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排序方式: 共有1038条查询结果,搜索用时 15 毫秒
21.
Zhao S Prasad C Robertson HJ Liu YM 《Fresenius' Journal of Analytical Chemistry》2001,369(3-4):220-224
A capillary electrophoresis (CE) method with laser induced fluorescence (LIF) detection is described for quantification of enterostatin (Val-Pro-Asp-Pro-Arg), a pentapeptide involved in appetite regulation and insulin secretion. Enterostatin and two other pentapeptides belonging to the enterostatin family (i.e. Ala-Pro-Gly-Pro-Arg and Val-Pro-Gly-Pro-Arg) were well separated from each other. The peptides were fluorescently tagged with naphthalene-2,3- dicarboxaldehyde (NDA) and separated by micellar electrokinetic chromatography (MEKC) in the presence of methanol as an organic modifier. Coupled with LIF detection, the method had a detection limit of 4.8 x 10(-6) M for enterostatin. The relative standard deviation was to be 4.0% from five determinations of enterostatin at 37.2 microM in a human cerebrospinal fluid (CSF) sample. Twenty-three human CSF samples were analyzed. The level of enterostatin ranged from 24 microM to 51 microM with a mean (+/- SEM) value of 41.7 +/- 2.0 microM. 相似文献
22.
J. K. Haywood I. Robertson K. Boddy 《Journal of Radioanalytical and Nuclear Chemistry》1979,48(1-2):117-124
A 14 MeV neutron generator system with a new sealed tube (Philips 18604) was evaluated for total body in vivo neutron activation
analysis (TBIVNAA). The neutron output, angular distribution, rise time, reproducibility of short irradiations and leakage
of tritium were investigated. The 18604 tube meets all the requirements of TBIVNAA within its normal operating specification. 相似文献
23.
A. E. Veatch J. D. Brockman V. L. Spate J. D. Robertson J. S. Morris 《Journal of Radioanalytical and Nuclear Chemistry》2005,264(1):33-38
Summary Selenium is a required trace-element that has been found to be protective against serious chronic diseases such as cancer and cardiovascular disease in some, but not all, epidemiological studies using both case-control and intervention designs. As a result, the fraction of the adult U.S. population now taking a daily selenium supplement is steadily increasing. In this study, we analyzed 10 or more replicate Se supplement tablets, from each of 15 different products representing 12 different brand names with most being sampled at two different times separated by approximately 30 months. Two chemical forms, seleno-yeast and selenate were tested in 50, 100 and 200 µg/tablet dosages (seleno-yeast) and 25 and 200 µg/tablet dosages (selenate). Variations in contemporary lots were evaluated at both sampling periods. The Se content provided on the product label is generally understated. One tablet contained 2.5 times more selenium than the stated dose. Selenate supplements are less accurately labeled and more highly variable compared to yeast supplements. One popular multivitamin, labeled at 200 µg/tablet, contained tablets in excess of 300 µg. Many subjects using this supplement will exceed the 400 µg/day tolerable upper limit of intake, recently established, for Se by the Institute of Medicine’s Food and Nutrition Board. 相似文献
24.
Katherine E. BashfordMatthew B. Burton Stuart CameronAnthony L. Cooper Rebecca D. HoggPeter D. Kane David A. MacManusChristopher A. Matrunola Christopher J. Moody Avril A.B. Robertson Mark R. Warne 《Tetrahedron letters》2003,44(8):1627-1629
The Bohlmann-Rahtz reaction has been used to prepare 2,3,6-trisubstituted pyridines suitable for use in library synthesis. The synthesis of piperidine substituted nicotinic acid derivative 9 has been optimised and carried out on a large scale to give ca. 500 g of scaffold which was used in the generation of the pyridine library 11. 相似文献
25.
J. M. Hammond J. F. Hooper W. G. P. Robertson 《Journal of polymer science. Part A, Polymer chemistry》1971,9(2):295-298
Polymerization of various cyclic ethers by BF3·O(C2H5)2 in the presence of polymeric glycol leads to the formation of hydroxyl terminated block copolymers. Where poly(oxyethylene glycol) is used as the polymeric glycol, fission of the poly(oxyethylene glycol) chain occurs, and block copolymers, containing shorter ethylene oxide unit sequences are obtained. With poly(oxypropylene glycol), on the other hand, the polymer chain remains intact. This may be due to the steric influence of the pendant methyl groups. The cyclic oligomers formed as by-products in the polymerizations are easily removed. 相似文献
26.
Cronin L McGregor PA Parsons S Teat S Gould RO White VA Long NJ Robertson N 《Inorganic chemistry》2004,43(25):8023-8029
The "one-pot" synthesis and characterization of a large 28-mer macrocycle (H(4)L(2)) with oxamido units capable of complexing guest ions through oxygen or nitrogen donor atoms is reported. Single-crystal structure determination of H(8)L(2)(NO(3))(4) and (Cu(2)[H(2)L(2)](H(2)O)(2))(NO(3))(2) demonstrated that the macrocycle contains two sites capable of complexing two nitrate anions or two copper(II) ions, involving a large structural reorganization in the conformation of the macrocyclic framework on coordination of the copper(II) ions when compared to the nitrate. Electrochemical and magnetic susceptibility measurements on the dinuclear Cu(II) complex and the related mononuclear and trinuclear Cu(II) complexes derived from the related 14-mer macrocycle were carried out and illustrate the role of the oxamido groups in mediating metal-metal interaction and delocalization. 相似文献
27.
The molecular structures of the title compounds have been determined by gas phase electron diffraction methods. The SiMn and GeMn bond lengths are 240.7 ? 0.5 and 248.7 ? 0.2 pm respectively and the CMnC angles in the silyl and germyl cases are 94.5 ± 2° and 97 ± 2° respectively. Comparisons are made with the reported structure of CH3Mn(CO)5 and HeI photoelectron spectra of these compounds in an attempt to determine the extent of d → d π-bonding in the SiMn or GeMn bonds. 相似文献
28.
Susan Robertson David Ellis Georgina M. Rosair Alan J. Welch 《Journal of organometallic chemistry》2003,680(1-2):286-293
The reaction of the labelled carborane ligand [3-Et-7,8-Ph2-7,8-nido-C2B9H8]2− with a source of {Pt(PMe2Ph)2}2+ affords non-isomerised 1,2-Ph2-3,3-(PMe2Ph)2-6-Et-3,1,2-closo-PtC2B9H8 (1). The analogous reaction between [3-F-7,8-Ph2-7,8-nido-C2B9H8]2− and {Pt(PMe2Ph)2}2+ yields 1,8-Ph2-2,2-(PMe2Ph)2-4-F-2,1,8-closo-PtC2B9H8 (3). Compound 1 has a heavily slipped structure (Δ 0.72 Å), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph2-2,2-(PMe2Ph)2-4-Et-2,1,8-closo-PtC2B9H8 (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB2 face of an intermediate based on the structure of 1. Compounds 1–3 were characterised by a combination of spectroscopic and crystallographic techniques. 相似文献
29.
考虑立体活性孤对电子附近次级键配位原子的贡献, 对文献报道的三十个氨基多羧酸锑(III)螯合物的晶体结构中配位多面体描述进行了全面的修正. 配位多面体的几何构型指定采用了单位球内截多面体的两面角判据及其相关的ANVPDA程序. 所有配位多面体几何构型的修正均得到了键价计算的有力支持. 相似文献
30.
Aucott SM Kilian P Milton HL Robertson SD Slawin AM Woollins JD 《Inorganic chemistry》2005,44(8):2710-2718
Titanocene 1,8-dithiolato-naphthalene and titanocene 2,2'-dithiolato biphenyl are produced by the reaction of naphtho[1,8-cd]-1,2-dithiole [or the biphenyl] with titanocene dicarbonyl (Ti(II)) in toluene at room temperature. The pro-ligands 2,7-di(tert-butyl)naphtho[1,8-cd]-1,2-dithiole, 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole, 4,5-dithioacephenanthrylene, and 13,14-dithiapicene have been used in similar reactions with titanocene dicarbonyl to investigate the effect of steric bulk and of varying the naphthalene backbone on the final complex. The resulting Cp(2)TiS(2)Ar complexes (Ar = naphthalene) have been shown by temperature-dependent (1)H NMR spectroscopy to exist in solution in an envelope conformation with the six-membered TiS(2)C(3) rings undergoing inversion on the NMR time scale while the similar Cp(2)TiS(2)Ar complexes (Ar = biphenyl, binaphthalene) interconvert more rapidly. Titanocene 2,2'-disulfinato biphenyl has been synthesized by the salt elimination reaction of titanocene dichloride (Ti(IV)) and the disodium salt of biphenyl 2,2'-disulfinic acid. Finally, the effect of using pro-ligands where the sulfur atoms have been mono- or di-oxidized has been studied, and an interesting oxygen elimination reaction is observed for the S=O fragments but not for the SO(2) groups. All complexes have been characterized spectroscopically and seven X-ray structures are reported. 相似文献