全文获取类型
收费全文 | 15418篇 |
免费 | 2674篇 |
国内免费 | 1879篇 |
专业分类
化学 | 11609篇 |
晶体学 | 184篇 |
力学 | 805篇 |
综合类 | 97篇 |
数学 | 1403篇 |
物理学 | 5873篇 |
出版年
2024年 | 53篇 |
2023年 | 279篇 |
2022年 | 520篇 |
2021年 | 567篇 |
2020年 | 654篇 |
2019年 | 647篇 |
2018年 | 574篇 |
2017年 | 480篇 |
2016年 | 769篇 |
2015年 | 722篇 |
2014年 | 869篇 |
2013年 | 1210篇 |
2012年 | 1385篇 |
2011年 | 1351篇 |
2010年 | 931篇 |
2009年 | 937篇 |
2008年 | 1046篇 |
2007年 | 944篇 |
2006年 | 850篇 |
2005年 | 760篇 |
2004年 | 618篇 |
2003年 | 530篇 |
2002年 | 575篇 |
2001年 | 399篇 |
2000年 | 294篇 |
1999年 | 305篇 |
1998年 | 254篇 |
1997年 | 226篇 |
1996年 | 203篇 |
1995年 | 165篇 |
1994年 | 141篇 |
1993年 | 113篇 |
1992年 | 110篇 |
1991年 | 105篇 |
1990年 | 70篇 |
1989年 | 58篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
以非离子型嵌段共聚物为模板剂、正硅酸乙酯为硅源,制备了一种比表面积为712m2·g-1、孔径6.93nm、孔容1.06cm3·g-1、粒径10μm的介孔SBA-15微球,采用扫描电镜考察了各种合成条件对介孔氧化硅微球形貌的影响,对SBA-15介孔微球的合成条件优化和形成机理进行了研究和探讨。结果表明:介孔氧化硅微球的生长可以看作一个由微小溶胶粒子发生渐进聚沉、成长为较大溶胶粒子的过程;共表面活性剂和无机盐的引入对介孔微球的形成具有辅助作用;合成体系的酸度和晶化阶段之前的陈化条件是介孔微球形成的关键所在。在共聚物的盐酸溶液(1mol·L-1)中,不添加共表面活性剂和无机盐,仅控制陈化条件于35℃静置24h,100℃水热处理24h,可得到大粒径的介孔SBA-15微球。 相似文献
992.
Lingyan Gao Zibin Zhang Shengyi Dong Min Xue 《Macromolecular rapid communications》2014,35(10):987-991
A linear supramolecular polymer based on the self‐assembly of an easily available copillar[5]arene monomer is efficiently prepared, which is evidenced by the NMR spectroscopy, viscosity measurement, and DOSY experiment. The single‐crystal X‐ray analysis reveals that the polymerization of the AB‐type monomer is driven by the quadruple CH•••π interactions and one CH•••O interaction.
993.
The article herein briefly introduces the story of the birth of click chemistry and its evolution after that. A new angle to interpret click reactions was proposed using the “reactivity‐availability‐functionality” trilogy. CuAAC (Copper‐catalyzed azide‐alkyne cycloaddition), the most popular click reaction by far, was revisited along with the thiol‐ene, metal‐free AAC, SuFEx (Sulfur(VI) fluoride exchange) and the lately discovered diazotransfer process. By encountering more and more near‐perfect reactions, click chemistry is evolving and expanding on the fringe of the chemistry and different scientific disciplines, destination unknown. 相似文献
994.
995.
996.
Purpose
Electron paramagnetic resonance (EPR) oximetry using variable length multi-probe implantable resonator (IR), was used to investigate the temporal changes in the ischemic and contralateral brain pO2 during stroke in rats.Material and methods
The EPR signal to noise ratio (S/N) of the IR with four sensor loops at a depth of up to 11 mm were compared with direct implantation of lithium phthalocyanine (LiPc, oximetry probe) deposits in vitro. These IRs were used to follow the temporal changes in pO2 at two sites in each hemisphere during ischemia induced by left middle cerebral artery occlusion (MCAO) in rats breathing 30% O2 or 100% O2.Results
The S/N ratios of the IRs were significantly greater than the LiPc deposits. A similar pO2 at two sites in each hemisphere prior to the onset of ischemia was observed in rats breathing 30% O2. However, a significant decline in the pO2 of the left cortex and striatum occurred during ischemia, but no change in the pO2 of the contralateral brain was observed. A significant increase in the pO2 of only the contralateral non-ischemic brain was observed in the rats breathing 100% O2. No significant difference in the infarct volume was evident between the animals breathing 30% O2 or 100% O2 during ischemia.Conclusions
EPR oximetry with IRs can repeatedly assess temporal changes in the brain pO2 at four sites simultaneously during stroke. This oximetry approach can be used to test and develop interventions to rescue ischemic tissue by modulating cerebral pO2 during stroke. 相似文献997.
Valence state parameters of all transition metal atoms in metalloproteins—development of ABEEMσπ fluctuating charge force field 下载免费PDF全文
Zhong‐Zhi Yang Jian‐Jiang Wang Dong‐Xia Zhao 《Journal of computational chemistry》2014,35(23):1690-1706
To promote accuracy of the atom‐bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc‐Zn, Y‐Cd, and Lu‐Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO‐3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. © 2014 Wiley Periodicals, Inc. 相似文献
998.
Using laser flash photolysis/transient absorption technique for the study of two photon photodissociation of carbon disulfide in acetonitrile solution at 266 nm, the transient UV-Vis absorption spectrum of Rydberg state CS2 (6sσg) within 240-370 nm and subsequent dissociation product CS (α^3П) with the maximum absorption at 260 nm were directly observed. The lifetime of CS (α^3П) in the nitrogen and oxygen saturated solution is also studied in our experiment. 相似文献
999.
1000.