全文获取类型
收费全文 | 29520篇 |
免费 | 1058篇 |
国内免费 | 167篇 |
专业分类
化学 | 19713篇 |
晶体学 | 279篇 |
力学 | 1005篇 |
综合类 | 1篇 |
数学 | 2699篇 |
物理学 | 7048篇 |
出版年
2023年 | 161篇 |
2022年 | 434篇 |
2021年 | 526篇 |
2020年 | 477篇 |
2019年 | 489篇 |
2018年 | 414篇 |
2017年 | 392篇 |
2016年 | 839篇 |
2015年 | 692篇 |
2014年 | 903篇 |
2013年 | 1645篇 |
2012年 | 2115篇 |
2011年 | 2336篇 |
2010年 | 1439篇 |
2009年 | 1269篇 |
2008年 | 1922篇 |
2007年 | 1806篇 |
2006年 | 1679篇 |
2005年 | 1535篇 |
2004年 | 1360篇 |
2003年 | 1054篇 |
2002年 | 1032篇 |
2001年 | 715篇 |
2000年 | 638篇 |
1999年 | 371篇 |
1998年 | 281篇 |
1997年 | 312篇 |
1996年 | 343篇 |
1995年 | 270篇 |
1994年 | 281篇 |
1993年 | 283篇 |
1992年 | 271篇 |
1991年 | 210篇 |
1990年 | 159篇 |
1989年 | 146篇 |
1988年 | 142篇 |
1987年 | 125篇 |
1986年 | 100篇 |
1985年 | 171篇 |
1984年 | 116篇 |
1983年 | 104篇 |
1982年 | 126篇 |
1981年 | 92篇 |
1980年 | 80篇 |
1978年 | 84篇 |
1977年 | 88篇 |
1976年 | 99篇 |
1975年 | 104篇 |
1974年 | 85篇 |
1973年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Miklos Kertesz Yong S. Lee James J. P. Stewart 《International journal of quantum chemistry》1989,35(2):305-313
It is shown that infinite long polyacene chains may have three energetically close but structurally distinct isomers (a symmetrical, sym, form and two lower symmetry forms: one with double bonds in a trans and another isomer with double bonds in a cis pattern). The energetics is based on solid state MNDO theory. We discuss that the symmetrical form has a substantial energy gap Eg in the Hartree–Fock approach owing to exact exchange terms, which are nonlocal. Broken symmetry Hartree–Fock (HF ) solutions for polyacene are also described. An angularly distorted structure suggested earlier on Jahn–Teller grounds is found to be energetically not favorable. 相似文献
992.
Asao N Takahashi K Lee S Kasahara T Yamamoto Y 《Journal of the American Chemical Society》2002,124(43):12650-12651
The reaction of o-alkynylbenzaldehydes 1 and alkynes 2 in the presence of a catalytic amount of AuCl3 in (CH2Cl)2 at 80 degrees C gave naphthyl ketone products in high yields. The AuCl3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuCl3, the formation of benzo[c]pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the Diels-Alder addition of alkynes 2 to the auric ate complex, and subsequent bond rearrangement. Similarly, the AuCl3-catalyzed reactions of o-alkynylacetophenone and o-alkynylbenzophenone with phenylacetylene afforded the corresponding naphthyl ketone products in good yields. 相似文献
993.
994.
995.
J. W. Lee S. J. Pearton C. J. Santana E. S. Lambers C. R. Abernathy W. S. Hobson F. Ren 《Plasma Chemistry and Plasma Processing》1996,16(3):365-378
Electron cyclotron resonance (ECR) plasma etching with additional rf-biasing produces etch rates 2,500 A/min for InGaP and AlInP in CH4/H2/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N2 addition to CH4/H2/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AlInP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to 200 Å from the sur face relative to the RIE samples. 相似文献
996.
Ogawa AK DeMattei JA Scarlato GR Tellew JE Chong LS Armstrong RW 《The Journal of organic chemistry》1996,61(18):6153-6161
We report our synthesis of the C(26)-C(37) fragment of serine/threonine protein phosphatase PP1 and PP2A inhibitor calyculin C (1). Outlined in this paper are synthetic approaches to the two components based on disconnection at the C(33)-N(3) amide bond. We report the successful synthesis of the C(33)-C(37) aza-sugar derived from D-lyxose which was coupled onto a C(26)-C(32) aminooxazole originating from L-pyroglutamic acid. Elaboration of the resulting amide to a fully deprotected C(26)-C(37) fragment of calyculin C completed our synthesis. This provided an appropriate phosphonium salt for use in a Wittig olefination for joining both halves of the natural product. 相似文献
997.
S. M. Fields R. C. Kong J. C. Fieldsted M. L. Lee P. A. Peaden 《Journal of separation science》1984,7(6):312-318
Fused silica capillary columns with internal diameters from 100 to 25 μm were coated with SE-54 and evaluated under supercritical fluid chromatographic conditions using carbon dioxide as mobile phase. Experimental results compared well with theoretical predictions. At ten times the optimum mobile phase velocity and for a capacity factor, k of 3, efficiencies of 2300 to 5600 plates m?1 were obtained for column diameters of 100 to 25 μm, respectively. 相似文献
998.
Marumo A Kumazawa T Lee XP Fujimaki K Kuriki A Hasegawa C Sato K Seno H Suzuki O 《Journal of AOAC International》2005,88(6):1655-1660
Seven phenothiazine derivatives, perazine, perphenazine, prochlorperazine, propericiazine, thioproperazine, trifluoperazine, and flupentixol, have been found to be extractable from human plasma and urine samples using disk solid-phase extraction (SPE) with an Empore C18 cartridge. Human plasma and urine (1 mL each) containing the 7 phenothiazine derivatives were mixed with 2 mL of 0.1M NaOH and 7 mL distilled water and then poured into the disk SPE cartridges. The drugs were eluted with 1 mL chloroform- acetonitrile (8 + 2) and determined by liquid chromatography with ammonium formate/formic acid-acetonitrile gradient elution. The detection was performed by ultraviolet absorption at 250 nm. The separation of the 7 phenothiazine derivatives from each other and from impurities was generally satisfactory using a SymmetryShield RP8 column (150 x 2.1 mm id, 3.5 microm particle size). The recoveries of the 7 phenothiazine derivatives spiked into plasma and urine samples were 64.0-89.9% and 65.1-92.1%, respectively. Regression equations for the 7 phenothiazine derivatives showed excellent linearity, with detection limits of 0.021-0.30 microg/mL for plasma and 0.017-0.30 microg/mL for urine. The within-day and day-to-day coefficients of variation for both samples were commonly below 9.0 and 14.9%, respectively. 相似文献
999.
Michelin SE Oliveira HL Kroin T Soares LS Veiteinheimer E Luz CA Lima MF Fujimoto MM Lee MT 《The Journal of chemical physics》2005,122(9):094309
In this work, we present a theoretical study on elastic electron collisions from three isoelectronic free radicals (CNN, NCN, and CCO) in the low incident energy range. More specifically, calculated differential, integral, and momentum transfer cross sections are reported in the 1-30 eV energy range. Calculations are performed in the static-exchange and static-exchange-polarization levels. The iterative Schwinger variational method is used to solve the scattering equations. Our study reveals that the calculated cross sections for the three targets are significantly different at incident energies below 10 eV. Above that energy, a remarkable similarity among the calculated results is seen. 相似文献
1000.
Kim MK Oh S Lee JH Im H Ryu YM Oh E Lee J Lee E Sul D 《Experimental & molecular medicine》2004,36(5):396-410
In this study, we investigated the effects of PAHs and dioxin on mRNA and plasma protein expression using genomic and proteomic analysis for automobile emission inspectors and waste incineration workers. About 54 workers from automobile emission inspection offices, 31 workers from waste incinerating company and 84 unexposed healthy subjects were enrolled in this study. Urine and air samples were collected and analyzed by HPLC and GC/MS. Comet assays were carried out to evaluate any DNA damage in mononuclear and polynuclear cells. A significant difference in Olive tail moments in mononuclear cells was observed between exposed and control subjects (P < 0.0001). To examine the differences of the gene expression profile in automobile emission inspectors and waste incineration workers, radioactive complementary DNA microarrays were used to evaluate changes in the expression of 1,152 total genes. The gene expression profiles showed that 11 genes were up-regulated and 4 genes were down-regulated in waste incinerating workers as compared with controls. Plasma proteins were analyzed by 2-dimentional electrophoresis with pH 3-10 NL IPG Dry strip. The protein expression profiles showed that 8 proteins were up- regulated and 1 protein, haptoglobin, was down- regulated in automobile emission inspectors and waste incineration workers. Serum paraoxonase/ arylesterase was found only in the plasma of waste incineration workers. The expression of genes and proteins involved in oxidative stress were up-regulated in both automobile emission inspectors and waste incineration workers. Several proteins, such as transthyrethin, sarcolectin and haptoglobin, that were highly up- or down-regulated, could serve as biological monitoring markers for future study. 相似文献