全文获取类型
收费全文 | 11582篇 |
免费 | 278篇 |
国内免费 | 86篇 |
专业分类
化学 | 8285篇 |
晶体学 | 115篇 |
力学 | 232篇 |
数学 | 1513篇 |
物理学 | 1801篇 |
出版年
2023年 | 62篇 |
2022年 | 92篇 |
2021年 | 118篇 |
2020年 | 157篇 |
2019年 | 146篇 |
2018年 | 120篇 |
2017年 | 110篇 |
2016年 | 222篇 |
2015年 | 227篇 |
2014年 | 282篇 |
2013年 | 505篇 |
2012年 | 665篇 |
2011年 | 856篇 |
2010年 | 418篇 |
2009年 | 355篇 |
2008年 | 769篇 |
2007年 | 775篇 |
2006年 | 811篇 |
2005年 | 825篇 |
2004年 | 720篇 |
2003年 | 589篇 |
2002年 | 556篇 |
2001年 | 151篇 |
2000年 | 137篇 |
1999年 | 127篇 |
1998年 | 148篇 |
1997年 | 166篇 |
1996年 | 181篇 |
1995年 | 107篇 |
1994年 | 116篇 |
1993年 | 113篇 |
1992年 | 88篇 |
1991年 | 80篇 |
1990年 | 55篇 |
1989年 | 58篇 |
1988年 | 59篇 |
1987年 | 63篇 |
1986年 | 49篇 |
1985年 | 94篇 |
1984年 | 90篇 |
1983年 | 62篇 |
1982年 | 69篇 |
1981年 | 83篇 |
1980年 | 81篇 |
1979年 | 61篇 |
1978年 | 48篇 |
1977年 | 43篇 |
1976年 | 32篇 |
1975年 | 38篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Sajal Sen Mark W. Perrin Adam C. Sedgwick Vincent M. Lynch Jonathan L. Sessler Jonathan F. Arambula 《Chemical science》2021,12(21):7547
Recent decades have witnessed the emergence of Au(i) bis-N-heterocyclic carbenes (NHCs) as potential anticancer agents. However, these systems exhibit little interaction with serum proteins (e.g., human serum albumin), which presumably impacts their pharmacokinetic profile and tumor exposure. Anticancer drugs bound to human serum albumin (HSA) often benefit from significant advantages, including longer circulatory half-lives, tumor targeted delivery, and easier administration relative to the drug alone. In this work, we present Au(i) bis-NHCs complexes, 7 and 9, capable of binding to HSA. Complex 7 contains a reactive maleimide moiety for covalent protein conjugation, whereas its congener 9 contains a naphthalimide fluorophore for non-covalent binding. A similar drug motif was used in both cases. Complexes 7 and 9 were prepared from a carboxylic acid functionalized Au(i) bis-NHC (complex 2) using a newly developed post-synthetic amide functionalization protocol that allows coupling to both aliphatic and aromatic amines. Analytical, and in vitro techniques were used to confirm protein binding, as well as cellular uptake and antiproliferative activity in A549 human lung cancer cells. The present findings highlight a hitherto unexplored approach to modifying Au(i) bis-NHC drug candidates for protein ligation and serve to showcase the relative benefits of covalent and non-covalent HSA binding.Au(i) bis-N-heterocyclic carbenes (NHCs) functionalized using an amide linker were found to bind to human serum albumin (HSA) in covalent and non-covalent fashion. The solubility and in vitro anti-cancer activity of these new conjugates were studied. 相似文献
132.
Ananthakrishnan Gunasekaran Thiruvalam Jayachandran Joseph H. Boyer Mark L. Trudell 《Journal of heterocyclic chemistry》1995,32(4):1405-1407
The reaction of glyoxime ( 4 ) and hydroxylamine hydrochloride in aqueous sodium hydroxide was found to be a safe and inexpensive method for the preparation of multigram quantities of diaminoglyoxime ( 5 ). Potassium hydroxide mediated dehydration of 5 furnished diaminofurazan ( 1 ) in good yield of exceptional purity. The ready availability of 1 and 5 has facilitated the synthesis of new energetic furazan derivative 8 . 相似文献
133.
Allwyn G Cole Laurie M Yoder Joseph J Shiang Neil A Anderson Larry A Walker Mark M Banaszak Holl Roseanne J Sension 《Journal of the American Chemical Society》2002,124(3):434-441
An ultrafast transient absorption study of the primary photolysis of ethyl- and n-propylcobalamin in water is presented. Data have been obtained for two distinct excitation wavelengths, 400 nm at the edge of the UV gamma-band absorption, and 520 nm in the strong visible alphabeta-band absorption. These data are compared with results reported earlier for the B(12) coenzymes, methyl- and adenosylcobalamin. The data obtained for ethylcobalamin and n-propylcobalamin following excitation at 400 nm demonstrate the formation of one major photoproduct on a picosecond time scale. This photoproduct is spectroscopically identifiable as a cob(II)alamin species. Excitation of methyl-, ethyl-, and n-propylcobalamin at 520 nm in the low-lying alphabeta absorption band results in bond homolysis proceeding via a bound cob(III)alamin MLCT state. For all of the cobalamins studied here competition between geminate recombination of caged radical pairs and cage escape occurs on a time scale of 500 to 700 ps. The rate constants for geminate recombination in aqueous solution fall within a factor of 2 between 0.76 and 1.4 ns(-1). Intrinsic cage escape occurs on time scales ranging from 相似文献
134.
Yuan Beibei Heiser Willem de Rooij Mark 《Advances in Data Analysis and Classification》2022,16(4):875-907
Advances in Data Analysis and Classification - The $$\delta $$ -machine is a statistical learning tool for classification based on dissimilarities or distances between profiles of the observations... 相似文献
135.
Mark J. Nielsen 《Geometriae Dedicata》1995,54(3):245-254
We show that given any simple closed curveJ in 2 and any lineL, the curveJ contains the four vertices of some rhombusR with two sides parallel toL. Furthermore, the cyclic order of the vertices ofR agrees with their cyclic order onJ. We also show that the diameters of the rhombi so produced (one for each lineL) may be bounded away from zero. 相似文献
136.
LetQ be any rectangle and letK
d
(d 2) be a continuum which is either symmetric across a hyperplane or symmetric through a pointz K. We show thatK contains the vertices of a rectangle similar toQ which exhibits the same symmetry as doesK. 相似文献
137.
Sharp Upper Bound to the First Nonzero Neumann Eigenvalue for Bounded Domains in Spaces of Constant Curvature 总被引:1,自引:0,他引:1
The main result of this paper is that for a domain containedin a hemisphere of the n-dimensional sphere Sn the first nonzeroNeumann eigenvalue µ1() is less than or equal to the firstnonzero Neumann eigenvalue µ1(D) where D is a geodesicball in Sn of the same measure as . Equality occurs if and onlyif is isometric to D. This result generalizes old results ofSzegö and Weinberger which gave the corresponding upperbound for µ1() in the Euclidean case, and a result ofChavel for domains in Sn which restricted to lie in a geodesicball of radius when n = 2and to even smaller geodesic balls for larger n. The techniquesused are analogous to those for our recent proof of the Payne-Pólya-Weinbergerconjecture: rearrangement inequalities and properties of specialfunctions are the key elements. The general approach is a directextension of Weinberger's for domains in Rn. 相似文献
138.
The development of a sensor for the direct and selective determination of atmospheric ethanol is in the initial stages. The sensor takes advantage of the selective chemical reaction between ethanol and vanadium oxinate. This reaction occurs in an organic medium where a red colored complex is the product. This reaction is determined spectrophotometrically where the absorbance maxima is 475 nm. The focus of this paper is to discuss the parameters necessary to develop a solid sorbent sampling-sensor which can be used to determine atmospheric ethanol. 相似文献
139.
140.