首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   30656篇
  免费   5278篇
  国内免费   3977篇
化学   22136篇
晶体学   354篇
力学   2023篇
综合类   329篇
数学   3631篇
物理学   11438篇
  2024年   75篇
  2023年   574篇
  2022年   920篇
  2021年   1081篇
  2020年   1253篇
  2019年   1211篇
  2018年   1055篇
  2017年   922篇
  2016年   1398篇
  2015年   1502篇
  2014年   1699篇
  2013年   2178篇
  2012年   2660篇
  2011年   2962篇
  2010年   1968篇
  2009年   1794篇
  2008年   1968篇
  2007年   1749篇
  2006年   1663篇
  2005年   1422篇
  2004年   1237篇
  2003年   1022篇
  2002年   1075篇
  2001年   896篇
  2000年   697篇
  1999年   648篇
  1998年   529篇
  1997年   432篇
  1996年   495篇
  1995年   453篇
  1994年   392篇
  1993年   297篇
  1992年   312篇
  1991年   259篇
  1990年   242篇
  1989年   189篇
  1988年   117篇
  1987年   113篇
  1986年   90篇
  1985年   103篇
  1984年   52篇
  1983年   54篇
  1982年   44篇
  1981年   30篇
  1980年   17篇
  1979年   11篇
  1977年   5篇
  1975年   6篇
  1969年   4篇
  1957年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Set-Valued and Variational Analysis - We aim to establish Karush-Kuhn-Tucker multiplier rules involving higher-order complementarity slackness under Hölder metric subregularity. These rules...  相似文献   
12.
13.
14.
15.
16.
A simple and rapid analytical method for the detection of trifloxystrobin, trifloxystrobin acid and tebuconazole in soil, brown rice, paddy plants and rice hulls was established and validated by liquid chromatography with tandem mass spectrometry. Acceptable linearity (R2 > 0.99), accuracy (average recoveries of 74.3–108.5%) and precision (intra- and inter-day relative standard deviations of 0.9–8.8%) were obtained using the developed determination approach. In the field trial, the half-lives of trifloxystrobin and tebuconazole in paddy plants were 5.7–8.3 days in three locations throughout China, and the terminal residue concentrations of trifloxystrobin and tebuconazole were <100 and 500 μg/kg (maximum residue limits set by China), respectively, at harvest, which indicated that, based on the recommended application procedure, trifloxystrobin and tebuconazole are safe for use on rice. The risk assessment results demonstrated that, owing to risk quotient values of both fungicides being <100%, the potential risk of trifloxystrobin and tebuconazole on rice was acceptable for Chinese consumers. These data could provide supporting information for the proper use and safety evaluation of trifloxystrobin and tebuconazole in rice.  相似文献   
17.
18.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160.  相似文献   
19.
20.
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号