全文获取类型
收费全文 | 39447篇 |
免费 | 129篇 |
国内免费 | 155篇 |
专业分类
系统科学 | 370篇 |
丛书文集 | 830篇 |
教育与普及 | 68篇 |
理论与方法论 | 125篇 |
现状及发展 | 18001篇 |
研究方法 | 1564篇 |
综合类 | 18184篇 |
自然研究 | 589篇 |
出版年
2013年 | 247篇 |
2012年 | 531篇 |
2011年 | 1153篇 |
2010年 | 237篇 |
2008年 | 647篇 |
2007年 | 817篇 |
2006年 | 690篇 |
2005年 | 744篇 |
2004年 | 786篇 |
2003年 | 723篇 |
2002年 | 698篇 |
2001年 | 1211篇 |
2000年 | 1177篇 |
1999年 | 767篇 |
1992年 | 754篇 |
1991年 | 539篇 |
1990年 | 600篇 |
1989年 | 573篇 |
1988年 | 554篇 |
1987年 | 579篇 |
1986年 | 622篇 |
1985年 | 780篇 |
1984年 | 552篇 |
1983年 | 475篇 |
1982年 | 436篇 |
1981年 | 498篇 |
1980年 | 555篇 |
1979年 | 1258篇 |
1978年 | 1003篇 |
1977年 | 983篇 |
1976年 | 784篇 |
1975年 | 787篇 |
1974年 | 1172篇 |
1973年 | 978篇 |
1972年 | 1007篇 |
1971年 | 1151篇 |
1970年 | 1572篇 |
1969年 | 1280篇 |
1968年 | 1116篇 |
1967年 | 1154篇 |
1966年 | 1045篇 |
1965年 | 794篇 |
1964年 | 251篇 |
1959年 | 430篇 |
1958年 | 756篇 |
1957年 | 509篇 |
1956年 | 415篇 |
1955年 | 395篇 |
1954年 | 417篇 |
1948年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
341.
B. A. Battelle E. A. Kravitz H. Stieve 《Cellular and molecular life sciences : CMLS》1979,35(6):778-780
Summary Radiochemical precursor compounds for neurotransmitters were incubated withLimulus ventral nerve photoreceptor preparations. Octopamine was preferentially synthesized by a photoreceptor rich fraction of the nerve, acetylcholine was made by a photoreceptor poor fraction, and -aminobutyric acid was made about equally well in both fractions. The possibility that the ventral nerve photoreceptor cells serve a neurosecretory function in the adultLimulus is discussed.From the Neurobiology Course, Marine Biological Laboratory, Woods Hole, Mass. The Neurobiology Course is supported by grants from the Grass, Sloan and Sandoz Foundation and from Merck, Sharp and Dohme Research Institute. 相似文献
342.
Cytological detection of mutagen-carcinogen exposure by sister chromatid exchange. 总被引:40,自引:0,他引:40
A staining technique that detects sister chromatid exchanges (SCEs) has been used to examine the response of chromosomes in cultured Chinese hamster cells to a wide variety of mutagens-carcinogens. The test gives a very sensitive and rapid method for detecting chromosome mutagenicity of chemical agents and provides a powerful new method for detecting environmental mutagens. 相似文献
343.
Non-encephalitogenic antigen-induced suppression and reversal of allergic encephalomyelitis. 总被引:1,自引:0,他引:1
G A Hashim 《Nature》1975,256(5518):953-955
344.
345.
Microsomes from livers of scorbutic guinea-pigs showed a reduced rate of acetanilide hydroxylation. The response of "scorbutic" liver microsomes to the inhibitor Metyrapone (2-methyl-1,2 di (3-pyridyl) propan-1-one) was different from that of liver microsomes from non-scorbutic guinea-pigs. 相似文献
346.
Computer simulation of protein folding. 总被引:27,自引:0,他引:27
A new and very simple representation of protein conformations has been used together with energy minimisation and thermalisation to simulate protein folding. Under certain conditions, the method succeeds in "renaturing" bovine pancreatic trypsin inhibitor from an open-chain conformation into a folded conformation close to that of the native molecule. 相似文献
347.
P. Pani A. Sanna M. I. Brigaglia A. Columbano L. Congiu 《Cellular and molecular life sciences : CMLS》1976,32(11):1449-1451
Summary Acute toxicity induced by DMN was partially prevented by previously administering methyl mercuric chloride (MMC), a chemical inhibitor of the drug metabolizing enzyme system (DMES). We have studied the early changes occurring during the course of DMN-intoxication, namely disaggregation of polysomal profiles and necrosis, evaluated morphologically and by the release of S-GPT.This work was supported by Consiglio Nazionale delle Ricerche, Roma, Italy. 相似文献
348.
Summary The serum activities of aspartate aminotransferase, alanine aminotransferase, -hydroxybutyrate dehydrogenase and creatine phosphokinase have been measured in the African elephant. In general, the values were broadly comparable with those of man except that alanine aminotransferase was much lower and creatine phosphokinase higher. No variation due to age, sex, season or location was observed. 相似文献
349.
350.
Membrane noise in Paramecium. 总被引:1,自引:0,他引:1