全文获取类型
收费全文 | 338903篇 |
免费 | 4358篇 |
国内免费 | 1353篇 |
专业分类
化学 | 179392篇 |
晶体学 | 4690篇 |
力学 | 14278篇 |
综合类 | 19篇 |
数学 | 44735篇 |
物理学 | 101500篇 |
出版年
2020年 | 1997篇 |
2019年 | 1959篇 |
2018年 | 3104篇 |
2017年 | 3262篇 |
2016年 | 4514篇 |
2015年 | 3738篇 |
2014年 | 4852篇 |
2013年 | 14545篇 |
2012年 | 13439篇 |
2011年 | 15385篇 |
2010年 | 9673篇 |
2009年 | 9484篇 |
2008年 | 12809篇 |
2007年 | 13101篇 |
2006年 | 12715篇 |
2005年 | 15197篇 |
2004年 | 13620篇 |
2003年 | 10928篇 |
2002年 | 9129篇 |
2001年 | 10295篇 |
2000年 | 7786篇 |
1999年 | 6223篇 |
1998年 | 4974篇 |
1997年 | 4792篇 |
1996年 | 4807篇 |
1995年 | 4395篇 |
1994年 | 4148篇 |
1993年 | 3960篇 |
1992年 | 4539篇 |
1991年 | 4387篇 |
1990年 | 4107篇 |
1989年 | 3893篇 |
1988年 | 4179篇 |
1987年 | 3825篇 |
1986年 | 3706篇 |
1985年 | 5344篇 |
1984年 | 5414篇 |
1983年 | 4392篇 |
1982年 | 4764篇 |
1981年 | 4800篇 |
1980年 | 4557篇 |
1979年 | 4686篇 |
1978年 | 4679篇 |
1977年 | 4659篇 |
1976年 | 4652篇 |
1975年 | 4535篇 |
1974年 | 4387篇 |
1973年 | 4559篇 |
1972年 | 2602篇 |
1971年 | 1903篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
953.
954.
955.
956.
We introduce and investigate the properties of Hochschild cohomology of algebras in an abelian monoidal category M. We show that the second Hochschild cohomology group of an algebra in M classifies extensions of A up to an equivalence. We characterize algebras of Hochschild dimension 0 (separable algebras), and of Hochschild dimension ≤1 (formally smooth algebras). Several particular cases and applications are included in the last section of the paper. 相似文献
957.
958.
Fabrication of bamboo-shaped GaN nanorods 总被引:1,自引:0,他引:1
H. Li J.Y. Li M. He X.L. Chen Z. Zhang 《Applied Physics A: Materials Science & Processing》2002,74(4):561-562
Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder
diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area
electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated
that the nanorods were single-crystal wurtzite GaN.
Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001 相似文献
959.
A model proposed in the literature for fish schools of relatively large size is studied for mathematical and qualitative properties. Existence, uniqueness and positivity of solutions are established and bifurcation properties relative to diffusion and alignment parameters are studied. 相似文献
960.
We study the connection between universal central extensions in the categories of precrossed and crossed modules. They are compared with several kinds of universal central extensions in the categories of groups, epimorphisms of groups, groups with operators and modules over a group. We study the relationship between the homologies defined in these categories. Applications to relative algebraic K-theory are also obtained. 相似文献