全文获取类型
收费全文 | 3247篇 |
免费 | 376篇 |
国内免费 | 329篇 |
专业分类
化学 | 1493篇 |
晶体学 | 36篇 |
力学 | 123篇 |
综合类 | 44篇 |
数学 | 264篇 |
物理学 | 1000篇 |
无线电 | 992篇 |
出版年
2024年 | 13篇 |
2023年 | 84篇 |
2022年 | 111篇 |
2021年 | 120篇 |
2020年 | 112篇 |
2019年 | 124篇 |
2018年 | 110篇 |
2017年 | 81篇 |
2016年 | 133篇 |
2015年 | 121篇 |
2014年 | 144篇 |
2013年 | 186篇 |
2012年 | 225篇 |
2011年 | 231篇 |
2010年 | 167篇 |
2009年 | 189篇 |
2008年 | 168篇 |
2007年 | 139篇 |
2006年 | 121篇 |
2005年 | 160篇 |
2004年 | 132篇 |
2003年 | 116篇 |
2002年 | 112篇 |
2001年 | 130篇 |
2000年 | 90篇 |
1999年 | 88篇 |
1998年 | 74篇 |
1997年 | 67篇 |
1996年 | 55篇 |
1995年 | 79篇 |
1994年 | 45篇 |
1993年 | 34篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 39篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 22篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 1篇 |
排序方式: 共有3952条查询结果,搜索用时 546 毫秒
81.
Cinabro D Henderson S Kinoshita K Liu T Saulnier M Wilson R Yamamoto H Sadoff AJ Ammar R Ball S Baringer P Coppage D Copty N Davis R Hancock N Kelly M Kwak N Lam H Kubota Y Lattery M Nelson JK Patton S Perticone D Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Zoeller MM Crawford G Fulton R Fujino D Gan KK Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Ross WR 《Physical review letters》1993,70(24):3700-3704
82.
Hu J Chekmenev EY Gan Z Gor'kov PL Saha S Brey WW Cross TA 《Journal of the American Chemical Society》2005,127(34):11922-11923
Recently available ultrahigh magnetic fields offer new opportunities for studies of quadrupole nuclei in biological solids because of the dramatic enhancement in sensitivity and resolution associated with the reduction of second-order quadrupole interactions. Here, we present a new approach for understanding the function and energetics of ion solvation in channels using solid-state 17O NMR spectroscopy of single-site 17O-labeled gramicidin A. The chemical shift and quadrupole coupling parameters obtained in powder samples of lyophilized material are similar to those shown in the literature for carbonyl oxygens. In lipid bilayers, it is found that the carbonyl 17O anisotropic chemical shift of Leu10, one of the three carbonyl oxygens contributing to the ion binding site in gramicidin A, is altered by 40 ppm when K+ ion binds to the channel, demonstrating a high sensitivity to such interactions. Moreover, considering the large breadth of the carbonyl 17O chemical shift (>500 ppm), the recording of anisotropic 17O chemical shifts in bilayers aligned with respect to magnetic field B0 offers high-quality structural restraints similar to 15N and 13C anisotropic chemical shifts. 相似文献
83.
用2-甲氧基-5-氯-1,3-苯二甲醛与含有不同取代基团X的邻氨基酚缩合,合成了一系列双Schiff碱L-X(X=OMe,diMe,Me,t-Bu,H,Cl,NO_2),它们与乙酸铜(Ⅱ)作用生成了一系列的双核配合物Cu_2L-X(OEt).用红外、紫外、磁天平、顺磁共振等手段对配合物进行了表征,并通过量化计算(CNDO/2法)探讨了配合物的成键性质。研究结果表明,该类配合物是一个较大的共轭体系,配合物中Cu(Ⅱ).Cu(Ⅱ)之间有较强的反铁磁性交换作用,其共轭程度和交换作用强弱皆随X基团的不同而呈现某种变化规律。 相似文献
84.
制得二(1,8-萘啶氮氧化物)合硝酸钍和铀酰配合物,元素分析确定其组成为Th(C_3H_6N_2O)_2(NO_3)_4和UO_2(C_3H_6N_2O)_2(NO_3)_2。通过红外光谱、荧光光谱、摩尔电导、差热热重分析等方法,研究了配合物的性质。 相似文献
85.
Beltrami I Bylsma BG DeBonte R Gan KK Koltick D Loeffler FJ Low EH McIlwain RL Miller DH Ng CR Ong PP Rangan LK Shibata EI Wilson RJ Derrick M Fernandez E Fries R Hyman L Kooijman P Loos JS Musgrave B Price LE Schlereth J Sugano K Weiss JM Wood DE Baranko G Baringer P Blockus D Brabson B Forden GE Gray SW Jung C Neal H Ogren H Rust DR Valdata-Nappi M Akerlof C Bonvicini G Chapman J Errede D Harnew N Kesten P Kooijman S Meyer DI Nitz D Rubin D Seidl AA Thun R Trinko T Willutzky W Cork B Keller L 《Physical review letters》1985,54(16):1775-1778
86.
87.
Jin Ling CHAI Yan Hong GAO Kong Shuang ZHAO Gan Zuo LI Gao Yong ZHANG 《中国化学快报》2005,16(9):1263-1266
The dielectric relaxation spectroscopy (DRS) of Winsor I -Ⅲ microemulsions for nonionic surfactant octyl polyglucoside CsG1.46/1-butanol/cyclohexanedwater system was studied. The experiment shows that the permittivity decreases with the increase in the frequency and clear dielectric relaxation phenomena were observed. Permittivity obviously decreases with the change of the microstructure of the microemulsion, W/O, B.C. and O/W can be distinguished by the permittivity. 相似文献
88.
É. Fenyvesi A. Ujházy J. Szejtli S. Potter T. G. Gan 《Journal of inclusion phenomena and macrocyclic chemistry》1996,25(1-3):185-189
Various disinfecting drugs (ethacridine lactate, methylene blue, gentian violet, brilliant green, fuchsin acid, cetylpyridinium chloride) were incorporated into CD bead polymers substituted with carboxymetbyl groups and a retarded release rate was measured. These polymers were successfully used as sustained release wound powders as well as in chewing gum formulations. 相似文献
89.
The m6A‐RNA modification is a dynamic and reversible process, which has emerged as a new RNA code for the regulation of gene expression. The functional network of methyltransferases (writers), demethylases (erasers), and binding proteins (readers) modulate the level of m6A modification. Dysfunction of RNA methylation has been associated with various fundamental biological processes and human diseases. Herein, we briefly introduce an understanding‐enabled manipulation on m6A‐RNA modification with an emphasis on the use of small‐molecule intervention. 相似文献
90.
The three-photon absorption effect (3PA) of two novel symmetrical charge transfer fluorene-based molecules (abbreviated as BASF and BMOSF) has been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 84 × 10−78 and 114 × 10−78 cm6 s2, respectively. The geometries and electronic excitations of these two molecules are systematically studied by PM3 and ZINDO/S methods. The relationships between 3PA cross-sections and intramolecular charge transfer are discussed micromechanically. The experimental and theoretical results have shown that the larger intramolecular charge transfer, which was characterized by the charge density difference between the ground state (S0) and the first excited state (S1), the greater enhancement of the 3PA cross-sections. 相似文献