全文获取类型
收费全文 | 30979篇 |
免费 | 4817篇 |
国内免费 | 3850篇 |
专业分类
化学 | 22525篇 |
晶体学 | 368篇 |
力学 | 1993篇 |
综合类 | 217篇 |
数学 | 3272篇 |
物理学 | 11271篇 |
出版年
2024年 | 58篇 |
2023年 | 496篇 |
2022年 | 736篇 |
2021年 | 951篇 |
2020年 | 1186篇 |
2019年 | 1117篇 |
2018年 | 983篇 |
2017年 | 897篇 |
2016年 | 1342篇 |
2015年 | 1296篇 |
2014年 | 1584篇 |
2013年 | 2264篇 |
2012年 | 2580篇 |
2011年 | 2689篇 |
2010年 | 1825篇 |
2009年 | 1835篇 |
2008年 | 2050篇 |
2007年 | 1857篇 |
2006年 | 1732篇 |
2005年 | 1575篇 |
2004年 | 1255篇 |
2003年 | 1067篇 |
2002年 | 1068篇 |
2001年 | 849篇 |
2000年 | 689篇 |
1999年 | 732篇 |
1998年 | 646篇 |
1997年 | 559篇 |
1996年 | 538篇 |
1995年 | 451篇 |
1994年 | 425篇 |
1993年 | 326篇 |
1992年 | 300篇 |
1991年 | 277篇 |
1990年 | 243篇 |
1989年 | 172篇 |
1988年 | 139篇 |
1987年 | 132篇 |
1986年 | 132篇 |
1985年 | 122篇 |
1984年 | 80篇 |
1983年 | 62篇 |
1982年 | 61篇 |
1981年 | 52篇 |
1980年 | 35篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1976年 | 20篇 |
1975年 | 19篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
941.
Dushmantha Kannangara Hailong Zhang Wei Shen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,280(1-3):203-215
The spreading and recoiling of water drops on several flat and macroscopically smooth model surfaces and on sized paper surfaces were studied over a range of drop impaction velocities using a high-speed CCD camera. The water drop spreading and recoiling results on several model hydrophobic and hydrophilic surfaces were found to be in agreement with observations reported in the literature. The maximum drop spreading diameter for those model surfaces at impact was found to be dependent upon the initial drop kinetic energy and the degree of hydrophobicity/hydrophilicity of the surface. The extent of the maximum drop recoiling was found to be much weaker for hydrophilic substrates than for hydrophobic substrates. Sized papers, however, showed an interesting switch of behaviour in the process of water drop impaction. They behave like a hydrophobic substrate when a water drop impacts on it, but like a hydrophilic substrate when water drop recoils. Although the contact angle between water and hydrophilic or hydrophobic non-porous surfaces changes from advancing to receding as reported in literature, the change of contact angle during water impact on paper surface is unique in that the level of sizing was found to have a smaller than expected influence on the degree of recoil. Atomic force microscopy (AFM) was used to probe fibres on a sized filter paper surface under water. The AFM data showed that water interacted strongly with the fibre even though the paper was heavily sized. Implications of this phenomenon were discussed in the context of inkjet print quality and of the surface conditions of sized papers. Results of this study are very useful in the understanding of inkjet ink droplet impaction on paper surfaces which sets the initial condition for ink penetration into paper after impaction. 相似文献
942.
943.
α-Bromo benzolymethylene triphenylphosphorane 3 has been synthesized by the reaction of benzoylmethylene triphenylphosphorane 1 with N-bromosuccinimide in the yield of 87% and can react with aromatic aldehydes 4 to give α-bromochalcones 5 in good yields. 相似文献
944.
A new rapid, selective and sensitive on-line microwave flow injection-kinetic method was developed for spectrophotometric determination of micro amounts of Ir(III), based on its catalytic effect on the m-acetylchlorophosphonazo (CPA-mA) and KIO(4) reaction in NaOH media. An on-line microwave oven was employed to accelerate the reaction. The reaction was followed spectrophotometrically by measuring the decrease of the absorbance of CPA-mA at 580 nm. The effect of five variables for the determination of Ir(III) was optimized by means of a multilayer artificial neural network using extended delta-bar-delta (EDBD) algorithms. Under the optimum experimental conditions, Ir(III) could be determined in the range 0.060-0.60 micro gZZZ;mL(-1) with detection limit of 0.02 micro gZZZ;mL(-1) and the sampling frequency of 34 h(-1). The proposed method was applied to the determination of micro amounts of Ir(III) in refined ore and secondary alloy with the recoveries from 91.4% to 109%. 相似文献
945.
946.
947.
用两束脉冲染料激光进行了CO的光学双共振四光子电离, 获得了转动分辩的CO A~(1Π)←X~(1Σ~+)和B~(1Σ~+)←A~(1Π)跃迁的光谱。观察到了在此2+1光子相继吸收中特有的选择定则。动力学研究表明CO基态到A~(1Π)态的双光子吸收是速率决定步骤, 其吸收截面约为1×10~(-49) cm~4 s。还测定了A~(1Π)态的单态转动传能截面。对于宇称指数e守恒、△J×±1的过程的截面约为0.05 nm; 随△J值增大而减小。对相同的△J, e正负变号的过程的截面总是小于e不变过程的截面。 相似文献
948.
C反应蛋白免疫电极的研究 总被引:1,自引:0,他引:1
C反应蛋白(CRP)是临床医学中重要的检验项目之一。本文以醋酸纤维素-戊二醛-己二胺载体膜与自制的原电极研制成非标记CRP免疫电极。研究了载体膜的组成对电极灵敏度的影响,并采用均匀设计法对载体膜的活化条件、抗原抗体结合时间以及电极测试条件等进行了优化。该电极响应快、灵敏度高、重现性和稳定性良好。在最佳实验条件下,电极线性范围为1.8~60μg/ml,所得线性回归方程为E=0.2+0.091[CRP];相关系数0.9989。在用于血清样品的测定中,取得满意结果。 相似文献
949.
A sandwiched structure of CdS/Ag/ZnO nanorod photoanode exhibits greatly enhanced photoelectrochemical activity for solar hydrogen generation, due to synergistic effect of CdS nanocrystallites and plasmonic Ag nanoparticles for the enhanced optical absorption and the promoted charge carrier separation. 相似文献
950.
Lynch CL Hale JJ Budhu RJ Gentry AL Finke PE Caldwell CG Mills SG MacCoss M Shen DM Chapman KT Malkowitz L Springer MS Gould SL DeMartino JA Siciliano SJ Cascieri MA Carella A Carver G Holmes K Schleif WA Danzeisen R Hazuda D Kessler J Lineberger J Miller M Emini E 《Organic letters》2003,5(14):2473-2475
[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1. 相似文献