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71.
72.
定义了拓扑指数Si(i=1,2,3,4),并选取包含双、三键、环及苯环的碳氢化合物为研究对象,计算了这些化合物的拓扑指数Si,同时用Si相关了它们的沸点.结果较文献值有所改善.并从Si中筛选出了S 相似文献
73.
Hongyuan Wang Toshinari Ugomori Yong Wang Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto Yasunori Suma 《Journal of Polymer Science.Polymer Physics》2000,38(13):1800-1811
Poly(ethylene oxide imide) segmented copolymer (PEO‐PI) membranes were crosslinked by the chemical reaction between ethylene glycol diglycidyl ether and benzylalcohol groups of diamine moieties in polyimide segments at high temperatures. Sorption and diffusion of penetrants took place in poly(ethylene oxide) segment microdomains. Sorption and desorption behavior of pure vapors such as benzene (Bz), cyclohexane (Cx) and n‐hexane (Hx) was classified as the Fickian diffusion. Sorption isotherms of binary liquid mixtures could be represented by the Flory–Rehner model, but the model overpredicted the sorption amounts of Cx and Hx, leading to small predictions of sorption selectivity αS for Bz/Cx and Bz/Hx systems. UNIFAC‐FV model fairly well predicted the sorption amounts of aromatic hydrocarbons, but significantly overestimated those of nonaromatic ones, leading to too small predictions of αS. Pervaporation (PV) behavior of PEO‐PI membranes was governed by sorption behavior followed by membrane swelling. Diffusion coefficient weakly depended on the minimum cross section of a penetrant. The diffusivity selectivity αD hardly depended on the feed composition and was about 1.4 and 0.75 for Bz/Cx and Bz/Hx, respectively. PV selectivity αPV was larger for Bz/Hx than for Bz/Cx because of larger αS. PEO‐PI membranes displayed high specific permeation flux Ql and reasonably high αPV for aromatic/nonaromatic hydrocarbons; for example, Ql = 60 Kg μm/(m2 h) and αPV = 8 for a feed mixture containing Bz, Tol, Hx, n‐Ot and i‐Ot of 20 wt % at 353 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1800–1811, 2000 相似文献
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A straightforward chiral pool synthesis for the glycosidase inhibitor calystegine A7 (isolated from Lycium chinense) from methyl α-d-glucopyranoside is described. Keysteps of this synthesis include a ultrasound assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst mediated ring closure metathesis. 相似文献
76.
Xiao-Tao Chen Bishan Zhou Samit K. Bhattacharya Clare E. Gutteridge Thomas R. R. Pettus Samuel J. Danishefsky 《Angewandte Chemie (International ed. in English)》1998,37(6):789-792
An “sp 2 –sp 3 Stille coupling” of the vinyl triflate 1 and the stannyl compound 2 is a key step toward the completion of the total synthesis of eleutherobin, a natural product exhibiting taxol-like cytotoxic activity. 相似文献
77.
Fernando P. Carvalho Jean-Pierre Villeneuve Chantal Cattini 《Trends in analytical chemistry : TRAC》1999,18(11):1005-664
A seaweed sample (Fucus sp.) was prepared, homogenised and distributed to laboratories worldwide as the IAEA-140 intercomparison material for the analysis of organochlorine compounds and petroleum hydrocarbons. A total of 80 laboratories from 51 countries reported results for this sample. The data sets reported by laboratories were evaluated statistically and the mean concentration values could be computed with 95% confidence limits for a large number of analytes. The accuracy of the analytical performance of each laboratory has been introduced by using Z-scores. The spread of results reported generally indicates that the accurate determination of many persistent organic pollutants, such as hexachlorobenzene, lindane, Aroclors or fluoranthene, is still difficult for many laboratories. The final results of this intercomparison exercise enable individual participants to assess their performance and, where necessary, to introduce appropriate modifications in their analytical procedures. Furthermore, as a series of statistical criteria was fulfilled for a number of compounds, the sample IAEA-140 can now be used as a reference material for quality control in the determination of chlorinated compounds and petroleum hydrocarbons in environmental samples. 相似文献
78.
Enkhbayar P Damdinsuren S Osaki M Matsushima N 《Computational Biology and Chemistry》2008,32(4):307-310
The problem of fitting a helix to data arises in analysis of protein structure, in nuclear physics, and in engineering. A continuous helix is described by five parameters: helix axis, helix radius, and helix pitch. One of these helix parameters is frequently predefined in the helix fitting. Other algorithms find only the helix axis or determine separately the helix axis, the helix radius, or the helix pitch. Here we describe a total least squares method, HELFIT, for helix fitting. HELFIT enables one to calculate simultaneously all five of the helix parameters with high accuracy. The minimum number of data points required for the analysis is only four. HELFIT is very insensitive to noise even in short helices. HELFIT also calculates a parameter, p = rmsd/(N − 1)1/2, which estimates the regularity of helical structures independent of the number of data points, where rmsd is the root mean square distance from the best-fit helix to data points and N is the number of data points. It should become a basic tool of structural bioinformatics. 相似文献
79.
(±)‐Eusiderin G and (±)‐Eusiderin M were first synthesized from pyrogallol, in which the Claisen Rearrangement was used to afford two important C6‐C3 units. 相似文献
80.