全文获取类型
收费全文 | 113762篇 |
免费 | 9275篇 |
国内免费 | 10671篇 |
专业分类
化学 | 51693篇 |
晶体学 | 724篇 |
力学 | 9404篇 |
综合类 | 1680篇 |
数学 | 33377篇 |
物理学 | 36830篇 |
出版年
2023年 | 1034篇 |
2022年 | 1580篇 |
2021年 | 2395篇 |
2020年 | 2684篇 |
2019年 | 2750篇 |
2018年 | 2475篇 |
2017年 | 2800篇 |
2016年 | 3333篇 |
2015年 | 2892篇 |
2014年 | 4119篇 |
2013年 | 7705篇 |
2012年 | 4838篇 |
2011年 | 5323篇 |
2010年 | 4508篇 |
2009年 | 6413篇 |
2008年 | 7033篇 |
2007年 | 7535篇 |
2006年 | 6708篇 |
2005年 | 5711篇 |
2004年 | 5129篇 |
2003年 | 5261篇 |
2002年 | 5295篇 |
2001年 | 4124篇 |
2000年 | 4012篇 |
1999年 | 3559篇 |
1998年 | 3336篇 |
1997年 | 2511篇 |
1996年 | 2142篇 |
1995年 | 2015篇 |
1994年 | 1915篇 |
1993年 | 1569篇 |
1992年 | 1565篇 |
1991年 | 1165篇 |
1990年 | 1005篇 |
1989年 | 827篇 |
1988年 | 753篇 |
1987年 | 630篇 |
1986年 | 556篇 |
1985年 | 587篇 |
1984年 | 592篇 |
1983年 | 303篇 |
1982年 | 458篇 |
1981年 | 509篇 |
1980年 | 369篇 |
1979年 | 365篇 |
1978年 | 280篇 |
1977年 | 258篇 |
1976年 | 177篇 |
1974年 | 130篇 |
1973年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
Valentin A. Semenov Dmitry O. Samultsev Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2020,58(6):532-539
The density functional theory calculation of 1H and 13C NMR chemical shifts in a series of ten 10 classically known Strychnos alkaloids with a strychnine skeleton was performed at the PBE0/pcSseg-2//pcseg-2 level. It was found that calculated 1H and 13C NMR chemical shifts provided a markedly good correlation with experiment characterized by a mean absolute error of 0.08 ppm in the range of 7 ppm for protons and 1.67 ppm in the range of 150 ppm for carbons, so that a mean absolute percentage error was as small as ~1% in both cases. 相似文献
52.
Dr. Wan‐Ling Liu Ni‐Shin Yang Ya‐Ting Chen Stephen Lirio Cheng‐You Wu Prof. Chia‐Her Lin Prof. Hsi‐Ya Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):115-119
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors. 相似文献
53.
Two highly ordered isonicotinamide (INA)‐functionalized mesoporous MCM‐41 materials supporting indium and thallium (MCM‐41‐INA‐In and MCM‐41‐INA‐Tl) have been developed using a covalent grafting method. A surface functionalization method has been applied to prepare Cl‐modified mesoporous MCM‐41 material. Condensation of this Cl‐functionalized MCM‐41 with INA leads to the formation of MCM‐41‐INA. The reaction of MCM‐41‐INA with In(NO3)3 or Tl(NO3)3 leads to the formation of MCM‐41‐INA‐In and MCM‐41‐INA‐Tl catalysts. The resulting materials were characterized using various techniques. These MCM‐41‐INA‐In and MCM‐41‐INA‐Tl catalysts show excellent catalytic performance in the selective oxidation of sulfides and thiols to their corresponding sulfoxides and disulfides. Finally, it is found that the anchored indium and thallium do not leach out from the surface of the mesoporous catalysts during reaction and the catalysts can be reused for seven repeat reaction runs without considerable loss of catalytic performance. 相似文献
54.
55.
飞行器液压导管受接头和卡箍等约束,在使用的振动环境中,会因弯曲应力而导致破裂,影响到飞行安全.本文对飞行器液压系统通用的不锈钢导管的裂纹萌生寿命进行了试验研究.首先在对8 mm、12 mm 无缺陷导管和含U 型缺口8 mm 导管的疲劳试验和有限元分析的基础上,得到了导管的最大拉应变-裂纹萌生寿命数据.然后采用基于强度极限和弹性模量估算法的Manson-Coffin 公式来预测导管裂纹萌生寿命.最后引入加载类型修正系数、表面质量修正系数、试样尺寸修正系数、应力集中敏感系数和有效应力集中系数,使修正后的公式对三种类型的导管均有较好的裂纹萌生寿命预测精度. 相似文献
56.
《中国物理 B》2021,30(7):76103-076103
It has been a long-standing puzzling problem that some glasses exhibit higher glass transition temperatures(denoting high stability) but lower activation energy for relaxations(denoting low stability). In this paper, the relaxation kinetics of the nanoconfined D-mannitol(DM) glass was studied systematically using a high-precision and high-rate nanocalorimeter.The nanoconfined DM exhibits enhanced thermal stability compared to the free DM. For example, the critical cooling rate for glass formation decreases from 200 K/s to below 1 K/s; the Tg increases by about 20 K–50 K. The relaxation kinetics is analyzed based on the absolute reaction rate theory. It is found that, even though the activation energy E~*decreases,the activation entropy S~*decreases much more for the nanoconfined glass that yields a large activation free energy G~*and higher thermal stability. These results suggest that the activation entropy may provide new insights in understanding the abnormal kinetics of nanoconfined glassy systems. 相似文献
57.
In this paper, the deformation of the Heisenberg algebra, consistent with both the generalized uncertainty principle and doubly special relativity, has been analyzed. It has been observed that, though this algebra can give rise to fractional derivative terms in the corresponding quantum mechanical Hamiltonian, a formal meaning can be given to them by using the theory of harmonic extensions of function. Depending on this argument, the expression of the propagator of the path integral corresponding to the deformed Heisenberg algebra, has been obtained. In particular, the consistent expression of the one dimensional free particle propagator has been evaluated explicitly. With this propagator in hand, it has been shown that, even in free particle case, normal generalized uncertainty principle and doubly special relativity show very much different result. 相似文献
58.
Inflation of balloons provides a straightforward way of achieving large biaxial deformations. Previous studies have shown that when a balloon bursts, crack propagation occurs at very high speed – much higher than would be expected from the low strain modulus and elastic wave velocity of the rubber. The present paper is concerned with studies of the deformation and fracture of cylindrical balloons. On inflation, the deformations of such a balloon pass through an unstable region but subsequently increase monotonically with pressure. In this relatively high pressure region, the ratio of the longitudinal and circumferential extension ratios is broadly in accord with expectations from high-strain elasticity theory when the ratio of the corresponding stresses is taken into account. On bursting, crack speeds up to around 300 m/s in this region. It is shown that these speeds are in accord with large increase in incremental moduli for the highly-strained rubber. Marked changes in crack tip profile observed at very high crack speeds are consistent with control of the rate of growth by inertia rather than by the viscoelastic properties of the rubber (as is believed to be the case at lower speeds). Consistent with this, various elastomers having different glass transition temperatures show similar crack growth behaviour in the very high speed region. 相似文献
59.
Yuta Yamamoto Shogo Nakano Fumio Seki Yasuteru Shigeta Sohei Ito Hiroaki Tokiwa Makoto Takeda 《Molecules (Basel, Switzerland)》2021,26(5)
Infection of hosts by morbilliviruses is facilitated by the interaction between viral hemagglutinin (H-protein) and the signaling lymphocytic activation molecule (SLAM). Recently, the functional importance of the n-terminal region of human SLAM as a measles virus receptor was demonstrated. However, the functional roles of this region in the infection process by other morbilliviruses and host range determination remain unknown, partly because this region is highly flexible, which has hampered accurate structure determination of this region by X-ray crystallography. In this study, we analyzed the interaction between the H-protein from canine distemper virus (CDV-H) and SLAMs by a computational chemistry approach. Molecular dynamics simulations and fragment molecular orbital analysis demonstrated that the unique His28 in the N-terminal region of SLAM from Macaca is a key determinant that enables the formation of a stable interaction with CDV-H, providing a basis for CDV infection in Macaca. The computational chemistry approach presented should enable the determination of molecular interactions involving regions of proteins that are difficult to predict from crystal structures because of their high flexibility. 相似文献
60.
Accuracy arguments are the en vogue route in epistemic justifications of probabilism and further norms governing rational belief. These arguments often depend on the fact that the employed inaccuracy measure is strictly proper. I argue controversially that it is ill-advised to assume that the employed inaccuracy measures are strictly proper and that strictly proper statistical scoring rules are a more natural class of measures of inaccuracy. Building on work in belief elicitation I show how strictly proper statistical scoring rules can be used to give an epistemic justification of probabilism.An agent's evidence does not play any role in these justifications of probabilism. Principles demanding the maximisation of a generalised entropy depend on the agent's evidence. In the second part of the paper I show how to simultaneously justify probabilism and such a principle. I also investigate scoring rules which have traditionally been linked with entropies. 相似文献