全文获取类型
收费全文 | 335739篇 |
免费 | 5311篇 |
国内免费 | 1096篇 |
专业分类
化学 | 186238篇 |
晶体学 | 4603篇 |
力学 | 13408篇 |
综合类 | 7篇 |
数学 | 39504篇 |
物理学 | 98386篇 |
出版年
2021年 | 1989篇 |
2020年 | 2406篇 |
2019年 | 2337篇 |
2018年 | 2536篇 |
2017年 | 2383篇 |
2016年 | 4835篇 |
2015年 | 3992篇 |
2014年 | 5170篇 |
2013年 | 15491篇 |
2012年 | 12409篇 |
2011年 | 15181篇 |
2010年 | 9320篇 |
2009年 | 9029篇 |
2008年 | 13798篇 |
2007年 | 13995篇 |
2006年 | 13445篇 |
2005年 | 12270篇 |
2004年 | 10908篇 |
2003年 | 9504篇 |
2002年 | 9289篇 |
2001年 | 10418篇 |
2000年 | 8018篇 |
1999年 | 6361篇 |
1998年 | 5065篇 |
1997年 | 4873篇 |
1996年 | 5007篇 |
1995年 | 4502篇 |
1994年 | 4257篇 |
1993年 | 4133篇 |
1992年 | 4590篇 |
1991年 | 4386篇 |
1990年 | 4093篇 |
1989年 | 3891篇 |
1988年 | 4182篇 |
1987年 | 3858篇 |
1986年 | 3745篇 |
1985年 | 5428篇 |
1984年 | 5473篇 |
1983年 | 4440篇 |
1982年 | 4805篇 |
1981年 | 4849篇 |
1980年 | 4590篇 |
1979年 | 4708篇 |
1978年 | 4709篇 |
1977年 | 4684篇 |
1976年 | 4632篇 |
1975年 | 4546篇 |
1974年 | 4381篇 |
1973年 | 4572篇 |
1972年 | 2591篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis
Dr. Damien Dambournet Dr. Karena W Chapman Dr. Mathieu Duttine Dr. Olaf Borkiewicz Dr. Peter J Chupas Dr. Henri Groult 《ChemistryOpen》2015,4(4):443-447
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties. 相似文献
82.
A fundamental question in random matrix theory is to quantify the optimal rate of convergence to universal laws. We take up this problem for the Laguerre β ensemble, characterized by the Dyson parameter β, and the Laguerre weight , in the hard edge limit. The latter relates to the eigenvalues in the vicinity of the origin in the scaled variable . Previous work has established the corresponding functional form of various statistical quantities—for example, the distribution of the smallest eigenvalue, provided that . We show, using the theory of multidimensional hypergeometric functions based on Jack polynomials, that with the modified hard edge scaling , the rate of convergence to the limiting distribution is , which is optimal. In the case , general the explicit functional form of the distribution of the smallest eigenvalue at this order can be computed, as it can for and general . An iterative scheme is presented to numerically approximate the functional form for general . 相似文献
83.
K.M.J. Rocha R.G. Leitão E.G. Oliveira-Barros M.A. Oliveira C.G.L. Canellas M.J. Anjos L.E. Nasciutti R.T. Lopes 《X射线光谱测定》2019,48(5):476-481
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease. 相似文献
84.
Martín D. Safe 《Journal of Graph Theory》2020,93(2):268-298
A graph is concave-round if its vertices can be circularly enumerated so that the closed neighborhood of each vertex is an interval in the enumeration. In this study, we give a minimal forbidden induced subgraph characterization for the class of concave-round graphs, solving a problem posed by Bang-Jensen, Huang, and Yeo [SIAM J. Discrete Math., 13 (2000), pp. 179–193]. In addition, we show that it is possible to find one such forbidden induced subgraph in linear time in any given graph that is not concave-round. As part of the analysis, we obtain characterizations by minimal forbidden submatrices for the circular-ones property for rows and for the circular-ones property for rows and columns and show that, also for both variants of the property, one of the corresponding forbidden submatrices can be found (if present) in any given matrix in linear time. We make some final remarks regarding connections to some classes of circular-arc graphs. 相似文献
85.
Dr. Liat Avram Dr. Václav Havel Ronit Shusterman-Krush Dr. Mark A. Iron Dr. Moritz Zaiss Prof. Vladimír Šindelář Dr. Amnon Bar-Shir 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1687-1690
The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF4− are mediated by the side chains on the receptor (100 s−1<kex<5000 s−1), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method. 相似文献
86.
87.
J. Conrad J. Cohen-Tanugi L. E. Strigari 《Journal of Experimental and Theoretical Physics》2015,121(6):1104-1135
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments. 相似文献
88.
89.
90.