全文获取类型
收费全文 | 37094篇 |
免费 | 6528篇 |
国内免费 | 4307篇 |
专业分类
化学 | 25590篇 |
晶体学 | 506篇 |
力学 | 2419篇 |
综合类 | 290篇 |
数学 | 4442篇 |
物理学 | 14682篇 |
出版年
2024年 | 35篇 |
2023年 | 763篇 |
2022年 | 830篇 |
2021年 | 1141篇 |
2020年 | 1476篇 |
2019年 | 1381篇 |
2018年 | 1237篇 |
2017年 | 1139篇 |
2016年 | 1733篇 |
2015年 | 1699篇 |
2014年 | 2079篇 |
2013年 | 2623篇 |
2012年 | 3224篇 |
2011年 | 3423篇 |
2010年 | 2336篇 |
2009年 | 2293篇 |
2008年 | 2515篇 |
2007年 | 2248篇 |
2006年 | 2152篇 |
2005年 | 1660篇 |
2004年 | 1331篇 |
2003年 | 1126篇 |
2002年 | 1046篇 |
2001年 | 838篇 |
2000年 | 875篇 |
1999年 | 800篇 |
1998年 | 717篇 |
1997年 | 669篇 |
1996年 | 681篇 |
1995年 | 616篇 |
1994年 | 540篇 |
1993年 | 431篇 |
1992年 | 424篇 |
1991年 | 326篇 |
1990年 | 301篇 |
1989年 | 238篇 |
1988年 | 203篇 |
1987年 | 171篇 |
1986年 | 154篇 |
1985年 | 153篇 |
1984年 | 103篇 |
1983年 | 70篇 |
1982年 | 60篇 |
1981年 | 36篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Xiaomin Xu Xiaohong Ding Bo Yuan Weiwei Li Yimei Wang Yi Jin Haiyan Xu 《Biomedical chromatography : BMC》2019,33(6)
A rapid, simple and sensitive LC–MS/MS method was established and validated for simultaneous quantification of ticagrelor and its active metabolite AR‐C124910XX in human plasma. After plasma samples were deproteinized with acetonitrile, the post‐treatment samples were chromatographed on a Dikma C18 column interfaced with a triple quadrupole tandem mass spectrometer. Electrospray negative ionization mode and multiple reaction monitoring were adopted to assay ticagrelor and AR‐C124910XX. Acetonitrile and 5 mΜ ammonium acetate was used as the mobile phase with a gradient elution at a flow rate of 0.5 mL/min. The method was linear in the range of 0.781–800 ng/mL for both ticagrelor and AR‐C124910XX with a correlation coefficient ≥0.994. The intra‐ and inter‐day precisions were within 12.61% in terms of relative standard deviation and the accuracy was within ±7.88% in terms of relative error. The LC–MS/MS method was fully validated for its sensitivity, selectivity, stability, matrix effect and recovery. This convenient and specific LC–MS/MS method was successfully applied to the pharmacokinetic study of ticagrelor and AR‐C124910XX in healthy volunteers after an oral dose of 90 mg ticagrelor. 相似文献
992.
Dr. Lei He Prof. Wen-Cui Li Shuang Xu Prof. An-Hui Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3209-3218
Microporous carbons afford high surface areas, large pore volumes, and good conductivity, and are fascinating over a wide range of applications. Traditionally synthesized microporous carbon materials usually suffer from some limitations, such as poor accessibility and slow mass transport of molecules due to the micrometer-scale diffusion pathways and space confinement imposed by small pore sizes. Two-dimensional microporous carbon materials, denoted as microporous carbon nanosheets (MCNs), possess nanoscale thickness, which allows fast mass and heat transport along the z axis; thus overcoming the drawbacks of their bulk counterparts. Herein, recent breakthroughs in the synthetic strategies for MCNs are summarized. Three typical methods are discussed in detail with several examples: pyrolysis of organic precursors with 2D units, a templating method that uses wet chemistry, and the molten salt method. Among them, molecular-based assembly of MCNs in the liquid phase shows more controllable morphology, thickness, and pore size distribution. Finally, challenges in this research area are discussed to inspire future explorations. 相似文献
993.
Jian Wang Jinjin Zhou Yu Xu Bingqi Zhu Huiyi Li 《Rapid communications in mass spectrometry : RCM》2019,33(17):1410-1419
994.
Zhangxin Chen Chang Su Xiaogang Zhu Ruoteng Xu Lihuan Xu Cheng Zhang 《Journal of polymer science. Part A, Polymer chemistry》2018,56(22):2574-2583
A novel organic conjugated polymer based on star-shaped triazine-functional triphenylamine framework poly[1,3,5-tris(4-diphenylamino-phenyl)triazine] (PTDAPTz) is designed and synthesized successfully by FeCl3-catalysted chemical oxidative polymerization. The polymer PTDAPTz powder exhibits a compactly packed pleated skirt shape-like morphology with a high surface area (~930 m2 g−1) and a bimodal pore size distribution ranging from micropores (~0.55 nm) to small diameter mesopores (~2–6 nm). As explored as the cathode material, the obtained PTDAPTz presents the double charge–discharge process characteristics of both the free radical redox of triphenylamine unit and the bipolar redox of triazine unit in the polymer and a well-defined multistage charge/discharge voltage plateau (~3.8 V for p-doped and ~2.0 V for n-doped) during the charge–discharge process. Also, the PTDAPTz demonstrates an improved capacity (stabilized at 123 mA h g−1 until 50th cycle) and the enhanced rate performance compared to polytriphenylamine (PTPAn). Specially, the discharge curve for the part of triphenylamine unit presents an obviously improved discharge plateau (~3.8 V for PTDAPTz compared to ~3.6 V for PTPAn) due to the electron-withdrawing effect of the triazine unit to triphenylamine. The elaborate structural design and created micro-/mesoporous morphology with the double charge–discharge process make PTDAPTz a potential candidate as the performance-improved cathode of Li-organic battery. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2574–2583 相似文献
995.
Ytterbium, erbium, aluminum tri-doped zinc oxide crystal was synthesized, which can turn color from red to green up-conversion luminescence through adjusting aluminum content. When the aluminum concentration reached 4?mol%, the color of up-conversion emission first turn from red to green. Meanwhile, the ratio of red to green emission reduced from 25.32 to 0.26, and the coordinates of chromaticity coordinate calculation changes from (0.5749, 0.3378) to (0.2190, 0.7169) with aluminum concentration range from 0 to 4?mol%. The up-conversion emission peaks at 521, 542, and 660?nm of sample originate from the transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 of erbium ions, respectively. X-ray diffraction patterns perform the better crystallization degree with increasing aluminum concentration. The scanning electron microscopy images show the porous and lamellar structures with different aluminum concentrations. A convenient but effective design to obtain ytterbium, erbium, aluminum tri-doped zinc oxide up-conversion luminescence is reported, which can turn color from red to green. 相似文献
996.
Xu Lei Zhao Yiping Wang Wei Liu Hao Wang Rui 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(6):1237-1241
Russian Journal of Physical Chemistry A - SrTiO3 nanofibers were fabricated by an electrospinning process. The phase, microstructure and photocatalytic activity of the obtained SrTiO3 nanofibers... 相似文献
997.
The extent to which drugs combine with trypsin is influenced by the interaction of tartrazine and trypsin, which may cause overdose or underdose of drugs. Therefore, the interaction of tartrazine and trypsin is investigated by methods of spectrometry in this paper. The binding rate of tartrazine to trypsin is 80.95–95.71% at 310?K, and Hill’s coefficients are almost 1. The effect of tartrazine on trypsin structure was studied by synchronous and circular dichroism. The results showed that the binding of tartrazine and trypsin induced the conformational change of trypsin, and quenched the endogenous fluorescence in trypsin. The results of molecular docking revealed that tartrazine is located in the catalytic active site of trypsin, and is consistent with that of experimental calculation. 相似文献
998.
The enhanced biological activities of three Zn (II) complexes based on different 1,2,4‐triazole fungicides 下载免费PDF全文
Guo‐yu Ren Jie Li Xu‐zhan Wei Jin‐hua Zhou Biao Yan Zhao‐qi Guo Ying‐hui Ren Xiao‐hong Sun Hai‐xia Ma 《应用有机金属化学》2018,32(9)
In order to screen effective fungicides, three Zn (II) complexes, [Zn L 1 4 (NO3)2]·2H2O·2EtOH ( 1 ), [Zn L 2 4 (NO3)2] ( 2 ), and [Zn L 3 4 (DMF)2](NO3)2 ( 3 ), ( L 1 = paclobutrazol, L 2 = diniconazole, and L 3 = hexaconazole), were synthesized and characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal XRD. The antifungal activities of these complexes were then evaluated against four selected fungi using the mycelial growth rate method. The resulting data indicate that all the complexes show the enhanced antifungal activities than the corresponding ligand and mixtures. And, the interactions between the metal salt and ligands in the three complexes seem to be synergistic. According to the study of the influence of the structures on the activity, complex 2 with C=C linkage and 2,4‐dichlorophenyl moieties enhances the bioactivity significantly, especially against Wheat gibberellic ( II ). Density functional theory (DFT) calculations were carried out to help explain the enhanced bioactivity of the Zn (II) complexes. Meanwhile, all complexes are excellent grow‐regulators, especially complex 3 . The resulting data show that the complexes based on triazole fungicides have the potential applications in agriculture. 相似文献
999.
LOCALIZED PATTERNS OF THE CUBIC-QUINTIC SWIFT-HOHENBERG EQUATIONS WITH TWO SYMMETRY-BREAKING TERMS 下载免费PDF全文
Homoclinic snake always refers to the branches of homoclinic orbits \mbox{near} a heteroclinic cycle connecting a hyperbolic or non-hyperbolic equilibrium and a periodic
orbit in a reversible variational system. In this paper, the normal form of a Swift-Hohenberg equation with two different symmetry-breaking terms (non-reversible term and non-k-symmetry term) are investigated by using multiple scale method, and their bifurcation diagrams are initially studied by numerical simulations. Typically, we predict numerically the existence of so-called round-snakes and round-isolas upon particular two symmetric-breaking perturbations. 相似文献
1000.
Using the so-called martingale difference correlation (MDC), we propose a novel censored-conditional-quantile screening approach for ultrahigh-dimensional survival data with heterogeneity (which is often present in such data). By incorporating a weighting scheme, this method is a natural extension of MDC-based conditional quantile screening, as considered in Shao and Zhang (2014), to handle ultrahigh-dimensional survival data. The proposed screening procedure has a sure-screening property under certain technical conditions and an excellent capability of detecting the nonlinear relationship between independent and censored dependent variables. Both simulation results and an analysis of real data demonstrate the effectiveness of the new censored conditional quantile-screening procedure. 相似文献