全文获取类型
收费全文 | 2984篇 |
免费 | 118篇 |
国内免费 | 36篇 |
专业分类
化学 | 1697篇 |
晶体学 | 13篇 |
力学 | 53篇 |
数学 | 761篇 |
物理学 | 614篇 |
出版年
2023年 | 20篇 |
2022年 | 15篇 |
2021年 | 64篇 |
2020年 | 42篇 |
2019年 | 60篇 |
2018年 | 82篇 |
2017年 | 53篇 |
2016年 | 112篇 |
2015年 | 110篇 |
2014年 | 113篇 |
2013年 | 190篇 |
2012年 | 180篇 |
2011年 | 229篇 |
2010年 | 120篇 |
2009年 | 143篇 |
2008年 | 171篇 |
2007年 | 167篇 |
2006年 | 153篇 |
2005年 | 148篇 |
2004年 | 159篇 |
2003年 | 108篇 |
2002年 | 98篇 |
2001年 | 46篇 |
2000年 | 32篇 |
1999年 | 30篇 |
1998年 | 40篇 |
1997年 | 37篇 |
1996年 | 48篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有3138条查询结果,搜索用时 500 毫秒
111.
Dr. Siddhartha De Dr. Alexandrine Flambard Dr. Delphine Garnier Patrick Herson Dr. Frank H. Köhler Dr. Abhishake Mondal Dr. Karine Costuas Dr. Béatrice Gillon Prof. Rodrigue Lescouëzec Dr. Boris Le Guennic Dr. Frédéric Gendron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12120-12136
The local magnetic structure in the [FeIII(Tp)(CN)3]− building block was investigated by combining paramagnetic Nuclear Magnetic Resonance (pNMR) spectroscopy and polarized neutron diffraction (PND) with first-principle calculations. The use of the pNMR and PND experimental techniques revealed the extension of spin-density from the metal to the ligands, as well as the different spin mechanisms that take place in the cyanido ligands: Spin-polarization on the carbon atoms and spin-delocalization on the nitrogen atoms. The results of our combined density functional theory (DFT) and multireference calculations were found in good agreement with the PND results and the experimental NMR chemical shifts. Moreover, the ab-initio calculations allowed us to connect the experimental spin-density map characterized by PND and the suggested distribution of the spin-density on the ligands observed by NMR spectroscopy. Interestingly, significant differences were observed between the pseudo-contact contributions of the chemical shifts obtained by theoretical calculations and the values derived from NMR spectroscopy using a simple point-dipole model. These discrepancies underline the limitation of the point-dipole model and the need for more elaborate approaches to break down the experimental pNMR chemical shifts into contact and pseudo-contact contributions. 相似文献
112.
Gerold Jäger Changxing Dong Boris Goldengorin Paul Molitor Dirk Richter 《Journal of Heuristics》2014,20(1):107-124
We introduce a reduction technique for large instances of the traveling salesman problem (TSP). This approach is based on the observation that tours with good quality are likely to share many edges. We exploit this observation by neglecting the less important tour space defined by the shared edges, and searching the important tour subspace in more depth. More precisely, by using a basic TSP heuristic, we obtain a set of starting tours. We call the set of edges which are contained in each of these starting tours as pseudo-backbone edges. Then we compute the maximal paths consisting only of pseudo-backbone edges, and transform the TSP instance to another one with smaller size by contracting each such path to a single edge. This reduced TSP instance can be investigated more intensively, and each tour of the reduced instance can be expanded to a tour of the original instance. Combining our reduction technique with the currently leading TSP heuristic of Helsgaun, we experimentally investigate 32 difficult VLSI instances from the well-known TSP homepage. In our experimental results we set world records for seven VLSI instances, i.e., find better tours than the best tours known so far (two of these world records have since been improved upon by Keld Helsgaun and Yuichi Nagata, respectively). For the remaining instances we find tours that are equally good or only slightly worse than the world record tours. 相似文献
113.
Malte Braack Martin F. Quaas Benjamin Tews Boris Vexler 《Journal of Optimization Theory and Applications》2018,178(3):950-972
The behavior of a fishing fleet and its impact onto the biomass of fish can be described by a nonlinear parabolic diffusion–reaction equation. Looking for an optimal fishing strategy leads to a non-convex optimal control problem with a bilinear control action. In this work, we present such an optimal control formulation, prove its well-posedness and derive first- and second-order optimality conditions. These results provide a basis for tailored finite element discretization as well as for Newton type optimization algorithms. First numerical test problems show typical features as so-called No-Take-Zones and maximal fishing quota (total allowable catches) as parts of an optimal fishing strategy. 相似文献
114.
Boris I. Kvasov 《Numerical Algorithms》2014,67(4):863-888
This paper presents methods for shape preserving spline interpolation. These methods are based on discrete weighted cubic splines. The analysis results in two algorithms with automatic selection of the shape control parameters: one to preserve the data monotonicity and other to retain the data convexity. Discrete weighted cubic B-splines and control point approximation are also considered. 相似文献
115.
Sautenkov Vladimir A. Saakyan Sergey A. Zelener Boris B. 《Journal of Russian Laser Research》2021,42(4):405-411
Journal of Russian Laser Research - We discuss the experimental research of an optical resonant saturation of a dipole–dipole-broadened atomic transition in the high-density rubidium vapor.... 相似文献
116.
Dr. Boris Schade Dr. Abhishek Kumar Singh Dr. Virginia Wycisk Dr. Jose Luis Cuellar-Camacho Dr. Hans von Berlepsch Prof. Rainer Haag Dr. Christoph Böttcher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(30):6919-6934
The syntheses of novel amphiphilic 5,5′,6,6′-tetrachlorobenzimidacarbocyanine (TBC) dye derivatives with aminopropanediol head groups, which only differ in stereochemistry (chiral enantiomers, meso form and conformer), are reported. For the achiral meso form, a new synthetic route towards asymmetric cyanine dyes was established. All compounds form J aggregates in water, the optical properties of which were characterised by means of spectroscopic methods. The supramolecular structure of the aggregates is investigated by means of cryo-transmission electron microscopy, cryo-electron tomography and AFM, revealing extended sheet-like aggregates for chiral enantiomers and nanotubes for the mesomer, respectively, whereas the conformer forms predominately needle-like crystals. The experiments demonstrate that the aggregation behaviour of compounds can be controlled solely by head group stereochemistry, which in the case of enantiomers enables the formation of extended hydrogen-bond chains by the hydroxyl functionalities. In case of the achiral meso form, however, such chains turned out to be sterically excluded. 相似文献
117.
Vladimir A. Potapov Svetlana V. Amosova Boris V. Petrov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):587-590
Reactions of dicyanodiselenide, selenenyl chlorides and bromides with acetylenes and some further transformations of obtained products have been studied. 相似文献
118.
Mikhail I. Smushkin Valentina G. Kharchenko Boris I. Drevko 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):621-624
It is shown using 1H NMR spectroscopy that 2,4,6-triphenyl-4H-seleno(thio)pyrans can be isomerized into 2H-isomers by the action of lithium perchlorate or lithium chloride in DMF or only by DMF. The reaction time is found to depend on the Lewis acidity of used salt. It is supposed that isomerization in presence of Lewis acids proceeds as endocyclic 1,3-proton transfer or as a series of two 1,2-hydride shifts. 相似文献
119.
120.
Anastasia E. Sleptsova Liudmila N. Alyabyeva Evgeny A. Gorbachev Ekaterina S. Kozlyakova Maxim A. Karpov Chen Xinming Alexander V. Vasiliev Boris P. Gorshunov Anatoly S. Prokhorov Pavel E. Kazin Lev A. Trusov 《Mendeleev Communications》2021,31(2):221-223
- Download : Download high-res image (184KB)
- Download : Download full-size image