全文获取类型
收费全文 | 1313621篇 |
免费 | 29593篇 |
国内免费 | 7676篇 |
专业分类
化学 | 654809篇 |
晶体学 | 19995篇 |
力学 | 74038篇 |
综合类 | 104篇 |
数学 | 239031篇 |
物理学 | 362913篇 |
出版年
2021年 | 13419篇 |
2020年 | 15886篇 |
2019年 | 16040篇 |
2016年 | 27251篇 |
2015年 | 20534篇 |
2014年 | 30344篇 |
2013年 | 74174篇 |
2012年 | 36977篇 |
2011年 | 32650篇 |
2010年 | 35737篇 |
2009年 | 38283篇 |
2008年 | 32410篇 |
2007年 | 27516篇 |
2006年 | 35448篇 |
2005年 | 26879篇 |
2004年 | 28836篇 |
2003年 | 27402篇 |
2002年 | 28769篇 |
2001年 | 27817篇 |
2000年 | 24451篇 |
1999年 | 22312篇 |
1998年 | 20919篇 |
1997年 | 20915篇 |
1996年 | 21023篇 |
1995年 | 19126篇 |
1994年 | 18536篇 |
1993年 | 18086篇 |
1992年 | 17963篇 |
1991年 | 18262篇 |
1990年 | 17451篇 |
1989年 | 17546篇 |
1988年 | 17059篇 |
1987年 | 17076篇 |
1986年 | 16013篇 |
1985年 | 22415篇 |
1984年 | 23694篇 |
1983年 | 19900篇 |
1982年 | 21598篇 |
1981年 | 20841篇 |
1980年 | 20164篇 |
1979年 | 20280篇 |
1978年 | 21656篇 |
1977年 | 21232篇 |
1976年 | 20941篇 |
1975年 | 19653篇 |
1974年 | 19275篇 |
1973年 | 19787篇 |
1972年 | 14278篇 |
1968年 | 12094篇 |
1967年 | 12483篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
Mathematical Notes - We prove the equivalence of a vector and a scalar equilibrium problem that naturally arise when studying the limit distribution of zeros of type I Hermite–Padé... 相似文献
822.
Lan-Lan Zhang Dr. Wen-Ke Miao Dr. Li-Jun Ren Yu-Kun Yan Dr. Yue Lin Prof. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13396-13401
Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)—a polynorbornene backbone with inorganic polyoxometalate cluster pendants—upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application. 相似文献
823.
Doklady Mathematics - In this paper, for the first time, we provide a quasi-polynomial time approximation scheme for the well-known capacitated vehicle routing problem formulated in metric spaces... 相似文献
824.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
825.
Ain Uddin Kyle N. Plunkett 《Journal of polymer science. Part A, Polymer chemistry》2020,58(22):3165-3169
A series of donor-acceptor copolymers with dicyclopenta[cd,jk]pyrene and dicyclopenta[cd,lm]perylene acceptor units was prepared via palladium catalyzed cyclopenta-annulation reactions. The acceptor units were paired with diethynyl containing donor groups based on benzo[1,2-b:4,5-b’]dithiophene, thieno[3,2-b]thiophene, and 4-octyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole to create six polymer variants. The cyclopentannulation polymerization resulted in copolymers with molecular weights (Mn) of 6–14 kDa and broad light absorption in the visible region with band gaps of 1.38–1.85 eV. The synthetic methodology, as well as optoelectronic properties, including thin-film absorption and cyclic voltammetry, of the donor-acceptor copolymers are presented. 相似文献
826.
Rongzhen Wu Hongyu Chen Dr. Ninghui Chang Yuzhi Xu Prof. Dr. Jiao Jiao Prof. Dr. Hailong Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1166-1195
Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014–present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1 , the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development. 相似文献
827.
Voskresenskaya Olga O. Skorik Nina A. 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):533-542
Monatshefte für Chemie - Chemical Monthly - A comparative analysis is performed on the stability constants $${\upbeta }_{1yn}$$ and intramolecular redox decomposition rate constants $$k_{n\; =... 相似文献
828.
829.
Lebedev V. T. Serebrov A. P. 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):1-5
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,... 相似文献
830.
Shaobo Cheng Vidushi Sharma Altug S. Poyraz Lijun Wu Xing Li Amy C. Marschilok Esther S. Takeuchi Kenneth J. Takeuchi Marivi Fernndez-Serra Yimei Zhu 《Chemical science》2020,11(19):4991
Tunneled metal oxides such as α-Mn8O16 (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K+ ions (which act as structure-stabilizing dopants) and H2O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K+-doped α-Mn8O16 (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H2O displaces K+ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K2+ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li+/Na+ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K2+) in the tunnels of hollandite. 相似文献