全文获取类型
收费全文 | 11020篇 |
免费 | 714篇 |
国内免费 | 1417篇 |
专业分类
化学 | 6776篇 |
晶体学 | 171篇 |
力学 | 660篇 |
综合类 | 70篇 |
数学 | 955篇 |
物理学 | 4519篇 |
出版年
2024年 | 13篇 |
2023年 | 160篇 |
2022年 | 167篇 |
2021年 | 199篇 |
2020年 | 222篇 |
2019年 | 252篇 |
2018年 | 211篇 |
2017年 | 305篇 |
2016年 | 328篇 |
2015年 | 276篇 |
2014年 | 479篇 |
2013年 | 677篇 |
2012年 | 786篇 |
2011年 | 816篇 |
2010年 | 619篇 |
2009年 | 820篇 |
2008年 | 821篇 |
2007年 | 840篇 |
2006年 | 724篇 |
2005年 | 641篇 |
2004年 | 556篇 |
2003年 | 402篇 |
2002年 | 372篇 |
2001年 | 276篇 |
2000年 | 259篇 |
1999年 | 275篇 |
1998年 | 227篇 |
1997年 | 248篇 |
1996年 | 148篇 |
1995年 | 145篇 |
1994年 | 136篇 |
1993年 | 140篇 |
1992年 | 134篇 |
1991年 | 84篇 |
1990年 | 62篇 |
1989年 | 54篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 9篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
An approximate method is developed to solve the full nonlinear equations governing two-dimensional irrotational flow in a free waterfall, falling under the influence of gravity, at high Froude number based on conditions far upstream. Schwarz—Christoffel transformation is used to map the region, in the complex potential-plane, onto the upper half-plane. The Hilbert transformation as well as the perturbation technique, for large Froude number, are used as a basis for the approximate solution of the problem. A complete solution, up to second-order approximation, for the downstream free-surfaces profiles, for different Froude number, is discussed and illustrated. The obtained approximate solutions are compared with those of other authors. Favourable agreement with other results suggests that this method is effective in dealing with flow problems strongly influenced by gravity and high Froude number. The results obtained by this method are sufficiently accurate for practical purposes. 相似文献
62.
The fluorescence dynamics parameters of the fluorescent transient flavin-luciferase species from the typesVibrio fischeri andPhotobacterium leiognathi are presented. The fluorescence anisotropy decay is a single exponential function for both types. The correlation time is 70 ns for theP. leiognathi fluorescent transient intermediate (2°C, aqueous buffer, pH 7.0), consistent with the rotational correlation time of the luciferase macromolecule (77 kD) to which the flavin fluorophore is rigidly attached. In contrast, for theV. fischeri species the observed correlation time for the anisotropy decay function is 133 ns. This suggests that protein self-association occurs in theV. fischeri case and this is confirmed by filtration, where the fluorescent transient fromV. fischeri does not pass through a 100,000 molecular weight cutoff membrane, whereas theP. leiognathi species does. The filtration method also demonstrates self-association in the luciferase peroxyflavin and photoflavin fromV. fischeri. A monomer-dimer equilibrium also explains the previously reported high correlation times for theV. harveyi luciferase-flavin species. It is proposed that the self-association competes with the lumazine protein interaction in the bioluminescence reaction. 相似文献
63.
64.
This paper is concerned with the quenching problem of a degenerate functional reaction-diffusion equation. The quenching problem and global existence of solution for the reaction-diffusion equation are derived and, some results of the positive steady state solutions for functional elliptic boundary value are also presented. 相似文献
65.
66.
Comparison of Two Reformulation-Linearization Technique Based Linear Programming Relaxations for Polynomial Programming Problems 总被引:3,自引:0,他引:3
In this paper, we compare two strategies for constructing linear programmingrelaxations for polynomial programming problems using aReformulation-Linearization Technique (RLT). RLT involves an automaticreformulation of the problem via the addition of certain nonlinear impliedconstraints that are generated by using the products of the simple boundingrestrictions (among other products), and a subsequent linearization based onvariable redefinitions. We prove that applying RLT directly to the originalpolynomial program produces a bound that dominates in the sense of being atleast as tight as the value obtained when RLT is applied to the jointcollection of all equivalent quadratic problems that could be constructed byrecursively defining additional variables as suggested by Shor. 相似文献
67.
meso-四(4-乙酰氧基苯)卟啉-铜(Ⅱ)-乳化剂OP体系荧光熄灭法测定微量铜(Ⅱ)的研究 总被引:1,自引:0,他引:1
本文研究了高灵敏的meso-四(4-乙酰氧基苯)卟啉[T(4-AOP)P]-铜(Ⅱ-乳化剂OP体系。在酸度为pH5.0~5.6范围内形成的三元络合物可引起T(4-AOP)P-OP荧光强度的定量熄灭,其Ex=413nm,EM=656.9nm,Cu(Ⅱ)浓度在0~0.150μg/ml范围内有良好的线性关系,回归方程F=25.51-8.45m,试验了14种离子的干扰影响,并用此法测定了小球藻中Cu的含量,回收率达96~104%。 相似文献
68.
69.
蔡建平 《Annals of Differential Equations》2004,20(1):14-20
This paper investigates the periodic boundary value problems for a class of second order functional differential equations. The monotone iterative technique and the maximum principle are applied to obtain the existence of maximal and minimal solutions. 相似文献
70.
考虑二阶非线性椭圆型微分方程∑^n_{i,j}∂/∂x_i{A_{i,j}(x,y)∂/∂x_j}+q(x)f(y)=0 (E),其中q(x)在外区域 Ω∈R\+n上变号. 利用偏Riccati变换和积分平均技巧, 建立了方程(E)所有解振动的充分准则. 相似文献