全文获取类型
收费全文 | 78592篇 |
免费 | 373篇 |
国内免费 | 383篇 |
专业分类
化学 | 24545篇 |
晶体学 | 810篇 |
力学 | 6737篇 |
数学 | 32063篇 |
物理学 | 15193篇 |
出版年
2021年 | 44篇 |
2019年 | 28篇 |
2018年 | 10447篇 |
2017年 | 10277篇 |
2016年 | 6090篇 |
2015年 | 857篇 |
2014年 | 334篇 |
2013年 | 358篇 |
2012年 | 3825篇 |
2011年 | 10540篇 |
2010年 | 5658篇 |
2009年 | 6072篇 |
2008年 | 6629篇 |
2007年 | 8780篇 |
2006年 | 259篇 |
2005年 | 1335篇 |
2004年 | 1557篇 |
2003年 | 1981篇 |
2002年 | 1017篇 |
2001年 | 252篇 |
2000年 | 294篇 |
1999年 | 157篇 |
1998年 | 194篇 |
1997年 | 150篇 |
1996年 | 197篇 |
1995年 | 124篇 |
1994年 | 80篇 |
1993年 | 100篇 |
1992年 | 57篇 |
1991年 | 69篇 |
1990年 | 59篇 |
1989年 | 59篇 |
1988年 | 64篇 |
1987年 | 59篇 |
1986年 | 63篇 |
1985年 | 50篇 |
1984年 | 54篇 |
1983年 | 41篇 |
1982年 | 44篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 46篇 |
1978年 | 35篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 42篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
Mihaly Mezei 《Journal of mathematical chemistry》2015,53(10):2184-2190
It is shown that the extent of deviation of a molecular shape from spherical can be characterized by comparing the distribution of the circular variances, a measure originally proposed to quantify angular spread, of the vectors from each atom to the rest of the molecule to the circular variance of a collection of atoms filling the unit sphere. Different measures for quantifying the difference between distribution are proposed and compared. 相似文献
53.
Trehalose is a naturally occurring disaccharide noted for its ability to preserve the biological function of proteins and cell membranes during periods of stress—such as water deprivation or extreme temperature—by stabilizing the conformations of the macromolecules within a glassy matrix. This phenomenon makes use of the propensity for trehalose to interact strongly with protein functional groups and solvent water molecules via hydrogen bonding. Previously, it has been shown that trehalose sugar glasses also support long-range charge transport in oxidation-reduction reactions occurring between spatially separated donors and acceptors. Here, through the use of bulk Arrhenius DC-conductivity measurements, we infer that this anomalously high carrier mobility is due to proton hopping along a hydrogen bonding network formed by sorbed “water wires,” a process known as the Grotthuss mechanism. Additionally, we find that the apparent activation energy of the conductivity depends non-monotonically on the bias voltage. The possibility is raised for novel photovoltaic devices based on the entrapment of photosynthetic proteins within these glasses. 相似文献
54.
Urban Larsson Richard J. Nowakowski Carlos P. Santos 《International Journal of Game Theory》2018,47(2):653-671
Combinatorial scoring games, with the property ‘extra pass moves for a player will do him no harm’, are characterized. The characterization involves an order embedding of Conway’s normal play games, and we call our class the universe of Guaranteed scoring games. Also, we give a theorem for comparing guaranteed games with scores (numbers) which extends Ettinger’s work on Dicot scoring games. 相似文献
55.
Shengjie Li Yangdong Xu Manxue You Shengkun Zhu 《Journal of Optimization Theory and Applications》2018,177(3):609-636
Image space analysis is a new tool for studying scalar and vector constrained extremum problems as well as generalized systems. In the last decades, the introduction of image space analysis has shown that the image space associated with the given problem provides a natural environment for the Lagrange theory of multipliers and that separation arguments turn out to be a fundamental mathematical tool for explaining, developing and improving such a theory. This work, with its 3 parts, aims at contributing to describe the state-of-the-art of image space analysis for constrained optimization and to stress that it allows us to unify and generalize the several topics of optimization. In this 1st part, after a short introduction of such an analysis, necessary and sufficient optimality conditions are treated. Duality and penalization are the contents of the 2nd part. The 3rd part deals with generalized systems, in particular, variational inequalities and Ky Fan inequalities. Some further developments are discussed in all the parts. 相似文献
56.
57.
Enyuan Wang Xiangguo Kong Shaobin Hu Zhonghui Li Quanlin Liu 《Transport in Porous Media》2018,121(3):703-724
With coal mining entering the geological environment of “high stress, rich gas, strong adsorption and low permeability,” the difficulty of joint coal and gas extraction clearly augments, the risk of solid–gas coupling dynamic disasters greatly increases, and the underlying mechanisms become more complex. In this paper, based on the characteristics of coal’s multi-scale structure and spatiotemporal variation, the multi-scale fractured coal gas–solid coupling model (MSFM) was built. In this model, the interaction between coal matrix and its fractures and the mechanical characteristics of gas-bearing coal were considered, as well as their coupling relationship. By MATLAB software, the stress–damage–seepage numerical computation programs were developed, which were applied into Comsol Multiphysics to simulate gas flow caused by coal mining. The simulation results showed the spatial variability of coal elastic modulus and cross-flow behaviors of coal seam gas, which were superior to the results of traditional gas–solid coupling model. And the numerical results obtained from MSFM were closer to the measured results in field, while the computation results of traditional model were slightly higher than the measured results. Furthermore, the MSFM in a large scale was verified by field engineering project. 相似文献
58.
Elimhan N. Mahmudov 《Journal of Optimization Theory and Applications》2018,177(2):345-375
The present paper studies a new class of problems of optimal control theory with Sturm–Liouville-type differential inclusions involving second-order linear self-adjoint differential operators. Our main goal is to derive the optimality conditions of Mayer problem for differential inclusions with initial point constraints. By using the discretization method guaranteeing transition to continuous problem, the discrete and discrete-approximation inclusions are investigated. Necessary and sufficient conditions, containing both the Euler–Lagrange and Hamiltonian-type inclusions and “transversality” conditions are derived. The idea for obtaining optimality conditions of Mayer problem is based on applying locally adjoint mappings. This approach provides several important equivalence results concerning locally adjoint mappings to Sturm–Liouville-type set-valued mappings. The result strengthens and generalizes to the problem with a second-order non-self-adjoint differential operator; a suitable choice of coefficients then transforms this operator to the desired Sturm–Liouville-type problem. In particular, if a positive-valued, scalar function specific to Sturm–Liouville differential inclusions is identically equal to one, we have immediately the optimality conditions for the second-order discrete and differential inclusions. Furthermore, practical applications of these results are demonstrated by optimization of some “linear” optimal control problems for which the Weierstrass–Pontryagin maximum condition is obtained. 相似文献
59.
Dariusz Zagrodny 《Journal of Optimization Theory and Applications》2018,178(2):660-671
In this note, some questions concerning the strong convergence of subgradients of convex functions along a given direction are recalled and posed. It is shown that some open problems in literature are linked to that of the existence of limits of subgradients from subdifferentials along a given segment. 相似文献
60.