全文获取类型
收费全文 | 11989篇 |
免费 | 4053篇 |
国内免费 | 760篇 |
专业分类
化学 | 2688篇 |
晶体学 | 280篇 |
力学 | 422篇 |
综合类 | 73篇 |
数学 | 363篇 |
物理学 | 12976篇 |
出版年
2024年 | 12篇 |
2023年 | 52篇 |
2022年 | 198篇 |
2021年 | 229篇 |
2020年 | 221篇 |
2019年 | 183篇 |
2018年 | 230篇 |
2017年 | 382篇 |
2016年 | 458篇 |
2015年 | 378篇 |
2014年 | 721篇 |
2013年 | 840篇 |
2012年 | 800篇 |
2011年 | 1075篇 |
2010年 | 685篇 |
2009年 | 820篇 |
2008年 | 952篇 |
2007年 | 1020篇 |
2006年 | 886篇 |
2005年 | 725篇 |
2004年 | 724篇 |
2003年 | 623篇 |
2002年 | 626篇 |
2001年 | 497篇 |
2000年 | 532篇 |
1999年 | 471篇 |
1998年 | 377篇 |
1997年 | 332篇 |
1996年 | 307篇 |
1995年 | 257篇 |
1994年 | 228篇 |
1993年 | 179篇 |
1992年 | 175篇 |
1991年 | 137篇 |
1990年 | 105篇 |
1989年 | 80篇 |
1988年 | 59篇 |
1987年 | 60篇 |
1986年 | 36篇 |
1985年 | 27篇 |
1984年 | 27篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
M. Chawda N. Patel K. C. Sebastian D. R. S. Somayajulu M. Sarkar R. P. Singh 《辐射效应与固体损伤》2013,168(6):361-364
Radiation-induced defects are studied in cubic rhodium metal, using the local probe technique ‘Time differential perturbed angular correlation’ (TDPAC) at liquid N2 temperature. Isochronal annealing was done at 300, 1073 and 1473 K temperatures. The irradiated sample showed two quadrupole interaction frequencies at 1150 and 93 MHz. The low frequency disappeared at room-temperature annealing, which was assigned to In trapped at a vacancy, whereas the higher frequency remained up to high temperatures and was attributed to In trapped at Rh–C complexes in the Rh matrix. 相似文献
993.
Lasers and amplifiers in a single fiber have been developed rapidly, especially for optical fiber communication and various sensors, in the recent years. However, remarkable progress and achievement have been made mainly in silica fiber doped with rare earth elements. In this paper, we report the progress on the development of the Yb3+-doped phosphate fiber laser. 相似文献
994.
Straightness Measurement Using Laser Diode and CCD Camera 总被引:4,自引:0,他引:4
HAO Qun ZHAO Yang LI Dacheng CAO Mang 《Chinese Journal of Lasers》1999,8(3):215-220
1IntroductionInmanufactureandasembleofmodernmachinesandinstruments,anindispensablerequirementisthecontrolofformandpositionero... 相似文献
995.
Xianglei Kong 《中国光学快报(英文版)》2008,6(6)
Direct mass spectrometric analysis of complex biological samples is very important and challenging. In this paper, nanodiamonds have been successfully used in matrix-assisted laser desorption/ionization mass spectrometric analysis of human serum and urine. As a practical tool and platform, it can be widely used in the field of humoral proteomics, and it plays a very promising role in clinical diagnosis, including identification of novel disease-associated biomarkers. 相似文献
996.
采用固体烧结法制备了Sr2-xSmxFeMoO6(x=0,0.03,0.05,0.08,0.10,0.13,0.15,0.20)多晶结构样品,用X射线衍射对材料的结构进行了检测。通过光热偏转技术方法对该材料的热扩散率进行了研究,给出了掺杂比例与材料热扩散率的关系曲线,结果发现Sr2FeMoO6样品随着参杂Sm浓度的增加,结构发生变化的同时,样品的热扩散率也随着波动变化。这与文献[1]中给出的结论有明显不同,从声子、电子、自旋及其相互作用角度揭示了与文献[1]不同的根本原因;并且从x射线和热扩散率两个角度给出了样品Sr2-xSmxFeMoO6结构转变的参杂比例在10—13%的范围,说明光热偏转技术方法是研究参杂镧系元素的双钙钛矿结构和电子参杂效应的可行有效方法。 相似文献
997.
998.
A groundwater management problem is presented involving pumping cost minimization with both well discharges and well locations as decision variables. A grid of candidate well locations is set up and optimal arrangements of wells are sought within this discrete space. A genetic algorithm approach is presented with the following particular features: (a) A suitable scaling is applied to the objective function in order to alleviate its regionally flat behavior. (b) No penalty functions are involved in constraint handling. Instead, the feasible region is transformed into a rectangular domain. The transformation introduced is proved to be bijective. (c) A binary representation of well configurations is presented and compared to a combinatorial one. The binary representation necessitates the introduction of specially designed genetic operators. Besides purely genetic algorithms, the concept of cellular automaton is introduced as the basis of an alternative formulation of the optimization problem. The lattice of the cellular automaton provides the discrete set of candidate well positions. The well configuration is represented by a group of agents occupying an equal number of lattice sites. The agents change positions as dictated by the structure of the automaton and, also, by an associated genetic algorithm, which directs the evolution of the whole scheme toward an optimal configuration. An improved performance of this approach is noted and discussed in comparison to the purely genetic algorithm schemes of the present work. A simulated annealing approach is also applied to the same problem for comparison purposes. Finally, a new and more efficient hybrid annealing–genetic approach is introduced and discussed. 相似文献
999.
Stochastic global search algorithms such as genetic algorithms are used to attack difficult combinatorial optimization problems.
However, genetic algorithms suffer from the lack of a convergence proof. This means that it is difficult to establish reliable
algorithm braking criteria without extensive a priori knowledge of the solution space. The hybrid genetic algorithm presented here combines a genetic algorithm with simulated
annealing in order to overcome the algorithm convergence problem. The genetic algorithm runs inside the simulated annealing
algorithm and provides convergence via a Boltzmann cooling process. The hybrid algorithm was used successfully to solve a
classical 30-city traveling salesman problem; it consistently outperformed both a conventional genetic algorithm and a conventional
simulated annealing algorithm.
This work was supported by the University of Colorado at Colorado Springs. 相似文献
1000.
Experimental measurements of power spectra of a single longitudinal and transverse mode ring dye laser are presented that reveal the critical slowing down of the laser near threshold. External pump noise serves as a probe of the frequency response of the dye laser. Detailed comparisons of the spectral characteristics with computer simulations and an approximate analytic theory are given. The dynamics of spatial pattern formation in a multimode dye laser is examined through measurements of first-passage-time distributions. A comparison of the experiments with computer simulations based on a simple theoretical model of the two-mode laser shows qualitative agreement. These measurements indicate that there are a variety of complex phenomena associated with the transverse mode pattern formation dynamics that need to be addressed theoretically and studied further experimentally. 相似文献