全文获取类型
收费全文 | 6834篇 |
免费 | 189篇 |
国内免费 | 52篇 |
专业分类
化学 | 4959篇 |
晶体学 | 67篇 |
力学 | 161篇 |
数学 | 699篇 |
物理学 | 1189篇 |
出版年
2023年 | 33篇 |
2022年 | 53篇 |
2021年 | 61篇 |
2020年 | 95篇 |
2019年 | 106篇 |
2018年 | 78篇 |
2017年 | 49篇 |
2016年 | 141篇 |
2015年 | 114篇 |
2014年 | 132篇 |
2013年 | 312篇 |
2012年 | 406篇 |
2011年 | 494篇 |
2010年 | 235篇 |
2009年 | 220篇 |
2008年 | 422篇 |
2007年 | 479篇 |
2006年 | 460篇 |
2005年 | 458篇 |
2004年 | 424篇 |
2003年 | 331篇 |
2002年 | 291篇 |
2001年 | 100篇 |
2000年 | 83篇 |
1999年 | 86篇 |
1998年 | 85篇 |
1997年 | 58篇 |
1996年 | 95篇 |
1995年 | 72篇 |
1994年 | 67篇 |
1993年 | 62篇 |
1992年 | 57篇 |
1991年 | 60篇 |
1990年 | 56篇 |
1989年 | 47篇 |
1988年 | 46篇 |
1987年 | 41篇 |
1986年 | 41篇 |
1985年 | 65篇 |
1984年 | 59篇 |
1983年 | 50篇 |
1982年 | 49篇 |
1981年 | 52篇 |
1980年 | 54篇 |
1979年 | 45篇 |
1978年 | 57篇 |
1977年 | 44篇 |
1976年 | 43篇 |
1975年 | 24篇 |
1974年 | 28篇 |
排序方式: 共有7075条查询结果,搜索用时 312 毫秒
1.
2.
Brian R. Holder Colleen A. McNaney David Luchetti Eric Schaeffer Dieter M. Drexler 《Biomedical chromatography : BMC》2015,29(9):1375-1379
Acetyl‐l ‐carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC‐MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high‐throughput scale, a new and simple HILIC‐MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via ‘dilute and shoot’ directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC‐MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high‐throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Transition Metal Chemistry - (η5-Dp)Ru(PPh3)2H (Dp?=?C8H9?, 1,2-dihydropentalenyl) was synthesized in 90% yield by reaction of (η5-Dp)Ru(PPh3)2Cl with sodium formate.... 相似文献
4.
Brian R. Hunt 《Proceedings of the American Mathematical Society》1998,126(3):791-800
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.
5.
Brian H. Bowditch 《Transactions of the American Mathematical Society》2002,354(3):1049-1078
We describe a means of constructing splittings of a one-ended finitely generated group over two-ended subgroups, starting with a finite collection of codimension-one two-ended subgroups. In the case where all the two-ended subgroups have two-ended commensurators, we obtain an annulus theorem, and a form of the JSJ splitting of Rips and Sela. The construction uses ideas from the work of Dunwoody, Sageev and Swenson. We use a particular kind of order structure which combines cyclic orders and treelike structures. In the special case of hyperbolic groups, this provides a link between combinarorial constructions, and constructions arising from the topological structure of the boundary. In this context, we recover the annulus theorem of Scott and Swarup. We also show that a one-ended finitely generated group which contains an infinite-order element, and such that every infinite cyclic subgroup is (virtually) codimension-one is a virtual surface group.
6.
NMR screening techniques in drug discovery and drug design 总被引:7,自引:0,他引:7
Brian J. Stockman Claudio Dalvit 《Progress in Nuclear Magnetic Resonance Spectroscopy》2002,41(3-4):187-231
7.
报道了两类典型元素替代的超导Y123相体系-YBa2(Cu1-xCox)3O7-δ(x=0.01,0.02)和YBa2(Cu1-yZny)3O7-δ(y=0.005,0.010)薄膜的电阻率-温度特性(ρ(T))和Hall效应(RH (T)).研究表明,Co掺杂的Y123相体系十分类似于氧欠掺杂的情况,对Co掺杂的薄膜样品,由电阻率-温度特性定义的赝能隙打开的温度T*分别为193和225K.而Zn掺杂的样品没有观察到赝能隙打开对电阻率-温度特性的影响.由Hall效应的测量和Hall角(cotθH)定义了另一个特征温度T 0,介于Tc与T*之间,这一特征温度与核磁共振(NMR)给出的赝能隙打开温度相近,说明可能源于电子自旋自由度上的能隙打开.在室温到Tc范围内,电阻率-温度特性和Hall效应分别定义了两类不同的转变温度(T*和T 0),可能分别源于电子电荷和自旋通道上的赝能隙的打开,预示着电荷和自旋自由度分别进入某种基态. 相似文献
8.
We investigate the conjecture that every circulant graph X admits a k‐isofactorization for every k dividing |E(X)|. We obtain partial results with an emphasis on small values of k. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 406–414, 2006 相似文献
9.
L. Brian Lawrence 《Transactions of the American Mathematical Society》2005,357(7):2535-2556
Working in ZFC, we give an example as indicated in the title.
10.
T. Brian Cavitt Brian Phillips Charles E. Hoyle Bo Pan Sukhendu B. Hait Kalyanaraman Viswanathan Sonny Jnsson 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):4009-4015
Three‐component photoinitiators comprised of an N‐arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron‐deficient N‐arylphthalimide resulted in a greater acrylate polymerization rate than an electron‐rich N‐arylphthalimide. Triplet energies of each N‐arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N‐arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron–proton transfer from an intermediate radical species to the N‐arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009–4015, 2004 相似文献