全文获取类型
收费全文 | 6129篇 |
免费 | 696篇 |
国内免费 | 498篇 |
专业分类
化学 | 1526篇 |
晶体学 | 84篇 |
力学 | 1251篇 |
综合类 | 29篇 |
数学 | 140篇 |
物理学 | 4293篇 |
出版年
2024年 | 11篇 |
2023年 | 29篇 |
2022年 | 100篇 |
2021年 | 128篇 |
2020年 | 85篇 |
2019年 | 119篇 |
2018年 | 89篇 |
2017年 | 184篇 |
2016年 | 238篇 |
2015年 | 178篇 |
2014年 | 311篇 |
2013年 | 409篇 |
2012年 | 246篇 |
2011年 | 474篇 |
2010年 | 348篇 |
2009年 | 472篇 |
2008年 | 422篇 |
2007年 | 531篇 |
2006年 | 458篇 |
2005年 | 328篇 |
2004年 | 293篇 |
2003年 | 216篇 |
2002年 | 194篇 |
2001年 | 207篇 |
2000年 | 165篇 |
1999年 | 152篇 |
1998年 | 155篇 |
1997年 | 115篇 |
1996年 | 81篇 |
1995年 | 105篇 |
1994年 | 96篇 |
1993年 | 69篇 |
1992年 | 62篇 |
1991年 | 57篇 |
1990年 | 37篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 19篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1957年 | 2篇 |
排序方式: 共有7323条查询结果,搜索用时 15 毫秒
151.
Oi-lian Song Guang-zhao Zhang Chi Wu 《高分子科学》2007,(5):441-445
Using a core(142 nm)made of linear polystyrene(PS)chains as a seed,we further polymerized a thin layer of cross-linked PS shell(7 nm)on it in water to form a core-shell particle.Such a particle swells in toluene,which enables linear PS chains inside the core to gradually diffuse out through the porous shell.Using a combination of static and dynamic laser light scattering,we examined the chain diffusion process by following the change of the scattering intensity(i.e.the average molar mass of the particles).For the first time,we have revealed that the diffusion exhibits three stages.In the first stage,the chain diffusion through the shell is even faster than their translational diffusion in a dilute solution.The three stages respectively correspond to the change of the solution in the core from concentrated to semidilute and then from semidilute to dilute. 相似文献
152.
Benturquia N Couderc F Sauvinet V Orset C Parrot S Bayle C Renaud B Denoroy L 《Electrophoresis》2005,26(6):1071-1079
Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples. 相似文献
153.
A capillary electrophoresis (CE) method with laser-induced fluorescence (LIF) detection was developed for the separation and detection of carnosine-related peptides (carnosine, anserine, and homocarnosine). A sensitive and fluorogenic regent, 3-(4-carboxybenzoyl) quinoline-2-carboxaldehyde (CBQCA) was selected as a precapillary labeling reagent for imidazole dipeptides to form isoindole derivatives. The optimized molar ratio between CBQCA and peptide was found to be 75:1, and 50 mmol/L borate buffer (pH 9.2) was used for the derivatization in order to achieve good efficiency. Three imidazole dipeptides were baseline-separated within 20 min by using 112 mmol/L sodium borate (pH 10.4-10.8) as running buffer. Concentration detection limits (signal-to-noise ratios) for carnosine, anserine, and homocarnosine were 4.73, 4.37, and 3.94 nmol/L, respectively. This method has been applied to the analysis of human cerebrospinal fluid (CSF) and meat dry powder of pig and sheep. Recoveries were in the range of 82.9-104.8% for homocarnosine in CSF. For carnosine and anserine, the recoveries are 98.3% and 80.2% in meat dry powder of pig and 111.2% and 112.8% in meat dry powder of sheep, respectively. 相似文献
154.
The hydrogen donation kinetics of four 3-aryl-benzofuranones with different chemical structures toward tert-butoxyl radicals were studied using laser flash photolysis (LFP) technique. The rate constants of hydrogen reactions, which can be used to evaluate the hydrogen donating abilities of 3-aryl-benzofuranones toward radicals, were obtained. The results showed that the position of substituted methyl group has a very important effect on the hydrogen donating ability of benzofuranone toward tert-butoxyl radicals, i.e. if the methyl group is on 2′-position, the hydrogen donation of 3-aryl-benzofuranone toward tert-butoxyl radicals will be prevented and the hydrogen donating ability will be weakened. 相似文献
155.
156.
157.
158.
横向激励大气压(transversely excited atmospheric,TEA)CO2激光器的放电稳定性是决定该类型激光器应用效果的关键因素。通过对采用电感充放电电路的紫外预电离激光器的实验研究,得到了激光器放电动态过程的规律,并发现残余振荡是主放电后发生弧光放电的主要原因。实验中采用不同配比的气体,并对电感充放电电路与改进后的硅堆充放电电路进行了比较。实验结果表明:增加充电电感值可以降低主放电结束后储能电容上的残余电压;而采用硅堆放电电路在主放电后仅有相对幅值很低的稳定残压,两种方案都大幅度抑制了弧光放电的形成,有效地提高了激光单脉冲能量。 相似文献
159.
通过仿真计算分析了激光在光束控制系统通道内传输所产生的热效应及其对远场光束质量的影响。激光传播由近轴波方程描述,用快速傅里叶变换技术求解;激光热效应引起的流场密度变化采用完全Navier-Stokes方程计算。计算给出了不同波长、不同吸收系数条件下的远场光斑情况。计算结果表明,在典型的工作条件和状态下,较高能量激光在光束控制系统通道内产生的热效应影响不容忽视,它会明显降低远场目标处的能量集中度,增大光斑的发散。 相似文献
160.
随着大型激光器的发展,对短波段减反膜的要求日益提高,其中钕玻璃激光三倍频(355nm)的减反射成为新的技术要点。采用溶胶-凝胶工艺合成SiO2溶胶,采用提拉镀膜法制备纳米多孔SiO2薄膜,薄膜厚度为75nm,折射率控制在1.22,镀制在石英基底上的薄膜其355nm波长的反射率仅为0.2%。通过氨处理工艺和薄膜的表面修饰,薄膜的抗磨擦性能和疏水性能大大提高,薄膜经过蘸有灰尘、乙醇的棉花球擦洗20次和50次后,透射率最大值仅分别降低0.13% 和 0.39%,与水珠的接触角达到110°。 相似文献