全文获取类型
收费全文 | 5987篇 |
免费 | 861篇 |
国内免费 | 616篇 |
专业分类
化学 | 2146篇 |
晶体学 | 60篇 |
力学 | 676篇 |
综合类 | 138篇 |
数学 | 1811篇 |
物理学 | 2633篇 |
出版年
2024年 | 10篇 |
2023年 | 41篇 |
2022年 | 108篇 |
2021年 | 125篇 |
2020年 | 207篇 |
2019年 | 189篇 |
2018年 | 186篇 |
2017年 | 184篇 |
2016年 | 229篇 |
2015年 | 200篇 |
2014年 | 295篇 |
2013年 | 517篇 |
2012年 | 342篇 |
2011年 | 352篇 |
2010年 | 300篇 |
2009年 | 392篇 |
2008年 | 367篇 |
2007年 | 376篇 |
2006年 | 361篇 |
2005年 | 333篇 |
2004年 | 303篇 |
2003年 | 273篇 |
2002年 | 244篇 |
2001年 | 186篇 |
2000年 | 198篇 |
1999年 | 147篇 |
1998年 | 151篇 |
1997年 | 142篇 |
1996年 | 95篇 |
1995年 | 103篇 |
1994年 | 84篇 |
1993年 | 63篇 |
1992年 | 64篇 |
1991年 | 59篇 |
1990年 | 34篇 |
1989年 | 32篇 |
1988年 | 32篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1973年 | 2篇 |
1959年 | 4篇 |
排序方式: 共有7464条查询结果,搜索用时 31 毫秒
1.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
2.
3.
V. V. Sagaradze N. V. Kataeva V. A. Zavalishin K. A. Kozlov V. V. Makarov A. R. Kuznetsov 《哲学杂志》2020,100(14):1868-1879
ABSTRACT The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti. 相似文献
4.
In this paper, we propose a sufficient and necessary condition for the boundedness of all the solutions for the equation with the critical situation that on g and p, where , is periodic and is bounded. 相似文献
5.
6.
西部开发中能源配置模型的研究 总被引:3,自引:0,他引:3
开发西部丰富的能源资源,解决东部地区能源紧缺的矛盾,是东西部经济合作、优势互补、东西联动双赢战略研究的一项重要课题.在国家投资主体和市场经济条件下,以能源消费效益最大为目标,建立了基于边际效益均衡的能源空间配置优化模型;兼顾经济效益与环境效益的能源部门配置优化模型.结果显示,各地区、部门要获得更多的能源,就必须提高能源的使用效率,提高能源消费的边际效益,降低污染排放水平. 相似文献
7.
利用Riccati变换求解同谐谐振子的定态薛定谔方程,求得了能谱及态函数
关键词:
同调谐振子
本征值谱
Riccati变换法 相似文献
8.
Mathematical Notes - 相似文献
9.
In this paper we study the Hankel convolution operators on the space of even and entire functions and on Schwartz distribution spaces. We characterize the Hankel convolution operators as those ones that commute with Hankel translations and with a Bessel operator. Also we prove that the Hankel convolution operators are hypercyclic and chaotic on the spaces under consideration. 相似文献
10.