全文获取类型
收费全文 | 1714篇 |
免费 | 80篇 |
国内免费 | 6篇 |
专业分类
化学 | 1299篇 |
晶体学 | 33篇 |
力学 | 13篇 |
数学 | 39篇 |
物理学 | 416篇 |
出版年
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 24篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 35篇 |
2015年 | 39篇 |
2014年 | 40篇 |
2013年 | 72篇 |
2012年 | 50篇 |
2011年 | 103篇 |
2010年 | 50篇 |
2009年 | 48篇 |
2008年 | 81篇 |
2007年 | 87篇 |
2006年 | 76篇 |
2005年 | 79篇 |
2004年 | 80篇 |
2003年 | 67篇 |
2002年 | 71篇 |
2001年 | 66篇 |
2000年 | 59篇 |
1999年 | 28篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 30篇 |
1995年 | 15篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 31篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 10篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 25篇 |
1979年 | 26篇 |
1978年 | 26篇 |
1977年 | 15篇 |
1976年 | 22篇 |
1975年 | 9篇 |
1974年 | 19篇 |
1973年 | 10篇 |
1968年 | 10篇 |
排序方式: 共有1800条查询结果,搜索用时 825 毫秒
1.
2.
Hiroto Kudo Nobuhito Ito Keiji Nakajima Masami Ochiai Tadatomi Nishikubo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4421-4429
The polyaddition of fluorine‐containing bis(epoxide)s and fluorine‐containing triazine di(aryl ether)s were examined to give the corresponding fluorine‐containing poly(cyanurate)s. It was observed that the synthesized fluoropolymers had good thermal stabilities and good film‐forming properties. The glass transition temperatures (Tg's) and refractive‐indices (nD's) of synthesized polymers were determined by differential scanning calorimetry and ellipsometry, respectively, and it was found that the values of Tg's and nD's were supported by their fluorine containing ratios and skeletons. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4421–4429, 2007 相似文献
3.
The running coupling and the Kugo-Ojima parameter of unquenched lattice Landau gauge are simulated and compared with the continuum
theory. Although the running coupling measured by the ghost and gluon dressing function is infrared suppressed, the running
coupling has a maximum of α0 ∼ 2 − 2.5 at around q = 0.5 GeV irrespective of the fermion actions (Wilson fermions and Kogut-Susskind (KS) fermions). The Kugo-Ojima parameter
c which saturated to about 0.8 in quenched simulations becomes consistent with 1 in the MILC configurations produced with the
use of the Asqtad action, after averaging the dependence on polarization directions caused by the asymmetry of the lattice.
The presence of the correction factor 1 + c
1/q
2 in the running coupling depends on the lattice size and the sea quark mass. In the large lattice size and small sea quark
mass, c
1 is confirmed of the order of a few GeV. The MILC configuration of a = 0.09 fm suggests also the presence of dimension-4 condensates with a sign opposite to the dimension-2 condensates. The
gluon propagator, the ghost propagator, and the running coupling are compared with recent pQCD results including an anomalous
dimension of fields up to the four-loop level. 相似文献
4.
R. Minami A. Kasugai K. Takahashi N. Kobayashi Y. Mitsunaka K. Sakamoto 《International Journal of Infrared and Millimeter Waves》2006,27(1):13-24
A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A
helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have
been optimized for the TE31.8 mode at 170 GHz and TE22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking
the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing
in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design.
High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the
thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of
high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons. 相似文献
5.
Trifluoromethylation onto the tetrafluorophthalonitrile and tetrafluoroisophthalonitrile has been carried out using CF3TMS-CuI-KF system, and it was demonstrated that these trifluoromethylation enabled us to successfully construct di- and/or tri-trifluoromethylated benzonitriles via the decyanotrifluoromethylation. 相似文献
6.
We have investigated the photoluminescence (PL) properties of trace amounts of Pr and Tb in single-crystal samples of yttria-stabilized zironia (YSZ), and found that Pr of the order of 10−6 mass% and Tb of the order of 10−5 mass% in YSZ can be detected by the PL spectroscopy. The PL spectra of the YSZ samples for the 280 nm excitation were comprised of several peaks and a broad emission. The peaks were attributed to transitions of Pr3+ and Tb3+ in the YSZ samples, whereas the broad emission seemed to be attributed to the yttria-associated oxygen vacancies. The peak intensities corresponded to the amounts of Pr and Tb in the YSZ samples, the amounts of which were analyzed by glow discharge mass spectrometry. In the PL excitation spectra, but not in the photoabsorption spectra, small peaks at 376 and 381 nm were observed, and were attributed to the transitions of Tb3+ in the YSZ samples. The results of the PL excitation spectra corresponding to the Pr3+ line emissions suggest that the charge transfer occurs between the YSZ and Pr ion in it. The trace amounts of these lanthanoids in YSZ would disturb the decay process of the photoinduced electrons to the yttria-associated oxygen vacancies. 相似文献
7.
Choyal Y. Minami K. Granatstein V.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2004,32(6):2157-2168
The linear dispersion relation of a backward-wave oscillator (BWO), derived earlier by the authors, is modified to include effects of RF surface current at the beam-vacuum interface. This modified dispersion relation results in an unstable interaction between the slow cyclotron mode (SCM) and the structure mode in addition to the conventional Cherenkov instability caused by the slow space charge mode. Numerical analysis is then carried out using parameters of a BWO experiment at University of Maryland. Fine structure of the SCM instability is elucidated. The analysis indicates that BWO radiation would not be suppressed near cyclotron absorption in an infinitely long system. 相似文献
8.
9.
Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification
M. Joma H. Hofukawa M. Nakajima M. Kawahara T. Kamijoh 《Fiber and Integrated Optics》1991,10(4):361-364
Polarization insensitive optical amplification was demonstrated in newly developed semiconductor optical amplifiers that have strained GalnAsP quantum well structures. We tailored the active region of the quaternary strained layer quantum well structure with a small biaxially tensile strain of 0.2% in the well layers for polarization insensitive operation. 相似文献
10.