全文获取类型
收费全文 | 19524篇 |
免费 | 2212篇 |
国内免费 | 2375篇 |
专业分类
化学 | 8273篇 |
晶体学 | 184篇 |
力学 | 668篇 |
综合类 | 171篇 |
数学 | 1305篇 |
物理学 | 4307篇 |
综合类 | 9203篇 |
出版年
2024年 | 71篇 |
2023年 | 293篇 |
2022年 | 486篇 |
2021年 | 532篇 |
2020年 | 491篇 |
2019年 | 451篇 |
2018年 | 415篇 |
2017年 | 424篇 |
2016年 | 609篇 |
2015年 | 679篇 |
2014年 | 1015篇 |
2013年 | 1143篇 |
2012年 | 1280篇 |
2011年 | 1441篇 |
2010年 | 1143篇 |
2009年 | 1170篇 |
2008年 | 1354篇 |
2007年 | 1227篇 |
2006年 | 1121篇 |
2005年 | 1072篇 |
2004年 | 816篇 |
2003年 | 727篇 |
2002年 | 808篇 |
2001年 | 763篇 |
2000年 | 685篇 |
1999年 | 581篇 |
1998年 | 433篇 |
1997年 | 393篇 |
1996年 | 393篇 |
1995年 | 295篇 |
1994年 | 307篇 |
1993年 | 254篇 |
1992年 | 252篇 |
1991年 | 201篇 |
1990年 | 168篇 |
1989年 | 163篇 |
1988年 | 120篇 |
1987年 | 88篇 |
1986年 | 64篇 |
1985年 | 35篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Song C Wang D Gu G Lin Y Yang J Chen L Fu X Hu Z 《Journal of colloid and interface science》2004,272(2):340-344
Silver-coated poly(methyl acrylic acid) (PSA) core-shell colloid particles were prepared by an in situ chemical reduction method. Crystalline silver/titania composite hollow spheres were obtained by coating the as-prepared PSA/silver particles with an amorphous titania layer and subsequently calcining in Ar atmosphere. SEM and TEM investigation indicated that the size of the as-prepared PSA/silver and PSA/silver/TiO(2) core-shell particles and silver/titania composite hollow particles was fairly uniform and the wall thickness of the hollow spheres was in the range of 40-80 nm. UV-vis absorption spectra were recorded to investigate their optical properties. 相似文献
172.
We consider the statistical mechanics of the traveling salesman problem (TSP) and develop some representations to study it. In one representation the mean field theory has a simple form and brings out some of the essential features of the problem. It shows that the system has spontaneous symmetry breaking at any nonzero temperature. In general the phase progressively changes as one decreases the temperature. At low temperatures the mean field theory solution is very sensitive to any small perturbations, due to the divergence of some local susceptibilities. This critical region extends down to zero temperature. We perform the quenched average for a nonmetric TSP in the second representation and the resulting problem is more complicated than the infinite-range spin-glass problem, suggesting that the free energy landscape may be more complex. The role played by frustration in this problem appears explicitly through the localization property of a random matrix, which resembles the tight binding matrix of an electron in a random lattice. 相似文献
173.
CeO2 nanotubes have been synthesized facilely using carbon nanotubes (CNTs) as templates by a liquid phase deposition method. The properties of the CeO2 nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) as well as thermogravimetry and differential thermal analysis (TG-DTA). The obtained CeO2 nanotubes with a polycrystalline face-centered cubic phase have a uniform diameter ranging from 40 to 50 nm. The CeO2 nanotubes are composed of many tiny interconnected nanocrystallites of about 10 nm in size. The pretreatment of CNTs and calcination temperature were confirmed to be the crucial factors determining the formation of CeO2 nanotubes. A possible formation mechanism has been suggested to explain the formation of CeO2 nanotubes. 相似文献
174.
175.
Mei Hong Fu Zhu Ju Wang Hong Jun Yang Mayila Maimai Jing Fang Li Ying Tang Lan Yang 《中国化学快报》2007,18(4):415-417
A new C21-steroidal glycoside with two known compounds were isolated from the root of Cynanchum Stauntonii.Based on thespectral analysis,including MS,1H NMR,13C NMR,DEPT,1H-1H COSY,13C-1H COSY,HMQC and HMBC,their chemicalstructures were determinated as glaucogenin-C 3-O-a-L-cymaropyranosyl-(1→4)-b-D-digitoxopyranosyl-(1→4)-β-D-canaropyranoside(1),stigmasterol(2)and ursolic acid(3). 相似文献
176.
ShuXiaCAO JianChenZHANG JunXU XinChengLIAO YuFenZHAO 《中国化学快报》2004,15(7):817-820
Hydrolysis procedure of N-phosphoryl phenylalanine (DIPP-Phe) was studied by HPLC-ESI-MS/MS. The results showed that (HO)(i-PrO)P(O)Phe was the main intermediate and the hydrolysis of DIPP-Phe also occurred through a penta-coordinate transition state. 相似文献
177.
178.
Host-guest complexes of cucubit[8]uril with phenanthrolines and some methyl derivatives 总被引:1,自引:0,他引:1
DAY Anthony I 《中国科学B辑(英文版)》2005,48(4):305-314
Cucurbituril a molecular container (or host) has a rigid hollow interior cavity which is large enough to accommodate, one or more, smaller molecules (or guests). The cavity is accessible through two carbonyl portal openings. Molecules or guests enter the … 相似文献
179.
180.
低热-高压法制备PLGA多孔支架及其体外降解研究 总被引:6,自引:1,他引:6
采用低热-高压法制备了聚(dl-丙交酯/乙交酯)75/25(PLGA75/25)组织工程多孔支架。该方法避免了使用有机溶剂,支架的孔隙率在90%以上,孔径大小分布均匀。多孔支架经过酒精处理后,支架表面产生许多微小的凹陷;用藻酸钙改性处理后,支架形态保持良好。两种处理都使支架的压缩强度有所增大,亲水性增强。虽然孔隙率高的支架降解速率稍慢,但其体外降解规律基本一致:特性粘数争力学强度衰减快,而质量损失较慢,降解6周后,支架的质量损失仅为3%左右;体外降解3周后,支架的形态保持良好,可望在细胞移植争组织修复的早期发挥支撑作用。 相似文献