全文获取类型
收费全文 | 1683篇 |
免费 | 195篇 |
国内免费 | 159篇 |
专业分类
化学 | 1267篇 |
晶体学 | 36篇 |
力学 | 68篇 |
综合类 | 15篇 |
数学 | 175篇 |
物理学 | 476篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 36篇 |
2021年 | 55篇 |
2020年 | 48篇 |
2019年 | 53篇 |
2018年 | 44篇 |
2017年 | 35篇 |
2016年 | 55篇 |
2015年 | 74篇 |
2014年 | 86篇 |
2013年 | 121篇 |
2012年 | 127篇 |
2011年 | 145篇 |
2010年 | 76篇 |
2009年 | 80篇 |
2008年 | 110篇 |
2007年 | 96篇 |
2006年 | 80篇 |
2005年 | 84篇 |
2004年 | 81篇 |
2003年 | 52篇 |
2002年 | 54篇 |
2001年 | 49篇 |
2000年 | 56篇 |
1999年 | 37篇 |
1998年 | 21篇 |
1997年 | 27篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有2037条查询结果,搜索用时 31 毫秒
21.
The drug-loaded alginate/poly-L-arginine/chitosan ternary complex microcapsules were prepared by mixing method, absorption method and the combined method of mixing and absorption, respectively. The effect of drug-loading methods on drug load, the encapsulation efficiency and the release properties of the complex microcapsules were investigated. The results showed that the absorption process is a dominating factor to greatly increase the drug load of Hb into microcapsules. Upon loading Hb into microcapsules by combined method of mixing and absorption, the drug load (19.9%) is up to the maximum value, and the encapsulation efficiency is 93.8%. Moreover, the drug release is a zero-order kinetics process for the ternary complex microcapsules made by mixing. For the complex microcapsules made by absorption, the drug release is a first-order kinetics. However, for the complex microcapsules made by combining the mixing and the absorption, the drug release obeys a first-order kinetics during the first eighteen hours, changing afterwards to a zero-order kinetics process. Effect of drug-loading methods on drug load and encapsulation efficiency of alginate/poly-L-arginine/chitosan ternary complex microcapsules. 相似文献
22.
考虑到手性毛细管电泳分离机理的复杂性,提出了不依赖于统计模型的二进制编码遗传算法多目标优化策略。根据实验参数的多少及其重要性,采用均匀设计安排完成初步实验。并用Derringer功效函数作为多指标同时优化的评价指标,以取得较高的分离度和较快分离速度;通过对实验参数给予编码,转化为二进制字符串,根据得到的总功效函数值大小进行遗传算法操作,产生新的一组实验条件。重复上述过程直到得到最佳分离条件为止。此方法成功地应用于华法令对映体的毛细管电泳分离条件优化。 相似文献
23.
ToF-SIMS analysis of the organometallic cluster Os3(μ-H)(CO)10(μ-SCH2CH2SH) chemically attached onto a silver or gold surface, and of the cluster fragment Os3(μ-H)(CO)10(μ-OSi) on a silica surface, allows for identification of the surface organometallic species, and also gives information on its reactivity. 相似文献
24.
25.
利用傅立叶变换红外(FT-IR)和拉曼(FT-Raman)光谱研究了高浓度磷脂酰胆碱(PC)与牛血清白蛋白(BSA)的相互作用,及Eu3+对该作用的影响.FT-IR结果显示,PC/BSA混合体系中二者的相互作用主要发生在PC头部极性基团,且这一作用随BSA含量的增加而增强,作用后蛋白质二级结构中α螺旋的比例有所增加. FT-Raman光谱说明PC与BSA的相互作用影响磷脂CH链的排列有序程度. PC/BSA/Eu3+体系的红外光谱显示, Eu3+与PC的磷氧键发生了强相互作用,并使蛋白α螺旋的比例进一步增加. 相似文献
26.
27.
Spherical, smooth-surfaced and mechanically stable alginate-poly(L-histidine) (PLHis) microcapsules with narrow particle size distributions were prepared by incubating calcium alginate beads in aqueous solutions of PLHis. The in vitro release characteristics, drug loading and encapsulation efficiency of the microcapsules were investigated using bovine erythrocytes hemoglobin (Hb) as a model drug. The results showed that the concentration of Ca(2+) ions had a considerable effect on the drug loading, encapsulation efficiency and in vitro release behavior of the microcapsules. When the concentration of CaCl(2) in the PLHis solution was increased from 0 to 3.0% (w/v), the drug loading and encapsulation efficiency decreased significantly from 38.0 to 4.3% and from 92.9 to 8.0%, respectively, while the total cumulative release of Hb from microcapsules in phosphate buffered saline solution (PBS, pH 6.8) decreased from 96.2 to 72.8% in 24 h. No significant protein release was observed during 70 h of incubation in hydrochloric acid solution (pH 1.2). However, under neutral conditions (PBS, pH 6.8), the Hb was completely and stably released within 24-70 h. An explosion test showed that the stability of alginate-PLHis microcapsules depended strongly on the concentration of PLHis and the calcium ions in solution. [Diagram: see text] Microscopy photo of Hb-loaded alginate-PLHis microcapsules. 相似文献
28.
CRYSTALLIZATION AND MECHANICAL PROPERTIES OF POLYPROPYLENE FILLED WITH SiO2 NANOPARTICLES 总被引:3,自引:0,他引:3
Bao-qing Shentu Ji-peng Li Zhi-xue Weng 《高分子科学》2007,(3):227-233
Oleic acid (OA)-modified SiO2 (OA-m-SiO2) nanoparticles were prepared using surface modification method. Infrared spectroscopy (IR) was used to investigate the structure of the OA-m-SiO2 nanoparticles, and the result showed that OA attached onto the surface of SiO2 nanoparticles through esterification. Effect of OA concentration on the dispersion stability of OA-m-SiO2 in heptane was also studied, and the result indicated that OA-m-SiO2 nanoparticles were dispersed in heptane more stably than the unmodified ones. OA-m-SiO2 nanoparticles can also be dispersed in polypropylene (PP) matrix in nano-scale. The effect of OA-m-SiO2 on crystallization of PP was studied by means of DSC. It was found that the introduction of OA-m-SiO2 resulted in significant increase in the crystallization temperature, crystallization degree and crystallization rate of PP, and OA-m-SiO2 could effectively induce the formation of β-crystal PP. Effect of OA-m-SiO2 content on mechanical properties of PP/OA-m-SiO2 nanocomposites was also studied. The results show that OA-m-SiO2 can significantly improve the mechanical properties of PP. 相似文献
29.
Guang‐Fei Liu Lin‐Lin Li Yong Zhang Jian‐Ping Lang Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(1):m1-m3
The title compound, [Cu(ClO4)2(C4H9N3O2)2][Cu(C4H9N3O2)2(CH4O)2](ClO4)2·2CH3OH, comprises two independent CuII species lying on different inversion sites. In the Cu complexes, a distorted octahedral geometry arises (from basic square‐planar N4 coordination) from the weak coordination of two perchlorate ions (as Cu—O) in one species and two methanol molecules in the other (also as Cu—O). Interactions between the O atoms of the perchlorate anions or methanol groups and the imide or amine NH groups afford an extensive intermolecular hydrogen‐bonding network. 相似文献
30.
(μ3-S)FeCo2(CO)7(dppfe)的合成和晶体结构 总被引:1,自引:0,他引:1
通过简单取代反应,合成了一个新的混金属簇合物(μ3-S)FeCo2(CO)7(dppfe) (2) (dppfe=Ph2PC5H4FeC5H4PPh2).利用IR,1H NMR,MS 和 X-ray单晶衍射的方法对簇合物2进行了结构表征.簇合物2的晶体属于三斜晶系,空间群为Pī.晶胞参数: a=1.132 4(15) nm, b=1.3670(17) nm, c=1.5769(2) nm,α=114.646(2)°,β=100.340(2)°,γ=100.113(3)°, V=2.0953(5) nm3. 相似文献