect the performance of our numerical results. Furthermore, a valid control method of stabilization is introduced to regulate the proposed system in such a way as to force all its states to adaptively tend toward the equilibrium point at zero. All theoretical findings in this work have been verified numerically using MATLAB software package. 相似文献
100.
In this article, we report a facile approach for the synthesis of an inexpensive catalyst of bimetallic Hg/Pd alloys comprising nanoparticles with various structures using a unique ultrasonic reaction that is conducted without the use of any reducing agent. The nanoparticles of Hg/Pd alloys (HgPd and Hg2Pd5) were achieved for the first time by sonicating an aqueous solution of Palladium (II) nitrate with metallic liquid mercury, as evidenced by XRD. EDS further confirmed the presence of Pd and Hg elements in the alloy. The surface morphology and structure of the nanoparticles have been systematically investigated by HRSEM, HRTEM and SAED pattern. In order to explore the catalytic activity of the as-synthesized nanoalloys, the catalytic reduction of 4-nitrophenol and a few other nitrophenol derivatives were investigated. Excellent catalytic activity was obtained for Hg/Pd (1:1) alloy, and the rate constant for the reduction of 4-NP with Hg/Pd at room temperature was found to be 58.4 × 10−3 s−1, which is possibly the highest ever reported. The catalyst exhibited superior stability and reusability when compared with those reported in the literature for other catalysts based on noble metals. 相似文献