全文获取类型
收费全文 | 15831篇 |
免费 | 2266篇 |
国内免费 | 2380篇 |
专业分类
化学 | 11979篇 |
晶体学 | 227篇 |
力学 | 1033篇 |
综合类 | 228篇 |
数学 | 1973篇 |
物理学 | 5037篇 |
出版年
2024年 | 36篇 |
2023年 | 272篇 |
2022年 | 438篇 |
2021年 | 501篇 |
2020年 | 590篇 |
2019年 | 558篇 |
2018年 | 440篇 |
2017年 | 447篇 |
2016年 | 772篇 |
2015年 | 686篇 |
2014年 | 854篇 |
2013年 | 1129篇 |
2012年 | 1319篇 |
2011年 | 1328篇 |
2010年 | 1105篇 |
2009年 | 949篇 |
2008年 | 1064篇 |
2007年 | 987篇 |
2006年 | 941篇 |
2005年 | 787篇 |
2004年 | 716篇 |
2003年 | 600篇 |
2002年 | 676篇 |
2001年 | 571篇 |
2000年 | 392篇 |
1999年 | 377篇 |
1998年 | 290篇 |
1997年 | 256篇 |
1996年 | 262篇 |
1995年 | 190篇 |
1994年 | 173篇 |
1993年 | 145篇 |
1992年 | 110篇 |
1991年 | 102篇 |
1990年 | 78篇 |
1989年 | 46篇 |
1988年 | 50篇 |
1987年 | 33篇 |
1986年 | 42篇 |
1985年 | 34篇 |
1984年 | 16篇 |
1983年 | 27篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1978年 | 6篇 |
1974年 | 4篇 |
1969年 | 3篇 |
1957年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
A novel diterpene derivative, 5-methyl-5-(4,8,12-trimethyl-tridecyl)-dihydro-furan-2-one (1) and a new chromone, 5-hydroxy-7-methoxy-3-methyl-chromen-4-one (2), along with a known compound, phytol (3) have been isolated from the aerial parts of Hypericum perforatum. Their structures were established on the basis of spectroscopic analysis and by comparison with published values. 相似文献
133.
研究了直流电场对含LiClO4的聚氧化乙烯(PEO)400与环氧树脂形成的液晶态互穿网络高分子忆禽子导体的电导率的影响。在室温至90℃范围内,电导率随外加电压增加面降低。外加电压越高,对电导率变化的影响越大。 相似文献
134.
135.
RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE CATALYZED BY NOVEL SINGLE COMPONENT RARE EARTH CALIXARENE COMPLEXES 总被引:2,自引:0,他引:2
Wei-puZhu JunLing HongXu Zhi-quanShen 《高分子科学》2005,(4):407-410
In this paper, ring-opening polymerization of trimethylene carbonate (TMC) with rare earth (Nd, Y, La) p-tert-butylcalix[n]arene (n=4, 6, and 8) complexes as catalysts has been studied. Poly(trimethylene carbonate) (PTMC) with Mv of 21,400 was produced by bulk polymerization under the conditions as follows: [TMC]0/[Nd] (molar ratio)=1000,80℃,8h. Mechanism study reveals that the polymerization proceeds via a coordination mechanism. 相似文献
136.
Han G Li J Chen G Ling L Li S Khorobrykh AA Zharmukhamedov SK Klimov VV Kuang T 《Journal of photochemistry and photobiology. B, Biology》2005,81(2):114-120
The efficiency of a trinuclear and two binuclear manganese complexes in reconstituting electron transport and O(2) evolution activity in Mn-depleted Photosystem II preparations is analyzed. The trinuclear Mn-complex is more efficient than two binuclear Mn-complexes in restoring oxygen evolution, but it is less effective as an electron donor than binuclear Mn-complexes. It is inferred from our results that recovery of electron transport and O(2) evolution with polynuclear Mn-complexes is affected with different factors. Moreover, the trinuclear Mn-complex is extremely sensitive to the addition of CaCl(2). It is suggested that there is an interaction between Ca(2+) and carboxyl within the trinuclear Mn-complex during photoactivation and this interaction benefits the ligation of Mn atom to the apo-WOC and form an active WOC. Binuclear Mn(III)Mn(III) complex shows slightly higher efficiency than binuclear Mn(III)Mn(IV) complex in restoration of O(2) evolution activity. The efficiency of three Mn-complexes in the reconstitution of WOC is in an order: trinuclear Mn(3)(III)>binuclear Mn(III)Mn(III)>binuclear Mn(III)Mn(IV). 相似文献
137.
Yu P Lin Y Xiang L Su L Zhang J Mao L 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9000-9006
This letter describes the formation and possible electrochemical applications of molecular films of water-miscible imidazolium-based ionic liquids (ILs) on glassy carbon (GC) electrodes. X-ray photoelectron spectroscopy (XPS) and electrochemical results indicate that the water-miscible ILs used in this study can interact with the GC electrode and form molecular films on the electrode surface. The formed molecular films are found to possess striking electrochemical properties such as electrocatalysis toward ascorbic acid (AA) and the capability to facilitate direct electron transfer of horseradish peroxidase (HRP). This demonstration would pave the way for new electrochemical applications of water-miscible ILs and is envisaged to be useful for the investigation of the electrochemical properties of water-miscible ILs in aqueous media provided the same counteranion is used as the supporting electrolyte. 相似文献
138.
Yong Zhong DU Fu Qiang HU Hong YUAN Shinzo OMI 《中国化学快报》2006,17(4):553-556
Stable poly(styrene-co-sodium styrene sulfonate) (P(St-NaSS) nanoparticles with broader size distribution were synthesized by thermal emulsion polymerization without any conventional initiators and emulsifiers. The obtained polymer nanoparticles have higher ξ potential, and the particle sizes have broad distribution. The stability of polymer particles originated from the addition of small amounts of ionic comonomer, NaSS, which can act as an emulsifier in somewhat. The monomer conversion could reach up to about 28 wt% in 48 h, and did not increase by further polymerization when higher polymerization temperature (120 ℃) was employed. This polymerization system may be give some further understand for mechanism of emulsion polymerization. 相似文献
139.
Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN. 相似文献
140.