全文获取类型
收费全文 | 90557篇 |
免费 | 7737篇 |
国内免费 | 7252篇 |
专业分类
化学 | 13033篇 |
晶体学 | 983篇 |
力学 | 10321篇 |
综合类 | 770篇 |
数学 | 20408篇 |
物理学 | 15745篇 |
综合类 | 44286篇 |
出版年
2024年 | 225篇 |
2023年 | 823篇 |
2022年 | 1406篇 |
2021年 | 1614篇 |
2020年 | 1943篇 |
2019年 | 1780篇 |
2018年 | 1781篇 |
2017年 | 2392篇 |
2016年 | 2696篇 |
2015年 | 2604篇 |
2014年 | 4320篇 |
2013年 | 5188篇 |
2012年 | 5183篇 |
2011年 | 5766篇 |
2010年 | 4699篇 |
2009年 | 5343篇 |
2008年 | 5101篇 |
2007年 | 6047篇 |
2006年 | 5271篇 |
2005年 | 4978篇 |
2004年 | 4410篇 |
2003年 | 4069篇 |
2002年 | 3603篇 |
2001年 | 3036篇 |
2000年 | 2756篇 |
1999年 | 2502篇 |
1998年 | 2206篇 |
1997年 | 1981篇 |
1996年 | 1762篇 |
1995年 | 1522篇 |
1994年 | 1353篇 |
1993年 | 1221篇 |
1992年 | 1144篇 |
1991年 | 971篇 |
1990年 | 877篇 |
1989年 | 765篇 |
1988年 | 659篇 |
1987年 | 462篇 |
1986年 | 262篇 |
1985年 | 177篇 |
1984年 | 143篇 |
1983年 | 64篇 |
1982年 | 85篇 |
1981年 | 67篇 |
1980年 | 40篇 |
1979年 | 60篇 |
1978年 | 43篇 |
1977年 | 49篇 |
1976年 | 20篇 |
1955年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
QI Yuanhua GUAN Daren & LIU Chengbu . Institute of Theoretical Chemistry Shandong University Jinan China . School of Physics Microelectronics Shandong University Jinan China 《中国科学B辑(英文版)》2006,49(6):492-498
The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied. 相似文献
962.
This work deals with uncertainty analysis of the thermal conductivity measurement using the transient hot wire method. The characterization is made from a sample of low-density, polyethylene BRALEN SA 200-22. The utilized experimental data are obtained from the test measurements performed on the air at room temperature. The sources of measurement errors are analyzed and the uncertainty of the measured value of the thermal conductivity is evaluated. The analysis shows that in the present case the uncertainty of the thermal conductivity measurement is about ±3.3% for 68% confidence level.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
963.
Based on the group theory analysis and quantum chemical calculations within the framework of SW X α method (in relativistic approximation for core electrons and non-relativistic for valence ones), the existence possibility of square planar complexes [M4C] and [M4C]2? (M = Al, Ga, In, Tl, Sc, and Y) in gas phase has been shown. The extraction of Kt2[M4C] square planar complexes of carbon in the crystal state is possible too. A high stability of these complexes, in comparison with usual tetrahedral, is achieved due to the formation of five-and four-center bonds (bonds M-M and M-C). 相似文献
964.
Molecular Replacement Studies of Cucurmosin from Cucurbita Moschata:Structure Homology with Trichosanthin 总被引:2,自引:0,他引:2
1 INTRODUCTION Many plants contain proteins that are capable of inactivating ribosomes and therefore are called ribosome-inactivating proteins or RIPs[1]. RIPs are RNA N-glycosidases that inactivate ribosomes through a site-specific deadenylation of the large ribosomal RNA[2, 3]. RIPs are also capable of inactivating many nonribosomal nucleic acid substrates and can be considered as polynucleotide: adenosine glycosidases[4~6]. There are two types of RIPs: type I, single chain pr… 相似文献
965.
本文研究了在表面活性剂存在性,铝与溴代二甲氨基苯基荧光酮的显色反应。在弱酸性介质中,Al^3+BDMAF-CTMAB三元配合物在水浴加热至70℃-80℃时形成,其最大吸收波长为577nm,Al^3+:BDMAF=1:2,表观摩尔吸光系数为1.34×10^5L.mol^-1.cm^-1,表观稳定常数为7.4×10^5。在PH9.5-10.5的氨性缓冲介质中,Al^3+-F^--BDMAF-非离子表面 相似文献
966.
967.
在稀H2SO4介质中,钼(Ⅵ)对硫酸联氨还原乙基橙的反应有强烈的催化作用。建立了催化动力学极谱法测定痕量钼的新体系,方法线性范围为20-300ng/mL,检出限为3.54ng/mL。方法应用于尿中中钼的测定,结果满意。 相似文献
968.
A. G. Schlijper 《Journal of statistical physics》1985,40(1-2):1-27
A new derivation is presented of some variational approximations for classical lattice systems that belong to the class of cluster-variation methods, among them the well-known Bethe-Peierls and Kramers-Wannier approximations. The limiting behavior of a hierarchical sequence of cluster-variation approximations, the so-calledC hierarchy, is discussed. It is shown that this hierarchy provides a monotonically decreasing sequence of upper boundsf
n on the free energy per lattice sitef and thatf
n f asn . Our results are based on extension theorems for states given on subsets of the lattice, which might be of some independent interest, and on an application of transfer matrix concepts to the variational characterization of translation-invariant equilibrium states. 相似文献
969.
Differential
scanning calorimetry (DSC) is a thermal analytical tool for preformulation
studies. Extrapolated melting temperature (TP)
and heat of fusion (ΔHf)
can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals
acetaminophen and nicotinamide are used in this study. Using a factorial design
for the experimental model and matrix analysis the results, the effect of
sample mass, heating rate and the nitrogen flow rate were evaluated on the
ΔHf values
and TP values. Two
levels for each of the procedural variables were used as a balanced experimental
design with two sample sizes, two heating rates and two nitrogen flow rates.
It was found that the change in the heating rate caused significant changes
in the ΔHf
values but not the Tp
values for acetaminophen. However, no significant effect was found for the Tp value but ΔHf value was affected to a
certain extent for nicotinamide. 相似文献
970.
稳定回归法用于复方氯丙嗪片的测定 总被引:1,自引:1,他引:1
本文应用稳定回归法用于紫外重叠光谱的分析。以复方氯丙嗪为例,不经分离,测定了盐酸氯丙嗪和盐酸异丙嗪的含量。与最小二乘回归法比较,提高了测定结果的准确度和精密度。结果满意。 相似文献