全文获取类型
收费全文 | 9171篇 |
免费 | 290篇 |
国内免费 | 47篇 |
专业分类
化学 | 5858篇 |
晶体学 | 57篇 |
力学 | 265篇 |
数学 | 1724篇 |
物理学 | 1604篇 |
出版年
2023年 | 54篇 |
2022年 | 122篇 |
2021年 | 149篇 |
2020年 | 153篇 |
2019年 | 181篇 |
2018年 | 185篇 |
2017年 | 169篇 |
2016年 | 325篇 |
2015年 | 287篇 |
2014年 | 292篇 |
2013年 | 579篇 |
2012年 | 655篇 |
2011年 | 695篇 |
2010年 | 406篇 |
2009年 | 358篇 |
2008年 | 527篇 |
2007年 | 485篇 |
2006年 | 456篇 |
2005年 | 438篇 |
2004年 | 367篇 |
2003年 | 321篇 |
2002年 | 252篇 |
2001年 | 146篇 |
2000年 | 129篇 |
1999年 | 95篇 |
1998年 | 81篇 |
1997年 | 70篇 |
1996年 | 74篇 |
1995年 | 57篇 |
1994年 | 71篇 |
1993年 | 54篇 |
1992年 | 52篇 |
1991年 | 78篇 |
1990年 | 75篇 |
1989年 | 66篇 |
1988年 | 54篇 |
1987年 | 47篇 |
1986年 | 35篇 |
1985年 | 54篇 |
1984年 | 80篇 |
1983年 | 41篇 |
1982年 | 57篇 |
1981年 | 48篇 |
1980年 | 56篇 |
1979年 | 37篇 |
1978年 | 40篇 |
1977年 | 53篇 |
1976年 | 37篇 |
1975年 | 39篇 |
1974年 | 36篇 |
排序方式: 共有9508条查询结果,搜索用时 15 毫秒
1.
Dr. Sabin Llona‐Minguez Dr. Matthieu Desroses Artin Ghassemian Dr. Sylvain A. Jacques Dr. Lars Eriksson Rebecka Isacksson Tobias Koolmeister Dr. Pål Stenmark Dr. Martin Scobie Prof. Thomas Helleday 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(20):7394-7398
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif. 相似文献
2.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
3.
4.
5.
6.
7.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
8.
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002. 相似文献
9.
G. Lujanienë 《Czechoslovak Journal of Physics》2003,53(1):A57-A65
In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of 137Cs and 7Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble 137Cs and 7Be were determined. The relation between activity concentrations of insoluble 7Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble 137Cs where the dry deposition becomes predominant. 相似文献
10.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献