全文获取类型
收费全文 | 296615篇 |
免费 | 2167篇 |
国内免费 | 631篇 |
专业分类
化学 | 142963篇 |
晶体学 | 4807篇 |
力学 | 14644篇 |
综合类 | 4篇 |
数学 | 42873篇 |
物理学 | 94122篇 |
出版年
2018年 | 10454篇 |
2017年 | 11374篇 |
2016年 | 6454篇 |
2015年 | 2598篇 |
2014年 | 2519篇 |
2013年 | 7951篇 |
2012年 | 9653篇 |
2011年 | 19475篇 |
2010年 | 11923篇 |
2009年 | 11927篇 |
2008年 | 16979篇 |
2007年 | 20685篇 |
2006年 | 6102篇 |
2005年 | 12700篇 |
2004年 | 8645篇 |
2003年 | 7917篇 |
2002年 | 5724篇 |
2001年 | 5936篇 |
2000年 | 4692篇 |
1999年 | 3551篇 |
1998年 | 2789篇 |
1997年 | 2796篇 |
1996年 | 2900篇 |
1995年 | 2618篇 |
1994年 | 2479篇 |
1993年 | 2367篇 |
1992年 | 2847篇 |
1991年 | 2737篇 |
1990年 | 2686篇 |
1989年 | 2718篇 |
1988年 | 2669篇 |
1987年 | 2669篇 |
1986年 | 2479篇 |
1985年 | 3351篇 |
1984年 | 3383篇 |
1983年 | 2807篇 |
1982年 | 2997篇 |
1981年 | 2932篇 |
1980年 | 2839篇 |
1979年 | 2999篇 |
1978年 | 3252篇 |
1977年 | 2992篇 |
1976年 | 2956篇 |
1975年 | 2800篇 |
1974年 | 2748篇 |
1973年 | 2792篇 |
1972年 | 1792篇 |
1968年 | 2026篇 |
1967年 | 2165篇 |
1966年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 95 毫秒
941.
A simple and effective technique for calculating the transient signals in three-level spin systems irradiated at one and two
frequencies is described. All possible signals are presented and discussed. The application of the two-frequency excitation
technique for the investigation of the inhomogeneity of the crystalline lattice is suggested. 相似文献
942.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
943.
In search of a noncontact underwater acoustic source 总被引:7,自引:0,他引:7
S. V. Egerev 《Acoustical Physics》2003,49(1):51-61
The history of studies of the photoacoustic effect in liquids and its applications to the development of a “virtual” source of underwater acoustic signals is briefly reviewed. The problem of the efficiency of the photoacoustic conversion is considered. The modes of laser generation of sound, i.e., the thermooptical, nonlinear surface, and nonlinear bulk modes of operation, are discussed taking into account the real features of the marine environment, the most important of them being the surface waves. A review of the publications concerned with the problem of a moving photoacoustic source is presented. Advances in the photoacoustic underwater remote sensing technology are described. 相似文献
944.
I. Longo D. Cros N. Tosoratti 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):273-277
We present a numerical and experimental characterization of high-Q whispering gallery resonant modes excited in a fused quartz spherical shell operated in the 18-26.5 GHz band; easy coupling
and selection of modes is a most advantageous feature of the proposed structure with respect to ordinary bulk resonators.
The numerical results, based on a finite element algorithm, well match experimental data, which also show the capability of
our device to perform gaseous spectroscopy measurements.
Received 25 October 2002 Published online 4 February 2003 相似文献
945.
946.
A synthesis of a series of macrocyclic diamides 3 in good yields by reacting the corresponding bis phenols 4 with the appropriate dihalo alkanes 6 either in solvent or in dry media under microwave irradiation. Thiation of 3 with P2S5 or Lawesson's reagent in solvent free conditions under microwave irradiation is also described. 相似文献
947.
Crystal Structure of the Zinc Amide Zn[N(SiMe3)2]2 X‐ray quality crystals of Zn[N(SiMe3)2]2 (monoclinic, P21/c) are obtained by sublimation of the zinc amide Zn[N(SiMe3)2]2 at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe3)2]2 contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds. 相似文献
948.
C.H Chung S.D KimH.J Kim F.O AdurodijaK.H Yoon J Song 《Solid State Communications》2003,126(4):185-190
The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering. 相似文献
949.
L. D. Popov 《Central European Journal of Mathematics》2004,2(1):76-86
For a linear complementarity problem with inconsistent system of constraints a notion of quasi-solution of Tschebyshev type
is introduced. It’s shown that this solution can be obtained automatically by Lemke’s method if the constraint matrix of the
original problem is copositive plus or belongs to the intersection of matrix classes P
0 and Q
0. 相似文献
950.
Here we prove a limit theorem in the sense of the weak convergence of probability measures in the space of meromorphic functions
for a general Dirichlet series. The explicit form of the limit measure in this theorem is given.
Partially supported by Lithuanian Foundation of Studies and Science 相似文献