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   74011篇
  免费   12391篇
  国内免费   7297篇
化学   50951篇
晶体学   657篇
力学   4739篇
综合类   310篇
数学   8202篇
物理学   28840篇
  2024年   279篇
  2023年   1601篇
  2022年   2716篇
  2021年   2919篇
  2020年   3107篇
  2019年   2907篇
  2018年   2563篇
  2017年   2336篇
  2016年   3569篇
  2015年   3473篇
  2014年   4140篇
  2013年   5307篇
  2012年   6738篇
  2011年   6734篇
  2010年   4475篇
  2009年   4255篇
  2008年   4591篇
  2007年   4109篇
  2006年   3754篇
  2005年   3129篇
  2004年   2425篇
  2003年   1919篇
  2002年   1751篇
  2001年   1471篇
  2000年   1356篇
  1999年   1533篇
  1998年   1304篇
  1997年   1291篇
  1996年   1289篇
  1995年   1050篇
  1994年   921篇
  1993年   763篇
  1992年   674篇
  1991年   580篇
  1990年   501篇
  1989年   384篇
  1988年   335篇
  1987年   274篇
  1986年   249篇
  1985年   204篇
  1984年   143篇
  1983年   102篇
  1982年   80篇
  1981年   67篇
  1980年   65篇
  1979年   33篇
  1978年   30篇
  1977年   40篇
  1976年   30篇
  1973年   28篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
An Y  Ji M  Baiyin M  Liu X  Jia C  Wang D 《Inorganic chemistry》2003,42(14):4248-4249
A novel layered K(4)Ag(2)Sn(3)S(9) x 2KOH was synthesized solvothermally. A mixture of ethanol and HSCH(2)CH(SH)CH(2)OH was used for the synthesis. The HSCH(2)CH(SH)CH(2)OH plays an important role and appears to serve as a mineralizer for the solvothermal reaction. A layer comprises Sn(3)S(9)(6)(-) clusters linked by Ag(+) ions and possesses two types of 1D channels in which potassium ions are located. The compound crystallizes in the monoclinic P2(1)/m space group [a = 7.8071(2) A, b = 27.3508(1) A, c = 10.5008(2) A, alpha = 90 degrees, beta = 103.874(1) degrees, gamma = 90 degrees, Z = 4]. Its crystal structure, composition analysis, and IR are presented.  相似文献   
122.
The occupational health impact of atmospheric pollution on exposed workers at one iron and steel complex was studied by instrumental neutron activation analysis of workers' hair samples and medical examination. The experimental results indicate that there is a positive correlation between the high inhalation amounts of iron and other trace elements by the exposed workers and the symptom of their high blood pressure and hypoglycemia, which implies that the atmospheric environment polluted by iron and steel industry has an adverse health impact on the exposed workers. The measures to relieve and abate the occupational diseases caused by air-borne particulate matter should be taken  相似文献   
123.
Hai-Xia Liu 《Tetrahedron letters》2005,46(20):3525-3528
Annonaceous acetogenins are a series of potent naturally occurring anticancer agents, which act as inhibitors of complex I in mitochondria. AA005, a mimicry of acetogenins, has been found as active as those natural products and to present high selectivities between cancer and normal cells. In order to investigate the further cell-based mechanism induced by AA005, a d4-labeled derivative of AA005 (AA005-d4) was designed to detect the drug permeation ability into the membranes. In this letter, the synthesis is reported of this deuterium-labeled compound, wherein a ethylene-d4 glycol unit is incorporated efficiently into the molecule skeleton by simple etherifications.  相似文献   
124.
A submicron light-emitting device (LED) was fabricated from lithographically fabricated parallel indium-tin oxide (ITO) finger electrodes (0.9 mum wide) separated by a 1.1 mum gap. A single layer of an amorphous (a) Ru(bpy)3(ClO4)2 film ( approximately 100 nm thick) was spin-coated on the electrode array. Ga:In or carbon paste was employed as a liftable upper contact electrode. Films ( approximately 1.5 mum thick) of single-crystal Ru(bpy)3(ClO4)2 (xyl) between two ITO electrodes in a sandwich cell were also prepared and produce electroluminescence. As with larger cells of this type, the high-resolution electroluminescence produced showed a high external efficiency ( approximately 3.4%), a low turn-on voltage (2.3 V), and reasonable stability. The single-crystal cells also behaved as photovoltaic devices and a short-circuit photocurrent was observed when they were irradiated without a bias voltage.  相似文献   
125.
Coupling of tris(trimethylsilyl)guanine (4) with 1,2-di-O-acetyl-3-Ochloromethyl glycerol (3), followed by removal of the protecting groups afforded 9-(2,3-dihydroxy-1-propoxy)guanine (1). Compound 1 exhibited potent antiviral activity.  相似文献   
126.
127.
本文提出了用分析型HPLC仪器制备β-大马酮标准品的方法及用HPLC测定β-大马酮含量的方法。制备色谱柱为Zorbax SIL 9.4 mmφ×25cm,流动相为石油醚(30~60℃)/乙醚98.5/1.5。分析用色谱柱为Shim CLC SIL 6 mmφ×15cm(岛津全多孔硅胶柱),流动相为石油醚(60—90℃)/无水乙醇99.88/0.12,检测器为紫外可见分光光度检测器。波长253nm或302nm,标准曲线的线性范围0~1.4mg/ml。峰高或峰面积均可用于测定,回收率100.7%。  相似文献   
128.
Jiang  Wenlin  Yu  Xiaobo  Li  Cheng  Zhang  Xisha  Zhang  Guanxin  Liu  Zitong  Zhang  Deqing 《中国科学:化学(英文版)》2022,65(9):1791-1797

Photoresists are essential for the fabrication of flexible electronics through all-photolithographic processes. Single component semiconducting photoresist exhibits both semiconducting and photo-patterning properties, and as a result, the device fabrication process can be simplified. However, the design of semiconducting polymeric photoresist with ambipolar semiconducting property remains challenging. In this paper, we report a single component semiconducting photoresist (PFDPPF4T-N3) by incorporating azide groups and noncovalent conformation locks into the side alkyl chains and conjugated backbones of a diketopyrrolopyrrole-based conjugated polymer, respectively. The results reveal that PFDPP4FT-N3 exhibits ambipolar semiconducting property with hole and electron mobilities up to 1.12 and 1.17 cm2 V?1 s?1, respectively. Moreover, field effect transistors with the individual photo-patterned thin films of PFDPPF4T-N3 also show ambipolar semiconducting behavior with hole and electron mobilities up to 0.66 and 0.80 cm2 V?1 s?1, respectively. These results offer a simple yet effective design strategy for high-performance single component semiconducting photoresists, which hold great potential for flexible electronics processed by all photolithography.

  相似文献   
129.
A micellar electrokinetic chromatography method was established for the quantitative analysis of seven podophyllum lignans in Podophyllum emodi Wall. var. chinesis sprague. The optimum buffer system was 10 mM NaH2PO4-5 mM borate-100 mM sodium dodecylsulfate-30% isopropanol (pH 7.20). Voltage was 18 kV and detection at 214 nm. The second derivative chromatogram was used to determine a low-content component and those not fully separated from adjacent ones. The RSD values of migration times and peak areas were <2.2 and <5.5%, respectively. The effects of several CE parameters on the resolutions were studied systematically.  相似文献   
130.
Liu LD  Liu Y  Wang HY  Sun Y  Ma L  Tang B 《Talanta》2000,52(6):991-999
Spectrophotometric determination of procaine hydrochloride is described. The procaine hydrochloride reacts with p-dimethylaminobenzalhyde in glacial acetic acid to form an Schiff base which is a yellow compound, and its maximum absorption wavelength is at 455nm, 455=3.46×104. The absorbance for procaine hydrochloride from 0.2 to 15 μg ml−1 obeys Beer's law. The linear regression equation of the calibration graph is C=5.866A−0.02, with a linear regression correlative coefficient is 0.9994 and relative standard deviation (RSD) of 1.7%; the detection limit is 0.1 μg ml−1; recovery is from 92.0 to 110.0%. Effects of reaction medium, temperature, gentamycin, beneylpenicillin, kanamycin, streptomycin, foreign ions, and stand for time on the determination of procaine hydrochloride have been examined. The results obtained by this method agreed with those by the official method (dead-stop titration). This method is rapid and simple, and can be used for the determination of procaine hydrochloride in injection solution of procaine hydrochloride.  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