全文获取类型
收费全文 | 24107篇 |
免费 | 745篇 |
国内免费 | 1116篇 |
专业分类
系统科学 | 587篇 |
丛书文集 | 624篇 |
教育与普及 | 279篇 |
理论与方法论 | 140篇 |
现状及发展 | 556篇 |
研究方法 | 1篇 |
综合类 | 23763篇 |
自然研究 | 18篇 |
出版年
2024年 | 46篇 |
2023年 | 145篇 |
2022年 | 296篇 |
2021年 | 298篇 |
2020年 | 289篇 |
2019年 | 252篇 |
2018年 | 283篇 |
2017年 | 374篇 |
2016年 | 424篇 |
2015年 | 596篇 |
2014年 | 1108篇 |
2013年 | 876篇 |
2012年 | 1443篇 |
2011年 | 1582篇 |
2010年 | 1106篇 |
2009年 | 1369篇 |
2008年 | 1427篇 |
2007年 | 1867篇 |
2006年 | 1602篇 |
2005年 | 1513篇 |
2004年 | 1238篇 |
2003年 | 1128篇 |
2002年 | 1052篇 |
2001年 | 881篇 |
2000年 | 726篇 |
1999年 | 552篇 |
1998年 | 470篇 |
1997年 | 440篇 |
1996年 | 408篇 |
1995年 | 323篇 |
1994年 | 288篇 |
1993年 | 306篇 |
1992年 | 247篇 |
1991年 | 224篇 |
1990年 | 197篇 |
1989年 | 214篇 |
1988年 | 165篇 |
1987年 | 95篇 |
1986年 | 55篇 |
1985年 | 41篇 |
1984年 | 19篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
161.
介绍了企业核心竞争力的内涵和特点,阐述了领导力与竞争力的关系,从学习能力、企业文化塑造、执行力、配置资源的能力等方面论述了企业领导力的培养。 相似文献
162.
163.
讨论了工艺过程中产生的界面态陷阱电荷Q(it)对高频MOS-CV特性线的形变规律,提出了一种沿电压方向形变的数据处理方法,以此算出Q(it)密度在禁带中的分布,并对常规高频CV法的测量误差作了讨论和修正,由于数据的采集和处理可以由微机完成,使这种方法变得简便、准确并易于在工艺线上推广使用。 相似文献
164.
Summary Apart from cancer and mutation induction, radiobiological effects on mammals are mostly attributable to cell death, defined as loss of proliferative capacity. Survival curves relate retention of that capacity to radiation dose, and often manifest a quasi-threshold (shoulder). The shoulder is attributable to an initial mechanism of repair (Q-repair) which is gradually depleted as dose increases. Another form of repair, which is not depleted (P-repair), increases the dose required to deliver an average of one lethal event per cell (dose D0). Neither form of repair can unambiguously be linked with repair of defects in isolated DNA. An important initial lesion may well be disruption of the complex structural relationship between the DNA, nuclear membrane and associated proteins. One form of P-repair may be restoration of that structural relationship. 相似文献
165.
B. Lindblad W. E. Burkel T. W. Wakefield L. M. Graham J. C. Stanley 《Cellular and molecular life sciences : CMLS》1988,44(3):223-224
Summary The most important effect of dihydroergotamine is venoconstriction, but certain metabolic effects and changes in vessel prostanoid activity have also been suggested. In this study endothelial cell production of 6-keto PGF1 and TxB2 was quantitated in vitro. No evidence of altered prostanoid production was noted after incubation with dihydroergotamine (exposure ranging from 5×10–3 to 5×10–7 g/l). Similarly, no effect of dihydroergotamine on the growth rates of endothelial cells or smooth muscle cells in vitro was documented. 相似文献
166.
本文应用EDAX-9100能谱仪,对家兔冠状动脉粥样硬化病变部位的微量元素进行显微分析,发现Zn/Cu比值大于1,提供了冠心病病因中“Zn/Cu假说”的实验论证。 相似文献
167.
朱公先 《首都师范大学学报(自然科学版)》1988,(2)
本文指出,《协同学》中将绝热近似与役使原理等同是不妥的,前者只是后者的特例。为此给出了役使原理的新表述,并探讨两者的关系。由此可将H.Haken的理论推广于非绝热近似的情形。 应用役使原理于过阻尼振子系统中,探讨绝热近似的适用条件,引进高级绝热近似的概念,并探讨其适用条件。由此可见考虑时滞。 相似文献
168.
J. Y. Toullec M. Chikhi A. van Wormhoudt 《Cellular and molecular life sciences : CMLS》1992,48(3):272-277
In crustaceans, all the steps in the assimilation of food take place in the hepatopancreas. To facilitate the study of this organ, a method for the dissociation of cell types was developed. The hepatopancreas of the prawnPalaemon serratus was mechanically dissociated and the cells separated by Percoll density-gradient centrifugation. The E and R cells had similar densities of around 1.05 g/ml. The F cells were separated into two distinct fractions with densities of 1.075 and 1.082 g/ml. The B cells sedimented at a density of 1.12 g/ml. The ratio between the two populations of F cells was found to vary during the intermolt cycle while B cells disappeared after the molt. When the density gradient fractions were incubated with3H-leucine, incorporation was highest in the F cell fractions. Measurements of -amylase activity, indicated that the two populations of F cells may be derived from the same cell type. 相似文献
169.
设计了一种以挥发性产物和非挥发性底物为特征的四相反应器——分离器。在此反应器中,生物催化剂被固定在固体柱填充物上并与含有底物的液相接触,汽相流过柱子而将挥发性产物蒸发迸入汽相。反应器由同方向流的浓缩器和反方向流的分离器两个基本汽——液流部分组成。并建立了吸附的单层细胞稳态群体数学模型和反应器平衡状态模型。 相似文献
170.
J. S. Nowak 《Cellular and molecular life sciences : CMLS》1985,41(1):88-89
Summary Somatic cell hybrids between Sp2/O-Ag14 mouse myeloma cells and lymphocytes derived from BALB/c mice hyperimmunized with sheep red blood cells (SRBC) were produced. One hybrid producing IgG1 antibody to SRBC was selected, cloned twice and subsequently transferred to BALB/c mice. After a number of transfers it was found that the antibody titer in ascitec fluid gradually decreased. Cytogenetic analysis revealed gradual chromosome loss in the hybrid clone, which produced progressively less antibody. 相似文献