全文获取类型
收费全文 | 7748篇 |
免费 | 237篇 |
国内免费 | 27篇 |
专业分类
化学 | 5778篇 |
晶体学 | 90篇 |
力学 | 127篇 |
数学 | 534篇 |
物理学 | 1483篇 |
出版年
2022年 | 36篇 |
2021年 | 65篇 |
2020年 | 90篇 |
2019年 | 108篇 |
2018年 | 69篇 |
2017年 | 51篇 |
2016年 | 131篇 |
2015年 | 131篇 |
2014年 | 163篇 |
2013年 | 367篇 |
2012年 | 406篇 |
2011年 | 444篇 |
2010年 | 251篇 |
2009年 | 234篇 |
2008年 | 469篇 |
2007年 | 511篇 |
2006年 | 505篇 |
2005年 | 443篇 |
2004年 | 398篇 |
2003年 | 356篇 |
2002年 | 331篇 |
2001年 | 134篇 |
2000年 | 107篇 |
1999年 | 87篇 |
1998年 | 68篇 |
1997年 | 99篇 |
1996年 | 108篇 |
1995年 | 58篇 |
1994年 | 82篇 |
1993年 | 68篇 |
1992年 | 62篇 |
1991年 | 65篇 |
1990年 | 45篇 |
1989年 | 49篇 |
1988年 | 59篇 |
1987年 | 43篇 |
1986年 | 47篇 |
1985年 | 104篇 |
1984年 | 112篇 |
1983年 | 53篇 |
1982年 | 94篇 |
1981年 | 100篇 |
1980年 | 91篇 |
1979年 | 98篇 |
1978年 | 91篇 |
1977年 | 78篇 |
1976年 | 77篇 |
1975年 | 50篇 |
1974年 | 51篇 |
1973年 | 74篇 |
排序方式: 共有8012条查询结果,搜索用时 437 毫秒
81.
Fumio Hamada Kyoko Ishikawa Riko Ito Hisanori Shibuya Sanyo Hamai Iwao Suzuki Tetsuo Osa Akihiko Ueno 《Journal of inclusion phenomena and macrocyclic chemistry》1994,20(1):43-51
-Cyclodextrin with two sodium anthranilate moieties (1) has been prepared as a sensor for detecting organic compounds including terpenoids and steroids. Compound1 shows a pure monomer fluorescence whose intensity is increased or decreased upon addition of the guest species examined. In this system, the sodium anthranilate moieties act either as a spacer, which enables the cyclodextrin to form a 1:1 host-guest complex by narrowing the -cyclodextrin cavity, or as a hydrophobic cap.1 recognizes steroids with much higher sensitivity than terpenoids, in which the appended moieties act as a hydrophobic cap for terpenoids and a spacer for steroids, respectively. 相似文献
82.
Yoshihiko Nishimori Katsuhiko Kanaizuka Dr. Masaki Murata Dr. Hiroshi Nishihara Prof. 《化学:亚洲杂志》2007,2(3):367-376
Films of linear and branched oligomer wires of Fe(tpy)2 (tpy=2,2′:6′,2′′‐terpyridine) were constructed on a gold‐electrode surface by the interfacial stepwise coordination method, in which a surface‐anchoring ligand, (tpy? C6H4N?NC6H4? S)2 ( 1 ), two bridging ligands, 1,4‐(tpy)2C6H4 ( 3 ) and 1,3,5‐(C?C? tpy)3C6H3 ( 4 ), and metal ions were used. The quantitative complexation of the ligands and FeII ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4 . STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron‐transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential‐step chronoamperometry (PSCA). The unique current‐versus‐time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox‐polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox‐complex moiety, k1 (s?1), as well as that for intrawire electron transfer between neighboring redox‐complex moieties, k2 (cm2 mol?1 s?1). The strong effect of the electrolyte concentration on both k1 and k2 indicates that the counterion motion limits the electron‐hopping rate at lower electrolyte concentrations. Analysis of the dependence of k1 and k2 on the potential gave intrinsic kinetic parameters without overpotential effects: k10=110 s?1, k20=2.6×1012 cm2 mol?1 s?1 for [n Fe 3 ], and k10=100 s?1, k20=4.1×1011 cm2 mol?1 s?1 for [n Fe 4 ] (n=number of complexation cycles). 相似文献
83.
Hiroshi Harada Kanichi Kamiya Hiroyuki Nasu Jun Matsuoka 《Journal of Sol-Gel Science and Technology》1997,10(3):291-300
The sodium dititanate, Na2O·2TiO2 glass was prepared by the sol-gel method. The structure of the glass, especially local environment of Ti4+ ions was examined using X-ray diffraction and X-ray absorption fine structure (XAFS) analyses, and was compared with that of the melt-derived glass with the same composition. It was found that Ti4+ ions are rather in five-fold coordination state, forming TiO5 pyramids with one doubly bonded Ti=O in the gel-glass, while they were in lower coordination state or four-fold coordination in the melt-derived glass. 相似文献
84.
85.
The triton binding energy, the percentages ofS, S, andD states, and the asymptotic normalization constants are presented for 5-, 18-, 26-, and 34-channel Faddeev calculations with some realistic two-nucleon potentials and the Tucson-Melbourne three-nucleon potential. For the two-nucleon interaction, we take the Reid soft-core, the Argonne, the Paris, and the de-Tourreil-Rouben-Sprung potentials. The convergence properties of these calculations are discussed in detail. It turns out that five-channel calculations are decisively insufficient. We also discuss some asymptotic properties, such as the asymptotic normalization constants, the charge radius, and the momentum distribution in the long-wave-length region. It is shown that these quantities do not depend on the specific dynamics of the system, but only on the binding energy. 相似文献
86.
Summary Pyridinium ylide complexes of methylcobaloxime were synthesized by the treatment of an ylide with Co(Hdmg)2 Me(SMe2). The crystal structure of one of the complexes, [Co(Hdmg)2Me C5H5NCHCOPh]C6H6 has been determined by x-ray diffraction techniques. The crystals are monoclinic, space group P21/c, witha = 10.456(5),b = 11.079(4),c = 24.58(1) Å, = 99.58(6), V = 2808 Å3, Z = 4. The Co-C (ylide) bond distance is 2.18 Å and Co-C(methyl) 2.04 Å. C(ylide)-Co-C(methyl) bond angle is 174.9°. The crystal, i.r. and1H n.m.r. data suggest that thetrans-influence of the ylide ligands is larger than that of py, Melm, OH2 or PPh3. 相似文献
87.
Hiroshi Saito Hitoshi Kurabe Eiichi Suzuki Fumio Watari 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1995,51(14)
The IR spectra (4000-250 cm−1) of CH3SCl and CD3SCl in solid argon have been obtained. Fundamental vibrations, except the torsional vibrations, have been assigned. Normal coordinate analysis has been carried out omitting the torsional modes. 相似文献
88.
Imahori H Fujimoto A Kang S Hotta H Yoshida K Umeyama T Matano Y Isoda S Isosomppi M Tkachenko NV Lemmetyinen H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7265-7275
Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics. 相似文献
89.
Yoshiharu Yamane Yozo Nakamura Hiroyuki Okamoto Hiroshi Ooshima Jyoji Kato 《Applied biochemistry and biotechnology》1995,50(3):317-322
Effects of pH and dissolved oxygen concentration on batchwise riboflavin production by a 5-fluorouracil (5-FU)-resistant mutant
ofArthrobacter sp. were investigated. The reaction was carried out in a jar fermentor. The optimal pH of culture medium was around 7.3.
Dissolved oxygen concentration was almost constant during fermentation at 600 rpm of agitation rate. Production of riboflavin
reached a maximum of 160 mg/L after 70 h fermentation under the agitation rate of 600 rpm, aeration rate of 1.0 L/min, and
pH 7.0. 相似文献
90.
To approach more realistic mechanisms for asymmetric aziridine synthesis from guanidinium ylides and aryl aldehydes, reactions were systematically carried out by using a variety of p-substituted benzaldehydes under modified conditions. Two kinds of reaction mechanisms controlled by the nature of the p-substituents of aryl aldehydes is proposed for the two-steps aziridine synthesis composed of a C-C bond formation by nucleophilic addition of guanidinium ylides to aryl aldehydes (step 1) and the fragmentation of intermediate adducts to aziridine products by intramolecular nucleophilic substitution (step 2). A SNi-like mechanism via cationic-like transition state is proposed for step 2 in the asymmetric synthesis using EDG-substituted benzaldehydes, whereas with EWG-substituted benzaldehydes, a SN2-like mechanism is proposed. Hammett analysis, based on the diastereomeric ratio in the aziridine products, is consistent with the proposed rate-determining steps in these two mechanisms. A second Hammett analysis, based on the enantiomeric ratio of the aziridine products, clearly reveals the difference in the susceptibilities to the electronic substituents effect between step 1 and step 2. 相似文献