全文获取类型
收费全文 | 32561篇 |
免费 | 249篇 |
国内免费 | 301篇 |
专业分类
化学 | 13285篇 |
晶体学 | 282篇 |
力学 | 1482篇 |
综合类 | 12篇 |
数学 | 9439篇 |
物理学 | 8611篇 |
出版年
2023年 | 41篇 |
2022年 | 62篇 |
2021年 | 100篇 |
2020年 | 114篇 |
2019年 | 111篇 |
2018年 | 1252篇 |
2017年 | 1491篇 |
2016年 | 827篇 |
2015年 | 653篇 |
2014年 | 602篇 |
2013年 | 850篇 |
2012年 | 3381篇 |
2011年 | 2626篇 |
2010年 | 1933篇 |
2009年 | 1642篇 |
2008年 | 840篇 |
2007年 | 884篇 |
2006年 | 871篇 |
2005年 | 4646篇 |
2004年 | 4090篇 |
2003年 | 2465篇 |
2002年 | 619篇 |
2001年 | 313篇 |
2000年 | 123篇 |
1999年 | 204篇 |
1998年 | 142篇 |
1997年 | 109篇 |
1996年 | 99篇 |
1995年 | 70篇 |
1994年 | 69篇 |
1993年 | 44篇 |
1992年 | 189篇 |
1991年 | 177篇 |
1990年 | 159篇 |
1989年 | 119篇 |
1988年 | 110篇 |
1987年 | 69篇 |
1986年 | 49篇 |
1985年 | 58篇 |
1984年 | 55篇 |
1983年 | 37篇 |
1979年 | 39篇 |
1978年 | 40篇 |
1976年 | 92篇 |
1975年 | 45篇 |
1974年 | 50篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1969年 | 37篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Enzyme stabilization strategies based on electrolytes and polyelectrolytes for biosensor applications 总被引:3,自引:0,他引:3
Chaniotakis NA 《Analytical and bioanalytical chemistry》2004,378(1):89-95
The achievements in the area of enzyme stabilization based on electrolytes, polyelectrolytes and polyols is reviewed, in the context of biosensor applications. Both the storage and operational stabilities of the biosensors can be improved using these stabilizers. The deactivation of the enzymes used for the development of biosensors from thermal shock, proteolytic degradation, and non-specific metal-catalyzed oxidation can be drastically reduced with the use of one or more of these stabilizers. It is attempted to deconvolute the effect of these additives on (a) the storage stability or shelf life, and (b) the operational stabilities of the biosensors. Even though there are a large number of techniques and reports dealing with enzyme stabilization, their application to biosensor technology is still very limited. It is thus concluded that the use of the existing enzyme stabilization techniques will have a drastic effect on the storage and operational stabilities of biosensors in the near future. 相似文献
992.
ZHAO Chunxia XU Guowang SHI Xianzhe MA Jianmei ZHANG Yan L?Shen & YANG Qing . Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian China . Cell Laboratory Second Affiliated Hospital Dalian Medical University Dalian China 《中国科学B辑(英文版)》2004,47(2):166-172
With the accomplishment of Human Genome Project (HGP), single nucleotide polymorphism (SNP) and mutation detection in human genome are becom-ing a new researching focus. These researches can help us to understand the phenotype diversity of indi-vidual, disease susceptibility and drug resistance of different colonies. Traditional method used for muta-tion detection is slab gel electrophoresis, which re-mains labor-intensive and time-consuming because of the requirement of radioactivity or te… 相似文献
993.
ZHENG Hong WANG Shaoqing & CHENG Huiming Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang China 《中国科学B辑(英文版)》2004,47(3):222-227
Hydrogen is a kind of clean, sustainable and renewable energy carrier. Of the problems to be solved for the utilization of hydrogen energy, how to store and transport hydrogen has been given high priority on the research agenda. Recently, carbon nanotubes (CNTs) were reported to be very promising candidates for hydrogen uptake[1], which may have possibility to satisfy the benchmark set by the US Department of Energy (DOE) Hydrogen Plan for fuel cell powered vehicles: a gravimetric density … 相似文献
994.
ZOUYi* HE Deping* & JIANG Jiaqiao Department of Material Science Engineering Southeast University Nanjing China 《中国科学B辑(英文版)》2004,47(5):407-413
The Ultra Light Metal Structure with variouskinds of pores (open, close) realizes the lightness andmultifunction of structural material. The functionsinclude lightness (ρ < 1), high specific strength, highenergy absorption, sound insulation, heat insulationand electromagnetism shield. It is one of the hotspotsin material research nowadays[1— . The requirements 6]of high speed movement and high technology make Alalloy foam, which has higher specific st… 相似文献
995.
Synthesis and Transformations of 5‐Chloro‐2,2′‐Dipyrrins and Their Boron Complexes, 8‐Chloro‐BODIPYs 下载免费PDF全文
Haijun Wang Prof. M. Graça H. Vicente Dr. Frank R. Fronczek Prof. Kevin M. Smith 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):5064-5074
Symmetric dipyrrylketones 1 a , b were synthesized in two steps from the corresponding α‐free pyrroles, by reaction with thiophosgene followed by oxidative hydrolysis under basic conditions. The dipyrrylketones produced the corresponding 5‐chloro‐dipyrrinium salts or 5‐ethoxy‐dipyrrins on reaction with phosgene or Meerwein’s salt, respectively. Boron complexation of the dipyrrins afforded the corresponding 8‐functionalized BODIPYs (borondipyrromethenes) in high yields. The 5‐chloro‐dipyrrinium salts reacted with methoxide or ethoxide ions to produce monopyrrole esters, presumably via a 5,5‐dialkoxy‐dipyrromethane intermediate. In contrast, 8‐chloro‐BODIPYs underwent a variety of nucleophilic substitutions of the chloro group in the presence of alkoxide ions, Grignard reagents, and thiols. In the presence of excess alkoxide or Grignard reagent, at room temperature or above, substitution at the boron center also occurred. The 8‐chloro‐BODIPY was a particularly useful reagent for the preparation of 8‐aryl‐, 8‐alkyl‐, and 8‐vinyl‐substituted BODIPYs in very high yields, using Pd0‐catalyzed Stille cross‐coupling reactions. The X‐ray structures of eleven BODIPYs and two pyrroles are presented, and the spectroscopic properties of the synthesized BODIPYs are discussed. 相似文献
996.
Spin‐State Ordering on One Sub‐lattice of a Mononuclear Iron(III) Spin Crossover Complex Exhibiting LIESST and TIESST 下载免费PDF全文
Dr. Kevin D. Murnaghan Dr. Chiara Carbonera Dr. Loic Toupet Dr. Michael Griffin Dr. Marinela M. Dîrtu Dr. Cédric Desplanches Prof. Dr. Yann Garcia Prof. Eric Collet Prof. Jean‐François Létard Dr. Grace G. Morgan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5613-5618
The two‐step spin crossover in mononuclear iron(III) complex [Fe(salpm)2]ClO4 ? 0.5 EtOH ( 1 ) is shown to be accompanied by a structural phase transition as concluded from 57Fe Mössbauer spectroscopy and single crystal X‐ray diffraction, with spin‐state ordering on just one of two sub‐lattices in the intermediate magnetic and structural phase. The complex also exhibits thermal‐ and light‐induced spin‐state trapping (TIESST and LIESST), and relaxation from the LIESST and TIESST excited states occurs via the broken symmetry intermediate phase. Two relaxation events are evident in both experiments, that is, two T(LIESST) and two T(TIESST) values are recorded. The change in symmetry which accompanies the TIESST effect was followed in real time using single crystal diffraction. After flash freezing at 15 K the crystal was warmed to 40 K at which temperature superstructure reflections were observed to appear and disappear within a 10 000 s time range. In the frame of the international year of crystallography, these results illustrate how X‐ray diffraction makes it possible to understand complex ordering phenomena. 相似文献
997.
Synthesis of New Lipid‐Inspired Ionic Liquids by Thiol‐ene Chemistry: Profound Solvent Effect on Reaction Pathway 下载免费PDF全文
Dr. Arsalan Mirjafari Dr. Richard A. O'Brien Dr. Kevin N. West Prof. James H. Davis Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7576-7580
The synthesis of a series of new lipid‐inspired ionic liquids through thiol‐ene “click” reaction with a single‐step process. This synthesis offers considerable promise as an efficient and orthogonal method to construct structurally diverse imidazolium‐type ionic liquids with linear and branched cationic tails, as well as versatility in the placement of the sulfur heteroatom. Profound solvent effect in this ene reaction regioselectivity has been observed. 相似文献
998.
Fan Shi Aaron M. Coffey Assist. Prof. Kevin W. Waddell Assist. Prof. Eduard Y. Chekmenev Assoc. Prof. Boyd M. Goodson 《Angewandte Chemie (International ed. in English)》2014,53(29):7495-7498
A novel variant of an iridium‐based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET‐SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the 1H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules. 相似文献
999.
1000.
Dissolution dynamic nuclear polarization (DNP) enables high‐sensitivity solution‐phase NMR experiments on long‐lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution‐state 1H NMR upon polarizing low‐γ nuclear species. Following solid‐state hyperpolarization of both 13C and 1H, solution‐phase 1H NMR experiments on dissolved samples revealed transient effects, whereby peaks arising from protons bonded to the naturally occurring 13C nuclei appeared larger than the typically dominant 12C‐bonded 1H resonances. This enhancement of the satellite peaks was examined in detail with respect to a variety of mechanisms that could potentially explain this observation. Both two‐ and three‐spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization‐transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross‐relaxation models were examined, and found to well describe the distinct patterns of growth and decay shown by the 13C‐bound 1H NMR satellite resonances. The dynamics of these novel cross‐relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced‐sensitivity 1H NMR traces was explored. 相似文献