全文获取类型
收费全文 | 31279篇 |
免费 | 195篇 |
国内免费 | 273篇 |
专业分类
化学 | 12344篇 |
晶体学 | 292篇 |
力学 | 1441篇 |
综合类 | 12篇 |
数学 | 9039篇 |
物理学 | 8619篇 |
出版年
2021年 | 60篇 |
2020年 | 83篇 |
2019年 | 76篇 |
2018年 | 1224篇 |
2017年 | 1464篇 |
2016年 | 774篇 |
2015年 | 604篇 |
2014年 | 518篇 |
2013年 | 759篇 |
2012年 | 3243篇 |
2011年 | 2442篇 |
2010年 | 1842篇 |
2009年 | 1610篇 |
2008年 | 683篇 |
2007年 | 715篇 |
2006年 | 739篇 |
2005年 | 4528篇 |
2004年 | 4012篇 |
2003年 | 2374篇 |
2002年 | 555篇 |
2001年 | 343篇 |
2000年 | 145篇 |
1999年 | 204篇 |
1998年 | 121篇 |
1997年 | 87篇 |
1996年 | 73篇 |
1995年 | 75篇 |
1994年 | 71篇 |
1993年 | 48篇 |
1992年 | 213篇 |
1991年 | 184篇 |
1990年 | 174篇 |
1989年 | 153篇 |
1988年 | 136篇 |
1987年 | 91篇 |
1986年 | 69篇 |
1985年 | 92篇 |
1984年 | 80篇 |
1983年 | 44篇 |
1982年 | 50篇 |
1979年 | 68篇 |
1978年 | 55篇 |
1977年 | 41篇 |
1976年 | 110篇 |
1975年 | 58篇 |
1974年 | 56篇 |
1973年 | 61篇 |
1972年 | 45篇 |
1969年 | 42篇 |
1968年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
981.
Janina Lulek Maurycy Opielewicz Katarzyna Szyrwińska Bart?omiej Milanowski 《Analytica chimica acta》2005,540(1):25-31
The database of the relative retention times (RRTs) of polychlorinated biphenyls (PCBs) reported in literature was used to calculate the retention indices (RIs) of all 209 PCB congeners on temperature programmed capillary column Rtx-5. Calculation of retention indices was based on reference series of seven congeners (PCB IUPAC Nos. 18, 52, 101, 143, 185, 203 and 206) that exhibit linear relative retention time behaviour as a function of chlorine number. The calculated indices were compared to those determined in our laboratory as well as to those obtained by other authors. The proposed indices system was applied for identification individual congeners in mixture of Aroclors 1242:1254:1260, using only reference series of PCBs. 相似文献
982.
San Vicente B Navarro Villoslada F Moreno-Bondi MC 《Analytical and bioanalytical chemistry》2004,380(1):115-122
A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10–100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL–1, respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL–1); relative standard deviations (RSD) were lower than 5.0%. 相似文献
983.
Hiroshi Hata Dr. Shigeru Yamaguchi Goro Mori Satomi Nakazono Taisuke Katoh Keishi Takatsu Satoru Hiroto Hiroshi Shinokubo Prof. Dr. Atsuhiro Osuka Prof. Dr. 《化学:亚洲杂志》2007,2(7):849-859
Highly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through C? H bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs. 相似文献
984.
H. Spieler H. J. K?rner K. E. Rehm M. Richter H. P. Rother 《Zeitschrift für Physik A Hadrons and Nuclei》1976,53(5):241-250
The reactions120Sn+72 MeV18O and122Sn+74 MeV16O were investigated with time of-flightE-E-telescopes. Data are presented for all quasi-elastic reaction channels. The two neutron stripping and pickup reactions (18O,16O), (18O,20O) and (16O,18O) are analyzed in detail. It is shown that these heavy ion induced two neutron transfer reactions proceed with essentially the same type of selectivity as the corresponding light ion induced reactions. The differential cross sections for transfer reactions leaving the120, 122Sn nuclei in their 2+ first excited states are shown to be influenced by interference effects due to additional inelastic excitations. 相似文献
985.
I. Tserruya R. Schulé H. Schmidt-B?cking K. Bethge 《Zeitschrift für Physik A Hadrons and Nuclei》1976,89(1):233-241
TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under32S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK
- andK
-lines and theK
/K
-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed. 相似文献
986.
987.
988.
Lubomír Kubá?ek 《Mathematica Slovaca》2012,62(4):765-774
An uncertainty of an estimated parameter can be, in general, decomposed into two parts, i.e. an uncertainty caused by errors in the actual experiment (the type A uncertainty) and an uncertainty caused by errors in preceding experiment, where some wanted constants were estimated (the type B uncertainty). These constants are necessary for an estimation of the useful parameters. The aim of the paper is to find a condition for elimination of the type B uncertainty. 相似文献
989.
990.
I. P. Studenyak V. E. Ponomaryov M. Kranj?ec Yu. V. Minets L. M. Suslikov 《Journal of Applied Spectroscopy》2012,79(1):83-86
The effect of anionic substitution of halogen atoms on the spectral position and shape of the optical absorption edge and
the dispersion of the refractive index of crystals of Cu6PS5I1–xClx solid solutions are studied. The concentration dependences of the width of the optical pseudogap, refractive index, and lattice
parameters are shown to be interrelated in these solid solution crystals. 相似文献