全文获取类型
收费全文 | 503690篇 |
免费 | 5251篇 |
国内免费 | 1663篇 |
专业分类
化学 | 253401篇 |
晶体学 | 8242篇 |
力学 | 23976篇 |
综合类 | 9篇 |
数学 | 60761篇 |
物理学 | 164215篇 |
出版年
2021年 | 4194篇 |
2020年 | 4554篇 |
2019年 | 5164篇 |
2018年 | 6962篇 |
2017年 | 7115篇 |
2016年 | 9974篇 |
2015年 | 5844篇 |
2014年 | 9732篇 |
2013年 | 23426篇 |
2012年 | 17629篇 |
2011年 | 21518篇 |
2010年 | 15668篇 |
2009年 | 15569篇 |
2008年 | 19468篇 |
2007年 | 19410篇 |
2006年 | 18087篇 |
2005年 | 15988篇 |
2004年 | 14874篇 |
2003年 | 13153篇 |
2002年 | 13115篇 |
2001年 | 15344篇 |
2000年 | 11595篇 |
1999年 | 9105篇 |
1998年 | 7622篇 |
1997年 | 7385篇 |
1996年 | 7024篇 |
1995年 | 6230篇 |
1994年 | 6137篇 |
1993年 | 6102篇 |
1992年 | 6575篇 |
1991年 | 6863篇 |
1990年 | 6522篇 |
1989年 | 6381篇 |
1988年 | 6205篇 |
1987年 | 6218篇 |
1986年 | 5827篇 |
1985年 | 7681篇 |
1984年 | 7912篇 |
1983年 | 6440篇 |
1982年 | 6685篇 |
1981年 | 6402篇 |
1980年 | 6213篇 |
1979年 | 6576篇 |
1978年 | 6613篇 |
1977年 | 6592篇 |
1976年 | 6677篇 |
1975年 | 6208篇 |
1974年 | 6174篇 |
1973年 | 6263篇 |
1972年 | 4425篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Teobald Kupka Małgorzata A. Broda Piotr P. Wieczorek 《Magnetic resonance in chemistry : MRC》2020,58(6):584-593
The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter γ-aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1H and 13C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin–spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents. 相似文献
142.
Chandrachood Pranav S. Jadhav Amol R. Garud Dinesh R. Deshpande Nirmala R. Puranik Vedavati G. Kashalkar Rajashree V. 《Research on Chemical Intermediates》2020,46(12):5219-5230
Research on Chemical Intermediates - A series of quinoxaline derivatives were efficiently synthesized by convenient and simple procedure in excellent yields using 1 wt.% of titanium silicate (TS-1)... 相似文献
143.
Harsha K. Tripathy Nair S.V. Manju Sreekanth Dittakavi Ram Murthi Bestha Ramesh Mullangi 《Biomedical chromatography : BMC》2020,34(12):e4953
Larotrectinib is a first-generation tropomyosin kinase inhibitor, approved for the treatment of solid tumors. In this paper, we present a validated dried blood spot (DBS) method for the quantitation of larotrectinib from mouse blood using HPLC–MS/MS, which was operated under multiple reaction monitoring mode. To the DBS disc cards, acidified methanol enriched with internal standard (IS; enasidenib) was added and extracted using tert-butyl methyl ether as an extraction solvent with sonication. Chromatographic separation of larotrectinib and the IS was achieved on an Atlantis dC18 column using 10 mm ammonium formate–acetonitrile (30:70, v/v) delivered at a flow-rate of 0.80 ml/min. Under these optimized conditions, the retention times of larotrectinib and the IS were ~0.93 and 1.37 min, respectively. The total run time was 2.50 min. Larotrectinib and the IS were analyzed using positive ion scan mode and parent–daughter mass to charge ion (m/z) transitions of 429.1 → 342.1 and 474.1 → 267.1, respectively, were used for the quantitation. The calibration range was 1.06–5,080 ng/ml. No matrix effect or carryover was observed. Hematocrit did not influence DBS larotrectinib concentrations. All of the validation parameters met the acceptance criteria. The applicability of the validated method was shown in a mouse pharmacokinetic study. 相似文献
144.
Karen Beatriz Méndez-Rodríguez Nicté Figueroa-Vega César Arturo Ilizaliturri-Hernandez Mónica Cardona-Alvarado Jaime Antonio Borjas-García Carlos Kornhauser Juan Manuel Malacara Rogelio Flores-Ramírez Francisco Javier Pérez-Vázquez 《Biomedical chromatography : BMC》2020,34(12):e4956
Metabolomics is a potential tool for the discovery of new biomarkers in the early diagnosis of diseases. An ultra-fast gas chromatography system equipped to an electronic nose detector (FGC eNose) was used to identify the metabolomic profile of Volatile Organic Compounds (VOCs) in type 2 diabetes (T2D) urine from Mexican population. A cross-sectional, comparative, and clinical study with translational approach was performed. We recruited twenty T2D patients and twenty-one healthy subjects. Urine samples were taken and analyzed by FGC eNose. Eighty-eight compounds were identified through Kovats's indexes. A natural variation of 30% between the metabolites, expressed by study groups, was observed in Principal Component 1 and 2 with a significant difference (p < 0.001). The model, performed through a Canonical Analysis of Principal coordinated (CAP), allowed a correct classification of 84.6% between healthy and T2D patients, with a 15.4% error. The metabolites 2-propenal, 2-propanol, butane- 2,3-dione and 2-methylpropanal, were increased in patients with T2D, and they were strongly correlated with discrimination between clinically healthy people and T2D patients. This study identified metabolites in urine through FGC eNose that can be used as biomarkers in the identification of T2D patients. However, more studies are needed for its implementation in clinical practice. 相似文献
145.
146.
147.
148.
149.
Dr. Jun Zeng Dr. Zhichao Wang Dr. Xin Huang Dr. Sabine S. Eckstein Prof. Dr. Xiaohui Lin Prof. Dr. Hailong Piao Prof. Dr. Cora Weigert Dr. Peiyuan Yin Prof. Dr. Rainer Lehmann Prof. Dr. Guowang Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(21):5427-5432
Mass spectrometry (MS) driven metabolomics is a frequently used tool in various areas of life sciences; however, the analysis of polar metabolites is less commonly included. In general, metabolomic analyses lead to the detection of the total amount of all covered metabolites. This is currently a major limitation with respect to metabolites showing high turnover rates, but no changes in their concentration. Such metabolites and pathways could be crucial metabolic nodes (e.g., potential drug targets in cancer metabolism). A stable-isotope tracing capillary electrophoresis–mass spectrometry (CE-MS) metabolomic approach was developed to cover both polar metabolites and isotopologues in a non-targeted way. An in-house developed software enables high throughput processing of complex multidimensional data. The practicability is demonstrated analyzing [U-13C]-glucose exposed prostate cancer and non-cancer cells. This CE-MS-driven analytical strategy complements polar metabolite profiles through isotopologue labeling patterns, thereby improving not only the metabolomic coverage, but also the understanding of metabolism. 相似文献
150.
JETP Letters - At the resonant passage of a plane elastic shear wave through an acoustically continuous heterostructure consisting of magnetic and nonmagnetic layers in a symmetric nonmagnetic... 相似文献