全文获取类型
收费全文 | 1142篇 |
免费 | 44篇 |
国内免费 | 56篇 |
专业分类
系统科学 | 50篇 |
丛书文集 | 17篇 |
教育与普及 | 15篇 |
理论与方法论 | 1篇 |
现状及发展 | 15篇 |
研究方法 | 11篇 |
综合类 | 1133篇 |
出版年
2024年 | 10篇 |
2023年 | 11篇 |
2022年 | 26篇 |
2021年 | 23篇 |
2020年 | 20篇 |
2019年 | 3篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 26篇 |
2013年 | 30篇 |
2012年 | 38篇 |
2011年 | 39篇 |
2010年 | 47篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 58篇 |
2006年 | 37篇 |
2005年 | 45篇 |
2004年 | 43篇 |
2003年 | 35篇 |
2002年 | 44篇 |
2001年 | 55篇 |
2000年 | 40篇 |
1999年 | 73篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 41篇 |
1995年 | 50篇 |
1994年 | 32篇 |
1993年 | 29篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有1242条查询结果,搜索用时 15 毫秒
951.
洋务运动时期,洋务派拉开留学运动的帷幕,随后留学生队伍不断壮大。到了民国末年,留学生群体基本完成了近代化转型,这是留学生自我构建的结果。除了通过留学这一基本途径外,留学生群体还通过参与社会建设、搭建发展平台来实现自我构建。 相似文献
952.
随着激光技术不断发展并走向成熟,如何防止激光损伤已经成为亟待解决的科学问题。铂(II)配合物因其结构稳定、光物理性质丰富、化学修饰性及光谱可调性强,以及激发态寿命长等特点,在光限幅材料领域中被广泛应用。当前,开发限幅性能优异、光学窗口宽且透光性高的铂(II)配合物光限幅材料成为激光防护领域中的研究热点。重点介绍了近年来报道的各类铂(II)配合物的光物理性质调控和光限幅性能研究,并对该领域的发展趋势进行了展望,以期为开发新型铂(II)配合物光限幅材料提供一定的参考。 相似文献
953.
Fossiliferous glacial erratics have been found in moraines of the Grove Mountains, east Antarctica since 1998 by Chinese National Antarctic Research Expedition (CHNARE) teams. These erratics were derived from a suite of glaciogene strata hidden beneath the Antarctic Ice Sheet in the Lambert glacier drainage system, and thus provide a record of Cenozoic paleoenvironmental conditions and fossil biotas that are so far unknown from outcrops and drill cores in this region.By microfossil analysis, sparse Neogene spores and pollen grains are revealed, including: Toroisporis (Lygodiaceae), Granulatisporites (Pteridaceae?), Osmunda (Osmundaceae), Polypodiaceae, Magnastriatites (Parkeriaceae), Deltoidospora, Araucariaceae, Taxodiaceae, Podocarpus (Podocarpaceae), Dacrydium (Podocarpaceae),Pinus (Pinaceae), Keteleeria (Pinaceae), Picea (Pinaceae), Tsuga (Pinaceae), Chenopodiaceae, Artemisia (Asteraceae), Asteraceae, Gramineae,Fraxinoipollenites (Oleaceae), Oleoidearumpollenites (Oleaceae), Oleaceae, Operculumpollis, Nothofagidites (Nothofagus), Rhus, Quercus (Fagaceae), Juglans (Juglandaceae), Pterocarya (Juglandaceae), Liquidambar (Hamamelidaceae), Ulmus (Ulmaceae), Ulmoidepites (Ulmaceae), Tilia, Proteacidites (Proteaceae) and Tricolpopollenites; but without any marine diatoms. Most of the spores and pollen grains in the erratics are considered to originate from local sources except for some older exotic components that might be recycled from
the basement sedimentary rocks by the ice sheet, so they are in situ sporo-palynological assemblages. Furthermore, since the source areas of the glaciogenic sedimentary rocks are assumed to be local or in the up glacier areas, the palynological assemblages in these erratics represent an inland terrestrial flora during a warmer period of the ice-sheet evolutionary history. The ages of these erratics are also discussed based on the occurrence of some diagnostic pollens such as the Artemisia, Chenopodiaceae and Nothofagus, which implies Neogene (most probably Pliocene). As a preliminary conclusion, we think that the existence of the Cenozoic glaciogenic rocks and their palynological assemblages present new evidence for a large scale glacial retreat event in the Grove Mountains of east Antarctica, and thus support a dynamic East Antarctic Ice Sheet (EAIS). Furthermore, the absence of marine fossils in the samples analyzed not only provides additional evidence for a terrestrial sedimentary environment of these erratics, but also indicates that there is no transportation
of Cenozoic marine fossils from the adjacent areas of the Grove Mountains. 相似文献
954.
4种沙棘雄配子体发育的研究 总被引:1,自引:0,他引:1
4种沙棘雄配子体的形成过程较一致,减数分裂中染色体发生了不同程度的变异,具有两种类型的绒毡层,这种现象很可能与种间的演化顺序有关。温度是影响沙棘雄配子体发育进程的重要因素。 相似文献
955.
以交联的聚芳醚酮酮和φ=20%的发烟硫酸合成了磺化聚芳醚酮酮树脂,并用于乙酸丁酯的催化合成。最佳条件:酸醇摩尔比为1:1.6,催化剂用量(质量分数,ω)为4.35%,反应温度115-120℃,反应时间为4h,酯化率达87.5%,催化剂易回收且可重复使用。 相似文献
956.
Progress and records in the study of endogenetic mineralization during collisional orogenesis 总被引:10,自引:0,他引:10
Yanjing Chen Huayong Chen Yulin Liu Guangjun Guo Yong Lai Shan Qin Baoling Huang Zengjie Zheng Yinghui Sui Chao Li Zhen Li Ping Li Xin Li Haihua Wang Meixiang Zhu Xiuli Gao Qiying Wei 《科学通报(英文版)》2000,45(1):1-10
To develop and perfect the theory of plate tectonics and regional metallogeny, metallogenesis during collisional orogenesis
should be thoroughly studied and will attract increasing attention of more and more scientists. This paper presents the main
aspects of research and discussions on metallogenesis during collisional orogenesis after the development of plate tectonics,
and accordingly divides the study history into two stages, i.e. the junior stage during 1971–1990 and the senior stage after
1990. Beginning with the negation of mineralization in the collision regime by Guild (1971), the focus of study was put on
whether there occurred any mineralization during collisional orogenesis at the junior stage. At the senior stage, which is
initiated by the advance of metallogenic and petrogenic model for collisional orogenesis, scientists begin to pay their attention
to the geodynamic mechanism of metallogenesis, spatial and temporal distribution of ore deposits, ore-forming fluidization,
relationship between petrogenesis and mineralization in collisional orogenesis, etc. Abundance of typical collisional orogens
such as Himalayan, China has best natural conditions to study collisional metallogenesis. Great progress in the study of metallogenesis
during collisional orogenesis has been made by Chinese geologists. Therefore, we hope that the’ Chinese geologists and Chinese
governments at various levels to pay more attention to the study of collisional metallogenesis. Some urgent problems are suggested
to be solved so as to bring about breakthroughs in the aspects concerned. 相似文献
957.
研制了一种Cr6Ni11Mn13MoTi奥氏体钢焊条用于高温服役(450~650℃)的Cr-Mo钢构件的异种金属焊接。结果表明:其异质接头具有良好力学性能和抗氧化性能,可以克服以往的异质接头服役过程中因碳迁移而导致的提前失效问题。 相似文献
958.
Goh YC Yap CT Huang BH Cronshaw AD Leung BP Lai PB Hart SP Dransfield I Ross JA 《Cellular and molecular life sciences : CMLS》2011,68(9):1581-1592
Heat-shock protein 60 (Hsp60) is a highly conserved stress protein which has chaperone functions in prokaryotes and mammalian
cells. Hsp60 is associated with the mitochondria and the plasma membrane through phosphorylation by protein kinase A, and
is incorporated into lipid membranes as a protein-folding chaperone. Its diverse intracellular chaperone functions include
the secretion of proteins where it maintains the conformation of precursors and facilitates their translocation through the
plasma membrane. We report here that Hsp60 is concentrated in apoptotic membrane blebs and translocates to the surface of
cells undergoing apoptosis. Hsp60 is also enriched in platelets derived from terminally differentiated megakaryocytes and
expressed at the surface of senescent platelets. Furthermore, the exposure of monocytic U937 cells to Hsp60 enhanced their
phagocytic activity. Our results suggests that externalized Hsp60 in apoptotic cells and senescent platelets influences events
subsequent to apoptosis, such as the clearance of apoptotic cells by phagocytes. 相似文献
959.
Sui Y Zhao HL Ma RC Ho CS Kong AP Lai FM Ng HK Rowlands DK Chan JC Tong PC 《Cellular and molecular life sciences : CMLS》2007,64(23):3119-3128
This study was performed to examine the effect of chronic renal impairment and renin-angiotensin system (RAS) activation induced
by unilateral nephrectomy (UNX) on the development of pancreatic islet β-cell deficit and glucose intolerance. Sprague-Dawley
rats were randomized into three groups: untreated UNX (n = 10), UNX treated with the angiotensin-converting enzyme inhibitor lisinopril (n = 8) and sham operation (n = 10). Blood glucose, serum insulin, renal function and histological changes of kidney and pancreas were examined 8 months
postoperation. Compared with the sham rats, UNX rats developed renal impairment, insulin deficiency and glucose intolerance.
Histological staining revealed an islet β-cell deficit associated with increased immunoreactivity for angiotensin and angiotensin
type 1 receptor in UNX rats. Treatment with lisinopril significantly improved renal dysfunction, hyperglycemia, insulin secretion
and islet RAS expression. These data suggest that chronic renal impairment and RAS activation may contribute to islet β-cell
loss and glucose intolerance. RAS blockade may therefore prevent these disorders.
Received 29 August 2007; received after revision 25 September 2007; accepted 27 September 2007 相似文献
960.
分析了残障学生特殊心理问题的形成及心理健康问题的原因, 并根据其分类的不同分析了肢残生挥之不去的自卑及对人生的茫然与朦胧; 指明了解决残障生心理健康问题的途径和方法。途径是一般性补偿和科学补偿。方法是教育心理学方法和特别研究设置的补偿方法, 还提出了因人施教、递进式教育方法及实施新科技教学方法。 相似文献