全文获取类型
收费全文 | 2948篇 |
免费 | 122篇 |
国内免费 | 16篇 |
专业分类
化学 | 1796篇 |
晶体学 | 5篇 |
力学 | 129篇 |
数学 | 617篇 |
物理学 | 539篇 |
出版年
2024年 | 2篇 |
2023年 | 30篇 |
2022年 | 65篇 |
2021年 | 126篇 |
2020年 | 74篇 |
2019年 | 92篇 |
2018年 | 68篇 |
2017年 | 52篇 |
2016年 | 115篇 |
2015年 | 110篇 |
2014年 | 125篇 |
2013年 | 191篇 |
2012年 | 226篇 |
2011年 | 249篇 |
2010年 | 146篇 |
2009年 | 109篇 |
2008年 | 202篇 |
2007年 | 174篇 |
2006年 | 160篇 |
2005年 | 165篇 |
2004年 | 114篇 |
2003年 | 105篇 |
2002年 | 94篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1937年 | 3篇 |
排序方式: 共有3086条查询结果,搜索用时 125 毫秒
831.
Guidotti S Camurati I Focante F Angellini L Moscardi G Resconi L Leardini R Nanni D Mercandelli P Sironi A Beringhelli T Maggioni D 《The Journal of organic chemistry》2003,68(14):5445-5465
The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle. 相似文献
832.
Barreca ML Gitto R Quartarone S De Luca L De Sarro G Chimirri A 《Journal of chemical information and computer sciences》2003,43(2):651-655
A three-dimensional pharmacophore model for the binding of noncompetitive AMPA receptor antagonists was developed in order to map common structural features of highly active compounds. This hypothesis, which consists of two hydrophobic regions, one hydrogen bond acceptor and one aromatic region, was successfully used as framework for the design of a new class of allosteric modulators containing a tetrahydroisoquinoline skeleton and for in silico screening. The promising biological results suggested that the identified molecules might be useful "lead compounds" for future drug development. 相似文献
833.
De Luca L Giacomelli G Porcheddu A Salaris M Taddei M 《Journal of combinatorial chemistry》2003,5(4):465-471
The synthesis of libraries of substituted pyrazoles and isoxazoles has been developed via in situ generation of polymer-bound enaminones. The synthetic protocol makes use of commercially available aniline cellulose, a low-cost and versatile biopolymer, under very mild conditions. This new support allowed us to carry out reactions in polar solvents under both conventional heating and MW irradiation without degradation of the polymer. The reaction between cellulose-bound enaminone and hydroxylamine or hydrazines to afford the target heterocycles in high yields directly in solution is the key step. The support can be conveniently recycled. 相似文献
834.
Sébastien?FerencziEmail author Charles?Holton Luca?Q.?Zamboni 《Journal d'Analyse Mathématique》2003,89(1):239-276
Astract We describe an algorithm for generating the symbolic sequences which code the orbits of points under an interval exchange
transformation on three intervals. The algorithm has two components. The first is an arithmetic division algorithm applied
to the lengths of the intervals. This arithmetic construction was originally introduced by the authors in an earlier paper
and may be viewed as a two-dimensional generalization of the regular continued fraction. The second component is a combinatorial
algorithm which generates the bispecial factors of the associated symbolic subshift as a function of the arithmetic expansion.
As a consequence, we obtain a complete characterization of those sequences of block complexity 2n+1 which are natural codings of orbits of three-interval exchange transformations, thereby answering an old question of Rauzy.
Partially supported by NSF grant INT-9726708. 相似文献
835.
Scolaro LM Romeo A Castriciano MA De Luca G Patanè S Micali N 《Journal of the American Chemical Society》2003,125(8):2040-2041
Simple irradiation by UV light of porphyrin TpyP and its zinc(II) and manganese(III) metal derivatives in chlorinated solvents leads to the deposition on silica of mesoscale aggregates. The process is due to the photochemical decomposition of the solvent with generation of HCl, which causes the precipitation of a protonated form. The morphology of the resulting objects is driven by the nature of the inserted metal ion. 相似文献
836.
We give the “boundary version” of the Boggess-PolkingCR extension theorem. LetM andN be real generic submanifolds of ℂ
n
withN ⊂M and letV be a “wedge” inM with “edge”N and “profile” Σ ⊂T
NM in a neighborhood of a pointz
o.We identify in natural manner
and assume that for a holomorphic vector fieldL tangent toM and verifying
we have that the Levi form
takes a value
. Then we prove thatCR functions onV extend ∀ω to a wedgeV
1 “attached” toV in direction of a vector fieldiV such that |pr(iV(z
0))−iv
0| < ε (where pr is the projection pr:T
NX →T
MX |
N
).We then prove that when the Levi cone “relative to Σ”iZ
Σ = convex hull
is open inT
MX, thenCR functions extend to a “full” wedge with edgeN (that is, with a profile which is an open cone ofT
NX). Finally, we prove that iff is defined in a couple of wedges ±V with profiles ±Σ such thatiZ
Σ =T
MX, and is continuous up toN, thenf is in fact holomorphic atz
o. 相似文献
837.
838.
The electrochemical oxidation of an atrazine solution obtained from a flushing treatment of a contaminated soil was investigated. The influence of ethanol on atrazine oxidation was studied. Results show that the electrogenerated Fenton's reagent provides a complete degradation of atrazine and its main chlorinated by-products via N-dehalkylation and dechlorination. This process therefore presents an effective alternative to the chemical oxidation treatment which necessarily needs a further biological state. 相似文献
839.
Michel E Porte G Cipelletti L Appell J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(3):984-990
The dynamic properties of a model transient network have been studied by dynamic light scattering. The network is formed by microemulsion droplets linked by telechelic polymers (modified hydrophilic polymers with two grafted hydrophobic stickers). We compare the properties of two networks that are similar but for the residence time of the hydrophobic stickers in the droplets. The results are interpreted according to the so-called two-fluids model, which was initially developed for semidilute polymer solutions and which we extend here to any Maxwellian viscoelastic medium characterized by its elastic modulus and terminal time as measured by rheology. This model is found to describe consistently and quantitatively the experimental observations. 相似文献
840.
Celebre G Concistrè M De Luca G Longeri M Pileio G Emsley JW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3599-3608
The (1)H NMR spectrum of a sample of acrolein dissolved in the nematic liquid crystal phase I52 has been analysed to yield 18 dipolar couplings between all the magnetic nuclei in the molecule; moreover, the (13)C and (13)C{(1)H} NMR spectra of a sample of acrolein in CDCl(3) were recorded and analysed to determine the indirect J(ij) couplings. The data were used to obtain the relative positions of the carbon and hydrogen atoms, assuming that these are independent of the conformations generated by rotation around the C--C bond through an angle phi, and to obtain a probability distribution P(phi). It has been found that in the liquid phase, the distribution is a maximum at the trans form whereas the abundance of the cis form is significantly smaller compared with that found by microwave spectroscopy or high level quantum mechanical calculations. Such calculations produced also a suitable force field needed to develop suitable strategies for vibrational correction procedure in the case of flexible molecules. 相似文献