全文获取类型
收费全文 | 667篇 |
免费 | 24篇 |
国内免费 | 21篇 |
专业分类
化学 | 407篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 167篇 |
物理学 | 126篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 23篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 35篇 |
2012年 | 46篇 |
2011年 | 44篇 |
2010年 | 28篇 |
2009年 | 31篇 |
2008年 | 51篇 |
2007年 | 55篇 |
2006年 | 57篇 |
2005年 | 39篇 |
2004年 | 42篇 |
2003年 | 29篇 |
2002年 | 32篇 |
2001年 | 8篇 |
2000年 | 1篇 |
1999年 | 13篇 |
1998年 | 4篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有712条查询结果,搜索用时 390 毫秒
161.
Greg Janzen 《Metaphysica》2011,12(2):101-115
Judith Thomson, David Lewis, and Ted Sider have each formulated different arguments that apparently pose problems for our ordinary claims of diachronic sameness, i.e., claims in which we assert that familiar, concrete objects survive (or persist) through time by enduring as numerically the same entity despite minor changes in their intrinsic and relational properties. In this paper, I show that all three arguments fail, in a rather obvious way??they beg the question??and so even though there may be arguments that provide grounds to fuss about whether our ordinary claims of diachronic sameness are defective, Thomson, Lewis, and Sider??s arguments are not among them. 相似文献
162.
Greg Knese 《Proceedings of the American Mathematical Society》2007,135(9):2759-2768
We prove a generalization of the infinitesimal portion of the classical Schwarz lemma for functions from the polydisk to the disk. In particular, we describe the functions which play the role of automorphisms of the disk in this context-they turn out to be rational inner functions in the Schur-Agler class of the polydisk with an added symmetry constraint. In addition, some sufficient conditions are given for a function to be of this type.
163.
164.
165.
Tim M. Brewer Christopher Szakal Greg Gillen 《Rapid communications in mass spectrometry : RCM》2010,24(5):593-598
A method to increase useful yields of organic molecules is investigated by cluster secondary ion mass spectrometry (SIMS). Glycerol drops were deposited onto various inkjet‐printed arrays and the organic molecules in the film were rapidly incorporated into the drop. The resulting glycerol/analyte drops were then probed with fullerene primary ions under dynamic SIMS conditions. High primary ion beam currents were shown to aid in the mixing of the glycerol drop, thus replenishing the probed area and sustaining high secondary ion yields. Integrated secondary ion signals for tetrabutylammonium iodide and cocaine in the glycerol drops were enhanced by more than a factor of 100 compared with an analogous area on the surface, and a factor of 1000 over the lifetime of the glycerol drop. Once the analyte of interest is incorporated into the glycerol microdrop, the solution chemistry can be tailored for enhanced secondary ion yields, with examples shown for cyclotrimethylenetrinitramine (RDX) chloride adduct formation. In addition, depositing localized glycerol drops may enhance analyte secondary ion count rates to high enough levels to allow for site‐specific chemical maps of molecules in complex matrices such as biological tissues. Published in 2010 by John Wiley & Sons, Ltd. 相似文献
166.
167.
William D. Fiers Greg J. Dodge Yang Li Janet L. Smith Robert A. Fecik Courtney C. Aldrich 《Chemical science》2015,6(8):5027-5033
Polyketide synthase (PKS) β-processing domains are responsible for much of the stereochemical complexity of polyketide natural products. Although the importance of β-processing domains has been well noted and significantly explored, key stereochemical details pertaining to cryptic stereochemistry and the impact of remote stereogenic centers have yet to be fully discerned. To uncover the inner workings of ketoreductases (KR) and dehydratases (DH) from the tylosin pathway a didomain composed of TylDH3-KR3 was recombinantly expressed and interrogated with full-length tetraketide substrates to probe the impact of vicinal and distal stereochemistry. In vitro product isolation analysis revealed the products of the cryptic KR as d-alcohols and of the DH as trans-olefins. Steady-state kinetic analysis of the dehydration reaction demonstrated a strict stereochemical tolerance at the β-position as d-configured substrates were processed more than 100 times more efficiently than l-alcohols. Unexpectedly, the k
cat/K
M values were diminished 14- to 45-fold upon inversion of remote ε- and ζ-stereocenters. This stereochemical discrimination is predicted to be driven by a combination of allylic A1,3 strain that likely disfavors binding of the ε-epimer and a loss of electrostatic interactions with the ζ-epimer. Our results strongly suggest that dehydratases may play a role in refining the stereochemical outcomes of preceding modules through their substrate stereospecificity, honing the configurational purity of the final PKS product. 相似文献
168.
We show that if P is an infinite poset whose proper order ideals have cardinality strictly less than ${|P|}$ and ${\kappa}$ is a cardinal number strictly less than ${|P|}$ , then P has a principal order ideal of cardinality at least ${\kappa}$ . We apply this result to characterize the possible sizes of unary Jónsson algebras. 相似文献
169.
Greg Friedman 《纯数学与应用数学通讯》2009,62(9):1265-1292
We construct geometric examples of pseudomanifolds that satisfy the Witt condition for intersection homology Poincaré duality with respect to certain fields but not others. We then compute the bordism theory of K‐Witt spaces for an arbitrary field K, extending results of Siegel for K = ?. © 2008 Wiley Periodicals, Inc. 相似文献
170.
Guo J Erickson GA Fitzgerald RN Matsuoka RT Rafferty SW Sharp MJ Sickles BR Wisowaty JC 《The Journal of organic chemistry》2006,71(21):8302-8305
An efficient synthesis of 2-{4-[({4-{[4-(4-methoxyphenyl)piperazin-1-yl]methyl}-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl}methyl)thio]phenoxy}-2-methylpropanoic acid (1), a potent PPARpan agonist, is described. The seven-step synthesis, which afforded 1 in 30% overall yield, includes a highly regioselective carbon-sulfur bond formation via coupling of a bishydroxymethylthiazole (3) with 4-hydroxythiophenol, displacement of the remaining alcohol through a three-step telescoped sequence involving an efficient cleavage of an aryl mesylate, and an efficient and practical method of introducing an isobutyric acid fragment. 相似文献