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   315082篇
  免费   4844篇
  国内免费   2660篇
化学   155545篇
晶体学   5280篇
力学   15696篇
综合类   198篇
数学   44972篇
物理学   100895篇
  2021年   1957篇
  2020年   2321篇
  2019年   2528篇
  2018年   11294篇
  2017年   12184篇
  2016年   8229篇
  2015年   3787篇
  2014年   4579篇
  2013年   10441篇
  2012年   12264篇
  2011年   21854篇
  2010年   13808篇
  2009年   13744篇
  2008年   18649篇
  2007年   21973篇
  2006年   7832篇
  2005年   13678篇
  2004年   9617篇
  2003年   9070篇
  2002年   6973篇
  2001年   6764篇
  2000年   5350篇
  1999年   3937篇
  1998年   3074篇
  1997年   2973篇
  1996年   3006篇
  1995年   2764篇
  1994年   2601篇
  1993年   2409篇
  1992年   3053篇
  1991年   2934篇
  1990年   2862篇
  1989年   2867篇
  1988年   2882篇
  1987年   2856篇
  1986年   2726篇
  1985年   3446篇
  1984年   3445篇
  1983年   2721篇
  1982年   2814篇
  1981年   2871篇
  1980年   2628篇
  1979年   2983篇
  1978年   2977篇
  1977年   3009篇
  1976年   2878篇
  1975年   2606篇
  1974年   2561篇
  1973年   2553篇
  1968年   1800篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
92.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
93.
94.
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
95.
96.

The adsorption and photocatalytic degradation of Ethyl methylphosphonate (EMPA) on powdery TiO2 film has experimentally investigated using attenuated total reflection-infrared Fourier transform spectroscopy (ATR-FTIR) in ambient condition. Characteristic IR frequency as P-O-C vibration mode as EtO was observed by EMPA adsorbed at the surface of TiO2. By TiO2 photocatalysis, the adsorbed EMPA was decomposed to methyl phosphonic acid and phosphoric acid. The increment of IR intensity of which is assigned to Ti–O-P-O-Ti of EMPA was accompanied with increasing the IR peak intensity assigned to MPA. About that, we suggest that the appearance of the Ti–O-P-O-Ti of EMPA by the TiO2 photocatalysis is regarded as acceleration of the hydrolysis of EMPA by the surface OH groups of TiO2. The plausible adsorption structure and the photocatalytic reaction mechanism of EMPA at the surface of TiO2 photocatalyst were elucidated.

  相似文献   
97.
98.
99.
100.
Journal of Thermal Analysis and Calorimetry - The operating temperature of Li-ion batteries used in modern electric vehicles should be maintained within an allowable range to avoid thermal runaway...  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