全文获取类型
收费全文 | 10008篇 |
免费 | 468篇 |
国内免费 | 92篇 |
专业分类
化学 | 6970篇 |
晶体学 | 67篇 |
力学 | 251篇 |
数学 | 1927篇 |
物理学 | 1353篇 |
出版年
2023年 | 79篇 |
2022年 | 53篇 |
2021年 | 281篇 |
2020年 | 220篇 |
2019年 | 216篇 |
2018年 | 194篇 |
2017年 | 162篇 |
2016年 | 362篇 |
2015年 | 333篇 |
2014年 | 400篇 |
2013年 | 668篇 |
2012年 | 704篇 |
2011年 | 842篇 |
2010年 | 550篇 |
2009年 | 496篇 |
2008年 | 645篇 |
2007年 | 670篇 |
2006年 | 587篇 |
2005年 | 539篇 |
2004年 | 438篇 |
2003年 | 325篇 |
2002年 | 331篇 |
2001年 | 143篇 |
2000年 | 102篇 |
1999年 | 105篇 |
1998年 | 71篇 |
1997年 | 87篇 |
1996年 | 103篇 |
1995年 | 68篇 |
1994年 | 59篇 |
1993年 | 54篇 |
1992年 | 65篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 52篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1975年 | 15篇 |
1974年 | 13篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
51.
Ana L. Montero Luis A. Montero Ricardo Martínez S. Spange 《Journal of Molecular Structure》2006,770(1-3):99-106
A quantum chemical model (Abinitio HF-MO and DFT-B3LYP) of polyfurfuryl alcohol crosslinking is shown. Two pathways were considered: (a) a Diels–Alder (D–A) reaction between a dihydrofuran moiety and a furan ring; (b) the addition reaction of electrophilic specimens on conjugated double bonds. The ability for the formation of D–A adducts (dienes and dienophiles) was investigated by the frontier molecular orbital (FMO) theory. Energy gaps between the FMO's of diene and dienophile structures suggest that the occurrence of the D–A reaction is possible. The results suggest that the carbons of the exo double bonds attached to dihydrofuran rings are the sites most likely to be attacked by electrophilic species, while the C3 and C4 atoms display the opposite tendency due to their low HOMO electron densities. Results of a thermochemical approach to these reactions at the MP2 level was in agreement with reactivity modelled by MO predictions. 相似文献
52.
A mean-field model of nonlinearly coupled oscillators with randomly distributed frequencies and subject to independent external white noises is analyzed in the thermodynamic limit. When the frequency distribution isbimodal, new results include subcritical spontaneous stationary synchronization of the oscillators, supercritical time-periodic synchronization, bistability, and hysteretic phenomena. Bifurcating synchronized states are asymptotically constructed near bifurcation values of the coupling strength, and theirnonlinear stability properties ascertained. 相似文献
53.
Manuel Fernández-López Eduardo García-Río Demir N. Kupeli 《Annals of Global Analysis and Geometry》2002,21(1):1-13
A characterization of time functions on a spacetime is made by using theMöbius equation. It is shown that a time function characterized in this wayyields past timelike geodesic incompleteness and local Lorentzian warpedproduct decomposition of spacetime, provided that the stress-energy tensoris a fluid. Also, by imposing additional assumptions on the stress-energytensor and global analytic structure of the spacetime, more restrictivedecompositions closer to Robertson–Walker spacetimes are obtained. 相似文献
54.
55.
We present two methods for solving the cosmological equations of the scalar-tetradic theory B [19] when a Friedmann-Robertson-Walker (FRW) geometry is assumed. Among the many solutions found there are several physically meaningful ones including inflationary universe solutions. 相似文献
56.
Manuel Barros 《Annals of Global Analysis and Geometry》1992,10(3):219-226
In this paper we deal with the following particular case of a weaker conjecture by B. Y. Chen: Are there 2-type Willmore surfaces in E 3? In particular we prove that the above question has a negative answer when the surface is the image under stereographic projection of a minimal surface in S 3. 相似文献
57.
Luiza Amália Moraes Luis Romero Grados 《Journal of Mathematical Analysis and Applications》2003,281(2):575-586
Let Au(BG) be the Banach algebra of all complex valued functions defined on the closed unit ball BG of a complex Banach space G which are uniformly continuous on BG and holomorphic in the interior of BG, endowed with the sup norm. A characterization of the boundaries for Au(BG) is given in case G belongs to a class of Banach spaces that includes the pre-dual of a Lorentz sequence space studied by Gowers in Israel J. Math. 69 (1990) 129-151. The non-existence of the Shilov boundary for Au(BG) is also proved. 相似文献
58.
Jean Dolbeault Maria J Esteban Michael Loss Luis Vega 《Journal of Functional Analysis》2004,216(1):1-21
We prove some sharp Hardy-type inequalities related to the Dirac operator by elementary, direct methods. Some of these inequalities have been obtained previously using spectral information about the Dirac-Coulomb operator. Our results are stated under optimal conditions on the asymptotics of the potentials near zero and near infinity. 相似文献
59.
A program to compute many functions dependent on the electron density ρ(r) from the results of ab initio molecular calculations is presented. The program allows the generation of different one-, two-, and three-dimensional grids for further graphical representation or numerical analysis. Other options like extracting separate atom contributions to the function computed or locating maximum and minimum values are also implemented. A number of illustrative applications regarding different ρ(r)-dependent functions are presented and the performance and portability of the program is discussed. 相似文献
60.
Manuel María Mahamud 《Applied Surface Science》2007,253(14):6019-6031
In this paper two series of active carbons obtained at different flow rates of the activating agent, CO2, are characterized in order to establish the different mechanisms of pore development during the activation step. This study complements previous works on textural development during the different steps in the process of obtaining active carbons: coal oxidation, coal pyrolysis and char gasification. As the characteristics of the original and intermediate materials are of capital importance in the pore development of active carbons, the properties of the active carbons, precursor chars and coals were considered and analyzed together. Mercury porosimetry and helium picnometry were used to determine classical textural parameters as well as to perform a more detailed study of the pore volume generation during the different conditions of the activation step. Data obtained from the mercury porosimetry determinations was also employed for fractal determinations according to the methodologies proposed by Friesen and Mikula, Zhang and Li and the procedure of Neimark. Average surface fractal dimensions as well as fractal profiles and local surface fractal dimensions were calculated. The use of different flow rates during the activation step produces changes not only in the ordinary textural parameters but also in the fractal characteristics of the active carbons. Activation at higher flow rates leads to smoother fractal profiles and also to lower values of the average surface fractal dimensions of the active carbons. 相似文献