全文获取类型
收费全文 | 50052篇 |
免费 | 8531篇 |
国内免费 | 6428篇 |
专业分类
化学 | 36092篇 |
晶体学 | 527篇 |
力学 | 3108篇 |
综合类 | 425篇 |
数学 | 6056篇 |
物理学 | 18803篇 |
出版年
2024年 | 186篇 |
2023年 | 1044篇 |
2022年 | 1703篇 |
2021年 | 1792篇 |
2020年 | 2147篇 |
2019年 | 2036篇 |
2018年 | 1728篇 |
2017年 | 1569篇 |
2016年 | 2433篇 |
2015年 | 2438篇 |
2014年 | 2835篇 |
2013年 | 3598篇 |
2012年 | 4436篇 |
2011年 | 4468篇 |
2010年 | 3099篇 |
2009年 | 2857篇 |
2008年 | 3244篇 |
2007年 | 2851篇 |
2006年 | 2654篇 |
2005年 | 2330篇 |
2004年 | 1883篇 |
2003年 | 1662篇 |
2002年 | 1845篇 |
2001年 | 1561篇 |
2000年 | 1168篇 |
1999年 | 1145篇 |
1998年 | 831篇 |
1997年 | 749篇 |
1996年 | 791篇 |
1995年 | 688篇 |
1994年 | 574篇 |
1993年 | 432篇 |
1992年 | 432篇 |
1991年 | 396篇 |
1990年 | 327篇 |
1989年 | 243篇 |
1988年 | 191篇 |
1987年 | 141篇 |
1986年 | 156篇 |
1985年 | 111篇 |
1984年 | 80篇 |
1983年 | 59篇 |
1982年 | 30篇 |
1981年 | 30篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1975年 | 2篇 |
1959年 | 1篇 |
1957年 | 9篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
本文利用统计计量学方法对山西省农民家庭消费水平和消费结构的变化及原因进行了实证分析。建立了山西省农民人均消费的消费函数和山西省农民总消费支出与食品、衣着、住房、日用品、燃料及文化生活服务支出的关系模型,并通过模型分析解释了农民的消费结构,也为决策者提供一些有效的参考资料。 相似文献
2.
3.
Qipeng Guo Fei Chen Ke Wang Ling Chen 《Journal of Polymer Science.Polymer Physics》2006,44(21):3042-3052
An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006 相似文献
4.
Yuxi Zheng 《Communications in Mathematical Physics》1991,135(3):581-594
We show that the weak-L
2 limit of a sequence of solutions of the two dimensional incompressible Euler equation is still a solution, provided that a (strong) concentration set for the reduced defect measure has locally finite one dimensional Hausdorff measure in space and time. 相似文献
5.
Qian-shun Chang Bo-ling GuoInstitute of Applied Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing ChinaInstitute of Applied Physics Computational Mathematics Beijing China 《应用数学学报(英文版)》2002,18(2):201-214
Abstract In this paper, a dissipative Zakharov equations are discretized by difference method.We make priorestimates for the algebric system of equations. It is proved that for each mesh size,there exist attractors forthe discretized system.The bounds of the Hausdorff dimensions of the discrete attractors are obtained,and thevarious bounds are dependent of the mesh sizes. 相似文献
6.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
7.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
8.
9.
10.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献