全文获取类型
收费全文 | 1195篇 |
免费 | 34篇 |
国内免费 | 3篇 |
专业分类
化学 | 903篇 |
晶体学 | 9篇 |
力学 | 4篇 |
综合类 | 2篇 |
数学 | 88篇 |
物理学 | 226篇 |
出版年
2022年 | 6篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 21篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 48篇 |
2012年 | 47篇 |
2011年 | 67篇 |
2010年 | 30篇 |
2009年 | 35篇 |
2008年 | 57篇 |
2007年 | 58篇 |
2006年 | 63篇 |
2005年 | 60篇 |
2004年 | 52篇 |
2003年 | 47篇 |
2002年 | 34篇 |
2001年 | 16篇 |
2000年 | 22篇 |
1999年 | 11篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 27篇 |
1983年 | 8篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 10篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 21篇 |
1971年 | 6篇 |
排序方式: 共有1232条查询结果,搜索用时 265 毫秒
991.
Yoshiaki Shoji Naoki Tanaka Yasuhiro Ikabata Hayato Sakai Taku Hasobe Norbert Koch Hiromi Nakai Takanori Fukushima 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202113549
We report the successful synthesis of tetramesityldiborane(4) (Mes4B2) through the reductive coupling of a dimesitylborinium ion. Owing to the steric protection conferred by the mesityl groups, Mes4B2 shows exceptional chemical stability and remains intact in water. Single-crystal X-ray analysis revealed that Mes4B2 has an orthogonal geometry, where the B–B center is completely hidden by the mesityl groups. Remarkably, Mes4B2 emits dual fluorescence at 460 and 620 nm, both in solution and in the solid state. Theoretical calculations showed that Mes4B2 in the excited S1 state adopts a twisted or planar geometry, which is responsible for the shorter- or longer-wavelength fluorescence, respectively. The intensity ratio of the dual fluorescence is sensitive to the viscosity of the medium, which suggests that Mes4B2 has potential as a ratiometric viscosity sensor. 相似文献
992.
A variety of Reformatsky reagents were added five times to [60]fullerene in good yield in the presence of a stoichiometric amount of a copper(I) complex. The penta-addition products C60(CH2CO2R)5H (R=Et, t-Bu, CH2CF3, (CH2CH2O)2Et, and CH2CH2CCSiMe3) can then be converted to the corresponding penta-hapto metal complexes. When the R group is a (-)-menthyl group, the corresponding metal complex comprises an organometallic complex with a coordination sphere consisting of a homochiral C5-symmetric environment. 相似文献
993.
Indium-catalyzed addition of 1,3-dicarbonyl compounds to 1-iodo-1-alkynes takes place exclusively in a syn-fashion to produce E-iodoalkenes. The iodine atom serves both as an activating group and as a group that controls the regioselectivity of the addition. The E-alkenyl iodide product can be further derivatized using either a one-pot or a two-pot procedure into trisubstituted olefins in high overall yield with retention of the stereochemistry. 相似文献
994.
A methylcellulose-immobilized weak cation-exchange (MC-WCX) silica-based restricted-access material (RAM) was developed. The MC-WCX consists of an MC outer surface and 2-carboxyethyl phase internal surface, allowing for direct analysis of basic drugs in plasma. The retention properties of the MC-WCX were evaluated for sulpiride, quinidine, ranitidine, and desipramine. The MC-WCX retained model drugs by cation-exchange, and retained drugs were eluted with the mobile phase containing small amount of acids or salts compared with the MC strong cation-exchanger (MC-SCX). These results indicated the ease of use of the MC-WCX solid-phase extraction (SPE) column when coupled to a reversed-phase analytical column in column-switching high-performance liquid chromatography (HPLC), and various detection principals. Further direct analysis of model drugs in plasma using the MC-WCX SPE column in a column-switching HPLC system successfully performed with sufficient recovery. It is concluded that the MC-WCX is useful for the analysis of basic drugs in plasma. 相似文献
995.
Koutarou Idegami Miyuki Chikae Kagan Kerman Naoki Nagatani Teruko Yuhi Tatsuro Endo Eiichi Tamiya 《Electroanalysis》2008,20(1):14-21
A sensitive immunosensor for the detection of pregnancy marker, human chorionic gonadotropin hormone (hCG), was developed using the direct electrical detection of Au nanoparticles. We utilized disposable screen‐printed carbon strips (SPCSs) for the development of our immunosensor, which provided cost‐effective tests with the required antigen sample volume as small as 2 μL. After the recognition reaction between the surface‐immobilized primary antibody and hCG, the captured antigen was sandwiched with a secondary antibody that was labeled with Au nanoparticles. Au nanoparticles were exposed to a preoxidation process at 1.2 V for 40 s, which was subsequently followed with a reduction scan on the same surface using differential pulse voltammetry (DPV). We could observe Au nanoparticle‐labeled antigen‐antibody complexes immobilized on the surface of SPCS using scanning electron microscopy (SEM). Additionally, the number of Au nanoparticles on the immunosensor was determined using SEM images, and showed a linear relationship with the current intensity obtained from the DPV measurements with a detection limit of 36 pg/mL hCG (612 fM, 3.6×10?4 IU/mL). Our immunosensor system, a combination of the screen‐printing technology with Au nanoparticles provides a promising biosensor for various applications in life sciences. 相似文献
996.
Akito Nakai Shin‐ichiro Ishida Takanori Soya Atsuhiro Osuka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(24):8281-8284
Ruthenium(II) π‐coordination onto [28]hexaphyrins(1.1.1.1.1.1) has been accomplished. Reactions of bis‐AuIII and mono‐AuIII complexes of hexakis(pentafluorophenyl) [28]hexaphyrin with [RuCl2(p‐cymene)]2 in the presence of NaOAc gave the corresponding π‐ruthenium complexes, in which the [(p‐cymene)Ru]II fragment sat on the deprotonated side pyrrole. A similar reaction of the bis‐PdII [26]hexaphyrin complex afforded a triple‐decker complex, in which the two [(p‐cymene)Ru]II fragments sat on both sides of the center of the [26]hexaphyrin framework. 相似文献
997.
Chien‐Pin Chou Aditya Wibawa Sakti Yoshifumi Nishimura Hiromi Nakai 《Chemical record (New York, N.Y.)》2019,19(4):746-757
The density‐functional tight‐binding (DFTB) method is one of the useful quantum chemical methods, which provides a good balance between accuracy and computational efficiency. In this account, we reviewed the basis of the DFTB method, the linear‐scaling divide‐and‐conquer (DC) technique, as well as the parameterization process. We also provide some refinement, modifications, and extension of the existing parameters that can be applicable for lithium‐ion battery systems. The diffusion constants of common electrolyte molecules and LiTFSA salt in solution have been estimated using DC‐DFTB molecular dynamics simulation with our new parameters. The resulting diffusion constants have good agreement to the experimental diffusion constants. 相似文献
998.
5,20‐Bis(ethoxycarbonyl)‐[28]hexaphyrin was synthesized by acid catalyzed cross‐condensation of meso‐diaryl‐substituted tripyrrane and ethyl 2‐oxoacetate followed by subsequent oxidation. This hexaphyrin was found to be a stable 28π‐antiaromatic compound with a dumbbell‐like conformation. Upon oxidization with PbO2, this [28]hexaphyrin was converted into an aromatic [26]hexaphyrin with a rectangular shape bearing two ester groups at the edge side. The [28]hexaphyrin can incorporate two NiII or CuII metals by using the ester carbonyl groups and three pyrrolic nitrogen atoms to give bis‐NiII and bis‐CuII complexes with essentially the same dumbbell‐like structure. The antiaromatic properties of the [28]hexaphyrin and its metal complexes have been well characterized. 相似文献
999.
Ion C. Baianu Thomas F. Kumosinski Adela Mora-Gutierrez Eiichi M. Ozu T. S. Lioutas P. J. Bechtel 《Macromolecular Symposia》1999,140(1):225-244
The mechanisms for the anionic and cationic interactions with myofibrillar proteins in aqueous solutions were investigated by nuclear magnetic resonance over a wide range of salt concentration. Markedly nonlinear dependeces of the 17O and 23Na NMR transverse relaxation rates on salt concentration were analyzed with a thermodynamic linkage model of salt-dependent solubility and hydration (ligand-induced association model), according to Wyman's theory of linked functions. Nonlinear regression analysis of both 17O and 23Na NMR data suggested cooperative, reversible binding of hydrated ions to myofibrillar proteins. Both ions and water were found to exchange fast, on the NMR timescale, between the binding sites of the myofibrillar proteins and the aqueous solution. At sodium chloride concentrations higher than about 0.1 grams salt/gram water, ion activities have marked effects upon the NMR relaxation rates of both ions and water. A salt activity model allowed quantitative fitting of the NMR data at high salt concentrations. The effect of neglecting the ion activity in solutions of myofibrillar proteins was also estimated and compared with the ligand-induced, cooperative association model for myofibrillar proteins. The comparison between the 17O and 23Na results strongly suggests that water is exchanged as the hydrated ion species between the myofibrillar protein binding sites and the bulk, aqueous solution. 相似文献
1000.
Eiichi Kobayashi Shojiro Kaita Sadahito Aoshima Junji Furukawa 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2283-2290
Homopolymerizations of butadiene (BD), isoprene (IP), and 2,3-dimethylbutadiene (DMBD) were carried out by a Gd(OCOCCl3)3-based catalyst, to investigate the effects of the energy levels of the monomers or the sterical factor of the methyl substituents on the polymerizability and the cis-selectivity of the monomers. The order of the polymerizability at 50°C was as follows: BD (4.5 kg of polymer/(mol of Gd h)) ∼ IP (4.8) > DMBD (0.6). On the other hand, the cis-selectivity of the polymers was as follows: BD (98%) > IP (94%) > DMBD (35%). These results suggest that the terminal BD and IP units are controlled by the cis configuration by the coordination between the penultimate cis-vinylene unit and the catalyst metal, whereas the penultimate DMBD unit unfavorably controls the terminal DMBD unit to the cis-1,4 configuration through the back-biting coordination with difficulty by two methyl substituents compared with the penultimate BD and IP units. The validity of the back-biting coordination was examined by MO calculation with σ-allylnickel complexes. According to the formation energy with respect to the BD–BD diad, the cis–cis form is somewhat preferable to the trans–cis form through the coordination of the penultimate BD unit by ΔE = 0.028 au (ca. 17.6 kcal/mol). © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2283–2290, 1998 相似文献