全文获取类型
收费全文 | 3642篇 |
免费 | 172篇 |
国内免费 | 10篇 |
专业分类
化学 | 2907篇 |
晶体学 | 36篇 |
力学 | 70篇 |
数学 | 145篇 |
物理学 | 666篇 |
出版年
2023年 | 31篇 |
2022年 | 34篇 |
2021年 | 42篇 |
2020年 | 73篇 |
2019年 | 89篇 |
2018年 | 68篇 |
2017年 | 28篇 |
2016年 | 77篇 |
2015年 | 92篇 |
2014年 | 85篇 |
2013年 | 178篇 |
2012年 | 206篇 |
2011年 | 203篇 |
2010年 | 107篇 |
2009年 | 127篇 |
2008年 | 229篇 |
2007年 | 189篇 |
2006年 | 236篇 |
2005年 | 193篇 |
2004年 | 179篇 |
2003年 | 140篇 |
2002年 | 118篇 |
2001年 | 68篇 |
2000年 | 66篇 |
1999年 | 41篇 |
1998年 | 22篇 |
1997年 | 26篇 |
1996年 | 38篇 |
1995年 | 40篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 50篇 |
1991年 | 35篇 |
1990年 | 44篇 |
1989年 | 46篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 61篇 |
1984年 | 52篇 |
1983年 | 18篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 39篇 |
1978年 | 31篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1975年 | 24篇 |
1974年 | 17篇 |
排序方式: 共有3824条查询结果,搜索用时 234 毫秒
1.
Nanostructure diamond (NSD) film with a hardness as high as 70 GPa and an average surface roughness of 10 nm has been synthesized by the two-step negative substrate bias method combined with post-growth Ar-H2 plasma irradiation. The Ar-H2 plasma irradiation has been confirmed to improve the uniformity of grain size and shape and increase the hardness of the NSD film. 相似文献
2.
Takayuki Yaegashi Shinya Yodoya Masahiko Nakamura Hiroki Takeshita Katsuhiko Takenaka Tomoo Shiomi 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):999-1007
Free‐radical homo‐ and copolymerization behavior of N,N‐diethyl‐2‐methylene‐3‐butenamide (DEA) was investigated. When the monomer was heated in bulk at 60 °C for 25 h without initiator, rubbery, solid gel was formed by the thermal polymerization. No such reaction was observed when the polymerization was carried out in 2 mol/L of benzene solution with with 1 mol % of azobisisobutyronitrile (AIBN) as an initiator. The polymerization rate (Rp) equation was Rp ∝ [DEA]1.1[AIBN]0.51, and the overall activation energy of polymerization was calculated 84.1 kJ/mol. The microstructure of the resulting polymer was exclusively a 1,4‐structure where both 1,4‐E and 1,4‐Z structures were included. From the product analysis of the telomerization with tert‐butylmercaptan as a telogen, the modes of monomer addition were estimated to be both 1,4‐ and 4,1‐addition. The copolymerizations of this monomer with styrene and/or chloroprene as comonomers were also carried out in benzene solution at 60 °C. In the copolymerization with styrene, the monomer reactivity ratios obtained were r1 = 5.83 and r2 = 0.05, and the Q and e values were Q = 8.4 and e = 0.33, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 999–1007, 2004 相似文献
3.
Akihide Itoh Taisuke Nagasawa Yanbei Zhu Kyue-Hyung Lee Eiji Fujimori Hiroki Haraguchi 《Analytical sciences》2004,20(1):29-36
In order to elucidate the distributions of the elements among the particulate and dissolved fractions in pond water, major-to-ultratrace elements in different sizes of particles as well as in the filtrate passed through the 0.05 microm filter were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The different sizes of particle samples (ca. 100-300 microg each) were collected on the membrane filters with pore sizes of 10, 3.0, 1.2, 0.4, 0.2 and 0.05 microm, respectively, by sequential fractionation. As a result, about 40 elements in different sizes of particles could be determined by ICP-AES and ICP-MS, after acid digestion using HNO3/HF/HClO4. Then, the fractional distribution factors of major-to-ultratrace elements among the particulate and dissolved fractions were estimated from the analytical results. The total contents of Al, Fe, Ti, REEs (rare earth elements), Bi, Pb and Ag in the particulate fractions (larger than 0.05 microm) were more than 80-90%, while those of Ca, Sr, Cs, W, Ba, Mn and Co in the dissolved fraction, which corresponded to the filtrate passed through the 0.05 microm membrane filter, were more than 80%. It was further found that the fractional distributions of Cu and Zn in the dissolved fraction were ca. 50%. In addition, the enrichment factors (EFs) of the elements in the particulate fractions with particle sizes of 3.0-10 microm and 0.05-0.2 microm were estimated to elucidate their geochemical characteristics in natural water. 相似文献
4.
Yasushi Seike Ryoko Fukumori Yukiko Senga Hiroki Oka Kaoru Fujinaga Minoru Okumura 《Analytical sciences》2004,20(1):139-142
A new and simple method for the determination of hydroxylamine in environmental water, such as fresh rivers and lakes using hypochlorite, followed by its gas choromatographic detection, has been developed. A glass vial filled with sample water was sealed by a butyl-rubber stopper and aluminum cap without head-space, and then sodium hypochlorite solution was injected into the vial through a syringe to convert hydroxylamine to nitrous oxide. The head-space in the glass vial was prepared with 99.9% grade N2 using a gas-tight syringe. After the glass vial was shaken for a few minutes, nitrous oxide in the gas-phase was measured by a gas chromatograph with an electron-capture detector. The dissolved nitrous oxide in the liquid-phase was calculated according to the solubility formula. The proposed method was applied to the analysis of fresh-water samples taken from Iu river and Hii river, flowing into brackish Lakes Nakaumi and Shinji, respectively. 相似文献
5.
We fabricated high-quality InAlN/GaN heterostructures by metal–organic vapor phase epitaxy (MOVPE). X-ray diffraction measurements revealed that InAlN/GaN heterostructures grown under optimal conditions have flat surfaces and abrupt heterointerfaces. Electron mobility from 1200 to 2000 cm2/V s was obtained at room temperature. To our knowledge, this mobility is the highest ever reported for InAlN/GaN heterostructures. We also investigated the relationship between the Al composition and sheet electron density (Ns) for the first time. Ns increased from 1.0×1012 to 2.7×1013 cm−2 when the Al composition increased from 0.78 to 0.89. 相似文献
6.
In this paper we consider the (t, n)-threshold visual secret sharing scheme (VSSS) in which black pixels in a secret black-white images is reproduced perfectly
as black pixels when we stack arbitrary t shares. This paper provides a new characterization of the (t, n)-threshold visual secret sharing scheme with such a property (hereafter, we call such a VSSS the (t, n)-PBVSSS for short). We use an algebraic method to characterize basis matrices of the (t, n)-PBVSSS in a certain class of matrices. We show that the set of all homogeneous polynomials each element of which yields
basis matrices of the (t, n)-PBVSSS becomes a set of lattice points in an (n−t+1)-dimensional linear space. In addition, we prove that the optimal basis matrices in the sense of maximizing the relative
difference among all the basis matrices in the class coincides with the basis matrices given by Blundo, Bonis and De Santis
[3] for all n≥ t ≥ 2. 相似文献
7.
A. Noda S. Nakamura Y. Iwashita S. Sakabe M. Hashida T. Shirai S. Shimizu H. Tongu H. Ito H. Souda A. Yamazaki M. Tanabe H. Daido M. Mori M. Kado A. Sagisaka K. Ogura M. Nishiuchi S. Orimo Y. Hayashi A. Yogo S. Bulanov T. Esirkepov A. Nagashima T. Kimura T. Tajima T. Takeuchi K. Matsukado A. Fukumi Z. Li 《Laser Physics》2006,16(4):647-653
In order to widely spread out particle beams utilized in cancer therapy, laser-produced ions are developed as the injection beam for an ion synchrotron dedicated for cancer therapy. Such a laser ion source is expected to contribute largely to the realization of compactness of the size and low cost of the cancer therapy accelerator. The energy spectrum of the laser-produced ions, however, has no peak, but their intensities decrease exponentially according to the increase of the energy. For the purpose of modifying such a situation, we have proposed a scheme to rotate the beam in the longitudinal phase space with the use of the RF electric field, which is phase-adjusted with the pulse laser. We aim for a reduction of the energy spread of ± 5% selected by an energy analyzer and slits to ±1% by such phase rotation. For this purpose, a quarter wavelength resonator with two gaps with the same resonant frequency as the source laser has already been fabricated, together with its RF power source. The above phase rotation system and its recent experimental realization are presented. 相似文献
8.
9.
Hiroki Matui 《Proceedings of the American Mathematical Society》2004,132(1):87-95
We show that there exists a locally compact Cantor minimal system whose topological spectrum has a given Hausdorff dimension.
10.
Edison Munaf Toyohide Takeuchi Hiroki Haraguchi 《Fresenius' Journal of Analytical Chemistry》1992,342(1-2):154-156
Summary A continuous flow analysis is described for the determination of total mercury by cold vapor atomic absorption spectrometry. Organic mercury compounds such as methylmercury(II) chloride, ethylmercury(II) chloride and phenylmercury(II) chloride were decomposed by potassium peroxodisulphate with addition of ferric chloride as catalytic reagent. The reducing reagent used was tin(II) chloride in sodium hydroxide solution. With 1,000 mg Fe/l added in the decomposition process, we found that methylmercury(II) chloride and ethylmercury(II) chloride gave response signals similar to those of mercury(II) chloride. The proposed method was applied to the analysis of total mercury in waste water.
Permanent address: Department of Chemistry, Faculty of Mathematics and Natural Sciences, Andalas University, Padang, West Sumatra, Indonesia 相似文献