全文获取类型
收费全文 | 47795篇 |
免费 | 8826篇 |
国内免费 | 7954篇 |
专业分类
化学 | 35698篇 |
晶体学 | 810篇 |
力学 | 2969篇 |
综合类 | 598篇 |
数学 | 5289篇 |
物理学 | 19211篇 |
出版年
2024年 | 149篇 |
2023年 | 874篇 |
2022年 | 1755篇 |
2021年 | 1930篇 |
2020年 | 1977篇 |
2019年 | 2036篇 |
2018年 | 1765篇 |
2017年 | 1858篇 |
2016年 | 2392篇 |
2015年 | 2606篇 |
2014年 | 3187篇 |
2013年 | 3964篇 |
2012年 | 4568篇 |
2011年 | 4586篇 |
2010年 | 3479篇 |
2009年 | 3514篇 |
2008年 | 3802篇 |
2007年 | 3197篇 |
2006年 | 2959篇 |
2005年 | 2394篇 |
2004年 | 1791篇 |
2003年 | 1475篇 |
2002年 | 1467篇 |
2001年 | 1208篇 |
2000年 | 966篇 |
1999年 | 793篇 |
1998年 | 606篇 |
1997年 | 516篇 |
1996年 | 450篇 |
1995年 | 372篇 |
1994年 | 361篇 |
1993年 | 282篇 |
1992年 | 223篇 |
1991年 | 188篇 |
1990年 | 179篇 |
1989年 | 121篇 |
1988年 | 99篇 |
1987年 | 72篇 |
1986年 | 85篇 |
1985年 | 59篇 |
1984年 | 27篇 |
1983年 | 34篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 22篇 |
1977年 | 12篇 |
1975年 | 8篇 |
1957年 | 9篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A simple and sensitive method was conducted for the determination of trace amounts of proteins with benzeneazo-8-acetylamino-1-naphthol-3,6-disulfonic acid sodium salt (azophloxine, AP) using a Rayleigh light-scattering (RLS) technique. At pH 2.60 and in the presence of an emulsifier OP microemulsion, the RLS of AP can be greatly enhanced by proteins, owing to the interaction between AP and protein. The enhanced intensity is proportional to the concentration of proteins. Four proteins, including bovine serum albumin (BSA), human serum albumin (HSA), lysozyme (Lys) and gamma globulin (gamma-G) have been tested. For example, the linear range of BSA was 0 - 0.06 microg mL(-1) with detection limits of 2.38 ng mL(-1). The method was applied to the analysis of protein in human urine and penicillin samples with satisfactory results. The relative standard deviation was in all instances less than 4.0%, and the recovery was in the range of 97.5 - 104%. 相似文献
122.
We study the average property of the isospin effects of reaction mechanism induced by neutron-halo nuclei within the isospin-dependent quantum molecular dynamics model. We find that the extended neutron density distribution for the neutron-halo projectile brings an important isospin effect into the reaction mechanism, which induces the decrease of nuclear stopping R; however, it induces the obvious increases of the neutron-proton ratio of nucleon emissions (n/p)nucl for all of the beam energies in this work, compared to the same mass stable colliding system. 相似文献
123.
The double neutron/proton ratio of nucleon emissions taken from two reaction systems using four isotopes of the same element, namely, the neutron/proton ratio in the neutron-rich system over that in the more symmetric system, has the advantage of reducing systematically the influence of the Coulomb force and the normally poor efficiencies of detecting low energy neutrons. The double ratio thus suffers less systematic errors. Within the IBUU04 transport model the double neutron/proton ratio is shown to have about the same sensitivity to the density dependence of nuclear symmetry energy as the single neutron/proton ratio in the neutron-rich system involved. The double neutron/proton ratio is therefore more useful for further constraining the symmetry energy of neutron-rich matter. 相似文献
124.
The authors consider the limiting behavior of various branches in a uniform recursive tree with size growing to infinity.The limiting distribution ofζ_(n,m),the number of branches with size m in a uniform recursive tree of order n,converges weakly to a Poisson distribution with parameter 1/m with convergence of all moments.The size of any large branch tends to infinity almost surely. 相似文献
125.
负关联噪声驱动下单模激光的定态分析 总被引:2,自引:1,他引:1
研究了负关联的加法和乘法高斯白噪声驱动下单模激光损失模型的定态情况。文中推导了负关联情况下,定态时的激光场幅的几率分布,光强的平均值,光强的协方差以及光强的偏斜率。并和文献〔1,2〕中正关联时的定态分析作了比较,发现了有意义的新现象。 相似文献
126.
7-Hydroxyderivativesofcholesteroldisplayawidevarietyofbiologicalactivities'-',mostofwhicharerelatedtothephysiologicalcontrolofcholesterolbiosynthesisandantitumoractivity.Inearlyreports',the7-hydroxycholesterolswerepreparedbythesequenceofacetylation,allylicchromicoxidation,andhydridereduction.Generally,theproductisamixtureof7a-and76-epimerswhichisdifficulttobeseparated.V.Kumaretal5improvedthisprocedurebyusingstereospecificreducingreagentsinsteadofthesimplehydride.7a-and7o-epimerscouldbeobtained… 相似文献
127.
128.
129.
130.