全文获取类型
收费全文 | 3150篇 |
免费 | 93篇 |
国内免费 | 6篇 |
专业分类
化学 | 2172篇 |
晶体学 | 24篇 |
力学 | 79篇 |
数学 | 463篇 |
物理学 | 511篇 |
出版年
2023年 | 33篇 |
2022年 | 65篇 |
2021年 | 81篇 |
2020年 | 81篇 |
2019年 | 72篇 |
2018年 | 47篇 |
2017年 | 35篇 |
2016年 | 106篇 |
2015年 | 91篇 |
2014年 | 95篇 |
2013年 | 200篇 |
2012年 | 210篇 |
2011年 | 252篇 |
2010年 | 125篇 |
2009年 | 116篇 |
2008年 | 152篇 |
2007年 | 156篇 |
2006年 | 162篇 |
2005年 | 128篇 |
2004年 | 84篇 |
2003年 | 99篇 |
2002年 | 86篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1998年 | 21篇 |
1997年 | 28篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 33篇 |
1993年 | 18篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 30篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 19篇 |
1972年 | 17篇 |
1971年 | 13篇 |
排序方式: 共有3249条查询结果,搜索用时 0 毫秒
81.
82.
83.
Samuel E. Horne Charles J. Carman 《Journal of polymer science. Part A, Polymer chemistry》1971,9(10):3039-3053
Titanates are versatile in the 1,4 polymerization of isoprene. The (R′O)4Ti/RAlCl2 catalyst gives either cis- or trans-1,4-polyisoprene, depending on the nature of both the titanate and the solvent. Primary titanates give cis-1,4-polyisoprene in both aliphatic and aromatic solvents. Secondary titanates give cis-polyisoprene in aliphatic solvents, and trans-1,4-polyisoprene in aromatic solvents. Tertiary titanates give trans-polyisoprene in both aliphatic and aromatic solvents. A mechanism is postulated which takes into consideration the role of the solvent. ESR studies of the various titanate–RAlCl2 catalysts were made; the paramagnetic structures are related to polymerization mechanisms. 相似文献
84.
Studies are reported resulting in a reliable procedure for estimating the thiamine content in human blood and urine. For the determination in blood, heparinized blood is hemolyzed with 0.3 N hydrochloric acid at 100 °C. Cocarboxylase is then converted to free thiamine by means of wheat germ acid phosphatase at pH 5.0 in an acetate buffer. The liberated thiamine is adsorbed to a CG-50 (Rohm & Haas) carboxylic acid ion exchange acrylic resin column and then eluted with 1 N H2SO4. The thiamine is then oxidized to thiochrome and extracted with n-butyl alcohol, at pH 9.8–10.0, in the presence of disodium phosphate. Readout is by fluorometry at an excitation wavelength of 371 nm and an emission wavelength of 425 nm. The range found for thiamine in whole blood by this procedure on 18 normal adults was 1.9–3.9 μg/100 ml, with a mean value of 2.77 μg/100 ml of whole blood. The mean recovery of 12 recovery experiments was 94.1%. The same procedure is applicable to the determination of thiamine in urine. Conversion of cocarboxylase to free thiamine is not necessary since it was determined that practically all of the thiamine found in urine is not phosphorylated. Urine values were variable, the range for 11 healthy adults being 5.6–77.9 μg/100 ml with a mean value of 19.2 μg/100 ml. This corresponds to a value of 346 μg of thiamine/24 hours. 相似文献
85.
86.
Kihachiro Takahara Masahide Sasaki Arthur J. Tomisek Samuel Natelson 《Microchemical Journal》1974,19(3):319-329
A reagent is developed for increasing the sensitivity of the direct o-toluidine procedure for glucose so that the reaction may be carried out at temperatures as low as 37 °C.The sensitivity is achieved by eliminating all water from the system, except for a minute percentage introduced with the samples and by using a high boric acid concentration. Under these conditions protein does not precipitate and lipids remain dissolved. At 55 °C, interference from bilirubin at a concentration of 20 mg/100 ml is 3.5%.Blood may be collected with sodium fluoride since it does not interfere in the procedure. The rate of color development is slower for aqueous standards than it is for serum at the lower temperatures. This may be corrected by preparing the standards in a 6% albumin solution.Results obtained by applying the reagent with the continuous flow system of analysis (Technicon), and with the discrete sample analyzers, Beckman DSA, Lars Jungberg Autolab (Sweden), Robot Chemist, and RaBA (Japan) are reported.The reagent is useful as a spray reagent for sugar identification on thin-layer chromatography plates. Heating at different temperatures permits the differentiation between certain sugars with similar Rf values. 相似文献
87.
Fernandez NF Sansone S Mazzini A Brancaleon L 《The journal of physical chemistry. B》2008,112(25):7592-7600
Porphyrins such as protoporphyrin IX (PPIX) are known to occasionally cause conformational changes in proteins for which they are specific ligands. It has also been established that irradiation of porphyrins noncovalently intercalated between bases or bound to one of the grooves can cause conformational effects on DNA. Conversely, there is no evidence reported in the literature of conformational changes caused by noncovalently bound PPIX to globular proteins for which the porphyrin is not a specific ligand. This study shows that the irradiation of the porphyrin in the PPIX/lactoglobulin noncovalent complex indeed causes a local and limited (approximately 7%) unfolding of the protein near the location of Trp19. This event causes the intrinsic fluorescence spectrum of the protein to shift to the red by 2 nm and the average decay lifetime to lengthen by approximately 0.5 ns. The unfolding of lactoglobulin occurs only at pH >7 because of the increased instability of the protein at alkaline pH. The photoinduced unfolding does not depend on the presence of O2 in solution; therefore, it is not mediated by formation of singlet oxygen and is likely the result of electron transfer between the porphyrin and amino acid residues. 相似文献
88.
Claire André Teddy Bagnost Samuel Limat Tijani Gharbi Yves Claude Guillaume 《Chromatographia》2008,68(9-10):807-810
In a previous paper (Bagnost et al., J Chromatogr B Analyt Technol Biomed Life Sci 853:38–46, 2007), an arginase chromatographic support was developed to study the association mechanism of arginase (an enzyme which can reduce endothelial dysfunction and blood pressure rising in spontaneously hypertensive rats) with nor-NOHA a potential inhibitor of its activity. In this report mutagenesis experiments associated with this biochromatographic approach confirmed that the active-site residue Hist 141 is protonated as imidazolium cation. Hist 141 could function as a general acid to protonate the leaving amino group of l-ornithine during catalysis. 相似文献
89.
The alkylation of aryl 3-oxopropanedithioate with α-haloketones under different reaction conditions afforded substituted aryl[2-(methylsulfanyl)-4-phenyl-3-thienyl]methanones and [3-aryl-5-(methylsulfanyl)-2-thienyl](phenyl)methanones. The same strategy was extended to 3-amino-1-aryl-3-thioxo-1-propanones to afford aryl[2-amino-4-phenyl-3-thienyl]methanones and ethyl 3-phenyl-5-piperidino-2-thiophene carboxylate. 相似文献
90.
Polydimethylsiloxane (PDMS) surfaces can be functionalized with biotin groups by adding biotinylated phospholipids to the PDMS prepolymer before curing. The addition of beta-D-dodecyl-N-maltoside (DDM) in the solution blocks non-specific protein binding on these functionalized PDMS surfaces. We characterize the surface by measuring fluorescently labeled streptavidin binding. Single molecule tracking shows that the phospholipids are not covalently linked to PDMS polymer chains, but the surface functionalization is not removed by washing. We demonstrate the immobilization of biotinylated antibodies and lectins through biotin-avidin interactions. 相似文献