全文获取类型
收费全文 | 9749篇 |
免费 | 552篇 |
国内免费 | 43篇 |
专业分类
化学 | 7275篇 |
晶体学 | 32篇 |
力学 | 159篇 |
数学 | 1502篇 |
物理学 | 1376篇 |
出版年
2023年 | 77篇 |
2022年 | 107篇 |
2021年 | 154篇 |
2020年 | 229篇 |
2019年 | 199篇 |
2018年 | 146篇 |
2017年 | 120篇 |
2016年 | 415篇 |
2015年 | 379篇 |
2014年 | 401篇 |
2013年 | 476篇 |
2012年 | 662篇 |
2011年 | 704篇 |
2010年 | 503篇 |
2009年 | 410篇 |
2008年 | 652篇 |
2007年 | 576篇 |
2006年 | 541篇 |
2005年 | 554篇 |
2004年 | 472篇 |
2003年 | 338篇 |
2002年 | 311篇 |
2001年 | 156篇 |
2000年 | 129篇 |
1999年 | 149篇 |
1998年 | 115篇 |
1997年 | 158篇 |
1996年 | 109篇 |
1995年 | 109篇 |
1994年 | 106篇 |
1993年 | 92篇 |
1992年 | 88篇 |
1991年 | 58篇 |
1990年 | 42篇 |
1989年 | 68篇 |
1988年 | 54篇 |
1987年 | 31篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 36篇 |
1983年 | 22篇 |
1982年 | 45篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1975年 | 22篇 |
1973年 | 16篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The well-known Jones matrix formalism, which can be directly applied to the propagation of the polarization of fundamental (TEM(00)) laser resonator modes, has to be modified for higher-order transverse modes. It is shown that this can be done in straightforward manner by using N x N matrices instead of the 2 x 2 Jones matrices, where N denotes the number of orthogonal polarization states of the transverse mode under consideration. The most common case of TEM(01) Hermite-Gaussian modes, where N is four, is discussed in detail. 相似文献
992.
Weerasekara A Rinzan M Matsik S Perera AG Buchanan M Liu HC von Winckel G Stintz A Krishna S 《Optics letters》2007,32(10):1335-1337
Terahertz detection using the free-carrier absorption requires a small internal work function of the order of a few millielectron volts. A threshold frequency of 3.2 THz (93 microm or approximately 13 meV work function) is demonstrated by using a 1 x 10(18) cm(-3) Si-doped GaAs emitter and an undoped Al(0.04)Ga(0.96)As barrier structure. The peak responsivity of 6.5 A/W, detectivity of 5.5 x 10(8) Jones, and quantum efficiency of 19% were obtained at 7.1 THz under a bias field of 0.7 kV/cm at 6 K, while the detector spectral response range spans from 3.2 to 30 THz. 相似文献
993.
Ciro Ciliberto Thomas Dedieu Concettina Galati Andreas Leopold Knutsen 《Mathematische Nachrichten》2023,296(2):574-587
We prove that certain Severi varieties of nodal curves of positive genus on general blow-ups of the twofold symmetric product of a general elliptic curve are nonempty and smooth of the expected dimension. This result, besides its intrinsic value, is an important preliminary step for the proof of nonemptiness of Severi varieties on general Enriques surfaces. 相似文献
994.
Beeke Gerken Christoph Mahr Jakob Stahl Tim Grieb Marco Schowalter Florian F. Krause Thorsten Mehrtens Lutz Mädler Andreas Rosenauer 《Particle & Particle Systems Characterization》2023,40(9):2300048
Hetero-contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero-aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero-aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X-ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero-aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high-angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEM images. 相似文献
995.
996.
997.
998.
999.
Harald Müller Michael Eggert Jürgen Czarske Lars Büttner Andreas Fischer 《Experiments in fluids》2007,43(2-3):223-232
The main advantage of the described Doppler global velocimeter (DGV) systems based on frequency modulation (FM) or frequency
shift keying (FSK) is that no reference detector is required. The frequency variation of the laser light during one modulation
period additionally allows an on-line calibration of the complete DGV system. Thus, the new method has the potential to reduce
the uncertainty of conventional DGV velocity measurements since time resolved velocity field measurements on a spinning disc
have shown standard deviations down to 0.02 m/s. On investigating flow fields, velocity components notably less than 0.5 m/s
were resolved. 相似文献
1000.
Identification of viscoelastic properties by means of nanoindentation taking the real tip geometry into account 总被引:1,自引:0,他引:1
Motivated by recent progress in viscoelastic indentation analysis, the identification of viscoelastic properties from nanoindentation
test data taking the real tip geometry into account is presented in this paper. Based on the elastic solution of the indentation
problem, the corresponding viscoelastic solution is obtained by the application of the method of functional equations. This
general solution, which accounts for the real geometric properties of the indenter tip, is specialized for the case of a trapezoidal
load history, commonly employed in nanoindentation testing. Three deviatoric creep models, the single dash-pot, the Maxwell,
and the three-parameter model are considered. The so-obtained expressions allow us to determine viscoelastic model parameters
via back calculation from the measured load–penetration history. The presented approach is illustrated by the identification
of short-term viscoelastic properties of bitumen. Hereby, the influence of loading rate, maximum load, and temperature on
the model parameters is investigated. 相似文献