全文获取类型
收费全文 | 63188篇 |
免费 | 10390篇 |
国内免费 | 8688篇 |
专业分类
化学 | 46114篇 |
晶体学 | 912篇 |
力学 | 3707篇 |
综合类 | 620篇 |
数学 | 7458篇 |
物理学 | 23455篇 |
出版年
2024年 | 177篇 |
2023年 | 1060篇 |
2022年 | 2024篇 |
2021年 | 2125篇 |
2020年 | 2278篇 |
2019年 | 2358篇 |
2018年 | 2051篇 |
2017年 | 2073篇 |
2016年 | 2835篇 |
2015年 | 3017篇 |
2014年 | 3666篇 |
2013年 | 4764篇 |
2012年 | 5599篇 |
2011年 | 5867篇 |
2010年 | 4239篇 |
2009年 | 4279篇 |
2008年 | 4699篇 |
2007年 | 4063篇 |
2006年 | 3706篇 |
2005年 | 3102篇 |
2004年 | 2387篇 |
2003年 | 1979篇 |
2002年 | 1974篇 |
2001年 | 1623篇 |
2000年 | 1348篇 |
1999年 | 1166篇 |
1998年 | 938篇 |
1997年 | 829篇 |
1996年 | 814篇 |
1995年 | 665篇 |
1994年 | 654篇 |
1993年 | 561篇 |
1992年 | 495篇 |
1991年 | 415篇 |
1990年 | 364篇 |
1989年 | 277篇 |
1988年 | 242篇 |
1987年 | 188篇 |
1986年 | 209篇 |
1985年 | 198篇 |
1984年 | 123篇 |
1983年 | 92篇 |
1982年 | 83篇 |
1981年 | 67篇 |
1980年 | 60篇 |
1979年 | 76篇 |
1978年 | 47篇 |
1977年 | 43篇 |
1974年 | 45篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Wei Wang Li-Ping Pang Zun-Quan Xia 《应用数学学报(英文版)》2007,23(1):29-38
In this paper,the UV-theory and P-differential calculus are employed to study second-order ex-pansion of a class of D.C.functions and minimization problems.Under certain conditions,some properties ofthe U-Lagrangian,the second-order expansion of this class of functions along some trajectories are formulated.Some first and second order optimality conditions for the class of D.C.optimization problems are given. 相似文献
162.
163.
Chii-Wann Lin Kuo-Ping Chen Ming-Chii Su Chih-Kung Lee Chih-Chung Yang 《Optical and Quantum Electronics》2005,37(13-15):1423-1437
We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure. 相似文献
164.
Richard Becker Mladen Prester Ping Hui Lin Mats Johnsson Ivica Zivkovic 《Journal of solid state chemistry》2007,180(3):1051-1059
Two new isostructural cobalt selenite halides Co5(SeO3)4Cl2 and Co5(SeO3)4Br2 have been synthesized. They crystallize in the triclinic system space group P−1 with the following lattice parameters for Co5(SeO3)4Cl2: a=6.4935(8) Å, b=7.7288(8) Å, c=7.7443(10) Å, α=66.051(11)°, β=73.610(11)°, γ=81.268(9)°, and Z=1. The crystal structures were solved from single-crystal X-ray data, R1=3.73 and 4.03 for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively. The new compounds are isostructural to Ni5(SeO3)4Br2.Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range. The anisotropic susceptibility is quantitatively interpreted within the zero-field splitting schemes for Co2+ and Ni2+ ions. Sharp low-temperature susceptibility features, at TN=18 and 20 K for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively, are ascribed to antiferromagnetic ordering in a minority magnetic subsystem. In isostructural Ni5(SeO3)4Br2 magnetically ordered subsystem represents a majority fraction (TN=46 K). Nevertheless, anisotropic susceptibility of Ni5(SeO3)4Br2 is dominated at low temperatures by a minority fraction, subject to single-ion anisotropy effects and increasing population of Sz=0 (singlet) ground state of octahedrally coordinated Ni2+. 相似文献
165.
166.
长江中下游的主要防洪工程是长江干堤 ,长江堤防线路长、工程浩大、堤基工程地质水文地质条件复杂 ,涉及大量的已有地质数据和资料。今后在整治加固堤防的工程地质勘察工作中 ,还需随时进行数据的收集、存储、检索、分析、统计和维护 ,随时调用这些数据进行综合处理、编制报告和图件 ;在防汛期间可以针对堤防险工险段的险情 ,随时查询和调用有关的资料、数据或者图件 ,提供采取抢险措施决策的地质依据。这既提高了地质数据的利用价值和利用率 ,又保证了信息的准确性、完整性和共享性。因此 ,建立合理的长江堤防工程地质信息处理模型及其成熟的技术方法具有重要的意义。 相似文献
167.
Jiang Tongsong Liu Yonghui Wei Musheng 《高校应用数学学报(英文版)》2006,21(1):113-118
This paper derives a theorem of generalized singular value decomposition of quaternion matrices (QGSVD),studies the solution of general quaternion matrix equation AXB -CYD= E,and obtains quaternionic Roth's theorem. This paper also suggests sufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation. 相似文献
168.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献
169.
A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors. 相似文献
170.