全文获取类型
收费全文 | 1856篇 |
免费 | 270篇 |
国内免费 | 174篇 |
专业分类
化学 | 759篇 |
晶体学 | 14篇 |
力学 | 479篇 |
综合类 | 58篇 |
数学 | 448篇 |
物理学 | 542篇 |
出版年
2024年 | 7篇 |
2023年 | 23篇 |
2022年 | 64篇 |
2021年 | 133篇 |
2020年 | 100篇 |
2019年 | 66篇 |
2018年 | 66篇 |
2017年 | 63篇 |
2016年 | 80篇 |
2015年 | 88篇 |
2014年 | 106篇 |
2013年 | 141篇 |
2012年 | 86篇 |
2011年 | 91篇 |
2010年 | 69篇 |
2009年 | 93篇 |
2008年 | 97篇 |
2007年 | 90篇 |
2006年 | 100篇 |
2005年 | 89篇 |
2004年 | 67篇 |
2003年 | 70篇 |
2002年 | 70篇 |
2001年 | 51篇 |
2000年 | 55篇 |
1999年 | 51篇 |
1998年 | 37篇 |
1997年 | 41篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 12篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有2300条查询结果,搜索用时 15 毫秒
111.
D. A. Konevetz I. E. Beck G. V. Shishkin V. V. Vlassov V. N. Silnikov 《Russian Chemical Bulletin》2002,51(7):1100-1111
The review surveys the results of our studies devoted to the design of highly efficient catalysts of hydrolysis of the phosphodiester bonds in RNA. These catalysts contain the imidazole residue in the catalytic domain, one or several bis-quaternized rings of 1,4-diazabicyclo[2.2.2]octane as a polycationic RNA-binding domain, and a lipophilic radical. A versatile approach to artificial ribonucleases of this type was proposed, which allows one to vary not only the number of positive charges in the RNA-binding domain, the structure of the catalytic site, and their mutual arrangement but also the domain structure of the molecule as a whole. Analysis of the catalytic properties of the synthesized constructs makes it possible to optimize the domain structure and the geometry of the molecule ensuring its maximum ribonuclease activity. 相似文献
112.
Lei Liu Wen-Guang Li Qing-Xiang Guo 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(3):291-298
The association constants (Ka) for the inclusion complexation of -cyclodextrin (-CD) with 72 mono- and 1,4-disubstituted benzenes were predicted successfully by an artificial neural network (ANN) with molar refraction (Rm) and hydrophobic constant () as input parameters, which reflect the volume and hydrophobicity of the substituents respectively. The predictions strongly suggested that the inclusion complexation of -CD with guest molecules was mainly driven by van der Waals forces and hydrophobic interactions 相似文献
113.
A quantum-mechanical theory of joint nonideal measurement of incompatible polarization observables is applied to an EPR-like experiment. It is demonstrated that this experiment yields both information satisfying and information violating the Bell inequalities. The measurement is also discussed in the context of a local hidden-variables theory. It is argued that the violation of an additional assumption of reproducibility of the hidden variable rather than violation of locality may be responsible for the violation of the Bell inequalities. 相似文献
114.
Kazuhiko Saigo Yukihiko Hashimoto Kazushi Kinbara Atsushi Sudo 《Journal of Chemical Sciences》1996,108(6):555-573
The review describes the mechanism of chiral discrimination of racemic amines upon crystallization and the induction of chirality
in organic reactions by using them as chiral auxiliaries. In order to form conglomerates, which can be resolved into the two
enantiomers upon alternative seeding, both formation and packing of 21-columns are essentially very important. On the other hand, in order to achieve high efficiency in resolution through diastereomeric
salt formation, which is the most practical method, one of a pair of diastereomeric salts derived from a racemic amine and
an enantiomerically pure resolving agent should at least have two 21-columns and planar boundary surfaces in its crystal structure. On the basis of this knowledge, we developed several artificial
chiral auxiliaries such as erythro-2-amino-1,2-diphenylethanol,cis-2-amino-1-acenaphthenol, andcis-2-amino-3,3-dimethyl-1-indanol. These were found to be very efficient chiral auxiliaries in asymmetric inductions: alkylation
of chiral imines, catalytic borane-reduction, and alkylation of chiral N-acylated oxazolidinone. 相似文献
115.
116.
117.
118.
In this paper two new architectures for optical image verification are proposed. Both architectures are based on conventional joint transform correlators (JTCs) adopting a Fourier hologram and can significantly improve the recovered image quality. First, an input phase-only function is Fourier transformed and then interferes with a reference wave that is diffracted from a plane wave incident on another random phase mask. Second, two phase-only functions are placed at the two input sides of a beamsplitter such that the interference pattern of their Fourier transforms can be detected. To obtain a predefined target image in the output plane, one of the input phase functions is iteratively retrieved by the use of the projection onto constraint sets algorithm. Simulation results show that the less mean squared error and better image quality are obtained for both the binary and grayscale images. 相似文献
119.
高频地波雷达下的多目标跟踪数据处理 总被引:1,自引:0,他引:1
根据高频地波雷达监测海上低速移动目标的要求及该类雷达的特点,提出了一种与高频地波雷达目标跟踪相适应的多目标跟踪数据处理方案。在该方案中对BTC(bayes tracking confirm)方法与BTT(bayes tracking termination)方法进行了改进,解决了上述两种方法在高频地波雷达实际应用中存在的问题。提出了贝叶斯准则与次数判定相结合的跟踪起始和终结方法。模拟结果表明,该方案能够稳定、有效地实现高频地波雷达密集回波下的多目标跟踪。 相似文献
120.