全文获取类型
收费全文 | 75691篇 |
免费 | 10723篇 |
国内免费 | 7628篇 |
专业分类
化学 | 51308篇 |
晶体学 | 713篇 |
力学 | 4908篇 |
综合类 | 584篇 |
数学 | 9176篇 |
物理学 | 27353篇 |
出版年
2024年 | 247篇 |
2023年 | 1473篇 |
2022年 | 2389篇 |
2021年 | 2594篇 |
2020年 | 2695篇 |
2019年 | 2637篇 |
2018年 | 2364篇 |
2017年 | 2087篇 |
2016年 | 3182篇 |
2015年 | 3347篇 |
2014年 | 3941篇 |
2013年 | 5239篇 |
2012年 | 6319篇 |
2011年 | 6443篇 |
2010年 | 4428篇 |
2009年 | 4371篇 |
2008年 | 4556篇 |
2007年 | 4132篇 |
2006年 | 3902篇 |
2005年 | 3384篇 |
2004年 | 2753篇 |
2003年 | 2157篇 |
2002年 | 2010篇 |
2001年 | 1734篇 |
2000年 | 1598篇 |
1999年 | 1744篇 |
1998年 | 1444篇 |
1997年 | 1264篇 |
1996年 | 1288篇 |
1995年 | 1123篇 |
1994年 | 1058篇 |
1993年 | 894篇 |
1992年 | 798篇 |
1991年 | 702篇 |
1990年 | 585篇 |
1989年 | 500篇 |
1988年 | 379篇 |
1987年 | 358篇 |
1986年 | 309篇 |
1985年 | 316篇 |
1984年 | 208篇 |
1983年 | 182篇 |
1982年 | 150篇 |
1981年 | 116篇 |
1980年 | 83篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 54篇 |
1975年 | 59篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Analysis of an aggregation‐based algebraic two‐grid method for a rotated anisotropic diffusion problem 下载免费PDF全文
A two‐grid convergence analysis based on the paper [Algebraic analysis of aggregation‐based multigrid, by A. Napov and Y. Notay, Numer. Lin. Alg. Appl. 18 (2011), pp. 539–564] is derived for various aggregation schemes applied to a finite element discretization of a rotated anisotropic diffusion equation. As expected, it is shown that the best aggregation scheme is one in which aggregates are aligned with the anisotropy. In practice, however, this is not what automatic aggregation procedures do. We suggest approaches for determining appropriate aggregates based on eigenvectors associated with small eigenvalues of a block splitting matrix or based on minimizing a quantity related to the spectral radius of the iteration matrix. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
962.
The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C2mim][OAc]. In addition to improving the solubility of the peptides in [C2mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced. 相似文献
963.
Dian‐Feng Chen Feng Zhao Yue Hu Liu‐Zhu Gong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(40):10939-10943
A combination of either ruthenium(II) or rhodium(II) complexes and quinine‐derived squaramide enables 3‐diazooxindoles, indoles, and nitroalkenes to undergo highly efficient asymmetric three‐component reactions, thus affording optically active 3,3′‐bis(indole)s through a consecutive C C bond‐forming sequence, which turned out to be applicable to the facile total synthesis of (−)‐folicanthine. 相似文献
964.
Ying Dong Bangyu Liu Peng Chen Qun Liu Mang Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(13):3510-3514
The insertion of an aryne into a C S bond can suppress the addition of an S nucleophile to the aryne in the presence of palladium. Catalyzed by Pd(OAc)2, a wide range of α‐carbamoyl ketene dithioacetals readily react with arynes to selectively afford functionalized 2‐quinolinones in high yields under neutral reaction conditions by a C S activation/aryne insertion/intramolecular coupling sequence. The attractive feature of the new strategy also lies in the versatile transformations of the alkythio‐substituted quinolinone products. 相似文献
965.
Determination of glutathione in single HepG2 cells by capillary electrophoresis with reduced graphene oxide modified microelectrode 下载免费PDF全文
Determination of intracellular bioactive species will afford beneficial information related to cell metabolism, signal transduction, cell function, and disease treatment. In this study, the electrochemically reduced graphene oxide modified carbon fiber microdisk electrode (ER‐GOME) was used as a detector of CZE‐electrochemical detection and developed to detect glutathione (GSH). The electrocatalytic activity of the modified microelectrode was characterized by cyclic voltammetry. Under optimized experimental conditions, the concentration linear range of GSH was from 1 to 60 μM. When the S/N ratio was 3, the concentration detection limit was 1 μM. Compared with the unmodified carbon fiber microdisk electrode, the sensitivity was enhanced more than five times. With the use of this method, the average contents of GSH in single HepG2 cells were found to be 7.13 ± 1.11 fmol (n = 10). Compared with gold/mercury amalgam microelectrode, which was usually used in determining GSH, the electrochemically reduced graphene oxide modified carbon fiber microdisk electrode was friendly to environment for free mercury. Furthermore, there were several merits of the novel electrochemical detector coupled with CE, such as comparative repeatability, easy fabrication, and high sensitivity, hold great potential for the single‐cell assay. 相似文献
966.
A silver-catalyzed reaction of 2-alkynylbenzaldoxime with arylsulfonyl chloride proceeds smoothly at room temperature to afford 4-tosyloxyisoquinolines in moderate to good yields. Additionally, the resulting 4-tosyloxyisoquinolines could be further elaborated through palladium-catalyzed coupling reactions leading to diverse isoquinolines. 相似文献
967.
Functionalized 6-substituted-thiosalicylates are key intermediates for the synthesis of pyrimidinyl(thio)salicylic acids, a group of important herbicides targeting plant acetohydroxyacid synthase. Therefore, it is of great interest to develop an efficient method for the syntheses of 6-substituted-thiosalicylates. Herein, we have developed a direct and efficient method for the synthesis of functionalized 6-substituted-thiosalicylates (4) from aryl iodide (1) by using an improved microwave-assisted Suzuki cross-coupling reaction. Almost all the reactions proceeded smoothly and afforded moderate to excellent yields of products. Moreover, this protocol is obviously superior to the traditional available methods and could be utilized to synthesize pyrimidinyl(thio)salicylic acid and its derivatives. 相似文献
968.
969.
The first total syntheses of fuzinoside (1b) were achieved from d-galactose through two strategies (BCA and ABC) in 11 (total yield: 5.0%) and 15 (total yield: 3.7%) steps, respectively. Comparison of NMR data of synthetic compound 1b and those of the fuzinoside isolated from the lateral roots of Aconitum carmicaelii suggests that the structure reported in the literature 1 and 2 might not be accurate. The synthetic fuzinoside (1b) exhibited moderate cardiac activity in the isolated bullfrog heart assay. 相似文献
970.