全文获取类型
收费全文 | 116602篇 |
免费 | 17386篇 |
国内免费 | 11909篇 |
专业分类
化学 | 82016篇 |
晶体学 | 1238篇 |
力学 | 6175篇 |
综合类 | 666篇 |
数学 | 15347篇 |
物理学 | 40455篇 |
出版年
2024年 | 250篇 |
2023年 | 2135篇 |
2022年 | 2970篇 |
2021年 | 3825篇 |
2020年 | 4502篇 |
2019年 | 4247篇 |
2018年 | 3820篇 |
2017年 | 3430篇 |
2016年 | 5438篇 |
2015年 | 5143篇 |
2014年 | 6339篇 |
2013年 | 8393篇 |
2012年 | 10187篇 |
2011年 | 10765篇 |
2010年 | 7286篇 |
2009年 | 6931篇 |
2008年 | 7651篇 |
2007年 | 6889篇 |
2006年 | 6488篇 |
2005年 | 5484篇 |
2004年 | 4357篇 |
2003年 | 3425篇 |
2002年 | 3176篇 |
2001年 | 2403篇 |
2000年 | 2087篇 |
1999年 | 2197篇 |
1998年 | 1851篇 |
1997年 | 1687篇 |
1996年 | 1721篇 |
1995年 | 1472篇 |
1994年 | 1351篇 |
1993年 | 1122篇 |
1992年 | 987篇 |
1991年 | 869篇 |
1990年 | 721篇 |
1989年 | 575篇 |
1988年 | 459篇 |
1987年 | 410篇 |
1986年 | 401篇 |
1985年 | 361篇 |
1984年 | 293篇 |
1983年 | 214篇 |
1982年 | 240篇 |
1981年 | 200篇 |
1980年 | 156篇 |
1979年 | 108篇 |
1978年 | 135篇 |
1977年 | 109篇 |
1976年 | 95篇 |
1975年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
The picosecond degenerate four-wave mixing reflectivity of semi-insulating gallium arsenide at 1.06 m is calculated in this paper. The dependence of the reflectivity on the pump and signal fluences is measured. Reflectivities of more than one are possible. The Fourier components of the excited-carrier densities are calculated as a function of the pump fluence. The wavefront-correction property of this reflectivity is demonstrated with a lens group in the signal beam. 相似文献
973.
In this paper we show a number of natural geometric optimization problems in the plane to becomplete for a classD
P
. The classD
p
contains both NP and Co-NP and is contained in
2
P
=P
NP. Completeness inD
p
is exhibited under many-one and positive reductions. Further anOptP(O(logn)) result is also obtained for some of these optimization problems.Work on this paper by the first author was supported in part by NSF Grant No. MIP 85-21356 and ARO Contract No. DAAG29-85-C-0018 under Cornell/MSI. Work by the second author was supported in part by NSF Grant No. DCR 86-06366 at Ohio State and ONR Grant No. N00014-k-0045 at Harvard.On leave from Ohio State University. 相似文献
974.
Daniel Berend 《Journal d'Analyse Mathématique》1988,50(1):123-142
Given measure preserving transformationsT 1,T 2,...,T s of a probability space (X,B, μ) we are interested in the asymptotic behaviour of ergodic averages of the form $$\frac{1}{N}\sum\limits_{n = 0}^{N - 1} {T_1^n f_1 \cdot T_2^n f_2 } \cdot \cdots \cdot T_s^n f_s $$ wheref 1,f 2,...,f s ?L ∞(X,B,μ). In the general case we study, mainly for commuting transformations, conditions under which the limit of (1) inL 2-norm is ∫ x f 1 dμ·∫ x f 2 dμ...∫ x f s dμ for anyf 1,f 2...,f s ?L ∞(X,B,μ). If the transformations are commuting epimorphisms of a compact abelian group, then this limit exists almost everywhere. A few results are also obtained for some classes of non-commuting epimorphisms of compact abelian groups, and for commuting epimorphisms of arbitrary compact groups. 相似文献
975.
Daniel S. Freed 《Inventiones Mathematicae》1988,92(2):243-254
Summary The index of a family of a family of Dirac operators is aK-Theory element in the parameter space. Sullivan's/k-manifolds are used to detect this index completely. For the first Chern class this gives a topological interpretation of Witten's global anomaly. The relationship with the geometry of the index bundle is considered.To my teacher Isadore M. SingerThe author is partially supported by an NSF Postdoctoral Research Fellowship 相似文献
976.
由肉桂酸生物合成L-苯丙氨酸 总被引:4,自引:0,他引:4
本文评述了L-苯丙氮酸的各种合成路线、国内外的研究现状及工业化情况,重点讨论了由肉桂酸和氨生物合成L-苯丙氨酸的路线,提出了在国内进一步工作的建议。 相似文献
977.
978.
J. T. Chayes L. Chayes Daniel S. Fisher T. Spencer 《Communications in Mathematical Physics》1989,120(3):501-523
Thed-dimensional, nearest-neighbor disordered Ising ferromagnet: $$H = - \sum {J_{ij} \sigma _i \sigma _j }$$ is studied as a function of both temperature,T, and a disorder parameter,λ, which measures the size of fluctuations of couplingsJ ij ≧0. A finite-size scaling correlation length,ζ f (T, λ), is defined in terms of the magnetic response of finite samples. This correlation length is shown to be equivalent, in the scaling sense, to the quenched average correlation lengthζ(T, λ), defined as the asymptotic decay rate of the quenched average two-point function. Furthermore, the magnetic response criterion which definesζ f is shown to have a scale-invariant property at the critical point. The above results enable us to prove that the quenched correlation length satisfies: $$C\left| {\log \xi (T)} \right|\xi (T) \geqq \left| {T - T_c } \right|^{ - {2 \mathord{\left/ {\vphantom {2 d}} \right. \kern-\nulldelimiterspace} d}}$$ which implies the boundv≧2/d for the quenched correlation length exponent. 相似文献
979.
Kim YK Auchincloss P Blanis D Bodek A Budd H Eno S Fry CA Harada H Ho YH Kumita T Mori T Olsen SL Shaw NM Sill A Thorndike EH Ueno K Zheng HW Imlay R Kirk P Lim J McNeil RR Metcalf W Myung SS Cheng CP Gu P Li J Li YK Mao ZP Xu YT Zhu YC Abashian A Gotow K Hu KP Low EH Mattson ME Piilonen L Sterner KL Lusin S Rosenfeld C Wang AT Wilson S Frautschi M Kagan H Kass R Trahern CG Breedon RE Kim GN Ko W Lander RL Maeshima K Malchow RL Smith JR Stuart D Williams MC Abe K Fujii Y Higashi Y Kim SK 《Physical review letters》1989,63(17):1772-1775
980.
Eno S Auchincloss P Blanis D Bodek A Budd H Fry CA Harada H Ho YH Kim YK Kumita T Mori T Olsen SL Shaw NM Sill A Thorndike EH Ueno K Zheng HW Imlay R Kirk P Lim J McNeil RR Metcalf W Myung SS Cheng CP Gu P Li J Li YK Mao ZP Xu YT Zhu YC Abashian A Gotow K Hu KP Low EH Mattson ME Piilonen L Sterner KL Lusin S Rosenfeld C Wang AT Wilson S Frautschi M Kagan H Kass R Trahern CG Breedon RE Kim GN Ko W Lander RL Maeshima K Malchow RL Smith JR Stuart D Williams MC Abe K Fujii Y Higashi Y Kim SK 《Physical review letters》1989,63(18):1910-1913