全文获取类型
收费全文 | 1703篇 |
免费 | 200篇 |
国内免费 | 177篇 |
专业分类
化学 | 1295篇 |
晶体学 | 36篇 |
力学 | 70篇 |
综合类 | 16篇 |
数学 | 192篇 |
物理学 | 471篇 |
出版年
2024年 | 6篇 |
2023年 | 28篇 |
2022年 | 37篇 |
2021年 | 51篇 |
2020年 | 49篇 |
2019年 | 57篇 |
2018年 | 47篇 |
2017年 | 40篇 |
2016年 | 59篇 |
2015年 | 75篇 |
2014年 | 84篇 |
2013年 | 121篇 |
2012年 | 131篇 |
2011年 | 145篇 |
2010年 | 80篇 |
2009年 | 77篇 |
2008年 | 111篇 |
2007年 | 93篇 |
2006年 | 80篇 |
2005年 | 87篇 |
2004年 | 82篇 |
2003年 | 54篇 |
2002年 | 53篇 |
2001年 | 51篇 |
2000年 | 55篇 |
1999年 | 36篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 32篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有2080条查询结果,搜索用时 31 毫秒
141.
Xinghong Zhang Lin Xu Wenbo Han Ling Weng Jiecai Han Shanyi Du 《Solid State Sciences》2009,11(1):156-161
Hot-pressed zirconium diboride (ZrB2) matrix composites containing 0–30 vol% silicon carbide (SiC) whiskers have been investigated to determine the effect of composition (i.e. amount of SiC whiskers) on the microstructure, mechanical properties and thermal properties. With increasing SiC whisker volume contents, the flexural strength and fracture toughness of the composites were improved compared to those of monolithic ZrB2. Flexural strength increased from 629 MPa for pure ZrB2 to 767 MPa for ZrB2–30 vol%SiCw. Likewise, fracture toughness ranged from 5.4 to 7.1 MPa m1/2 over the same composition range. Specific heat capacity increased with SiC whisker addition, while thermal diffusivity and thermal conductivity decreased slightly with the increase of SiC whisker content. 相似文献
142.
We study Deligne products for forgetful maps between moduli spaces of marked curves by offering a closed formula for tautological
line bundles associated to marked points. In particular, we show that the Deligne products for line bundles on the total spaces
corresponding to “forgotten” marked points are positive integral multiples of the Weil-Petersson bundles on the base moduli
spaces.
Partially supported by the Japan Society for the Promotion of Science. 相似文献
143.
Alexeff I. Weng Lock Kang 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(1):32-33
Corona discharges in the air are intensified if a small amount of nonelectronegative gas is fed into the limited region around each corona point. The ions produced in the active region then migrate into the air, to produce an intensified negative and positive ion plasma 相似文献
144.
Paul Ronald Jones Todd E Albanesi Ralph D Gillespie Priscilla C Jones Seik Weng Ng 《应用有机金属化学》1987,1(6):521-528
Six bis(silyl)acetylenes (XMe2Si? C?C? SiMe2X) with the following varied silicon substituents X were prepared: 1 (Me, Me); 2 (H, H); 3 (C1, H); 4 (CI, CI); 5 (MeO, H); 6 (MeO, MeO). While 1 and 2 may be prepared by the reaction of dilithio- or bis(bromomagnesium)-acetylide with the appropriate chlorosilane, similar reactions designed to give 3–6 yielded oligomers, XMe2Si? (? C?C? SiMe2)n? X, 7, X=CI, MeO, as the major products, indicating that the acetylenic functionality on silicon activates the chlorosilane towards nucleophilic substitution. Compounds 3 and 4 were prepared by free radical chlorination of 2. Methanolysis of 3 and 4 gave quantitative yields of 5 and 6 respectively. Compounds 1–6 undergo a Diels–Alder reaction with α-pyrone to produce, after loss of carbon dioxide, bis(silyl)-substituted benzene derivatives. The order of reactivity has been determined to be: 4=6>3=5>1>2, indicating that chloro or alkoxy substituents favor the cycloaddition with 2- pyrone. The adducts formed by compounds 3–6 undergo an unusually facile hydrolysis or elimination to give 1,1,3,3-tetramethyl-1,3-disila-2-oxaindane. 相似文献
145.
The feasibility of using spirulina as adsorbent for the treatment of low-level liquid radwaste is studied. The experimental results indicate that the sorption capacity of spirulina is good for the di- and trivalent metallic ions at pH 3-7, but rather poor for the mono-valent metallic ions and non-metallic ions. Some factors affecting metal ion uptake by spirulina such as the content of detergent, sodium ion in liquid radwaste and the stability of spirulina under gamma irradiation were also investigated. 相似文献
146.
交联壳聚糖对Mo(Ⅵ)、Bi(Ⅲ)吸附性能的研究 总被引:2,自引:0,他引:2
研究了以环氧氯丙烷为交联剂制备的交联壳聚糖(CCTS)对Mo(Ⅵ)、Bi(Ⅲ)的吸附性能。结果表明:在pH=3.0时,CCTS对Mo(Ⅵ)、Bi(Ⅲ)的吸附率分别为98.0%、100%,吸附平衡时间分别为20min和5min,饱和吸附量分别为21.4,620.8g/kg,用1.00mL、0.1mL的NaOH溶液和4.00mL、5.0mol/L的HCl溶液可将吸附在CCTS上的Mo(Ⅵ)、Bi(Ⅲ)宣洗脱下来,脱附率分别为93%和96.5%。 相似文献
147.
In this article we generalize the CM method for elliptic and hyperelliptic curves to Picard curves. We describe the algorithm in detail and discuss the results of our implementation.
148.
Betti base‐derived tetradentate ligand 2 has been successfully designed and synthesized through the condensation of Betti base with glyoxal. Its application in N‐arylation of imidazoles has been investigated which opens a new field for application of Betti base derivatives in organic transformation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
149.
Shih Hsi Chu Zhi Hao Chen Zun Yao Weng Elizabeth C. Rowe Edward Chu Ming-Yu Wang Chu 《Journal of heterocyclic chemistry》1987,24(4):989-995
Amino analogs of BAU (5-benzylacyclouridine) and BBAU (5-benzyloxybenzylacyclouridine) and their 2′-hydroxymethyl derivatives were synthesized for evaluation as inhibitors of uridine phosphorylase and hence potential cancer chemotherapeutic agents. Both aminomethyl analogs were found to be potent inhibitors of this enzyme and good potentiators of the anti-tumor action of FUdR. 相似文献
150.
翁慧明 《浙江大学学报(理学版)》1990,17(4):385-389
本文研究用BepaiuTefta多项式逼近可微函数·改进了现有结果,建立了一个含有点态因子的渐近等式; 相似文献