全文获取类型
收费全文 | 19526篇 |
免费 | 39篇 |
国内免费 | 71篇 |
专业分类
系统科学 | 168篇 |
丛书文集 | 288篇 |
教育与普及 | 43篇 |
理论与方法论 | 119篇 |
现状及发展 | 8777篇 |
研究方法 | 1043篇 |
综合类 | 8883篇 |
自然研究 | 315篇 |
出版年
2013年 | 151篇 |
2012年 | 379篇 |
2011年 | 691篇 |
2010年 | 157篇 |
2009年 | 118篇 |
2008年 | 388篇 |
2007年 | 420篇 |
2006年 | 438篇 |
2005年 | 456篇 |
2004年 | 448篇 |
2003年 | 379篇 |
2002年 | 377篇 |
2001年 | 639篇 |
2000年 | 593篇 |
1999年 | 404篇 |
1992年 | 342篇 |
1991年 | 280篇 |
1990年 | 293篇 |
1989年 | 265篇 |
1988年 | 245篇 |
1987年 | 301篇 |
1986年 | 306篇 |
1985年 | 333篇 |
1984年 | 300篇 |
1983年 | 231篇 |
1982年 | 205篇 |
1981年 | 207篇 |
1980年 | 270篇 |
1979年 | 628篇 |
1978年 | 487篇 |
1977年 | 502篇 |
1976年 | 331篇 |
1975年 | 379篇 |
1974年 | 583篇 |
1973年 | 502篇 |
1972年 | 505篇 |
1971年 | 568篇 |
1970年 | 759篇 |
1969年 | 555篇 |
1968年 | 456篇 |
1967年 | 560篇 |
1966年 | 467篇 |
1965年 | 326篇 |
1959年 | 169篇 |
1958年 | 276篇 |
1957年 | 212篇 |
1956年 | 180篇 |
1955年 | 150篇 |
1954年 | 156篇 |
1948年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
I. J. Miller N. K. McCallum C. M. Kirk B. M. Peake 《Cellular and molecular life sciences : CMLS》1982,38(2):230-231
Summary The free radical oxidation of 1 and 6-tetrahydrocannabinol has been examined by spin trapping techniques and intermediates that would lead to cannabinol have been trapped. The 1st step in the oxidation of 1-THC involves the removal of 3-H, while for 6-THC, either 2-H or 5-H. Intermediates were isolated which could be pyrolysed to the diene and cannabinol. 相似文献
132.
C Radanyi G Redeuilh E Eigenmann M C Lebeau N Massol C Secco E E Baulieu H Richard-Foy 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(2):255-258
The antibodies against estrogen receptor were obtained after injecting Rabbits with a cytoplasmic receptor fraction isolated from Calf uterus. The estrogen receptor was partially proteolysed by the action of trypsin and subsequently purified by affinity chromatography (purification 4,000 to 10,000 fold, to a purity of 5-20%). The affinity of the antibody for the proteolysed receptor is KD approximately 1 nM and serum titres have reached values of approximately 50 nM. The values remained constant after the third injection. Preliminary results indicate that the antibody has approximately the same affinity for "native" cytoplasmic estrogen receptor from Calf uterus, as well as for the "trypsinized" forms of estrogen receptor isolated from Calf uterine cytosol and Hen oviduct nuclei. 相似文献
133.
S André N Farjaudon C Pareyre E Séguin 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(14):1095-1097
Comparing cytotoxicity of tubulosine and of six newly synthesized pseudo-tubulosines in the Allium test, we have characterized all the current features of protein inhibition. Nevertheless cytotoxicity of the six pseudotubulosines is much weaker. Furthermore, "floating poles anaphasis", a disturbance characteristic of the action of tubulosine, has been found with a lesser intensity with the other compounds. 相似文献
134.
Summary Synthetic 3-methylcyclohex-3-en-1-one, or 3,3-MCH, decreased by 77% the flight aggregation ofDendroctonus pseudotsugae (Scolytidae) to sticky traps containing attractant (frontalin, -pinene, and resin). However, windthrown trees were protected by 3,3-MCH much less than is known to occur with the isomer 3,2-MCH.This research was supported in part by NSF grants BMS 72-02522 and DEB 77-11361 and the O.S.U. School of Forestry. We thank the administration of the Siuslaw National Forest for study sites, and Dr L.M. Libbey for GC/MS of 3,3-MCH. Oregon State University Ag. Exp. Sta. Tech. Paper No. 4313. 相似文献
135.
Field stimulation of isolated, spirally-cut cervix from day-22 pregnant rats produced contractions which could be inhibited by tetrodotoxin or hyoscine and potentiated by propranolol. The rat cervix would appear to receive both cholinergic and noradrenergic innervations whose transmitters activate muscarinic cholinoceptors and beta-adrenoceptors respectively. 相似文献
136.
Summary An intermediate stage between the elementary and the initial bodies of theRickettsiella genus is defined as the beginning of an intracellular cycle. It is characterized by several structural changes in the dense elementary body: the cytoplasm becomes less electron-dense; thus, the nucleoid and the ribosomes are visible. The inner layer of the cell-wall becomes progressively clearer and the trilamellar structure of the inner and outer membranes appears distinctly. Preinitial body is proposed as name of this stage of development. 相似文献
137.
MEASUREMENT of the absolute value of absorption by water vapour at microwave frequencies is difficult because the effect is so small. Far in the wings of the absorption lines, in the so-called 'windows' of the spectrum, it is especially difficult to achieve high accuracy in the free atmosphere. But it is in these windows that the behaviour of the absorption is important from both applied and scientific points of view. Satellite communications, remote sensing of the atmosphere, and radioastronomy, are all influenced by this behaviour. Measurements on an Earth-space path are reported here; the results indicate a nonlinear relationship between absorption and water-vapour content. 相似文献
138.
139.
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
140.
Rat pituitary MAO activity was reduced by constant darkness and by additions of melatonin in vitro and was increased by constant light and by pinealectomy. Hypothalamic MAO activity followed the same pattern but was less dramatically affected. The data suggest that MAO may be a target enzyme for melatonin. 相似文献