全文获取类型
收费全文 | 72812篇 |
免费 | 7789篇 |
国内免费 | 5330篇 |
专业分类
化学 | 41767篇 |
晶体学 | 768篇 |
力学 | 3975篇 |
综合类 | 290篇 |
数学 | 13683篇 |
物理学 | 25448篇 |
出版年
2024年 | 178篇 |
2023年 | 971篇 |
2022年 | 1664篇 |
2021年 | 1822篇 |
2020年 | 1941篇 |
2019年 | 1900篇 |
2018年 | 2760篇 |
2017年 | 2811篇 |
2016年 | 2887篇 |
2015年 | 2640篇 |
2014年 | 3176篇 |
2013年 | 3985篇 |
2012年 | 7099篇 |
2011年 | 6255篇 |
2010年 | 4508篇 |
2009年 | 4038篇 |
2008年 | 3342篇 |
2007年 | 3131篇 |
2006年 | 2959篇 |
2005年 | 6279篇 |
2004年 | 5335篇 |
2003年 | 3475篇 |
2002年 | 1714篇 |
2001年 | 1318篇 |
2000年 | 867篇 |
1999年 | 1062篇 |
1998年 | 877篇 |
1997年 | 793篇 |
1996年 | 783篇 |
1995年 | 672篇 |
1994年 | 572篇 |
1993年 | 468篇 |
1992年 | 581篇 |
1991年 | 500篇 |
1990年 | 423篇 |
1989年 | 346篇 |
1988年 | 253篇 |
1987年 | 179篇 |
1986年 | 179篇 |
1985年 | 155篇 |
1984年 | 110篇 |
1983年 | 92篇 |
1982年 | 66篇 |
1981年 | 53篇 |
1976年 | 82篇 |
1975年 | 38篇 |
1974年 | 41篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
X. Luo F. Y. Shi J. X. Lin 《International Journal of Infrared and Millimeter Waves》1991,12(2):141-147
Detection of COCl2, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN2 cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC 相似文献
122.
123.
The Randi? index R(G) of a (chemical) graph G is also called connectivity index. Hansen and Mélot [Variable neighborhood search for extremal graphs 6: analyzing bounds for the connectivity index, J. Chem. Inf. Comput. Sci. 43 (2003) 1-14] in their paper, characterized the chemical trees of given order and number of pendent vertices which have the minimum and maximum Randi? index, respectively. In this note, we point out the mistakes in the proofs of their results Theorems 8 and 10, while we still believe that the two theorems are true, and then we give their corrected proofs. 相似文献
124.
Shuguan Ji Zhenxin Liu Shaoyun Shi 《Journal of Mathematical Analysis and Applications》2007,325(2):1306-1313
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate boundary value problems for a class of second order differential equations on the half-line. Some applications are presented to illustrate the potential of this method. 相似文献
125.
126.
Mingyang Zhao Warren T. Ford Stefan H. J. Idziak Nicholas C. Maliszewskyj Paul A. Heiney 《Liquid crystals》1994,16(4):583-599
The hexa-4-dodecyloxybenzoyl derivative 1 of azacrown [18]-N6 was originally reported to have a 'tubular' mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of 1 under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of 1 is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative 2 of azacrown [18]-N6 has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH2)11 spacer and 75-84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N6 mesogen. The polysiloxanes also display a liquid crystalline phase. 相似文献
127.
Andrzej Wi?nicki 《Journal of Mathematical Analysis and Applications》2002,267(1):158-172
We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory. 相似文献
128.
YBa2Cu3O7-δ and Tl2Ba2CaCu2O8 thin films for microwave filters were synthesized by pulsed laser deposition and the two-step thalliation process. Substrate
quality requirements and the relation of thin film morphology, microstructure with microwave surface resistance were discussed. 相似文献
129.
记Ore2=min{d(y) d(x)|x,y∈V(G),d(x,y)=2},本得到:若n阶图G的Ore2≥n 1,则G是[5;n]泛连通图。此是比Faudree等人的定理进一步的结果。 相似文献
130.
Let φ be a normal function on [0,1) and A'(φ)(1
相似文献