全文获取类型
收费全文 | 8738篇 |
免费 | 106篇 |
国内免费 | 52篇 |
专业分类
系统科学 | 151篇 |
丛书文集 | 60篇 |
教育与普及 | 7篇 |
理论与方法论 | 51篇 |
现状及发展 | 3623篇 |
研究方法 | 342篇 |
综合类 | 4579篇 |
自然研究 | 83篇 |
出版年
2016年 | 61篇 |
2015年 | 82篇 |
2013年 | 51篇 |
2012年 | 255篇 |
2011年 | 354篇 |
2010年 | 51篇 |
2008年 | 143篇 |
2007年 | 176篇 |
2006年 | 153篇 |
2005年 | 333篇 |
2004年 | 625篇 |
2003年 | 577篇 |
2002年 | 269篇 |
2001年 | 235篇 |
2000年 | 315篇 |
1999年 | 177篇 |
1992年 | 128篇 |
1991年 | 95篇 |
1990年 | 108篇 |
1989年 | 96篇 |
1988年 | 83篇 |
1987年 | 88篇 |
1986年 | 96篇 |
1985年 | 159篇 |
1984年 | 99篇 |
1983年 | 92篇 |
1982年 | 76篇 |
1981年 | 73篇 |
1980年 | 86篇 |
1979年 | 191篇 |
1978年 | 160篇 |
1977年 | 163篇 |
1976年 | 150篇 |
1975年 | 172篇 |
1974年 | 198篇 |
1973年 | 157篇 |
1972年 | 155篇 |
1971年 | 212篇 |
1970年 | 277篇 |
1969年 | 218篇 |
1968年 | 194篇 |
1967年 | 202篇 |
1966年 | 177篇 |
1965年 | 121篇 |
1964年 | 59篇 |
1959年 | 67篇 |
1958年 | 82篇 |
1957年 | 82篇 |
1956年 | 52篇 |
1954年 | 54篇 |
排序方式: 共有8896条查询结果,搜索用时 31 毫秒
31.
32.
V. Pli<ska 《Cellular and molecular life sciences : CMLS》1991,47(3):216-221
Summary Binding studies in various biological systems frequently indicate the presence of several binding sites for a biologically active ligand. They differ in their affinity for the ligand in question, binding capacity, and Hill coefficient, which suggests differences in the mechanisms of the binding site-ligand interactions. Identification of the true receptors (sites initiating a cellular response) appears to be difficult. Three clusters of binding sites for oxytocin were found on rat myometrial cells. The oxytocin receptor seems to be linked to the medium-affinity site; the cooperation between the high-and medium-affinity sites in eliciting the uterotonic response seems likely, but lacks experimental proof. Dose-response analysis in partially irreversibly inhibited uterus preparations, the method of equipotent doses (Furchgott-Bursztyn method), and structure-activity analysis of oxytocin-like peptides acting as competitive inhibitors of oxytocin, turned out to be suitable for pharmacological analysis of this receptor system. 相似文献
33.
Summary Tamoxifen is an anticancer drug widely used in the treatment of estrogen-dependent breast cancer. In hatchling alligators it acts as a pure antiestrogen in that it completely blocks the effect of estradiol-induced oviductal hypertrophy and completely blocks the estradiol-induced hepatic vitellogenin secretion. Paradoxically, when injected into alligator eggs incubated at 33°C, a temperature which would normally result in 100% male hatchlings, tamoxifen sex reverses the embryos into apparently normal female hatchlings. 相似文献
34.
A. V. Edwards M. A. Ghatei S. R. Bloom 《Cellular and molecular life sciences : CMLS》1994,50(8):725-726
Mean plasma insulin concentration was reduced and mean plasma glucose concentration increased following the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mol kg–1 i.a.) in conscious calves given continuous infusions of exogenous glucose (30–60 mol min–1 kg–1 i.v.). It is concluded that the rise in plasma insulin concentration which occurs in these animals in response to glucose is mediated, at least in part, by a nitric oxide-related factor (NOx). 相似文献
35.
36.
光伏功率预测在现代电力系统调度和运行中起着重要作用.针对光伏发电功率的多变性和复杂性,提出了一种基于新型相似日选取和北方苍鹰算法(Northern Goshawk Optimization, NGO)优化双向门控循环单元(Bidirectional Gated Recurrent Unit, BiGRU)的短期光伏功率预测方法.首先,利用斯皮尔曼相关系数选取主要气象因子,通过变分模态分解(Variational Mode Decomposition, VMD)将原始光伏功率和最大气象因子分解重构为一系列子信号.其次,通过构建新的评价指标筛选出相似日数据集,利用一组BiGRU建立以相似日子信号为网络输入的深度学习模型,并利用NGO对每个BiGRU网络的超参数进行有效优化.最后,对各子信号的预测结果进行综合,得到最终的光伏功率预测值.仿真结果表明,所提混合深度学习方法在预测精度和计算效率方面均优于其他方法. 相似文献
37.
S. F. Wang J. C. Braekman D. Daloze J. Pasteels P. Soetens N. V. Handjieva P. Kalushkov 《Cellular and molecular life sciences : CMLS》1996,52(6):628-630
The isolation of N-quinaldyl-L-arginine·HCl (1) from the CoccinellidaeSubcoccinella-24-punctata is reported. The structure, first established on the basis of the analysis of the spectral properties of1, has been confirmed by synthesis. The alkaloid is of endogenous origin and markedly deterrent to ants. 相似文献
38.
Molecular evidence for increased hematopoietic proliferation in the spleen of the b/b laboratory rat
S. Savković S. Pavlović T. Mitrović M. Joksimović J. Marjanović V. Glišin Z. Popović 《Cellular and molecular life sciences : CMLS》1996,52(8):807-811
The splenomegaly and the appearance of a significant number of CFU-E (erythroid colony-forming units) and BFU-E1 (erythroid burst-forming units) in the Belgrade laboratory rat (b/b) spleen prompted us to analyse further the molecular evidence for increased hematopoietic proliferation in the b/b spleen. Messenger RNAs (mRNAs) specific for globins, proteins for iron transport and deposition and the band 3 protein were used in rat erythropoietic tissues as markers for proliferation and erythroid differentiation. In the b/b spleen, all mRNAs analysed display an erythroid-specific pattern of expression. This analysis also revealed an enhanced level of mRNA for ferritin in the +/b spleen, whereas erythrocyte-specific mRNA production was normal. 相似文献
39.
40.
F. V. DeFeudis L. M. Orensanz Muñoz M. A. Vidal G. Corrochano M. Sanchez del Alamo 《Cellular and molecular life sciences : CMLS》1978,34(9):1169-1170
Summary High-affinity, Na+-independent binding of -alanine to a synaptosomal fraction of rat brain was potently inhibited by glycine and by some other -amino acids, but not by taurine or GABA. This binding mechanism, which was also sensitive to both bicuculline and strychnine, might involve synaptic receptors for both -alanine and glycine.This study was supported in part by Centro Ramón y Cajal and Fundacion Juan March. 相似文献