全文获取类型
收费全文 | 6260篇 |
免费 | 96篇 |
国内免费 | 17篇 |
专业分类
化学 | 2963篇 |
晶体学 | 76篇 |
力学 | 261篇 |
数学 | 852篇 |
物理学 | 2221篇 |
出版年
2022年 | 73篇 |
2021年 | 108篇 |
2020年 | 113篇 |
2019年 | 132篇 |
2018年 | 151篇 |
2017年 | 141篇 |
2016年 | 195篇 |
2015年 | 105篇 |
2014年 | 178篇 |
2013年 | 291篇 |
2012年 | 264篇 |
2011年 | 260篇 |
2010年 | 249篇 |
2009年 | 223篇 |
2008年 | 273篇 |
2007年 | 245篇 |
2006年 | 261篇 |
2005年 | 216篇 |
2004年 | 178篇 |
2003年 | 153篇 |
2002年 | 161篇 |
2001年 | 148篇 |
2000年 | 144篇 |
1999年 | 87篇 |
1998年 | 105篇 |
1997年 | 84篇 |
1996年 | 83篇 |
1995年 | 56篇 |
1994年 | 62篇 |
1993年 | 59篇 |
1992年 | 70篇 |
1991年 | 58篇 |
1990年 | 86篇 |
1989年 | 55篇 |
1988年 | 55篇 |
1987年 | 66篇 |
1986年 | 61篇 |
1985年 | 59篇 |
1984年 | 69篇 |
1983年 | 58篇 |
1982年 | 73篇 |
1980年 | 56篇 |
1979年 | 49篇 |
1978年 | 49篇 |
1977年 | 62篇 |
1976年 | 62篇 |
1975年 | 57篇 |
1974年 | 62篇 |
1973年 | 74篇 |
1969年 | 48篇 |
排序方式: 共有6373条查询结果,搜索用时 281 毫秒
141.
N. V. Ivanov 《Journal of Mathematical Sciences》1984,26(1):1646-1664
The goal of the paper is to calculate the homotopy type of the space of diffeomorphisms for most orientable three-dimensional manifolds with finite fundamental group containing the Klein bottle. The fundamental group of such a manifold Q has the form <a, b ¦abab
–1=1,a
mb2n=1>. As m and n one can have any relatively prime natural numbers; these numbers m, n determine the manifold Q up to diffeomorphism. Let K be a Klein bottle lying in Q and let P be a closed tubular neighborhood in Q of this Klein bottle K. We denote by Diffo(Q) the connected component of the space of diffeomorphisms QQ containing id Q, and by E0(K, Q) the connected component of the space of imbeddings KQ containing the inclusion KQ; analogously we define E0(K, P). The main results of the paper are the following two theorems. THEOREM 1. If m, n1, then the space Diffo(Q) is homotopy equivalent with a circle. THEOREM 2. If m, n1, then the inclusion E0(K, P) E0(K, Q) is a homotopy equivalence. With the help of familiar results on spaces of diffeomorphisms of irreducible manifolds which are sufficiently large, Theorem 1 reduces without difficulty to Theorem 2. The main difficulty is the proof of Theorem 2. This proof develops a technique of Hatcher and the author which deals with spaces of PL-homeomorphisms and diffeomorphisms of irreducible manifolds which are sufficiently large. In the paper we use a different structure definition of the class of manifolds considered. It is easy to verify that these definitions are equivalent.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 122, pp. 72–103, 1982. 相似文献
142.
Nikolay Tyutyulkov Ivo Kanev Oskar Polansky Jürgen Fabian 《Theoretical chemistry accounts》1977,46(3):191-203
The analysis of experimental data for singlet transitions (E
n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E
(I)/E
(II)=E
(I)/E
(III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap. 相似文献
143.
V. A. Ivanov 《Mathematical Notes》1978,23(1):3-16
For anyx ∈ r put $$c(x) = \overline {\mathop {\lim }\limits_{t \to \infty } } \mathop {\min }\limits_{(p,q\mathop {) \in Z}\limits_{q \leqslant t} \times N} t\left| {qx - p} \right|.$$ . Let [x0; x1,..., xn, ...] be an expansion of x into a continued fraction and let \(M = \{ x \in J,\overline {\mathop {\lim }\limits_{n \to \infty } } x_n< \infty \}\) .Forx∈M put D(x)=c(x)/(1?c(x)). The structure of the set \(\mathfrak{D} = \{ D(x),x \in M\}\) is studied. It is shown that $$\mathfrak{D} \cap (3 + \sqrt 3 ,(5 + 3\sqrt 3 )/2) = \{ D(x^{(n,3} )\} _{n = 0}^\infty \nearrow (5 + 3\sqrt 3 )/2,$$ where \(x^{(n,3)} = [\overline {3;(1,2)_n ,1} ].\) This yields for \(\mu = \inf \{ z,\mathfrak{D} \supset (z, + \infty )\}\) (“origin of the ray”) the following lower bound: μ?(5+3√3)/2=5.0n>(5 + 3/3)/2=5.098.... Suppose a∈n. Put \(M(a) = \{ x \in M,\overline {\mathop {\lim }\limits_{n \to \infty } } x_n = a\}\) , \(\mathfrak{D}(a) = \{ D(x),x \in M(a)\}\) . The smallest limit point of \(\mathfrak{D}(a)(a \geqslant 2)\) is found. The structure of (a) is studied completely up to the smallest limit point and elucidated to the right of it. 相似文献
144.
Xiaoyi Wang Mark D. Wilkinson Xiaoyan Lin Ren Ren Keith R. Willison Aleksandar P. Ivanov Jake Baum Joshua B. Edel 《Chemical science》2020,11(4):970
Actin is a key protein in the dynamic processes within the eukaryotic cell. To date, methods exploring the molecular state of actin are limited to insights gained from structural approaches, providing a snapshot of protein folding, or methods that require chemical modifications compromising actin monomer thermostability. Nanopore sensing permits label-free investigation of native proteins and is ideally suited to study proteins such as actin that require specialised buffers and cofactors. Using nanopores, we determined the state of actin at the macromolecular level (filamentous or globular) and in its monomeric form bound to inhibitors. We revealed urea-dependent and voltage-dependent transitional states and observed the unfolding process within which sub-populations of transient actin oligomers are visible. We detected, in real-time, filament-growth, and drug-binding at the single-molecule level demonstrating the promise of nanopore sensing for in-depth understanding of protein folding landscapes and for drug discovery.Nanopipettes were used for real-time investigation into actin dynamics and drug binding at single-molecule resolution, showing promise for a better understanding of the mechanism of protein–protein interactions and drug discovery. 相似文献
145.
A new blue emitting 2‐allyl‐6‐(2‐dimethylaminoethyloxy)‐benzo[de]isoquinoline‐1,3‐dione, bearing an allylic group has been designed and synthesized. Bulk radical copolymerization has been carried out in order to prepare a fluorescent copolymer, based on styrene. The main photophysical characteristics of the monomeric and polymeric fluorophores have been investigated both in the absence and presence of metal cations and protons. It has been found that the monomeric naphthalimide can be used as a sensor for protons and Zn2+, Ni2+, Ce3+, Cu2+, Co2+, Ag+ cations. The polymeric fluorophore has been shown to be a selective chemosensor for Cu2+ cations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
146.
A method of determination of adsorbed and absorbed hydrogen on palladium catalysts with carbon carriers is suggested and verified. The method allows Had and Hab to be determined with an accuracy of about 10% using catalysts containing at least 5% Pd.
- . . . 10% , , - , 5% Pd.相似文献
147.
L. V. Grishchuk E. I. Ivanov V. E. Kuz'min A. M. Turyanskaya R. Yu. Ivanova 《Chemistry of Heterocyclic Compounds》2003,39(3):340-343
The reaction of 4-aryl-2-hydrazino-3-nitro-6-R-quinolines with NaNO2 in AcOH gives the corresponding tetrazolo[1,5-a]quinolines. In contrast to tetrazolo[1,5-c]pyrimidines they cannot be converted to 6-R-4-phenyl[1,2,5]oxadiazolo[3,4-b]quinoline-3-oxides by heating in THF, toluene, or AcOH. Total energy quantum-chemical calculations using the MINDO/3 and MNDO methods show that [1,2,5]oxadiazolo[3,4-b]quinoline-3-oxides are significantly higher in energy (230-280 kcal/mol) than the mentioned tetrazolo[1,5-a]quinolines and hence their formation is unlikely. 相似文献
148.
The homotopic method has been used to analyze the kinetic model of three-stageCO oxidation on two nonuniform surface patches conjugated byCO
2 spillover. Diagrams of steady states depending on the portion of surface patchm
1 at various temperatures and pressure ratiosP(O
2)/P(CO) have been constructed. The ratios of different type patches corresponding to the maximum overall reaction rate have been found. 相似文献
149.
V. L. Ivanov V. A. Artemov L. A. Rodinovskaya A. M. Shestopalov V. N. Nesterov Yu. T. Struchkov V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1996,32(1):105-111
Substituted pyrido,[3',2':4,5]thieno[3,2-b]pyndines were obtained by the reaction of 3-amino-2-benzoylthieno [2,3-b]pyridines with malononitrile and the reaction of 3-cyanopyridine-2(IH)-thiones with 2-aryl-3-bromo-I,I-dicyanopropene. 2-Amino-4-(4-bromophenyl)-7, 9-dimethyl-3-cyanopyrido [3',2':4,5]thieno[3, 2-b]-pyridine was used for the synthesis of a derivative of pyrido[3",2":4', 5']thieno[2',3':5,6]pyrido[2,3-d]-pyrimidine. The structure of these compounds was confirmed by spectral data and x-ray diffraction structural analysis.Deceased. 相似文献
150.
Ihalainen JA Croce R Morosinotto T van Stokkum IH Bassi R Dekker JP van Grondelle R 《The journal of physical chemistry. B》2005,109(44):21150-21158
Light-harvesting complex I (LHCI), which serves as a peripheral antenna for photosystem I (PSI) in green plants, consists mainly of four polypeptides, Lhca1-4. We report room temperature emission properties of individual reconstituted monomeric Lhca proteins (Lhca1, -2, -3, and -4) and dimeric Lhca1/4, performed by steady-state and time-resolved fluorescence techniques. The emission quantum yields of the samples are approximately 0.12, 0.085, 0.081, 0.041, and 0.063 for Lhca1, -2, -3, -4, and the -1/4 dimer, respectively, which is considerably lower than the value of 0.22 found for light-harvesting complex II (LHCII), the main peripheral antenna complex of photosystem II in green plants. The decay components of LHCI proteins can be divided in two categories: Lhca1 and Lhca3 have decay times of 1.1-1.6 ns and 3.3-3.6 ns, and Lhca2 and Lhca4 have decay times of 0.7-0.9 ns and 3.1-3.2 ns. These categories seem to correlate with the pigment composition of the samples. All decay times are faster than that observed previously for LHCII. When the absolute emission yields and the lifetimes of the Lhca samples are combined, the overall emission properties of the individual Lhca proteins are expressed in terms of their emitting dipole moment strength. In the samples without extreme red states, that is, Lhca1 and Lhca2, the emitting dipole moment has a value close to unity (relative to monomeric chlorophyll in acetone), which is similar to that for LHCII, whereas, in the samples with the red-most state (F-730), that is, Lhca3, -4, and the -1/4 dimer, the emitting dipole moment has a value less than unity (0.6-0.8), which can be explained by mixing the red-most (exciton) state with a dark charge-transfer state, as suggested in previous PSI red pigment studies. In addition, we find a lifetime component of approximately 50-150 ps in all red-pigment-containing samples, which cannot be due to "slow" energy transfer, but is instead assigned to an unrelaxed state of the pigment-protein, which, on this time-scale, is converted into the final emitting state. 相似文献