全文获取类型
收费全文 | 383704篇 |
免费 | 4817篇 |
国内免费 | 1267篇 |
专业分类
化学 | 199315篇 |
晶体学 | 5652篇 |
力学 | 17243篇 |
综合类 | 37篇 |
数学 | 47179篇 |
物理学 | 120362篇 |
出版年
2021年 | 3742篇 |
2020年 | 4047篇 |
2019年 | 4477篇 |
2018年 | 6225篇 |
2017年 | 6260篇 |
2016年 | 8956篇 |
2015年 | 5606篇 |
2014年 | 8524篇 |
2013年 | 19062篇 |
2012年 | 15760篇 |
2011年 | 18367篇 |
2010年 | 13178篇 |
2009年 | 12729篇 |
2008年 | 16269篇 |
2007年 | 16273篇 |
2006年 | 14832篇 |
2005年 | 13215篇 |
2004年 | 12159篇 |
2003年 | 10667篇 |
2002年 | 10501篇 |
2001年 | 11439篇 |
2000年 | 8600篇 |
1999年 | 6656篇 |
1998年 | 5482篇 |
1997年 | 5275篇 |
1996年 | 5051篇 |
1995年 | 4314篇 |
1994年 | 4309篇 |
1993年 | 4155篇 |
1992年 | 4562篇 |
1991年 | 4719篇 |
1990年 | 4504篇 |
1989年 | 4384篇 |
1988年 | 4110篇 |
1987年 | 4235篇 |
1986年 | 3946篇 |
1985年 | 5117篇 |
1984年 | 5172篇 |
1983年 | 4229篇 |
1982年 | 4408篇 |
1981年 | 4080篇 |
1980年 | 4010篇 |
1979年 | 4263篇 |
1978年 | 4232篇 |
1977年 | 4221篇 |
1976年 | 4230篇 |
1975年 | 3971篇 |
1974年 | 3939篇 |
1973年 | 3954篇 |
1972年 | 2750篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
13.
S. A. Gurevich T. A. Zaraiskaya S. G. Konnikov V. M. Mikushkin S. Yu. Nikonov A. A. Sitnikova S. E. Sysoev V. V. Khorenko V. V. Shnitov Yu. S. Gordeev 《Physics of the Solid State》1997,39(10):1691-1695
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material. 相似文献
14.
Elizabeth S. Senger 《School science and mathematics》1997,97(3):139-149
Thirteen fifth graders were given an assignment to invent their own numeration systems, following a unit on bases and a look at early events in the history of numbers. The task presented options that required the students to make decisions (such as whether to use a base, which base to use, design of symbols, etc.), and build a rationale for the elements of their system. Analyses of patterns embedded in their invented systems provided an assessment of student understanding of numeration. The progression of more and less complex thinking related to the student's choice of a base other than 10, consistency of logic throughout the system in words and symbols, rationale for change, and perception of real life examples that would change if the system was adopted. The invention task is presented as another way to make connections. 相似文献
15.
16.
The simple relation between representations of the covering groups of SL2 and GL2 makes it possible to fuse and extend the recent metaplectic results of Shimura, Waldspurger, Flicker, and ourselves. By giving a new (purely local andL-function theoretic) treatment of the Waldspurger-Shintani correspondence, we also simplify some of Waldspurger’s original results. 相似文献
17.
18.
19.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
20.