全文获取类型
收费全文 | 14600篇 |
免费 | 2761篇 |
国内免费 | 4179篇 |
专业分类
化学 | 12371篇 |
晶体学 | 387篇 |
力学 | 834篇 |
综合类 | 406篇 |
数学 | 1866篇 |
物理学 | 5676篇 |
出版年
2024年 | 23篇 |
2023年 | 136篇 |
2022年 | 416篇 |
2021年 | 374篇 |
2020年 | 396篇 |
2019年 | 521篇 |
2018年 | 422篇 |
2017年 | 563篇 |
2016年 | 577篇 |
2015年 | 776篇 |
2014年 | 882篇 |
2013年 | 1147篇 |
2012年 | 1293篇 |
2011年 | 1279篇 |
2010年 | 1104篇 |
2009年 | 1161篇 |
2008年 | 1324篇 |
2007年 | 1124篇 |
2006年 | 1084篇 |
2005年 | 1060篇 |
2004年 | 845篇 |
2003年 | 659篇 |
2002年 | 694篇 |
2001年 | 663篇 |
2000年 | 595篇 |
1999年 | 351篇 |
1998年 | 273篇 |
1997年 | 226篇 |
1996年 | 187篇 |
1995年 | 154篇 |
1994年 | 179篇 |
1993年 | 159篇 |
1992年 | 131篇 |
1991年 | 118篇 |
1990年 | 116篇 |
1989年 | 90篇 |
1988年 | 87篇 |
1987年 | 56篇 |
1986年 | 70篇 |
1985年 | 49篇 |
1984年 | 42篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1965年 | 5篇 |
1936年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The possibility of determining various electroactive organic compounds, e.g., erythromycin and riboflavin, by adsorptive preconcentration at constant potential on a mercury-coated carbon-fibre electrode in a flow system prior to stripping with a reductive constant current, is demonstrated. The advantages of measuring the electrode potential vs. time instead of current vs. electrode potential during stripping, the possibility of operating with non-deoxygenated solutions, the increased linear calibration range is in the multiple scanning mode, and the possibility of using the technique for detection in liquid chromatography, are discussed. An analytical procedure for the determination of erythromycin at the 10(-6)M level in urine after extraction with diethyl ether is described. 相似文献
22.
A three-dimensional global potential energy surface for the ground (X (1)Sigma(+)(g))electronic state of HgH(2) is constructed from more than 13,00 ab initio points. These points are generated using an internally contracted multireference configuration interaction method with the Davidson correction and a large basis set. Low-lying vibrational energy levels of HgH(2), HHgD, and HgD(2) calculated using the Lanczos algorithm are found to be in good agreement with the available experimental band origins. The majority of the vibrational energy levels up to 9000 cm(-1) are assigned with normal mode quantum numbers. Our results indicate a gradual transition for the stretching vibrations from the normal mode regime at low energies to the local mode regime near 9000 and 8000 cm(-1) for HgH(2) and HgD(2), respectively, as evidenced by a decreasing energy gap between the (0,0,n(3)) and (1,0,n(3)-1) vibrational states and bifurcation of the corresponding wave functions. 相似文献
23.
IntroductionCatal}ticrcactionsaffcctcdb}'diffosionaIlimitationincatal}'stporcshavcbccnextensive1}dcaltx`ithinlit.rat.rcll~5I.Scvcraltcchniqucsonthcspccialcase0fFischcr-Tropschs}'nthcsis(FTS)t\crcapplicdtocxplorcthebchaviorofthiscatal}ticrcactionundercxpcrimcntalandopcrationaIconditionsI3~5l.It`"ouldbeofvaluctoindicatchcrcthatthcseinvcstigationsx"ercmainl}'bascdonthesimplcstkineticsofthcfirstordcrinH2proposedbyAndersonl6]attheearIystages.However-thesetboents,striCtlyspeaking,areinvalidfor… 相似文献
24.
Ai‐Hua Zhao Yan Zhang Zhao‐Hui Xu Jian‐Wen Liu Wei Jia 《Helvetica chimica acta》2004,87(12):3160-3166
Three new enmein‐type ent‐kaurenoids, i.e., the two pairs 1 and 2 of 20‐epimers and the (20R)‐isomer 3 , besides the seven known diterpenoids 4 – 10 , were isolated from the aerial parts of Isodon serra. Their structures were elucidated by spectroscopic techniques and X‐ray diffraction. The immunosuppressive effect for T‐lymphocytes proliferation induced by Con A in BALB/c mouse was evaluated for the isolates 1 – 10 . They all displayed a remarkable inhibitory effect, with multi‐glycosides of Tripterygium wilfordii as positive reference substance (Table 3). 相似文献
25.
Reactions of the substituted 2‐formyl chromones with aroylhydrazines gave corresponding 2‐(aroylhydrazonomethylidyne) chromones. Then 2‐(3′‐acetyl‐5′‐aryl‐2′,3′‐dihydro‐1′,3′,4′‐oxadiazol‐2′‐yl) chromones were prepared by these 2‐(aroylhydrazonomethylidyne) chromones under refluxing with Ac2O. All target compounds were characterized through elemental analysis and IR, 1H NMR, MS. 相似文献
26.
27.
PengZHANG JiCunREN ZuoJunSHEN 《中国化学快报》2004,15(9):1091-1094
In this paper, we first presented a novel method for quantification of circulating DNA in human serum based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). The serum was digested by proteinase to release free DNA, and then CZE-LIF system was used for the quantification of total circulating DNA. This method was successfully used to quantify the circulating DNA levels in sera from healthy individuals and certain cancer patients.We found the significantly elevated circulating DNA levels in certain prostate cancer patients. Our results demonstrated that CZE-LIF system has good linearity, excellent sensitivity (0.5 ng/mL DNA),satisfactory reproducibility (RSDs in one day and between days were both less than 5%) and reliability, and is well suitable to the quantification of the circulating DNA in human serum or plasma. 相似文献
28.
一种液晶环氧树脂固化中扩散控制动力学研究 总被引:3,自引:0,他引:3
根据扩散控制反应的基本原理 ,建立了合适的反应模型 ,描述了 4 ,4′ 二 ( 2 ,3 环氧丙氧基 )偶氮苯(DGEAP) / 4,4′ 二氨基二苯甲烷 (DDM)环氧树脂的固化行为 .该模型认为 ,随着环氧基团反应程度的提高 ,基团的反应半径将受到影响 .当体系中出现了介晶基元的有序排列时 ,与之相连的反应基团的分布也受到影响 ,有序区内的局部浓度将变大 ,产生假浓度效应 ,并最终影响扩散控制反应动力学 .通过与普通环氧树脂固化动力学的比较 ,证实了这一效应 . 相似文献
29.
Mutation of the active-site residue Cys38 of N-Ada converts it from a sacrificial DNA repair protein to an enzyme that uses methanethiol as an external sacrificial reagent to repair DNA methyl phosphotriesters catalytically. 相似文献
30.