全文获取类型
收费全文 | 1862篇 |
免费 | 71篇 |
国内免费 | 12篇 |
专业分类
化学 | 1508篇 |
晶体学 | 31篇 |
力学 | 22篇 |
数学 | 122篇 |
物理学 | 262篇 |
出版年
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 26篇 |
2019年 | 37篇 |
2018年 | 24篇 |
2017年 | 16篇 |
2016年 | 49篇 |
2015年 | 35篇 |
2014年 | 54篇 |
2013年 | 120篇 |
2012年 | 106篇 |
2011年 | 128篇 |
2010年 | 84篇 |
2009年 | 61篇 |
2008年 | 116篇 |
2007年 | 102篇 |
2006年 | 100篇 |
2005年 | 94篇 |
2004年 | 90篇 |
2003年 | 88篇 |
2002年 | 69篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 25篇 |
1998年 | 19篇 |
1997年 | 26篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1970年 | 9篇 |
1969年 | 10篇 |
排序方式: 共有1945条查询结果,搜索用时 31 毫秒
11.
Takayuki Yamanaka Hideki Fukano Ken Tsuzuki Munehisa Tamura Ryuzo Iga Matsuyuki Ogasawara Yasuhiro Kondo Tadashi Saitoh 《光学学报》2003,23(Z1)
A comprehensive analysis of multi-quantum-well electroabsorption modulators buried with semi-insulating (SI)-InP is presented. We quantitatively demonstrate that suppression of Zn diffusion into the burying and optical core layers plays a key role in high-speed and high-extinction operation. 相似文献
12.
Adachi I Aihara H Dijkstra HB Enomoto R Fujii H Fujii K Fujii T Fujimoto J Fujiwara N Hayashii H Higashi S Iida N Imanishi A Ikeda H Ishii T Itoh R Iwasaki H Iwata S Kajikawa R Kamae T Kato S Kawabata S Kichimi H Kishida T Kobayashi M Kuroda S Kusuki N Maruyama A Maruyama K Masuda H Matsuda T Miyamoto A Morimoto T Nakamura K Nitoh O Noguchi S Ochiai F Okuno H Okusawa T Ohshima T Ozaki H Sato T Sai F Shimonaka J Shimozawa K Shirahashi A Sugahara R Sugiyama A Suzuki S Suwada T Takahashi K 《Physical review letters》1988,60(2):97-100
13.
Tasuku Nakajima Takayuki Kurokawa Hidemitsu Furukawa Qiu Ming Yu Yoshimi Tanaka Yoshihito Osada Jian Ping Gong 《高分子科学》1996,(1):1-9
Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft & wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels. 相似文献
14.
Arakawa R Shimomae Y Morikawa H Ohara K Okuno S 《Journal of mass spectrometry : JMS》2004,39(8):961-965
A low molecular mass polyester was analyzed by desorption/ionization on porous silicon (DIOS) mass spectrometry. The results were compared with those of matrix-assisted laser desorption ionization (MALDI) mass spectrometry using matrixes of alpha-cyano-4-hydroxycinnamic acid (CHCA) and 10,15,20-tetrakis(pentafluorophenyl)porphyrin (F20TPP). The CHCA matrix was not suitable for characterization of low molecular mass components of the polyester because the matrix-related ions interfered with the component ions. On the other hand, the F20TPP matrix showed no interference because no matrix-related ions appeared below m/z 822. However, the solvent selection for determining optimal conditions of sample preparation was limited, because F20TPP does not dissolve readily in any of the available organic solvents. In the DIOS spectra, the polymer ions were observed at high sensitivity without a contaminating ion. No matrix is needed for DIOS spectra of low molecular mass polyesters, facilitating sample preparation and selectivity of a precursor ion in post-source decay measurements. 相似文献
15.
16.
Summary Electronic structure of hydrogen nitryl HNO2, a yet not identified entity, and the path of its possible isomerization totrans-HONO have been investigated byab initio SCF and MRD-CI computations using the 6-31G** basis set. HNO2 isC
2v
-symmetric and its ground state (1
A
1) is less stable thantrans-HONO by 66 kJ/mol (with the SCF vibrational zero-point energy correction). The lowest two excited singlet states (1
A
2 and1
B
1) are nearly degenerate, their vertical excitation energies being predicted to be 4.8 eV. The isomerization path is traced by the CASSCF procedure and the activation barrier height is evaluated by the CI treatment. HNO2 in its ground state isomerizes totrans-HONO by maintaining the planar (C
s-symmetric) structure. The activation energy is calculated to be 171 kJ/mol, which is clearly lower than the calculated H-N bond energy (253 kJ/mol). The transition state seems to be more adequately described as an interacting system of proton and the nitrite anion rather than as a pair of two fragment radicals. 相似文献
17.
Takayuki Abe Shingo Higashide Mitsuhiro Inoue Satoshi Akamaru 《Plasma Chemistry and Plasma Processing》2007,27(6):799-811
Fine particles were modified with a thin film of SnO2 by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO2 were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal
SnO2 were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under
the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO2. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin
film of SnO2 in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W. These measured thicknesses
coincided with the values estimated from the interference colors of the samples. 相似文献
18.
Takayuki Doi 《Tetrahedron letters》2004,45(29):5727-5729
Catch and release method utilizing polymer-support was investigated in the separation of 1α,25-(OH)2 pre- and provitamin D3. Polymer-supported alkyldiisopropylsilyl triflate selectively captured the previtamin D3 from a 26:74 mixture of pre- and provitamin D3 produced by photoisomerization of provitamin D3. 相似文献
19.
Takayuki Hibi 《Order》1987,3(4):383-389
A finite poset Q is called integral over a field k if there exists an ASL (algebra with straightening laws) domain on Q{–} over k. We classify all trees (rank one connected posets without cycles) which are integral over an infinite field. 相似文献
20.
Abou El-Nasr EA Fujii A Yahagi T Ebata T Mikami N 《The journal of physical chemistry. A》2005,109(11):2498-2504
Geometric structures and excited-state proton dislocation of size-selected salicylic acid clusters (salicylic acid and 5-methoxysalicylic acid) with water were studied by using laser spectroscopic techniques. Fluorescence excitation, dispersed fluorescence, and infrared (IR) spectra of those clusters in supersonic jets were examined for both the electronic ground (S0) and first excited (S1) states. The geometric structures of the clusters were determined on the basis of the IR spectra of the OH stretch region with the help of quantum chemical calculations. The hydroxyl group of the water moiety in the clusters forms a ring involving the carboxylic group of the salicylic acid moiety. The IR spectra in S0 show that the intramolecular hydrogen bond in the salicylic acid moiety is still held upon cluster formation, but the phenolic OH stretch band intensity is remarkably weaken in the clusters. The IR spectra in the S1 state and dispersed fluorescence spectra indicated that the intramolecular excited state proton dislocation is hardly affected by the microsolvation with water, in contrast with the strong suppression of the dislocation in the self-solvation. 相似文献