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   1860篇
  免费   44篇
  国内免费   14篇
化学   1032篇
晶体学   18篇
力学   44篇
数学   379篇
物理学   445篇
  2022年   15篇
  2021年   14篇
  2020年   26篇
  2019年   15篇
  2018年   30篇
  2017年   30篇
  2016年   61篇
  2015年   59篇
  2014年   48篇
  2013年   108篇
  2012年   102篇
  2011年   111篇
  2010年   96篇
  2009年   70篇
  2008年   100篇
  2007年   91篇
  2006年   63篇
  2005年   67篇
  2004年   73篇
  2003年   42篇
  2002年   58篇
  2001年   31篇
  2000年   43篇
  1999年   29篇
  1998年   18篇
  1997年   20篇
  1996年   26篇
  1995年   12篇
  1994年   17篇
  1993年   18篇
  1992年   15篇
  1991年   15篇
  1990年   14篇
  1989年   15篇
  1988年   10篇
  1985年   10篇
  1984年   15篇
  1983年   13篇
  1982年   12篇
  1981年   14篇
  1980年   15篇
  1979年   10篇
  1978年   17篇
  1977年   12篇
  1974年   12篇
  1966年   9篇
  1962年   9篇
  1957年   23篇
  1956年   13篇
  1955年   15篇
排序方式: 共有1918条查询结果,搜索用时 31 毫秒
51.
For a nonempty setE of nonnegative integers letH E p, q, a andH E p be the closed linear span of
  相似文献   
52.
Zusammenfassung Es wird über Messungen der Adsorption von Lithiumbromid an unbehandelter und an Thioglykolat/CH3J behandelter Austral-A-Wolle zwischen +20 und +80 °C im Konzentrationsbereich zwischen 6 und 10 molarer L?sung berichtet. Die Me?ergebnisse werden mit denen von differentialcalorimetrischen Untersuchungen an denselben Systemen verglichen. Dabei ergibt sich, da? die maximal adsorbierte Menge LiBr ebenso wie die entwickelte W?rmemenge linear mit der Konzentration der LiBr-L?sungen zunimmt. Man erkennt ferner, da? bei unbehandelter Wolle das Maximum der adsorbierten Menge LiBr mit steigender Konzentration der L?sung nach h?heren Temperaturen verschoben wird (9 m: 47 °C; 10 m: 60 °C). An Thioglykolat/CH3J behandelter Wolle mit 4,2% Cystin (gegenüber 11,4% der unbehandelten) tritt das Maximum der LiBr-Adsorption in 10 m-L?sung bereits bei 40 °C auf in übereinstimmung mit den differentialcalorimetrischen Messungen. Damit ist offensichtlich erwiesen, da? der differentialcalorimetrisch exotherme Vorgang zwischen Wolle und LiBr-L?sungen symbat mit der Adsorption des LiBr sowohl in Bezug auf W?rmemenge als auch der Temperaturlage verl?uft. Diese Untersuchungen werden fortgeführt, und wir werden in einiger Zeit über weitere Ergebnisse berichten. Herrn Prof. Dr. F. H. Müller danke ich für anregende Diskussionen, der Deutschen Forschungsgemeinschaft für die gro?zügige finanzielle Unterstützung. Frau U. Hende? hat in dankenswerter Weise bei der Durchführung dieser Arbeiten mitgewirkt.  相似文献   
53.
54.
This paper describes the use of IBC’s AnaLig® Sr-01 molecular recognition technology product to effectively and selectively pre-concentrate, separate, and recover strontium from urine samples. This method uses two-stage columns separation consisting of two different commercial products Eichrom’s Pre-filter Material and AnaLig® Sr-01 column from IBC Advanced Technologies. This method does not involve co-precipitation of strontium as phosphates and oxalates from urine samples. The new rapid method separates strontium-90 with high chemical recovery.  相似文献   
55.
56.
A series of hydrogels from 2‐ethyl‐2‐oxazoline and three bis(2‐oxazoline) crosslinkers—1,4‐butylene‐2,2′‐bis(2‐oxazoline), 1,6‐hexamethylene‐2,2′‐bis(2‐oxazoline), and 1,8‐octamethylene‐2,2′‐bis(2‐oxazoline)—are prepared. The hydrogels differ by the length of aliphatic chain of crosslinker and by the percentage of crosslinker (2–10%). The influence of the type and the percentage of the crosslinker on swelling properties, mechanical properties, and state of water is studied. The equilibrium swelling degree in water ranges from 2 to 20. With a proper selection of the crosslinker, Young's modulus can be varied from 10 kPa to almost 100 kPa. To evaluate the potential for medical applications, the cytotoxicity of extracts and the contact toxicity toward murine fibroblasts are measured. The hydrogels with the crosslinker containing a shorter aliphatic exhibit low toxicity toward fibroblast cells. Moreover, the viability and the proliferation of pancreatic β‐cells incubated inside hydrogels for 12 days are analyzed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1548–1559  相似文献   
57.
New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases.  相似文献   
58.
59.
Accuracy, precision, repeatability and long-term stability, are the most important requirements to enable reliable airborne humidity measurements, which are needed for climate models or to validate e.g. remote sensing instrumentation like satellites. However, various hygrometer artifacts which depend on the individual sensor principle and the application profile frequently cause problems and significantly complicate the hygrometer choice. Sensor intercomparisons are one way of providing the information for an optimal choice. In this paper we present the first part of a blind, static, laboratory-based intercomparison of a new, calibration-free, 1.4 μm diode laser-based, optical hygrometer (SEALDH) with the two most important measurement principles for airborne hygrometry (frost-point hygrometers, FPH, and Lyman-alpha fluorescence hygrometers, LAFH). During three days of measurement, the TDL-hygrometer achieved a H2O resolution of up to 0.5 ppmv (Δt=2 sec) at tropospheric pressure and H2O concentration levels (100–800 hPa, 10 to 8000 ppmv H2O). Its absolute accuracy was investigated via blind intercomparison with two reference FPHs and a LAFH. Without any calibration of SEALDH, i.e. without a comparison to a water vapor standard, we achieve an excellent agreement with the reference sensors, with an average systematic offset (over all three days) of ?3.9 %±1.5 %, which is fully consistent with the sensor’s uncertainty bounds. Further we also reevaluated the SEALDH data of day 2 and 3 in a calibrated mode using an independent set of FPH data from the first day and found an 8-fold accuracy improvement, yielding an excellent overall relative deviation of only 0.52 %±1.5 % with respect to a LAFH and a D/FH sensor.  相似文献   
60.
A hybrid PLD system with ion bombardment of films was developed. Growing DLC films were modified during the laser deposition (10 J?cm?2) by argon ions with energy in the range from 40 eV to 210 eV and cathode current of 0.15 A and 0.5 A. The content of sp2 “graphitic” and sp3 “diamond” bonds was measured using XPS. Sp3 bonds changed from 60 % to 81 %. We found the highest sp3 content for energy of 40 eV. Hardness (and reduced Young’s modulus) were determined by nanoindentation and reached 49 GPa (277 GPa). Film adhesion was studied using the scratch test and was up to 14 N for titanium substrates. Relations among deposition conditions and measured properties are presented.  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