全文获取类型
收费全文 | 4519篇 |
免费 | 122篇 |
国内免费 | 243篇 |
专业分类
系统科学 | 215篇 |
丛书文集 | 112篇 |
教育与普及 | 65篇 |
理论与方法论 | 17篇 |
现状及发展 | 24篇 |
研究方法 | 15篇 |
综合类 | 4435篇 |
自然研究 | 1篇 |
出版年
2024年 | 22篇 |
2023年 | 52篇 |
2022年 | 89篇 |
2021年 | 115篇 |
2020年 | 59篇 |
2019年 | 25篇 |
2018年 | 44篇 |
2017年 | 46篇 |
2016年 | 55篇 |
2015年 | 111篇 |
2014年 | 142篇 |
2013年 | 158篇 |
2012年 | 149篇 |
2011年 | 192篇 |
2010年 | 165篇 |
2009年 | 200篇 |
2008年 | 197篇 |
2007年 | 194篇 |
2006年 | 181篇 |
2005年 | 170篇 |
2004年 | 107篇 |
2003年 | 133篇 |
2002年 | 143篇 |
2001年 | 153篇 |
2000年 | 143篇 |
1999年 | 235篇 |
1998年 | 185篇 |
1997年 | 191篇 |
1996年 | 175篇 |
1995年 | 167篇 |
1994年 | 172篇 |
1993年 | 147篇 |
1992年 | 130篇 |
1991年 | 123篇 |
1990年 | 87篇 |
1989年 | 92篇 |
1988年 | 59篇 |
1987年 | 43篇 |
1986年 | 20篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1973年 | 1篇 |
排序方式: 共有4884条查询结果,搜索用时 15 毫秒
171.
解红丽 《温州大学学报(自然科学版)》2012,(2):82-87
东北易帜是张学良亲掌东北权柄后作出的一项重大抉择。张学良本人的口述史料清晰地再现其东北易帜时的心理活动,从崭新的角度揭示了其东北易帜的原因:顺应民族自救、国家统一的时代主流;能力远不及父亲,应付不了当时复杂的局面,主要是应付不了日本人的纠缠;渴望祖国统一,从无思求地盘之心;日本炸死父亲,国仇家恨加重了易帜的决心。 相似文献
172.
以企业家精神代表创新和创业精神,用1996—2008年的统计数据实证分析了河南省和全国企业家的创新、创业精神与经济增长之间的关系,以及两者的动态趋势,得出创新、创业精神与区域经济增长之间存在很强的正相关关系,河南企业家的创新、创业精神与全国其他省分的企业家表现基本相同.在研究结论的基础上,为河南发展企业家精神提供了几条建议. 相似文献
173.
文章分析了当前给排水工程行业中调节阀的现状、常出现的问题以及维护的方法,便于施工人员的安装维修及调换;节约施工单位的维护成本. 相似文献
174.
本文结合实例介绍了膜结构在景观领域的应用现状,并从结构、材料、价格、形态、环保等四个方面论述了其具有良好的发展前景。 相似文献
175.
通过乳液聚合的方法制备了水相苯丙乳液(PSBA),并将其应用于静电纺丝制备出微纳米纤维结构。采用红外光谱、差示扫描量热仪(DSC)和动态光散射仪分析并表征了聚合物的化学组成、热稳定性,并得到了均一稳定的苯丙乳液。通过扫描电镜(SEM)研究了纺丝电压及纺丝液中苯丙乳液与聚乙烯醇(PVA)质量比对苯丙乳液电纺微纳米纤维结构的影响,结果表明,改变纺丝液PSBA、PVA质量比能够得到可控性的纤维结构;纺丝电压对纤维中串珠状结构形成有一定影响,且电压越高,纤维直径越小。 相似文献
176.
As a basic and advanced machining technique,the high-speed milling process plays an important role in realizing the goal of high performance manufacturing.From the viewpoint of machining dynamics,obtaining chatter-free machining parameters is a prerequisite to guaranteeing machining accuracy and improving machining efficiency.This paper gives an overview on recent progress in time domain semi-analytical methods for chatter stability analysis of milling processes.The state of art methods of milling stability prediction in milling processes and their applications are introduced in detail.The bottlenecks involved are analyzed,and potential solutions are discussed.Finally,a brief prospect on future works is presented. 相似文献
177.
We investigated the dynamic properties of a two-section composite chain of beads under vertical vibration.By analyzing the chain’s motion,including phase-shift,mean dilation,center-of-mass displacement,and energy,we found that with different bead arrangements,the chain behaved in different ways.We believe that interaction existing at the interface between bead sections provides the underlying cause.This interaction causes different energy in different arrangements,which leads to different dynamic characteristics. 相似文献
178.
Surface pollen assemblages of human-disturbed vegetation and their relationship with vegetation and climate in Northeast China 总被引:1,自引:0,他引:1
ManYue Li YueCong Li QingHai Xu RuiMing Pang Wei Ding ShengRui Zhang ZhiGuo He 《科学通报(英文版)》2012,57(5):535-547
Pollen assemblages of 53 surface pollen samples from farmlands and wastelands in Northeast China were analyzed. Tree pollen percentages were usually higher than 30%, with Pinus (26.9%), Quercus (0.9%), Betula (0.9%) and Populus (0.7%) as the major types, and herb pollen percentages were usually higher than 50%, with weedy Poaceae (8.7%), Chenopodiaceae (7.1%), Artemisia (1.9%) and Compositae (3.5%) as the major taxa. Thus, the pollen assemblages were consistent with the regional vegetation compositions. However, there were differences in pollen assemblages among regions, especially among different geomorphological units. For example, in the mountains, there were more types of tree pollen and higher total percentages (average 42%) than in other areas, while cereal pollen percentages were lowest (11.2%). In the hills and high plains, herbs made up more than 60% of the pollens, with cereals (average 53.6%) the dominant type. In the low plains, pollen types were similar to those in the hills and high plains, but total pollen concentrations and the proportion of Concentricystes were much higher, while cereal pollen percentages were slightly lower (average 41.6%). Pollen assemblages in different land use types also differed. For example, in farmland, cereal pollen percentages were more than 40% and Chenopodiaceae was usually less than 2.5%, while in wasteland, weedy Poaceae was usually less than 10% and Chenopodiaceae was usually higher than 25%. Total pollen concentrations in farmland (average 3909 grains/g) were much lower than in wasteland (average 15074 grains/g). Redundancy analysis revealed that pollen assemblages were significantly negatively correlated with mean annual temperature (-0.73) and July mean temperature (-0.81) and significantly positively correlated with mean annual precipitation (0.48), indicating that pollen assemblages in the artificial or human-disturbed vegetation reflect regional climate well. Comparison of pollen assemblages in different areas of northern China showed that pollen concentrations reflect the intensities of human impact to some degree. For example, pollen concentrations decrease as human impacts increase in intensity. The cereal pollen proportions in farmland differed by area. In Northeast China, cereal pollen proportions were distinctly higher than in most other areas of northern China, suggesting differences in planting habits and climate. 相似文献
179.
丁耀全 《曲靖师范学院学报》2011,30(1):79-81
光绪二十九年,藏事告急之际,有泰接任驻藏大臣一职。有泰受命之始,曾到许多部衙咨询藏事,大有世受国恩,立誓办好西藏事务之志。然而,当他到达成都后,接触到在川省的大批官员,其中有些是曾在西藏和在川边任满返回的官员,具体得知西藏危机的形势和进藏路途的艰辛生活,特别是川省官员对当时朝廷腐败、贿赂盛行颇多议论。继而,有泰的政治态度由立志报国逐渐转向颟顸误国。 相似文献
180.