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   455631篇
  免费   4890篇
  国内免费   1353篇
化学   230606篇
晶体学   7471篇
力学   21154篇
综合类   9篇
数学   55262篇
物理学   147372篇
  2021年   3912篇
  2020年   4291篇
  2019年   4818篇
  2018年   6472篇
  2017年   6777篇
  2016年   9552篇
  2015年   5496篇
  2014年   9180篇
  2013年   21509篇
  2012年   16354篇
  2011年   19657篇
  2010年   14495篇
  2009年   14402篇
  2008年   17868篇
  2007年   17712篇
  2006年   16518篇
  2005年   14461篇
  2004年   13453篇
  2003年   11997篇
  2002年   11878篇
  2001年   14018篇
  2000年   10440篇
  1999年   8150篇
  1998年   6775篇
  1997年   6573篇
  1996年   6206篇
  1995年   5504篇
  1994年   5450篇
  1993年   5232篇
  1992年   5877篇
  1991年   5998篇
  1990年   5737篇
  1989年   5620篇
  1988年   5369篇
  1987年   5555篇
  1986年   5178篇
  1985年   6698篇
  1984年   6814篇
  1983年   5782篇
  1982年   5926篇
  1981年   5531篇
  1980年   5457篇
  1979年   5857篇
  1978年   5894篇
  1977年   5808篇
  1976年   5806篇
  1975年   5555篇
  1974年   5493篇
  1973年   5675篇
  1972年   3920篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
181.
Here, we demonstrate the applicability of self-assembling linear-dendritic block copolymers (LDBCs) and their nanoaggregates possessing varied surfaces as therapeutic nanocarriers. These LDBCs are comprised of a hydrophobic, linear polyester chemically coupled to a hydrophilic dendron polyamidoamine (PAMAM)—the latter of which acts as the surface of the self-assembled nanoaggregate in aqueous media. To better understand how surface charge density affects the overall operability of these nanomaterials, we modified the nanoaggregate surface to yield cationic (NH3+), neutral (OH), and anionic (COO) surfaces. The effect of these modifications on the physicochemical properties (i.e., size, morphology, and surface charge density), colloidal stability, and cellular uptake mechanism of the polymeric nanocarrier were investigated. This comparative study demonstrates the viability of nanoaggregates formed from PDLLA-PAMAM LDBCs to serve as nanocarriers for applications in drug delivery.  相似文献   
182.
Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed.  相似文献   
183.
184.
185.
186.
Kinetics and Catalysis - Boron and barium were employed as dopants for the VMgO system. The catalysts were characterized by ICP-OES, BET, IR, powder XRD, EDX, TPR-H2, TPD-NH3, XPS, and 51V MAS NMR....  相似文献   
187.
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557  相似文献   
188.
Journal of Thermal Analysis and Calorimetry - The effect of monoaluminum phosphate (Al(H2PO4)3) addition in the thermochemical process of a kaolinitic clay was studied and compared with the pure...  相似文献   
189.
Russian Journal of Organic Chemistry - The Reformatsky reaction of (3R,4R)-4-acetoxy-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)­azetidin-2-one with ethyl 4-bromo-3-oxopentanoate gave...  相似文献   
190.
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