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   9208篇
  免费   1543篇
  国内免费   1046篇
化学   6842篇
晶体学   81篇
力学   530篇
综合类   55篇
数学   1089篇
物理学   3200篇
  2024年   31篇
  2023年   237篇
  2022年   418篇
  2021年   389篇
  2020年   529篇
  2019年   442篇
  2018年   382篇
  2017年   319篇
  2016年   445篇
  2015年   464篇
  2014年   572篇
  2013年   674篇
  2012年   823篇
  2011年   868篇
  2010年   559篇
  2009年   513篇
  2008年   500篇
  2007年   467篇
  2006年   475篇
  2005年   359篇
  2004年   277篇
  2003年   232篇
  2002年   279篇
  2001年   165篇
  2000年   170篇
  1999年   180篇
  1998年   129篇
  1997年   127篇
  1996年   141篇
  1995年   113篇
  1994年   97篇
  1993年   64篇
  1992年   67篇
  1991年   58篇
  1990年   49篇
  1989年   42篇
  1988年   40篇
  1987年   18篇
  1986年   26篇
  1985年   21篇
  1984年   12篇
  1983年   5篇
  1981年   6篇
  1980年   1篇
  1959年   1篇
  1957年   4篇
  1935年   1篇
  1931年   1篇
  1930年   3篇
  1922年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
在pH9.5NH3NH4Cl缓冲溶液中,Mn(Ⅱ)与邻菲口罗啉形成的配合物在-1.36V(vs.SCE)处产生一灵敏的吸附波,一阶导数峰电流与Mn(Ⅱ)浓度在5×10-85×10-6mol/L范围内呈线性关系,检出限为2×10-8mol/L对极谱性质及反应机理进行了研究,用该法测定了大豆和茶叶中的微量锰,结果满意  相似文献   
52.
气相色谱法测定三聚氰氯的研究李秀梅赵树岚*田锦霞*孙维星(东北师范大学化学系长春130024)关键词气相色谱法三聚氰氯三聚氰氯(CNCl)3是活性染料的重要中间体及合成树脂、橡胶、塑料等的防老剂,也常用于除草剂、增白剂、药物、炸药等的生产中。传统的分...  相似文献   
53.
铜在HOPG上电沉积过程的现场ECSTM研究   总被引:3,自引:1,他引:3  
谢兆雄  毛秉伟 《电化学》1996,2(2):164-169
用自制的电化学扫描隧道显微镜(ECSTM)现场研究Cu在HOPG上的电沉积过程.结果表明Cu在HOPG上的电沉积为三维成核的过程.当电位较低或Cu2+离子浓度较低时,铜在本体金属生长主要沿着台阶方向.过电位较高时,铜的成核数目增加,沉积层的晶粒有所细化.同时,非现场ECSTM比较研究表明,STM针尖对针尖局部区域的电沉积起屏蔽作用,针尖所在区域Cu的沉积速度比其它区域明显减小  相似文献   
54.
All four stereoisomers of 2-alkyl-3,4-iminobutanoic acid, a novel class of beta-amino acids bearing a chemically versatile aziridine ring, were synthesized starting with aspartic acid. The synthetic strategy involves the introduction of an alkyl group at the beta-position of fully protected optically active aspartic acid followed by the construction of an aziridine ring making use of the alpha-carboxylate and alpha-amino groups. The alpha-carboxylate was reduced to the corresponding alcohol, which was then subjected to cyclization to form an aziridine ring with the N-protected amino group. Removal of the protection groups yielded the target compounds.  相似文献   
55.
The hydrothermal reaction of VOSO4, As2O5, piperazine and H2O produces [H2N(CH2)4NH2]4[β‐As8V14O42(SO4)]·2HSO4 ( 1 ), which is the first arsenic‐vanadium cluster containing a spherical β‐As8V14O42 shell. The structure of this compound was characterized by single crystal X‐ray diffraction, elemental analysis, TG, and IR spectrum. Crystal data for 1 : Orthorhombic, Cmcm, a = 15.369(1) Å, b = 16.404(1) Å, c = 25.772(1) Å, V = 6497.4(9) Å3, Z = 4.  相似文献   
56.
We optimized the hot water extraction of polysaccharides from the root of Henry wood betony (RHWPs) using a uniform test and explored their anti-tumor activities in vitro and in vivo. The optimal extraction conditions were as follows: 40 min extraction time, liquid/solid ratio 30 mL/g, 100 min soaking time, two extraction cycles, 100% ethanol concentration, and extraction temperature of 80 °C. The molecular weight distribution of RHWPs with MWs was 228,600 g/mol and 5001 g/mol. The IR spectrum further indicated that RHWPs are acidic polysaccharides containing pyranose and furan rings. The main monosaccharides found in RHWPs were mannose, ribose, l-rhamnose monohydrate, glucuronic acid, galacturonic acid, glucose, galactose, xylose, arabinose, and fucose. RHWPs inhibited the proliferation of S180 tumor cells and induced apoptosis in vitro. Oral administration of RHWPs to tumor-bearing mice significantly inhibited the growth of the S180 xenografts, accelerated apoptosis in tumor cells, and expanded the necrotic regions. Furthermore, RHWPs also markedly increased the levels of TNF-α, IFN-γ, and IL-2 in the sera of tumor-bearing mice, and activated immune cells such as lymphocytes, NK cells, and macrophages, thereby inducing tumor cell apoptosis. Taken together, RHWPs are a promising anti-tumor agent that ought to be explored further.  相似文献   
57.
SDS胶束对孔雀绿褪色反应的影响   总被引:4,自引:0,他引:4  
研究了十二烷基硫酸钠(SDS)表而活性剂胶束和预胶束对孔雀绿褪色可逆反应的影响,建立了1-1型可逆反应的胶束催化模型和预胶束催化模型,获得了胶束相中正逆反应的速率常数和预胶束的平均聚集数.结果表明,SDS胶束和预胶束对正反应有禁阻作用,而对逆反应有催化作用.  相似文献   
58.
Qu DH  Wang QC  Ren J  Tian H 《Organic letters》2004,6(13):2085-2088
[reaction: see text] A molecular shuttle containing an alpha-CD macrocycle, an azobenzene unit, and two different fluorescent naphthalimide units was synthesized. The cis-trans photoisomerization of the azobenzene unit resulted in the motion of the CD macrocycle on the track. Because of the easy regulation and full reversibility of the fluorescence change of the two stopper units, the molecular shuttle could be used as a molecular storage medium or switch with all-optical inputs and outputs.  相似文献   
59.
Liu X  Song D  Zhang Q  Tian Y  Zhang H 《Talanta》2004,62(4):773-779
Surface plasmon resonance (SPR) has been successfully applied for the simple, rapid, and label-free assay of various biomolecules. This assay evaluates a novel wavelength modulation SPR biosensor for the detection of tetanus toxin. The wavelength modulation SPR biosensor is designed based on fixing the incident angle of light and measuring the reflected intensities in the resonance wavelength range spanning 400-800 nm simultaneously. Tetanus toxin (TeNT), one of the most potent toxins known, is synthesized as a 150 kDa single polypeptide chain. The SPR biosensor has been shown to be capable of directly detecting concentration of tetanus toxin as low as 0.028 Lf ml−1. Under selected experimental conditions, the SPR biosensor has a good reproducibility, sensitivity and reversibility. The results illustrate how wavelength modulation SPR biosensor can be used to detect biomolecular interactions.  相似文献   
60.
Four distinct biochars were employed to remove three typical pollutants, meanwhile, path analysis, a multi-statistical regression method, was performed to elucidate the dominant factors of biochar adsorption. This work can provide a new insight to prepare a targeted biochar as adsorbents.  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