全文获取类型
收费全文 | 3505篇 |
免费 | 125篇 |
国内免费 | 154篇 |
专业分类
系统科学 | 135篇 |
丛书文集 | 139篇 |
教育与普及 | 89篇 |
理论与方法论 | 8篇 |
现状及发展 | 18篇 |
研究方法 | 24篇 |
综合类 | 3370篇 |
自然研究 | 1篇 |
出版年
2024年 | 17篇 |
2023年 | 47篇 |
2022年 | 65篇 |
2021年 | 61篇 |
2020年 | 58篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 40篇 |
2016年 | 36篇 |
2015年 | 72篇 |
2014年 | 110篇 |
2013年 | 101篇 |
2012年 | 131篇 |
2011年 | 151篇 |
2010年 | 120篇 |
2009年 | 133篇 |
2008年 | 144篇 |
2007年 | 153篇 |
2006年 | 105篇 |
2005年 | 139篇 |
2004年 | 96篇 |
2003年 | 108篇 |
2002年 | 103篇 |
2001年 | 101篇 |
2000年 | 97篇 |
1999年 | 188篇 |
1998年 | 160篇 |
1997年 | 192篇 |
1996年 | 182篇 |
1995年 | 156篇 |
1994年 | 126篇 |
1993年 | 103篇 |
1992年 | 92篇 |
1991年 | 84篇 |
1990年 | 73篇 |
1989年 | 79篇 |
1988年 | 48篇 |
1987年 | 45篇 |
1986年 | 16篇 |
1985年 | 5篇 |
排序方式: 共有3784条查询结果,搜索用时 15 毫秒
951.
This review summarizes the recent literature on the synthesis, characterization, and adsorption properties of meal-organic framework MOF-177. MOF-177 is a porous crystalline material that consists of Zn4O tetrahedrons connected with benzene tribenzoate (BTB) ligands. It is an ideal adsorbent with an exceptionally high specific surface area (BET4500 m2/g), a uniform micropore size distribution with a median pore diameter of 12.7 ?, a large pore volume (2.65 cm3/g), and very promising adsorption properties for hydrogen storage and other gas separation and purification applications. A hydrogen adsorption amount of 19.6 wt.% on MOF-177 at 77 K and 100 bar was observed, and a CO2 uptake of 35 mmol/g on MOF-177 was measured at 45 bar and an ambient temperature. Other hydrogen properties (kinetics and heat of adsorption) along with adsorption of other gases including CO2, CO, CH4, and N2O on MOF-177 were also be discussed. It was observed in experiments that MOF-177 adsorbent tends to degrade or decompose when it is exposed to moisture. Thermogravimetric analysis showed that the structure of MOF-177 remains intact at temperatures below 330℃ under a flow of oxygen, but decomposes to zinc oxide at 420℃. 相似文献
952.
研究生心理压力应对策略 总被引:1,自引:0,他引:1
本文分析了研究生心理压力的现状,提出从自我调整和学校社会外部支持两方面进行应对研究生心理压力的策略,从而为提高研究生的心理健康水平起到一定积极作用。 相似文献
953.
在一般的条件下 ,得到一类具有反射边界的随机微分方程解的存在性和唯一性结果 ,该类方程的反射边界是随机的而且是随时间而变化的 ,并讨论了该解的连续性估计问题 . 相似文献
954.
文章根据钢和泰生前有关来往信件,就其所谓"一稿两用"事件作一简述,藉此我们可以从钢和泰对事件处理的全过程中学习某些有益的东西。 相似文献
955.
研究了锦屏一级电站在施工期,竣工蓄水后,水库水位消涨期对鸟兽的影响及应采取的对策。 相似文献
956.
957.
The characterization of the algaeAnabaena cylindrica solution with Fe (III) was investigated using fluorescence emission and synchronous-scan spectroscopy. The ranges of concentrations
of algae and Fe (III) in aqueous solutions were 5.0×108 2.5×108 cell/L and 1060 μmol/L. respectively. The effective characterization method used was synchronous-scan fluorescence spectroscopy
(SFS). The wavelength difference (Δλ) of 90 nm, was maintained between excitation wavelength (λen) and emission wavelength
(λen). The peak was observed at about (λex) (λem) 326 nm for synchronous scan fluorescence spectroscopy. The fluorescence
quenching in system of algae Fe(III)-HA was studied using synchronous-scan spectroscopy for the first time, Fe(III) was clearly
the effective quencher. The relationship betweenI I (quenching efficiency) andc (concentration of Fe (III) added) was, a linear correlation for the algae solution with Fe(III). Also, Aldrich humie acid
(HA) was found to be an effective quencher.
Foundation item: Supported by the National Natural Science Foundation of China (20177017) and the Scientific Research Foundation of Wuhan
Environmental Protection Bureau
Biography: LIU Xian li(1965), male. Ph.D. Associate professor, research direction: environmental chemistry. 相似文献
958.
Chao Gu YongRui Du Yan Gao Zhi Yao Xin Gu QiuYue Zhang JingJing Xu WeiMin Deng 《科学通报(英文版)》2012,57(11):1288-1297
There is accumulating evidence that cancer stem cells (CSCs) play an important role in tumor progression. Novel strategies targeting CSCs have been widely researched. In the present study, we explored whether such CSCs existed in human ovarian cancer (OVCA) cell line and whether anti-CD44 antibody had effects on such subpopulation. We isolated and identified spheroid cells from SKOV-3. Then we used A3D8, an anti-CD44 mAb to treat spheroid cells with so-called "stemness". Effects of A3D8 on spheroid cells’ biological behaviors were examined. Our findings showed that there was a small subpopulation that had so-called "stemness" in SKOV-3 cell line. Against spheroid cells, A3D8 can (1) inhibit cell proliferation; (2) change cell cycle distribution and expression of p21, CDK2 and cyclinA; (3) enhance cisplatin (DDP)-induced apoptosis; (4) promote cell differentiation; (5) inhibit clone formation efficiency; (6) reduce invasive efficacy; (7) inhibit tumorigenicity. Thus, to sum up points which we have just showed, spheroid cells isolated from SKOV-3 can be used as an appropriate in vitro model for relevant study of human ovarian CSCs. And our results reasoned that anti-CD44 therapy may become a potential promising strategy for OVCA treatment. 相似文献
959.
Deng Weineng 《科学之友》2012,(14)
笔者结合自己多年的工作经验,阐述了建筑工程测量技术的相关问题及其应用. 相似文献
960.