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   4051篇
  免费   630篇
  国内免费   592篇
化学   3170篇
晶体学   46篇
力学   201篇
综合类   45篇
数学   487篇
物理学   1324篇
  2024年   9篇
  2023年   68篇
  2022年   104篇
  2021年   124篇
  2020年   169篇
  2019年   163篇
  2018年   146篇
  2017年   127篇
  2016年   178篇
  2015年   177篇
  2014年   208篇
  2013年   268篇
  2012年   331篇
  2011年   367篇
  2010年   250篇
  2009年   232篇
  2008年   301篇
  2007年   212篇
  2006年   210篇
  2005年   190篇
  2004年   160篇
  2003年   160篇
  2002年   194篇
  2001年   158篇
  2000年   115篇
  1999年   94篇
  1998年   78篇
  1997年   46篇
  1996年   95篇
  1995年   69篇
  1994年   48篇
  1993年   31篇
  1992年   32篇
  1991年   27篇
  1990年   30篇
  1989年   16篇
  1988年   17篇
  1987年   17篇
  1986年   11篇
  1985年   15篇
  1984年   3篇
  1983年   5篇
  1982年   5篇
  1981年   5篇
  1980年   3篇
  1979年   2篇
  1974年   1篇
  1957年   1篇
  1936年   1篇
排序方式: 共有5273条查询结果,搜索用时 22 毫秒
991.
The alternate dielectric component is introduced into a nanowall skeleton for the first time. As a photoelectrode, this novel model can optimize the process of photon absorption, charge separation/migration and surface reaction, resulting in superior photoelectrochemical performance.  相似文献   
992.
K2NaH2 [BW12O40]·12H2O, prepared by the conventional aqueous method, is characterized by single crystal XRD and IR spectroscopy.  相似文献   
993.
994.
Trypsin was immobilized on cellulose-coated glass fibers via a condensation reaction between the aldehyde groups of the oxidized cellulose and the primary amino groups of trypsin. A piece of the modified fiber was inserted into the main channel of a poly(methyl methacrylate) microchip to form a microfluidic proteolytic bioreactor. Scanning electron microscopy of the cross section of the fiber revealed a rough film on the surface of the fiber glass. The performance of the bioreactor was demonstrated by the tryptic digestion of hemoglobin and cytochrome c, where the time for digestion was reduced to <10?s. The digests were identified by MALDI-TOF-MS to obtain peptide mass fingerprint spectra. The results indicated that the digestion in the microfluidic bioreactor is comparable to that of a 12-h solution tryptic digest and thus provides a promising platform for the high throughput identification of proteins.
Figure
Covalent immobilization of trypsin on oxidized cellulose-coated glass fiber cores in microchip for highly efficient proteolysis  相似文献   
995.
The article studies on the effects of six inorganic ions (Ca2+, Mg2+, Cl?, SO 4 2? , H2PO 4 ? , and HCO 3 ? ) on titanium dioxide (TiO2)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO2 and photocatalytic degradation of HA. The results indicate that Ca2+ and Mg2+ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO2. However, the complex is more difficult to be degraded than HA. The effects of Cl? and SO 4 2? are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO2, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO 3 ? and H2PO 4 ? can inhibit the photocatalytic degradation process seriously, because HCO 3 ? and H2PO 4 ? are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO2 due to adsorption competition.  相似文献   
996.
The possibility of applying activated carbon and polymeric sorbents poly(4-vinylpyridine), polytrimethylsilylpropyne (PTMSP), bromo-substituted PNMSP (Br-PNMSP), poly(N-methyl-4-vinylpyridinium iodide) for the sorption recovery of iodine from a 0.5 M solution of sodium chloride is studied. The dependence of iodine sorption on the pH of solution, the amount of adsorbent, and the duration of contact between the solution and adsorbent is studied. The highest sorption capacity (G = 616.78 mg/g) is attained by using poly(N-methyl-4-vinylpyridinium iodide) anionite with the addition of iodine to form complex triiodide ions. The dynamics of iodine adsorption on poly(4-vinylpyridine) is described by a kinetic model of pseudosecond order. The composition and structure of the iodine compounds sorbed by polymers and activated carbon are studied by Raman spectroscopy (RS).  相似文献   
997.
Bao C  Jin M  Li B  Xu Y  Jin J  Zhu L 《Organic & biomolecular chemistry》2012,10(27):5238-5244
A series of anticancer prodrugs with different chemical functional groups were prepared, in which the styryl conjugated 2-nitrobenzyl derivatives were introduced as the phototrigger to regulate the drug (chlorambucil) release. Compared to the common 4,5-dimethoxy-2-nitrobenzyl caged compounds, most of the prodrugs exhibited large and redshifted one-photon absorption within the visible range. One-photon excitation for the drug release was studied by measuring UV-vis absorption, FT-IR, and HPLC spectra, which suggested that chlorambucil was released effectively and precisely by manipulating external light conditions. And the introduction of different functional groups made this type of prodrug a good platform to further react with some typical drug carriers and to further form excellent visible light responsive drug delivery systems. Moreover, the drug also could be effectively released under the excitation of two-photon at 800 nm with comparable photorelease efficiencies.  相似文献   
998.
A novel activity of halohydrin dehalogenases towards spiroepoxides has been found. The enzyme from Arthrobacter sp. (HheA) catalysed highly regioselective azidolysis of spiroepoxides containing 5, 6 and 7-membered cycloalkane rings, while the enzyme from Agrobacterium radiobacter (HheC), besides high regioselectivity, also displayed moderate to high enantioselectivity (E up to >200) that can be applied for the kinetic resolution of chiral spiroepoxides. The orientations of spiroepoxides in the active site of halohydrin dehalogenases were studied by quantum-chemical calculations and docking simulations. Analyses of the complexes obtained revealed the origins of diastereoselectivity and enantioselectivity of the investigated biotransformations.  相似文献   
999.
本文讨论了极限圆型Hamilton算子乘积的自伴性,利用Calkin方法及奇异Hamilton系统自伴扩张的一般构造理论,给出了在极限圆型时判定Hamilton算子乘积自伴的一个充要条件.  相似文献   
1000.
采用高效液相色谱法测定氨基酸口服液中L-色氨酸的含量,对测量结果的不确定度进行评定。结果表明,标准曲线校准和测量重复性是测量过程中不确定度的主要来源,其中标准曲线校准对合成不确定度的影响最大。当氨基酸口服液中L-色氨酸的测定结果为8.8μg/mL时,其扩展不确定度为1.1μg/mL。  相似文献   
[首页] « 上一页 [95] [96] [97] [98] [99] 100 下一页 » 末  页»
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