全文获取类型
收费全文 | 23798篇 |
免费 | 718篇 |
国内免费 | 766篇 |
专业分类
化学 | 4443篇 |
晶体学 | 868篇 |
力学 | 524篇 |
综合类 | 70篇 |
数学 | 16514篇 |
物理学 | 2863篇 |
出版年
2023年 | 81篇 |
2022年 | 104篇 |
2021年 | 183篇 |
2020年 | 177篇 |
2019年 | 530篇 |
2018年 | 587篇 |
2017年 | 399篇 |
2016年 | 378篇 |
2015年 | 375篇 |
2014年 | 733篇 |
2013年 | 1267篇 |
2012年 | 797篇 |
2011年 | 1514篇 |
2010年 | 1526篇 |
2009年 | 1770篇 |
2008年 | 1849篇 |
2007年 | 1807篇 |
2006年 | 1407篇 |
2005年 | 1094篇 |
2004年 | 990篇 |
2003年 | 778篇 |
2002年 | 665篇 |
2001年 | 543篇 |
2000年 | 495篇 |
1999年 | 494篇 |
1998年 | 427篇 |
1997年 | 368篇 |
1996年 | 468篇 |
1995年 | 424篇 |
1994年 | 433篇 |
1993年 | 374篇 |
1992年 | 309篇 |
1991年 | 193篇 |
1990年 | 189篇 |
1989年 | 198篇 |
1988年 | 123篇 |
1987年 | 133篇 |
1986年 | 134篇 |
1985年 | 175篇 |
1984年 | 120篇 |
1983年 | 74篇 |
1982年 | 122篇 |
1981年 | 98篇 |
1980年 | 84篇 |
1979年 | 45篇 |
1978年 | 70篇 |
1977年 | 72篇 |
1976年 | 52篇 |
1975年 | 16篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Norbert Poschadel 《Mathematische Semesterberichte》2002,49(1):45-54
Zusammenfassung. Eine Abbildung zwischen metrischen R?umen hei?t abstandsvertr?glich, wenn der Abstand der Bilder zweier Punkte nur vom Abstand der Punkte selbst abh?ngt. Wir zeigen, dass eine Abbildung genau dann abstandsvertr?glich ist, wenn der Cauchyschen Funktionalgleichung genügt, also ein Endomorphismus der Gruppe ist. Ein entsprechendes Resultat gilt auch für die abstandsvertr?glichen Abbildungen des Kreises (mit der Multiplikation komplexer Zahlen als Gruppenverknüpfung). Damit kann man sowohl alle messbaren abstandsvertr?glichen Abbildungen von bzw. in sich angeben, als auch einen Nachweis für die Existenz nichtmessbarer abstandsvertr?glicher Abbildungen auf und erbringen.
Eingegangen am 20. Juni 2001 / Angenommen am 13. September 2001 相似文献
103.
104.
105.
The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keV and grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated.For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations. 相似文献
106.
In this paper, we report that the phase transformation of Ni-B, Ni-P diffusion barriers deposited electrolessly on Cu, for the reason that the Ni-P layer is a more effective diffusion barrier than the Ni-B layer. The Ni3B crystallized was decomposed to Ni and B2O3 above 400 °C and the Ni3P crystallized was decomposed to Ni and P2O5 above 600 °C respectively in Ar atmosphere. Also, the Ni3B was decomposed to Ni and free B above 400 °C and the Ni3P was decomposed to Ni and free P above 600 °C respectively in H2 atmosphere. The decomposed Ni formed a solid solution with Cu. The Cu diffusion occurred above 400 °C for Ni-B layer and above 600 °C for Ni-P layer, respectively. Because the decomposition temperature of Ni-P layer is about 200 °C higher than that of Ni-B layer, the Ni-P layer is a more effective barrier for Cu than the Ni-B layer. 相似文献
107.
Historians have always seen jabr (restoration) and muqābala (confrontation) as technical terms for specific operations in Arabic algebra. This assumption clashes with the fact that the words were used in a variety of contexts. By examining the different uses of jabr, muqābala, ikmāl (completion), and radd (returning) in the worked-out problems of several medieval mathematics texts, we show that they are really nontechnical words used to name the immediate goals of particular steps. We also find that the phrase al-jabr wa'l-muqābala was first used within the solutions of problems to mean al-jabr and/or al-muqābala, and from there it became the name of the art of algebra. 相似文献
108.
Robert Hochberg 《Combinatorica》2006,26(1):47-64
We prove that the class of homogeneous quasi-arithmetic progressions has unbounded discrepancy. That is, we show that given any 2-coloring of the natural numbers and any positive integer D, one can find a real number α≥1 and a set of natural numbers of the form {0, [α], [2α], [3α], . . . , [kα]} so that one color appears at least D times more than the other color. This was already proved by Beck in 1983, but the proof given here is somewhat simpler and
gives a better bound on the discrepancy. 相似文献
109.
A magic labelling of a set system is a labelling of its points by distinct positive integers so that every set of the system has the same sum,
the magic sum. Examples are magic squares (the sets are the rows, columns, and diagonals) and semimagic squares (the same, but without
the diagonals). A magilatin labelling is like a magic labelling but the values need be distinct only within each set. We show that the number of n × n magic or magilatin labellings is a quasipolynomial function of the magic sum, and also of an upper bound on the entries in
the square. Our results differ from previous ones because we require that the entries in the square all be different from
each other, and because we derive our results not by ad hoc reasoning but from a general theory of counting lattice points in rational inside-out polytopes. We also generalize from
set systems to rational linear forms.
Dedicated to the memory of Claudia Zaslavsky, 1917–2006
Received August 10, 2005 相似文献
110.
Application of Electron-Shelving Detection via 423 nm Transition in Calcium-Beam Optical Frequency Standard 下载免费PDF全文
A new scheme of small compact optical frequency standard based on thermal calcium beam with application of 423 nm shelving detection and sharp-angle velocity selection detection is proposed. Combining these presented techniques, we conclude that a small compact optical frequency standard based on thermal calcium beam will outperform the commercial caesium-beam microwave dock, like the 5071 Cs clock (from Hp to Agilent, now Symmetricom company), both in accuracy and stability. 相似文献