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   425746篇
  免费   2984篇
  国内免费   1036篇
化学   216423篇
晶体学   6292篇
力学   20876篇
综合类   11篇
数学   54455篇
物理学   131709篇
  2021年   4334篇
  2020年   4723篇
  2019年   5449篇
  2018年   6797篇
  2017年   6867篇
  2016年   9514篇
  2015年   4982篇
  2014年   8350篇
  2013年   18874篇
  2012年   14600篇
  2011年   17548篇
  2010年   13186篇
  2009年   13161篇
  2008年   16625篇
  2007年   16516篇
  2006年   15017篇
  2005年   13430篇
  2004年   12452篇
  2003年   11140篇
  2002年   11085篇
  2001年   11757篇
  2000年   9094篇
  1999年   7050篇
  1998年   6110篇
  1997年   5977篇
  1996年   5533篇
  1995年   5010篇
  1994年   5013篇
  1993年   4807篇
  1992年   5059篇
  1991年   5466篇
  1990年   5235篇
  1989年   5205篇
  1988年   5041篇
  1987年   4900篇
  1986年   4703篇
  1985年   5856篇
  1984年   6215篇
  1983年   5220篇
  1982年   5417篇
  1981年   5094篇
  1980年   4795篇
  1979年   5193篇
  1978年   5401篇
  1977年   5278篇
  1976年   5271篇
  1975年   5039篇
  1974年   4889篇
  1973年   5153篇
  1972年   3749篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Abstract

On behalf of the Umweltbundesamt the Fraunhofer Gesellschaft has developed a software system (SAR-system) comprising more than 90 estimation models for endpoints relevant in environmental risk assessment. These estimation models are based on the approach of quantitative structure-activity relationships (QSAR). All models were checked for their validity and application range. In the last months the Umweltbundesamt started to test the applicability of some models concerning the endpoints fish acute toxicity, daphnia acute toxicity and ready (i.e., ultimate) biodegradability in the daily routine of the notification procedure. For testing these models the corresponding confidential data given in the dossiers of substances notified 1993 in Germany, were used. We were able to make calculations for 36% of the notified substances. For the remaining 64% of the chemicals it was impossible to accomplish SAR estimations due to several reasons, e.g., ionic structure of the compounds. Different results for the applicability of the mentioned endpoints are obtained. The predictions of the fish and Daphnia toxicity are in sufficient agreement with the experimental results, in case of the fish toxicity we receive 58% agreement, for the Daphnia toxicity 56% The corresponding values which were obtained in the US EPA/E.C. Joint Project on the evaluation of (quantitative) structure activity relationships were 82.3% and 70.9% About 300 different models were used for the calculations of these endpoints within the framework of the EPA/EC project. The SAR-system presented here contains 8 models for estimating the fish toxicity and 6 models for the Daphnia toxicity. For the prediction of the biodegradability the results obtained with the SAR-system are rather poor and have to be improved. Meanwhile the SAR-system is commercially available and can be ordered at the Fraunhofer Institute for Environmental Chemistry and Ecotoxicology, Schmallenberg (Germany).  相似文献   
992.
JETP Letters - The temperature dependences of attenuation and the velocity of ultrasonic waves at frequencies of 26–158 MHz in a CaF2 fluorite crystal at the substitution of...  相似文献   
993.
JETP Letters - The vibrational properties of yttrium iron garnet Y3Fe5O12 at a high quasihydrostatic pressure are studied by the Raman spectroscopy method. Raman spectra are measured in a...  相似文献   
994.
JETP Letters - Low-temperature (5 K) microphotoluminescence has been measured in order to study individual luminescent centers formed by the cores of partial dislocations in a CdTe/Si film and a...  相似文献   
995.
Gusakov  E. Z.  Popov  A. Yu. 《JETP Letters》2021,114(3):138-142
JETP Letters - The possibility of the localization of longitudinal waves in the intermediate frequency range in the edge transport barrier of a toroidal nuclear fusion facility is discovered. It is...  相似文献   
996.
Volkov  M. K.  Pivovarov  A. A. 《JETP Letters》2021,114(6):309-313
JETP Letters - The partial width of the $$\tau \to {{K}^{ - }}{{K}^{0}}{{\nu }_{\tau }}$$ decay has been calculated within the extended Nambu–Jona-Lasinio model including the contact and...  相似文献   
997.
Udintseva  M. S.  Efremov  A. V.  Smirnov  D.  Makarova  A.  Naumov  S. V.  Shamin  S. N.  Galakhov  V. R. 《JETP Letters》2021,114(8):475-478
JETP Letters - The oxygen K-edge X-ray absorption spectra in EuBaCo2O5.52 ± 0.02 and EuBaCo2O5.24 ± 0.02 cobaltites are measured at temperatures of 300 and 440 K, which are below and...  相似文献   
998.
Niyazov  R. A.  Aristov  D. N.  Kachorovskii  V. Yu. 《JETP Letters》2021,113(11):689-700
JETP Letters - We review recent studies of the spin-dependent tunneling transport via an Aharonov–Bohm interferometer (ABI) formed by helical edge states. We focus on the experimentally...  相似文献   
999.
Zubarev  N. M.  Mesyats  G. A. 《JETP Letters》2021,113(4):259-264
JETP Letters - A mechanism for the initiation of explosive electron emission at the interface between the cathode and a dense gas is proposed. It is based on the accumulation of positive ions,...  相似文献   
1000.
Yakushkin  E. D.  Sandler  V. A. 《JETP Letters》2021,113(5):352-355
JETP Letters - A magnetically induced deceleration of the initial stage of the isothermal phase transition of ferroelastic-superprotonic cesium hydrogen sulfate has been detected. The effect is...  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