全文获取类型
收费全文 | 157573篇 |
免费 | 29800篇 |
国内免费 | 14379篇 |
专业分类
化学 | 121790篇 |
晶体学 | 1745篇 |
力学 | 8929篇 |
综合类 | 721篇 |
数学 | 16687篇 |
物理学 | 51880篇 |
出版年
2024年 | 298篇 |
2023年 | 2517篇 |
2022年 | 3796篇 |
2021年 | 4678篇 |
2020年 | 6069篇 |
2019年 | 6996篇 |
2018年 | 5090篇 |
2017年 | 4518篇 |
2016年 | 8992篇 |
2015年 | 8801篇 |
2014年 | 10110篇 |
2013年 | 12836篇 |
2012年 | 13926篇 |
2011年 | 13866篇 |
2010年 | 10422篇 |
2009年 | 10053篇 |
2008年 | 10257篇 |
2007年 | 8895篇 |
2006年 | 8107篇 |
2005年 | 7040篇 |
2004年 | 5429篇 |
2003年 | 4454篇 |
2002年 | 4952篇 |
2001年 | 3832篇 |
2000年 | 3426篇 |
1999年 | 2982篇 |
1998年 | 2375篇 |
1997年 | 2211篇 |
1996年 | 2322篇 |
1995年 | 1895篇 |
1994年 | 1784篇 |
1993年 | 1439篇 |
1992年 | 1348篇 |
1991年 | 1200篇 |
1990年 | 975篇 |
1989年 | 704篇 |
1988年 | 556篇 |
1987年 | 456篇 |
1986年 | 469篇 |
1985年 | 388篇 |
1984年 | 278篇 |
1983年 | 199篇 |
1982年 | 163篇 |
1981年 | 125篇 |
1980年 | 84篇 |
1979年 | 45篇 |
1978年 | 34篇 |
1976年 | 37篇 |
1975年 | 34篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
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
912.
The He1 photoelectron (PE) spectra of both 2(5H) furanone and itstrans-chair-dimeric-compound (t-c-DFN) are reported. The assignment of the PES bands is made on the basis of band shapes, the PES results of the molecules
which have the similar atomic groups, and the restricted Hartree-Fock (RHF) calculations for the molecules studied. From the
results of both PES experimental and theoretical calculations, it is proved that the ionization potential (IPS) of the HOMO
for the dimeric-compound is lower than that of the HOMO for the monomer. And the total energy computed for thet-c-DFN is the lowest in the four possible configurations of dimeric-compounds of 2(5H) furanone. Therefore the synthesis oft-c-DFN is also the easiest.
Project supported by the National Natural Science Foundation of China. 相似文献
913.
简述了聚氧化乙烯介质中的铽、铕、铥、钆、钇、镓、锰掺杂的硫化锌纳米晶的制备方法以及紫外吸收光谱、激发光谱和光激发发射光谱.制成的硫化锌纳米晶直径为3.0~3.5nm. 相似文献
914.
A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed.
The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate
theory are discussed. It is found that the total wavccurrent field consists of pure wave, pure current and interaction components.
The shear current not only directly changes the flow field, but also indirectly does so by changing the wave parameters due
to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear
superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is
used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the
best.
Project supported by the Chinese Academy of Sciences. 相似文献
915.
奚欧根 《宁波大学学报(理工版)》1991,(1)
本文定义了Γ-环的b-理想与拟b-理想,论述了Γ-环中都有一个Baer根,一个b-根与一个拟强b-根,并且还证得了Γ-环的Baer根=b-根=拟b-根。 相似文献
916.
Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates. 相似文献
917.
大型稀疏无约束最优化问题的行列修正算法 总被引:3,自引:0,他引:3
本文提出了一类适用于大型稀疏最优化问题的简单易行的行列修正算法,获得了新算法的局部超一性收敛性,大量的数值试验表明这是一个较为理想的修正算不。新算法同样可以用来求解大型对称性非线性方程组。 相似文献
918.
用三维样边界元法分析水闸闸室结构。底板,闸墩和载水墙等为其子结构,交通桥,工作桥和胸墙等处理为内部支撑。地基和边载可以是任意的,只要能给定地表位移面力关系。在各种工况下,不论是设置平板门还是弧形门,是平底板是反拱底板,即使在稀疏剖分下也能给出高精度的位移场,应力场和地基反力场。 相似文献
919.
Yazhen Wang 《Statistics & probability letters》1994,20(5):347-352
For testing the equality of normal variances with an increasing alternative, under the null hypothesis the likelihood ratio test statistic is asymptotically distributed as a mixture of chi-squared distributions. In this paper a Bartlett-type adjustment is proposed to improve the approximation of the null distribution of the likelihood ratio test statistic with an ordered alternative. 相似文献
920.