全文获取类型
收费全文 | 9950篇 |
免费 | 1896篇 |
国内免费 | 1535篇 |
专业分类
化学 | 7852篇 |
晶体学 | 141篇 |
力学 | 619篇 |
综合类 | 94篇 |
数学 | 1327篇 |
物理学 | 3348篇 |
出版年
2024年 | 17篇 |
2023年 | 153篇 |
2022年 | 210篇 |
2021年 | 314篇 |
2020年 | 370篇 |
2019年 | 430篇 |
2018年 | 351篇 |
2017年 | 310篇 |
2016年 | 518篇 |
2015年 | 591篇 |
2014年 | 604篇 |
2013年 | 759篇 |
2012年 | 892篇 |
2011年 | 894篇 |
2010年 | 717篇 |
2009年 | 680篇 |
2008年 | 714篇 |
2007年 | 581篇 |
2006年 | 518篇 |
2005年 | 486篇 |
2004年 | 440篇 |
2003年 | 401篇 |
2002年 | 510篇 |
2001年 | 423篇 |
2000年 | 265篇 |
1999年 | 221篇 |
1998年 | 188篇 |
1997年 | 133篇 |
1996年 | 120篇 |
1995年 | 108篇 |
1994年 | 84篇 |
1993年 | 67篇 |
1992年 | 55篇 |
1991年 | 56篇 |
1990年 | 34篇 |
1989年 | 28篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
<正>LiCl-promoted superbase catalysts were found to be stable and highly selective to ethene for oxidative dehydrogenation of ethane,giving 84%ethane conversion and 74%ethene yield at 923 K.Results indicated that the stronger the basicity of LiC1-based catalysts,the better the catalytic performance. 相似文献
992.
We continue our study on arithmetical Fourier series by considering two Fourier series which are related to Diophantine analysis. The first one was studied by Hardy and Littlewood in connection with the classification of numbers and the second one was studied by Hartman and Wintner by Lebesgue integration theory. 相似文献
993.
This paper reports a simple and highly selective method for preconcentrating and separating of trace Pd(II) and Pt(IV) with silica gel bonded by aminopropyl-benzoylazo-4-(2-pyridy-lazo)-resorcinol (ABPR-SG). ABPR-SG is stable in solution from 6 mol/L HCl to pH 7.0 and in common organic solvents. The maximum adsorptive capacity of Pd(n) on ABPR-SG is 362 μmol/g. After preconcentration and separation by using ABPR-SG column, Pd(II) and Pt(IV) of μg/L level in artificial water samples can be measured reliably by common spedrophotometry. The maximum concentration factors of Pd(II) and Pt(IV) on ABPR-SG column are 143 and 125 respectively. The chromatographic column packed with ABPR-SG can be reused. The method is simple and efficient. 相似文献
994.
Asymmetric 1,4‐conjugation addition of dialkylzinc (diethylzinc and dimethylzinc) to cyclic enones, chalcone and nitroalkenes was achieved by a 25 mol% (R)‐6,6′‐Br2‐BINOL( 1f ), 25 mol% CuSPh and 100 mol% dicyclohexylmethylamin(Cy2NMe) catalyst system. The Cu(I) catalyst system enables the cyclic enone, chalcone and nitroalkene generality with high enantioselectivity (up to 84% ee) and isolated yield (up to 94%) under mild reaction conditions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
995.
SlflsltlC!fi10,dn8VOflOI!gflsfl.W3SISOhtCdnOffiSlhQltICtiffiIC3VCSsfldhdIflhibltOYy卜388cellactlvltyl.巨histypeofnaturalproductshaveshownvariousbloactlvltyandreceivedconsiderableattentionfromsyntheticchemlstsy.Wewishtoreportastereoselectlvetotalsynthesisofslnaltlclnfromreadilyavailablestartingmaterials(land4).OursyntheticdesignIsbaseduponconstructionofthesubstitutedbenzouioxanering,to!lowedbyformationof*theX**flavanonolmoietyFromSchemel,wecansee!natInnilssynthesisofs… 相似文献
996.
Weibin Liu Yingtang Zhang Wen Guan William Kinsman Xinqiang Yuan Ziyu Chen 《Physica B: Condensed Matter》2012,407(17):3405-3407
The magnetic properties of the perovskite form of LaMnO3 have been shown strong interest in recent years due to its high potential for use in magnetic devices. In this paper, the magnetic properties of a 30% terbium-doped LaMnO3 (LMTO) perovskite manganite synthesized by a conventional solid-state reaction were investigated. Data on these properties was recorded periodically via SQUID and VSM to reveal it to be best described magnetically as a spin glass system. Thus, the time effect must be taken into consideration in instantaneously determining this material’s spin glass state as well as the overall magnetic properties in the absence of a magnetic field. The results of this paper point to a more in-depth understanding of the change in magnetic properties associated with doped LaMnO3. 相似文献
997.
Kai Li Li Ding Zhong‐Lin Yang E‐Hu Liu Lian‐Wen Qi Ping Li Yu‐Zhu Hu 《Biomedical chromatography : BMC》2010,24(5):550-555
Asperosaponin VI (also named akebia saponin D) is a typical bioactive triterpenoid saponin isolated from the rhizome of Dipsacus asper Wall (Dipsacaceae). In this work, a sensitive high‐performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC‐ESI‐MS) assay has been established for determination of asperosaponin VI in rat plasma. With losartan as the internal standard (IS), plasma samples were prepared by protein precipitation with methanol. Chromatographic separation was performed on a C18 column with a mobile phase of 10 mm ammonium acetate buffer containing 0.05% formic acid–methanol (32 : 68, v/v). The analysis was performed on an ESI in the selected ion monitoring mode using target ions at m/z 951.4 for asperosaponin VI and m/z 423.2 for the IS. The calibration curve was linear over the range 3–1000 ng/mL and the lower limit of quantification was 3.0 ng/mL. The intra‐ and inter‐assay variability values were less than 9.5 and 7.8%, respectively. The accuracies determined at the concentrations of 3.0, 100.0, 300.0 and 1000 ng/mL for asperosaponin VI were within ±15.0%. The validated method was successfully applied to a pharmacokinetic study in rats after oral administration of asperosaponin VI. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
998.
999.
Instudyonnewpharmaceuticalsandagrochemicals,theapplicationofheterocyclesisaveryimportantmethod,whichcanimprovethebiologicalactivities.Intheseyears.moreandmorenewagrochemicalshavebeensynthesizedwhichhavethestructurescontainingheterocycles.especiallypy... 相似文献
1000.
Xu Jie Zhao Shanghong Hou Rui Li Xiaoliang Wu Jili Li Yunxia Meng Wen Ni Yanhui Ma Lihua 《Optics and Lasers in Engineering》2009,47(7-8):800-806
To complete a successful laser jamming to imaging charge coupled device (CCD) based on combined fiber lasers, the interactions between CCD and combined fiber lasers were analyzed in detail. The saturation and crosstalk thresholds of CCD were achieved, which are lower than 10 mW/cm2. Through theoretical analysis and numerical simulations, the thermal processes under single pulse, multi-pulses and continuous laser irradiations were developed. The simulation results have proved the possibility of hard damage caused by multi-pulses and continuous laser irradiations. The combined fiber lasers is suitable to deploy optical saturation jamming at present. The further applications of combined fiber lasers need a more powerful laser source and a more accurate tracking and pointing system. 相似文献