全文获取类型
收费全文 | 7240篇 |
免费 | 1522篇 |
国内免费 | 1526篇 |
专业分类
化学 | 5795篇 |
晶体学 | 225篇 |
力学 | 446篇 |
综合类 | 94篇 |
数学 | 872篇 |
物理学 | 2856篇 |
出版年
2024年 | 25篇 |
2023年 | 210篇 |
2022年 | 358篇 |
2021年 | 341篇 |
2020年 | 424篇 |
2019年 | 393篇 |
2018年 | 310篇 |
2017年 | 303篇 |
2016年 | 358篇 |
2015年 | 411篇 |
2014年 | 435篇 |
2013年 | 582篇 |
2012年 | 686篇 |
2011年 | 640篇 |
2010年 | 449篇 |
2009年 | 470篇 |
2008年 | 528篇 |
2007年 | 493篇 |
2006年 | 428篇 |
2005年 | 407篇 |
2004年 | 272篇 |
2003年 | 233篇 |
2002年 | 233篇 |
2001年 | 221篇 |
2000年 | 179篇 |
1999年 | 145篇 |
1998年 | 100篇 |
1997年 | 84篇 |
1996年 | 103篇 |
1995年 | 76篇 |
1994年 | 66篇 |
1993年 | 54篇 |
1992年 | 49篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
在水溶液条件下以六缺位的[H2P2W12O48)]12-和Eu髥为反应前躯体得到了1个新的多金属氧酸盐化合物[Eu3(H2O)17(α2-HP2W17O61)].5H2O(1),对其进行了元素分析、红外光谱、热重、荧光等表征,并用X-射线单晶衍射测定了它的晶体结构。化合物1含有双支撑的多阴离子簇[{Eu(H2O)7}2{Eu(H2O)3(α2-P2W17)}2]8-,并进一步通过Eu髥连接形成了延c轴方向的一维链。室温条件下的荧光光谱研究表明:化合物1显示了强的红光发射。 相似文献
992.
993.
994.
995.
H. Y. Zhang H. Li G. Liu T. T. Liu F. Yue J. D. Wang 《Russian Journal of Coordination Chemistry》2011,37(11):839-844
One-pot reaction containing Zn(NO3)2, Cd(NO3)2, NH4SCN, and 4-amino-1,2,4-triazole (Atrz) proceeded by refluxing for different periods and gave different products. When the
mixture was refluxed for 1 h, the product was a 1D chain polymer [Cd(Atrz)2(SCN)2]
n
. However, when the refluxing time was increased to 3 h, a novel 3D 3d-3d heterometallic framework complex [Cd2.84Zn2.16(Atrz)6(SCN)10] · 4H2O (I) with 66 topology was obtained. The fluorescent property of I in the solid state was discussed. 相似文献
996.
Dong M Si YQ Sun SY Pu XP Yang ZJ Zhang LR Zhang LH Leung FP Lam CM Kwong AK Yue J Zhou Y Kriksunov IA Hao Q Lee HC 《Organic & biomolecular chemistry》2011,9(9):3246-3257
Human CD38 is a novel multi-functional protein that acts not only as an antigen for B-lymphocyte activation, but also as an enzyme catalyzing the synthesis of a Ca(2+) messenger molecule, cyclic ADP-ribose, from NAD(+). It is well established that this novel Ca(2+) signaling enzyme is responsible for regulating a wide range of physiological functions. Based on the crystal structure of the CD38/NAD(+) complex, we synthesized a series of simplified N-substituted nicotinamide derivatives (Compound 1-14). A number of these compounds exhibited moderate inhibition of the NAD(+) utilizing activity of CD38, with Compound 4 showing the highest potency. The crystal structure of CD38/Compound 4 complex and computer simulation of Compound 7 docking to CD38 show a significant role of the nicotinamide moiety and the distal aromatic group of the compounds for substrate recognition by the active site of CD38. Biologically, we showed that both Compounds 4 and 7 effectively relaxed the agonist-induced contraction of muscle preparations from rats and guinea pigs. This study is a rational design of inhibitors for CD38 that exhibit important physiological effects, and can serve as a model for future drug development. 相似文献
997.
Chien CC Zhang G Hwu Y Liu P Yue W Sun J Li Y Xu H Xue H Xu LX Wang CH Chen N Lu CH Lee TK Yang YC Lu YT Ching YT Shih TF Yang PC Je JH Margaritondo G 《Analytical and bioanalytical chemistry》2011,401(3):827-835
Refractive-index (phase-contrast) radiology was able to detect lung tumors less than 1 mm in live mice. Significant micromorphology differences were observed in the microradiographs between normal, inflamed, and lung cancer tissues. This was made possible by the high phase contrast and by the fast image taking that reduces the motion blur. The detection of cancer and inflammation areas by phase contrast microradiology and microtomography was validated by bioluminescence and histopathological analysis. The smallest tumor detected is less than 1 mm(3) with accuracy better than 1 × 10(-3) mm(3). This level of performance is currently suitable for animal studies, while further developments are required for clinical application. 相似文献
998.
Long LH Wu PF Guan XL Zhang JQ Jin Y Zhang Z Wang Y Li YY Chen JG Wang F 《Analytical and bioanalytical chemistry》2011,399(6):2267-2274
Protein-bound methionine (Met) oxidation has been associated with normal aging and a variety of age-related diseases, including
Alzheimer’s disease and Parkinson’s disease. Monitoring the changes of protein-bound methionine content in the brain in response
to normal aging and oxidative stress is of great interest and could be used as an indicator of oxidative stress of rats in
pathological conditions. We have developed a rapid analytical method for the determination of oxidized products of protein-bound
methionine in rat brain. The assay involved rapid acid proteolysis with microwave irradiation and solid-phase extraction of
the free amino acids followed by LC-ESI-ITMS analysis. Detection was achieved in positive ionization with an ion trap mass
spectrometer operating in multiple-reaction monitoring mode. The calibration curves of the analytes were linear (r
2 > 0.99) in the range between 0.098 and 1.560 μg/mL. Intra- and inter-day relative standard deviation percentages were <9%
and <8%, respectively. The assay performance was sufficient to support a rapid analytical tool for monitoring brain protein-bound
methionine oxidation levels. The content of protein-bound Met and methionine sulfoxide (MetO) in the hippocampus of adult
and old rats with or without H2O2 treatment was determined by employing the new method. The content of protein-bound MetO was significantly increased in old
rats after exposure to H2O2. This result indicates increased sensitivity to Met oxidation in the hippocampus of old rats. 相似文献
999.
In this paper,we study the controllability of the nonlinear evolution systems.We establish the controllability results by using the monotone operator theory.No compactness assumptions are imposed in the main results.We present an example to illustrate our results. 相似文献
1000.
For each surface Σ, we define Δ(Σ) = max{Δ(G)|Gis a class two graph of maximum degree Δ(G) that can be embedded in Σ}. Hence, Vizing's Planar Graph Conjecture can be restated as Δ(Σ) = 5 if Σ is a plane. In this paper, we show that Δ(Σ) = 9 if Σ is a surface of characteristic χ(Σ) = ?5. © 2010 Wiley Periodicals, Inc. J Graph Theory 68:148‐168, 2011 相似文献