全文获取类型
收费全文 | 30549篇 |
免费 | 1004篇 |
国内免费 | 507篇 |
专业分类
化学 | 5915篇 |
晶体学 | 272篇 |
力学 | 851篇 |
综合类 | 129篇 |
数学 | 16610篇 |
物理学 | 8283篇 |
出版年
2023年 | 124篇 |
2022年 | 223篇 |
2021年 | 194篇 |
2020年 | 238篇 |
2019年 | 580篇 |
2018年 | 404篇 |
2017年 | 423篇 |
2016年 | 310篇 |
2015年 | 267篇 |
2014年 | 523篇 |
2013年 | 1340篇 |
2012年 | 858篇 |
2011年 | 1281篇 |
2010年 | 838篇 |
2009年 | 1272篇 |
2008年 | 1426篇 |
2007年 | 1446篇 |
2006年 | 1234篇 |
2005年 | 908篇 |
2004年 | 1220篇 |
2003年 | 1379篇 |
2002年 | 1955篇 |
2001年 | 1941篇 |
2000年 | 1822篇 |
1999年 | 1936篇 |
1998年 | 1688篇 |
1997年 | 1052篇 |
1996年 | 631篇 |
1995年 | 396篇 |
1994年 | 312篇 |
1993年 | 209篇 |
1992年 | 210篇 |
1991年 | 187篇 |
1990年 | 255篇 |
1989年 | 210篇 |
1988年 | 179篇 |
1987年 | 134篇 |
1986年 | 206篇 |
1985年 | 299篇 |
1984年 | 250篇 |
1983年 | 96篇 |
1982年 | 183篇 |
1981年 | 274篇 |
1980年 | 261篇 |
1979年 | 132篇 |
1978年 | 216篇 |
1977年 | 149篇 |
1976年 | 97篇 |
1975年 | 92篇 |
1974年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
21.
采用顶部籽晶提拉法(TSSG)生长出Yb:KY(WO4)2(Yb:KYW)激光晶体.对预烧后的原料及晶体进行了XRD分析,结果表明,分别在920℃和600℃预烧8h后的熔质和助熔剂基本上形成一相,抑止了实验中的挥发问题;所生长的晶体为β-Yb:KYW,计算其晶格常数为a=1.063nm,b=1.034nm,c=0.755nm,β=130.75°.测得不同厚度样品的吸收光谱,结果表明样品在933nm和981nm有较强的吸收峰,计算出主峰981nm的吸收截面σ关键词:
Yb:KYW
TSSG法
晶体结构
光谱参数 相似文献
22.
以高纯ZnS粉末为基质,采用高温转相、扩散,以及表面涂敷工艺,制得了147Pm激发的ZnS:Cu,Cl发光粉。分析了ZnS:Cu,Cl的晶体结构,测量了ZnS:Cu,Cl的激发光谱、发射光谱、发光亮度。其晶体结构主要是六方纤锌矿型结构,激发光谱峰值波长为341nm,发射光谱峰值波长为513nm,初始发光亮度达到312mcd/m2。由激发光谱的峰值波长341nm推算得到六方ZnS晶体的禁带宽度为3.64eV。分析了147Pm激发的ZnS:Cu,Cl发光粉的发光寿命,其发光寿命达到5年以上。还探讨了该放射性发光粉的发光机理。147Pm激发的ZnS:Cu,Cl的稳定发光,实际上是激发过程与复合过程的准平衡。ZnS:Cu,Cl的绿色发光来源于深施主-深受主对的复合发射。实验结果的分析表明,ZnS:Cu,Cl中深施主-深受主之间的能级间隔约为2.42eV。 相似文献
23.
Knut Smoczyk 《Mathematische Zeitschrift》2002,240(4):849-883
We prove that symplectic maps between Riemann surfaces L, M of constant, nonpositive and equal curvature converge to minimal symplectic maps, if the Lagrangian angle for the corresponding Lagrangian submanifold in the cross product space satisfies . If one considers a 4-dimensional K?hler-Einstein manifold of nonpositive scalar curvature that admits two complex structures J, K which commute and assumes that is a compact oriented Lagrangian submanifold w.r.t. J such that the K?hler form w.r.t.K restricted to L is positive and , then L converges under the mean curvature flow to a minimal Lagrangian submanifold which is calibrated w.r.t. .
Received: 11 April 2001 / Published online: 29 April 2002 相似文献
24.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
25.
Dean A. Carlson 《Journal of Mathematical Analysis and Applications》2002,276(2):561-588
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate feedback Nash equilibria for a class of n-person differential games. Both the finite-horizon and infinite-horizon cases are considered. Examples are given to illustrate the presented results. 相似文献
26.
Mikhail Andramonov 《Journal of Global Optimization》2002,24(2):115-132
We consider applications of disjunctive programming to global optimization and problems with equilibrium constraints. We propose a modification of the algorithm of F. Beaumont for disjunctive programming problems and show its numerical efficiency. 相似文献
27.
Let T and S be invertible measure preserving transformations of a probability measure space (X, ℬ, μ). We prove that if the group generated by T and S is nilpotent, then exists in L
2-norm for any u, v∈L
∞(X, ℬ, μ). We also show that for A∈ℬ with μ(A)>0 one has . By the way of contrast, we bring examples showing that if measure preserving transformations T, S generate a solvable group, then (i) the above limits do not have to exist; (ii) the double recurrence property fails, that
is, for some A∈ℬ, μ(A)>0, one may have μ(A∩T
-n
A∩S
-
n
A)=0 for all n∈ℕ. Finally, we show that when T and S generate a nilpotent group of class ≤c, in L
2(X) for all u, v∈L
∞(X) if and only if T×S is ergodic on X×X and the group generated by T
-1
S, T
-2
S
2,..., T
-c
S
c
acts ergodically on X.
Oblatum 19-V-2000 & 5-VII-2001?Published online: 12 October 2001 相似文献
28.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
29.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献
30.
Boban Marinković 《Mathematical Methods of Operations Research》2006,63(3):513-524
We present local sensitivity analysis for discrete optimal control problems with varying endpoints in the case when the customary regularity of boundary conditions can be violated. We study the behavior of the optimal solutions subject to parametric perturbations of the problem. 相似文献