全文获取类型
收费全文 | 8090篇 |
免费 | 418篇 |
国内免费 | 203篇 |
专业分类
化学 | 4837篇 |
晶体学 | 81篇 |
力学 | 343篇 |
综合类 | 25篇 |
数学 | 1216篇 |
物理学 | 2209篇 |
出版年
2023年 | 79篇 |
2022年 | 186篇 |
2021年 | 199篇 |
2020年 | 207篇 |
2019年 | 211篇 |
2018年 | 194篇 |
2017年 | 173篇 |
2016年 | 254篇 |
2015年 | 260篇 |
2014年 | 293篇 |
2013年 | 568篇 |
2012年 | 517篇 |
2011年 | 571篇 |
2010年 | 367篇 |
2009年 | 314篇 |
2008年 | 423篇 |
2007年 | 356篇 |
2006年 | 347篇 |
2005年 | 287篇 |
2004年 | 221篇 |
2003年 | 220篇 |
2002年 | 196篇 |
2001年 | 175篇 |
2000年 | 153篇 |
1999年 | 114篇 |
1998年 | 75篇 |
1997年 | 69篇 |
1996年 | 76篇 |
1995年 | 63篇 |
1994年 | 101篇 |
1993年 | 72篇 |
1992年 | 83篇 |
1991年 | 70篇 |
1990年 | 68篇 |
1989年 | 50篇 |
1988年 | 50篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 74篇 |
1984年 | 75篇 |
1983年 | 50篇 |
1982年 | 67篇 |
1981年 | 66篇 |
1980年 | 61篇 |
1979年 | 55篇 |
1978年 | 62篇 |
1977年 | 52篇 |
1976年 | 50篇 |
1975年 | 38篇 |
1973年 | 41篇 |
排序方式: 共有8711条查询结果,搜索用时 9 毫秒
41.
We focused our work on the separation of phenothiazines that are important drugs used for the treatment of psychic diseases. For a better understanding of the metabolism of these solutes, we wanted to separate not only a mixture of 12 phenothiazines but also a mixture containing phenothiazines and their N-demethyl metabolites by capillary electrophoresis. Separations in capillary zone electrophoresis were performed using 3 x 10(-2) mol/L H3PO4 (pH 2.5) but the obtained resolutions were not entirely satisfactory especially with regard to phenothiazine -N-demethyl derivative pairs. To improve the obtained results, we have performed separations by using micellar electrokinetic chromatography. In this approach, we used a running electrolyte containing 3 x 10(-2) mol/L H3PO4 electrolyte (pH 2.5) and octaethylene glycol monododecyl ether (C12E8) as neutral surfactant. By introducing 2 x 10(-3) mol/L C12E8 in the electrolyte, 11 out of 12 phenothiazines have been baseline separated. With respect to the separation of a mixture containing 3 phenothiazines and their 3 demethyl derivatives, we obtained an excellent separation by using a running electrolyte prepared with 7.5 x 10(-4) mol/L C12E8 and 3 x 10(-2) mol/L H3PO4. 相似文献
42.
43.
The cellular mechanism based on P-glycoprotein (PGP) for its drug pump function has become very important in multidrug resistance (MDR) research. A method has been established to characterize PGP on single K562 cell by coupling capillary electrophoresis with laser induced fluorescence detection. A permeable intact cell after the immunoassay binding with fluorescence labeling antibody was injected into the capillary and directly separated without lysis. It was found that once 5-10 optional cells were detected in batch, the PGP amount on this cell line could be outlined and calculated clearly. The PGP amount on K562 MDR cell line is 3.88 times higher than that on K562 sensitive cell line. These two cell lines with immunoassay binding were also analyzed by injection of multi-cells in order to improve the throughput. A resistance factor so called multidrug resistance multiple (MRM) was introduced to evaluate the MDR difference between cell lines. The MRM values of the cell line K562 measured by single cell analysis are well correlated with those by flow cytometry, which also prove the validity of our method in single cell analysis for the possibility of cancer diagnosis, pharmacokinetics and drug screening in future. 相似文献
44.
The association of a C3v-symmetrical calix[6]tris-amine with different concave tris-carboxylic acids of various degrees of flexibility has been explored by 1H NMR spectroscopy. In all cases, self-assembled structures directed by the selective inclusion of a neutral guest molecule were obtained, the more preorganized being stable in protic solvents. With a rigid C3-symmetrical cap, chiral guest recognition in the calixarene cavity resulted. A large tris-acidic partner gave a unique molecular ditopic receptor that is able to simultaneously accommodate two neutral molecules in two distinct hydrophobic cavities with different binding processes. 相似文献
45.
Perfluoromethyl Element Ligands. XXIX. Preparation and Spectroscopic Investigation of M(CO)4L2 Complexes (M ? Cr, Mo, W; L ? Me2PSMe, Me2PSeMe, (CF3)2PSMe, (CF3)2PSMe) The complexes M(CO)4L2 (see Inhaltsübersicht) have been prepared by the reaction of tetracarbonyl norbornadiene metal compounds M(CO)4NBD with L at room temperature or 35°C, respectively. The cis-complexes formed in the first step undergo rearrangement to trans-isomers at higher temperatures. New compounds have been characterized by analytical and spectroscopic (IR, NMR, MS) methods. 相似文献
46.
Myint U Khin Mg Myoe Ba Han J. Tölgyessy 《Journal of Radioanalytical and Nuclear Chemistry》1995,201(2):97-103
A simple radiometric flow injection analyzer with NaI(Tl) detector was used for the study of some experimental parameters of137Cs and60Co determination. A sample transfer system was developed employing both merging zone and sample injection principle. 相似文献
47.
Bohumír Grüner Jaroslav Ba?kovský Bohumil Štíbr 《Journal of organometallic chemistry》2005,690(11):2850-2852
The compounds with a single and double -CH2C6H4CH2- spacer, [CpFeC3B8H10-NH-CH2C6H4CH2-NH-C3B8H10FeCp] and [CpFeC3B8H10-N-(CH2C6H4CH2)2-N-C3B8H10FeCp], represent the first example of designed shaping by extremely stable cyclopentadienyl-ferratricarbollide (CpFeTCB) cages into rigid molecular constructions approaching linear arrangement. 相似文献
48.
Syntheses of new sulfinylcinnolines, quinoxalines, quinazolines and phtalazines have been investigated starting from the appropriate halogenobenzodiazine derivatives. The latter were converted in one step to the corresponding sulfanyl benzodiazines which upon oxidation with m-CPBA led to the corresponding sulfoxide derivatives of benzodiazines in moderate to good yields. In parallel to this study, an improved method for the synthesis of 2-methylsulfinylquinoxaline starting from 2-sulfanylquinoxaline is also described and in the quinazoline series a synthetic route has been developed to prepare 2-tert-butyl-5-phenylsulfinylquinazoline with satisfactory yield as well as 2-tert-butyl-5-tert-butylsulfinyl-4(3H)-quinazolinone and 2-tert-butyl-8-tert-butylsulfinyl-4(3H)-quinazolinone. 相似文献
49.
Abstract— A thin layer of chlorophyll a (around 2000 Å). a p -type organic semiconductor. was sandwiched between two different metals. aluminum and silver. We used the photovoltaic effect in order to study the efficiency of light conversion by the crystalline and anhydrous forms of Chl a . When the photovoltaic cell is illuminated through the semi-transparent aluminum electrode. an action spectrum similar to the visible absorption spectrum of Chl a is obtained. The anhydrous form. always shows a maximum, in the red, at 672 nm and the crystalline one at 746 nm to 738 nm depending on the amount of water vapor present in the measuring area. The light conversion efficiency has been measured at the maximum absorption in the red for both forms of Chl a . For the anhydrous form, we found values as high as 0.036%, which is very significant even compared to 0.21%, the highest value found for the crystalline form. In both cases. the incident light power was approximately 10 μW on the cell. The light conversion efficiency of both forms of Chl a cells was found to depend on a combine effect of the nature of the gas (O1 . N2 . air. Ar. N2 O. SF 6 , H2 ) and the amount of water vapor present in the measuring area. The best conversion efficiency was obtained with O 2 , or air saturated with water. This combined effect was very large for the crystalline form whereas the anhydrous form was only slightly affected. 相似文献
50.
N. SanzJ. Zaccaro L. DelmotteC. Le Luyer A. Ibanez 《Journal of solid state chemistry》2002,165(1):25-34
Organic nanocrystals of N-4-nitrophenyl-l-prolinol (NPP) have been grown in sol-gel matrices prepared from silicon alkoxide precursors. Our process is based on the control of the nucleation and growth kinetics of the dye in the pores of dense gels. Nanocomposites gel-glasses are obtained with a high optical quality due to the small size of the nanocrystals (10-20 nm). Differential scanning calorimetry experiments evidenced clearly the melting point of NPP nanocrystals, which is registered 51°C above that of NPP powder. Micro-Raman and solid state NMR spectroscopies allowed us to demonstrate that our nanocrystallization process does not chemically modify NPP molecules. We specified also the nature of interactions existing between the NPP nanocrystals and the xerogels. These strong interactions, which explain the important increase of the melting point of the nanocrystals in comparison to the NPP powder, are hydrogen bonds between nitro groups of NPP and uncondensed silanol functions of the silicate network. 相似文献