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   1649篇
  免费   56篇
  国内免费   10篇
化学   1051篇
晶体学   15篇
力学   59篇
数学   256篇
物理学   334篇
  2023年   13篇
  2022年   22篇
  2021年   57篇
  2020年   40篇
  2019年   40篇
  2018年   29篇
  2017年   23篇
  2016年   79篇
  2015年   49篇
  2014年   55篇
  2013年   135篇
  2012年   126篇
  2011年   119篇
  2010年   74篇
  2009年   90篇
  2008年   139篇
  2007年   117篇
  2006年   86篇
  2005年   51篇
  2004年   59篇
  2003年   41篇
  2002年   43篇
  2001年   24篇
  2000年   21篇
  1999年   17篇
  1998年   10篇
  1997年   15篇
  1996年   11篇
  1995年   10篇
  1994年   12篇
  1993年   7篇
  1992年   2篇
  1991年   9篇
  1990年   7篇
  1989年   4篇
  1988年   8篇
  1987年   2篇
  1986年   4篇
  1985年   3篇
  1984年   8篇
  1983年   5篇
  1982年   8篇
  1981年   11篇
  1980年   6篇
  1979年   3篇
  1978年   2篇
  1977年   4篇
  1976年   4篇
  1974年   2篇
  1970年   2篇
排序方式: 共有1715条查询结果,搜索用时 218 毫秒
1.
2.
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...  相似文献   
3.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
4.
Autologous bone grafts, used mainly in extensive bone loss, are considered the gold standard treatment in regenerative medicine, but still have limitations mainly in relation to the amount of bone available, donor area, morbidity and creation of additional surgical area. This fact encourages tissue engineering in relation to the need to develop new biomaterials, from sources other than the individual himself. Therefore, the present study aimed to investigate the effects of an elastin and collagen matrix on the bone repair process in critical size defects in rat calvaria. The animals (Wistar rats, n = 30) were submitted to a surgical procedure to create the bone defect and were divided into three groups: Control Group (CG, n = 10), defects filled with blood clot; E24/37 Group (E24/37, n = 10), defects filled with bovine elastin matrix hydrolyzed for 24 h at 37 °C and C24/25 Group (C24/25, n = 10), defects filled with porcine collagen matrix hydrolyzed for 24 h at 25 °C. Macroscopic and radiographic analyses demonstrated the absence of inflammatory signs and infection. Microtomographical 2D and 3D images showed centripetal bone growth and restricted margins of the bone defect. Histologically, the images confirmed the pattern of bone deposition at the margins of the remaining bone and without complete closure by bone tissue. In the morphometric analysis, the groups E24/37 and C24/25 (13.68 ± 1.44; 53.20 ± 4.47, respectively) showed statistically significant differences in relation to the CG (5.86 ± 2.87). It was concluded that the matrices used as scaffolds are biocompatible and increase the formation of new bone in a critical size defect, with greater formation in the polymer derived from the intestinal serous layer of porcine origin (C24/25).  相似文献   
5.
Applied Biochemistry and Biotechnology - The human exposure to bisphenol A (BPA) occurs frequently. Once, this compound was one of the highest volume chemicals produced worldwide and used as a...  相似文献   
6.
The Efficient Determination Criterion (EDC) generalizes the AIC and BIC criteria and provides a class of consistent estimators for the order of a Markov chain with finite state space. In this note, we derive rates of convergence for the EDC estimates. *Partially supported by CNPq, CAPES/PROCAD, FAPDF/PRONEX, FINATEC and FUNPE/UnB. **Partially supported by CAPES.  相似文献   
7.
The thermotropic liquid-crystalline phase behaviour of a homologous set of bis[N-[[4-[4-(alkoxy)benzoyloxy]2-hydroxyphenyl]methylene]alkanamino] copper(II) complexes is examined. New data are reported and taken into account in addition to those previously reported in this Journal. The influence of alkoxy and alkanamine groups on the nature and stability of the mesophase is underlined. As a general trend, with some notable exception, smectic (C type) mesomorphism is favoured by longer alkoxy and alkanamine chains. Data concerning some Pd(II) and Ni(II) homologous complexes are also reported. The mesophase stability (nematic phase) is higher for palladium and nickel complexes than for the copper containing homologues.  相似文献   
8.
Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation. Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence of screw dislocations within the grown nanostructures further supports this observation. PACS 81.07.-b; 68.37.Ps; 81.16.Nd  相似文献   
9.
A highly active thermostable β-glucosidase was purified to homogeneity from a strain ofTrichoderma sp. The enzyme was an extracellular glycoprotein and showed hydrolytic activity toward several β-glucosides. Cellobiose was found to be the substrate of choice for this enzyme. This finding could suggest future technological applications of the purified protein.  相似文献   
10.
Sunto Si ha l'intenzione d'incominciare lo studio sistematico della teoria abbozzata da John Nash circa venticinque anni fa, dove si associa a una varietà algebrica singolare X spazi i cui ponti corrispondono genericamente a troncature di certi rami analitici parametrizati su X. In questo articolo si presentano accuratamente i fondamenti della teoria. Inoltre, con questi metodi (e nozioni della teoria della equisingolarità per le curve sghembe) s'introducono nuovi invarianti di una singolarità, si spera di studiarli più accuratamente in futuri lavori.  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