全文获取类型
收费全文 | 12657篇 |
免费 | 1040篇 |
国内免费 | 709篇 |
专业分类
化学 | 8488篇 |
晶体学 | 121篇 |
力学 | 504篇 |
综合类 | 51篇 |
数学 | 1491篇 |
物理学 | 3751篇 |
出版年
2023年 | 165篇 |
2022年 | 301篇 |
2021年 | 300篇 |
2020年 | 320篇 |
2019年 | 336篇 |
2018年 | 257篇 |
2017年 | 268篇 |
2016年 | 405篇 |
2015年 | 416篇 |
2014年 | 490篇 |
2013年 | 724篇 |
2012年 | 901篇 |
2011年 | 1026篇 |
2010年 | 651篇 |
2009年 | 677篇 |
2008年 | 769篇 |
2007年 | 734篇 |
2006年 | 647篇 |
2005年 | 563篇 |
2004年 | 532篇 |
2003年 | 455篇 |
2002年 | 404篇 |
2001年 | 330篇 |
2000年 | 270篇 |
1999年 | 206篇 |
1998年 | 162篇 |
1997年 | 139篇 |
1996年 | 175篇 |
1995年 | 131篇 |
1994年 | 150篇 |
1993年 | 124篇 |
1992年 | 117篇 |
1991年 | 96篇 |
1990年 | 106篇 |
1989年 | 82篇 |
1988年 | 90篇 |
1987年 | 61篇 |
1986年 | 69篇 |
1985年 | 95篇 |
1984年 | 69篇 |
1983年 | 68篇 |
1982年 | 49篇 |
1981年 | 46篇 |
1980年 | 47篇 |
1979年 | 34篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1975年 | 34篇 |
1974年 | 48篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
Metalloproteins have inspired chemists for many years to synthesize artificial catalysts that mimic native enzymes.As a complementary approach to studying native enzymes or making synthetic models,biosynthetic approach using small and stable proteins to model native enzymes has offered advantages of incorporating non-covalent secondary sphere interactions under physiological conditions.However,most biosynthetic models are restricted to natural amino acids.To overcome this limitation,incorporating unnatural amino acids into the biosynthetic models has shown promises.In this review,we summarize first synthetic,semisynthetic and biological methods of incorporates unnatural amino acids(UAAs)into proteins,followed by progress made in incorporating UAAs into both native metalloproteins and their biosynthetic models to fine-tune functional properties beyond native enzymes or their variants containing natural amino acids,such as reduction potentials of azurin,O_2 reduction rates and percentages of product formation of HCO models in Mb,the rate of radical transport in ribonucleotide reductase(RNR)and the proton and electron transfer pathways in photosystemⅡ(PSⅡ).We also discuss how this endeavour has allowed systematic investigations of precise roles of conserved residues in metalloproteins,such as Metl21 in azurin,Tyr244 that is cross-linked to one of the three His ligands to CuB in HCO,Tyr122,356,730 and 731 in RNR and TyrZ in PSⅡ.These examples have demonstrated that incorporating UAAs has provided a new dimension in our efforts to mimic native enzymes and in providing deeper insights into structural features responsible high enzymatic activity and reaction mechanisms,making it possible to design highly efficient artificial catalysts with similar or even higher activity than native enzymes. 相似文献
922.
Improvement of interfacial adhesion in PP/PS blends enhanced with supersonic atmosphere plasma spraying surface‐treated carbon fiber 下载免费PDF全文
The effects of surface treatment of a carbon fiber (CF) by supersonic atmosphere plasma spraying (SAPS) on the interfacial adhesion behavior and morphology of polypropylene/polystyrene (PP/PS) matrix blends filled CF composites were investigated. Effects of surface treated a commercial CF on mechanical properties are studied. Contact angle was measured to examine the changes in wettability of the CF. The chemical and morphological changes were characterized by using X‐ray photoelectron spectroscopy and scanning electron microscopy. PP/PS/CF composites were fabricated with and without SAPS treatment, and their interlaminar fracture toughnesses were compared. The results showed that the interlaminar shear strength of composites has been greatly improved filled SAPS modification CF. The water contact angle of resin sample decreased 50% after addition of SAPS surface‐treated CF. Scanning electron microscopy results on the fractured surface exhibited PP/PS blends adhered well around the CFs of the SAPS‐treated specimen compared with that of the untreated specimen. This attributed to the CF interlock, and it improves the wetting between fibers and resins. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
923.
Pei‐Hong Ni Qi‐Sheng Pan Liu‐Sheng Zha Chang‐Chun Wang Abdelhamid Elaïssari Shou‐Kuan Fu 《Journal of polymer science. Part A, Polymer chemistry》2002,40(4):624-631
A novel, near‐monodisperse, well‐defined ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(propylene oxide)‐b‐poly[2‐(dimethylamino)ethyl methacrylate], was synthesized via oxyanion‐initiated polymerization. The initiator was a telechelic‐type potassium alcoholate prepared from poly(propylene glycol) and KH in dry tetrahydrofuran. The copolymers produced were characterized by Fourier transform infrared, 1H NMR, and gel permeation chromatography (GPC). GPC and 1H NMR analyses showed that the products obtained were the desired copolymers, with narrow molecular weight distributions (ca. 1.09–1.11) very close to that of the original poly(propylene glycol). 1H NMR, surface tension measurements, and dynamic light scattering all indicated that the triblock copolymer led to interesting aqueous solution behaviors, including temperature‐induced micellization and very high surface activity. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 624–631, 2002; DOI 10.1002/pola.10144 相似文献
924.
Po-Tsung Hsieh Ricky Wen-Kuei Chuang Chao-Qun Chang Chih-Ming Wang Shoou-Jinn Chang 《Journal of Sol-Gel Science and Technology》2011,58(1):42-47
Yttrium-doped ZnO gel was spin-coated on the SiO2/Si substrate. The as-prepared ZnO:Y (YZO) thin films then underwent a rapid thermal annealing (RTA) process conducted at
various temperatures. The structural and photoluminescence characteristics of the YZO films were discussed thereafter. Our
results indicated that the grain size of YZO thin films being treated with various annealing temperatures became smaller as
compared to the ones without being doped with yttrium. Furthermore, unlike other ZnO films, the grains of YZO thin films appeared
to separate from one another rather than aggregating together as both types of the films were annealed under the same environment.
The photoluminescence characteristic measured showed that the UV emission was the only radiation obtained. However, the UV
emission intensity of YZO thin film was much stronger than that of the ZnO thin film after annealing them with the same condition.
It was also found that the intensity increased with an increase in the annealing temperature, which was caused by the exciton
generated and the texture surface of the YZO thin film. 相似文献
925.
926.
The aminolysis of a novel activated ester resin was utilized for kinetic study via continuous in situ fluorescence measurements. A variety of resin compositions (polystyrene, JandaJel, ArgoPore, TentaGel, NovaGel, and PEGA) and solvents (dimethylformamide, acetonitrile, tetrahydrofuran, 1,2-dichlorethane, and toluene) were tested to compare their effects on the reaction rate. A linear relationship between the reaction rate and (solvent polarity x swelling of resin) was elucidated for the aminolysis reaction. 相似文献
927.
Nanocomposites of Tantalum‐Based Pyrochlore and Indium Hydroxide Showing High and Stable Photocatalytic Activities for Overall Water Splitting and Carbon Dioxide Reduction 下载免费PDF全文
Meng‐Chun Hsieh Guan‐Chang Wu Dr. Wei‐Guang Liu Prof. William A. Goddard III Prof. Dr. Chia‐Min Yang 《Angewandte Chemie (International ed. in English)》2014,53(51):14216-14220
Nanocomposites of tantalum‐based pyrochlore nanoparticles and indium hydroxide were prepared by a hydrothermal process for UV‐driven photocatalytic reactions including overall water splitting, hydrogen production from photoreforming of methanol, and CO2 reduction with water to produce CO. The best catalyst was more than 20 times more active than sodium tantalate in overall water splitting and 3 times more active than Degussa P25 TiO2 in CO2 reduction. Moreover, the catalyst was very stable while generating stoichiometric products of H2 (or CO) and O2 throughout long‐term photocatalytic reactions. After the removal of In(OH)3, the pyrochlore nanoparticles remained highly active for H2 production from pure water and aqueous methanol solution. Both experimental studies and density functional theory calculations suggest that the pyrochlore nanoparticles catalyzed the water reduction to produce H2, whereas In(OH)3 was the major active component for water oxidation to produce O2. 相似文献
928.
New Conjugated Molecules with Two and Three Dithienyldiketopyrrolopyrrole (DPP) Moieties Substituted at meta Positions of Benzene toward p‐ and n‐Type Organic Photovoltaic Materials 下载免费PDF全文
Chenmin Yu Dr. Chang He Yang Yang Zhengxu Cai Hewei Luo Wenqiang Li Dr. Qian Peng Dr. Guanxin Zhang Dr. Zitong Liu Prof. Deqing Zhang 《化学:亚洲杂志》2014,9(6):1570-1578
Two conjugated molecules, TADPP3 and TADPP2‐TT , are reported, in which three and two dithienyldiketopyrrolopyrrole (DPP) moieties, respectively, are substituted at the meta positions of benzene. Based on cyclic voltammetry and absorption data, TADPP3 and TADPP2‐TT possess similar HOMO and LUMO energies of about ?5.2 and ?3.4 eV, respectively. Thin films of TADPP3 and TADPP2‐TT exhibit p‐type semiconducting behavior with hole mobilities of 2.36×10?3 and 3.76×10?4 cm2 V?1 s?1 after thermal annealing. Molecules TADPP3 and TADPP2‐TT were utilized as p‐type photovoltaic materials to fabricate organic solar cells after blending with phenyl C71 butyric acid methyl ester ( PC71BM ) and phenyl C61 butyric acid methyl ester ( PC61BM ). The relatively low JSC and fill factor values can be attributed to poor film morphologies based on AFM and XRD studies. A solar cell with a thin film of TADPP3 with PC71BM in a weight ratio of 1:2 exhibits a high open‐circuit voltage (VOC) of 0.99 V and a power conversion efficiency (PCE) of 2.47 %. Interestingly, TADPP3 can also be employed as an n‐type photovoltaic material. The blended thin film of TADPP3 with P3HT in a weight ratio of 1:2 gave a high VOC of 1.11 V and a PCE of 1.08 % after thermal annealing. 相似文献
929.
930.
Sieving properties of end group‐halogenated Pluronic polymer matrix in DNA separation under nondenaturing CE analysis 下载免费PDF全文
Hee Sung Hwang Gi Won Shin Aaron Cohen Chang Yeol Ryu Gyoo Yeol Jung 《Electrophoresis》2014,35(20):2946-2950
CE‐SSCP analysis is a well‐established DNA separation method that is based on variations in mobility caused by sequence‐induced differences in the conformation of single‐stranded DNA. The resolution of CE‐SSCP analysis was improved by using a Pluronic polymer matrix, and it has been successfully applied in various genetic analyses. Because the Pluronic polymer forms a micellar cubic structure in the capillary, it provides a stable internal structure for high‐resolution CE‐SSCP analysis. We hypothesized that formation of micellar cubic structure is influenced by the end hydroxyl group of the Pluronic polymer, which affords structural stability through hydrogen bonding. To test this hypothesis, the hydroxyl group was halogenated to eliminate the hydrogen bonding without disturbing the polarity of polymer matrix. CE‐SSCP resolution of two DNA fragments with a single base difference was significantly worse in the halogenated polymer matrices due to band broadening. The viscoelastic properties of control (which has hydroxyl group), chlorinated, and brominated F108 solution upon heating were also investigated by rheological experiments, and we found that gelation was significantly associated with resolution. In this series of experiments, the effect of the hydroxyl group in Pluronic polymer matrix on separation resolution of CE‐SSCP analysis was demonstrated. 相似文献