全文获取类型
收费全文 | 23639篇 |
免费 | 729篇 |
国内免费 | 125篇 |
专业分类
化学 | 15615篇 |
晶体学 | 243篇 |
力学 | 695篇 |
数学 | 2184篇 |
物理学 | 5756篇 |
出版年
2023年 | 149篇 |
2022年 | 416篇 |
2021年 | 576篇 |
2020年 | 428篇 |
2019年 | 433篇 |
2018年 | 382篇 |
2017年 | 360篇 |
2016年 | 675篇 |
2015年 | 578篇 |
2014年 | 815篇 |
2013年 | 1395篇 |
2012年 | 1700篇 |
2011年 | 1907篇 |
2010年 | 1206篇 |
2009年 | 1048篇 |
2008年 | 1605篇 |
2007年 | 1387篇 |
2006年 | 1431篇 |
2005年 | 1208篇 |
2004年 | 1071篇 |
2003年 | 898篇 |
2002年 | 848篇 |
2001年 | 527篇 |
2000年 | 473篇 |
1999年 | 329篇 |
1998年 | 210篇 |
1997年 | 205篇 |
1996年 | 270篇 |
1995年 | 184篇 |
1994年 | 197篇 |
1993年 | 202篇 |
1992年 | 151篇 |
1991年 | 123篇 |
1990年 | 125篇 |
1989年 | 97篇 |
1988年 | 68篇 |
1987年 | 72篇 |
1986年 | 50篇 |
1985年 | 74篇 |
1984年 | 50篇 |
1983年 | 42篇 |
1982年 | 63篇 |
1981年 | 62篇 |
1979年 | 46篇 |
1978年 | 45篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 36篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
A bent-shaped bipyridine ligand containing a dendritic aliphatic side chain has been synthesized as a ligand and complexed with silver ion through a self-assembling process. The resulting complexes were observed to self-assemble into supramolecular structures that differ significantly as a function of the counteranion size in the solid state, as confirmed by 1-D and 2-D X-ray diffraction experiments. The secondary structure of a cationic coordination chain appears to be dependent on the size of the counteranion. As the size of anion increases, the secondary structure of the coordination chain changes, from a helical chain, via a dimeric cycle, to a zigzag chain in the solid state. Interestingly, dilute solutions of the complexes exhibiting a columnar structure in polar solvents undergo spontaneous gelation and the resulting gels display a significant Cotton effect in the chromophore of the aromatic unit. These results represent a significant example that small variation in the anion size can provide a useful strategy to manipulate the secondary structure of linear chain and thereby solid-state supramolecular structure. 相似文献
982.
Styrene was polymerized in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to yield polystyrene-TEMPO (PS-TEMPO) macroinitiator. The PS-TEMPO macroinitiator with different molecular weight was reacted with 4-vinyl pyridine (4-VP) to synthesize polystyrene-block-poly(4-vinyl pyridine) (PS-b-PVP), which was then quaternized with n-octyl iodide. Antibacterial activity of the quaternized copolymers was assessed against a gram negative bacterium (Pseudomonas aeruginosa) and a gram positive one (Staphylococcus aureus) by using the shake flask test method, and the results were compared with those of poly(styrene-random-4-vinyl pyridine) (P(ST-r--VP)). The quaternized copolymers inhibited greatly the growth of the bacteria, and PS-b-PVP was more active than P(ST-r-VP), which was ascribed to the fact that the content of quaternized 4-VP units on the surface of the particles of the former copolymer was higher than that corresponding to the latter one. 相似文献
983.
Enhancing the organic dye adsorption on porous xerogels 总被引:4,自引:0,他引:4
Zhijian Wu Ik-Sung Ahn Chang-Ha Lee Jung-Hyun Kim Yong Gun Shul Kangtaek Lee 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,240(1-3):157-164
We investigate the adsorption of four different organic dyes (i.e., methyl orange, alizarin red S, brilliant blue FCF, and phenol red) on porous xerogels. To understand the factors affecting the adsorption capacity of the xerogels, we vary the hydrophobicity and the textural properties of the xerogels as well as the solution pH. We control the hydrophobicity by mixing two different precursors (i.e., vinyltriethoxysilane (VTES) and tetraethoxysilane (TEOS)) and the textural properties by using cetyltrimethylammonium bromide (CTAB) as a templating agent. We find that the adsorption capacity is enhanced as the organic/inorganic hybrid xerogel or the templated xerogel is used instead of the purely inorganic or the untemplated xerogel. In all the cases studied, adsorption decreases as the pH is increased due to the electrostatic repulsion between the dyes and the xerogel surface. We find that both the hydrophobic surface and larger pore size/volume are required to enhance the adsorption capacity significantly. 相似文献
984.
Gustavsson S Rosén A Grennberg H Bolton K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(9):2223-2227
Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds. 相似文献
985.
Thanh Nga Pham Huu Dien Pham Dinh Kim Dang Thi Thuy Duong Thi Phuong Quynh Le Quang Duong Nguyen 《Natural product research》2019,33(9):1345-1348
Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO4. 相似文献
986.
Amol Maruti Jadhav Sandip Gangadhar Balwe Jong Su Kim Kwon Taek Lim Yeon Tae Jeong 《Tetrahedron letters》2019,60(7):560-565
An efficient, inexpensive and environmentally friendly synthesis of novel 3-amino-2-benzoyl-1-aryl-1H-pyrazolo[1,2-b]phthalazine-5,10-dione and 3-amino-2-benzoyl-1-aryl-1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives has been developed via one-pot three-component reaction of phthalhydrazide or maleic hydrazide, aldehydes and arylacetonitrile in the presence of catalytic amount of InCl3 as a Lewis acid catalyst under solvent-free conditions. The most important features of the present protocol are mild reaction conditions, short reaction times, high yields, and a wide range of functional group tolerance. 相似文献
987.
Seungju Kim Huanting Wang Young Moo Lee 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17674-17689
Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes. 相似文献
988.
989.
Seunghoon Lee Jaeyoung Kim Hyunwoo Yang Emiliano Corts Seungwoo Kang Sang Woo Han 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(44):16037-16041
Designing plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle‐in‐a‐frame nanostructures with well‐defined sub‐2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface‐enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure. 相似文献
990.
YS Kim A Cha JY Shin HJ Jeon JH Shim C Lee SG Lee 《Chemical communications (Cambridge, England)》2012,48(71):8940-8942
Gold nanoparticles (AuNPs) were assembled with high density onto multi-walled carbon nanotubes, which were functionalized with zwitterionic poly(imidazoliumsulfonate). The AuNP/zwitterionic CNT hybrids exhibited decent electrocatalytic activity in oxygen reduction reaction as the AuNP-based catalysts. 相似文献