全文获取类型
收费全文 | 1271篇 |
免费 | 22篇 |
国内免费 | 8篇 |
专业分类
化学 | 847篇 |
晶体学 | 19篇 |
力学 | 26篇 |
数学 | 85篇 |
物理学 | 324篇 |
出版年
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 26篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 22篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 60篇 |
2012年 | 55篇 |
2011年 | 65篇 |
2010年 | 31篇 |
2009年 | 23篇 |
2008年 | 73篇 |
2007年 | 68篇 |
2006年 | 94篇 |
2005年 | 61篇 |
2004年 | 45篇 |
2003年 | 33篇 |
2002年 | 50篇 |
2001年 | 40篇 |
2000年 | 29篇 |
1999年 | 18篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 16篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 17篇 |
1973年 | 20篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1935年 | 6篇 |
排序方式: 共有1301条查询结果,搜索用时 0 毫秒
51.
52.
Chelsea C. Buck Patrick B. Dennis Maneesh K. Gupta Marcus T. Grant Marquise G. Crosby Joseph M. Slocik Peter A. Mirau Kellie A. Becknell Kristen K. Comfort Rajesh R. Naik 《Macromolecular bioscience》2019,19(3)
The suckerin family of proteins, identified from the squid sucker ring teeth assembly, offers unique mechanical properties and potential advantages over other natural biomaterials. In this study, a small suckerin isoform, suckerin‐12, is used to create enzymatically crosslinked, macro‐scale hydrogels. Upon exposure to specific salt conditions, suckerin‐12 hydrogels contracted into a condensed state where mechanical properties are found to be modulated by the salt anion present. The rate of contraction is found to correlate well with the kosmotropic arm of the Hofmeister anion series. However, the observed changes in hydrogel mechanical properties are better explained by the ability of the salt to neutralize charges in suckerin‐12 by deprotonization or charge screening. Thus, by altering the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin‐12 hydrogels. The potential for suckerins to add new properties to materials based on naturally‐derived proteins is highlighted. 相似文献
53.
T. J. Grant 《The Journal of the Operational Research Society》1986,37(1):41-57
This paper compares operational research (O.R.) with the currently fashionable topic of artificial intelligence (A.I.) at a detailed level. A.I. concepts, techniques and history are summarized, and O.R. and A.I. approaches compared. A case study-the development of a potential aid to scheduling repair jobs on RAF squadrons—is described. The paper shows where A.I. concepts and techniques were used in the prototype program, known as the Fault Identification & Expediting Repair (FIXER) system. Finally, some lessons for O.R. are drawn. 相似文献
54.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
55.
Lipschitz regularity for solutions to nonsmooth problems in the calculus of variations is considered, where we allow for extended-real-valued Lagrangians. Conditions for regularity are given in terms of subdifferentiability properties of the value function. In particular, it is shown that there exists a Lipschitz minimizer as long as the limiting subgradient of the value function is nonempty at the point in question. The results improve upon previous results in the literature, even in the case of finite Lagrangians. 相似文献
56.
Mark Grant 《Topology and its Applications》2012,159(1):88-97
We show how locally smooth actions of compact Lie groups on a manifold X can be used to obtain new upper bounds for the topological complexity TC(X), in the sense of Farber. We also obtain new bounds for the topological complexity of finitely generated torsion-free nilpotent groups. 相似文献
57.
Dilip S. Sundaram Vigor Yang Terrence L. Connell Grant A. Risha Richard A. Yetter 《Proceedings of the Combustion Institute》2013,34(2):2221-2228
Flame propagation of aluminum–ice (ALICE) mixtures is studied theoretically and experimentally. Both a mono distribution of nano aluminum particles and a bimodal distribution of nano- and micron-sized aluminum particles are considered over a pressure range of 1–10 MPa. A multi-zone theoretical framework is established to predict the burning rate and temperature distribution by solving the energy equation in each zone and matching the temperature and heat flux at the interfacial boundaries. The burning rates are measured experimentally by burning aluminum–ice strands in a constant-volume vessel. For stoichiometric ALICE mixtures with 80 nm particles, the burning rate shows a pressure dependence of rb = aPn, with an exponent of 0.33. If a portion of 80 nm particles is replaced with 5 and 20 μm particles, the burning rate is not significantly affected for a loading density up to 15–25% and decreases significantly beyond this value. The flame thickness of a bimodal-particle mixture is greater than its counterpart of a mono-dispersed particle mixture. The theoretical and experimental results support the hypothesis that the combustion of aluminum–ice mixtures is controlled by diffusion processes across the oxide layers of particles. 相似文献
58.
59.
Daniel S. Grant Jakaria Ahmed Jason D. Whittle Andrew Michelmore Krasimir Vasilev Kateryna Bazaka Mohan V. Jacob 《Molecules (Basel, Switzerland)》2021,26(16)
If plasma polymer thin films are to be synthesised from sustainable and natural precursors of chemically heterogeneous composition, it is important to understand the extent to which this composition influences the mechanism of polymerisation. To this end, a well-studied monoterpene alcohol, terpinen-4-ol, has been targeted for a comparative study with the naturally occurring mix of terpenes (viz. Melaleuca alternifolia oil) from which it is commonly distilled. Positive ion mode mass spectra of both terpinen-4-ol and M. alternifolia oil showed a decrease in disparities between the type and abundance of cationic species formed in their respective plasma environments as applied plasma power was increased. Supplementary biological assay revealed the antibacterial action of both terpinen-4-ol and M. alternifolia derived coatings with respect to S. aureus bacteria, whilst cytocompatibility was demonstrated by comparable eukaryotic cell adhesion to both coatings. Elucidating the processes occurring within the reactive plasmas can enhance the economics of plasma polymer deposition by permitting use of the minimum power, time and precursor pre-processing required to control the extent of monomer fragmentation and fabricate a film of the desired thickness and functionality. 相似文献
60.
Fused-sphere surfaces can be used to mimic a molecular boundary associated with a constant value of the electron density. The simplest of such fused-sphere models are constructed by using the atomic radii for the spherical isodensity surfaces of individual atoms. In this work, we discuss the extension of this model to molecules containing atoms beyond the second row. In these many- electron systems, the computation of electron densities is usually simplified by adopting a pseudopotential (or effective-core potential) approach. Here, we discuss the performance of large- and small-core pseudo-potential calculations as a tool to derive atomic radii. Our results provide an optimum set of variable radii that can be used to build fused-sphere surfaces. This continuum of surfaces provides a simple approximation to the low-electron-density regions around molecules with heavy atoms. 相似文献