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   3142篇
  免费   141篇
  国内免费   7篇
化学   2578篇
晶体学   8篇
力学   47篇
数学   306篇
物理学   351篇
  2023年   25篇
  2022年   76篇
  2021年   129篇
  2020年   87篇
  2019年   89篇
  2018年   63篇
  2017年   27篇
  2016年   115篇
  2015年   100篇
  2014年   129篇
  2013年   197篇
  2012年   225篇
  2011年   272篇
  2010年   156篇
  2009年   156篇
  2008年   236篇
  2007年   176篇
  2006年   173篇
  2005年   180篇
  2004年   141篇
  2003年   117篇
  2002年   102篇
  2001年   37篇
  2000年   33篇
  1999年   16篇
  1998年   14篇
  1997年   22篇
  1996年   20篇
  1995年   5篇
  1994年   14篇
  1993年   12篇
  1992年   13篇
  1991年   17篇
  1990年   15篇
  1989年   9篇
  1988年   7篇
  1987年   12篇
  1986年   5篇
  1985年   8篇
  1984年   5篇
  1983年   4篇
  1982年   8篇
  1981年   10篇
  1980年   8篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1973年   2篇
  1878年   2篇
  1862年   1篇
排序方式: 共有3290条查询结果,搜索用时 31 毫秒
111.
112.
Point-of-care (POC) testing of glucose (glucometers) represents a convenient alternative to monitor glycemia since the measurement procedure is performed without delay after sampling of the capillary blood, thereby avoiding the metabolism by the blood cells of glucose present in plasma. Likely because of sample instability, there is no proficiency test provider in Brazil for this type of POC sample. In this context, this study aimed to evaluate the analytical performance of glucometers used in a tertiary care hospital. The glucometers used were the Accu-Chek Performa® model from Roche Diagnostics, which use the principle of amperometry. The reference method was the reaction with modified hexokinase/glucose-6-phosphate in a Dimension® device. The stability evaluation of the control samples showed that it can be performed up to 90 min after the collection of whole blood samples. In the two rounds performed, only one result of the 17 glucometers evaluated was out of the threshold of two standard deviation. Thus, this method for control of glucometers met the expectations and enabled comparing the glucometers in a hospital. Given the current quality guidelines, daily internal quality control of glucometers is recommended, besides at least two annual comparisons between the results of the glucometers and the reference method and one EQA every 3 months.  相似文献   
113.
114.
The reactions of [Ni16(C2)2(CO)23]4? and [Ni38C6(CO)42]6? with CuCl afforded mixtures of the previously reported [HNi42C8(CO)44(CuCl)]7? bimetallic octa-carbide cluster and the new [HNi43C8(CO)45]7? and [HNi44C8(CO)46]7? homo-metallic octa-carbides. The three species have very similar properties resulting always in co-crystals such as [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·6.5MeCN (x = 0.14) (86% [HNi42C8(CO)44(CuCl)]7?, 14%[HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?) and [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·5.5MeCN (x = 0.30) (70% [HNi42C8(CO)44(CuCl)]7?, 30% [HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?). The new homo-metallic octa-carbides can be obtained free from the Ni–Cu octa-carbido cluster by reacting [Ni10(C2)(CO)16]2? in thf with a stoichiometric amount of CuCl, and crystals of [NMe4]6[H2Ni43+xC8(CO)45+x]·6MeCN (x = 0.72), which contain [H2Ni44C8(CO)46]6? (72%) and [H2Ni43C8(CO)45]6? (28%), have been obtained. Despite the different charges and compositions, these anions display almost identical structures, which are also closely related to those previously reported for the bimetallic Ni–Cd octa-carbido clusters [Ni42+xC8(CO)44+x(CdCl)]7? and [HNi42+xC8(CO)44+x(CdBr)]6?. Indeed, all these clusters are based on the same Ni42C8 cage decorated by miscellaneous [CdX]+ (X = Cl, Br), [CuCl] and [Ni(CO)] fragments.  相似文献   
115.
116.
Malva sylvestris is a species used worldwide as an alternative to anti‐inflammatory therapies; however, its mechanism of action remains unknown. In this paper, the anti‐inflammatory effects of M. sylvestris alcoholic extracts were evaluated by measuring the pro‐inflammatory mediators PGE2 and PGD2 in desferrioxamine‐stimulated phorbol 12‐myristate 13‐acetate‐differentiated U937 cells. An HPLC‐DAD fingerprint of the M. sylvestris extract was performed and caffeic acid, ferulic acid and scopoletin were identified and quantified. An HPLC‐MS/MS method was developed and validated to separate and measure the prostaglandins. The lower limits of detection (~0.5 ng/mL for PGE2 and PGD2) and quantification (1.0 ng/mL for PGE2 and PGD2) indicated that the method is highly sensitive. The calibration curves showed excellent coefficients of correlation (r > 0.99) over the range of 1.0–500.0 ng/mL, and at different levels, the accuracy ranged from 96.4 to 106.4% with an RSD < 10.0% for the precision study. This method was successfully applied using U937‐d cells. A significant dose‐dependent reduction of PGE2 and PGD2 levels occurred using 10 µg/mL (10.74 ± 2.86 and 9.60 ± 6.89%) and 50 µg/mL of extract (48.37 ± 3.24 and 53.06 ± 6.15%), suggesting that the anti‐inflammatory mechanisms evoked by M. sylvestris may be related to modulation of these mediators. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
117.
The molecule of the title compound, [AuCl(C27H36N2)], which belongs to a class of potentially catalytically active N‐heterocyclic carbene complexes, has crystallographic C2 symmetry and approximate C2v symmetry. The structure is isostructural with the CuI and AgI analogues. A previous report of the structure of the title compound as its toluene solvate [Fructos et al. (2005). Angew. Chem. Int. Ed. 44 , 5284–5288] has inaccurate geometry for the complex molecule as a consequence of probable incorrect refinement in the space group Cc, instead of C2/c [Marsh (2009). Acta Cryst. B 65 , 782–783]. The Au—C bond length of 1.998 (4) Å in the title compound is more consistent with the mean distance of 1.979 (14) Å found in 52 other reported [AuCl(carbene)] complexes than with the shorter distance of 1.942 (3) Å given for the refinement in the space group Cc for the toluene solvate and the value of 1.939 Å obtained from the recalculation of that structure in C2/c.  相似文献   
118.
Journal of Thermal Analysis and Calorimetry - Samples of potato starch (PS), sweet potato starch (SPS) and their binary mixtures, with moisture levels of 10, 15 and 20% (db), were submitted to...  相似文献   
119.
120.
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