全文获取类型
收费全文 | 11916篇 |
免费 | 541篇 |
国内免费 | 122篇 |
专业分类
化学 | 8171篇 |
晶体学 | 111篇 |
力学 | 330篇 |
综合类 | 10篇 |
数学 | 1137篇 |
物理学 | 2820篇 |
出版年
2023年 | 62篇 |
2022年 | 194篇 |
2021年 | 245篇 |
2020年 | 198篇 |
2019年 | 209篇 |
2018年 | 176篇 |
2017年 | 171篇 |
2016年 | 332篇 |
2015年 | 328篇 |
2014年 | 426篇 |
2013年 | 749篇 |
2012年 | 827篇 |
2011年 | 930篇 |
2010年 | 582篇 |
2009年 | 475篇 |
2008年 | 810篇 |
2007年 | 727篇 |
2006年 | 732篇 |
2005年 | 664篇 |
2004年 | 558篇 |
2003年 | 492篇 |
2002年 | 446篇 |
2001年 | 287篇 |
2000年 | 249篇 |
1999年 | 172篇 |
1998年 | 103篇 |
1997年 | 88篇 |
1996年 | 108篇 |
1995年 | 121篇 |
1994年 | 90篇 |
1993年 | 99篇 |
1992年 | 80篇 |
1991年 | 53篇 |
1990年 | 65篇 |
1989年 | 60篇 |
1988年 | 45篇 |
1987年 | 51篇 |
1986年 | 23篇 |
1985年 | 55篇 |
1984年 | 43篇 |
1983年 | 25篇 |
1982年 | 48篇 |
1981年 | 44篇 |
1980年 | 34篇 |
1979年 | 45篇 |
1978年 | 38篇 |
1977年 | 39篇 |
1976年 | 27篇 |
1975年 | 25篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2'-O,O-(1,1'-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and alpha-dehydroamino acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for alpha-dehydroamino acid derivatives). 相似文献
132.
高效石墨浮选剂的合成金婵,薛玉,汪进,刘欣荣,秦英海(哈尔滨工业大学应用化学系哈尔滨150001)(大庆石化总公司大庆)关键词石墨,浮选剂,合成,混合烃由于石墨具有良好的力学性能、导电、高熔点等性质,广泛用于原子能、宇航和民用工业。隐晶质石墨属于微晶... 相似文献
133.
A fast and matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) compatible protein staining method in one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1- and 2-D SDS-PAGE) is described. It is based on the counterion dye staining method that employs oppositely charged two dyes, zincon (ZC) and ethyl violet (EV) to form an ion-pair complex. The protocol, including fixing, staining and quick washing steps, can be completed in 1-1.5 h depending upon gel thickness. It has a sensitivity of 4-8 ng, comparable to that of colloidal Coomassie Brilliant Blue G (CBBG) staining with phosphoric acid in the staining solution. The counterion dye stain does not induce protein modifications that complicate interpretation of peptide mapping data from MS. Considering the speed, sensitivity and compatibility with MS, the counterion dye stain may be more practical than any other dye-based protein stains for routine proteomic researches. 相似文献
134.
Rauter AP Martins A Borges C Ferreira J Jorge J Bronze MR Coelho AV Choi YH Verpoorte R 《Journal of chromatography. A》2005,1089(1-2):59-64
The anti-hyperglycemic flavonoid extract obtained from Genista tenera was first studied by liquid chromatography (LC)-diode array detection (DAD) which showed the presence of two major compounds. One of them was identified as genistein-7-O-glucoside. Luteolin-7-O-glucoside was detected as a minor constituent, while luteolin-7,3'-di-O-glucoside and rutin were found in trace amounts. LC-DAD-ESI-MS and NMR were used to confirm the structure of these compounds and allowed the elucidation of the structure of the unknown major compound, which is the flavonoid 5,7,4'-trihydroxyisoflavone-8-C-glucoside. 相似文献
135.
The stereo- and regioselective synthetic route to pimaraditerpenes, employing an angular hydroxymethyl directed intramolecular Diels-Alder reaction of the decaline intermediate, has been developed. This synthetic approach allows prompt access to both natural pimaraditerpenes and the unnatural regioisomers, which would be potentially new anti-inflammatory pimaraditerpenes. 相似文献
136.
Electrochemical synthesis of nanostructured ZnO films utilizing self-assembly of surfactant molecules at solid-liquid interfaces 总被引:3,自引:0,他引:3
Choi KS Lichtenegger HC Stucky GD McFarland EW 《Journal of the American Chemical Society》2002,124(42):12402-12403
An electrochemical synthesis strategy for the production of nanostructured films was developed by combining self-assembly of surfactant-inorganic aggregates at solid-liquid interfaces and an electrodeposition process. Through this approach high quality nanostructured ZnO films were cathodically deposited from a plating solution containing 0.1 wt % of sodium dodecyl sulfate (SDS). The resulting ZnO films possess lamellar structures with two different repeat distances, d001 = 31.7 A and d001* = 27.5 A, both of which feature well-defined long range order. Due to kinetically controlled surfactant-inorganic assembly during the deposition process, the film exhibits a wide distribution of the stacking directions of the ZnO layers, which will allow facile access of the guest molecules and analytes to the interlayers. The synthetic mechanism used here can be generalized to generate nanostructured films of other semiconducting and metallic materials with architectures that cannot be assembled by other means. 相似文献
137.
A background-free, fast protein staining method in polyacrylamide gel electrophoresis using an acidic dye, zincon (ZC) and a basic dye, ethyl violet (EV) is described. It is based on the counterion dye staining technique that employs two oppositely charged dyes to form an ion-pair complex in staining solution. The selective binding of free dye molecules to proteins in acidic solution produces bluish violet-colored bands. It is a rapid and end-point staining procedure, involving only fixing and staining steps that are completed in 1-1.5 h. The detection limit of this method is 8-15 ng of protein that is comparable to the sensitivity of the colloidal Coomassie Brilliant Blue G (CBBG) stain. Due to its sensitivity and speed, this stain may be more practical than any other dye-based stains for routine laboratory purposes. 相似文献
138.
(13)C spin-lattice relaxation studies on bis(2-ethylhexyl) adipate (DOA) plasticized poly(vinylchloride) (PVC) membranes are reported for plasticization levels ranging from 25 to 100 wt% plasticizer. The interaction between DOA and PVC molecules in these membranes appears to involve an entrapment of the plasticizer molecule within the polymer matrix. This is based on the constancy of the characteristic segmental motions of the plasticizer chains throughout the concentration range studied. The segmental mobility of the plasticizer component is modified by water absorption in the membrane. The pattern of characteristic segmental motions of the plasticizer is altered, the effect depending on the amount of added salt in the membrane. The results show water has a weak influence on the microviscosity of the membrane matrix. 相似文献
139.
Kleitz F Solovyov LA Anilkumar GM Choi SH Ryoo R 《Chemical communications (Cambridge, England)》2004,(13):1536-1537
Exceptional control of the phase behavior of highly ordered large pore mesostructured silica (with the choice of Fm3m, Im3m or p6mm symmetry) is achieved using a triblock copolymer (EO(106)PO(70)EO(106)) and butanol at low acid concentrations. 相似文献
140.
Hong KM Choi YB Hong JH Chang HS Rhee KI Park H Paik MK 《Experimental & molecular medicine》1999,31(1):30-35
C-Terminal carboxyl methylation of a human placental 23 kDa protein catalyzed by membrane-associated methyltransferase has been investigated. The 23 kDa protein substrate methylated was partially purified by DEAE-Sephacel, hydroxyapatite and Sephadex G-100 gel filtration chromatographies. The substrate protein was eluted on Sephadex G-100 gel filtration chromatography as a protein of about 29 kDa. In the absence of Mg2+, the methylation was stimulated by guanine nucleotides (GTP, GDP and GTPgammaS), but in the presence of Mg2+, only GTPgammaS stimulated the methylation which was similar to the effect on the G25K/rhoGDI complex. AFC, an inhibitor of C-terminal carboxyl methylation, inhibited the methylation of human placental 23 kDa protein. These results suggests that the substrate is a small G protein different from the G25K and is methylated on C-terminal isoprenylated cysteine residue. This was also confirmed by vapor phase analysis. The methylated substrate protein was redistributed to membrane after in vitro methylation, suggesting that the methylation of this protein is important for the redistribution of the 23 kDa small G protein for its putative role in intracellular signaling. 相似文献