全文获取类型
收费全文 | 3427篇 |
免费 | 367篇 |
国内免费 | 292篇 |
专业分类
化学 | 2579篇 |
晶体学 | 55篇 |
力学 | 170篇 |
综合类 | 25篇 |
数学 | 339篇 |
物理学 | 918篇 |
出版年
2023年 | 35篇 |
2022年 | 58篇 |
2021年 | 104篇 |
2020年 | 105篇 |
2019年 | 124篇 |
2018年 | 98篇 |
2017年 | 79篇 |
2016年 | 141篇 |
2015年 | 168篇 |
2014年 | 184篇 |
2013年 | 248篇 |
2012年 | 306篇 |
2011年 | 282篇 |
2010年 | 195篇 |
2009年 | 205篇 |
2008年 | 238篇 |
2007年 | 192篇 |
2006年 | 172篇 |
2005年 | 170篇 |
2004年 | 114篇 |
2003年 | 109篇 |
2002年 | 107篇 |
2001年 | 65篇 |
2000年 | 48篇 |
1999年 | 47篇 |
1998年 | 40篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 29篇 |
1994年 | 30篇 |
1993年 | 18篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1982年 | 5篇 |
1980年 | 25篇 |
1978年 | 23篇 |
1977年 | 48篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 11篇 |
1973年 | 6篇 |
1970年 | 5篇 |
1968年 | 5篇 |
1943年 | 10篇 |
排序方式: 共有4086条查询结果,搜索用时 15 毫秒
951.
952.
Margarita Juárez-Montiel J. Antonio Ibarra Griselda Chávez-Camarillo César Hernández-Rodríguez Lourdes Villa-Tanaca 《Applied biochemistry and biotechnology》2014,172(5):2530-2539
Dipeptidyl aminopeptidases are enzymes involved in the posttranslational control of bioactive peptides. Here we identified the gene dapUm in Ustilago maydis by homology with other fungal dipeptidyl aminopeptidases. Analysis of the dapUm-deduced amino acid sequence indicated that it encodes for membrane-type serine protease with a characteristic prolyl oligopeptidase catalytic motif triad: Ser, Asp, His. In order to overexpress the DapUm, the gene encoding for it was cloned and transformed into Pichia. Using this system, we observed a ~125-kDa recombinant protein with an optimal enzymatic activity at pH 6.0 and at 40 °C for the Ala-Pro-p-nitroanilide substrate and an experimental pH of 6.9. U. maydis DapUm was specifically inhibited by phenylmethylsulfonyl fluoride and Pefabloc, confirming the presence of a serine residue in the active site. To our knowledge, this study is the first report on the cloning and expression of a DPP IV dipeptidyl aminopeptidase from a basidiomycete organism. Moreover, the use of recombinant DapUm will allow us to further study and characterize this enzyme, in addition to testing chemical compounds for pharmaceutical purposes. 相似文献
953.
The denitrification of low-temperature flue gas is a difficult problem facing the industry. OH radicals can effectually oxidize NO in flue gas, which can achieve denitrification of low-temperature flue gas. Heterogeneous Fenton reaction is an important method for the formation of OH radicals. A four-step reaction mechanism of the formation of OH radicals by heterogeneous Fenton reaction is proposed and investigated in this paper. Theoretical results show that activation energy of the formation of OH radicals catalyzed by ZSM5-Si/Fe is much lower than that without catalyst. After doping Al/Ce/Ti, the activation energy is further reduced significantly. The activity is related to the active center atom of the catalyst. By comparing, ZSM5-Ce/Al–Fe has better catalytic performance because of its more fluffy structure. This study would provide an important theoretical reference for the design of the catalysts in heterogeneous Fenton reaction and their industrial applications. 相似文献
954.
Lei Sang Sheng-Li Chen Guimei Yuan Zheng Zhou Rui Li Aicheng Chen Min Zheng Ju You State 《天然气化学杂志》2012,(3):352-359
Mesoporous γ-aluminas with large pore size(up to 19 nm,denoted as MA19) are prepared from dispersed pseudo-boehmite using pluronic P123 as template.It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size(5 nm).At 60°C and atmospheric pressure with WHSV = 1 h-1,the similar stable conversions of butene(ca.55%) for all the 13 wt% Re 2 O 7 /alumina catalysts were obtained near the chemical equilibrium,and the stable working life-spans of Re 2 O 7 /MA19 were far longer than that of Re 2 O 7 /Al 2 O 3,being about 70 h and 20 h,respectively. 相似文献
955.
Jingjing Hui Lei Bao Siqiao Li Yi Zhang Yimei Feng Prof. Dr. Lin Ding Prof. Dr. Huangxian Ju 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(28):8251-8255
Live cell imaging of protein‐specific glycoforms is important for the elucidation of glycosylation mechanisms and identification of disease states. The currently used metabolic oligosaccharide engineering (MOE) technology permits routinely global chemical remodeling (GCM) for carbohydrate site of interest, but can exert unnecessary whole‐cell scale perturbation and generate unpredictable metabolic efficiency issue. A localized chemical remodeling (LCM) strategy for efficient and reliable access to protein‐specific glycoform information is reported. The proof‐of‐concept protocol developed for MUC1‐specific terminal galactose/N ‐acetylgalactosamine (Gal/GalNAc) combines affinity binding, off‐on switchable catalytic activity, and proximity catalysis to create a reactive handle for bioorthogonal labeling and imaging. Noteworthy assay features associated with LCM as compared with MOE include minimum target cell perturbation, short reaction timeframe, effectiveness as a molecular ruler, and quantitative analysis capability. 相似文献
956.
957.
Le Thi Kim Van Tran Manh Hung Soo Hyun Kim Jin Cheol Kim MinKyun Na Hyun Ju Jung Seung Jun Kwack Kee Tae Kweon Jae Sue Choi Hyeong Kyu Lee KiHwan Bae Byung‐Sun Min 《Helvetica chimica acta》2010,93(9):1803-1807
A new stereoisomer of a tetrahydrofuranoid lignan, acerifuranoid A ( 1 ), and two new oleanane‐type triterpenoids, aceriphyllic acids J and K ( 2 and 3 ), were isolated from the roots of Aceriphyllum rossii. Their structures were elucidated on the basis of spectroscopic analyses and chemical evidence. These isolated compounds exhibited weak cytotoxic activity against various cancer cell lines with IC50>150 μM . 相似文献
958.
A reformulation of the Thomson-Haskell method is presented for calculating the reflection coefficients of multilayer structure immersing in the coupling fluid. Instead of directly multiplying the layer propagator matrix, the new method splits the layer propagator matrix and excursively determines the interface stiffness matrix starting from the bottom half-space with known stiffness. A formulation for the reflection coefficients is derived based on the obtained interface stiffness matrix of the top layer. This scheme can be applied to a single solid layers or layered structures containing both fluid and solid layers. It keeps the simplicity but naturally excludes the exponential growth term and thus can be applied at any frequency range. Its validity and feasibility were experimentally proved by the measurement of the reflection coefficients of a three layered structure of aluminum–glass–aluminum and a sandwiched layer structure of two 250 μm stainless plates filled with 100 μm deionized water based on the inversion of V(z, t) technique. The result of experiments is consistent with the theoretical calculation. The reformulation of the Thomson-Haskell method offers an efficient and effective solution for calculating the acoustic reflection coefficients of multilayer structures of any configurations. 相似文献
959.
Prof. Dr. Long‐Li Lai Shun‐Ju Hsu Hui‐Chu Hsu Sheng‐Wei Wang Dr. Kung‐Lung Cheng Chun‐Jung Chen Tsai‐Hui Wang Prof. Dr. Hsiu‐Fu Hsu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(21):6542-6547
Two series of unconventional triazine‐based dendrimers with C2 symmetry and C3 symmetry were prepared. The newly prepared C3‐symmetrical dendrimers were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD showed that the C3‐symmetrical dendrimers display columnar liquid‐crystalline phases during thermal treatment, but the C2‐symmetrical dendrimers were not observed to behave correspondingly. The molecular conformations of C3‐ and C2‐symmetrical dendrimers were obtained by computer simulation with the MM2 model of the CaChe program in the gas phase. The simulation results reasonably explain the different mesogenicities of C3‐ and C2‐symmetric dendrimers. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks for displaying columnar liquid‐crystalline behavior. 相似文献
960.
Thedithiolenesanddiiminesandtheirmetalcomplexesareanimportantresearchfieldintheorganicandcoordinationchemistry'-'.Metalcomplexesofadithioleneandadiiminehaveexcellentelectronicfullctionsduetotheintramolecularchargetransferfromaligandtootherligand(LL'C... 相似文献