全文获取类型
收费全文 | 8970篇 |
免费 | 571篇 |
国内免费 | 541篇 |
专业分类
化学 | 2861篇 |
晶体学 | 88篇 |
力学 | 190篇 |
综合类 | 21篇 |
数学 | 2302篇 |
物理学 | 4620篇 |
出版年
2023年 | 77篇 |
2022年 | 98篇 |
2021年 | 129篇 |
2020年 | 189篇 |
2019年 | 171篇 |
2018年 | 147篇 |
2017年 | 140篇 |
2016年 | 158篇 |
2015年 | 178篇 |
2014年 | 258篇 |
2013年 | 641篇 |
2012年 | 391篇 |
2011年 | 471篇 |
2010年 | 413篇 |
2009年 | 522篇 |
2008年 | 566篇 |
2007年 | 687篇 |
2006年 | 522篇 |
2005年 | 352篇 |
2004年 | 337篇 |
2003年 | 386篇 |
2002年 | 363篇 |
2001年 | 350篇 |
2000年 | 344篇 |
1999年 | 327篇 |
1998年 | 264篇 |
1997年 | 181篇 |
1996年 | 167篇 |
1995年 | 147篇 |
1994年 | 129篇 |
1993年 | 112篇 |
1992年 | 99篇 |
1991年 | 112篇 |
1990年 | 64篇 |
1989年 | 69篇 |
1988年 | 50篇 |
1987年 | 57篇 |
1986年 | 33篇 |
1985年 | 65篇 |
1984年 | 40篇 |
1983年 | 33篇 |
1982年 | 46篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1974年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
L.O. Leal 《Trends in analytical chemistry : TRAC》2011,30(5):761-770
This review outlines automated methodologies developed for measuring arsenic in environmental samples. We report the state of the art of the most significant methods exploiting multicommutation flow techniques coupled to hydride generation-atomic fluorescence determination. We review analytical methods used and present a comparative evaluation of them. We also discuss the on-line pre-concentration procedure as being of particular interest in the development of fully automated methods. 相似文献
972.
973.
The development of new enzyme immobilization techniques that do not affect catalytic activity or conformation of a protein is an important research task in biotechnology including biosensor applications and heterogeneous reaction systems. One of the most promising approaches for controlled protein immobilization is based on the immobilized metal ion affinity chromatography (IMAC) principle originally developed for protein purification. Here we describe the current status and future perspectives of immobilization of His-tagged proteins on electrode surfaces. Recombinant proteins comprising histidine-tags or histidine rich native proteins have a strong affinity to transition metal ions. For metal ion immobilization at the electrode surface different matrices can be used such as self-assembled monolayers or conductive polymers. This specific technique allows a reversible immobilization of histidine-tagged proteins at electrodes in a defined orientation which is an important prerequisite for efficient electron transfer between the electrode and the biomolecule. Any application requiring immobilized biocatalysts on electrodes can make use of this immobilization approach, making future biosensors and biocatalytic technologies more sensitive, simpler, reusable and less expensive while only requiring mild enzyme modifications. 相似文献
974.
Patrick J. West 《Journal of organometallic chemistry》2011,696(17):2886-2893
The complexes trans-[Os(CCC6H4-4-CCR)Cl(dppe)2] (R = SiPri31, H 2), trans,trans-[(dppe)2ClOs(CCC6H4-4-CC)RuX(dppe)2] (X = Cl 3, CCC6H4-4-CCSiPri34), trans-[Os(CCC6H4-4-CCC6H4-4-CCR)Cl(dppe)2] (R = SiPri35, H 6), and trans,trans-[(dppe)2ClOs(CCC6H4-4-CCC6H4-4-CC)RuCl(dppe)2] (7) have been synthesized, and the identities of 1, 2, and 6 confirmed by single-crystal X-ray diffraction studies. Cyclic voltammetry shows that the mononuclear complexes 1, 2, 5, and 6 are oxidized at potentials within a narrow range (0.45-0.49 V), in processes centered on the osmium ethynyl neighbourhood and for simplicity assigned as OsII/III, while the heterobinuclear complexes 3, 4, and 7 exhibit lower oxidation potentials for OsII/III and a second oxidation process assigned in a similar fashion to RuII/III; the difference in potential between the Os- and Ru-localized processes decreases as the π-bridge is lengthened. UV-vis-NIR spectroelectrochemical studies on 1 and 5 reveal the appearance on oxidation of a low-energy band ascribed to chloro to metal-ethynyl charge transfer. Osmium-centered oxidation at the heterobinuclear complexes 4 and 7 results in appearance of a low-energy band, which blue-shifts and increases in intensity on further oxidation to 42+ and 72+. 相似文献
975.
976.
Ji Z Li Y Pritchett TM Makarov NS Haley JE Li Z Drobizhev M Rebane A Sun W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(8):2479-2491
The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker. 相似文献
977.
978.
疏水缔合聚丙烯酰胺与双子表面活性剂的相互作用 总被引:4,自引:0,他引:4
制备了一种脂肪酸酯双磺酸盐型双子表面活性剂, 利用粘度法、界面张力法和原子力显微镜研究了疏水缔合聚丙烯酰胺与双子表面活性剂在溶液中的相互作用. 实验结果表明: 疏水缔合聚丙烯酰胺在溶液中能够通过自组装形成疏水微区并发展成网络结构, 疏水微区与表面活性剂在溶液中能形成混合胶束; 当一定量的表面活性剂加入时, 对疏水缔合聚丙烯酰胺的自组装起促进作用, 而过多双子表面活性剂的加入又会对聚合物分子的自组装起抑制作用, 从而显著影响疏水缔合聚丙烯酰胺的溶液性质, 随着表面活性剂浓度的增加, 聚合物溶液粘度先增加、再降低; 同时, 疏水缔合聚丙烯酰胺对双子表面活性剂的界面性能也有较大影响, 聚合物的加入使双子表面活性剂降低油/水界面张力的能力下降, 油/水界面张力达到平衡所需时间延长. 相似文献
979.
Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (2 values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity. 相似文献
980.
Ming Zhang Yi Li Lifeng Bi Wei Zhuang Sibing Wang Yuanli Chen Baozong Li Yonggang Yang 《中国化学》2011,29(5):933-941
The morphologies and pore architectures of mesoporous ethenylene‐silica were controlled using cetyltrimethylammonium bromide (CTAB) as template and (S)‐β‐citronellol as a co‐structure‐directing agent under basic conditions. When the (S)‐β‐citronellol/CTAB molar ratios are in the range of 0.75–2.0, helical nanofibers were obtained. With increasing the (S)‐β‐citronellol/CTAB molar ratio, the lengths of the nanofibers increases. Lamellar mesopores were identified on the surfaces of the nanofibers prepared in the (S)‐β‐citronellol/CTAB molar ratio range of 1.5–2.0. At the (S)‐β‐citronellol/CTAB molar ratio of 2.5:1, nanoparticles with nanoflakes on the surfaces were obtained. The field emission scanning electron microscopy images taken after different reaction times indicated that the helical pitches of the nanofibers decreased with increasing the reaction time. Helical 1,4‐phenylene‐silica and methylene‐silica nanofibers were also prepared. The results indicated that the morphologies and pore architectures of the obtained organic‐inorganic hybrid silicas are also sensitive to the hybrid silica precursors. Helical ethenylene‐silica nanofibers with lamellar mesopores on their surfaces can be also prepared using the mixtures of CTAB and racemic citronellol within a narrower citronellol/CTAB molar ratio range. 相似文献