全文获取类型
收费全文 | 17228篇 |
免费 | 42篇 |
国内免费 | 53篇 |
专业分类
系统科学 | 253篇 |
丛书文集 | 444篇 |
教育与普及 | 36篇 |
理论与方法论 | 50篇 |
现状及发展 | 7949篇 |
研究方法 | 724篇 |
综合类 | 7719篇 |
自然研究 | 148篇 |
出版年
2012年 | 203篇 |
2011年 | 409篇 |
2010年 | 97篇 |
2009年 | 94篇 |
2008年 | 272篇 |
2007年 | 344篇 |
2006年 | 289篇 |
2005年 | 298篇 |
2004年 | 271篇 |
2003年 | 325篇 |
2002年 | 260篇 |
2001年 | 609篇 |
2000年 | 609篇 |
1999年 | 344篇 |
1992年 | 328篇 |
1991年 | 253篇 |
1990年 | 298篇 |
1989年 | 271篇 |
1988年 | 262篇 |
1987年 | 276篇 |
1986年 | 284篇 |
1985年 | 338篇 |
1984年 | 242篇 |
1983年 | 219篇 |
1982年 | 200篇 |
1981年 | 238篇 |
1980年 | 261篇 |
1979年 | 568篇 |
1978年 | 463篇 |
1977年 | 469篇 |
1976年 | 351篇 |
1975年 | 374篇 |
1974年 | 583篇 |
1973年 | 455篇 |
1972年 | 413篇 |
1971年 | 510篇 |
1970年 | 656篇 |
1969年 | 573篇 |
1968年 | 492篇 |
1967年 | 528篇 |
1966年 | 439篇 |
1965年 | 330篇 |
1964年 | 86篇 |
1959年 | 198篇 |
1958年 | 293篇 |
1957年 | 192篇 |
1956年 | 172篇 |
1955年 | 167篇 |
1954年 | 159篇 |
1948年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
P. J. Müller P. Masner Maria Kälin W. S. Bowers 《Cellular and molecular life sciences : CMLS》1979,35(5):704-705
Summary Corpora allata fromOncopeltus fasciatus incubated in vitro in medium containing 10–5.35 M (1 g/ml) of precocene II lose their ability to secrete juvenile hormone when reimplanted into last instar larvae.Acknowledgments. We thank Mr K. Dorn, Mrs L. Dolezal, Mrs V. Nötzli-Graf, Mr K.H. Trautmann and Mr A. Schuler for technical help, Dr W. Vogel and Dr A. Dübendorfer for valuable discussions. 相似文献
92.
93.
C. P. Sigdestad D. J. Grdina K. Ando 《Cellular and molecular life sciences : CMLS》1979,35(6):815-817
Summary Cells from a murine fibrosarcoma (FSa) have been grown in vitro as multicell tumor spheroids (MTS). The growth rate of these MTS was determined. Follwing selected periods of growth, MTS were made into a single cell suspension and separated on linear density gradients of Renografin. While only 1 population of cells was separated from small spheroids (400 m diameter), at least 3 subpopulations of tumor cells were separated and isolated from large spheroids (800 m in diameter).This investigation was supported in part by grants numbered CA-18628 and CA-06294, awarded by the National Cancer Institute, DHEW. 相似文献
94.
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
95.
96.
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
97.
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
98.
Possible role for cyclic nucleotides and phosphorylated membrane proteins in postsynaptic actions of neurotransmitters. 总被引:2,自引:0,他引:2
P Greengard 《Nature》1976,260(5547):101-108
The postsynaptic actions of some neurotransmitters may be mediated through cyclic nucleotides and cyclic nucleotide-dependent phosphorylation of specific membrane proteins in postsynaptic cells. In addition to providing a molecular basis for the actions of several neurotransmitters and of certain drugs affecting behaviour, the model suggests a mechanism by which neurotransmitter signals may be converted into electrophysiological responses in postsynaptic cells. 相似文献
99.
The hyperthermic effect of a bacterial pyrogen has been studied in rabbits pretreated or not with p-chlorophenylalanine or 5, 6-dihydroxytryptamine. The results obtained indicate that a selective reduction of cerebral 5-hydroxytryptamine levels by these drugs do not significantly affect pyrogen hypertermia. 相似文献
100.
A. J. Rein D. D. Saperstein S. H. Pines P. C. Radlick 《Cellular and molecular life sciences : CMLS》1976,32(10):1352-1354
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