全文获取类型
收费全文 | 53203篇 |
免费 | 2442篇 |
国内免费 | 2101篇 |
专业分类
化学 | 26163篇 |
晶体学 | 831篇 |
力学 | 2079篇 |
综合类 | 112篇 |
数学 | 4760篇 |
物理学 | 16038篇 |
无线电 | 7763篇 |
出版年
2022年 | 631篇 |
2021年 | 679篇 |
2020年 | 664篇 |
2019年 | 794篇 |
2018年 | 910篇 |
2017年 | 887篇 |
2016年 | 1293篇 |
2015年 | 1120篇 |
2014年 | 1561篇 |
2013年 | 2676篇 |
2012年 | 2714篇 |
2011年 | 3066篇 |
2010年 | 2355篇 |
2009年 | 2486篇 |
2008年 | 2706篇 |
2007年 | 2721篇 |
2006年 | 2427篇 |
2005年 | 2145篇 |
2004年 | 1979篇 |
2003年 | 1648篇 |
2002年 | 1633篇 |
2001年 | 1948篇 |
2000年 | 1447篇 |
1999年 | 1172篇 |
1998年 | 911篇 |
1997年 | 843篇 |
1996年 | 734篇 |
1995年 | 656篇 |
1994年 | 635篇 |
1993年 | 597篇 |
1992年 | 629篇 |
1991年 | 621篇 |
1990年 | 587篇 |
1989年 | 508篇 |
1988年 | 517篇 |
1987年 | 470篇 |
1986年 | 416篇 |
1985年 | 472篇 |
1984年 | 497篇 |
1983年 | 362篇 |
1982年 | 395篇 |
1981年 | 387篇 |
1980年 | 334篇 |
1979年 | 408篇 |
1978年 | 382篇 |
1977年 | 412篇 |
1976年 | 400篇 |
1975年 | 350篇 |
1974年 | 330篇 |
1973年 | 343篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
121.
The Hawking radiation of Dirac particles on the event horizon of a nonuniformly rectilinearly accelerating black hole is studied in this paper. First, we construct the symmetrized null tetrad from which the spin coefficients and Dirac equation are derived. Next, by proposing generalized tortoise coordinate transformation, the decoupling problem of the Dirac equation with nonzero rest mass is solved. Finally, by analytic continuation, the Hawking thermal spectrum formula of Dirac particle for nonuniformly rectilinearly accelerating black hole is obtained. 相似文献
122.
The crystal structure of [N(CH3)4]3[As2Cl9] is determined at 293 K. It crystallizes in trigonal space group P31c: a = 9.2199(8), c = 21.065(3)Å, Z = 2, R1 = 0.0505, wR2 = 0.1283. The crystal is built of the discrete bioctahedral [As2Cl9]3— anions and the deformed tetramethylammonium cations. A structural phase transition in [N(CH3)4]3[As2Cl9] is detected by the DSC and dilatometric techniques at 146/151 K (on cooling/heating). Dielectric relaxation studies in the frequency range 75 kHz — 5 MHz indicate reorientations of the tetramethylammonium cations within the high temperature phase. Optical observations show the existence of the ferroelastic domain structure below 146 K. The possible mechanism of phase transition is discussed on the basis of the presented results. 相似文献
123.
Z. Kassai V. Koprda K. Bauerová M. Harangozó P. Bendová A. Bujnová A. Kassai 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(3):669-672
The composition and the permeation properties of the skin are dependent on age. In the animal models for permation studies, age affects the mechanical as well as the permeation properties significantly. The time dependence of permeation of 147Pm3+ from aqueous solution was established by the animal skin model and the age dependence of promethium permeation through the skin was examined. The aim was to find the optimum rat skin age model for radionuclide permeation studies and to assess the relative importance of the main permeation pathways: transepidermal and transfollicular permeation. The skin from 5-day-old rats (5DR) was found to represent the optimum animal model to study transepidermal permeation of ions. The skin from 9-day-old rats (9DR) was selected to study transfollicular permeation of ions. Comparison of the permeated amounts of promethium through the skin without hairs (3 DR to 6 DR) and with hairs (7DR to 12DR) showed that the additional permation mode via follicles significantly contributed to the permeation rate and extent. 相似文献
124.
Pezeshki A. Scharf L.L. Azimi-Sadjadi M.R. Yingbo Hua 《Signal Processing, IEEE Transactions on》2005,53(1):121-135
The problem of two-channel constrained least squares (CLS) filtering under various sets of constraints is considered, and a general set of solutions is derived. For each set of constraints, the solution is determined by a coupled (asymmetric) generalized eigenvalue problem. This eigenvalue problem establishes a connection between two-channel CLS filtering and transform methods for resolving channel measurements into canonical or half-canonical coordinates. Based on this connection, a unified framework for reduced-rank Wiener filtering is presented. Then, various representations of reduced-rank Wiener filters in canonical and half-canonical coordinates are introduced. An alternating power method is proposed to recursively compute the canonical coordinate and half-canonical coordinate mappings. A deflation process is introduced to extract the mappings associated with the dominant coordinates. The correctness of the alternating power method is demonstrated on a synthesized data set, and conclusions are drawn. 相似文献
125.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
126.
The process of muon (pion) pair production with small invariant mass in electron-positron high-energy annihilation, accompanied by emission of a hard photon at large angles, is considered. We find that the Drell-Yan picture for the differential cross section is valid in the charge-even experimental setup. Radiative corrections both for the electron block and for the final-state block are taken into account. 相似文献
127.
S.BOUZID Z.AZARI 《宁波大学学报(理工版)》2003,16(4):354-362
冲蚀过程是一个与颗粒反复冲击物体表面而移除物质相关的表面现象.本文研究了玻璃的冲蚀坑的几何尺寸和体积,给出了冲蚀移除物质如何依赖于颗粒流动速度、颗粒尺寸和冲击角的理论关系.通过理论与实验结果相比较,定义了一定冲蚀坑尺度的有效域. 相似文献
128.
129.
We establish some liminf theorems on the increments of a (N,d)-Gaussian process with the usual Euclidean norm, via estimating upper bounds of large deviation probabilities on the suprema
of the (N,d)-Gaussian process.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
130.
In the elastic angular distributions of the systems composed of tightly bound α-nuclei, 12C+12C, 16O+16O and 16O+12C, the higher-order Airy minima are observed in the energy region between 5 and 10 MeV per nucleon. The obtained optical potentials are deeply attractive and with incomplete absorption. The same potentials successfully describe the lower-energy (molecular resonances) and the higher-energy (first Airy minimum) data. 相似文献