全文获取类型
收费全文 | 2841篇 |
免费 | 122篇 |
国内免费 | 8篇 |
专业分类
化学 | 2348篇 |
晶体学 | 22篇 |
力学 | 21篇 |
数学 | 163篇 |
物理学 | 417篇 |
出版年
2023年 | 26篇 |
2022年 | 21篇 |
2021年 | 39篇 |
2020年 | 68篇 |
2019年 | 56篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 64篇 |
2015年 | 64篇 |
2014年 | 80篇 |
2013年 | 141篇 |
2012年 | 177篇 |
2011年 | 194篇 |
2010年 | 105篇 |
2009年 | 88篇 |
2008年 | 204篇 |
2007年 | 188篇 |
2006年 | 195篇 |
2005年 | 188篇 |
2004年 | 183篇 |
2003年 | 138篇 |
2002年 | 140篇 |
2001年 | 41篇 |
2000年 | 44篇 |
1999年 | 47篇 |
1998年 | 37篇 |
1997年 | 40篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 7篇 |
排序方式: 共有2971条查询结果,搜索用时 281 毫秒
941.
Reiko Saito Toshifumi Kanahara Masahiro Oguchi Hiroshi Nakaseko 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):362-368
In order to control microphase separation of polystyrene-silica nanocomposites, perhydropolysilazane (PHPS), which is a preceramic of silica, and epoxidized poly(styrene-block-butadiene-block-styrene) triblock copolymer [E-SBS, Mw = 8.0 × 104, styrene: 40 mol%, degree of epoxidization of butadiene: 20 mol%] or poly(styrene-block-butadiene-block-styrene) triblock copolymer [SBS, Mw = 1.40 × 105, styrene: 30 mol%] as templates of microphase separation were blended, following the calcination of composites in steam at 60°C. Well-arranged microphase separation was formed with E-SBS, though the macrophase separation was formed with SBS. The morphology of the microphase separation of the composites with E-SBS and PHPS was widely controlled by varying the PHPS content based on Molau's law. Silica domains were formed in polybutadiene domains. NMR analysis indicated the interaction between silanyl group of PHPS and epoxy group in E-SBS. The composites on the substrate were highly transparent and the surface of the composite with 73.5 vol% of silica was harder than 4H. 相似文献
942.
Tsutomu Kawai Yoichi Kodera Shigeru Oae Masahiro Ishida Takashi Takeda Shoji Wakabayashi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):139-148
Abstract Ligand coupling reactions take place not only between benzyl and 2-pyridyl groups and two 2-pyridyl groups in the treatment of benzyl, alkyl and aryl 2-pyridyl sulfoxides with Grignard reagents, but also between such groups as p-benzenesulfonylphenyl, 4-pyridyl, 2-quinolyl and 2-pyrimidyl, and the benzyl group. There are cases in which ligand exchange precedes ligand coupling, especially with 2-heteroaryl groups. In addition, even some alkyl groups were found to couple with the 2-pyridyl group. The ease of coupling seems to be associated with the electronegativity of the coupling carbon atom of the ligand, when one compares the 13C NMR chemical shifts. 相似文献
943.
Takayuki Iijima Masahiro Abe Take‐Aki Koizumi Atsushi Fukaya Kyohei Usami Kenichiro Kami Takakazu Yamamoto 《先进技术聚合物》2013,24(10):927-933
The reaction of 2,5‐diiodo‐1,4‐benzenedicarbonyl chloride, C6H2I2(COCl)2‐p, with 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO‐ol) gave I–Ph(COO–TEMPO)2–I, Monomer‐1. Pd‐catalyzed polycondensation of Monomer‐1 with Me3Sn‐Th‐SnMe3 (2,5‐bis(trimethylstannyl)thiophene) and Bu3Sn–CH = CH–SnBu3 (1,2‐bis‐(tributylstannyl)ethylene) gave the corresponding π‐conjugated polymers, Polymer‐1 and Polymer‐2, respectively. Monomer‐1 was converted to a diethynyl compound, H–C ≡ C–Ph(COO–TEMPO)2–C ≡ C–H (Monomer‐1'), and Pd‐catalyzed polycondensation between Monomer‐1 and Monomer‐1' gave a π‐conjugated poly(arylene ethynylene) type polymer, Polymer‐3. According to the expansion of the π‐conjugation system by the polymerization, the UV–vis peaks of Monomer‐1 (λmax = 323 nm) and Monomer‐1' (327 nm) are shifted to longer wavelengths (λmax = 365 nm, 385 nm, and 396 nm for Polymer‐1, Polymer‐2, and Polymer‐3, respectively). Polymer‐1–Polymer‐3 showed ESR signals at about g = 2.01 with reasonable intensities. They are electrochemically active and showed a peak current anodic (oxidation) peak at about 0.9 V versus Ag/AgCl, which is reasonable for TEMPO polymers. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
944.
Masahiro Fukuzumi Waka Nakanishi Tsutomu Ishikawa Takuya Kumamoto 《Helvetica chimica acta》2014,97(11):1453-1468
We report the synthesis and potential chirality of ortho‐phenylenebisguanidines (BGs) with substituents at C(3) and C(6). Guanidinylation of 3,6‐disubstituted benzene‐1,2‐diamines with 2‐chloro‐4,5‐dihydro‐1,3‐dimethyl‐1H‐imidazolium chloride gave the corresponding BGs. X‐Ray crystallography showed that the two guanidine moieties occupy different faces of the benzene ring, creating potential chirality, although optical resolution of tBu‐substituted BG by chiral HPLC failed. However, a methylated acyclic bisguanidinium salt (BGms) was obtained as a chiral crystal with a space group of P212121. 相似文献
945.
We developed a new one-pot reaction of phenolic acids to afford the corresponding esters and amides through acyl-protected and activated phenolic acid intermediates. The simultaneous protection/activation of phenolic acids with alkylchloroformates proceeded readily in the presence of DMAP at room temperature; subsequent addition of alcohols or amines afforded the corresponding esters or amides. The use of iso-butyloxycarbonyl as the protecting and activating group in the one-pot reactions afforded phenolic esters or amides in 91% average yield. As a practical example of this convenient synthesis, caffeic acid phenethyl ester (CAPE) was readily synthesized from commercially available caffeic acid and phenethyl alcohol in 95% yield, and an isotopomer of CAPE, [3,10-13C2]CAPE, was synthesized in 91% yield from [3-13C]caffeic acid and 2-[1-13C]phenethyl alcohol. This method may be useful for the convenient esterification and amidation of diverse phenolic acids. 相似文献
946.
Asymmetric hydrogenation of ketones (AHK) was revolutionized in 1987 and again in 1995 when Ru(CH3COO)2(binap)/HCl and RuCl2(binap)/diamine, respectively, were developed. Since then, the number of reports on Ru-catalyzed AHK has increased exponentially, and the utility of other precious metals (Os, Rh, Ir, and Pd) has also been shown. The utilization of inexpensive base metals (Fe, Co, Ni, and Cu) has been a recent trend. This digest summarizes the key advances in AHK in the past decade by categorizing the chiral ligands into six types: (i) diphosphines, (ii) diphosphines/diamines, (iii) tridentate or tetradentate phosphine amines, (iv) diamines, (v) tetradentate amines, and (vi) tetradentate thioether amines. 相似文献
947.
Kosuke Nakashima Shin-ichi Hirashima Masahiro Kawada Yuji Koseki Norihiro Tada Akichika Itoh Tsuyoshi Miura 《Tetrahedron letters》2014
The novel pyrrolidine-diaminomethylenemalononitrile organocatalyst 7 promotes the asymmetric conjugate addition of a carbonyl compound to a nitroalkene to afford the corresponding adduct in high yield with up to 99% ee, under solvent-free conditions. 相似文献
948.
Masahiro Kurakake Yoshikazu Kanbara Yoshiki Murakami 《Applied biochemistry and biotechnology》2014,172(5):2650-2660
Streptomyces sp I10-1 α-l-arabinofuranosidase efficiently produced l-arabinose from high arabinose-content corn hull arabinoxylan (ratio of arabinose to xylose, 0.6). The optimum pH at 40 °C was around 6, and the enzyme was stable from pH 5 to 11. The optimum temperature was 50 °C at pH 5, and the activity was stable at 40 °C. The enzymatic activity against corn hull arabinoxylan was 2.3 times higher than towards p-nitrophenyl-α-l-arabinofuranoside. Approximately 45 % l-arabinose recovery was achieved from corn hull arabinoxylan. It was considered that l-arabinose residues not removed by the enzyme were attributable to those linked with ferulic acid. The open reading frame of the enzyme gene consisted of 1,224 bp, and the predicted peptide was 408 amino acids, which corresponded to a molecular size of 45, 248 Da. It was presumed that the smaller molecular size (31,000 Da) estimated on SDS-PAGE resulted from proteolysis by proteases. I10-1 α-l-arabinofuranosidase belongs to the Alpha-l-AF C superfamily, which is associated with glycoside hydrolase family 51, but the properties were unique. 相似文献
949.
950.
We propose a scalable and practical implementation of spin amplification which does not require individual addressing nor a specially tailored spin network. We have demonstrated a gain of 140 in a solid-state nuclear spin system of which the spin polarization has been increased to 0.12 using dynamic nuclear polarization with photoexcited triplet electron spins. Spin amplification scalable to a higher gain opens the door to the single spin measurement for a readout of quantum computers as well as practical applications of nuclear magnetic resonance spectroscopy to infinitesimal samples which have been concealed by thermal noise. 相似文献