全文获取类型
收费全文 | 1716篇 |
免费 | 55篇 |
国内免费 | 7篇 |
专业分类
化学 | 1285篇 |
晶体学 | 17篇 |
力学 | 21篇 |
数学 | 172篇 |
物理学 | 283篇 |
出版年
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 38篇 |
2013年 | 87篇 |
2012年 | 61篇 |
2011年 | 102篇 |
2010年 | 45篇 |
2009年 | 66篇 |
2008年 | 82篇 |
2007年 | 113篇 |
2006年 | 105篇 |
2005年 | 114篇 |
2004年 | 89篇 |
2003年 | 74篇 |
2002年 | 82篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 28篇 |
1998年 | 18篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 7篇 |
1985年 | 25篇 |
1984年 | 30篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 25篇 |
1979年 | 25篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 20篇 |
1974年 | 13篇 |
1973年 | 9篇 |
1967年 | 8篇 |
排序方式: 共有1778条查询结果,搜索用时 15 毫秒
191.
Akira Hasegawa Takao Nagahama Hitoshi Ohki Kenji Hotta Hideharu Ishida Makoto Kiso 《Journal of carbohydrate chemistry》2013,32(3):493-498
Development of an efficient α-glycoside synthesis of sialic acids is critically significant for the syntheses of sialoglycoconjugates, especially gangliosides which carry important biological functions1 in biological systems. Previously, we demonstrated2 a new α-glycosylation of sialic acids by use of dimethyl(methylthio)sulfonium triflate (DMTST)3 as the glycosyl promoter, the suitably protected glycosyl acceptors and the methyl 2-thioglycoside 1 of N-acetylneuraminic acid (Neu5Ac) as the donor in acetonitrile under kinetically controlled conditions, and accomplished4 the syntheses of a variety of gangliosides and their analogs. 相似文献
192.
Shin-ichiro Hayashi Munenori Yoshioka Shuji Usui Kiyofumi Haneda Takahiro Kondo Kim B. McAuley Takahiro Tominaga 《Radiation Physics and Chemistry》2010,79(7):803-808
In radiotherapy treatment, polymer gel dosimetry can be used for verifying three-dimensional (3D) dose distributions. Gelatin is generally used as a gelling agent in the dosimeters. In this paper, another role of gelatin in a methacrylic-acid-based gel dosimeter (MAGAT) is investigated. Temperature increases due to exothermic polymerization in the irradiated gel are measured directly. Dose–R2 responses are also obtained using MRI. It is shown that no appreciable increases in either temperature or R2 are observed in MAGAT dosimeters made without gelatin, and that significant temperature and R2 increases are observed when very low gelatin concentrations are used. These results indicate that gelatin is an important enabler for radiation-induced free-radical polymerization in methacrylic-acid-based gels. When gelatin is replaced by amino acids, changes in temperature are observed, along with small changes in R2. The resulting dosimeter solutions remain transparent because the polymer does not precipitate as it does in regular MAGAT dosimeters containing gelatin. When the amino acids are replaced by acids without amino groups, no temperature or R2 changes are observed, indicating that no polymer forms. These results show that amino groups (and possibly other functional groups) on the gelatin catalyze the radiation-induced free-radical polymerization that occurs in MAGAT dosimeters. 相似文献
193.
Takao Yamaguchi 《Journal of Mathematical Sciences》1999,94(2):1270-1310
The paper contains a systematic exposition of results due to the author and K. Fukaya on manifolds of almost nonnegative curvature.
The final part contains several conjectures and modern problems. Bibliography: 79 titles.
Dedicated to Professor Tsunero Takahashi on his sixtieth birthday
Published inZapiski Nauchnykh Seminarov POMI, Vol. 234, 1996, pp. 201–260. 相似文献
194.
Teppei Yoshioka Md Zahangir Alam Tomonari Ogata Takamasa Nonaka Seiji Kurihara 《Liquid crystals》2004,31(9):1285-1291
Several chiral azobenzene compounds having different chiral substituents were synthesized. A cholesteric phase was induced by mixing each chiral azobenzene compound with a host non-chiral nematic liquid crystal (E44). The helical twisting power (HTP) as well as the change in HTP by trans-cis photoisomerization of the chiral azobenzene compound was dependent on the structure of the chiral substituents. A compensated nematic phase was induced by combination of E44, a chiral azobenzene compound and a non-photochromic chiral compound. Reversible switching between the compensated nematic phase and cholesteric phase was brought about by trans-cis photoisomerization of the chiral azobenzene compound in the liquid crystalline systems. An azobenzene compound substituted with a menthyl group showed the highest efficiency as the trigger for the switching; this efficiency was related to the compactness of the chiral group substituted within the azobenzene core moiety. 相似文献
195.
Ichiro Tsunenari Jyoji Yamate Masae Iwaki Mitsuru Kuwamura Takao Kotani Sadashige Sakuma 《Microscopy and microanalysis》2003,9(6):532-541
Angiogenesis, a biologic process whereby endothelial cells divide and migrate to form new blood vessels, is a key step in tumor growth, invasion, and metastasis. In the present study, we investigated the differences in angioarchitecture between two different tumors induced by cloned cell lines (MT-8 and MT-9), derived from a transplantable rat malignant fibrous histiocytoma, by scanning electron microscopy of vascular corrosion casts. During a 3-week observation period after implantation, the growth of MT-8 tumors appeared to be faster than that of MT-9 tumors. Histologically, MT-8 tumors were of the uniformly undifferentiated sarcoma type arranged in characteristic organoid structures, and MT-9 tumors showed a storiform growth pattern. In MT-8 tumors, neovascularization occurred by sprouting at postimplantation (PI) week 1, and the newly formed capillaries gradually became more tortuous. In MT-9 tumors, at PI week 1, the corrosion casts of newly formed capillaries mainly showed a wavy course but no finger-like outgrowths of capillaries were seen. At PI weeks 2 and 3, the sprouting was seen specifically in MT-9 tumors, forming basket-like structures and glomeruloid structures of capillaries. These results indicate that angiogenesis or angioarchitecture of MT-8 tumors is different from that of MT-9 tumors, depending on the differences in their tumor histology and by the features like absence or presence of basket-like structures and glomeruloid structures of capillaries. 相似文献
196.
A theory of transport in the quantum-Hall regime is developed for separately contacted double-layer electron systems. Inter-layer tunneling provides a channel for equilibration of the distribution functions in the two layers at the edge states. Resistances and transresistances for various configurations of the electrodes are calculated as functions of the inter-layer tunneling amplitude. Induced current in one of the layer by a current in the other is also calculated. It is shown that reflection at the leads causes change in the results for some electrode configurations. The results obtained in this work is consistent with recent experiments. 相似文献
197.
Kōta Yoshioka 《manuscripta mathematica》2003,110(4):433-465
In this note, we define the twisted stability for a purely 1-dimensional sheaf and study the problem of the preservation
of the stability condition under the relative Fourier-Mukai transform on an elliptic surface. As an application, we compute
the Hodge polynomials of some moduli spaces of sheaves on an elliptic surface. We also construct the moduli space of twisted
semi-stable sheaves.
Received: 29 January 2002 / Revised version: 16 October 2002 Published online: 24 January 2003
Mathematics Subject Classification (2000): 14D20 相似文献
198.
This paper presents numerical results on chaotic vibrations of a shallow cylindrical shell-panel under harmonic lateral excitation. The shell, with a rectangular boundary, is simply supported for deflection and the shell is constrained elastically in an in-plane direction. Using the Donnell--Mushtari--Vlasov equation, modified with an inertia force, the basic equation is reduced to a nonlinear differential equation of a multiple-degree-of-freedom system by the Galerkin procedure. To estimate regions of the chaos, first, nonlinear responses of steady state vibration are calculated by the harmonic balance method. Next, time progresses of the chaotic response are obtained numerically by the Runge--Kutta--Gill method. The chaos accompanied with a dynamic snap-through of the shell is identified both by the Lyapunov exponent and the Poincaré projection onto the phase space. The Lyapunov dimension is carefully examined by increasing the assumed modes of vibration. The effects of the in-plane elastic constraint on the chaos of the shell are discussed. 相似文献
199.
Yukio Fujimori Takashi Kaneko Takahiko Kaku Naoki Yoshioka Hiroyuki Nishide Eishun Tsuchida 《先进技术聚合物》1992,3(8):437-441
The polymerization behavior and photoinitiation process in the visible light-cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long-lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post-curing by the residual radical proceeded effectively in the deeper part of the resin. 相似文献
200.