全文获取类型
收费全文 | 32567篇 |
免费 | 5262篇 |
国内免费 | 4786篇 |
专业分类
化学 | 24661篇 |
晶体学 | 521篇 |
力学 | 1677篇 |
综合类 | 339篇 |
数学 | 3623篇 |
物理学 | 11794篇 |
出版年
2024年 | 115篇 |
2023年 | 616篇 |
2022年 | 1164篇 |
2021年 | 1234篇 |
2020年 | 1380篇 |
2019年 | 1406篇 |
2018年 | 1205篇 |
2017年 | 1250篇 |
2016年 | 1617篇 |
2015年 | 1704篇 |
2014年 | 2000篇 |
2013年 | 2539篇 |
2012年 | 3015篇 |
2011年 | 3056篇 |
2010年 | 2317篇 |
2009年 | 2186篇 |
2008年 | 2317篇 |
2007年 | 2083篇 |
2006年 | 1972篇 |
2005年 | 1595篇 |
2004年 | 1191篇 |
2003年 | 923篇 |
2002年 | 892篇 |
2001年 | 757篇 |
2000年 | 670篇 |
1999年 | 576篇 |
1998年 | 393篇 |
1997年 | 356篇 |
1996年 | 302篇 |
1995年 | 287篇 |
1994年 | 244篇 |
1993年 | 197篇 |
1992年 | 169篇 |
1991年 | 151篇 |
1990年 | 133篇 |
1989年 | 99篇 |
1988年 | 92篇 |
1987年 | 58篇 |
1986年 | 76篇 |
1985年 | 65篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
硅杂环丁烷在有机硅化学中是一类非常重要的小分子环系化合物。由于硅杂环丁烷和环丁烷的环张力相似,因而显示出较高的反应活性。例如能与某些试剂作用,生成开环产物;在光解或热解条件下,产生具有Si=C结构的高活性中间体,可用以合成多种有机硅化合物。 相似文献
102.
103.
A simply fabricated microfluidic device using a green organic light emitting diode (OLED) and thin film interference filter as integrated excitation source is presented and applied to fluorescence detection of proteins. A layer-by-layer compact system consisting of glass/PDMS microchip, pinhole, excitation filter and OLED is designed and equipped with a coaxial optical fiber and for fluorescence detection a 300 microm thick excitation filter is employed for eliminating nearly 80% of the unwanted light emitted by OLEDs which has overlaped with the fluorescence spectrum of the dyes. The distance between OLED illuminant and microchannels is limited to approximately 1 mm for sensitive detection. The achieved fluorescence signal of 300 microM Rhodamine 6G is about 13 times as high as that without the excitation filter and 3.5 times the result of a perpendicular detection structure. This system has been used for fluorescence detection of Rhodamine 6G, Alexa 532 and BSA conjugates in 4% linear polyacrymide (LPA) buffer (in 1 x TBE, pH 8.3) and 1.4 fmol and 35 fmol mass detection limits at 0.7 nl injection volume for Alexa and Rhodamine dye have been obtained, respectively. 相似文献
104.
In this paper, the NO-to-NO
2
conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO
x
removal experiments in N
2
+NO
x
and N
2
+O
2
+NO
x
gaseous mixtures, it is supposed that the reverse reaction NO
2
+ONO+O
2
may not only limit NO
2
production in N
2
+NO
x
mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON
2
+O, induce negligible NO removal provided the O
2
concentration is larger than 3.6%. With adding H
2
O into the reactor, the produced NO
2
per unit removed NO can be significantly reduced due to NO
2
oxidation. NH
3
injection could also significantly decrease the produced NO
2
via NH and NH
2
- related reduction reactions. Almost 100% of NO
2
can be removed in gaseous mixtures of N
2
+O
2
+H
2
O+NO
2
with negligible NO production. 相似文献
105.
106.
107.
Conformations of fold part in isotactic polypropylene lamella with diamond lattice model 总被引:1,自引:0,他引:1
Inthefieldofpolymerphysics,thecrystallinestateofpolymershaslongbeenofinterest.TheexistenceofpolymersinglecrystalwasfirstdiscoveredbyJaccodine[1]in1955.Thethicknessofmostsolutiongrowthcrystalsisfoundtobeoftheorderof~10nm.Thisobservationissomewhatsurprising.S… 相似文献
108.
109.
Yong Ding Baochun Ma Qiang Gao Guixian Li Liang Yan Jishuan Suo 《Journal of molecular catalysis. A, Chemical》2005,230(1-2):121-128
The epoxidation of cyclopentene with hydrogen peroxide catalyzed by 12-heteropolyacids of molybdenum and tungsten (H3PMo12−nWnO40, n = 1–11), 12-tungstophosphoric acid and 12-molybdophosphoric acid combined with cetylpyridinium bromide as a phase transfer reagent was carried out in acetonitrile. Among 13 heteropolyacids investigated, catalyst of H3PMo6W6O40 showed the highest activity, giving a conversion of 60% and a selectivity of 95% in the epoxidation of cyclopentene. The fresh catalysts and the catalysts under reaction condition were characterized by UV–vis, FT-IR and 31P NMR spectroscopy, which has revealed that all of the molybdotungstophosphoric acids were degraded in the presence of hydrogen peroxide to form a considerable amount of phosphorus-containing species. The active species resulted from H3PMo6W6O40 are new kinds of phosphorus-containing species, which is different from {PO4[WO(O2)2]4}3−. 相似文献
110.