全文获取类型
收费全文 | 3771篇 |
免费 | 88篇 |
国内免费 | 10篇 |
专业分类
化学 | 2162篇 |
晶体学 | 56篇 |
力学 | 57篇 |
数学 | 606篇 |
物理学 | 988篇 |
出版年
2020年 | 43篇 |
2019年 | 51篇 |
2018年 | 39篇 |
2017年 | 32篇 |
2016年 | 73篇 |
2015年 | 67篇 |
2014年 | 69篇 |
2013年 | 139篇 |
2012年 | 130篇 |
2011年 | 136篇 |
2010年 | 109篇 |
2009年 | 87篇 |
2008年 | 127篇 |
2007年 | 105篇 |
2006年 | 109篇 |
2005年 | 111篇 |
2004年 | 105篇 |
2003年 | 76篇 |
2002年 | 94篇 |
2001年 | 67篇 |
2000年 | 95篇 |
1999年 | 78篇 |
1998年 | 56篇 |
1997年 | 61篇 |
1996年 | 60篇 |
1995年 | 53篇 |
1994年 | 78篇 |
1993年 | 77篇 |
1992年 | 62篇 |
1991年 | 55篇 |
1990年 | 57篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 46篇 |
1986年 | 60篇 |
1985年 | 61篇 |
1984年 | 51篇 |
1983年 | 55篇 |
1982年 | 48篇 |
1981年 | 43篇 |
1980年 | 65篇 |
1979年 | 44篇 |
1978年 | 56篇 |
1977年 | 58篇 |
1976年 | 52篇 |
1975年 | 57篇 |
1974年 | 44篇 |
1973年 | 51篇 |
1972年 | 34篇 |
1971年 | 32篇 |
排序方式: 共有3869条查询结果,搜索用时 15 毫秒
71.
Abstract An optical autoclave for phase studies on mixtures in the temperature range from 80 to 373 K and for pressures up to 200 MPa is described. The cell is fitted with sapphire windows and employs magnetic stirring. Measurements are performed according to the synthetical (e.g. by visual observation) or analytical method (e.g. by sampling and online gaschromatography). Results for the crystallization and fluid phase equilibria of the binary systems nitrogen + trifluoromethane and argon + trifluoromethane from 110 K to 230 K and up to 200 MPa are presented and discussed in comparison with other N2- and CHF3-systems. 相似文献
72.
K. Büchler K. H. Althoff G. Anton J. Arends W. Beulertz M. Breuer P. Detemple H. Dutz E. Kohlgarth D. Krmer W. Meyer G. Nldeke W. Schneider W. Thiel B. Zucht 《Nuclear Physics A》1994,570(3-4):580-598
The differential cross section of the reaction γp→π+n has been measured with the PHOENICS detector at ELSA in Bonn. For the first time this cross section has been determined simultaneously over a large range of photon energies (Eγ = 220−900 MeV) and pion angles (Θc.m.pi = 35°−135°) with a tagged photon facility. The experimental set-up allowed a considerable kinematic overdetermination of the investigated reaction. Accordingly, the background contributions have been suppressed to below 1%. The measured differential cross section is in good agreement with existing data. The comparison with different model calculations is presented. 相似文献
73.
F. Kastenholz E. Grell J. W. Bats G. Quinkert K. Brand H. Lanig F. W. Schneider 《Journal of fluorescence》1994,4(3):243-246
Two newly synthesized cryptands act as sensitive Na+- and K+-selective indicators for cation concentrations above 20 M. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N–H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1–T
x
energy gap as a consequence of bridgehead nitrogen protonation.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993. 相似文献
74.
J. Schneider D. Hauschild Ch. Frerichs L. Wetenkamp 《International Journal of Infrared and Millimeter Waves》1994,15(11):1907-1922
We report highly efficient CW fiber lasers at 2.7µm in an Er3+-doped and weakly Pr3+-codoped fluorozirconate fiber. The fiber lasers were pumped in three pump wavelength ranges around 650, 795 and 980 nm. Higher output powers of nearly 30 mW and a broader potential tuning range of 180 nm compared to Er3+ singly doped fiber lasers are demonstrated. Laser efficiencies of more than 13% were achieved. It is shown that the fiber laser can be tuned to longer wavelengths by increasing the pump power or, in certain cases, by increasing the pump wavelength. Furthermore, we present the wavelength tuning of the Er3+:Pr3+-codoped system by an external grating. The relationships between laser wavelength and pump rates are described, and the reasons for the improvements with Pr3+-codoping are given. 相似文献
75.
B. Hitti S. R. Kreitzman T. L. Estle R. L. Lichti K. H. Chow J. W. Schneider C. D. Lamp P. Mendels 《Hyperfine Interactions》1994,86(1):673-679
The radio frequencySR technique developed at TRIUMF was used to measure the temperature dependence of the diamagnetic muon, Mu, and Mu* amplitudes in silicon between 10 K and 500 K. Six samples doped with phosphorus (n-type) and boron (p-type) in the concentration range 1011 to 1015 cm–3 were studied. In pure Si a very good fit over the whole temperature range is obtained from a model that includes the ionization of Mu* and Mu to a bond centered
+ followed at high temperature by charge exchange involving Mu. 相似文献
76.
P. Boher M. Renaud J.M. Lopez-Villegas J. Schneider J.P. Chane 《Applied Surface Science》1987,30(1-4):100-107
A multipolar plasma passivation scheme controlled by in-situ ellipsometry has been developed to produce a high electrical quality InGaAs/Si3N4 interface. We have demonstrated the possibility to remove all native oxides at the InGaAs surface by heating the sample at 240°C, then using the action of a multipolar H2 plasma at 185°C, without optical degradation of the surface. The passivation by a native nitride layer is then performed using a N2 plasma, and Si3N4 is deposited. The treatment induces a reduction of the density of interface states Nss(E), and also a change of the nature of these interface states as shown by a reduction in the capture cross section σn(E). 相似文献
77.
M. Schneider A. Hinz A. Groh K. M. Evenson W. Urban 《Applied physics. B, Lasers and optics》1987,44(4):241-245
Frequency stabilization of the CO laser using a CO lamb-dip is achieved in the range from 5.0–6.3 m. The CO saturation signal is obtained from a low-pressure discharge in absorption and is detected using optogalvanic, detection. The frequency stability and reproducibility has been verified to be better than 100 kHz; this is an improvement of more than one order of magnitude compared with locking techniques using CO laser gain profiles.Alexander von Humboldt Awardee from National Bureau of Standards, Boulder, Colorado, USA 相似文献
78.
79.
H. -J. Keim B. Kohlmeyer H. Stege H. A. Bösser F. Pühlhofer W. F. W. Schneider 《Zeitschrift für Physik A Hadrons and Nuclei》1987,327(1):101-107
Protons and α-particles were measured in coincidence with fusion residues for the reaction48Ti+45Sc at 16 MeV/u beam energy. Their velocity distributions show a drastic broadening to higher as well as to lower velocities as compared to the calculated equilibrium emission pattern. This is interpreted as a kinematical effect of variations of the initial velocity of the emitting system, which are attributed to the preequilibrium emission of heavier clusters from the projectile or the target nucleus in incomplete fusion processes. The measured widths of the velocity distributions of the fusion residues are consistent with this mechanism. A peak in the product mass spectrum at masses between 6 and 18 is tentatively identified with the postulated cluster emission. 相似文献
80.