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   52085篇
  免费   143篇
  国内免费   208篇
系统科学   438篇
丛书文集   1053篇
教育与普及   117篇
理论与方法论   192篇
现状及发展   23398篇
研究方法   1909篇
综合类   24403篇
自然研究   926篇
  2013年   358篇
  2012年   713篇
  2011年   1607篇
  2010年   301篇
  2008年   837篇
  2007年   999篇
  2006年   967篇
  2005年   1012篇
  2004年   1034篇
  2003年   931篇
  2002年   910篇
  2001年   1486篇
  2000年   1411篇
  1999年   938篇
  1992年   926篇
  1991年   747篇
  1990年   809篇
  1989年   735篇
  1988年   715篇
  1987年   748篇
  1986年   758篇
  1985年   1003篇
  1984年   763篇
  1983年   638篇
  1982年   550篇
  1981年   586篇
  1980年   748篇
  1979年   1671篇
  1978年   1315篇
  1977年   1283篇
  1976年   1024篇
  1975年   1113篇
  1974年   1518篇
  1973年   1319篇
  1972年   1390篇
  1971年   1604篇
  1970年   2172篇
  1969年   1650篇
  1968年   1426篇
  1967年   1535篇
  1966年   1387篇
  1965年   1025篇
  1964年   299篇
  1959年   580篇
  1958年   1018篇
  1957年   733篇
  1956年   617篇
  1955年   529篇
  1954年   581篇
  1948年   422篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
391.
Ca2+-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45 degrees C, but for temperatures higher than 48 degrees C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present during heat treatment.  相似文献   
392.
A A Hakim 《Experientia》1976,32(8):1057-1059
Trypsin-like protease with wide spectrum of enzymatic activities have been isolated from cell-free medium from in vivo cultured human mammary carcinoma cells, and from peripheral blood lymphocytes of patients with mammary carcinoma cultured in presence of cell-membrane carcinoma-associated glycoprotein.  相似文献   
393.
Summary Daily injections of phenylephrine or isoprenaline for 4 or 7 days lowered the chronotropic sensitivity of -adrenoreceptors in isolated rat atria.This study was supported by grants from the National Science Council of Finland.  相似文献   
394.
Summary The three enzymes of ethanol metabolism alcohol dehydrogenase, aldehyde dehydrogenase and acetyl-CoA synthetase in the obligate aerobic yeastRhodotorula gracilis are repressed by glucose and induced by C2 metabolic fuels with a regulatory pattern indicating a correlation in the control mechanisms. To try an identification of the molecular signals involved in the transmission of the inducing stimulus, experiments were carried out by blocking with 2 mM pyrazole the ethanol acetaldehyde metabolic step. Results indicate that ethanol is not specifically required as a molecular signal for induction.This work was supported by a grant from the Italian Consiglio Nazionale delle Ricerche.  相似文献   
395.
Summary The central and the peripheral areas of the head-fold stage rat embryo ectoderm develop into both the neural tissue and the epidermis when grafted under the kidney capsule of adult rats.This investigation was supported by the grant No. IV/3 from the Research Foundation of S.R. Croatia, and in part by NIH PL 480 Agreement No. 02-038-1.  相似文献   
396.
Summary Tryptic treatment of muscle thick filaments reveals the underlying backbones of aggregatedl-meromyosin as a coli of 3 secondary filaments (helical repeat 130 nm) each in turn a coli of a 3 finer ones.  相似文献   
397.
Summary Using Raman spectroscopy, we demonstrate that low levels of -carotene, lycopene, and xanthophyll give rise to resonance enhanced bands in blood plasma. These results explain the significance of previously unidentified spectral maxima which have been related to the state of health of the blood donor.  相似文献   
398.
Summary Assays of 8 synthetic analogues of human calcitonin in rats showed that their hypocalcaemic activity was drastically reduced by deletion of the C-terminal amide group, chain-shortening or opening of the disulphide ring, but unaffected or enhanced by modification of the N-terminal amino group.

II. vgl.R. Maier, B. Kamber, B. Riniker andW. Rittel, Hormon. Metab. Res.7, 511 (1975).

Die hier verwendete, abgekürzte Schreibweise für Peptide folgt den Empfehlungen der IUPAC-IUB Kommission für Biochemische Nomenklatur, J.B.C.247, 977 (1972). Weitere Abkürzungen: HCT, Human-Calcitonin; PCT, Schweinecalcitonin; Bmp, -Mercaptopropionsäure (Desaminocystein); NMet, Normethionin (S-Methylcystein); -OMe, Methylester.  相似文献   
399.
D-6-Methyl-8-[-isopropylaminoethyl] ergoline-I [VÚFB-10726], beginning from the dose of 0.05 mg/kg p.o., suppresses lactation through the inhibition of prolactin secretion in nursing rats.  相似文献   
400.
Summary Rat brain mitochondria contain a significant proportion of poly(A) associated RNA which is higher than that found in microsomes from the same source. When steady state poly(A) RNA of brain mitochondria was analyzed by microelectrophoresis, it displayed a characteristic separation pattern with a large amount of free poly(A).  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