全文获取类型
收费全文 | 28869篇 |
免费 | 1558篇 |
国内免费 | 5193篇 |
专业分类
化学 | 30515篇 |
晶体学 | 331篇 |
力学 | 495篇 |
综合类 | 301篇 |
数学 | 1563篇 |
物理学 | 2415篇 |
出版年
2024年 | 37篇 |
2023年 | 282篇 |
2022年 | 555篇 |
2021年 | 837篇 |
2020年 | 836篇 |
2019年 | 845篇 |
2018年 | 735篇 |
2017年 | 946篇 |
2016年 | 1091篇 |
2015年 | 1025篇 |
2014年 | 1247篇 |
2013年 | 2573篇 |
2012年 | 2034篇 |
2011年 | 1651篇 |
2010年 | 1407篇 |
2009年 | 1679篇 |
2008年 | 1731篇 |
2007年 | 1934篇 |
2006年 | 1788篇 |
2005年 | 1691篇 |
2004年 | 1559篇 |
2003年 | 1271篇 |
2002年 | 1102篇 |
2001年 | 804篇 |
2000年 | 799篇 |
1999年 | 681篇 |
1998年 | 547篇 |
1997年 | 581篇 |
1996年 | 495篇 |
1995年 | 453篇 |
1994年 | 394篇 |
1993年 | 332篇 |
1992年 | 324篇 |
1991年 | 242篇 |
1990年 | 193篇 |
1989年 | 189篇 |
1988年 | 145篇 |
1987年 | 104篇 |
1986年 | 81篇 |
1985年 | 63篇 |
1984年 | 68篇 |
1983年 | 32篇 |
1982年 | 53篇 |
1981年 | 34篇 |
1980年 | 28篇 |
1979年 | 31篇 |
1978年 | 31篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity. 相似文献
52.
Kinetic parameters of amino acid cations in an MK-40 ion-exchange membrane are calculated from the conductivity data. A theoretical quantum-chemical analysis of experimental activation energies for conduction suggests a mechanism of elementary act of transport of amino acid cations in the membrane. 相似文献
53.
54.
The stereoselective synthesis of E-rhinocerotinoic acid has been achieved in five steps from (−)-sclareol in an overall yield of 32%. This constitutes a significant improvement on the previous synthesis of this anti-inflammatory compound. 相似文献
55.
The potential of an N-Troc-protected sialic acid donor, equipped with phenylsulfenyl functionality as a leaving group, has been explored. As a result, the entitled donor was proven to be highly reactive and to have broad applicability toward the synthesis of variant sialo-glycans, which have N-glycolyl, de-N-acetyl, 1,5-lactam and 8-O-sulfo sialic acid analogs. 相似文献
56.
本文用变换群理论对运动水平平板混合对流边界层流动的动量、能量和浓度扩散方程进行了分析,得到了与X4/(7-5n)成正比的壁面温度分布和浓度分布,同时壁面运动速度正比于X(3-n)/(7-5n)时存在相似性解.导出了相似性解方程,用四阶Runge-Kutta方法进行了计算,给出了Pr=0.72 和Sc,K1,K2,K3参数下的速度、温度和浓度分布,得出了各参数对流场、温度场的影响。 相似文献
57.
Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer. 相似文献
58.
脂肪乳剂Intralipid代谢产物的高效液相色谱测定 总被引:2,自引:0,他引:2
本文介绍了利用HPLC色谱柱前衍生化技术简便,正确和灵敏地测定血清中游离脂肪酸的方法。在最佳条件下,一些脂肪酸的最低检知量为0.04μg。方法已用于脂肪乳剂Intralipid在诱发急性坏死性胰腺炎动物体内代谢产物测定。 相似文献
59.
Tatsien Li 《Mathematical Methods in the Applied Sciences》2006,29(13):1543-1553
By means of a direct and constructive method based on the theory of semi‐global C2 solution, the local exact boundary observability and an implicit duality between the exact boundary controllability and the exact boundary observability are shown for 1‐D quasilinear wave equations with various boundary conditions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
60.
《Journal of Chemical Sciences》2005,117(5):525-531
The silicon atom may increase its coordination number to values greater than four, to form pentacoordinated compounds. It
has been observed experimentally that, in general, pentacoordinated compounds show greater reactivity than tetracoordinated
compounds. In this work, density functional theory is used to calculate the global softness and the condensed softness of
the silicon atom for SiH
n
F4−n
and SiH
n
F
5−n
1−
. The values obtained show that the global and condensed softness are greater in the pentacoordinated compounds than in the
tetracoordinated compounds, a result that explains the enhanced reactivity. If the results are analysed through a local version
of the hard and soft acids and bases principle, it is possible to suggest that in nucleophilic substitution reactions, soft
nucleophiles preferably react with SiH
n
F
5−n
1−
, and hard nucleophiles with SiH
n
F4−n
. 相似文献