全文获取类型
收费全文 | 9506篇 |
免费 | 232篇 |
国内免费 | 32篇 |
专业分类
化学 | 6788篇 |
晶体学 | 61篇 |
力学 | 135篇 |
数学 | 1364篇 |
物理学 | 1422篇 |
出版年
2020年 | 93篇 |
2019年 | 91篇 |
2016年 | 167篇 |
2015年 | 169篇 |
2014年 | 136篇 |
2013年 | 328篇 |
2012年 | 296篇 |
2011年 | 369篇 |
2010年 | 212篇 |
2009年 | 227篇 |
2008年 | 328篇 |
2007年 | 354篇 |
2006年 | 326篇 |
2005年 | 366篇 |
2004年 | 329篇 |
2003年 | 267篇 |
2002年 | 238篇 |
2001年 | 160篇 |
2000年 | 152篇 |
1999年 | 153篇 |
1998年 | 143篇 |
1997年 | 162篇 |
1996年 | 153篇 |
1995年 | 158篇 |
1994年 | 149篇 |
1993年 | 151篇 |
1992年 | 134篇 |
1991年 | 141篇 |
1990年 | 108篇 |
1989年 | 141篇 |
1988年 | 140篇 |
1987年 | 135篇 |
1986年 | 141篇 |
1985年 | 168篇 |
1984年 | 141篇 |
1983年 | 131篇 |
1982年 | 140篇 |
1981年 | 112篇 |
1980年 | 125篇 |
1979年 | 125篇 |
1978年 | 109篇 |
1977年 | 109篇 |
1976年 | 102篇 |
1974年 | 114篇 |
1973年 | 110篇 |
1967年 | 91篇 |
1961年 | 145篇 |
1960年 | 197篇 |
1959年 | 111篇 |
1958年 | 118篇 |
排序方式: 共有9770条查询结果,搜索用时 15 毫秒
971.
972.
973.
974.
V. A. Ivanshin R. Schauwecker M. Warden P. Erhart H. Keller H. -J. Guentherodt H. P. Lang V. Thommen-Geiser 《Physica C: Superconductivity and its Applications》1996,260(3-4):167-172
Methods of electron-spin resonance (ESR) and direct, non-linear field-modulated microwave absorption (FMMA) were applied for the measurements in low- and high-purity samples of rubidium-doped fullerene, Rb3C60. The coexistence of the normal strong ESR signals and regular series of weak absorption lines similar to those seen in systems of Josephson junctions was observed in the high-purity sample. The possible influence of the vortex lattice on the ESR signals was also studied. We determined from FMMA investigations using the Portis model the critical field μ0H* = 40 μT, the depinning current density Jc*(μ0H0 = 1 mT) 4 × 108 A/m2 in low magnetic field and Jc*(μ0H0 > 100 mT) 1.6 × 108 A/m2 in higher fields. These values were generally one order of magnitude higher than the highest corresponding values previously observed in high-temperature superconductors (HTS's). 相似文献
975.
In Part I of this paper [1] experimental results were presented and discussed. In this part, we investigate theoretically the dynamics of end-pumped solid-state lasers due to enhanced spatial hole burning. This becomes possible by a fast numerical implementation of the saturated gain in the presence of strong spatial hole burning that allows to treat the multimode case for an arbitrary pumping level. We find for a wide range of laser parameters that the mode spacing of the cw running modes is essentially determined by the length of the gain medium and only weakly depends on the absorption depth of the pump transition. It is shown that spatial hole burning can lead to a completely flat saturated gain profile over half of the gain bandwidth. In mode-locked lasers, the flat gain due to spatial hole burning results in shorter pulses. But the pulses are neither Gaussian-nor sech-shaped as they are in actively or passively mode-locked lasers without spatial hole burning. Further, we show that soliton-like pulse shaping can be used to restore a transform-limited sech-shaped pulse in an end-pumped solid-state laser while exploiting the full gain bandwidth of the laser material. 相似文献
976.
Rare-earth doped fibers suffer from relatively high attenuation in comparison to conventional communication fibers. In order to improve the properties of such fibers, understanding of the mechanisms involved in scattering effects is of great importance. The effect of Nd-doping, Al-codoping and of the drawing temperature on the scattering effect was investigated for several different optical fibers. To this end a measuring setup was realized which allows absolute measurements of the scattering coefficient at different positions along a fiber. Also separation of total attenuation and scattering effects is possible. The presented results indicate scattering effects as primary source for increased attenuation compared with undoped fibers. 相似文献
977.
X. Wang W. Zimmermann K. C. Ng A. Chakraboty J. U. Keller 《Journal of Thermal Analysis and Calorimetry》2004,76(2):659-669
This article presents results of the experimental investigation on the adsorption of the water vapor on silica gel. Two independent
experimental methods has been used, viz. the constant-volume-variable-pressure (CVVP) system and variable pressure thermogravimetry
(TG). Results from these two methods are compared with each other. Also the isosteric heat of adsorption of this system has
been determined from the equilibrium data. The silica gels investigated here are Fuji Davison type 'A' and type 'RD'. Adsorption
isotherm of water vapor have been measured under a variety of conditions all referring to chiller operation cycles, i.e. temperatures
from 303 to 358 K and pressures from 500 to 7000 Pa. The data collected from the two independent experiments compare very
favorably with each other and their trends are consistent with those of the adsorption chiller manufacturer. This lends significant
weight to our experimental data on silica gel+water systems as being valuable to the adsorption chiller manufacturers and
the scientific community.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
978.
A flow‐condition‐based interpolation finite element scheme is presented for use of triangular grids in the solution of the incompressible Navier–Stokes equations. The method provides spatially isotropic discretizations for low and high Reynolds number flows. Various example solutions are given to illustrate the capabilities of the procedure. This article and been retracted and replaced. See retraction and replacement notice DOI: 10.1002/fld.1247 . Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
979.
Gerhard Quinkert Stefan Scherer Dietmar Reichert Hans-Peter Nestler Helma Wennemers Andreas Ebel Klaus Urbahns Klaus Wagner Klaus-Peter Michaelis Gerhard Wiech Günter Prescher Bernd Bronstert Bernd-Jürgen Freitag Ilka Wicke Dietmar Lisch Pavel Belik Thorsten Crecelius Dirk Hrstermann Gottfried Zimmermann Jan W. Bats Gerd Dürner Dieter Rehm 《Helvetica chimica acta》1997,80(6):1683-1772
The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction). 相似文献
980.