全文获取类型
收费全文 | 17746篇 |
免费 | 2056篇 |
国内免费 | 2326篇 |
专业分类
化学 | 7990篇 |
晶体学 | 173篇 |
力学 | 2185篇 |
综合类 | 277篇 |
数学 | 7374篇 |
物理学 | 4129篇 |
出版年
2024年 | 42篇 |
2023年 | 187篇 |
2022年 | 345篇 |
2021年 | 470篇 |
2020年 | 579篇 |
2019年 | 533篇 |
2018年 | 523篇 |
2017年 | 632篇 |
2016年 | 750篇 |
2015年 | 494篇 |
2014年 | 786篇 |
2013年 | 1507篇 |
2012年 | 995篇 |
2011年 | 1010篇 |
2010年 | 857篇 |
2009年 | 1088篇 |
2008年 | 1147篇 |
2007年 | 1204篇 |
2006年 | 993篇 |
2005年 | 897篇 |
2004年 | 815篇 |
2003年 | 727篇 |
2002年 | 671篇 |
2001年 | 593篇 |
2000年 | 540篇 |
1999年 | 538篇 |
1998年 | 425篇 |
1997年 | 376篇 |
1996年 | 341篇 |
1995年 | 321篇 |
1994年 | 268篇 |
1993年 | 208篇 |
1992年 | 187篇 |
1991年 | 185篇 |
1990年 | 124篇 |
1989年 | 118篇 |
1988年 | 90篇 |
1987年 | 79篇 |
1986年 | 71篇 |
1985年 | 70篇 |
1984年 | 62篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 43篇 |
1980年 | 34篇 |
1979年 | 36篇 |
1978年 | 15篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
In the development of therapeutic proteins, analytical assessment of structural stability and integrity constitutes an important activity, as protein stability and integrity influence drug efficacy, and ultimately patient safety. Existing analytical methodologies solely rely on relative changes in optical properties such as fluorescence or scattering upon thermal or chemical perturbation. Here, we present an absolute analytical method for assessing protein stability, structure, and unfolding utilizing Taylor dispersion analysis (TDA) and LED-UV fluorescence detection. The developed TDA method measures the change in size (hydrodynamic radius) and intrinsic fluorescence of a protein during in-line denaturation with guanidinium hydrochloride (GuHCl). The conformational stability of the therapeutic antibody adalimumab and human serum albumin were characterized as a function of pH. The simple workflow and low sample consumption (40 ng protein per data point) of the methodology make it ideal for assessing protein characteristics related to stability in early drug development or when having a scarce amount of sample available. 相似文献
992.
993.
Wen-mei Wei Ren-hui Zheng Yan Tian Tian-jing He Li He Dong-ming Chen Fan-chen Liu 《化学物理学报(中文版)》2007,20(2):126-134
The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+G*//B3LYP/6-311+G* level of theory. The results demonstrated that there are four low-lying energy channels: (i) the NN bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014:8e-46:0=RT , k7(T)=1013:7e-42:1=RT , k8(T)=1013:6e-51:8=RT and k9(T)=1015:6e-54:3=RT s-1, respectively. The calculated overall rate constants is 6.9£10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the NN bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures. 相似文献
994.
Margarita A. Epishina Alexander S. Kulikov Leonid L. Fershtat 《Molecules (Basel, Switzerland)》2022,27(8)
A series of novel 1,4-dihydrobenzo[1,2,4][e]triazines bearing an acetyl or ester moiety as a functional group at the C(3) atom of the 1,2,4-triazine ring were synthesized. The synthetic protocol is based on an oxidative cyclization of functionally substituted amidrazones in the presence of DBU and Pd/C. It was found that the developed approach is suitable for the preparation of 1,4-dihydrobenzo[e][1,2,4]triazines, but the corresponding Blatter radicals were isolated only in few cases. In addition, a previously unknown dihydrobenzo[e][1,2,4]triazolo[3,4-c][1,2,4]triazine tricyclic open-shell derivative was prepared. Studies of thermal behavior of the synthesized 1,4-dihydrobenzo[1,2,4][e]triazines revealed their high thermal stability (up to 240–250 °C), which enables their application potential as components of functional organic materials. 相似文献
995.
Effendy Ronald R. Fenton Leonard F. Lindoy Jason R. Price Brian W. Skelton Tania Strixner Gang Wei Allan H. White 《Journal of inclusion phenomena and macrocyclic chemistry》2001,41(1-4):185-191
As part of an ongoing investigation of the factors influencing metal ionrecognition, we have investigated structure/function relationships involvingthe metal-ion binding by three new N-benzyl-substituted, 15- and 16-membered,macrocyclic ligands incorporating N2O 3- and N 3O 3-donor sets (withthe N 3O 3-system consisting of a N 2O 3-macrocyclic ring with an attachedCH 2CH 2NCH 2C 6H 5 pendant arm). Selected solid complexes of thelatter ligand were isolated and the X-ray structures of individual Ni(II) and Ag(I) complexeswere obtained.Where solubility permitted, potentiometric titration studies in 95% methanolwere employed to investigate the binding affinities of all three ligand derivativestowards Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II). The 15-memberedN 2O 3-ring was found to be selective for Ag(I) over the other six metalsinvestigated, including Cu(II). However, the presence of a further nitrogen donorin the form of the pendant benzylamine functionality in the N 3O 3-donorsystem results in an increase in its binding affinity for Ag(I) but an even greaterincrease occurs for Cu(II). As a consequence, the latter ion is now more stronglybound than Ag(I). The factors influencing these respective selectivities are discussed. 相似文献
996.
997.
利用不同煤种的煤和生物油制备了不同浓度的生物油煤浆,考察了生物油煤浆的成浆浓度、表观黏度、流变特性和稳定性。结果表明,生物油煤浆是具有一定屈服应力的非牛顿流体,其流变特性可用宾汉姆方程来描述;生物油煤浆的屈服应力和表观黏度都随着固体浓度的增加而增大;随着剪切速率的增加,生物油煤浆的表观黏度减小;四种煤中,无烟煤的成浆浓度最高,可达42%,其含碳量高达49%,相当于同种煤制成的74%的水煤浆含量。烟煤次之,褐煤最低;生物油与煤粉之间能够形成絮凝性的大分子网络结构,使得生物油煤浆存在屈服应力并能够保持良好的静态稳定性,4.0~5.0 d天没有软沉淀产生,数月没有硬沉淀产生。 相似文献
998.
The bulk crystal of LiSrBO3 (8.39 g) with a size of 21mm×20mm×15mm was grown by high temperature solution growth method. The relationship between growth habit and crystal structure was discussed. The transmission spectrum shows an UV absorption edge at about 300 nm. The melting temperature of this crystal was determined to be 942 ℃ by DTA-TG measurement. The band structure of the LiSrBO3 crystal was studied by means of the first principle method. An indirect band gap was found to be about 4.0 eV,and a low dielectric constant was estimated to be about 1.9 in terms of theoretical results. 相似文献
999.
1000.
有机-无机杂化卤化物钙钛矿太阳能电池(perovskite solar cells, PSCs)由于其成本低廉、制备工艺简单、光电转换率高等优点引起了越来越多的关注,在下一代半导体光伏技术中显示出巨大的发展潜力。然而PSCs器件在商业化生产应用之前,必须解决某些关键问题,例如器件在湿度、光照和过热条件下缺乏稳定性,性能会急剧衰退。层状二维(two-dimensional, 2D)钙钛矿由于其优异的环境稳定性而受到研究人员的广泛关注。通过引入不同种类的疏水性大体积有机铵阳离子可以在钙钛矿体内形成稳定的2D结构。然而,由于绝缘有机间隔阳离子的存在,使其电荷输运能力受阻并影响光电转换性能。本文根据不同种类2D钙钛矿光伏器件的发展进程,总结了影响2D钙钛矿结构和性能的关键问题,如晶体垂直取向设计、量子阱调控和有机层间隔阳离子替换工程等。最后对2D PSCs的未来发展进行展望。 相似文献