全文获取类型
收费全文 | 1438篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
化学 | 1033篇 |
晶体学 | 29篇 |
力学 | 28篇 |
数学 | 160篇 |
物理学 | 261篇 |
出版年
2023年 | 17篇 |
2022年 | 23篇 |
2021年 | 26篇 |
2020年 | 48篇 |
2019年 | 42篇 |
2018年 | 41篇 |
2017年 | 32篇 |
2016年 | 51篇 |
2015年 | 35篇 |
2014年 | 65篇 |
2013年 | 94篇 |
2012年 | 74篇 |
2011年 | 105篇 |
2010年 | 55篇 |
2009年 | 48篇 |
2008年 | 79篇 |
2007年 | 78篇 |
2006年 | 59篇 |
2005年 | 58篇 |
2004年 | 40篇 |
2003年 | 35篇 |
2002年 | 30篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1969年 | 8篇 |
1968年 | 9篇 |
1963年 | 8篇 |
1962年 | 8篇 |
1961年 | 13篇 |
1958年 | 7篇 |
排序方式: 共有1511条查询结果,搜索用时 15 毫秒
991.
Application of Privileged Molecular Framework of 7‐Fluoro‐1,4‐benzodiazepin‐2‐one‐5‐methylcarboxylate to the Synthesis of Its 1‐ and 5‐Disubstituted Analogs of Medicinal Interest
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Synthetic potential of the privileged molecular framework of 7‐fluoro‐1,4‐benzodiazepin‐2‐one containing a methyl carboxylate substituent at its 5‐position was exploited to develop efficient protocols to the synthesis of several novel 5‐(1′,3′,4′)oxadiazole ring incorporated analogs of medicinal interest, appended with the Mannich's base motifs at the nitrogen atom in its seven‐membered ring. 相似文献
992.
Application of Dimethylaminomethylene Ketone in Heterocycles Synthesis: Synthesis of 2‐(Isoxazolo,Pyrazolo, and Pyrimido) Substituted Analogs of 1,4‐Benzodiazepin‐5‐carboxamides Linked through an Oxyphenyl Bridge
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Navjeet Kaur Ruchi Tyagi Manish Srivastava D. Kishore 《Journal of heterocyclic chemistry》2014,51(Z1):E50-E54
Versatility of dimethylaminomethylene ketone derivative of 2‐(4′‐acetyl)‐phenoxyl‐5‐carboxamido‐1,4‐benzodiazepin‐5‐(4′‐methylpiperazinyl)‐carboxamide ( 6 ) was explored to provide an easy one‐pot access to its 2‐(isoxazolo, pyrazolo, and pyrimido) substituted analogs 8 , 9 , 10 , 11 , 12 , and 13 , respectively. 相似文献
993.
4‐Oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde (chromone‐3‐carboxaldehyde or 3‐formylchromone) 1 is an important biologically active compound. It can serve as a precursor in the synthesis of a wide range of heterocyclic systems having chromone moiety, many of which exhibit broad spectrum of biological activities such as anti‐mutagenisity, cytotoxicity, thymidine phosphorylase inhibitor, and anti‐HIV activity. During the last decade, the title compound was studied extensively. The review presents an overall survey of the synthesis, chemical reactivity, and biological activities of 4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehydes and some of its derivatives. 相似文献
994.
Sanjay Anand Kishore R. Rollakanti Ronald L. Horst Tayyaba Hasan Edward V. Maytin 《Photochemistry and photobiology》2014,90(5):1126-1135
Photodynamic therapy (PDT), in which 5‐ALA (a precursor for protoporphyrin IX, PpIX) is administered prior to exposure to light, is a nonscarring treatment for skin cancers. However, for deep tumors, ALA‐PDT is not always effective due to inadequate production of PpIX. We previously developed and reported a combination approach in which the active form of vitamin D3 (calcitriol) is given systemically prior to PDT to improve PpIX accumulation and to enhance PDT‐induced tumor cell death; calcitriol, however, poses a risk of hypercalcemia. Here, we tested a possible strategy to circumvent the problem of hypercalcemia by substituting natural dietary vitamin D3 (cholecalciferol; D3) for calcitriol. Oral D3 supplementation (10 days of a 10‐fold elevated D3 diet) enhanced PpIX levels 3‐ to 4‐fold, and PDT‐mediated cell death 20‐fold, in subcutaneous A431 tumors. PpIX levels and cell viability in normal tissues were not affected. Hydroxylated metabolic forms of D3 were only modestly elevated in serum, indicating minimal hypercalcemic risk. These results show that brief oral administration of cholecalciferol can serve as a safe neoadjuvant to ALA‐PDT. We suggest a clinical study, using oral vitamin D3 prior to PDT, should be considered to evaluate this promising new approach to treating human skin cancer. 相似文献
995.
Solid-phase organic synthesis is a rapidly expanding area of synthetic chemistry which is being widely exploited in the search for new medicinally important compounds using combinatorial techniques. In recent decades, a large number of reports related to solid-phase synthesis of heterocycles have appeared because of the wide variety in their biological activity. In this review, we report the important role of solid-phase synthesis in the synthesis of oxygen-bearing heterocycles. 相似文献
996.
Sridhar Madabhushi Kishore Kumar Reddy Mallu Raveendra Jillella Srinivas Kurva Rajpal Singh 《Tetrahedron letters》2014
A simple and efficient method for the preparation of 2,4-disubstituted quinazoline 3-oxides by reaction of a hydroxamic acid with 2-aminoaryl ketones using zinc(II) triflate as the catalyst is described. 相似文献
997.
Quantum Mechanical and Experimental Validation that Cyclobis(paraquat‐p‐phenylene) Forms a 1:1 Inclusion Complex with Tetrathiafulvalene
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Karel J. Hartlieb Dr. Wei‐Guang Liu Dr. Albert C. Fahrenbach Anthea K. Blackburn Dr. Marco Frasconi Dr. Nema Hafezi Dr. Sanjeev K. Dey Dr. Amy A. Sarjeant Charlotte L. Stern Prof. William A. Goddard III Prof. J. Fraser Stoddart 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2736-2745
The promiscuous encapsulation of π‐electron‐rich guests by the π‐electron‐deficient host, cyclobis(paraquat‐p‐phenylene) (CBPQT4+), involves the formation of 1:1 inclusion complexes. One of the most intensely investigated charge‐transfer (CT) bands, assumed to result from inclusion of a guest molecule inside the cavity of CBPQT4+, is an emerald‐green band associated with the complexation of tetrathiafulvalene (TTF) and its derivatives. This interpretation was called into question recently in this journal based on theoretical gas‐phase calculations that reinterpreted this CT band in terms of an intermolecular side‐on interaction of TTF with one of the bipyridinium (BIPY2+) units of CBPQT4+, rather than the encapsulation of TTF inside the cavity of CBPQT4+. We carried out DFT calculations, including solvation, that reveal conclusively that the CT band emerging upon mixing TTF with CBPQT4+ arises from the formation of a 1:1 inclusion complex. In support of this conclusion, we have performed additional experiments on a [2]rotaxane in which a TTF unit, located in the middle of its short dumbbell, is prevented sterically from interacting with either one of the two BIPY2+ units of a CBPQT4+ ring residing on a separate [2]rotaxane in a side‐on fashion. This [2]rotaxane has similar UV/Vis and 1H NMR spectroscopic properties with those of 1:1 inclusion complexes of TTF and its derivatives with CBPQT4+. The [2]rotaxane exists as an equimolar mixture of cis‐ and trans‐isomers associated with the disubstituted TTF unit in its dumbbell component. Solid‐state structures were obtained for both isomers, validating the conclusion that the TTF unit, which gives rise to the CT band, resides inside CBPQT4+. 相似文献
998.
999.
This study has investigated the microstructure and magnetic properties of Fe40Ni38B18Mo4 at various degrees of crystallization from the amorphous state. TEM and XRD studies confirmed that phases forming after crystallization at temperatures around 414 and 522 °C were cubic (Fe, Ni, Mo)23B6 phase and FCC (Fe, Ni) solid solution. The growth behavior and morphology of the nanocrystalline phases have been studied as a function of time and temperature. Nanoparticles were lying in the size range of 10–20 nm and they were stable below 522 °C. Kissinger approach, Ozawa method and Yi Qun Gao method were employed to determine and compare the kinetic parameters of the crystallization processes. A growth mechanism of crystallizing phases was proposed on the basis of these results. Magnetic properties mainly coercivity and saturation magnetization of as-received and heat-treated samples were evaluated. 相似文献
1000.
The synthesis of trans-1,8,12,13-tetraoxadispiro[4.1.4.2]tridecanes, a new class of peroxide skeletons using Birch reduction of aromatic compounds followed by ozonolysis and acid catalysed cyclisation is described. 相似文献