全文获取类型
收费全文 | 10800篇 |
免费 | 266篇 |
国内免费 | 114篇 |
专业分类
化学 | 6724篇 |
晶体学 | 116篇 |
力学 | 221篇 |
数学 | 2247篇 |
物理学 | 1872篇 |
出版年
2022年 | 81篇 |
2021年 | 80篇 |
2020年 | 123篇 |
2019年 | 146篇 |
2018年 | 123篇 |
2017年 | 87篇 |
2016年 | 232篇 |
2015年 | 169篇 |
2014年 | 198篇 |
2013年 | 574篇 |
2012年 | 507篇 |
2011年 | 581篇 |
2010年 | 337篇 |
2009年 | 291篇 |
2008年 | 527篇 |
2007年 | 504篇 |
2006年 | 603篇 |
2005年 | 580篇 |
2004年 | 481篇 |
2003年 | 414篇 |
2002年 | 432篇 |
2001年 | 154篇 |
2000年 | 128篇 |
1999年 | 122篇 |
1998年 | 137篇 |
1997年 | 151篇 |
1996年 | 182篇 |
1995年 | 119篇 |
1994年 | 121篇 |
1993年 | 114篇 |
1992年 | 123篇 |
1991年 | 110篇 |
1990年 | 94篇 |
1989年 | 99篇 |
1988年 | 82篇 |
1987年 | 98篇 |
1986年 | 79篇 |
1985年 | 134篇 |
1984年 | 161篇 |
1983年 | 116篇 |
1982年 | 123篇 |
1981年 | 154篇 |
1980年 | 154篇 |
1979年 | 130篇 |
1978年 | 134篇 |
1977年 | 105篇 |
1976年 | 118篇 |
1975年 | 127篇 |
1974年 | 127篇 |
1973年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Krzysztof Ejsmont Joel Boeglin Claude Didierjean Gilles Guichard Christian Jelsch 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(6):o292-o294
The crystal structure of the title compound, C16H23N3O4·CH3CN, was refined using a multipolar atom model transferred from an experimental electron‐density database. The refinement showed some improvement in crystallographic statistical indices compared with the independent atom model. The triazepane ring adopts a twist‐boat conformation. In the crystal structure, the molecule forms intermolecular contacts with 14 different neighbours. There are two N—H...O and one C—H...O intermolecular hydrogen bond. 相似文献
962.
Nathan A. Lacher Qian Wang Rachel K. Roberts Heidi J. Holovics Serdar Aykent Michael R. Schlittler Melissa R. Thompson Charles W. Demarest 《Electrophoresis》2010,31(3):448-458
A CGE method for monitoring the disulfide isomer distribution characteristic of IgG2 MAbs is presented. Disulfide heterogeneity of MAbs has been studied using various chromatographic and electrophoretic methods. Although CGE operates using a different selectivity mechanism from that of sorption chromatographic techniques, similar trends are present in the data, which allow the CGE method to be used as a complementary method for studying disulfide isomer distribution. This article focuses on the optimization of a capillary‐based gel electrophoresis method that can be used to support antibody development including bioprocess optimization, antibody characterization, release, and formulation stability assessment. 相似文献
963.
The immobilization of biomolecules onto an insoluble carrier surface has always been a subject of great interest to enhance their resistance to pH and temperature, which aids in an increased activity lifespan as well as easy reuse of the said biomolecules. However, traditional methods are only able to provide single-layer biomolecular binding and require multiple chemical reactions to prepare the final substrate before the immobilization can be carried out properly. Here we report a facile one-step chemical synthesis of a new aldehyde-bearing graft copolymer via atom transfer radical polymerization (ATRP) for covalent protein capture in a multilayered approach to covalently capture bovine serum albumin (BSA) onto a polymeric membrane. The resultant protein-bound membrane illustrated the retention of BSA's stereoselective discrimination ability by binding to an excess of 2 mol of tryptophan/mol of BSA and demonstrated an enantioresolution of a 0.184 mM racemic tryptophan mixture with a time-averaged-separation factor of 2.9. 相似文献
964.
Johnson MM Naidoo JM Fernandes MA Mmutlane EM van Otterlo WA de Koning CB 《The Journal of organic chemistry》2010,75(24):8701-8704
Reaction of (2,4,5-trimethoxyphenyl)(2-hydroxyphenyl)methanone with ceric ammonium nitrate furnished the xanthone, 2,3-dimethoxy-9H-xanthen-9-one. Under the same conditions the related (1,4-dimethoxynaphthalen-2-yl)(2-hydroxyphenyl)methanone resulted in the formation of 12a-methoxy-5H-benzo[c]xanthenes 5,7(12aH)-dione. Other examples of this novel transformation are also outlined. 相似文献
965.
Carl R. Kemnitz Prof. Joel L. Mackey Mark J. Loewen Julie L. Hargrove Joshua L. Lewis Whitney E. Hawkins Adam F. Nielsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6942-6949
The potential origins of stability in branched alkanes are investigated, paying close attention to two recent hypotheses: geminal steric repulsion and protobranching. All alkane isomers through C6H14 along with heptane and octane were investigated at the MPW1B95/6‐311++G(d,p) level. Their geminal steric repulsion, total steric repulsion, and orbital interactions were evaluated by using natural bond orbital analysis. All measures of steric repulsion fail to explain the stability of branched alkanes. The extra stability of branched alkanes and protobranching, in general, is tied to stabilizing geminal σ→σ* delocalization, particularly of the type that involves adjacent C? C bonds and, thus, preferentially stabilizes branched alkanes. This picture is corroborated by valence bond calculations that attribute the effect to additional ionic structures (e.g., CH3+ :CH2 :CH3? and CH3:? CH2: CH3+ for propane) that are not possible without protobranching. 相似文献
966.
Wen‐Yong Lai Dr. Ruidong Xia Dr. Donal D. C. Bradley Prof. Dr. Wei Huang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(28):8471-8479
We present herein a novel design and the efficient synthesis towards a “homogeneous” starburst fluorene system based on the novel 2,3,7,8,12,13‐hexaaryltruxene scaffold. Controlled microwave heating provides a facile and powerful approach for each step in the synthesis of these bulky materials with large steric hindrance, suggesting an avenue to access structurally well‐defined complex organic semiconductors (OSCs) rapidly and conveniently with high yield and purity. The resulting materials exhibited good thermal stability and an excellent glassy structure as revealed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as wide‐angle X‐ray diffraction (WAXD) studies. Moreover, compared with their corresponding three‐arm‐substituted counterparts T1 – T4 , the introduction of the ortho substituents around the truxene core in Tr1 – Tr4 results in significant blueshifts (of 7–24 nm) of the absorption maxima λmax and higher energy optical gaps (Eg). Comparative studies with corresponding linear, rod‐shaped oligofluorene counterparts (OFX) have revealed that the longest para‐conjugated segment in the TrX (X=1–4) structures plays the dominant role in determining their electronic properties. UV/Vis data and cyclic voltammetry (CV) investigations have indicated that there is little electronic interaction between the arms, even for the shortest armed oligomer Tr1 . A clear linear relationship of both 1/λmax and Eg with the inverse of (n+1) for these branched systems was found. Our findings highlight a novel molecular design comprising an ortho‐substituted, multiarmed architecture that would allow the introduction of isotropic physical and/or mechanical properties, while at the same time maintaining most of the important electronic properties of the rod‐shaped constituents of a fully conjugated system. 相似文献
967.
News and Announcements
VIM3 Corrigendum available online 相似文献968.
In our previous research, multifunctional carboxylic acids have been used as flame retardants to reduce the flammability of cotton fleece so that the garment made of cotton fleece can pass the US mandatory requirement specified by the government regulation “Standard for the Flammability of Clothing Textiles” (16 CFR 1610). In this research, we studied and compared the effectiveness of the polycarboxylic acids having different numbers of carboxylic groups as the durable flame retardants for cotton fleece. The cotton fabrics were treated with 1,2,3,4-butanetetracarboxylic acid (BTCA), citric acid (CA), succinic acid (SUA) and malic acid (MLA). We compared the reactivity of those polycarboxylic acids to esterify cotton cellulose and their effectiveness to reduce the flammability of the cotton fleece. The data indicated that the polycarboxylic acids with higher functionalities (BTCA and CA) form more esterlinkages on cotton and are more durable to home launderings than that treated with their bifunctional counter parts (SUA and MLA, respectively). In addition, the cotton fabrics treated with BTCA and CA have higher dimensional stability and higher strength loss. All those differences can be attributed to the fact that only those acids with three or more carboxylic groups, i.e., BTCA and CA, are able to crosslink cotton cellulose whereas the bifunctional acids (SUA and MLA) only form single esterlinkage with cotton. 相似文献
969.
970.