全文获取类型
收费全文 | 408996篇 |
免费 | 4695篇 |
国内免费 | 1295篇 |
专业分类
化学 | 223249篇 |
晶体学 | 6572篇 |
力学 | 16686篇 |
综合类 | 13篇 |
数学 | 44309篇 |
物理学 | 124157篇 |
出版年
2020年 | 3240篇 |
2019年 | 3659篇 |
2018年 | 4394篇 |
2017年 | 4359篇 |
2016年 | 6780篇 |
2015年 | 4471篇 |
2014年 | 6830篇 |
2013年 | 18727篇 |
2012年 | 13421篇 |
2011年 | 16586篇 |
2010年 | 11266篇 |
2009年 | 11197篇 |
2008年 | 14833篇 |
2007年 | 14853篇 |
2006年 | 13832篇 |
2005年 | 12735篇 |
2004年 | 11479篇 |
2003年 | 10432篇 |
2002年 | 10079篇 |
2001年 | 12028篇 |
2000年 | 9056篇 |
1999年 | 7092篇 |
1998年 | 5804篇 |
1997年 | 5765篇 |
1996年 | 5366篇 |
1995年 | 5133篇 |
1994年 | 4832篇 |
1993年 | 4762篇 |
1992年 | 5595篇 |
1991年 | 5548篇 |
1990年 | 5322篇 |
1989年 | 5287篇 |
1988年 | 5338篇 |
1987年 | 5330篇 |
1986年 | 5067篇 |
1985年 | 6720篇 |
1984年 | 6841篇 |
1983年 | 5501篇 |
1982年 | 5964篇 |
1981年 | 5891篇 |
1980年 | 5563篇 |
1979年 | 5928篇 |
1978年 | 6075篇 |
1977年 | 6120篇 |
1976年 | 6104篇 |
1975年 | 5475篇 |
1974年 | 5559篇 |
1973年 | 5829篇 |
1972年 | 3777篇 |
1968年 | 3078篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
991.
B. A. Usievich D. Kh. Nurligareev V. A. Sychugov K. M. Golant 《Optics and Spectroscopy》2006,101(6):930-934
A system of tunnel-coupled rectilinear waveguides is studied. The dependence of the number of modes in this system on the number of waveguides N, the distance between the waveguides, and the number of modes in a separate waveguide is considered. It is shown that the modes of the m = N and N + 1 orders in such a system are Bragg modes; i.e., the angle between the direction of their propagation and the system axis is close to the Bragg angle. The effective refractive indices n * of these modes change stepwise. The step size Δn * is found to be dependent on the distance s between the waveguides and on the number of modes in a separate waveguide. A system of single-mode waveguides with the number of guided modes M = 34 < N = 50 is studied experimentally. It is shown that the Bragg modes of the system lie among the leakage modes of the system and have rather low losses. It is demonstrated that the localization of the Bragg modes among the leakage modes may be favorable for their selection upon light generation. 相似文献
992.
Water suppression by diffusive attenuation was used to measure Brix in intact cellular tissue of apple and strawberry. Given
the signal-to-noise ratio, the correlation for apple was established without repeated acquisition, so this protocol should
also be useful for rapid, on-line measurements at low spectrometer frequencies. Water suppression by theT
1-Null method fails with cellular tissue because of the considerable variation in the longitudinal relaxation times of vacuolar
and cytoplasmic water. 相似文献
993.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
994.
The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keV and grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated.For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations. 相似文献
995.
A. A. Lamberov E. V. Dement’eva Kh. Kh. Gil’manov S. R. Egorova N. V. Romanova 《Russian Journal of Applied Chemistry》2006,79(9):1453-1457
The effect of the paste molding pressure on the physicomechanical and texture characteristics of catalysts was studied. An indirect criterion is suggested to evaluate the molding pressure in industrial extruders, whose optimal value ensures good physicomechanical properties of the catalysts and kinetic control over the catalyzed reaction. The results obtained were verified in paste molding on various industrial extruders, and this enabled the optimal choice of the molding equipment. 相似文献
996.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献
997.
998.
N. Ponpandian A. Narayanasamy D. Prabhu K. Ganesan M. Manivel Raja K. Chattopadhyay 《Journal of magnetism and magnetic materials》2006
The Fe73.5Cu1Nb3Si13.5B9 FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys. 相似文献
999.
1000.