全文获取类型
收费全文 | 6810篇 |
免费 | 532篇 |
国内免费 | 38篇 |
专业分类
化学 | 5332篇 |
晶体学 | 31篇 |
力学 | 181篇 |
综合类 | 1篇 |
数学 | 1094篇 |
物理学 | 741篇 |
出版年
2022年 | 34篇 |
2021年 | 62篇 |
2020年 | 79篇 |
2019年 | 124篇 |
2018年 | 71篇 |
2017年 | 74篇 |
2016年 | 232篇 |
2015年 | 254篇 |
2014年 | 247篇 |
2013年 | 417篇 |
2012年 | 329篇 |
2011年 | 371篇 |
2010年 | 310篇 |
2009年 | 317篇 |
2008年 | 371篇 |
2007年 | 313篇 |
2006年 | 294篇 |
2005年 | 250篇 |
2004年 | 295篇 |
2003年 | 238篇 |
2002年 | 289篇 |
2001年 | 158篇 |
2000年 | 151篇 |
1999年 | 80篇 |
1998年 | 71篇 |
1997年 | 89篇 |
1996年 | 92篇 |
1995年 | 66篇 |
1994年 | 77篇 |
1993年 | 73篇 |
1992年 | 72篇 |
1991年 | 45篇 |
1990年 | 49篇 |
1989年 | 52篇 |
1988年 | 44篇 |
1987年 | 44篇 |
1986年 | 41篇 |
1985年 | 55篇 |
1984年 | 69篇 |
1983年 | 58篇 |
1982年 | 73篇 |
1981年 | 75篇 |
1980年 | 77篇 |
1979年 | 88篇 |
1978年 | 81篇 |
1977年 | 85篇 |
1976年 | 76篇 |
1975年 | 78篇 |
1974年 | 75篇 |
1973年 | 53篇 |
排序方式: 共有7380条查询结果,搜索用时 783 毫秒
31.
32.
The synthesis of the title compounds has been achieved in concise, highly regiocontrolled fashion from commercially available (+)-sclareolide. In addition, we offer evidence that the structure of a newly reported natural product from Zingiber ottensii is incorrect. 相似文献
33.
In the introduction of the Arithmetica Diophantus says that in order to solve arithmetical problems one has to “follow the way he (Diophantus) will show.” The present paper has a threefold objective. Firstly, the meaning of this sentence is discussed, the conclusion being that Diophantus had elaborated a program for handling various arithmetical problems. Secondly, it is claimed that what is analyzed in the introduction is definitions of several terms, the exhibition of their symbolism, the way one may operate with them, but, most significantly, the main stages of the program itself. And thirdly, it is argued that Diophantus' intention in the Arithmetica is to show the way the stages of his program should be practically applied in various arithmetical problems. 相似文献
34.
35.
36.
Theoretical investigations and the results of computer modeling of the optical, thermophysical, and thermochemical processes during laser interaction with ocular tissues are reviewed in this paper. Physical-mathematical models and results of numerical simulation of the processes are presented. The computer modeling was applied for investigations of laser heating and coagulation of ocular tissues for treatment of retina diseases and intraocular tumors, cyclophotocoagulation of the ciliary body for treatment of glaucoma, and laser thermal keratoplasty of the cornea. The influence of radiation parameters on the selectivity of laser coagulation of laminated ocular tissues is considered. The results obtained are of essential interest for laser applications in ophthalmology and can be used for investigation of heating and coagulation of tissues in different fields of laser medicine. 相似文献
37.
A series of 7-amino- and polyaminosterol analogues of squalamine and trodusquemine were synthesized involving a new stereoselective titanium reductive amination reaction in high chemical yields of up to 95% in numerous cases. These derivatives were evaluated for their in vitro antimicrobial properties against human pathogens. All the compounds present excellent activities against Gram-positive bacteria exhibiting similar results against Staphylococcus aureus and Streptococcus faecalis with minimum inhibitory concentrations (MICs) varying from 2.5 to 10 μg/mL. Numerous derivatives possess also MICs against Gram-negative Escherichia coli bacteria (MICs varying from 2.5 to 10 μg/mL) suggesting that nature of the amino group attached to the sterol moiety plays an important role on the activities of such products. 相似文献
38.
39.
We show a faithful restriction theorem among infinite chains which implies a reconstructibility conjecture of Halin. This incite us to study the reconstructibility in the sense of Fraïssé and to prove it for orders of cardinality infinite or ≥ 3 and for multirelations of cardinality infinite or ≥ 7, what improves the theory obtained by G. Lopez in the finite case. For this work we had to study the infinite classes of difference which have to be a linear order of type ω, ω* or ω* + ω; this complete the theory made by G. Lopez for the finite case ([13]). We show also Ulam-reconstructibility for linear orders which have a fixed point. 相似文献
40.
Ginette Ratovo Jean‐Pierre Souchard Pascale Urizzi Yvon Coulais Franoise Nepveu Etienne Hollande 《应用有机金属化学》2004,18(1):1-8
Pancreatic cancer has an extremely poor prognosis, due, in part, to lack of methods for early diagnosis. The present study was designed to evaluate the potential of labeling low‐density lipoprotein (LDL) with a radionuclide using a lipid chelating agent, bis(stearylamide) of diethylenetriaminepentaacetic acid (L), to detect pancreatic tumors by gamma‐scintigraphy. Previous studies indicated that the difficulty of visualization of pancreatic tumors was due to their poor vascularization. This study compares the ability of two radiotracers, 111In–L–LDL and 153Gd–L–LDL to target highly vascularized rat pancreatic tumors (AR4‐2J) implanted in nude mice. Biodistribution studies showed that the tumor uptake of 111In–L–LDL and 153Gd–L–LDL tracers was twofold and fivefold higher respectively than with the controls (111In citrate and 153Gd citrate respectively). These tracers would thus be suitable for scintigraphic imaging. We show here that LDL could be employed as a delivery system for tracers such as 111In or 153Gd when these two radionuclides are complexed by a lipid‐chelating anchor, and that 111In–L–LDL and 153Gd–L–LDL enabled better visualization of the pancreatic tumor tissues, with a better result with 153Gd–L–LDL. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献