全文获取类型
收费全文 | 6618篇 |
免费 | 505篇 |
国内免费 | 180篇 |
专业分类
化学 | 5011篇 |
晶体学 | 58篇 |
力学 | 253篇 |
综合类 | 14篇 |
数学 | 464篇 |
物理学 | 1503篇 |
出版年
2023年 | 61篇 |
2022年 | 111篇 |
2021年 | 158篇 |
2020年 | 157篇 |
2019年 | 147篇 |
2018年 | 152篇 |
2017年 | 142篇 |
2016年 | 274篇 |
2015年 | 239篇 |
2014年 | 316篇 |
2013年 | 471篇 |
2012年 | 581篇 |
2011年 | 569篇 |
2010年 | 412篇 |
2009年 | 345篇 |
2008年 | 453篇 |
2007年 | 414篇 |
2006年 | 376篇 |
2005年 | 344篇 |
2004年 | 252篇 |
2003年 | 241篇 |
2002年 | 214篇 |
2001年 | 133篇 |
2000年 | 92篇 |
1999年 | 71篇 |
1998年 | 53篇 |
1997年 | 53篇 |
1996年 | 65篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 30篇 |
1992年 | 21篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1972年 | 7篇 |
排序方式: 共有7303条查询结果,搜索用时 31 毫秒
1.
2.
Sung Hwan Koo Dong Jun Li Taeyeong Yun Dong Sung Choi Kyung Eun Lee Gil Yong Lee Youngtak Oh Joonwon Lim Suchithra Padmajan Sasikala Ho Jin Lee In Ho Kim Hong Ju Jung Rishabh Jain Sang Ouk Kim 《Particle & Particle Systems Characterization》2019,36(7)
Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS2, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec?1 and a charge transfer resistance (Rct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer. 相似文献
3.
Elsye Agustina Jeungchoon Goak Suntae Lee Youngho Seo Jun-Young Park Naesung Lee 《ChemistryOpen》2015,4(5):613-619
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs. 相似文献
4.
5.
Stanislav Man 《Tetrahedron letters》2006,47(39):6961-6963
Two different procedures for β-allenyloxime cyclization are described. One leads to substituted 1-hydroxypyrrolidines and the other represents a new route to pyrroline-N-oxides. 相似文献
6.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
7.
Andrea Mühlbauer Stephan Seip Alexander Nowak VanSung Tran 《Helvetica chimica acta》2003,86(6):2065-2072
Chemical investigation of the roots of the Vietnamese plant Tacca paxiana resulted in the isolation of five new steroidal compounds, taccalonolide R ( 6 ), S ( 7 ), T ( 8 ), U ( 9 ), and V ( 10 ). Their structures were established on the basis of NMR and mass‐spectral data. In addition, the five known taccalonolides A ( 1 ), B ( 2 ), E ( 3 ), K ( 4 ), and N ( 5 ) were also isolated and identified. 相似文献
8.
This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well. 相似文献
9.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
10.
A least‐squares meshfree method based on the first‐order velocity–pressure–vorticity formulation for two‐dimensional incompressible Navier–Stokes problem is presented. The convective term is linearized by successive substitution or Newton's method. The discretization of all governing equations is implemented by the least‐squares method. Equal‐order moving least‐squares approximation is employed with Gauss quadrature in the background cells. The boundary conditions are enforced by the penalty method. The matrix‐free element‐by‐element Jacobi preconditioned conjugate method is applied to solve the discretized linear systems. Cavity flow for steady Navier–Stokes problem and the flow over a square obstacle for time‐dependent Navier–Stokes problem are investigated for the presented least‐squares meshfree method. The effects of inaccurate integration on the accuracy of the solution are investigated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献