全文获取类型
收费全文 | 7608篇 |
免费 | 1516篇 |
国内免费 | 974篇 |
专业分类
化学 | 5483篇 |
晶体学 | 172篇 |
力学 | 505篇 |
综合类 | 112篇 |
数学 | 698篇 |
物理学 | 3128篇 |
出版年
2024年 | 39篇 |
2023年 | 187篇 |
2022年 | 323篇 |
2021年 | 351篇 |
2020年 | 463篇 |
2019年 | 396篇 |
2018年 | 345篇 |
2017年 | 324篇 |
2016年 | 480篇 |
2015年 | 530篇 |
2014年 | 567篇 |
2013年 | 711篇 |
2012年 | 754篇 |
2011年 | 744篇 |
2010年 | 524篇 |
2009年 | 443篇 |
2008年 | 454篇 |
2007年 | 401篇 |
2006年 | 324篇 |
2005年 | 309篇 |
2004年 | 231篇 |
2003年 | 190篇 |
2002年 | 195篇 |
2001年 | 152篇 |
2000年 | 87篇 |
1999年 | 74篇 |
1998年 | 58篇 |
1997年 | 40篇 |
1996年 | 38篇 |
1995年 | 18篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1974年 | 10篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Sesquiterpene Lactone Glycosides from Carpesium macrocephalum 总被引:1,自引:0,他引:1
Two new sesquiterpene lactone glycosides were isolated from the seeds of Carpesium meacrocephalum. Their structures were elucidated as 2α-O-β-D-glucopyranosy-5α,11αH-eudesma-4(15)-en-12,8β-olide and 2α-O-β-D-glucopyranosy-5αH-eudesma-4(15),11(13)-dien-12,8β-olide by spectral methods (HRMS,1D and 2D NMR). 相似文献
22.
A capillary electrophoresis (CE) method was developed for the separation of heparin oligosaccharides compatible to study the interactions between the oligosaccharides and granulocyte-colony stimulating factor (G-CSF). Unfractionated heparin was eliminitively degraded to heparin oligosaccharides by an endolytic heparinase. The degraded smaller oligosaccharides (M(r) < 1000) were baseline-separated by CE under a 50 mM phosphate buffer (pH 9.0) in 10 min. Standard heparin disaccharides and larger oligosaccharides (1000 < M(r) < 8000) were all separated under optimized separation conditions. Compared with standard heparin disaccharides, smaller oligosaccharides contained one nonsulfated, two monosulfated, and two disulfated disaccharides, but trisulfated disaccharides were not found. The smaller oligosaccharides were also identified and molecular mass was deduced by electrospray ionization-mass spectrometry (ESI-MS). Furthermore, interactions between G-CSF and the oligosaccharides were studied by using capillary zone electrophoresis (CZE) under the above separation conditions. It was found that larger oligosaccharides could interact with G-CSF while smaller oligosaccharides were not observed to bind to G-CSF under the experimental conditions. In conclusion, the purified heparinase could selectively degrade heparin into oligosaccharides and the interaction between G-CSF and heparin was correlated with the chain length of heparin. 相似文献
23.
We have developed a coarse-grained multiscale molecular simulation method for soft matter systems that directly incorporates stereochemical information. We divide the material into disjoint groups of atoms or particles that move as separate rigid bodies; we call these groups "rigid blobs," hence the name coarse-grained rigid blob model. The method is enabled by the construction of transferable interblob potentials that approximate the net intermolecular interactions, as obtained from ab initio electronic structure calculations, other all-atom empirical potentials, experimental data, or any combination of the above. We utilize a multipolar expansion to obtain the interblob potential-energy functions. The series, which contains controllable approximations that allow us to estimate the errors, approaches the original intermolecular potential as the number of terms increases. Using a novel numerical algorithm, we can calculate the interblob potentials very efficiently in terms of a few interaction moment tensors. This reduces the labor well beyond what is required in standard molecular-dynamics calculations and allows large-scale simulations for temporal scales commensurate with characteristic times of nano- and mesoscale systems. A detailed derivation of the formulas is presented, followed by illustrative applications to several systems showing that the method can effectively capture realistic microscopic details and can easily extend to large-scale simulations. 相似文献
24.
GuoXiangCHENG GuangLingPEI LingGangZENG LiYongZHANG ChaoLIU 《中国化学快报》2004,15(2):242-245
In this paper, the surface imprinted cross-linked polystyrene beads were prepared via suspension polymerization with styrene (St), divinylbezene (DVB), polyvinyl alcohol (PVA1788),the mixture of Span 85 and xylene or the mixture of Span 85 and paraffin as monomer,cross-linking agent, dispersion stabilizer and templates, respectively. The results indicate that there are dense cavities on the surface of beads, and the diameter and density of cavity are related with the composition and amount of emulsion template. The forming mechanism of cavity from thermodynamics and dynamics was proposed. 相似文献
25.
四(三苯基膦)化钯催化的若干菲啶类化合物的合成 总被引:1,自引:0,他引:1
邻甲酰基芳基硼酸与取代邻溴苯胺经四(三苯基膦)化钯催化偶联缩合, 合成了9个菲啶衍生物。邻溴苯胺的取代基无论是吸电子或供电子基团, 反应均可顺利进行。 相似文献
26.
在分析当前省属工科院校教育以能力为导向培养目标完成实施过程中遇到国际化困难问题的基础上,以青岛大学材料学科为例,提出了基于国际化产科教融合实训平台的教学模式改革举措,并经过实践验证证实其切实可行。包括:充分整合校内外材料学科整体资源,建立了国际化的产科教深度融合实训平台,构建了高效的国际化产科教深度融合协同育人实训平台动态管理运行机制;以实训平台为依托实现师资队伍、教学内容、教学模式、科研等全方位的国际化改革;基于国际化产教研融合实训平台的教学模式改革的实践收到显著成效,对全国省属高等院校理工学科专业建设国际化改革的推广有较好的示范作用。 相似文献
27.
Changzheng Wu Qing Yang Chao Huang Ping Yin Yi Xie 《Journal of solid state chemistry》2004,177(10):3522-3528
Pure hexagonal aluminum nitride (AlN) nanowhiskers have been successfully synthesized by directly reacting AlCl3 with NaN3 in non-solvent system at the low temperature of 450 °C for 24 h. The obtained products are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction, which show that the obtained products are hexagonal phase AlN nanowhiskers with width from 10 to 80 nm and length up to several micrometers. The influencing factors of the formation of AlN nanowhiskers were discussed and a possible growth mechanism for AlN nanowhiskers was proposed. Additionally, the study on the corresponding optical properties and catalytic properties is also carried out. 相似文献
28.
meso -四 (α ,α ,α ,α - 0 -苯乙酰苯 )卟啉诱导的单抗 (MAb)导致meso -四 (α,α ,α ,α - 0 -苯乙酰苯 )卟啉Soret带来巨大红移 ,并且在meso -四 (α ,α ,α ,α - 0 -苯乙酰苯 )卟啉上产生巨大的诱导Cotton效应 (ICD) .借用ICD定量分析meso -四 (α ,α ,α ,α - 0 -苯乙酰苯 )卟啉同抗体的结合 ,表明在抗体超过meso -四 (α ,α ,α ,α - 0 -苯乙酰苯 )卟啉的情况下 ,既有 1∶1结合 ,又有 2∶1结合〔结合位点 :meso -四 (α ,α ,α ,α - 0 -苯乙酰苯 )卟啉〕 相似文献
29.
Fashui?HongEmail author Xuefeng?Wang Chao?Liu Guoxing?Su Weiping?Song Kang?Wu Ye?Tao Guiwen?Zhao 《中国科学B辑(英文版)》2003,46(1):42-50
It was studied by spectroscopy that PSII reaction center complex consisting of three polypeptides, D1, D2 and Cytb559, were purified from PSII particle of CeCl3 treated spinach. The results of the experiment show that Ce3+ could improve the growth of spinach, and accelerate electron transport of PSII particles. Of chl-a of UV-Vis spectrum of
D1/D2/Cytb559 complex, Soret band was blue-shifted by 3 nm and Q band by 2 nm, respectively, and the fluorescence emission
peak was blue-shifted by 5 nm in CeCl3-treated spinach compared with the one in control. By the extended X-ray absorption fine structure (EXAFS) spectroscopy methods,
it has been found that Ce3+ is coordinated with 8 nitrogen atoms in the first coordination shell with Ce-N bond length of 0.253 nm, and Ce3+ with 6 oxygen atoms in the second coordination shell with Ce-O bond length of 0.32 nm. However, the secondary structure of
D1/D2/Cytb559 complex by circular dichroism (CD) spectroscopy has no significant change after CeCl3 treated. It might be that Ce3+ binds to porphyrin rings of chlorophyll and oxygen of amino acid residue of polypeptide in D1/D2/Cytb559 complex, and then
accelerates the primary reaction of PSII, intensifies function of P680+ primary electron donor of D1/D2/Cytb559, but there is little change in conformation of PSII reaction center complex. 相似文献
30.