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   859篇
  免费   30篇
  国内免费   2篇
化学   665篇
晶体学   5篇
力学   8篇
数学   45篇
物理学   168篇
  2023年   5篇
  2022年   6篇
  2021年   10篇
  2020年   15篇
  2019年   12篇
  2018年   10篇
  2017年   7篇
  2016年   16篇
  2015年   18篇
  2014年   18篇
  2013年   41篇
  2012年   43篇
  2011年   38篇
  2010年   22篇
  2009年   21篇
  2008年   48篇
  2007年   30篇
  2006年   37篇
  2005年   57篇
  2004年   43篇
  2003年   38篇
  2002年   55篇
  2001年   23篇
  2000年   26篇
  1999年   14篇
  1998年   4篇
  1997年   5篇
  1996年   9篇
  1995年   10篇
  1994年   8篇
  1993年   9篇
  1992年   13篇
  1991年   11篇
  1990年   19篇
  1989年   12篇
  1988年   6篇
  1987年   8篇
  1986年   12篇
  1985年   19篇
  1984年   14篇
  1983年   11篇
  1982年   9篇
  1981年   6篇
  1980年   8篇
  1979年   11篇
  1978年   6篇
  1975年   3篇
  1973年   3篇
  1970年   5篇
  1968年   4篇
排序方式: 共有891条查询结果,搜索用时 15 毫秒
11.
An IgE RIA kit (Sandwich method; Dainabott), is used to obtain the following results. (1) Standard curve: Since the range of reproduction rate show 3.16-7.07% (C.V.), the curve become steep. (2) Incubations under controlled situation: Both of the incubations are controlled at 15-30 degrees C for 2 h. (3) Reproducibility test: Coefficients of variation (C.V.) of intra-assay and inter-assay variation are 2.32-3.94% and 2.92-3.92% respectively. (4) Recovery test: A result of the recovery test range between 100.1-101.7%. (5) Dilution test: Multiple dilution effects are observed. (6) Average counts of the serum IgE for the controlled and diseased groups: The average counts of the serum IgE for the controlled group, atopic diseased group, allergic rhinitis group and allergic bronchial asthma are 144.9 +/- 183.2 IU/ml, 1,099.0 +/- 2,782.4 IU/ml, 1,150.9 +/- 2,063.3 IU/ml and 600.7 +/- 686.4 IU/ml respectively. The value of the diseased groups have tendency to show higher averages than the controlled group. Since the controlled and diseased groups show wide distributions of the serum IgE level, there is no significant difference of two variations. However the diseased groups have tendency to show higher ratio of the serum IgE level in blood than the controlled groups. These basic researches are quite meaningful, because they are able to apply for a supplemental diagnosis of the atopic and parasitic disease.  相似文献   
12.
The linear sandwich tripalladium complexes [Pd3{Ar(CH=CH)4Ar}2[BArf]2 (Ar = Ph, p-t-Bu-C6H4, p-styryl-C6H4) undergo photoinduced isomerization involving face-inversion of the tetraene ligands. Irradiation of these complexes with visible light (>510 nm) resulted in rac (staggered sandwich) to meso (eclipsed sandwich) isomerization. The structures of rac and meso isomers are determined by X-ray crystallographic analyses.  相似文献   
13.
The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces.  相似文献   
14.
A highly convergent total synthesis of gymnocin-A, a cyctotoxic polyether marine natural product, has been achieved. The synthesis features Suzuki-Miyaura coupling of the ABCD and FGHIJKLMN rings, stereoselective introduction of the C17 hydroxyl group, ring-closure of the F ring, and a late-stage incorporation of a 2-methyl-2-butenal side chain.  相似文献   
15.
This review covers the literature on simple indole alkaloids and those with a nonrearranged monoterpenoid unit from the beginning up to the end of 2004. Newly isolated alkaloids, structure determinations, total synthesis and biological activities are included.  相似文献   
16.
Neutron activation analysis was applied to determine sodium and chlorine in high purity water samples. After irradiation of the sample,38Cl was purified from82Br and other nuclides by carbon tetrachloride extraction and silver chloride precipitation, and24Na was separated from other alkali elements and other nuclides by adsorption of24Na on HAP. The activities of both elements were measured by conventional G.M. counter. The contamination of the elements from container walls during neutron irradiation and the interference with38Ar(n, p)38Cl reaction on argon dissolved in water were also examined. Water samples containing 3 ppb of chlorine could not be determined accurately, owing to the above mentioned interfering reaction.  相似文献   
17.
Five ceramides, JC-1-JC-5, and four glucocerebrosides, JCer-1-JCer-4, have been isolated from their parent ceramide and glucocerebroside molecular species JC and JCer obtained from the less polar lipid fraction of the chloroform/methanol extract of the feather star Comanthus japonica. The structures of these sphingolipids have been determined on the basis of chemical and spectroscopic evidence. Reversed-phase HPLC was effective at isolating these sphingolipids, revealing very close resemblance in their structures. JC-1, JC-3, JC-4, JC-5 and JCer-2, JCer-4 are newly found ceramides and glucocerebrosides, respectively.  相似文献   
18.
Two new glucocerebrosides, luidiacerebroside A (2) and B (6), were isolated from the cerebroside molecular species obtained from the less polar fraction of the CHCl3/MeOH extract of the starfish Luidia maculata using HPLC. Four known cerebrosides, CE-2b (1), astrocerebroside B (3), acanthacerebroside B (4), and CE-3-2 (5) have also been isolated and characterized. The structures of these cerebrosides were determined on the basis of chemical and spectroscopic evidence. Mass spectrometry of dimethyl disulfide derivatives was useful for the determination of the double-bond position in the long-chain base.  相似文献   
19.
New proton exchange membranes (PEMs) were prepared by pre-irradiation induced grafting of α-methylstyrene (AMS)/styrene (STY)/divinylbenzene (DVB) into the crosslinked polytetrafluoroethylene (RX-PTFE) films and successively sulfonated. The new PEMs showed the improved glass transition temperature and chemical stability as compared with the PEMs prepared by pre-irradiation induced grafting of STY/DVB. The balance of the cost, grafting kinetic, thermal properties and the properties of the resulted proton exchange membrane is the key point of this work.  相似文献   
20.
The theory is derived to determine the dimer-formation constant,K 2, of a crown ethermetal salt 111 complex in organic solvents of low dielectric constant by solvent extraction. The theoretical predictions are verified experimentally by extraction of sodium picrate (NaA) with 15-crown-5 (15C5) into carbon tetrachloride. All the experiments were conducted at 25°C. The logK 2 value of the Na(15C5)A complex in carbon tetrachloride has been determined to be 4.05±0.11. Moreover, the partition constant of the complex is calculated.  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