全文获取类型
收费全文 | 60348篇 |
免费 | 880篇 |
国内免费 | 308篇 |
专业分类
化学 | 28516篇 |
晶体学 | 1048篇 |
力学 | 3209篇 |
综合类 | 8篇 |
数学 | 4755篇 |
物理学 | 24000篇 |
出版年
2022年 | 545篇 |
2021年 | 491篇 |
2020年 | 464篇 |
2019年 | 438篇 |
2018年 | 586篇 |
2017年 | 503篇 |
2016年 | 923篇 |
2015年 | 669篇 |
2014年 | 1020篇 |
2013年 | 2547篇 |
2012年 | 2399篇 |
2011年 | 3087篇 |
2010年 | 2177篇 |
2009年 | 2216篇 |
2008年 | 2829篇 |
2007年 | 2684篇 |
2006年 | 2530篇 |
2005年 | 2258篇 |
2004年 | 2073篇 |
2003年 | 1829篇 |
2002年 | 1722篇 |
2001年 | 3037篇 |
2000年 | 2182篇 |
1999年 | 1565篇 |
1998年 | 1103篇 |
1997年 | 1068篇 |
1996年 | 908篇 |
1995年 | 804篇 |
1994年 | 720篇 |
1993年 | 640篇 |
1992年 | 969篇 |
1991年 | 961篇 |
1990年 | 866篇 |
1989年 | 759篇 |
1988年 | 741篇 |
1987年 | 801篇 |
1986年 | 671篇 |
1985年 | 898篇 |
1984年 | 849篇 |
1983年 | 577篇 |
1982年 | 580篇 |
1981年 | 552篇 |
1980年 | 514篇 |
1979年 | 631篇 |
1978年 | 664篇 |
1977年 | 682篇 |
1976年 | 582篇 |
1975年 | 493篇 |
1974年 | 530篇 |
1973年 | 465篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Y. Takashima 《Journal of Radioanalytical and Nuclear Chemistry》1993,171(1):95-100
The Kyushu Museum of Energy, funded by the Kyushu Electric Power Company, Inc., was opened in September 1982. The planning and design were done by Dentsu, Inc., and the actual construction was shared among several construction and manufacturing companies. I was retained as the principal scientific advisor for the museum, both prior to its construction, throughhout the planning of the exhibits, and afterwards when it was opened to the public. This is an educational museum, which shows how people have developed and depended on energy and energy sources since the discovery of fire in prehistory. There are four major sections, devoted to fire itself, electricity, nuclear power by fission, and nuclear power by fusion. In addition, the museum will track visitors through the exhibits, in terms of The History of Energy as a beginning point for their tour, lead them through Present Energy Needs and Uses, and thence to Future Energy Developments and Needs. The museum is of a hands-on active display type design, with many large and attractive display panels, working models, pleasant mixes of sound, light, and images, and educational levels that encompass general public interest to semitechnical explanations that will satisfy the undergraduate with a technical, background. Visitors can not only operate the models themselves, but join in a variety of games based on energy consumption, usage, and needs. It is very much a participatory museum, and visitors are exposed to the many facets of day-to-day energy generation and consumption, as well as the estimated needs for the future, and possible ways to supply these needs. To date, there have been well over 200,000 visitors recorded. *** DIRECT SUPPORT *** A0653119 00004 相似文献
992.
N,N-dimethyl-N,N-dihexyl-3-oxapentanediamide, DMDHOPDA, N,N-dihexyl-3-thiopentanediamide, DHTPDA and N,N-dihexyl-3-oxapentanediamide, DHOPDA were synthesized and tested for the synergistic extraction of Eu3+, Th4+, UO
2
2+
, NpO
2
+
and Am3+ with thenoyltrifluoroacetone (HTTA). Although Eu3+, Th4+, UO
2
2+
and Am3+ were not extracted by DHTPDA or DHOPDA alone, they were extracted synergistically when combined with HTTA. Analysis of the dependency of extraction on pH and extractant concentration indicated that the dominant extracted species were Eu(TTA)3(A), Th(TTA)3(A)(X), UO2(TTA)2(A) and Am(TTA)3(A) (where A is diamide, and X is chloroacetate or ClO
4
–
). 相似文献
993.
J. C. Y. Le Blanc D. Beuchemin K. W. M. Siu R. Guevremont S. S. Berman 《Journal of mass spectrometry : JMS》1991,26(10):831-839
The effects of beat on the electrospray mass spectra of eight globular proteins in solution were studied. These ranged from hardly noticeable to a dramatic shift in the mass spectrometric profile and a concomitant increase in ion abundance. This change is believed to be the result of thermal denaturation of the protein species in solution resulting in a transition from a more compact to a less compact conformation. We accounted for this transition by means of a recently proposed model based on aqueous solution acid/base equilibria. For cytochrome c, profiles calculated by means of this model agree well with experimental data. The ΔH of the denaturation reaction of cytochrome c in aqueous solution containing 0.2% acetic acid was calculated from experimental data to be 103.8 ± 9.2 kJ mol?1, in good agreement with previous measurements. 相似文献
994.
Simple heteroarenes such as pyrroles and indoles undergo addition reactions to C-C triple bonds in the presence of a catalytic amount of Pd(OAc)(2) under very mild conditions, affording cis-heteroarylalkenes in most cases. The cleavage of aromatic C-H bonds is the possible rate-determining step in CH(2)Cl(2), and the addition of heteroaromatic C-H bonds to C-C triple bonds is in a trans-fashion. 相似文献
995.
[reaction: see text] A microwave-assisted reaction was developed to facilitate the construction of 4,5-disubstituted pyrazolopyrimidines. This one-pot two-step process involves a sequential S(N)Ar displacement of the C4 chloro substituent with various anilines and amines, followed by a Suzuki coupling reaction with different boronic acids. Using microwave irradiation leads to high product conversion, low side product formation, and shorter reactions. 相似文献
996.
A new study of the enzymatic hydrolysis of carboxymethyl cellulose with a bulk acoustic wave sensor 总被引:4,自引:0,他引:4
A new bulk acoustic wave (BAW) cellulase sensing technique, which is based on the enzymatic hydrolysis process of sodium carboxymethylcellulose (CMC) by cellulase, was established. The frequency shift curves of BAW sensor indicated that the viscosity of the tested solutions decreased during the hydrolysis process. The hydrolysis rate of CMC by cellulase was calculated from the frequency shift curves. The hydrolysis rate of CMC under different pH conditions at 30°C showed that cellulase had high hydrolysis ability approximately at pH 5.0. Kinetic parameters (the Michaelis constant Km and the maximum rate Vmax) of the process were estimated by using a linear method of Lineweaver–Burk plot. Km is 1.95±0.25 mg ml−1 and Vmax is −(4.25±0.58)×10−3 g1/2 cm−3/2 cP1/2 min−1. Also the activation energy (Ea) of the enzymatic hydrolysis, with a value of 51.99±1.26 kJ mol−1, was estimated in this work. 相似文献
997.
Lyudmila V. Chernykh Jitka Eysseltova Mikhail Y. Skripkin 《Monatshefte für Chemie / Chemical Monthly》2003,124(1):751-761
Solubility isotherms in the CuBr2−MBr−H2O (M
+ = Li+, Na+, Cs+) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide
systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated
solutions was performed. 相似文献
998.
We propose a numerical procedure for the calculation of the electrostatic repulsion force between two identical, parallel surfaces immersed in anab electrolyte solution. These surfaces are coated with an ion-penetrable membrane carrying fixed charges. The amount of fixed charges is governed by the dissociation of the functional groups in the membrane phase. The effect of pH on the degree of dissociation of these functional groups is taken into account. The difficulty of extensive use of Jacobi elliptic function in the numerical treatment of Poisson-Boltzmann equation can be circumvented by resorting to the present algorithm. 相似文献
999.
K. Nomura H. Reuther E. Richter Y. Ujihira 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(2):299-313
Changes in the magnetic structure of Fe–Si–Al films due to Al and N ion implantation were studied by57Fe Conversion Electron Mössbauer Spectrometry (CEMS). The peaks of the magnetic sextets due to the crystalline films became broader by implantation with 5×1016 Al/cm2, suggesting the formation of amorphous phases. In the CEM spectrum of one sample with large grains implanted with 1×1017 Al/cm2 a crystalline -Fe phase appeared. N implantation with the same dose did not amorphize the sample but the components with high magnetic hyperfine fields were enhanced. 相似文献
1000.
Y. Akiyama F. Mizukami H. Izutsu M. Sato K. Maeda Y. Kiyozumi K. Sakaguchi 《Journal of Sol-Gel Science and Technology》1998,13(1-3):421-425
A novel organic-inorganic composite was prepared by a sol-gel process using hydrolysis and condensation of tetraethoxysilane (TEOS) reacted with a saccharide. During the process, ethoxy groups of the TEOS were replaced with hydroxyl groups of the saccharide and, consequently, saccharide molecules were combined with silica through their hydroxyl groups. Samples obtained under different reaction conditions were used for optical resolution of a metal chelate compound. The resolution ability of the composites was affected by the amount of water added for hydrolysis and of the saccharide. In particular, the amount of water drastically influenced the optical resolution performance. Composites obtained at the lower H2O/TEOS ratio gave the metal chelate compound a higher optical rotation. Three types of composites with the same composition were prepared by kneading, impregnation and by the sol-gel method, and were compared. The sol-gel composite showed the best optical resolution ability. It was concluded that the optical resolution ability was closely related to dispersibility of saccharide in the silica matrix. 相似文献