全文获取类型
收费全文 | 22095篇 |
免费 | 3977篇 |
国内免费 | 4956篇 |
专业分类
化学 | 16836篇 |
晶体学 | 356篇 |
力学 | 1244篇 |
综合类 | 411篇 |
数学 | 2939篇 |
物理学 | 9242篇 |
出版年
2024年 | 56篇 |
2023年 | 355篇 |
2022年 | 747篇 |
2021年 | 836篇 |
2020年 | 834篇 |
2019年 | 896篇 |
2018年 | 744篇 |
2017年 | 782篇 |
2016年 | 948篇 |
2015年 | 1097篇 |
2014年 | 1269篇 |
2013年 | 1657篇 |
2012年 | 1886篇 |
2011年 | 1913篇 |
2010年 | 1482篇 |
2009年 | 1599篇 |
2008年 | 1715篇 |
2007年 | 1469篇 |
2006年 | 1379篇 |
2005年 | 1234篇 |
2004年 | 1008篇 |
2003年 | 801篇 |
2002年 | 882篇 |
2001年 | 804篇 |
2000年 | 821篇 |
1999年 | 576篇 |
1998年 | 421篇 |
1997年 | 365篇 |
1996年 | 305篇 |
1995年 | 289篇 |
1994年 | 237篇 |
1993年 | 252篇 |
1992年 | 194篇 |
1991年 | 160篇 |
1990年 | 160篇 |
1989年 | 138篇 |
1988年 | 132篇 |
1987年 | 104篇 |
1986年 | 84篇 |
1985年 | 62篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 61篇 |
1981年 | 38篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1965年 | 10篇 |
1964年 | 9篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Cyril Prknyi Hui Liang Yuan Bo H. E. Strmberg Ariella Evenzahav 《Journal of heterocyclic chemistry》1992,29(4):749-753
The synthesis of ten new substituted 1,3,4-thiadiazolyl-4(3H)-quinazolinones 8–11, 13, 17 , and 20–23 is reported. Compounds 8–11 were prepared by condensation of 5-fluoro-2-methyl-3,1-benzoxazin-4-one (3) and 5-substituted 2-amino-1,3,4-thiadiazoles 4–7. Compound 13 was obtained by condensation of 5-fluoro-2-methyl-3,1-benzoxazin-4-one (3) with DL-α-amino-?-caprolactam (12) . Compound 17 was synthesized by condensation of 6-bromo-2-methyl-3,1-benzoxazin-4-one (16) and 2-amino-5-t-butyl-1,3,4-thiadiazole (5) . Compounds 20–23 were obtained by condensation of 5-chloro-6,8-dibromo-2-methyl-3,1-benzoxazin-4-one (19) and 5-substituted 2-amino-1,3,4-thiadiazoles 4–7, respectively. The substituted 3,1-benzoxazin-4-ones 3, 16, and 19 were obtained in good yield by refluxing the appropriate anthranilic acid, 1,15 , and 18 with acetic anhydride (2) . 相似文献
112.
Pei Yuan Wu 《Integral Equations and Operator Theory》1984,7(6):899-904
If T is a contraction on the Hilbert space H and there is an invariant subspace K for T such that T/K is similar to a backward shift, then T is reflexive. If similarity is replaced by quasi-similarity, then the same conclusion holds under the additional condition that the defect index of T be finite.This research was partially supported by National Science Council (Republic of China). 相似文献
113.
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
114.
115.
Abstract— Giant cell induction was studied in cultured bladder tumor cells (MGH-Ul; commonly referred to as "EJ") following hematoporphyrin derivative (HpD)-sensitized photoirradiation. Eight days after treatment, control colonies (no treatment, HpD alone, light alone) were generally uniform in size and density and contained few giant cells. Colony heterogeneity and giant cell frequency increased with light dose in the presence of HpD. The morphology and frequency of giant cell formation, with respect to survival levels, were comparable to those observed in 280 kVp X-irradiation of the same cells. 相似文献
116.
117.
PRODUCTION OF LIGHTOLEFINS FROM CO_2 HYDROGENATION OVER Fe/SILICALITE-2 CATALYST Ⅱ. PROMOTION EFFECT OF MnO PROMOTER 下载免费PDF全文
IntroductionItilasbeenshot'-nthattileadditionofMnOpromotertoFocatal}stcanresultinaremarkableimprovementinthesclectivit}'to11ghtalkenesforCOh}!drogenationll'l.Ho-c'cvcr.thecadetofMnOonCH4formationandCOconversionisvery'ambigUouslltolMoreover.MnOpromotergrca… 相似文献
118.
Jun-Lin Yuan Zhi-Jun Zhang Xiao-Jun Wang Hao-Hong Chen Guo-Bin Zhang 《Journal of solid state chemistry》2007,180(4):1365-1371
Three rare earth borosilicate oxyapatites, RE5Si2BO13 (RE=La, Gd, Y), were synthesized via wet chemical method, of which RE5Si2BO13 (RE=Gd, Y) were first reported in this work. In the three oxyapatites, [BO4] and [SiO4] share the [TO4] tetrahedral oxyanion site, and RE3+ ions occupy all metal sites. The differential scanning calorimetry-thermo gravimetry measurements and high temperature powder X-ray diffraction pattern revealed a vitrification process within 300-1200 °C, which was due to the glass-forming nature of borosilicates. From the VUV excitation spectra of Eu3+ and Tb3+ in RE5Si2BO13, the optical band gaps were found to be 6.31, 6.54 and 6.72 eV for RE5Si2BO13 (RE=La, Gd, Y), respectively. The emission and excitation bands of Eu3+ and Tb3+ are discussed relating with their coordination environments. Among the three hosts, Y5Si2BO13 would be the best for Eu3+ and Tb3+-doped phosphors. 相似文献
119.
Shyan-Ming Yuan 《BIT Numerical Mathematics》1991,31(1):53-68
To maintain consistency on a distributed database system, a commit protocol is often employed to ensure that either all the sub-transactions of a transaction commit or all abort. Special care needs to be taken to ensure the correct functioning of a commit protocol in the face of node failures during the execution of the protocol. A protocol is said to be fault-tolerant if it properly commits or aborts, even if nodes fail.In this paper, we present a fault tolerant decentralized commit protocol which is message optimal in the absence of failures. Furthermore, the protocol (FTDCP) ensures that all sites can achieve a consistent final decision by at most 4 extra messages in the single site failure situation. 相似文献
120.