全文获取类型
收费全文 | 1228篇 |
免费 | 40篇 |
国内免费 | 4篇 |
专业分类
化学 | 813篇 |
晶体学 | 56篇 |
力学 | 20篇 |
数学 | 73篇 |
物理学 | 310篇 |
出版年
2023年 | 13篇 |
2022年 | 17篇 |
2021年 | 34篇 |
2020年 | 30篇 |
2019年 | 38篇 |
2018年 | 34篇 |
2017年 | 22篇 |
2016年 | 42篇 |
2015年 | 28篇 |
2014年 | 40篇 |
2013年 | 83篇 |
2012年 | 71篇 |
2011年 | 72篇 |
2010年 | 62篇 |
2009年 | 53篇 |
2008年 | 73篇 |
2007年 | 56篇 |
2006年 | 38篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 29篇 |
2000年 | 52篇 |
1999年 | 60篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1977年 | 12篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1272条查询结果,搜索用时 687 毫秒
131.
A nonenzymatic method for the selective detection and quantification of serum uric acid (UA) using 2-thiouracil (2-TU) tailored Au nanoparticles is developed. The H-bonding interaction of UA with functionalized Au nanoparticles brings instantaneous visible color change and paves the way for the visible sensing of UA. 相似文献
132.
Hanane El Hajaji Nadya Lachkar Katim Alaoui Yahya Cherrah Abdellah Farah Abdesslam Ennabili Brahim El Bali Mohammed Lachkar 《Arabian Journal of Chemistry》2011,4(3):321-324
We evaluated the in vitro antioxidant property and phytochemical constituents of the crude ethyl acetate and methanol extract of the three genders of carob tree barks (spontaneous male, spontaneous female, and grafted female). The scavenging activity on DPPH (1,1-diphenyl-2-picrylhydrazyl) was determined, as well as the phenolic contents (Folin–Ciocalteu method) of both the extracts. The highest antioxidant activity and the higher amounts of total phenols were shown in methanol crude bark extract for the three genders. Variety significantly affected the phenol content and the antioxidant activity, with the spontaneous male variety globally showed a higher polyphenol concentration and antioxidant activity than the grafted female and spontaneous female. 相似文献
133.
Ritwik Raj Prashant K. Purohit 《Journal of the mechanics and physics of solids》2011,59(10):2044-2069
We model long rod-like molecules, such as DNA and coiled-coil proteins, as one-dimensional continua with a multi-well stored energy function. These molecules suffer a structural change in response to large forces, characterized by highly typical force-extension behavior. We assume that the structural change proceeds via a moving folded/unfolded interface, or phase boundary, that represents a jump in strain and is governed by the Abeyaratne–Knowles theory of phase transitions. We solve the governing equations using a finite difference method with moving nodes to represent phase boundaries. Our model can reproduce the experimental observations on the overstretching transition in DNA and coiled-coils and makes predictions for the speed at which the interface moves. We employ different types of kinetic relations to describe the mobility of the interface and show that this leads to different classes of experimentally observed force-extension curves. We make connections with several existing theories, experiments and simulation studies, thus demonstrating the effectiveness of the phase transitions-based approach in a biological setting. 相似文献
134.
In this paper, we have investigated Bianchi type I inflationary universe in the presence of massless scalar field with a flat
potential. To get an inflationary solution, we have considered a flat region in which potential V is constant. The inflationary scenario of the model is discussed in detail. 相似文献
135.
We report laser oscillations in Cd II on 4d
95s
2
2
D
5/2 − 4d
105p
2
P
3/2 transition at 441.6 nm using laser produced tungsten plasma as a pumping source. Mach Zehnder interferometer is used to measure
electron density. Design and working of the crossed heat pipe used in the studies is discussed. 相似文献
136.
S. Raj Mohan 《Solid State Communications》2006,139(4):181-185
Field and temperature dependence of hole mobility in N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) doped in polystyrene (PS) is studied using the transient photoconductivity technique. We observe both the positive and negative field dependence of mobility with increasing field and temperature. The field and temperature at which negative field dependence begins is low compared with earlier reports on similar systems (with 20 wt% dopant concentration). Results are discussed on the basis of the Gaussian disorder model (GDM), which predicts that the interplay of both the energetic and positional disorder of dopant molecules in the sample decides the slope of the logμ versus E1/2 plot. The observed mobility dependence is rationalized on the basis of low energetic disorder in the sample. The reason for low energetic disorder is purely due to the film morphology of the sample. Even for a dopant concentration of 20 wt%, we observe clustering and chaining of TPD molecules, which may provide low energetic and positional disorder. 相似文献
137.
A. M. Yacomotti F. Raineri G. Vecchi I. Sagnes M. Strassner L. Le Gratiet R. Raj A. Levenson 《Applied physics. B, Lasers and optics》2005,81(2-3):333-336
We report the fast switching capabilities of a two-dimensional Al0.3Ga0.7As photonic crystal slab around 1.5 μm. The slab is supported by an AlOx low-index thick layer that plays the role of an efficient heat sink. By pumping at 0.8 μm in the absorption of the Al0.3Ga0.7As quantum wells, the optical response is modified in the transparency region: a 200% change in the reflectivity is obtained with a total response time of 8ps. 相似文献
138.
139.
Hans Raj Tiwary 《Discrete and Computational Geometry》2008,40(3):469-479
For polytopes P
1,P
2⊂ℝ
d
, we consider the intersection P
1∩P
2, the convex hull of the union CH(P
1∪P
2), and the Minkowski sum P
1+P
2. For the Minkowski sum, we prove that enumerating the facets of P
1+P
2 is NP-hard if P
1 and P
2 are specified by facets, or if P
1 is specified by vertices and P
2 is a polyhedral cone specified by facets. For the intersection, we prove that computing the facets or the vertices of the
intersection of two polytopes is NP-hard if one of them is given by vertices and the other by facets. Also, computing the
vertices of the intersection of two polytopes given by vertices is shown to be NP-hard. Analogous results for computing the
convex hull of the union of two polytopes follow from polar duality. All of the hardness results are established by showing
that the appropriate decision version, for each of these problems, is NP-complete. 相似文献
140.