全文获取类型
收费全文 | 124064篇 |
免费 | 5290篇 |
国内免费 | 3945篇 |
专业分类
化学 | 43807篇 |
晶体学 | 1047篇 |
力学 | 8493篇 |
综合类 | 273篇 |
数学 | 34924篇 |
物理学 | 25347篇 |
无线电 | 19408篇 |
出版年
2024年 | 148篇 |
2023年 | 909篇 |
2022年 | 1004篇 |
2021年 | 1318篇 |
2020年 | 1362篇 |
2019年 | 1277篇 |
2018年 | 12643篇 |
2017年 | 12249篇 |
2016年 | 8293篇 |
2015年 | 2467篇 |
2014年 | 2269篇 |
2013年 | 2867篇 |
2012年 | 7142篇 |
2011年 | 14505篇 |
2010年 | 8806篇 |
2009年 | 8761篇 |
2008年 | 9327篇 |
2007年 | 11592篇 |
2006年 | 2198篇 |
2005年 | 3238篇 |
2004年 | 2943篇 |
2003年 | 3258篇 |
2002年 | 2047篇 |
2001年 | 1051篇 |
2000年 | 1145篇 |
1999年 | 1089篇 |
1998年 | 1033篇 |
1997年 | 916篇 |
1996年 | 1065篇 |
1995年 | 805篇 |
1994年 | 706篇 |
1993年 | 632篇 |
1992年 | 559篇 |
1991年 | 472篇 |
1990年 | 372篇 |
1989年 | 298篇 |
1988年 | 247篇 |
1987年 | 218篇 |
1986年 | 214篇 |
1985年 | 177篇 |
1984年 | 143篇 |
1983年 | 103篇 |
1982年 | 87篇 |
1981年 | 76篇 |
1980年 | 67篇 |
1979年 | 64篇 |
1978年 | 57篇 |
1977年 | 43篇 |
1975年 | 50篇 |
1914年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Michael Struwe 《Calculus of Variations and Partial Differential Equations》2003,16(4):431-437
Extending our previous work [5] on this subject we show global existence of smooth solutions to the Cauchy problem for wave
maps from the (1 + 2)-dimensional Minkowski space to an arbitrary smooth, compact Riemannian manifold without boundary, for
arbitrary smooth, radially symmetric data.
Received: 14 December 2001 / Accepted: 1 March 2002 / Published online: 6 August 2002 相似文献
152.
We consider the differential operators Ψ
k
, defined by Ψ1(y) =y and Ψ
k+1(y)=yΨ
k
y+d/dz(Ψ
k
(y)) fork ∈ ℕ fork∈ ℕ. We show that ifF is meromorphic in ℂ and Ψ
k
F has no zeros for somek≥3, and if the residues at the simple poles ofF are not positive integers, thenF has the formF(z)=((k-1)z+a)/(z
2+β
z+γ) orF(z)=1/(az+β) where α, β, γ ∈ ℂ. If the residues at the simple poles ofF are bounded away from zero, then this also holds fork=2. We further show that, under suitable additional conditions, a family of meromorphic functionsF is normal if each Ψ
k
(F) has no zeros. These conditions are satisfied, in particular, if there exists δ>0 such that Re (Res(F, a)) <−δ for all polea of eachF in the family. Using the fact that Ψ
k
(f
′/f) =f
(k)/f, we deduce in particular that iff andf
(k) have no zeros for allf in some familyF of meromorphic functions, wherek≥2, then {f
′/f :f ∈F} is normal.
The first author is supported by the German-Israeli Foundation for Scientific Research and Development G.I.F., G-643-117.6/1999,
and INTAS-99-00089. The second author thanks the DAAD for supporting a visit to Kiel in June–July 2002. Both authors thank
Günter Frank for helpful discussions. 相似文献
153.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
154.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r
ϕ(z),B(r, ϕ)=sup|z|=r
ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics. 相似文献
155.
Lihong Wang 《Annals of the Institute of Statistical Mathematics》2004,56(2):251-264
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L
2-estimates) and the least absolute deviation estimates (L
1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which
has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies
of the above estimators. 相似文献
156.
157.
158.
159.
The vibrational dynamics of protein folding is analyzed in the framework of Tsallis statistics. We employ exact expressions
for classical harmonic oscillators by considering the unnormalized constraints. As q→1, we show that these approximations agree with the result of Gaussian network model. 相似文献
160.
A Low-Power CMOS Linear-in-Decibel Variable Gain Amplifier With Programmable Bandwidth and Stable Group Delay 总被引:1,自引:0,他引:1
Tsou S.-C. Li C.-F. Huang P.-C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1436-1440
This brief presents a new circuit architecture for linear-in-decibel, constant-bandwidth variable gain amplifier (VGA). To obtain high linearity under low-voltage operation, this VGA is a closed-loop structure. In loop amplifier design, two techniques are applied: first, the loop amplifier is given finite input impedance. This arrangement keeps the VGA bandwidth constant under different gain setting. Second, a current-buffered compensation is applied for loop stability. Compared to the Miller compensation, this method achieves wider bandwidth. The prototype chip using 0.18-mum CMOS technology demonstrates that -10- to 20-dB gain and 0.5- to 30-MHz bandwidth can be programmed independently. The group delay difference within 30-dB gain control range is smaller than 1%. The total circuit dissipates 1.35 mA from a 1.8-V supply 相似文献