全文获取类型
收费全文 | 8185篇 |
免费 | 1238篇 |
国内免费 | 746篇 |
专业分类
化学 | 5673篇 |
晶体学 | 132篇 |
力学 | 484篇 |
综合类 | 72篇 |
数学 | 785篇 |
物理学 | 3023篇 |
出版年
2024年 | 33篇 |
2023年 | 179篇 |
2022年 | 309篇 |
2021年 | 305篇 |
2020年 | 373篇 |
2019年 | 350篇 |
2018年 | 300篇 |
2017年 | 253篇 |
2016年 | 411篇 |
2015年 | 401篇 |
2014年 | 528篇 |
2013年 | 605篇 |
2012年 | 672篇 |
2011年 | 693篇 |
2010年 | 457篇 |
2009年 | 374篇 |
2008年 | 498篇 |
2007年 | 425篇 |
2006年 | 379篇 |
2005年 | 321篇 |
2004年 | 214篇 |
2003年 | 218篇 |
2002年 | 166篇 |
2001年 | 124篇 |
2000年 | 154篇 |
1999年 | 151篇 |
1998年 | 129篇 |
1997年 | 131篇 |
1996年 | 151篇 |
1995年 | 110篇 |
1994年 | 108篇 |
1993年 | 89篇 |
1992年 | 78篇 |
1991年 | 69篇 |
1990年 | 72篇 |
1989年 | 47篇 |
1988年 | 49篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
Additive hazards model with random effects is proposed for modelling the correlated failure time data when focus is on comparing the failure times within clusters and on estimating the correlation between failure times from the same cluster, as well as the marginal regression parameters. Our model features that, when marginalized over the random effect variable, it still enjoys the structure of the additive hazards model. We develop the estimating equations for inferring the regression parameters. The proposed estimators are shown to be consistent and asymptotically normal under appropriate regularity conditions. Furthermore, the estimator of the baseline hazards function is proposed and its asymptotic properties are also established. We propose a class of diagnostic methods to assess the overall fitting adequacy of the additive hazards model with random effects. We conduct simulation studies to evaluate the finite sample behaviors of the proposed estimators in various scenarios. Analysis of the Diabetic Retinopathy Study is provided as an illustration for the proposed method. 相似文献
172.
173.
Chao He Xiaohui Zhang Ruofeng Huang Jing Pan Jiaqiang Li Xuege Ling Yan Xiong Xiangming Zhu 《Tetrahedron letters》2014
Under open-flask conditions, an efficient method to assemble a series of diversely functionalized diarylketones in the presence of commercially available NBS has been developed. Yields of up to 99% have been achieved employing diarylmethanes as starting material. Based on 18O-labeled experiment, the addition of stoichiometric water eventually leads to excellent yields in all carbonylation cases. 相似文献
174.
以爆炸条件下溶菌酶的反应产物为研究对象,运用基质辅助激光解吸-飞行时间质谱的方法研究其反应产物与不同炸药的反应特征性.结果显示,雷管的使用不会对溶菌酶有影响,而在有爆炸物爆炸的条件下,除了正常溶菌酶酶解多肽信号外,一些[MH+17]+,[MH+18]+,[MH+28]+,[MH+32]+和[MH+44]+的加合峰信号也能被检测到.这可能是在炸药爆炸过程中产生的一些活性小分子(如NH3,H2O,CO/N2,O2,CO2)与溶菌酶发生反应得到的反应产物.不同炸药生成的活性小分子能够分别与溶菌酶的某些反应位点反应生成特征性的反应产物,有利于这些炸药的分析与检测. 相似文献
175.
Protonation and alkali-metal cation adduction are the most important ionization processes in soft-ionization mass spectrometry.Studies on the fragmentation mechanism of protonated and alkali-metal-cationized compounds in tandem mass spectrometry are essential and helpful for structural analysis.In some cases,it was often observed that a compound attached by different alkali-metal cations(or proton)exhibits similar fragmentation patterns but the relative abundances of product ions are different.This difference was considered to derive from the different electrostatic interactions of alkali-metal cations(or the bonded effect of proton)with the analyte.The alkali-metal cation with a smaller ionic radius shows stronger electrostatic interaction with the molecule because of its higher charge density.In addition,the bonded effect of the proton is stronger than the electrostatic interaction of the alkali-metal cation.In the present study,which used McLafferty-type rearrangements of even-electron ions([M+Cat]+,Cat=H,Li,Na,K)as model reactions,the effect of cation size in mass spectrometric fragmentation reactions is highlighted.These considerations were also successfully applied to interpret the similar but distinct fragmentation behavior of proton and alkali-metal cation adducts of a synthetic compound(2-(acetamido(phenyl)methyl)-3-oxobutanoate)and a drug(entecavir). 相似文献
176.
Effects of substrate and transfer on CVD-grown graphene over sapphire-induced Cu films 总被引:1,自引:0,他引:1
HU BaoShan WEI ZiDong AGO Hiroki JIN Yan XIA MeiRong LUO ZhengTang PAN QingJiang LIU YunLing 《中国科学:化学(英文版)》2014,57(6):895-901
We differentiated the effects of Cu films deposited on single crystalline a-,r-,and c-plane sapphire substrates upon graphene films synthesized with atmospheric pressure chemical vapor deposition(CVD).The data illustrate that the realization of high-crystalline Cu film is dependent not only on the crystallinity of underlying substrate,but also on the symmetric match of crystallographic geometry between metal film and substrate.We also systematically investigated the effects of PMMA removal on the Raman ID/IG and IG/I2D values of transferred graphene.The results reveal that different PMMA removal methods do not alter the ID/IG values;instead,the residue of PMMA increases the IG/I2D values and the thermal decomposition of PMMA leads to higher IG/I2D values than the removal of PMMA with acetone.The effects of PMMA removal on variations of the Raman spectra are also discussed. 相似文献
177.
Lu Xiang Yunlong Zhu Shuai Gu Dongyang Chen Xian Fu Yindong Zhang Guipeng Yu Chunyue Pan Yuehua Hu 《Macromolecular rapid communications》2015,36(17):1566-1571
A hypercrosslinked conjugated microporous polymer (HCMP‐1) with a robustly efficient absorption and highly specific sensitivity to mercury ions (Hg2+) is synthesized in a one‐step Friedel–Crafts alkylation of cost‐effective 2,4,6‐trichloro‐1,3,5‐triazine and dibenzofuran in 1,2‐dichloroethane. HCMP‐1 has a moderate Brunauer–Emmett–Teller specific surface (432 m2 g−1), but it displays a high adsorption affinity (604 mg g−1) and excellent trace efficiency for Hg2+. The π–π* electronic transition among the aromatic heterocyclic rings endows HCMP‐1 a strong fluorescent property and the fluorescence is obviously weakened after Hg2+ uptake, which makes the hypercrosslinked conjugated microporous polymer a promising fluorescent probe for Hg2+ detection, owning a super‐high sensitivity (detection limit 5 × 10−8 mol L−1).
178.
Wen‐Jian Zhang Chun‐Yan Hong Cai‐Yuan Pan 《Macromolecular rapid communications》2015,36(15):1428-1436
Similar to the traditional self‐assembly strategy, polymerization induced self‐assembly and reorganization (PISR) can produce a myriad of polymeric morphologies through morphology transitions. Besides the chain length ratio (R) of the hydrophobic to the hydrophilic blocks, the chain mobility in the intermediate nano‐objects, which is a requisite for morphology transition, is a determining factor in the formation of the final morphology. Although various morphologies have been fabricated, hexagonally packed hollow hoops (HHHs) with highly ordered internal structure have not, to the best of our knowledge, been prepared by PISR. In this article, the fabrication of HHHs through morphology transition from large compound vesicles to HHHs is reported. HHHs with highly regular internal structure may have significance in theoretical research and practical applications of nanomaterials.
179.
Qingqing Cheng Yiming Pan Qianjin Wang Tao Li Shining Zhu 《Laser \u0026amp; Photonics Reviews》2015,9(4):392-398
Recent realization of nontrivial topological phases in photonic systems has provided unprecedented opportunities in steering light flow in novel manners. Based on the Su–Schriffer–Heeger (SSH) model, a topologically protected optical mode was successfully demonstrated in a plasmonic waveguide array with a kinked interface that exhibits a robust nonspreading feature. However, under the same excitation conditions, another antikinked structure seemingly cannot support such a topological interface mode, which appears to be inconsistent with the SSH model. Theoretical calculations are carried out based on the coupled‐mode theory, in which the mode properties, excitation conditions, and the robustness are studied in detail. It is revealed that under the exact eigenstate excitations, both kinked and antikinked structures do support such robust topological interface modes; however, for a realistic single‐waveguide input only the kinked structure does so. It is concluded that the symmetry of interface eigenmodes plays a crucial role, and the odd eigenmode in a kinked structure offers the capacity to excite the nonspreading interface mode in the realistic excitation of a one‐waveguide input. Our finding deepens the understanding of mode excitation and propagation in coupled waveguide systems, and could open a new avenue in optical simulations and photonic designs.
180.
Simulation of nuclide migration in a middle- and low-level radioactive waste repository based on GMS
Wang Litao Cheng Jianfeng Bao Chenyang Wang Yanhui Jiang Qiao Pan Yuelong Liu Yu Hong Tao Tuo Xianguo Leng Yangchun 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2159-2167
Journal of Radioanalytical and Nuclear Chemistry - Groundwater is the most important factor contributing to the diffusion and migration of radionuclides in the repository. In this paper, the... 相似文献