全文获取类型
收费全文 | 32086篇 |
免费 | 4644篇 |
国内免费 | 3724篇 |
专业分类
化学 | 17760篇 |
晶体学 | 317篇 |
力学 | 1457篇 |
综合类 | 255篇 |
数学 | 2790篇 |
物理学 | 9289篇 |
无线电 | 8586篇 |
出版年
2024年 | 53篇 |
2023年 | 760篇 |
2022年 | 809篇 |
2021年 | 1099篇 |
2020年 | 1233篇 |
2019年 | 1121篇 |
2018年 | 901篇 |
2017年 | 934篇 |
2016年 | 1320篇 |
2015年 | 1321篇 |
2014年 | 1604篇 |
2013年 | 2081篇 |
2012年 | 2615篇 |
2011年 | 2549篇 |
2010年 | 1841篇 |
2009年 | 1886篇 |
2008年 | 2139篇 |
2007年 | 1999篇 |
2006年 | 1915篇 |
2005年 | 1613篇 |
2004年 | 1233篇 |
2003年 | 1068篇 |
2002年 | 948篇 |
2001年 | 756篇 |
2000年 | 767篇 |
1999年 | 852篇 |
1998年 | 714篇 |
1997年 | 595篇 |
1996年 | 609篇 |
1995年 | 517篇 |
1994年 | 473篇 |
1993年 | 403篇 |
1992年 | 351篇 |
1991年 | 303篇 |
1990年 | 277篇 |
1989年 | 180篇 |
1988年 | 141篇 |
1987年 | 105篇 |
1986年 | 113篇 |
1985年 | 88篇 |
1984年 | 41篇 |
1983年 | 43篇 |
1982年 | 41篇 |
1981年 | 23篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 793 毫秒
991.
Study of SPG membrane emulsification processes for the preparation of monodisperse core-shell microcapsules 总被引:1,自引:0,他引:1
Chu LY Xie R Zhu JH Chen WM Yamaguchi T Nakao S 《Journal of colloid and interface science》2003,265(1):187-196
Experimental investigations on the Shirasu-porous-glass (SPG)-membrane emulsification processes for preparing monodisperse core-shell microcapsules with porous membranes were carried out systematically. The results showed that, to get monodisperse oil-in-water (O/W) emulsions by SPG membrane emulsification, it was more important to choose an anionic surfactant than to consider hydrophile-lipophile balance (HLB) matching. Increasing the viscosity of either the disperse phase or the continuous phase or decreasing the solubility of the disperse phase in the continuous phase could improve both the monodispersity and the stability of emulsions. With increasing monomer concentration inside the disperse phase, the monodispersity of emulsions became slightly worse and the mean diameter of emulsions gradually became smaller. Monodisperse monomer-containing emulsions were obtained when the SPG membrane pore size was larger than 1.0 micro m, and from these emulsions satisfactory monodisperse core-shell microcapsules with a porous membrane were prepared. On the other hand, when the SPG membrane pore size was smaller than 1.0 mciro m, no monodisperse emulsions were obtained because of the formation and chokage of solid monomer crystals in the pores or at the end of the pores of the SPG membrane. This was due to the remarkable solvation and diffusion of the solvent in water. With increasing the emulsification time the average emulsion diameter generally decreased, and the monodispersity of the emulsions gradually became worse. 相似文献
992.
Yang HH Zhu QZ Li DH Lin P Ding MT Xu JG 《Fresenius' Journal of Analytical Chemistry》2001,370(1):88-91
A new fluorimetric immunoassay for alpha-fetoprotein (AFP) has been developed using a novel promising mimetic peroxidase, iron(III) tetrasulfonatophthalocyanine (FeTSPc), as a labeling reagent to catalyze the fluorescence reaction of P- hydroxyphenylacetic acid (P-HPA) and hydrogen peroxide (H2O2). In the competitive immunoassay, anti-AFP antibody was coated on a 96-well plate (polystyrene) and a constant amount of FeTSPc-labeled AFP and a known amount of test solution were added. Non-labeled and FeTSPc-labeled AFP compete for binding to the plate-bound antibody. After the immunoreaction, the immunochemically adsorbed FeTSPc-AFP conjugate moiety was determined by measuring the fluorescence produced in a solution containing P-HPA and H2O2. AFP can be determined in the concentration range of 1-300 ng mL(-1) with a detection limit of 0.5 ng mL(-1). 相似文献
993.
Measurement of iron and manganese is very important in evaluating the quality of natural waters. We have constructed an automated Fe(II), total dissolved iron(TDI), Mn(II), and total dissolved manganese(TDM) analysis system for the quality control of underground drinking water by reverse flow injection analysis and chemiluminescence detection(rFIA-CL). The method is based on the measurement of the metal-catalyzed light emission from luminol oxidation by potassium periodate. The typical signal is a narrow peak, in which the height is proportional to light emitted and hence to the concentration of metal ions. The detection limits were 3 x 10(-6)mug ml(-1) for Fe(II) and the linear range extents up to 1.0 x 10(-4) and 5 x 10(-6)mug ml(-1) for Mn(II) cover a linear range to 1.0 x 10(-4)mug ml(-1). This method was used for automated in-situ monitoring of total dissolved iron and total dissolved manganese in underground water during water treatment. 相似文献
994.
Two new C18-norditerpenoid alkaloids from Aconitum delavayi 总被引:2,自引:0,他引:2
Shan Hao Jiang Hai Qing Wang Yi Ming Li Shuang Jun Lin Jun Jie Tan Da Yuan Zhu 《中国化学快报》2007,18(4):409-411
Further phytochemical investigation of the unique C18-norditerpenoid alkaloids from the roots of Aconitum delavayi Franch ledto the isolation of two new norditerpenoid alkaloids,delavaconitine F 1 and delavaconitine G 2.Their structures were determinedfrom spectroscopic evidence. 相似文献
995.
996.
Interlayer energy transfer between 2,3-naphthol-10-hexadecylaza-15-crown-5(NC16) and N-[1-(9-methoxyanthryl)] decylaza-15-crown-5(A10C) within multilayer Langmuir-Blodgett films has been studied by steady-state fluorescence spectra. The donor and acceptor could be separated precisely by inserting stearic acid (SA) spacers. The efficiency of the energy transfer increases with the decrease in the donor-acceptor distance by a quadratic manner, suggesting the donor excitations are delocalized in the layer. 相似文献
997.
998.
本文应用γ效应以及Suter-Flory的聚丙烯构象内旋转模型,计算了一组两端全部为全同2单元组(meso),中间为11单元组不同立构缺陷的高全同聚丙烯(IPP)分子链中心甲基碳的相对化学位移。将其与67.8MHz ~(13)C-NMR观测值比较,说明IPP中主要缺陷是孤立的rr,此外还有长间同序列的分子链混合,而不是孤立的rrrr缺陷分布在IPP分子链上。 相似文献
999.
1000.
Xie Yongshu Ni Jia Liu Xueting Liu Qingliang Xu Xiaolong Du Chenxia Zhu Yu 《Transition Metal Chemistry》2003,28(3):367-370
Novel 1:2 and 1:1 (M:L) copper(II) complexes have been prepared from the tridentate ligand 2-(1-methyl-2-aza-5-oxapentyl)phenol (H2L1). The crystal structure of [Cu(HL1)2] (1) exhibits a noncentrosymmetric square-planar geometry with a slightly tetrahedral distortion. The CuII atom is coordinated by two amino N and two phenoxo O atoms of two (HL1)– ligands. The phenoxo and the alkoxy groups are involved in two strong intramolecular hydrogen bonds. The coordination moieties are further connected to a 1D linear structure by the action of intermolecular hydrogen bonds between the alkoxyl and the amino groups. The importance of steric hindrance introduced by the methyl group in the molecular structure and the packing of the complex molecules has been demonstrated. The e.p.r. parameters of (1) have been obtained: g
= 2.231, g
= 2.005, g
iso = 2.080, A
= 185.0 G, A
iso = 86.5 G, A
= (3A
iso – A
)/2 = 37.3 G. These results confirm a distorted square planar stereochemistry with a (
)1 ground state. 相似文献