全文获取类型
收费全文 | 2865篇 |
免费 | 107篇 |
国内免费 | 14篇 |
专业分类
化学 | 2260篇 |
晶体学 | 30篇 |
力学 | 34篇 |
数学 | 167篇 |
物理学 | 495篇 |
出版年
2023年 | 15篇 |
2021年 | 16篇 |
2020年 | 40篇 |
2019年 | 65篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 51篇 |
2015年 | 42篇 |
2014年 | 45篇 |
2013年 | 136篇 |
2012年 | 155篇 |
2011年 | 170篇 |
2010年 | 89篇 |
2009年 | 103篇 |
2008年 | 169篇 |
2007年 | 159篇 |
2006年 | 177篇 |
2005年 | 150篇 |
2004年 | 114篇 |
2003年 | 106篇 |
2002年 | 113篇 |
2001年 | 56篇 |
2000年 | 44篇 |
1999年 | 31篇 |
1998年 | 32篇 |
1997年 | 29篇 |
1996年 | 28篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 28篇 |
1992年 | 33篇 |
1991年 | 27篇 |
1990年 | 37篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 34篇 |
1985年 | 31篇 |
1984年 | 42篇 |
1983年 | 29篇 |
1982年 | 40篇 |
1981年 | 34篇 |
1980年 | 37篇 |
1979年 | 29篇 |
1978年 | 38篇 |
1977年 | 33篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1974年 | 25篇 |
1973年 | 24篇 |
排序方式: 共有2986条查询结果,搜索用时 15 毫秒
991.
Hayashi Y Pirozhkov AS Kando M Fukuda Y Faenov A Kawase K Pikuz T Nakamura T Kiriyama H Okada H Bulanov SV 《Optics letters》2011,36(9):1614-1616
The interaction between a 25 TW laser and Xe clusters at a peak intensity of 1 × 101? W/cm2 has been investigated. Xe K-shell x rays, whose energies are approximately 30 keV, were clearly observed with a hard x-ray CCD at 3.4 MPa. Moreover, we studied the yield of the Xe K-shell x rays by changing the pulse duration of the laser at a constant laser energy and found that the pulse duration of 40 fs is better than that of 300 fs for generating Xe K-shell x rays. 相似文献
992.
Yoshihiro Furukawa Kiyoharu Tadanaga Akitoshi Hayashi Masahiro Tatsumisago 《Solid State Ionics》2011,192(1):185-187
This study demonstrates that humidity, temperature, and the interlayer anions influence ionic conductivities of Mg–Al layered double hydroxides (LDHs) intercalated with inorganic anions. Results show that Mg–Al LDH intercalated with Br? exhibited the highest ionic conductivity among Mg–Al LDHs intercalated with CO32?, Cl?, Br?, NO3? and SO42?. Its ionic conductivity was 1.1 × 10? 2 S cm? 1 at 80 °C under 80% relative humidity. The electromotive force for the hydroxide ion concentration cell using Mg?Al CO32? LDH showed the same behavior with that using an anion exchange membrane, indicating that Mg–Al CO32? LDH can be a hydroxide ion conductor. 相似文献
993.
Kawaguchi M Okabe T Okudaira S Hanaoka K Fujikawa Y Terai T Komatsu T Kojima H Aoki J Nagano T 《Journal of the American Chemical Society》2011,133(31):12021-12030
Nucleotide pyrophosphatases/phosphodiesterases (NPPs) are ubiquitous membrane-associated or secreted ectoenzymes that have a role in regulating extracellular nucleotide and phospholipid metabolism. Among the members of the NPP family, NPP1 and -3 act on nucleotides such as ATP, while NPP2, -6, and -7 act on phospholipids such as lysophosphatidylcholine and sphingomyelin. NPP6, a recently characterized NPP family member, is a choline-specific glycerophosphodiester phosphodiesterase, but its functions remain to be analyzed, partly due to the lack of highly sensitive activity assay systems and practical inhibitors. Here we report synthesis of novel NPP6 fluorescence probes, TG-mPC and its analogues TG-mPC(3)C, TG-mPC(5)C, TG-mPENE, TG-mPEA, TG-mPhos, TG-mPA, TG-mPMe, and TG-mPPr. Among the seven NPPs, only NPP6 hydrolyzed TG-mPC, TG-mPC(3)C, and TG-mPENE. TG-mPC was hydrolyzed in the cell lysate from NPP6-transfected cells, but not control cells, showing that it is suitable for use in cell-based NPP6 assays. We also examined the usefulness of TG-mPC as a fluorescence imaging probe. We further applied TG-mPC to carry out high-throughput NPP6 inhibitor screening and found several NPP6-selective inhibitors in a library of about 80,000 compounds. Through structure-activity relationship (SAR) analysis, we identified a potent and selective NPP6 inhibitor with an IC(50) value of 0.21 μM. Our NPP6-selective fluorescence probe, TG-mPC, and the inhibitor are expected to be useful to elucidate the biological function of NPP6. 相似文献
994.
Hayashi H Nihashi W Umeyama T Matano Y Seki S Shimizu Y Imahori H 《Journal of the American Chemical Society》2011,133(28):10736-10739
Liquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnar structure exhibited highly efficient ambipolar charge-transport character, demonstrating the potential utility of the strategy in organic electronics. 相似文献
995.
Takayoshi Oshima Tom Ichibha Kenji Oqmhula Keisuke Hibino Hiroto Mogi Shunsuke Yamashita Kotaro Fujii Yugo Miseki Kenta Hongo Daling Lu Ryo Maezono Kazuhiro Sayama Masatomo Yashima Koji Kimoto Hideki Kato Masato Kakihana Hiroshi Kageyama Kazuhiko Maeda 《Angewandte Chemie (International ed. in English)》2020,59(24):9736-9743
Undoped layered oxynitrides have not been considered as promising H2‐evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K2LaTa2O6N, as an exceptional example of a water‐tolerant photocatalyst for H2 evolution under visible light. The material underwent in‐situ H+/K+ exchange in aqueous solution while keeping its visible‐light‐absorption capability. Protonated K2LaTa2O6N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H2 evolution in the presence of I? as an electron donor and under visible light; the activity was six times higher than Pt/ZrO2/TaON, one of the best‐performing oxynitride photocatalysts for H2 evolution. Overall water splitting was also achieved using the Ir‐loaded, protonated K2LaTa2O6N in combination with Cs‐modified Pt/WO3 as an O2 evolution photocatalyst in the presence of an I3?/I? shuttle redox couple. 相似文献
996.
Jian‐Ming Lv Yao‐Hui Gao Huan Zhao Takayoshi Awakawa Ling Liu Guo‐Dong Chen Xin‐Sheng Yao Dan Hu Ikuro Abe Hao Gao 《Angewandte Chemie (International ed. in English)》2020,59(32):13531-13536
The alkyne is a biologically significant moiety found in many natural products and a versatile functional group widely used in modern chemistry. Recent studies have revealed the biosynthesis of acetylenic bonds in fatty acids and amino acids. However, the molecular basis for the alkynyl moiety in acetylenic prenyl chains occurring in a number of meroterpenoids remains obscure. Here, we identify the biosynthetic gene cluster and characterize the biosynthetic pathway of an acetylenic meroterpenoid biscognienyne B based on heterologous expression, feeding experiments, and in vitro assay. This work shows that the alkyne moiety is constructed by an unprecedented cytochrome P450 enzyme BisI, which shows promiscuous activity towards C5 and C15 prenyl chains. This finding provides an opportunity for discovery of new compounds, featuring acetylenic prenyl chains, through genome mining, and it also expands the enzyme inventory for de novo biosynthesis of alkynes. 相似文献
997.
Yuma Otake Yusuke Shibata Yoshihiro Hayashi Susumu Kawauchi Hiroyuki Nakamura Shinichiro Fuse 《Angewandte Chemie (International ed. in English)》2020,59(31):12925-12930
The development of a robust amide‐bond formation remains a critical aspect of N‐methylated peptide synthesis. In this study, we synthesized a variety of dipeptides in high yields, without severe racemization, from equivalent amounts of amino acids. Highly reactive N‐methylimidazolium cation species were generated in situ to accelerate the amidation. The key to success was the addition of a strong Brønsted acid. The developed amidation enabled the synthesis of a bulky peptide with a higher yield in a shorter amount of time compared with the results of conventional amidation. In addition, the amidation can be performed by using either a microflow reactor or a conventional flask. The first total synthesis of naturally occurring bulky N‐methylated peptides, pterulamides I–IV, was achieved. Based on experimental results and theoretical calculations, we speculated that a Brønsted acid would accelerate the rate‐limiting generation of acyl imidazolium cations from mixed carbonic anhydrides. 相似文献
998.
C.N. Soekiman K. Miyake Y. Hayashi Y. Zhu M. Ota H. Al-Jabri R. Inoue Y. Hirota Y. Uchida S. Tanaka C.Y. Kong N. Nishiyama 《Materials Today Chemistry》2020
In this study, we have developed a new method to synthesize mesoporous titanium silicalite-1 (TS-1) with a higher content of active titanium in the framework (more than 5%) than that obtained from the conventional hydrothermal synthesis. The new method combines two methods as follows: (1) a sol-gel method in tetrahydrofuran for the synthesis of TiO2–SiO2 composite with highly dispersed Ti species and (2) a dry gel conversion method for the crystallization to TS-1. This investigation revealed that the dispersion of Ti in the starting materials was quite important to synthesize mesoporous TS-1 with high content of Ti besides dry conversion method. The obtained mesoporous TS-1 with a high content of titanium showed higher catalytic activity in 1-hexene epoxidation than conventional TS-1. This high activity is likely to originate from the high content of titanium in the framework. 相似文献
999.
Elucidation of Pseurotin Biosynthetic Pathway Points to Trans‐Acting C‐Methyltransferase: Generation of Chemical Diversity 下载免费PDF全文
Dr. Yuta Tsunematsu Manami Fukutomi Dr. Takayoshi Saruwatari Prof. Dr. Hiroshi Noguchi Prof. Dr. Kinya Hotta Prof. Dr. Yi Tang Prof. Dr. Kenji Watanabe 《Angewandte Chemie (International ed. in English)》2014,53(32):8475-8479
Pseurotins comprise a family of structurally related Aspergillal natural products having interesting bioactivity. However, little is known about the biosynthetic steps involved in the formation of their complex chemical features. Systematic deletion of the pseurotin biosynthetic genes in A. fumigatus and in vivo and in vitro characterization of the tailoring enzymes to determine the biosynthetic intermediates, and the gene products responsible for the formation of each intermediate, are described. Thus, the main biosynthetic steps leading to the formation of pseurotin A from the predominant precursor, azaspirene, were elucidated. The study revealed the combinatorial nature of the biosynthesis of the pseurotin family of compounds and the intermediates. Most interestingly, we report the first identification of an epoxidase C‐methyltransferase bifunctional fusion protein PsoF which appears to methylate the nascent polyketide backbone carbon atom in trans. 相似文献
1000.
Naoya Morohashi Kazutoshi Nagata Tomoko Hayashi Tetsutaro Hattori 《Journal of inclusion phenomena and macrocyclic chemistry》2014,78(1-4):161-170
Sulfonyl-bridged oligo(benzoic acid)s 7 n (n = 2–4) are prepared from the corresponding triflate esters (8 n ) of sulfur-bridged oligophenols by palladium-catalyzed methoxycarbonylation of the triflate moieties, followed by hydrolysis of the resulting methyl esters, and subsequent oxidation of the sulfur bridges. X-ray analysis reveals that dimer 7 2 forms supramolecular zig-zag chains through intermolecular hydrogen bonds between the carboxy groups. As for the crystal of trimer 7 3 , two molecules are associated through two couples of intermolecular hydrogen bonds between terminal and central carboxy groups to form a cyclic dimer, which connects with two adjacent dimers with the remaining carboxy groups to construct an infinite columnar structure. Tetramer 7 4 adopts a monomolecular cyclic structure through intramolecular hydrogen bonds between the terminal carboxy groups, and a molecule connects with each of two adjacent molecules through two couples of intermolecular hydrogen bonds between inner carboxy and sulfonyl groups. Solvent extraction experiments reveal that the oligo(benzoic acid)s exhibit high extractability toward lanthanoid ions (Ln3+); the performance follows the order 7 4 ≈ 7 3 > 7 2 . Moderate extraction selectivity is observed for the extraction of Pr3+, Gd3+, and Yb3+ with 7 2 . X-ray crystallographic analysis of cluster [Tb4L4(H2O)6](Et3NH)4, which was prepared from 7 4 (H4L) and Tb(NO3)3·6H2O in the presence of Et3N, reveals that no sulfonyl oxygens coordinate to the metal centers. This indicates that the high extractability of 7 4 originates from the electron-withdrawing nature of the sulfonyl function, which increases the acidity of two adjacent carboxy groups. 相似文献