全文获取类型
收费全文 | 14724篇 |
免费 | 1783篇 |
国内免费 | 2405篇 |
专业分类
化学 | 13948篇 |
晶体学 | 190篇 |
力学 | 820篇 |
综合类 | 196篇 |
数学 | 769篇 |
物理学 | 2989篇 |
出版年
2024年 | 39篇 |
2023年 | 214篇 |
2022年 | 714篇 |
2021年 | 696篇 |
2020年 | 706篇 |
2019年 | 623篇 |
2018年 | 569篇 |
2017年 | 822篇 |
2016年 | 938篇 |
2015年 | 826篇 |
2014年 | 954篇 |
2013年 | 1233篇 |
2012年 | 1079篇 |
2011年 | 1100篇 |
2010年 | 813篇 |
2009年 | 945篇 |
2008年 | 836篇 |
2007年 | 856篇 |
2006年 | 746篇 |
2005年 | 636篇 |
2004年 | 550篇 |
2003年 | 443篇 |
2002年 | 390篇 |
2001年 | 283篇 |
2000年 | 276篇 |
1999年 | 249篇 |
1998年 | 214篇 |
1997年 | 212篇 |
1996年 | 181篇 |
1995年 | 144篇 |
1994年 | 118篇 |
1993年 | 85篇 |
1992年 | 65篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 38篇 |
1988年 | 41篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1976年 | 4篇 |
1971年 | 3篇 |
1959年 | 5篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
151.
在硼氢化钾碱性溶液中对金属氢化物(MH)电极的表面进行化学还原处理,提高了MH电极的放电容量、活化性能和电催化活性.用其为负极组装的AA型MH-Ni电池进行了封口化成,电池放电容量达到1150mAh,5C下电池的放电容量达到0.2C下容量的80%以上,电池在1C100%DOD(放电深度)充放电条件下,循环寿命由原来的100次左右提高到200次以上 相似文献
152.
采用二硫化碳重结晶富勒烯混合物或二硫化碳二次抽提烟灰以提取高富勒烯(higherfulerenes,Cn,n>70)。产物经高效液相色谱分析,高富勒烯的含量从1%分别提高到4%和6%;经激光飞行时间质谱证明,产物中除含主要成分C60和C70以外,还含有C76、C78、C82、C84以及更高碳原子的富勒烯。 相似文献
153.
Poly(N-isopropylacrylamide) (PNIPAM) has a low critical solution temperature (LCST) at 32°C in water and the hydrophilicity changes through the LCST. The microspheres whose surface was composed of PNIPAM exhibited phase transition behavior around 32°C. Therefore, the interactions between PNIPAM micropheres and granulocytes depended on the temperature. That is, the oxygen consumption and active oxygen production by cells in contact with PNIPAM-containing microspheres and adhesion of the microspheres to the cell surface were more enhanced above the LCST of PNIPAM than below it, whereas no significant temperature dependence of cell–microspheres interaction was observed in nonthermosensitive microsphere systems. It was suggested that the function of cells could be controlled with temperature using the temperature-sensitive microspheres. 相似文献
154.
Huwe A Mazitschek R Giannis A 《Angewandte Chemie (International ed. in English)》2003,42(19):2122-2138
Cell division (mitosis) is one of the basic requirements for multicellular oranisms. The capability of a cell to replicate enables a complex assembly to be created. Faulty regulation of the control mechanism in the cell cycle leads to an excessive cell proliferation and is the cause of cancer. The key position of the cyclin-dependent kinases (CDKs) and their direct partners, as well as the fact that the majority of malign illnesses show defects in at least one of these key players of the cell cycle, is of great interest for the development of low-molecular-weight CDK inhibitors. In this Review an overview of the different structural classes of ATP-competitive inhibitors of CDKs are given, whose devlopment was aimed at battling cancer. The Review shows how far the development of selective CDK inhibitors has progressed and to what extent the expectations for such drugs have so far been fulfilled. 相似文献
155.
The filtration performance of yeast cell harvesting was greatly improved by using an oscillatory flow mixing technique in both tubular and flat sheet membrane systems; flux increases of several fold were achieved. The effects of various operating parameters such as frequency, amplitude and ratio of net forward flow rate to oscillatory flow rate were investigated. A simple alternative to the dual head pump, which involved the use of solenoid valves for producing flow reversal, was developed. The flux was significantly increased using this new operating mode. As the only increase of power consumption was from inertia loss due to change of flow direction the additional power consumption is minimal. 相似文献
156.
Shigeru Matsuo Tomoyoshi Murakami Ryuichi Takasawa 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3439-3446
Crystalline poly(arylene ether nitrile) could be prepared by the polycondensation of 2,6-dihalobenzonitrile with resorcinol at 200°C in N-methylpyrrolidone in the presence of sodium carbonate. A reaction temperature of at least 200°C was necessary to attain high molecular weight polymer. Spectral data indicated that the polymer had the structure of a poly(meta-phenylene ether) with pendent nitrile groups on every other phenylene unit. Despite this structure, the crystallinity and the crystallization rate of the polymer were greater than those of the corresponding polymer with a para-linked structure. The glass transition temperature and the melting temperature of the polymer were almost the same as those of poly(etheretherketone) (PEEKTM). A series of other new poly(arylene ether nitriles) were also examined. The polymers derived from 4,4′-biphenol, dihydroxytetra-phenylmethane, dihydroxydiphenylsulfone, and 1,5-isoquinolinediol had high glass transition temperatures. The poly(arylene ether nitriles) exhibited excellent tensile strength compared with the corresponding ketone- or sulfone-containing polymers. Comparing the three different kinds of polymers containing the same bisphenol units, the order of glass transition temperature was found to be sulfone- > nitrile- > ketone-containing polymers, while the order of tensile strength was nitrile- > ketone- > sulfone-containing polymers. The excellent mechanical properties are attributable to dipole-dipole interactions of nitrile groups. © 1993 John Wiley & Sons, Inc. 相似文献
157.
Two ferrates, K2FeO4 and BaFeO4, had been prepared and characterized by XRD, IR and SEM. The electrochemical tests of the samples were carried out in the voltage range of 0.8~2.0 V and current density of 0.5~3.0 mA·cm-2. The results indicated that performance of Zn-BaFeO4 battery was superior to that of Zn-MnO2 and Zn-K2FeO4 batteries. Nanometer SrTiO3 prepared by Sol-gel methode with different ratio was added to the BaFeO4 cathode in order to improve the discharge performance. The discharge capacity of the BaFeO4 cathode was increased from 224 mAh·g-1 to 246 mAh·g-1 by addition of 5% nanometer SrTiO3. The reason of enhancing BaFeO4 electrochemical performance was discussed. 相似文献
158.
Akihiko Kanazawa Tomiki Ikeda Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1993,31(2):335-343
Various polymeric phosphonium salts and the corresponding low-molecular-weight model compounds were prepared and their antibacterial activities against Staphylococcus aureus and Escherichia coli were explored by the viable cell counting method in sterile distilled water. Antibacterial activity of the polymers was found to be higher than that of the corresponding model compounds, particularly against S. aureus. Furthermore, the polymeric phosphonium salt exhibited a higher activity by 2 orders of magnitude than the polymeric quaternary ammonium salt with the same structure except the cationic part. Compounds with the longest alkyl chain (octyl) studied were found to exhibit particularly high activity, and this finding may be ascribed to the contribution of the increased hydrophobicity of the compounds to the cidal activity. © 1993 John Wiley & Sons, Inc. 相似文献
159.
无机胶体法制备Pt/C催化剂及其性能表征 总被引:3,自引:0,他引:3
采用无机胶体法制备用于质子交换膜燃料电池(PEMFC)的Pt/C催化剂。研究了影响PtO2胶体生成和稳定性的因素(溶液的pH值、浓度和温度条件等)以及不同还原剂浓度对Pt/C催化剂性能的影响。透射电子显微镜测试结果表明,采用经优化的工艺条件所制备的Pt/C催化剂平均粒径为3 nm,且分散性好、粒度均匀。X-射线衍射分析表明,催化剂中Pt(111)晶面的相对含量较高,有利于加速氧还原反应。单体PEMFC的电压/电流密度曲线测试表明,所制备的Pt/C催化剂具有良好的电化学性能。 相似文献
160.
A new diamine monomer containing flexible sulfone, sulfide, and amide units was prepared via three steps. Nucleophilic chloro displacement reaction of 4‐aminothiophenol with 4‐nitrobenzoyl chloride in the presence of propylene oxide afforded N‐(4‐mercapto‐phenyl)‐4‐nitrobenzamide and subsequent reduction of the nitro intermediate led to 4‐amino‐N‐(4‐mercapto‐phenyl)benzamide. Two moles of this amino thiophenol compound was reacted with bis‐(4‐chloro phenyl)sulfone to provide a novel diamine monomer. The diamine was reacted with aromatic dianhydrides to form polyimides via a two‐step polycondensation method, formation of poly(amic acid)s, followed by chemical imidization. The resulting polymers were characterized and their physical properties including thermal behavior, thermal stability, solubility and inherent viscosity were studied. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献