全文获取类型
收费全文 | 876篇 |
免费 | 26篇 |
国内免费 | 67篇 |
专业分类
系统科学 | 40篇 |
丛书文集 | 20篇 |
教育与普及 | 10篇 |
理论与方法论 | 7篇 |
现状及发展 | 64篇 |
研究方法 | 2篇 |
综合类 | 818篇 |
自然研究 | 8篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 25篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 20篇 |
2016年 | 13篇 |
2015年 | 26篇 |
2014年 | 24篇 |
2013年 | 19篇 |
2012年 | 48篇 |
2011年 | 46篇 |
2010年 | 31篇 |
2009年 | 48篇 |
2008年 | 49篇 |
2007年 | 76篇 |
2006年 | 62篇 |
2005年 | 43篇 |
2004年 | 40篇 |
2003年 | 39篇 |
2002年 | 39篇 |
2001年 | 33篇 |
2000年 | 22篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 1篇 |
排序方式: 共有969条查询结果,搜索用时 312 毫秒
61.
本文研究了薏苡的花序形态及其分化的过程。观察到薏苡可育雌小穗有两花均结实、雌蕊有三个柱头及雄穗有结实(无壳)的现象。将其穗分化过程划分为五个主要时期。 相似文献
62.
63.
64.
对“古文”“古文字”“古汉字”这一组汉字学术语的使用情况进行了分析和辨别,并在此基础之上分别给这几个术语进行了定义,希望能够有助于消除以往的一些错误认识,正确地使用相关术语。 相似文献
65.
Cecchi C Liguri G Fiorillo C Bogani F Gambassi M Giannoni E Cirri P Baglioni S Ramponi G 《Cellular and molecular life sciences : CMLS》2004,61(14):1775-1784
An acylphosphatase (AcPase) overexpression study was carried out on SH-SY5Y neuroblastoma cells, using a
green fluorescent fusion protein (AcP-GFP), with GFP acting as a reporter protein. The cellular proliferation rate
was significantly reduced by overexpression of AcPase by a factor of ten. In contrast, clones transfected with two
inactive AcPase mutants showed a growth rate comparable to control cells. This suggests that AcPase catalyzes the
proliferative down-regulation. AcPase-overexpressing clones showed a physiological mortality rate as assessed by an
MTT reduction test and by evaluation of necrotic markers. DNA fragmentation analysis and assays of caspase-3 and
poly (ADP-ribose) polymerase (PARP)-active fragments showed no evidence of any apoptotic pattern. AcPase
overexpression led to a marked increase in PARP activity as well as Bcl-2 content; these are commonly up-regulated
during differentiative processes in neuronal cells. In fact, the typical differentiation marker,
growth-associated-protein 43, was significantly up-regulated. Microscopic observations also showed a clear
increase in the differentiative phenotype in AcPase-overexpressing cells. Our results clearly show that AcPase
plays a primary causative role in neuronal differentiation.Received 3 May 2004; accepted 25 May 2004 相似文献
66.
复杂性与社会分化——卢曼社会系统理论研究 总被引:1,自引:0,他引:1
在卢曼看来,社会系统总是处于极端的复杂状态,同时也处于一种复杂化的过程之中。系统的复杂性征使其在面对环境的影响时,出现各种内在的危机和各种不平衡现象,并产生一系列的运作难题,使社会系统无法以其原来对付环境的原则进行实际运作,迫使社会系统不断地进行复杂性的化约和自我的区分化以化解危机,而社会系统也在此一过程中实现自身的演化和进化。 相似文献
67.
《科学通报(英文版)》2007,52(20)
In regard to such challenging analysis problems as scientific identification and quality evaluation of Chinese traditional medicine, the electrochemical fingerprint technique of Chinese traditional medi- cine has been researched. The principle, traits, functions, etc., of the electrochemical fingerprint have detailedly been analyzed and discussed by the B-Z oscillatory system using malonic acid as main dissipation substance, characterized by the fact that different influences of different Chinese traditional medicines on the mechanism of the oscillatory reaction cause different changes of the shape of the potential-time curve of the oscillatory system under the conditions of constant tem- perature and pressure. An economical, simple and convenient, easy pushing and effective scientific method for distinguishing and evaluating multifarious Chinese traditional medicines has success- fully been put forward. 相似文献
68.
变化及复杂织物组织的计算机生成 总被引:2,自引:0,他引:2
采用织物组织的数学函数组织异化法,对三原变化组织进行计算机模拟,并在此基础上,对复杂组织的处理方法进行探索,旨在建立一种高效简单的织物组织的计算机生成方法,最后给出计算机模拟效果图. 相似文献
69.
Wolf spiders are predators in large quantities in the fields. How wolf spiders keep their dominant species status under long-period pesticide force? To answer this question, eight geographical populations of Pardosa pseudoannulata were used as materials to test the influence of geographical habitats on their genomic DNA polymorphism. The RAPD pattern showed polymorphic variations among and within different populations. Total 84 bands amplified by 10 random primers, of which 62 (73.81%) are polymorphic, were generated from 55 individuals of eight geographical populations. Meanwhile, Shannon’s index (Ho= 0.5177) showed a rich genetic diversity of P. pseudoannulata, and most of the genetic variation (64.24%) was found within populations. Multiple regression analysis suggested that it is the climatic variation (such as annual average temperature etc.) that results in adaptive eco-geographic differentiation, and it is the long-period pesticide force that speeds up the genetic differentiation of P. pseudoannulata which changed the genetic diversity of the population. 相似文献
70.
《上海交通大学学报》2007,(Z1)
基于豪泰林的地点差异化模型的分析研究,以摩托罗拉网络服务为例,分析了摩托罗拉作为跨国大公司在面对市场中采用低价策略的国内小电信网络服务公司的竞争时,采取差异化策略推出一系列的新型移动网络服务产品,从而获得竞争优势的内在因素和实施方法.从而进一步表明:为避免价格竞争,获取市场份额和利润,差异化是竞争战略的重要手段;作为国际性大企业,类似摩托罗拉公司,有能力、有条件实施差异化,提供差异化服务,并最终在绩效上有了良好的表现;差异化和消费者的赶路成本、偏好紧密相关,产品差异化要满足不同用户不同地点的不同需求. 相似文献