全文获取类型
收费全文 | 3334篇 |
免费 | 141篇 |
国内免费 | 205篇 |
专业分类
化学 | 2536篇 |
晶体学 | 19篇 |
力学 | 113篇 |
综合类 | 3篇 |
数学 | 130篇 |
物理学 | 879篇 |
出版年
2024年 | 6篇 |
2023年 | 71篇 |
2022年 | 62篇 |
2021年 | 36篇 |
2020年 | 49篇 |
2019年 | 61篇 |
2018年 | 37篇 |
2017年 | 49篇 |
2016年 | 134篇 |
2015年 | 115篇 |
2014年 | 118篇 |
2013年 | 252篇 |
2012年 | 204篇 |
2011年 | 223篇 |
2010年 | 205篇 |
2009年 | 248篇 |
2008年 | 183篇 |
2007年 | 222篇 |
2006年 | 163篇 |
2005年 | 148篇 |
2004年 | 143篇 |
2003年 | 94篇 |
2002年 | 79篇 |
2001年 | 68篇 |
2000年 | 61篇 |
1999年 | 74篇 |
1998年 | 81篇 |
1997年 | 49篇 |
1996年 | 57篇 |
1995年 | 46篇 |
1994年 | 52篇 |
1993年 | 39篇 |
1992年 | 30篇 |
1991年 | 51篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 21篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1967年 | 2篇 |
排序方式: 共有3680条查询结果,搜索用时 15 毫秒
131.
Three standardised, capillary zone electrophoresis-electrospray ionisation mass spectrometry (CZE-ESI-MS) methods were developed for the analysis of six drug candidates and their respective process-related impurities comprising a total of 22 analytes with a range of functional groups and lipophilicities. The selected background electrolyte conditions were found to be: 60/40 v/v 10 mM ammonium formate pH 3.5/organic, 60/40 v/v 10 mM ammonium acetate pH 7.0/organic and 10 mM piperidine, pH 10.5, where the organic solvent is 50/50 v/v methanol/acetonitrile. The coaxial sheath flow consisted of either 0.1% v/v formic acid in 50/50 v/v methanol/water, or 10 mM ammonium acetate in 50/50 v/v methanol/water, depending on the mixture being analysed. Factor analysis and informational theory were used to quantify the orthogonality of the methods and predict their complementarities. The three selected CZE-ESI-MS methods allowed the identification of 21 out of 22 of all the drug candidates and their process-related impurities and provided orthogonality with four established high-performance liquid chromatography-mass spectrometry (HPLC-MS) methods. These methodologies therefore form the basis of a generic approach to impurity profiling of pharmaceutical drug candidates and can be applied with little or no analytical method development, thereby offering significant resource and time savings. 相似文献
132.
133.
基于多肽(Polypeptides PC2~PC6)中富有巯基(-SH)官能团,其与单溴二胺(Monobromobimanes mBBr)能够发生缩合反应,生成具有荧光信号的多肽衍生物;通过优化色谱分离条件,建立了高效液相色谱(荧光检测器)测定多肽的方法;试验中利用质谱鉴定了PCs与mBBr缩合反应的比例关系。结果显示,通过比较PCs标记前后化合物的质谱图,PCs与mBBr反应比例关系为1∶1,稳定性好;高效液相色谱-荧光法测定多肽化合物,五种化合物间分离度较好,出峰时间集中在16.6~22.0min间;PC2,PC3,PC4,PC5和PC6线性相关性系数>0.999 1,方法定量限分别为0.3,0.05,0.3,0.5和0.8 mg·L-1,回收率范围为83.0%~102.0%;重线性较好,RSD<2.0%,该方法实现了多肽类化合物快速、准确定量分析。 相似文献
134.
135.
Suely L. Galdino Maria C. A. Lima Alexandre J. S. Góes Ivan R. Pitta Cuong Luu-Duc 《光谱学快报》2013,46(7-8):1013-1021
In the present investigation, a study of the electron impact mass spectrometry data is reported for seven compounds of a series of some 3-(4-chlorobenzyl)-5-benzylidene-imidazolidine-2, 4-diones and 3-(4-fluoro or chlorobenzyl)-5-benzylidene-thiazolidine-2, 4-diones previously synthesized. 相似文献
136.
《International journal of environmental analytical chemistry》2013,93(3):123-132
Heating a suspension of Bisphenol A diglycidyl ether (BADGE) in 20 : 80 tetrahydrofuran/water at 70°C and subsequent passage of the resulting solution through C18 columns allowed isolation and purification to > 97% of each of the two hydrolysis products 2-[4-(2,3-dihydroxypropoxy) phenyl]-2-[4-(2,3-epoxypropoxy)phenyl]propane (1HP) and 2,2-bis[4-(2,3-dihydroxypropoxy)phenyl] propane (2HP), which were characterized by UV, IR, 1H and I3C NMR spectroscopy and mass spectrometry. 相似文献
137.
M. H. Elnagdi M. A. Selim F. M. Abd El Latif S. Samia 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):1175-1182
5-Acetyl-2-cyanomethyl-4-methylthiazole, 2-aminothiazole, and 5-N-benzoylamino-1,3,4-thiadiazole-2-yl-acetonitrile react with acetone, and malononitrile derivatives in the presence of sulfur to yield the corresponding thiophene derivatives. Also, 4-furylmethylene-2-phenyl-2-oxazolin-5-ones react with thiophenol, and/or thionaphthol to give the thiolester derivatives in one-pot synthesis. The structures of the products were based on IR, 1 H NMR, and elemental analysis. 相似文献
138.
Thibaut Van Acker Stijn J.M. Van Malderen Marjolein Van Heerden James Eric McDuffie Filip Cuyckens Frank Vanhaecke 《Analytica chimica acta》2016
Two-dimensional elemental mapping (bioimaging) via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on 5 μm thick formalin-fixed, paraffin-embedded kidney tissue sections from Cynomolgus monkeys administered with increasing pharmacological doses of cisplatin. Laterally resolved pixels of 1 μm were achieved, enabling elemental analysis on a (sub-)cellular level. Zones of high Pt response were observed in the renal cortex, where proximal tubules are present, the epithelium of which is responsible for partial reabsorption of cisplatin. Histopathological evaluation, of hematoxylin and eosin-stained serial sections, adjacent to the sections probed via LA-ICP-MS, revealed minimal to mild cisplatin-related lesions (<100 μm) in the renal cortex. Necrotic proximal tubules with sloughed epithelial cells in their lumen could be linked directly to the areas with the highest accumulation of cisplatin, indicating a direct link between cellular concentration and toxicity, thereby providing more insight into the mechanisms through which renal damage occurs. 相似文献
139.
《Journal of Coordination Chemistry》2012,65(22):2449-2460
The synthesis and characterization of [Cu(4-MeOsal)2(2-pyme)2] (1) and [Cu(3-Mesal)2(2-pyme)2] (2) (where 4-MeOsal?=?4-methoxysalicylate, 3-Mesal?=?3-methylsalicylate and 2-pyme?=?2-pyridylmethanol) are reported. The composition and stereochemistry as well as the mode of coordination have been determined by elemental analysis, IR, electronic and EPR spectra as well as magnetization measurements over the temperature range 1.8–300?K. The crystal structures of Cu(4-MeOsal)2(2-pyme)2 and Cu(3-Mesal)2(2-pyme)2 have been determined. 相似文献
140.
David M. Rackham 《光谱学快报》2013,46(8):517-520
Paper 16 in this series1, 2, 3 was concerned with the equilibrium binding constants (K) of the shift reagent Europium tris (2, 2, 6, 6-tetramethylheptane-3, 5-dionate), Eu(thd)3, with primary, secondary and tertiary amines. One nitrogen heterocycle, pyridine, and two of its derivatives (see Table) were included. In the present paper we describe the binding constants for a further 9 nitrogen containing heterocycles and relate these to basicity and steric effects. 相似文献