首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1998篇
  免费   375篇
  国内免费   231篇
化学   1423篇
晶体学   15篇
力学   91篇
综合类   6篇
数学   276篇
物理学   793篇
  2024年   6篇
  2023年   47篇
  2022年   51篇
  2021年   47篇
  2020年   68篇
  2019年   62篇
  2018年   72篇
  2017年   60篇
  2016年   87篇
  2015年   74篇
  2014年   93篇
  2013年   127篇
  2012年   162篇
  2011年   172篇
  2010年   100篇
  2009年   128篇
  2008年   133篇
  2007年   118篇
  2006年   125篇
  2005年   101篇
  2004年   75篇
  2003年   58篇
  2002年   56篇
  2001年   62篇
  2000年   52篇
  1999年   63篇
  1998年   34篇
  1997年   45篇
  1996年   46篇
  1995年   33篇
  1994年   19篇
  1993年   26篇
  1992年   30篇
  1991年   28篇
  1990年   23篇
  1989年   10篇
  1988年   9篇
  1987年   10篇
  1986年   9篇
  1985年   8篇
  1984年   9篇
  1983年   6篇
  1982年   10篇
  1981年   5篇
  1980年   4篇
  1979年   5篇
  1978年   3篇
  1976年   4篇
  1974年   3篇
  1973年   5篇
排序方式: 共有2604条查询结果,搜索用时 421 毫秒
121.
利用均相反应器,在没有添加剂的条件下合成了具有多孔结构的Cu2O微球.考察了合成时间以及反应器旋转速度对Cu2O微球结构的影响.通过增加聚乙烯吡咯烷酮(PVP)的用量,使得Cu2O从多孔微球转变为立方体孪晶,最终形成十四面体孪晶结构.同时,将不同结构的Cu2O多晶应用于催化高氯酸铵(AP)的热分解,结果表明:多孔Cu2O微球较其它结构的Cu2O对AP的热分解具有更高的催化活性,使得AP的低温分解温度降低了37.4°C,而AP在低温阶段的分解量也由8.7%增加至49.0%.  相似文献   
122.
探讨了纳米激光粒度仪测定生物药品团聚物质量浓度的方法。以SALD–7500nano颗粒测试仪为例,介绍其在测量纳米级颗粒物粒度范围方面的应用。通过进一步分析颗粒浓度与光强度成正比的关系获得以质量浓度形式给出的粒度分布数据。通过牛血清蛋白(BSA)团聚物测量的实例,验证了颗粒物质量浓度的测试方法。该方法可用于生物制药领域对团聚物的监控测量以及评价药品药效、安全性能等。  相似文献   
123.
A liposome‐based co‐delivery system composed of a fusogenic liposome encapsulating ATP‐responsive elements with chemotherapeutics and a liposome containing ATP was developed for ATP‐mediated drug release triggered by liposomal fusion. The fusogenic liposome had a protein–DNA complex core containing an ATP‐responsive DNA scaffold with doxorubicin (DOX) and could release DOX through a conformational change from the duplex to the aptamer/ATP complex in the presence of ATP. A cell‐penetrating peptide‐modified fusogenic liposomal membrane was coated on the core, which had an acid‐triggered fusogenic potential with the ATP‐loaded liposomes or endosomes/lysosomes. Directly delivering extrinsic liposomal ATP promoted the drug release from the fusogenic liposome in the acidic intracellular compartments upon a pH‐sensitive membrane fusion and anticancer efficacy was enhanced both in vitro and in vivo.  相似文献   
124.
Reductive metalation of [44]decaphyrin with [Pd2(dba)3] provided a Hückel aromatic [46]decaphyrin PdII complex, which was readily oxidized upon treatment with DDQ to produce a Hückel antiaromatic [44]decaphyrin PdII complex. In CH2Cl2 solution the latter complex underwent slow tautomerization to a Möbius aromatic [44]decaphyrin PdII complex which exists as a mixture of conformers in dynamic equilibrium. To the best of our knowledge, these three PdII complexes represent the largest Hückel aromatic, Hückel antiaromatic, and Möbius aromatic complexes to date.  相似文献   
125.
采用溶胶-沉积法合成了高选择性的Au/ZnO催化剂,用于1,3-丙二醇选择性氧化酯化为3-羟基丙酸甲酯的反应.研究了保护剂PVA用量、金溶胶合成温度、金负载量及催化剂循环利用对反应的影响,且优化了反应温度和反应压力,并对催化剂进行了XRD和TEM表征.结果表明,PVA∶Au(m/m)=1∶4、金溶胶合成温度25℃、金负载量1%的Au/ZnO对目标反应的催化活性最好,在100℃和Po2=2MPa的条件下1,3-丙二醇的转化率达82.8%,产物3-羟基丙酸甲酯的选择性达95.4%.Au纳米粒子的粒径影响催化性能,在Au平均粒径为2.8~6.1nm的范围内,产物选择性随Au纳米粒子的粒径的减小而增大,平均粒径在2.8~4.8nm的范围内时,催化剂具有较好的产物选择性(大于90%);Au/ZnO催化剂循环利用4次后催化性能(转化率和选择性)无明显下降;并推测了无碱条件下Au/ZnO选择性催化氧化1,3-丙二醇合成3-羟基丙酸甲酯的反应机制.  相似文献   
126.
127.
An asymmetric copper-catalyzed Sonogashira type coupling between alkynes and α-bromoamides has been developed. This method represents a facile approach to synthetically useful β, γ-alkynyl amides from two readily available starting materials in a highly enantioselective manner. A Bisoxazoline diphenylanaline (BOPA) serves as the effective chiral ligand. Preliminary mechanistic studies support the formation of alkyl radical species .  相似文献   
128.
Low-energy inverse photoelectron spectroscopy (LEIPS) and ultraviolet photoelectron spectroscopy (UPS) incorporated into the multitechnique XPS system were used to probe the ionization potential and the electron affinity of organic materials, respectively. By utilizing gas cluster ion beam (GCIB), in situ analyses and depth profiling of LEIPS and UPS were also demonstrated. The band structures of the 10-nm-thick buckminsterfullerene (C60) thin film on Au (100 nm)/indium tin oxide (100 nm)/glass substrate were successfully evaluated in depth direction.  相似文献   
129.
In this work, a novel quick, easy, cheap, effective, rugged, and safe technique with hydrophobic natural deep eutectic solvent as both extractant and analyte protectant was developed and combined with gas chromatography–tandem mass spectrometry to analyze pyrethroid residues in tomatoes. Eight hydrophobic natural deep eutectic solvents were first evaluated as analyte protectants and those with decanoic acid or lactic acid as hydrogen bond donor were demonstrated to be effective in compensating for the matrix effects of pyrethroids in the gas chromatography system. Hence, they were added to solvent standards for correcting the quantitation errors instead of matrix‐matched calibration standards. Then the abilities of these acid‐based deep eutectic solvents to extract pyrethriods from tomatoes were evaluated. Results showed the recoveries of all pyrethroids reached to over 80% with only 5 mL menthol:decanoic acid (1:1) used, and good phase separation was easily achieved without the addition of inorganic salt in the extraction step, indicating hydrophobic natural deep eutectic solvent could be a green substitute for acetonitrile in the quick, easy, cheap, effective, rugged, and safe extraction. Compared with the conventional method, the proposed protocol improved the recoveries, reduced the matrix effects, and simplified the extraction step, demonstrating to be an effective, fast, and green method.  相似文献   
130.
Adaptivity is an essential trait of life. One type of adaptivity is the reconfiguration of a functional system states by correlating sensory inputs. We report polymer transformers, which can adaptively reconfigure their composition from a state of a mixed copolymer to being enriched in either monomer A or B. This is achieved by embedding and hierarchically interconnecting two chemically fueled activation/deactivation enzymatic reaction networks for both monomers via a joint activation pathway (network level) and an AB linker monomer reactive to both A and B (species level). The ratio of enzymes governing the individual deactivation pathways (our external signals) control the enrichment behavior in the dynamic state. The method shows high programmability of the reconfigured state, rejuvenation of transformation cycles, and quick in situ adaptation. As a proof‐of‐concept, we showcase this dynamic reconfiguration for colloidal surface functionalities.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号