全文获取类型
收费全文 | 7653篇 |
免费 | 1128篇 |
国内免费 | 474篇 |
专业分类
化学 | 3961篇 |
晶体学 | 28篇 |
力学 | 773篇 |
综合类 | 188篇 |
数学 | 1982篇 |
物理学 | 2323篇 |
出版年
2024年 | 4篇 |
2023年 | 102篇 |
2022年 | 213篇 |
2021年 | 287篇 |
2020年 | 387篇 |
2019年 | 256篇 |
2018年 | 237篇 |
2017年 | 343篇 |
2016年 | 407篇 |
2015年 | 349篇 |
2014年 | 464篇 |
2013年 | 472篇 |
2012年 | 487篇 |
2011年 | 456篇 |
2010年 | 385篇 |
2009年 | 473篇 |
2008年 | 439篇 |
2007年 | 453篇 |
2006年 | 426篇 |
2005年 | 362篇 |
2004年 | 331篇 |
2003年 | 284篇 |
2002年 | 233篇 |
2001年 | 183篇 |
2000年 | 173篇 |
1999年 | 138篇 |
1998年 | 139篇 |
1997年 | 111篇 |
1996年 | 95篇 |
1995年 | 107篇 |
1994年 | 87篇 |
1993年 | 70篇 |
1992年 | 60篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 25篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 29篇 |
1984年 | 16篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有9255条查询结果,搜索用时 31 毫秒
41.
42.
In this work, we designed and studied a feasible dual-layer binary metagrating, which can realize controllable asymmetric transmission and beam splitting with nearly perfect performance. Owing to ingenious geometry configuration, only one meta-atom is required to design for the metagrating system. By simply controlling air gap between dual-layer metagratings, high-efficiency beam splitting can be well switched from asymmetric transmission to symmetric transmission. The working principle lies on gap-induced diffraction channel transition for incident waves from opposite directions. The asymmetric/symmetric transmission can work in a certain frequency band and a wide incident range. Compared with previous methods using acoustic metasurfaces, our approach has the advantages of simple design and tunable property and shows promise for applications in wavefront manipulation, noise control and one-way propagation. 相似文献
43.
Dr. Ulrich Lücking 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(56):e202201993
Extension of the medicinal chemistry toolbox is in the vital interest of drug designers. However, the diffusion of an innovation can be a lengthy process. Along these lines, it took almost 70 years before the use of the sulfoximine group reached a critical mass in medicinal chemistry. Even though interest in this versatile functional group has increased exponentially in recent years, there is ample room for further innovative applications. This Review highlights emerging trends and opportunities for drug designers for the utilization of the sulfoximine group in medicinal chemistry, such as in the construction of complex molecules, proteolysis targeting chimeras (PROTACs), antibody-drug conjugates (ADCs) and novel warheads for covalent inhibition. 相似文献
44.
45.
In this article, we mainly consider the existence problem of a group divisible design GDD of type . We present two recursive constructions for this configuration using candelabra systems and construct explicitly a few small examples admitting given automorphism groups. As an application, several new infinite classes of GDD s of type are produced. Meanwhile a few new infinite families on candelabra quadruple systems with group sizes being odd and stem size greater than one are also obtained. 相似文献
46.
47.
Lianghao Song Tiantian Xu Daowei Gao Prof. Xun Hu Prof. Cuncheng Li Prof. Shun Li Prof. Guozhu Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6621-6627
CeO2-based catalysts are widely studied in catalysis fields. Developing one novel synthetic approach to increase the intimate contact between CeO2 and secondary species is of particular importance for enhancing catalytic activities. Herein, an interfacial reaction between metal–organic framework (MOF)-derived carbon and KMnO4 to synthesize CeO2−MnO2, in which carbon is derived from the pyrolysis of Ce-MOFs under an inert atmosphere, is described. The MOF-derived carbon is found to restrain the growth of CeO2 crystallites under a high calcination temperature and, more importantly, intimate contact within CeO2/C is conveyed to CeO2/MnO2 after the interfacial reaction; this is responsible for the high catalytic activity of CeO2−MnO2 towards CO oxidation. 相似文献
48.
Necessary conditions for the existence of a super‐simple, decomposable, near‐resolvable ‐balanced incomplete block design (BIBD) whose 2‐component subdesigns are both near‐resolvable ‐BIBDs are (mod ) and . In this paper, we show that these necessary conditions are sufficient. Using these designs, we also establish that the necessary conditions for the existence of a super‐simple near‐resolvable ‐RBIBD, namely (mod ) and , are sufficient. A few new pairwise balanced designs are also given. 相似文献
49.
We show that the Smith normal form of a skew‐symmetric D ‐optimal design of order is determined by its order. Furthermore, we show that the Smith normal form of such a design can be written explicitly in terms of the order , thereby proving a recent conjecture of Armario. We apply our result to show that certain D ‐optimal designs of order are not equivalent to any skew‐symmetric D ‐optimal design. We also provide a correction to a result in the literature on the Smith normal form of D ‐optimal designs. 相似文献
50.
John Asplund Gregory Clark Garner Cochran va Czabarka Arran Hamm Gwen Spencer Lszl Szkely Libby Taylor Zhiyu Wang 《组合设计杂志》2019,27(10):586-597
The crossing number of a graph is the smallest number of edge crossings over all drawings of in the plane. For any , the ‐planar crossing number of , is defined as the minimum of over all graphs with . Pach et al [Comput. Geom.: Theory Appl. 68 (2018), pp. 2–6] showed that for every , we have and that this bound does not remain true if we replace the constant by any number smaller than . We improve the upper bound to as . For the class of bipartite graphs, we show that the best constant is exactly for every . The results extend to the rectilinear variant of the ‐planar crossing number. 相似文献